Tesis sobre el tema "Titanium and composite materials"

The thesis describes a study of the modifications of orthopaedic Ti-based substrates using nanomaterials, and the evaluation of their biocompatibility for further use as implant material, with the aim to develop new, biocompatible β-Ti/CNT composite materials. Traditionally, CNTs require the presence of a transition metal catalyst such as Fe, Ni, Co, for successful growth. Different aspects of a catalyst-assisted CVD MWCNTs growth on various Ti-based substrates including bulk, thin films and 3D porous scaffolds, have been investigated. Low concentrations of catalyst were deposited using spin coating on titanium substrates of various forms and shapes. A strong influence of the surface topography was observed. In contrast, no effect of the elemental composition of the substrate could be detected. To evaluate the biocompatibility of the newly created materials, cell culture studies using fetal human osteoblasts (fHobs) were performed. It was shown that β-Ti/MWCNTs samples possess good initial osteoblast attachment, but no long-term osteoblast activity. Hence the biocompatibility of isolated (i.e. without a Ti substrate) MWCNTs was studied, using MWCNT carpets and various types of MWCNTs buckypapers. All the samples revealed very low cell activity. While β-Ti/MWCNTs samples did not exhibit good biocompatibility, alternative β-Ti/TiC samples were synthesized with a simple CVD method and revealed good osteoblast response with increased mineralization. Moreover, good corrosion resistance and mechanical properties of β-Ti/TiC samples have been reported. Finally, successful method for non-catalytic CVD MWCNTs growth on Ti substrates was developed for the first time, thereby excluding potentially toxic catalysts from the implant material. CVD was performed with acetylene precursor on bulk titanium substrates etched with Piranha solution, which generated an appropriate surface to foster MWCNTs growth. A combination of the change in the surface roughness, improved hydrophilicity, and elemental composition of the surface as a result of the Piranha etching is likely to be responsible for the successful formation of MWCNTs.

This thesis describes the synthesis, characterization and photocatalytic applications of carbon nitride (C3N4) and titanium dioxide (TiO2) materials. C3N4 was prepared from the thermal decomposition of a trichloromelamine (TCM) precursor. Several different reactor designs and decomposition temperatures were used to produce chemically and thermally stable orange powders. These methods included a low temperature glass Schlenk reactor, a high mass scale stainless steel reactor, and decomposition at higher temperatures by the immersion of a Schlenk tube into a furnace. These products share many of the same structural and chemical properties when produced by these different methods compared to products from more common alternate precursors in the literature, determined by infrared spectroscopy (IR), nuclear magnetic resonance spectroscopy (NMR), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and elemental analysis. C3N4 is capable of utilizing light for photocatalysis due to its moderate band gap (Eg), measured to be between 2.2 and 2.5 eV. This enables C3N4 to be used in the photocatalytic degradation of organic dyes and the production of hydrogen via the water-splitting reaction. C3N4 degraded methylene blue dye to less than 10% of its initial concentration in less than an hour of UV light illumination and 60% under filtered visible light in 150 minutes. It also degraded methyl orange dye to below 20% in 70 minutes under UV light and below 60% in 150 minutes under visible light. Using precious metal co-catalysts (Pt, Pd, and Ag) photo-reduced onto the surface of C3N4, hydrogen was produced from a 10% aqueous solution of triethanolamine at rates as high as 260 μmol h-1 g-1. C3N4 was also modified by mixing the precursor with different salts (NaCl, KBr, KI, KSCN, and NH4SCN) as hard templates. Many of these salts reacted with TCM by exchanging the anion with the chlorine in TCM. The products were mostly prepared using the high temperature Schlenk tube reactor, and resulted in yellow, orange, or tan-brown products with Eg values between 2.2 and 2.7 eV. Each of these products had subtle differences in the IR spectra and elemental composition. The morphology of these C3N4 products appeared to be more porous than unmodified C3N4, and the surface area for some increased by a factor of 4. These products demonstrated increased activity for photocatalytic hydrogen evolution, with the product from TCM-KI reaching a peak rate as high as 1,300 µmol h-1 g-1. C3N4 was coated onto metal oxide supports (SiO2, Al2O3, TiO2, and WO3) with the goal of utilizing enhanced surface area of the support or synergy between two different semiconductors. These products typically required higher temperature synthesis conditions in order to fully form. The compositions of the SiO2 and Al2O3 products were richer in nitrogen and hydrogen compared to unmodified C3N4. The higher temperature reactions with C3N4 and WO3 resulted in the formation of the HxWO3 phase, and an alternate approach of coating WO3 on C3N4 was used. The degradation of methyl orange showed a significant increase in adsorption of dye for the composites with SiO2 and Al2O3, which was not seen with any of the individual components. The composite between C3N4 and TiO2 showed improved activity for hydrogen evolution compared to unmodified C3N4. The surface of TiO2 was modified by the reductive photodeposition of several first row transition metals (Mn, Fe, Co, Ni, and Cu). This process resulted in the slight color change of the white powder to shades of light yellow, blue or grey. Bulk elemental analysis showed that these products contained between 0.04-0.6 at% of the added metal, which was lower than the targeted deposit amount. The Cu modified TiO2 had the largest enhancement of photocatalytic hydrogen evolution activity with a rate of 8,500 µmol h-1 g-1, a factor of 17 higher than unmodified TiO2.

Thesis (M.S. in mechanical engineering)--Washington State University, May 2010.
Title from PDF title page (viewed on July 16, 2010). "School of Engineering and Computer Science." Includes bibliographical references (p. 109-112).

Hybrid Titanium Composite Laminates (HTCL) have vast potential for future commercial aircraft development. In order for this potential to be properly utilized the HTCLs material properties must first be well understood and obtained through experimentation. Crack initiation and crack growth characteristics of HTCLs are dependent on the heat treatment of the embedded constituent titanium foil. While high strength titanium foils may delay crack initiation, there may be an adverse effect of unsuitable crack growth rates in the HTCLs. Literature has indicated that when properly designed, cracks in HTCLs can arrest due to fiber bridging mechanisms and other crack closure mechanisms. Traditional surface inspection techniques employed on facesheet laminate evaluations will not be able to properly monitor the internal crack growth and damage progression for the internal plies. The main objective of the this joint Georgia Tech/Boeing research project was to determine and compare crack initiation and crack growth characteristics of different heat-treated -Ti 15-3 titanium foil embedded in HTCLs. Georgia Tech utilized a unique capability of x-raying the internal foils of the HTCL specimen in a servo-hydraulic test frame while under load. The titanium foil in this study represented four different heat treatments that result in four increasing levels of strength and decreasing levels of elongation. Specifically, open-hole HTCL coupons were tested at four stress load levels under constant amplitude fatigue cycles to determine a-N curves for the HTCL layups evaluated. The layup evaluated was [45/0/-45/0/Ti/0/-45/0/45]. Crack growth rates were determined once the initiated crack was detected via radiographic exposure. Radiographic delamination analysis and thermoelastic stress analysis techniques were employed to determine additional damage mechanisms in the laminate. Analytical and finite element methods were utilized to determine ply stresses. Additionally, titanium foil properties were determined via dog-bone coupons for each of the four heat treatment conditions.

Metal/ceramic composites have attracted considerable attention in the last 20 years, primarily due to the flexibility they offer when designing material with tailored properties. Melt infiltration is a popular fabricating method for such composites, as it allows the production of near-net shape components with high ceramic content. Capillaric melt infiltration is a simpler process since the liquid penetrates the preform under the action of a capillary pressure. This work deals with the fabrication and evaluation of a TiC/Al composite produced by melt infiltration. Pre-sintered preforms, having different void fraction and pore size, where infiltrated with pure Al, in an argon atmosphere, at various temperatures. The infiltration was carried out using the contact and the capillary dip methods to study the mechanical properties and infiltration behaviour, respectively.
The material exhibited a wide range of properties, depending on the ceramic content. Optimum tensile strengths of up to 480MPa were obtained for composites containing between 67 and 75% TiC, and infiltrated at 1050-1200$ sp circ$C. The extent of pre-sintering of the TiC was seen to play a crucial role in the strengthening of the microstructure, as well as the fracture mechanism by which the material failed. The elastic modulus was seen to increase with increasing TiC content, from values of 120 to 290GPa. The hardness also increased with TiC content, to values as high as 800kg/mm$ sp2,$ but decreased with higher infiltration temperatures due to the breakdown of the TiC network and grain coarsening.
An experimental set-up was designed to measure the rate of infiltration by continually monitoring the weight changes of the preform as a result of the penetration of Al. Infiltration profiles were generated as a function of pore size, pore volume and temperature. At low temperatures, an incubation period was evident as a result of the transient contact angle between the two phases. Moreover, infiltration was inhibited at lower pore volume fraction. Finally, the Activation energy for the system increased from 90 to 450kJ/mol, with increasing pore size, suggesting a transition from a diffusion controlled process to one activated by a surface reaction for larger pore sizes.

Thesis submitted in fulfilment of the requirements for the degree Master of Technology: Biomedical Technology In the Faculty of Health and Wellness Sciences At Cape Peninsula University of Technology 2013
Newly developed and commercial dental resins which are commonly used nowadays have to be tested for their antimicrobial susceptibility. The purpose of this in vitro study was to investigate the antimicrobial activity of a titanium oxide (TiO2) nano-composite which was prepared with different antibacterial substances and used as restoratives in dentistry to combat certain selected bacteria that are considered the principle causes of some tooth diseases, for example, tooth decay and to prevent unsuccessful dental restoration. The TiO2 nano-composite was prepared and divided into four groups: The first group was an untreated TiO2 nano-composite. The second group was silane-treated TiO2 nano-composite. The third group was treated TiO2 nano-composite which was combined with chlorhexidine gluconate (CHxG). The fourth group was treated TiO2 nano-composite which was combined with benzalkonium chloride (BzCl). Five of the selected bacteria were grown overnight in Petri dishes. Four of them, namely, Escherichia coli (E. coli) ATCC 11775, Staphylococcus aureus (S. aureus) ATCC 12600, Enterococcus faecalis (E. faecalis) ATCC 29212, and Pseudomonas aeruginosa (P. aeruginosa) ATCC 10145, were grown on Müller-Hinton Agar (MHA). Streptococcus mutans (S. mutans) ATCC 25175 was grown on Brain Heart Infusion (BHI) agar. All these bacteria were tested against the TiO2 nano-composite, and incubated for 24 hours at 37°C, except S. mutans, which was incubated separately and exposed to CO2. It was placed into a CO2 water-jacketed incubator in an atmosphere of 5% CO2 for 24 hours at 37°C. The obtained results showed that neither of the groups of TiO2 nano-composites, (untreated TiO2 nano-composite and treated TiO2 nano-composite) exhibited antimicrobial activity against the pathogens. Only preparations of TiO2 nano-composites at a concentration of 3 %m/m of both CHxG and BzCl showed antimicrobial activity against S. aureus. Antimicrobial activity against S. mutans, E. coli, P. aeruginosa, E. faecalis and S. aureus, were only realized at a concentration of 10 %m/m for both CHxG and BzCl..

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2010.
Hybrid polymeric composites (HPC) are widely used for the design of aerospace, automobile and civil engineering structures. One of the major challenges posed by these materials and structures is their brittle nature. When subjected to impact and dynamic loads, the polymeric composite structures undergo micro cracking. The cracks coalesce, propagate and can lead to catastrophic failure of the material and structures. In this thesis, an intelligent hybrid polymeric composite (IHPC) beam with healing ability was developed and tested. The IHPC beam developed consisted of a 3% prestrained 1mm diameter Ni-Ti shape memory alloy (SMA) wire actuator embedded in the polymeric host matrix. The function of the embedded Ni-Ti shape memory alloy was to enhance intelligence and healing ability to the IHPC beam. Upon electric current resistance heating, the Ni-Ti SMA actuator responds by contracting as a result of detwinned martensite → austenite phase transformation. Contraction of the SMA in the IHPC beam was utilized to stiffen and enhance healing by retarding crack growth and recovery of the strain induced in the loaded IHPC beam. This can result to increase of the flexural stiffness EI (defined as the product of the Young’s Modulus E of the material and the moment of inertia I of the geometry of the beam) and mode I fracture stress intensity factor KIC of the IHPC beam. One (1) mm diameter Ni-Ti SMA wire was used in the experimental work in this thesis. The wire was cut into 35 pieces, 200 mm long each. Ni-Ti SMA wires were heated in the furnace to a temperature of 250ºC for ten (10) hours then were left to cool in the ambient air. The heat treatment was aimed to release any residual stress and to stabilize the austenite start (AS) and austenite finish (Af) transformation temperatures of the Ni-Ti SMA. After heat treatment, the Ni-Ti SMA wires were prestrained by 3% (based on a gauge length of 150mm) on a tensile testing machine. Prestraining of the Ni-Ti SMA wires was aimed to induce detwinned martensite volume fraction in them hence increasing the transformation strain and recovery force of the Ni-Ti SMA actuator. Intelligent hybrid polymeric composite (IHPC) beams and polymeric virgin (PV) beams, all of dimensions 150mmx25mmx10mm were manufactured by casting 60D polyurethane thermosetting epoxy resin in a silicon mould. transformation strain and recovery force of the Ni-Ti SMA actuator.

Dans l’industrie aérospatiale, l’utilisation des matériaux hybrides CFRP/Ti montre une tendance à la hausse en raison de leurs propriétés mécaniques/physiques améliorées ainsi que des fonctions structurelles plus flexibles. En dépit de leurs nombreuses applications, l’usinage CFRP/Ti en perçage en une seule passe reste le principal défi scientifique et technologique de l’assemblage multi-matériaux. Par rapport au coût de production élevé et le temps des recherches basées sur des approches exclusivement expérimentales de l’usinage multi-matériaux, cette étude a pour objectif d’amener une meilleure compréhension de la coupe CFRP/Ti à travers une approche physique hybride qui fait dialoguer les méthodes numériques et expérimentales. Un modèle EF utilisant le concept de zone cohésive a été développé pour étudier l’usinabilité anisotrope de pièces structurales CFRP/Ti à des fins d’assemblage. L’approche numérique explicite, par des études préliminaires, les mécanismes de coupe clés qui contrôlent l’usinage CFRP/Ti. Par la suite, l’approche expérimentale a été conduite sous différentes conditions d’usinage en configuration de coupe orthogonale et de perçage. Une attention spéciale a été consacrée aux effets des stratégies des séquences de coupe CFRP/Ti sur la formation des endommagements d’interface induits. Ces études expérimentales et numériques ont permit (i) d’expliciter les mécanismes physiques activés qui contrôlent la coupe à l’interface ainsi que les endommagements induits par celle-ci, (ii) de préciser les effets des différentes stratégies d’assemblage multi-matériaux sur l’usinage CFRP/Ti, (iii) de définir la classification d’usinabilité CFRP/Ti, et (iv) d’analyser enfin les effets paramétriques géométrie/matériau d’outil régissant l’opération d’usinage CFRP/Ti
In modern aerospace industry, the use of hybrid CFRP/Ti stacks has experienced an increasing trend because of their enhanced mechanical/physical properties and flexible structural functions. In spite of their widespread applications, machining hybrid CFRP/Ti stacks in one-shot time still consists of the main scientific and technological challenge in the multi-material fastening. Compared to the high cost of pure experimental investigations on the multi-material machining, this study aims to provide an improved CFRP/Ti cutting comprehension via both numerical and experimental methodologies. To this aim, an FE model by using the cohesive zone concept was established to construct the anisotropic machinability of the bi-material structure. The numerical work aims to provide preliminary inspections of the key cutting mechanisms dominating the hybrid CFRP/Ti stack machining. Afterward, some systematic experimental work including orthogonal cutting and hole drilling was carefully performed versus different input cutting conditions. A special focus was made on the study of the effects of different cutting-sequence strategies on CFRP/Ti cutting output and induced interface damage formation. The combined numerical-experimental studies provide the key findings aiming to (i) reveal the activated mechanisms controlling interface cutting and subsequent interface damage formation, (ii) clarify the influences of different cutting-sequence strategies on hybrid CFRP/Ti stack machining, (iii) outline the machinability classification of hybrid CFRP/Ti stacks, and (iv) analyze finally the parametric effects of the material/tool geometry on cutting CFRP/Ti stacks

Ni/TiC metal matrix composites have been processed using the laser engineered net shaping (LENS) process. As nickel does not form an equilibrium carbide phase, addition of a strong carbide former in the form of titanium reinforces the nickel matrix resulting in a promising hybrid material for both surface engineering as well as high temperature structural applications. Changing the relative amounts of titanium and carbon in the nickel matrix, relatively low volume fraction of refined homogeneously distributed carbide precipitates, formation of in-situ carbide precipitates and the microstructural changes are investigated. The composites have been characterized in detail using x-ray diffraction, scanning electron microscopy (including energy dispersive spectroscopy (XEDS) mapping and electron backscatter diffraction (EBSD)), Auger electron spectroscopy, and transmission (including high resolution) electron microscopy. Both primary and eutectic titanium carbides, observed in this composite, exhibited the fcc-TiC structure (NaCl-type). Details of the orientation relationship between Ni and TiC have been studied using SEM-EBSD and high resolution TEM. The results of micro-hardness and tribology tests indicate that these composites have a relatively high hardness and a steady-state friction coefficient of ~0.5, both of which are improvements in comparison to LENS deposited pure Ni.

The aim of this study was to understand the processing – structure – property relationships in spark plasma sintered (SPS) boron carbide (B4C) and B4C-titanium diboride (TiB2) ceramic composites. SPS allowed for consolidation of both B4C and B4C-TiB2 composites without sintering additives, residual phases, e.g., graphite, and excessive grain growth due to long sintering times. A selection of composite compositions in 20% TiB2 feedstock powder increments from 0% to 100%, was sintered at 1900°C for 25 minutes hold time. A homogeneous B4C-TiB2 composite microstructure was determined with excellent distribution of TiB2 phase, while achieving ~99.5% theoretical density. An optimum B4C-23 vol.% TiB2 composite composition with low density of ~3.0 g/cm3 was determined that exhibited ~30-35% increase in hardness, fracture toughness, and flexural bend strength compared to commercial armor-grade B4C. This is a result of a) no residual graphitic carbon in the composites, b) interfacial microcrack toughening due to thermal expansion coefficient differences placing the B4C matrix in compression and TiB2 phase in tension, and c) TiB2 phase aids in crack deflection thereby increasing the amount of intergranular fracture. Collectively, the addition of TiB2 serves as a strengthening and toughening agent, and SPS shows promise for the manufacture of hybrid ceramic composites.

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Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

The mixing of polymers and nanoparticles makes it possible to give advantageous macroscopic material performance by tailoring the microstructure of composites. In this thesis, five combinations of nano inclusion and polymer matrix have been investigated. The first type of composites is titanium dioxide/ polyaniline combination. The effects of 4 different doping-acids on the microstructure, morphology, thermal stability and thermoelectric properties were discussed, showing that the sample with HCl and sulfosalicylic dual acids gave a better thermoelectric property. The second combination is titanium dioxide/polystyrene composite. Avrami equation was used to investigate the crystallization process. The best fit of the mass derivative dependence on temperature has been obtained using the double Gaussian dependence. The third combination is titanium dioxide/polyaniline/ polystyrene. In the titanium dioxide/polyaniline/ polystyrene ternary system, polystyrene provides the mechanical strength supporting the whole structure; TiO2 nanoparticles are the thermoelectric component; Polyaniline (PANI) gives the additional boost to the electrical conductivity. We also did some investigations on Polyethylene odide-TiO2 composite. The cubic anatase TiO2 with an average size of 13nm was mixed with Polyethylene-oxide using Nano Debee equipment from BEE international; Single wall carbon nanotubes were introduced into the vinyl acetate-ethylene copolymer (VAE) to form a connecting network, using high pressure homogenizer (HPH). The processing time has been reduced to 1/60 of sonication for HPH to give better sample quality. Theoretical percolation was derived according to the excluded volume theory in the expression of the threshold as a function of aspect ratio.

It is widely believed that hydrogen will, within a few years, become the means of storing and transporting energy. The reason is the depletion of hydrocarbons and the relatively facile production of hydrogen from various renewable sources of energy. Hydrogen can be combusted in an efficient way in a fuel cell with water as emission product. The overall goal of the project was to deevlop the knowledge base for solid-state hydrogen storage technology suitable for stationary and mobile applications. The aim of this research was to develop a novel composite hydrogen storage material with high wt% storage capacity, high intrinsic safety, appropriate thermodynamics, high mechanical strength, reversibility of the system and fast kinetics based on a well known "
low temperature"
intermetallic alloy (Ti/Fe) as the core.

Thesis (M.S.)--Miami University, Dept. of Paper Science and Engineering, 2002.
Title from first page of PDF document. Document formatted into pages; contains vii, 107 p. : ill. Includes bibliographical references (p. 73-75).

Bone defects resulting from disease or traumatic injury is a major health care problem worldwide. Tissue engineering offers an alternative approach to repair and regenerate bone through the use of a cell-scaffold construct. The scaffold should be biodegradable, biocompatible, porous with an open pore structure, and should be able to withstand the applied forces. Phosphate-based glasses (PGs) may be used as reinforcing agents in degradable composites since their degradation can be predicted and controlled through their chemistry. This doctoral dissertation describes the development and evaluation of PGs reinforced biodegradable polyesters for intended applications in bone augmentation and regeneration. This research was divided into three main objectives: 1) Investigating the composition dependent properties of novel PG formulations by doping a sodium-free calcium phosphate-based glass with SiO2, Fe2O3, and TiO2. Accordingly, (50P2O5-40CaO- xSiO2-(10-x)Fe2O3, where x = 10, 5 and 0 mol.%) and (50P2O5-40CaO-xSiO2-(10-x)TiO2 where x = 10, 7, 5, 3 and 0 mol.%) formulations were developed and characterised. SiO2 incorporation led to increased solubility, ion release, pH reduction, as well as hydrophilicity, surface energy, and surface polarity. In contrast, doping with Fe2O3 or TiO2 resulted in more durable glasses, and improved cell attachment and viability. It was hypothesised that the presence of SiO2 in the TiO2-doped formulations could up-regulate the ionic release from the PG leading to higher alkaline phosphatase activity of MC3T3-E1 cells. 2) Incorporating Si, Fe, and Ti doped PGs as fillers, either as particulates (PGPs) or fibres (PGFs), into biodegradable polyesters (polycaprolactone (PCL) and semi-crystalline and amorphous poly(lactic acid) (PLA and PDLLA)) with the aim of developing degradable bone analogous composites. It was found that PG composition and geometry dictated the weight loss, ionic release, and mechanical properties of the composites. It was also hypothesised that a potential reaction between Si and the ester bond led to the formation of carboxylate by-products resulting in a lower molecular weight polymer, thus affecting the mechanical properties of the composites. Cytocompatibility assessment with MC3T3-E1 preosteoblasts showed that these composites were cytocompatible, and cell alignment along the PGFs was observed possibly due to their favourable ionic release properties. 3) Investigating the solid-state foaming using carbon dioxide (CO2) of PDLLA-PGP composites with up to 30 vol.% filler content. While PDLLA foams resulted in 92% porosity, the porosity of the composites ranged between 79 and 91% which decreased with PGP content. In addition, a reduction in pore size was observed with increasing PGP content; however, the pore size maintained its range of 200-500 µm in all composite foams, suitable for bone tissue engineering applications. The percentage of open pores increased significantly with PGP content (up to 78% at 30 vol.% PGP). Compressive strength and modulus of PDLLA-PGP foams showed up to approximately 3-fold increase at 30 vol.% PGP content compared to neat PDLLA foams.
Les défauts osseux découlant de maladies ou de traumatismes constituent un problème de santé majeur à l'échelle mondiale. Le génie tissulaire représente une autre option pour réparer et régénérer des os en faisant appel à l'échafaudage cellulaire. L'échafaudage ainsi produit devrait fournir un milieu adéquat pour la prolifération et la différentiation des ostéoblastes et entraîner, à terme, la formation d'os. L'échafaudage doit être biodégradable, biocompatible, poreux à structure ouverte, et doit pouvoir résister aux forces appliquées. Des verres à base de phosphate (PG) peuvent être utilisés comme agents de renforcement dans des composites biodégradables puisque leur dégradation peut être prédite et maîtrisée par l'intermédiaire de leurs propriétés chimiques. La présente thèse de doctorat décrit la mise au point et l'évaluation de polymères biodégradables renforcés avec des PG pour des applications d'augmentation et de régénération osseuses. La recherche présentée visait les trois principaux objectifs suivants : 1) l'étude des propriétés dépendantes de la composition de nouvelles formulations de PG par le dopage de verres de calcium à base de phosphate exempts de sodium (50P2O5-40CaO, en % molaire) avec du SiO2, du Fe2O3 et du TiO2. Ainsi, des formulations de (50P2O5-40CaO-xSiO2-(10-x)Fe2O3, où x = 10, 5 et 0 % mol) et (50P2O5-40CaO-xSiO2-(10-x)TiO2 où x = 10, 7, 5, 3 et 0 % mol) ont été mises au point et caractérisées. L'incorporation de SiO2 s'est traduite par une augmentation de la solubilité, de la libération d'ions, de la réduction du pH, ainsi que de l'hydrophilicité, de l'énergie de surface et de la polarité. En revanche, le dopage au Fe2O3 ou au TiO2 a donné des verres plus durables, en plus d'améliorer la fixation et la viabilité cellulaires. Il a été postulé que la présence de SiO2 dans les formulations dopées au TiO2 pourrait accroître la libération d'ions des PG, entraînant ainsi une activité de l'ALP accrue des cellules MC3T3-E1. 2) l'incorporation de PG dopés aux Si, Fe et Ti comme charges, sous forme de particules ou de fibres, dans des polyesters biodégradables (polycaprolactone (PCL) et acides polylactiques amorphes (PLA et PDLLA)) dans le but de mettre au point des composites dégradables analogues aux os. Il a été établi que la composition et la géométrie des PG déterminent la perte de poids, la libération d'ions, et les propriétés mécaniques des composites. Il a également été postulé qu'une réaction potentielle entre le Si et le lien ester entraînait la formation de sous-produits de carboxylate, ce qui se traduirait par un polymère de poids moléculaire réduit et aurait ainsi une incidence sur les propriétés mécaniques des composites. L'évaluation de la cytocompatibilité avec les préostéoblastes MC3T3-E1 a démontré que ces composites étaient cytocompatibles, et un alignement de cellules le long des PGF a été observé, qui pourrait être dû à leurs propriétés de libération d'ions favorables. 3) l'investigation du moussage en milieu solide avec du dioxyde de carbone (CO2) de composites de PDLLA-PGP contenant jusqu'à 30 % vol de charge. Alors que les mousses de PDLLA présentaient 92 % de porosité, la porosité des composites allait de 79 % à 91 %, diminuant avec la teneur en PGP. En outre, une réduction de la taille des pores a été observée avec l'augmentation de la teneur en PGP; la fourchette de dimensions des pores est toutefois demeurée la même (de 200 µm à 500 µm) pour toutes les mousses de composites, qui conviennent à des applications en génie tissulaire osseux. Le pourcentage de pores ouverts a augmenté significativement avec la teneur en PGP (jusqu'à 78 % à 30 % vol de PGP). La résistance à la compression et le module d'élasticité en compression des mousses PDLLA-PGP avaient à peu près triplé à 30 % vol de PGP par rapport à celles des mousses seulement constituées de PDLLA.

This thesis work was conducted in the Department of Mechanical Engineering at the Cape Peninsula University of Technology (CPUT) and was submitted towards the partial fulfilment of the Masters Degree in Technology: Mechanical Engineering.
Recent years have witnessed a tremendous growth and significant advances in “smart” composites and “smart” composite structures. These smart composites integrate active elements such as sensors and actuators into a host structure to create improved or new functionalities through a clever choice of the active elements and/or a proper design of the structure. Such composites are able to sense a change in the environment and make a useful response by using an external feedback control system. Depending on their applications, smart composites usually make use of either the joint properties of the structure or the properties of the individual elements within the composites. The accumulation in the understanding of materials science and the rapid developments in computational capabilities have provided an even wider framework for the implementation of multi-functionality in composites and make “smart” composites “intelligent”.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
O campo dos nanomateriais tem se expandido enormemente nas últimas décadas principalmente devido às suas propriedades especiais. As experiências descritas na literatura em grande gama de aplicações mostram propriedades elétricas, magnéticas, ópticas e outras, extremamente aperfeiçoadas com relação aos sisstemas macroscópios. A ciência e tecnologia trabalham atualmente com inúmeras técnicas químicas para a obtenção de óxidos e dentre elas destaca-se o Método Poliol por ser vantajoso e adequado na preparação de nanopartículas com variadas morfologias, dimensões e crisalinidade. Entretanto, poucos estudos foram realizados sobre a síntese e a caracterização de compósitos com o propósito de investigar as propriedades resultantes da possível sinergia obtida a partir da interação entre dois óxidos nanoestruturados. Este trabalho teve como objetivo a síntese e a caracterização de compósito nanoestruturado formado de dois óxidos multifuncionais: o óxido de zinco e o dióxido de titânio. Para a síntese foram utilizados o acetato de zinco dihidratado e o isopropóxido de titânio para a obtenção do ZnO e do TiO2, respectivamente. o compósito foi obtido pelo Método Poliol a partir da interrupção momentânea da síntese dos óxidos isolados seguido da mistura das soluções. O compósito, assim como os óxidos sintetizados isoladamente, foram caracterizados po9r difração de raios X (DRX), análise térmicas (TG/DTA), medidas de adsorção de gás nitrogênio (BET), microscopia eletrônica de varredura (MEV), espectroscopia de adsorção de luz na região do ultravioleta, visível e infravermelho, espectroscopia Raman. O compósito formado pelo Método Poliol apresentou o ZnO na forma aglomerado, porém nanoestruturado, e o TiO2 após tratamento térmico de 400º C. Foi verificada ainda a presença de resíduos orgânicos nos materiais como... (Resumo completo, clicar acesso
The field of nanomaterials has expanded greatly in recent decades mainly due to its special propoerties. The experiments described in the literature in a wide variety of applications show electrical properties, magnetic, optical and others, extremely improvement properties with respect to macroscopic systems. Science a technology are currently working with numerous chemical techniques to achieve oxides and them stands out the Polyol Method to be advantageous and appropriate in the preparation of nanoparticles with various morphologies, size and crystallinity. However, few studies have been done on the synthesis and characterization of composites in order to investigate the resultants properties from possible synergy obtained from the interaction between two nanoestructured oxides. This work aimed to the synthesis and characterization nanostructured composites formed by two multifunctional oxides, zinc oxide and titanium dioxide. For the synthesis were used zinc acetate dihydrate and titanium isopropoxide to obtain the ZnO and TiO2, respectively. The composite was obtained by Polyol from the interruption of the synthesis of single oxides followed by mixing the solutions. The composite, as weell as oxides separately synthesized, were characterized by X-ray diffraction (XRD), thermal analysis (TG/DTA), meassurements of nitrogen gas adsorption (BET), scanning electron microscopy (SEM), YV-VIS and IR absorption spectroscopy and Raman spectroscopy. The composite obtained by the Polyol Method presented ZnO as agglomerate, however nanostructured, and TiO2 after heat treatment of 400ºC. It was also verified the presence of organic waste in the materials as synthesized and titanium glycolate as an intermediate in the reaction of titanium dioxide. A comparison of optical behavior, as synthesized composite formed by ZnO and titanium... (Complete abstract click electronic access below)

Orientador: Dayse Iara dos Santos
Banca: Alejandra Hortencia Miranda González
Banca: Marcela Mohallem Oliveira
Resumo: O campo dos nanomateriais tem se expandido enormemente nas últimas décadas principalmente devido às suas propriedades especiais. As experiências descritas na literatura em grande gama de aplicações mostram propriedades elétricas, magnéticas, ópticas e outras, extremamente aperfeiçoadas com relação aos sisstemas macroscópios. A ciência e tecnologia trabalham atualmente com inúmeras técnicas químicas para a obtenção de óxidos e dentre elas destaca-se o Método Poliol por ser vantajoso e adequado na preparação de nanopartículas com variadas morfologias, dimensões e crisalinidade. Entretanto, poucos estudos foram realizados sobre a síntese e a caracterização de compósitos com o propósito de investigar as propriedades resultantes da possível sinergia obtida a partir da interação entre dois óxidos nanoestruturados. Este trabalho teve como objetivo a síntese e a caracterização de compósito nanoestruturado formado de dois óxidos multifuncionais: o óxido de zinco e o dióxido de titânio. Para a síntese foram utilizados o acetato de zinco dihidratado e o isopropóxido de titânio para a obtenção do ZnO e do TiO2, respectivamente. o compósito foi obtido pelo Método Poliol a partir da interrupção momentânea da síntese dos óxidos isolados seguido da mistura das soluções. O compósito, assim como os óxidos sintetizados isoladamente, foram caracterizados po9r difração de raios X (DRX), análise térmicas (TG/DTA), medidas de adsorção de gás nitrogênio (BET), microscopia eletrônica de varredura (MEV), espectroscopia de adsorção de luz na região do ultravioleta, visível e infravermelho, espectroscopia Raman. O compósito formado pelo Método Poliol apresentou o ZnO na forma aglomerado, porém nanoestruturado, e o TiO2 após tratamento térmico de 400º C. Foi verificada ainda a presença de resíduos orgânicos nos materiais como... (Resumo completo, clicar acesso
Abstract: The field of nanomaterials has expanded greatly in recent decades mainly due to its special propoerties. The experiments described in the literature in a wide variety of applications show electrical properties, magnetic, optical and others, extremely improvement properties with respect to macroscopic systems. Science a technology are currently working with numerous chemical techniques to achieve oxides and them stands out the Polyol Method to be advantageous and appropriate in the preparation of nanoparticles with various morphologies, size and crystallinity. However, few studies have been done on the synthesis and characterization of composites in order to investigate the resultants properties from possible synergy obtained from the interaction between two nanoestructured oxides. This work aimed to the synthesis and characterization nanostructured composites formed by two multifunctional oxides, zinc oxide and titanium dioxide. For the synthesis were used zinc acetate dihydrate and titanium isopropoxide to obtain the ZnO and TiO2, respectively. The composite was obtained by Polyol from the interruption of the synthesis of single oxides followed by mixing the solutions. The composite, as weell as oxides separately synthesized, were characterized by X-ray diffraction (XRD), thermal analysis (TG/DTA), meassurements of nitrogen gas adsorption (BET), scanning electron microscopy (SEM), YV-VIS and IR absorption spectroscopy and Raman spectroscopy. The composite obtained by the Polyol Method presented ZnO as agglomerate, however nanostructured, and TiO2 after heat treatment of 400ºC. It was also verified the presence of organic waste in the materials as synthesized and titanium glycolate as an intermediate in the reaction of titanium dioxide. A comparison of optical behavior, as synthesized composite formed by ZnO and titanium... (Complete abstract click electronic access below)
Mestre

The indentation behaviour and erosion properties of two commercially available ceramic materials, a silicon carbide (Hexoloy SA) and silicon carbide-titanium diboride composite (Hexoloy ST) have been investigated over a range of experimental conditions. The microstructure of both materials has been examined using reflected light and scanning electron microscopy. Hexoloy SA is a single phase material with a grain size typically ranging from 4 to 8 mum, while Hexoloy ST is a two phase particulate composite, containing about 16 vol% of discrete titanium diboride particles in a silicon carbide matrix, with a more uniform grain size. The materials have both been shown to have weak grain boundaries. The silicon carbide-titanium diboride interface is weak and this is believed to be due to tensile residual stresses arising from the mismatch in coefficients of thermal expansion of the two phases. Vickers indentation testing indicated that both materials have similar hardness values, but that the composite was significantly tougher than the monolithic material. Sub-surface crack profiles have been examined with a particular regard to radial and lateral cracking. It was found that the scale of lateral cracking was not directly proportional to the length of radial cracks in these materials. Indeed, lateral cracks were not seen when the radial/median system was fully formed, but only when it was partially formed. This is an important observation since one of the fundamental assumptions of two models of erosion is that radial and lateral length are directly proportional. Another important finding of the indentation study was that lateral cracking occurred to a greater extent in the composite than in the monolithic materials at low loads, indicating that wear of the composite may be relatively more extensive for the smaller erodent sizes. Erosion testing has been performed using a gas blast apparatus. Different sizes of silica and silicon carbide erodent have been used for tests from room temperature to 1000°C. With the silica erodent, material loss progressed by small scale cracking. The mechanisms of material removal involved grain boundary cracking in the monolithic material and grain boundary cracking and cracking along the particuiate-matrix interface in the composite. For the silicon carbide erodent, lateral cracking has been shown to be the dominant mechanism of material removal. In the monolithic SIC the lateral cracking scales with erodent size, while in the composite the TiB2 particles inhibit growth of the laterals generated by the largest erodent, but proved to be detrimental when using the smallest erodent. This observation was consistent with the observations from quasi-static Indentation. The presence of an easily removed oxide on the surface of the TiB2 particles has led to an increase in the erosion rate of the composite at temperatures greater than 800 °C for the silica erodent. At lower temperatures both materials behaved similarly. When using the silicon carbide erodent, increasing the temperature resulted in an increase in the erosion rate for both materials although at the lower temperatures, the composite was more erosion resistant than the monolithic material. As the temperature increased, the erosion rates converged, suggesting that the toughening mechanisms of the composite were decreasing in effectiveness. Thus, it has been shown that the presence of TiB2 particles can lead to increased or decreased erosion resistance relative to the monolithic material, depending on the precise erosion conditions. In general, the composite has the lower wear rate at lower temperatures and larger erodent sizes. Also, it has been shown that cracking due to quasi-static indentation using a sharp indenter is consistent with the damage produced by hard, sharp erodent particles at room temperature.

This thesis explores new methods for achieving load-carrying joints between the dissimilar materials of continuous fibre reinforced polymer matrix composites and structural metals. The new composite-to-metal joining methods investigated in this work exploit the metal-to-metal joining techniques of arc micro-welding, resistance spot welding, and metal filler brazing, to form novel micro-architectured metal adherends that can be used for enhanced composite-to-metal joining. Through a combination of equipment instrumentation and metallographic inspection of fabricated prototype joints, understanding is gained of how materials respond when processed by manufacturing techniques that have not previously been exploited for dissimilar material joining. Mechanical testing of prototype joints; both to ultimate loading strength and partial failure states, with subsequent inspection of specimens and comparative performances evaluation enabled joining performance characterisation of the new joining methods. Key results include: the identification of micropin reinforced adhesive joints to exhibit pseudo-ductile failure characteristics, resistance spot weld reinforcement of adhesive joints to boost bonding performance, and the use of a polymer infused metal foam to overcome difficulties of thermoplastic to metal adhesion. Through this work knowledge of how novel micro-architectures reacted under mechanical loading enabled insights to be gained into how perceived manufacturing defects can benefit joining performance. Such examples include, localised material weakness that lead to global pseudo-ductile failure behaviour, and low-strength secondary joining mechanisms boosting primary load transfer systems. By comparison of the diverse joining methods investigated in this work, trends were identified that suggest joining performance between the two dissimilar materials is improved by increasing the direct interaction between the composite reinforcement fibres and the metal structure. It is demonstrated that joining improvements are gained by forming mechanical connections between metals and composite precursory material before the final manufacturing process of the composite.

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Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Abstract My Ph.D. project focused on the tailoring of the surface properties of oxide substrates for the preparation of advanced composite materials and devices. The initial focus of my research activity was the surface modification of halloysite nanotubes (HNT), a natural material with unique structural features. I then extended my investigation to other oxides (titanium dioxide, TiO2, and Superparamagnetic Iron Oxide Nanoparticles, SPION), applying the surface modification approaches developed for HNT substrates. The resulting oxide-based hybrid systems showed promising properties as stimuli-responsive devices for health and environmental applications, and as fillers for polymeric nanocomposites with enhanced durability. The main results obtained for each oxide material will be presented in the following sections. 1. Halloysite nanotubes (HNT) Halloysite is a polymorph of kaolinite which naturally wraps itself to form tubular structures (Figure 1A). It is one of the few nanotubular systems presenting an inner lumen and an outer surface characterized by different surface charge and structural composition: the internal surface exposes aluminium hydroxyl groups, while the outermost layer is silica[1]. Among its many potential applications, its tubular dual structure has sparked interest in the field of nanomedicine and polymer nanocomposites[2]. However, only few reports investigated the possibility of a selective functionalization of the inner and outer HNT surfaces. During my first year of PhD, I investigated the selective functionalization of HNT with phosphonates, hetero-organic compounds bearing a C PO(OH)2 group, as potential site-specific linkers for the grafting of active molecules. I took advantage of the phosphonic acid selectivity towards certain oxides (especially aluminium oxides) to achieve surface-specific functionalization of HNT. An in-depth comprehension of such hybrid systems is no trivial matter, as the inner and outer HNT surfaces possess different accessibility and reactivity but are not separable. For this reason, beside HNT, I used purposely prepared model oxides, mimicking the inner and outer nanotube surfaces, to better study the actual selectivity towards SiO2 and AlOOH exhibited by the phosphonate moiety. Octylphosphonic acid (OPA) was chosen as functionalizing agent, as its alkyl chain allowed me to monitor the surface modification through changes in the water contact angle (θ). I found that the oxide isoelectric point (pHIEP) plays a major role in determining a stable OPA adsorption: while AlOOH showed good reactivity towards OPA, SiO2, which is negatively charged at the impregnation pH (pH 4), did not react with the phosphonate heads. The functionalization reversibility was also assessed: Samples showed OPA release at pH values more alkaline than the oxide isoelectric point, when the surface charge is negative. Overall, these results support an OPA-oxide bond governed both by electrostatic and covalent forces. The selective functionalization of HNT inner lumen was also demonstrated via a combination of characterization techniques, including FTIR spectroscopy, ζ-potential measurement and water dispersibility assay. Another scantly investigated topic regarding HNT nanosystems is their covalent modification. Covalent grafting allows for a superior control over the release kinetics of active principles, as the initial release burst observed in the case of electrostatically bound compounds is greatly reduced. In this respect, I studied the covalent attachment of a biologically active molecule to HNT via an imine bond. This type of covalent bond was chosen to open up the possibility for a controlled release of the bioactive molecule activated by pH changes. To this purpose, HNT was functionalized with (3 aminopropyl)triethoxysilane (APTES), a bifunctional linker which can cover the oxide surface with amino groups. Despite being non-selective for either of the two phases, it was chosen based on the relative ease with which it can be grafted to the substrate. Then, tetrathia[7]helicene aldehyde (7-THA) was bound to HNT via APTES, exploiting imine chemistry. 7-THA belongs to a group of polyaromatic molecules capable, thanks to their peculiar helicoidal shape, of intercalating DNA strands, which is at the basis of anti-sense therapy[3]. Nonetheless, HNT abysmal water solubility highly reduces their bioavailability and makes the use of hydrophilic nanocarriers necessary. I tested the relative release efficiency of 7-THA under slightly different pH conditions, representative of lysosomal, tumoral and healthy extracellular pH values. The resulting HNT-7TH system was studied in detail via XPS and angle-resolved near edge X-ray absorption fine structure spectroscopy (NEXAFS) at the Material Science Beamline of the Elettra synchrotron facility. The latter characterization technique required the synthesis and functionalization of oxide films replicating HNT surfaces, in order to probe the orientation of a population of adsorbed molecules with respect to the surface plane. NEXAFS results suggested a preferential orientation of the aromatic rings of helicene normal to the oxide surface, possibly as a result of π-π stacking interactions (Figure 1B). XPS analyses were performed at each stage of the preparation process of HNT-7TH and after the release test at pH 5 (Figure 1C): the observed change in the elemental composition indicated a release of 70% of the loaded 7-THA as a result of pH change. Given the interest for tumour therapy applications, in vitro tests were carried out to assess the selectivity of this system on cancer cells. The effect of HNT-7TH on the viability of bladder cancer cells was tested by Dr Riccardo Vago at the IRCCS San Raffaele Scientific Institute. Two different cell lines, named 5637 and HT-1376, with an extracellular pH of 7.2 and 6.8 respectively, were subjected to increasing concentrations of HNT 7TH and bare HNT as control. HNT 7TH was found to cause a more marked reduction in cell viability on the HT-1376 cell line, suggesting a faster release of the cytotoxic 7-THA at slightly acidic pH values. Release kinetics also supported this hypothesis: a new model system utilizing benzodithiophene (BDT), a more water-soluble mimic of 7-THA, was prepared analogously to the HNT-7TH powders. The release of BDT was monitored via UV-vis spectroscopy at pH 5.0, 6.8 and 7.4. The amount of released BDT at pH 7.4 was negligible even after 48 h; decreasing the pH value to 6.8 visibly increased release rates, while the release efficiency was highest for the treatment at pH 5.0. The natural origin of HNT causes a marked variability in its physicochemical features, such as its morphology and surface charge, depending on the extraction site[4]. I investigated this aspect, often overlooked in the literature, with respect to the integration of HNT as nanofillers in polymer composites. Halloysite has been investigated as filler owing to its low cost, thermal and mechanical resistance, and high aspect ratio, which is crucial to guarantee strong polymer-filler interactions[5]. In this regard, I investigated also the effect of surface functionalization in promoting HNT compatibility with the chosen polymer matrix, Polyamide 6 (PA6). PA6 has a broad range of applications, from the automotive sector to the textile industry, owing to its good mechanical performances and high thermal resistance. However, when exposed to humid conditions, it suffers from degradation in a matter of few weeks[6], as water can interpenetrate within the hydrogen bonds between –NH and C=O groups and disrupt them, leading to the loss of tensile strength and elasticity[6–9]. The addition of nanotubular fillers represents a viable strategy for overcoming this issue, although the additive/polymer interface at high filler content can become a privileged site for moisture accumulation[10]. For this reason, HNT were added to PA6 in very low amounts (< 5%w). The roles played in the reinforcement of the polymer by the physicochemical properties of HNT from two different sources and their functionalization with APTES were investigated in composites prepared by two different dispersion techniques (in situ polymerization vs. melt blending). The aspect ratio (5 vs. 15) and surface charge (−31 vs. −59 mV) of the two HNT samples proved crucial in determining their distribution within the polymer matrix: both in situ and melt blending dispersion techniques showed that lower surface area, higher aspect ratio and greater surface charge enhance filler incorporation and improve the final composite performance. Finally, filler surface modification with APTES played a major role in the durability of the PA6-HNT nanocomposites: after 1680 h of hydrothermal ageing, functionalized HNT reduced the diffusion of water into the polymer, lowering water uptake after 600 h up to 90%, increasing the materials durability. Positive effects could also be measured regarding the molecular weight distribution and rheological behaviour. These improvements could be related to the presence of amino groups on the HNT surface, which lowered the filler surface energy and prevented the diffusion of water molecules into the nanocomposites[11]. 2. Titanium dioxide TiO2 is arguably the most extensively investigated semiconductor for photocatalytic applications, from solar cells to pollutant abatement. However, applications of TiO2 for the preparation of smart surfaces are comparatively less common. My research interest in TiO2 started with the preparation of surfaces with controlled wetting features. First, the surface of commercial TiO2 powders was functionalized with perfluorinated alkylsilanes. Then, I employed the photocatalytic features of TiO2 films to produce patterned surfaces with superhydrophilic/superhydrophobic contrast by means of photocatalytic lithography. During the course of my second year of PhD, I focused on the deposition of TiO2 films with controlled porosity followed by their surface modification to impart them functional properties. These systems were applied as photo renewable coatings for electrochemical sensors and stimuli-responsive surfaces for the controlled release of active compounds. Control over film porosity was achieved by a hard-template approach using polystyrene (PS) nanospheres of different sizes, both commercial and synthesized in-house following a classical procedure[12]. Different film deposition strategies were investigated. First, I deposited a TiO2 layer on top of a porous SiO2 coating on a FTO electrode. Extensive characterization via cyclic voltammetry showed that the addition of a TiO2 layer increased peak currents due to the promoted diffusion of the analyte in the porous structure, driven by capillary effects[13] (Figure 2A). Furthermore, the TiO2 layer promoted the light-activated regeneration of the electrode surface after having been fouled. Starting from there, I investigated the possibility of pure TiO2 mesoporous films, a task made difficult by the intrinsic incompatibility between an alcohol-based TiO2 sol, extremely prone to hydrolysis, and a water-based PS suspension. This issue was solved by either adopting an aqueous TiO2 sol, slowly evaporated in presence of the particle templates (Figure 2B), or by performing a solvent exchange procedure on the PS suspension. The latter procedure resulted in pure TiO2 films with easily tuneable thickness and homogeneous porosity, opening the door to a fine tuning of the cyclovoltammetric response. The self-cleaning features of the pure TiO2 films were also tested by purposely fouling their surface with long-alkyl chain substituents: a fast and complete regeneration of the surface was achieved upon irradiation with UV light. The prepared pure TiO2 porous films were also used as substrates for the loading of bioactive substances. Cinnamaldehyde, a natural substance known for its antimicrobial properties but unstable in environmental conditions, was anchored to the film surface via APTES linkers through an imine bond, using a protocol similar to the one developed for 7-THA-loaded HNT. The immobilized cinnamaldehyde proved stable to environmental conditions for months and tests of pH triggered release performed at pH 5.5 and 7.4, showed a faster release at lower pH values. Finally, the photoactive nature of the oxide substrate could be used to promote the self-cleaning of the fouled surface after usage: after UV-light regeneration, the TiO2 film could be functionalized anew and reused. 3. Superparamagnetic Iron Oxide Nanoparticles (SPION) During my third year of PhD, I spent six months at the Technische Universiteit Delft, Netherlands, in the Advanced Soft Matter group, under the supervision of Dr Laura Rossi. There my research focused on the synthesis and surface modification of Ultrasmall SPION. SPION have gained increasing attention thanks to their peculiar behaviour: being smaller than a single magnetic crystal domain, they are free to rotate unless a specific orientation is induced by an external field. Due to their magnetic properties, they can be adopted in hyperthermia, drug delivery and as contrast agents (CA) for magnetic resonance imaging (MRI)[14]. Contrast agents are commonly used to speed up either T1 or T2 relaxation, enhancing the local contrast in pathological tissue to produce more detailed images. T1 CA are commonly represented by gadolinium complexes, while SPION are generally adopted as T2 CA. The first are preferred by radiologists, while the latter are less favoured because the darker tones they provide can be mistaken with low resolution and background interference[15,16]. Nonetheless, Gd-based CA present a serious health risk for those patients unable to efficiently remove these heavy metal complexes due to pre-existent kidney or liver pathologies[17]. While most SPION act as T2 CA, several papers report their potential use as T1 CA if their size is sufficiently small, indicatively less than 4 nm[18,19]. These materials are known as Ultrasmall SPION, or USPION. My aim was to develop a synthetic protocol to prepare USPION suitable as T1 contrast agents via co-precipitation, to minimize synthetic requirements. To this purpose, the influence of several parameters such as reaction temperature, base type, purification procedure, stabilizing agent and precursor concentration was investigated. Particles were synthesised at room temperature (RT) and 50°C, using NH4OH, N(CH3)4OH or NaOH as base. Particle purification was performed via magnetic decantation, centrifugation and dialysis against different solutions (water, citric acid and sodium citrate solutions). Sodium oleate, (3-aminopropyl)triethoxysilane (APTES) and citric acid were tested as stabilizing agents and precursor concentration was varied between 1 M and 0.5 M. It was found that the best results were obtained at room temperature and that the peptizing effect of the tetramethylammonium ion is crucial to guarantee an optimal colloidal stability, making N(CH3)4OH the base of choice. The concentration of starting precursor solutions proved to be the determining factor acting on particle size, as halving it led to a narrow particle size distribution centred around 3 nm, a significant shift from the starting 7 nm (Figure 3). Centrifugation was ineffective when adopted to wash the nanoparticles, but it proved a promising size-selection tool that could be combined with dialysis in an efficient work up protocol. Dialysis proved to be the most efficient technique to remove potentially toxic impurities, but it negatively impacted the colloidal stability, which could be mitigated by the use of a proper stabilizing agent. To preserve a high colloidal stability even after the removal of N(CH3)4OH, surface modification with several stabilizing agents was tested. Among the tested molecules, citric acid was the only one to show positive effects on particle size and aggregation, more so when added before the start of particle nucleation. These results represent a promising advance in the development of efficient T1 contrast agents based on USPION in terms of lowering the synthetic requirements: monodisperse magnetic nanoparticles were prepared through a simple co-precipitation procedure, performed at room temperature, without the aid of any polymeric additive. References [1] Y. Lvov, W. Wang, L. Zhang, R. Fakhrullin, Halloysite Clay Nanotubes for Loading and Sustained Release of Functional Compounds, Adv. Mater. 28 (2016) 1227–1250. doi:10.1002/adma.201502341. [2] E. Abdullayev, V. Abbasov, A. Tursunbayeva, V. Portnov, H. Ibrahimov, G. Mukhtarova, Y. Lvov, Self-healing coatings based on halloysite clay polymer composites for protection of copper alloys, ACS Appl. Mater. Interfaces. 5 (2013) 4464–4471. doi:10.1021/am400936m. [3] E. Licandro, S. Cauteruccio, D. Dova, Thiahelicenes, in: 2016: pp. 1–46. doi:10.1016/bs.aihch.2015.12.001. [4] E. Joussein, S. Petit, J. Churchman, B. Theng, D. Righi, B. Delvaux, Halloysite clay minerals – a review, Clay Miner. 40 (2005) 383–426. doi:10.1180/0009855054040180. [5] M.R. Ayatollahi, S. Shadlou, M.M. Shokrieh, M. Chitsazzadeh, Effect of multi-walled carbon nanotube aspect ratio on mechanical and electrical properties of epoxy-based nanocomposites, Polym. Test. 30 (2011) 548–556. doi:10.1016/j.polymertesting.2011.04.008. [6] I. Ksouri, O. De Almeida, N. Haddar, Long term ageing of polyamide 6 and polyamide 6 reinforced with 30% of glass fibers: physicochemical, mechanical and morphological characterization, J. Polym. Res. 24 (2017) 133. doi:10.1007/s10965-017-1292-6. [7] H. Shinzawa, J. Mizukado, Water absorption by polyamide (PA) 6 studied with two-trace two-dimensional (2T2D) near-infrared (NIR) correlation spectroscopy, J. Mol. Struct. 1217 (2020) 128389. doi:10.1016/j.molstruc.2020.128389. [8] K.R. Rajeesh, R. Gnanamoorthy, R. Velmurugan, Effect of humidity on the indentation hardness and flexural fatigue behavior of polyamide 6 nanocomposite, Mater. Sci. Eng. A. 527 (2010) 2826–2830. doi:10.1016/j.msea.2010.01.070. [9] D.P.N. Vlasveld, J. Groenewold, H.E.N. Bersee, S.J. Picken, Moisture absorption in polyamide-6 silicate nanocomposites and its influence on the mechanical properties, Polymer (Guildf). 46 (2005) 12567–12576. doi:10.1016/j.polymer.2005.10.096. [10] K.P. Pramoda, T. Liu, Effect of moisture on the dynamic mechanical relaxation of polyamide-6/clay nanocomposites, J. Polym. Sci. Part B Polym. Phys. 42 (2004) 1823–1830. doi:10.1002/polb.20061. [11] K. Prashantha, M.F. Lacrampe, P. Krawczak, Processing and characterization of halloysite nanotubes filled polypropylene nanocomposites based on a masterbatch route: effect of halloysites treatment on structural and mechanical properties, Express Polym. Lett. 5 (2011) 295–307. doi:10.3144/expresspolymlett.2011.30. [12] J.W. Goodwin, J. Hearn, C.C. Ho, R.H. Ottewill, Studies on the preparation and characterization of monodisperse polystyrene latices, Colloid Polym. Sci. 252 (1974) 464–471. [13] L. Rimoldi, V. Pifferi, D. Meroni, G. Soliveri, S. Ardizzone, L. Falciola, Three-dimensional mesoporous silica networks with improved diffusion and interference-abating properties for electrochemical sensing, Electrochim. Acta. 291 (2018) 73–83. doi:10.1016/j.electacta.2018.08.131. [14] J. Dulińska-Litewka, A. Łazarczyk, P. Hałubiec, O. Szafrański, K. Karnas, A. Karewicz, Superparamagnetic Iron Oxide Nanoparticles—Current and Prospective Medical Applications, Materials (Basel). 12 (2019) 617. doi:10.3390/ma12040617. [15] Y. Okuhata, Delivery of diagnostic agents for magnetic resonance imaging, Adv. Drug Deliv. Rev. 37 (1999) 121–137. doi:10.1016/S0169-409X(98)00103-3. [16] J.-C. Brisset, M. Sigovan, F. Chauveau, A. Riou, E. Devillard, V. Desestret, M. Touret, S. Nataf, J. Honnorat, E. Canet-Soulas, N. Nighoghossian, Y. Berthezene, M. Wiart, Quantification of Iron-Labeled Cells with Positive Contrast in Mouse Brains, Mol. Imaging Biol. 13 (2011) 672–678. doi:10.1007/s11307-010-0402-1. [17] M. Rogosnitzky, S. Branch, Gadolinium-based contrast agent toxicity: a review of known and proposed mechanisms, BioMetals. 29 (2016) 365–376. doi:10.1007/s10534-016-9931-7. [18] H. Wei, O.T. Bruns, M.G. Kaul, E.C. Hansen, M. Barch, A. Wiśniowska, O. Chen, Y. Chen, N. Li, S. Okada, J.M. Cordero, M. Heine, C.T. Farrar, D.M. Montana, G. Adam, H. Ittrich, A. Jasanoff, P. Nielsen, M.G. Bawendi, Exceedingly small iron oxide nanoparticles as positive MRI contrast agents, Proc. Natl. Acad. Sci. 114 (2017) 2325–2330. doi:10.1073/pnas.1620145114. [19] Y. Bao, J.A. Sherwood, Z. Sun, Magnetic iron oxide nanoparticles as T 1 contrast agents for magnetic resonance imaging, J. Mater. Chem. C. 6 (2018) 1280–1290. doi:10.1039/C7TC05854C.

Orientador: Cecilia Amelia de Carvalho Zavaglia
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia mecanica
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Resumo: Existe uma crescente demanda de materiais que possibilitam a remodelação e reconstrução de partes ósseas. A indicação de biomateriais para reconstrução dos defeitos cranianos depois do trauma, tumor ou infecção, ocorre devido a razões estéticas e proteção de estruturas intracraniais. Várias técnicas cirúrgicas vários materiais já foram utilizados na confecção dessas próteses crâniomaxilofaciais, mas é importante avaliar o comportamento desse material quanto à estabilidade fisiológica e resistência mecânica. O objetivo principal deste trabalho é desenvolver biomateriais para uso em preenchimento de defeitos ósseos. A hidroxiapatita, cerâmica bioativa semelhante à parte mineral do tecido ósseo, é um material que poderia ser utilizado para essa finalidade. Porém, essa cerâmica possui baixas tenacidade à fratura e resistência mecânica à compressão. Com a finalidade de obter materiais mais adequados para restaurações ósseas e implantes crâniomaxilofaciais, foram associadas a hidroxiapatita obtida no laboratório de materiais cerâmicos do DEMA-FEM-UNICAMP, partículas de reforço de três cerâmicas: zircônia, alumina e titânia, nas proporções de 30,40 e 50% em peso para cada composição. Os compósitos obtidos e sinterizados foram caracterizados por medida de tamanho de partículas, Microscopia Eletrônica de Varredura, Difração de Raios X e Espectroscopia de Fluorescência de Raios X e tiveram suas densidades aparentes, densidades teóricas, absorção de água, volumes aparentes e porosidades aparentes determinadas pelo ensaio de Archimedes. Algumas propriedades mecânicas como resistência à compressão, dureza e tenacidade à fratura foram determinadas. Os compósitos que tiveram melhor comportamento geral foram escolhidos para continuidade do trabalho (ensaios ¿ in vitro" e ¿Hin vivo ")
Abstract: There is a growing demand of materiaIs that make the remodeling and reconstruction of bone parts possible. Reconstruction of defects of the skulI after trauma, tumor or infection is indicated for aesthetic reasons and for protection of internal structures. Different materiaIs have been used for this purpose and alI of them must be evaluated as for their stability in physiological environments and mechanical strength. The main objective of this work is to develop biomaterials for use in fulfilIing of bone defects. The hydroxyapatite, similar bioactive ceramics to the mineral part of the tissue bone, is a material that could be used for this purpose. However, this ceramics possess decreases tenacity to the breaking and resistance mechanics the compression. With the purpose to get more adequate materiaIs for bone restorations and craniomaxilofacials implantations associates had been hydroxyapatite gotten in the laboratory of ceramic materiaIs of the DEMA-FEM-UNICAMP, particles of three ceramics bioinert, zirconia, alumina and titania, in the ratios of 30%, 40% and 50% in weight for each composition. The composites obtained and sintered were characterized by particles size measure, Scanning Electronic Microscopy, X Rays Difratometry and Spectroscopy of Fluorescence of X Rays and had its apparent densities and apparent porosity determined by the assay of Archimedes. Some mechanical properties as compressive strength, hardness and tenacity to the breaking had been performanced. The composites that had general behavior had been better chosen for continuity ofthe work (assays "in vitro" and "in vivo")
Mestrado
Materiais e Processos de Fabricação
Mestre em Engenharia Mecânica

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Environmental issues such as climate change are leading to important sustainability challenges in the aerospace industry. Composites are light materials that are extensively used to replace metals and reduce the aircraft weight, the goal being to decrease the fuel consumption in flight and limit the emission of greenhouse gases. However, these high performance materials are associated with a complex supply chain including energy-consuming processes. Most of the decommissioned composite products are currently landfilled and nothing proves that the weight reduction allowed by these materials compensates those negative aspects. The purpose of this master thesis is to determine if the introduction of composites in aero-engines can be sustainable and how it can be achieved. To do so, three polymer-matrix composite components from GKN Aerospace have been studied and compared with their metallic baseline from environmental, social and economic perspectives. Several options for materials selection, manufacturing processes and recycling possibilities have been investigated in the same way. The assessment on GKN Aerospace’s components showed that the weight savings provided by composites have a strong and positive influence on their sustainability. Component B shows the best results: with 16% of weight savings with composites versus the titanium baseline, it appears clearly that the composite version is the most sustainable one. Component A2 composite version also provides interesting weight savings (14%) but has an aluminum baseline, which makes the composite component more sustainable in some aspects but not all of them, especially economically speaking. Finally, for component A1, the composite version, which does not provide weight savings, is more economically feasible, but quite tight with the titanium baseline on environmental and social aspects. Therefore, it appears that composite components are more likely to be sustainable if they provide significant weight reduction and if the baseline is titanium. A few strategies would merit attention to make future composite components more sustainable. On the one hand, using thermoplastic composites have potential to reduce the environmental, social and economic impact. In fact, these materials can be fully recycled and reused, present less risks to handle and can be produced for a lower cost. Nevertheless, the knowledge on these materials is more limited than on thermoset composite and the implementation of such a solution will take time. On the second hand, introducing composite recycling processes in the products lifecycle can increase a lot the sustainability of composite components. The manufacturing scrap and the decommissioned products can both be recycled in order to reduce the environmental impact and generate benefits by re-using or selling the recycled material.

Les alliages à mémoire de forme Nickel-Titane sont connus pour leurs propriétés de superélasticité associées à une transformation martensitique élastique, de ferroélasticité liées à la réorientation de variantes de martensite et enfin de mémoire de forme. Les propriétés des matériaux architecturés NiTi, tels que des tricots, des matériaux cellulaires,… dépendent de celles de l'alliage NiTi constituant et de la structure géométrique. L'étude porte sur des matériaux architecturés composites constitués par des matériaux architecturés NiTi saturés par des élastomères silicones. De tels matériaux possèdent potentiellement une gamme étendue de propriétés dépendant à la fois des matériaux constitutifs, mais également des interfaces et de la topologie.La première partie du travail porte sur l'étude de l'interface NiTi silicone. Parmi les solutions testées, le traitement de surface par plasma a été particulièrement étudié. L'influence des paramètres du traitement plasma sur la qualité des interfaces a tout d'abord été étudiée grâce à des essais de pull-out réalisés sur des fils de NiTi enrobés dans des silicones. Les paramètres optimaux de traitement par plasma ont ensuite été appliqués pour élaborer des matériaux architecturés tubulaires constitués d'un tricot NiTi enrobé d'élastomère. Le comportement mécanique du composite ainsi obtenu a été caractérisé par des essais de traction et de gonflement.La deuxième partie de l'étude porte sur le comportement de l'élastomère silicone. Une campagne expérimentale a été menée afin de déterminer l'influence de la température sur le comportement mécanique du silicone, en particulier sur l'accommodation du matériau après la première charge (effet Mullins), l'hystérésis mécanique et la relaxation. Une loi de comportement prenant en compte l'hystérésis mécanique a ensuite été proposée. Inspirée par de nombreux travaux en mécanique des élastomères, l'approche utilise une décomposition de l'espace en un nombre fini de directions. Une loi monodimensionnel incluant les effets d'hystérésis est écrite pour chacune des directions. Ce modèle a été implémenté dans un code de calculs par éléments finis (Abaqus) et a été testé avec des calculs de structures.Dans la troisième partie de l'étude, le formalisme précédent a été utilisé afin de proposer un modèle pour le comportement mécanique du NiTi, en se restreignant dans cette première contribution à la superélasticité. La confrontation des résultats de simulation avec ceux de tests expérimentaux de la littérature sur des plaques isotropes et anisotropes montre les perspectives prometteuses d'une telle approche
Shape memory alloys Nickel-Titanium are well known for their superelastic properties associated with a martensitic elastic transformation, ferroelasticity due to the reorientation of martensite and finally shape memory effects. The properties of architectured NiTi materials, such a knitted NiTi, cellular materials,… depend on the constituting NiTi and of the geometry. The study deals with architectured composite materials made of architectured NiTi materials and silicone rubber elastomer. Such materials present numerous different properties, depending on the constituting materials and also on the interfaces and the topology.The first part of the study focuses on the interface between NiTi and silicone rubber. Among the tested solutions, plasma treatments were especially studied. The influence of treatment parameters on the interface resistance was firstly investigated by means of pull-out tests carried out on NiTi wires embedded in a silicone rubber matrix. Optimized parameters for plasma treatment were then applied in order to elaborate a tubular architectured material made of knitted NiTi and silicone rubber. The mechanical behavior of this composite was characterized by means of tensile and swelling tests.The second part of the study deals with silicone rubber behavior. Experiments were performed in order to evaluate the influence of temperature on the mechanical behavior of silicone rubbers, especially on the stress softening (Mullins Effect), mechanical hysteresis and stress relaxation. A model taking into account the mechanical hysteresis was then proposed. Based on numerous works in the field of rubber mechanics, the approach used a decomposition of the space in a finite number of directions. A monodimensional constitutive equation including hysteresis effects is written for each direction. This model was implemented in a finite elements software (ABAQUS) and was tested with structure simulations. In the third part of the study, the previous formalism was used model the mechanical behavior of NiTi, only In case of superelasticity. The results of the simulations carried out are in good agreement with those reported in the literature for tests on isotropic and anisotropic NiTi plates, which highlights the great interest of such an approach

Resinas compostas comumente utilizadas em restaurações, anteriores e posteriores, resultam em maior acúmulo de biofilme bacteriano do que outros materiais restauradores, o que contribui para a formação de cáries secundárias e levam à falha das restaurações. Métodos para inibir a formação do biofilme sobre materiais restauradores dentais vêm sendo estudados há décadas e a inserção de nanopartículas (NPs) representa o que há de mais avançado nos estudos de formulação de materiais dentários antibacterianos. A literatura recente relata que resinas compostas contendo NPs de óxidos metálicos, tais como óxido de zinco (ZnO) e dióxido de titânio (TiO2), têm demonstrado capacidade antibacteriana, contribuindo para o controle do biofilme oral cariogênico. Por outro lado, a inserção dessas NPs pode alterar a cor e as propriedades mecânicas para níveis clínicos inaceitáveis e até mesmo dificultar o processo de fotopolimerização, se inseridas em grandes quantidades. Uma vez que o efeito antibacteriano e as propriedades de resinas compostas modificadas com NPs de óxidos de metais não foram amplamente estudados, esse estudo visou a compreensão destes aspectos, a partir da síntese e caracterização de nanopartículas de ZnO e TiO2 dopados ou não com Ag, inclusão em uma resina composta comercial e análise de propriedades físicas, mecânicas e biológicas do compósito modificado. As sínteses foram realizadas por diversas rotas químicas, resultando em NPs de TiO2 de alta área superficial e NPs de ZnO com morfologia tridimensional, incluindo nanoplates e nanorods que formam estruturas em formato de flores. A modificação da resina composta com NPs de TiO2.Ag alterou drasticamente a resistência à compressão do material, enquanto a adição de NPs de ZnO.Ag manteve a resistência em valores muito próximos ao da resina não modificada. A cor da resina composta sofreu grande alteração quando imergida em solução de café, especialmente após a adição de NPs de ZnO.Ag. A atividade antibacteriana, contra Streptococcus mutans da resina modificada foi considerada significativa, principalmente após a adição de 1 e 2% de NPs de TiO2. A análise dessas propriedades foi importante para o avanço das pesquisas que visam o desenvolvimento de uma resina composta antibacteriana que proporcione estética e propriedades mecânicas adequadas para a confecção de restaurações.
Composite resins used in restorations, anterior and posterior, resulting in greater accumulation of bacterial biofilm than other restorative materials, which contributes to the formation of secondary caries and lead to failure of restorations. Methods for inhibiting biofilm formation on dental restorative materials have been studied for decades and the insertion of nanoparticles (NPs) represents the most advanced in formulation studies of antibacterial dental materials. Recent literature reports that composites containing nanoparticles of metal oxides such as zinc oxide (ZnO) and titanium dioxide (TiO2) have demonstrated antibacterial ability, contributing to the control of oral cariogenic biofilms. On the other hand, NPS inclusion can change the color for unacceptable clinical levels and even hinder the polymerization process, if they are entered as large amounts. Since the antibacterial effect of composite resins modified with nanoparticles of metal oxides has not been widely studied, this study aimed at understanding these aspects, from the synthesis and characterization of nanoparticles of Ag doped and undoped ZnO and TiO2 NPs, inclusion in a composite business and examining their physical, mechanical and biological properties. The synthesis resulted in high surface area TiO2 NPs and three-dimensional ZnO NPs, including nanoplates and nanorods assembled flowers. The modification of the composite with TiO2.Ag NPs changed dramatically the compressive strength of the material, while adding ZnO.Ag NPs maintained compressive strength similar to the unmodified resin. The compostie color stability changed greatly when immersed in a coffee solution, especially after inclusion of ZnO.Ag NPs. The antibacterial activity, against S. mutans, of modified resin was considered significant, especially after addition of 1 and 2% TiO2 NPs. The analysis of these properties is important for the advancement of research aimed at developing an antibacterial composite that provides aesthetic and mechanical properties suitable for dental restorations.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Titanium is one of the most used biomateriais in manufacturing dental implants, especially titanium grade 4. However, titanium is a bioinert material, i.e. the interface between titaiiiun-i and host bone is a simple interlocking bonding, which can iead to the loosening ofthe implant and the eventual failure of the implantation. Bone neoformation and long terrn stability can be achieved by using bioactive materiais. Tricalcium phosphate (TCP) is one of the best options among bioactive materiais, due to its chernical and crystallographic structure being similar to that of bone mineral. However, one ofits primary restrictions on clinical use as a ioad-bearing implant is its poor mechanical properties. A good combination of the bioactivity of TCP and the mechanical properties of titanium is considered to be a promising approach to fabricating more suitable biornedical materiais for load-bearing àpplications. Therefore, the aim of this study was to ~eve1op bioactive composites by powder metallurgy using titanium hydride and tricalciuin phosphate to enhance the biocompatibility and the osseointegratjon of dental irnplants. Titanium based composites were prepared from titanium hydride (TiH2) with 2.5, 5, 7.5 and 10% in volume of β-TCP. The TiH2 was provided by Centro Técnico Aeroespacial (CTA) with a mean particle sige of l5μm. The β-TCP was provided by Cerarnic Group from UDESC with particle size below 180 nm. The mixtures were prepared with alcohol and zirconia baus in a high energy mili for five hours, foilowed by drying in a rotating evaporator. The mixtures were then pressed at 15OMPa and sintered at 1200°C for 2 hours in either vacuum or argon atinosphere. The materiais were characterized by scanning eiectron microscopy, transmission electron microscopy, X-ray diffraction and thermal analysis. The decomposition of β-TCP occuned at approximately 1100°C leading to the formation of Ti, CaTiO3, TiO2 and TixPy phases for the composites sintered in argon. For the composites sintered in vacuum it was found the sarne phases, except rutile. The composites sintered in vacuurn were better sintered exhibiting higher densificatjon than those sintered in argon. A main crystal phase of calcium titanate with a needie-like morphology was observed in the porosity of the composites. This phase was found in higher amount in the composite sintered in argon because this material presented higher porosity. This morphology is related to the presence of pores, which allow the growth of calcium titanate on a free surface.
O titânio é um dos biomateriais mais utilizados na confecção de implantes dentários. Dentre os tipos de titânio comercialmente puro (Ti cp), o mais utilizado em implantologia é o da classe quatro. Porém, o titânio é um material bioinerte, ou seja, a fixação óssea sobre a sua superficie acontece por aderência biomecânica. Em materiais bioativos, a fixação ocorre por ligação físico- química. O TCP-13 é um politipo de fosfato de cálcio que desperta muito interesse na utilização em medicina e odontologia por causa da neoformação óssea, porém, as suas propriedades mecânicas são muito baixas, inviabilizando a sua utilização na forma pura. Muitos trabalhos têm sido relatados em que a junção do titânio e fosfatos tem contribuído no desenvolvimento de biomateriais compósitos com características bioativas. O presente trabalho teve por objetivo desenvolver compósitos bioativos ~por metalurgia do pó, utilizando hidreto de titânio / fosfato tricálcico, para melhorar a biocompatibilidade e a osseointegração de implantes dentários. Foram elaborados os compósitos a base de hidreto de titânio (TiH2) com 2,5; 5; 7,5 e 10% em volume de TCP-β. O TiH2 foi doado pelo Centro Tecnológico Aeroespacial (CTA), e apresentava granulometria média de 15 μm. O TCP-β foi fornecido pelo grupo de biomateriais cerâmicos da UDESC com tamanho de partícula inferior a 180 nm. As misturas foram elaboradas com álcool e esferas dé zircônia em moinho atritor de alta energia durante cinco horas, seguidas de secagem em evaporador rotativo. Em seguida as misturas foram compactadas uniaxialmente a frio em matriz cilíndrica e retangular sob pressão de 150 MPa. Os compactados foram sinterizados em atmosfera de argônio e a vácuo nas condições de 1200 °C, durante duas horas. Os materiais foram caracterizados por microscopia eletrônica de varredura, microscopia eletrônica de transmissão, difração de raios-X, e análise térmica pelos métodos de calorimetria diferencial e dilatometria. A decomposição do TCP-β ocorreu a aproximadamente 1100 °C resultando na formação de titanato de cálcio e fosfetos de titânio. As fases resultantes da sinterização em atmosfera de argônio foram Ti, CaTiO3, TiO2 e TixPy. As fases identificadas nos compósitos sinterizados a vácuo foram as mesmas com exceção do rutilo. O compósito sinterizado a vácuo apresentou urna densificação melhor que o sinterizado em argônio. A porosidade e o aparecimento de titanato de cálcio na forma de agulhas foram maiores nos compósitos sinterizados em atmosfera de argônio por causa da maior porosidade.

Un composite à matrice métallique et à renfort particulaire de carbure de titane (25vol.%) produit par la société Mecachrome par métallurgie des poudres est l'objet de cette étude. Le process industriel suit trois étapes : broyage à haute énergie des poudres d'acier et de carbure de titane (TiC) ; consolidation de la poudre composite par extrusion ou consolidation isostatique à chaud (HIP) ; traitements thermiques d'austénitisation. Les principales évolutions concernent la taille de particule, la taille de cristallite, le paramètre de maille et la composition chimique du renfort TiC. Dans cette étude, nous nous sommes concentrés uniquement sur l'évolution du renfort (les évolutions de la matrice sont développées dans le travail de M. Mourot). Afin de caractériser les particules de TiC à chaque étape du process, nous avons mis en place une procédure de dissolution chimique sélective de la matrice acier. Le TiC ainsi " extrait " de la matrice a ensuite été caractérisé de façon méthodique par microscopie électronique à balayage (MEB), microscopie électronique en transmission (MET), diffraction des rayons X (DRX) et analyse chimique élémentaire. Ces techniques ont permis de révéler des changements importants indiquant des interactions physico-chimiques durant les étapes d'élaboration du composite. Ces évolutions du renfort et l'étude thermodynamique des systèmes C-Fe-Ti et C-Fe-O-Ti ont permis de proposer les mécanismes réactionnels à prendre en compte lors de l'élaboration du composite acier/TiC

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Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

L'objectif de cette these etait de developper des composites ceramique-metal nanocristallins obtenus durant le broyage par reaction entre un alliage precurseur et l'atmosphere de broyage. On trouvera en premier lieu un rappel sur les technologies du broyage et leurs utilisations, ainsi qu'une etude du fonctionnement du broyeur vibrant. Nous etudions ensuite la premiere etape du broyage, qui genere une nanocristallisation du broyat. La formation de joints de grains pendant les impacts est modelisee en terme de puissance et comparee avec la puissance dissipee par deformation plastique. Ensuite, la faisabilite de la nitruration de metaux dans un broyeur vibrant a ete verifiee dans les cas de poudres de titane et de fer broyees sous atmosphere d'azote. Du nitrure de titane tin, a enthalpie de formation fortement negative, a pu etre produit, tandis que les nitrures de fer, a enthalpie de formation faiblement negative, n'ont pu etre obtenus. Des alliages precurseurs ont ete prepares par solidification rapide puis broyes sous azote ou a l'air. Dans les cas du broyage de cu-ti et fe-ti sous azote, il a ete forme des composites a matrice de fer ou cuivre renforces en tin, dont la nature nanocristalline est conservee pendant les recuits a haute temperature. Les proprietes, mecaniques et electriques de cu-tin, et magnetiques de fe-tin, ont ete evaluees

Apprenant de la nature, les architectures spécifiques de certains organismes vivants sont devenues l'une des idées dominantes dans le développement de nouvelles générations de matériaux synthétiques. Dans cette optique, la structure lamellaire de la nacre peut servir de modèle pour la fabrication de nouveaux matériaux composites à matrices métalliques. Un nouveau procédé de métallurgie des poudres, appelée métallurgie des poudres « plaquettes » (FPM), a ainsi été développée pour fabriquer des matériaux composites à matrice métallique à structure lamellaire.L’objectif de ce travail de thèse est l'utilisation du procédé FPM (en utilisant le broyage mécanique (BM) et le frittage SPS), pour la fabrication de matériaux architecturés lamellaires et bioinspirés de structure nacre. Nous avons montré la possibilité de fabriquer, à partir de poudre plaquettes, des matériaux lamellaires anisotropes monolithiques à base de titane et d’alliages de titane ainsi que des matériaux composites Ti/C. Nous avons également montré les avantages de l'architecture multicouches sur l'amélioration des propriétés mécaniques (dureté) du Ti et de TA6V avec une anisotropie de la dureté entre les sections transversale et longitudinale. L’augmentation de la dureté de ces matériaux lamellaires, par rapport aux matériaux non-lamellaire, est liée principalement à l'épaisseur des "plaquettes" qui est contrôlée par le temps de BM, ainsi que par l’effet de la microstructure affinée et de l’écrouissage du matériau lamellaire.Nous avons également montré la possibilité de fabriquer des matériaux composites lamellaires in-situ Ti/TiC par BM (en présence d'acide stéarique) et frittage SPS, avec la possibilité de contrôler la teneur en TiC en jouant sur les conditions de BM (temps BM et taux d’acide stéarique). Ce matériau composite permet une amélioration de la dureté et du module de Young attribuée à la phase de TiC formée
Learning from nature, biological design has become one of the prevailing ideas in developing new generations of synthetic materials. In the strengthening and toughening exploration of composite materials, nacre lamellar structure may serves as a model system of tremendous interest. A novel powder metallurgy (PM) strategy, called flake PM, was developed to fabricate bulk metal matrix composite materials with laminated structure.The aims of this thesis is the use of flakes PM (using ball milling and SPS sintering), for the fabrication of biomimetic titanium and titanium alloys nacre’s laminated structures and of titanium/carbon composite materials. This process showed the possibility of the fabrication of laminar material with anisotropic microstructure. We proved the advantages of the layer’s architecture on the improvement of Ti and TA6V mechanical properties (hardness) with hardness anisotropy between the cross section and the longitudinal one. The hardness of this material is related to the thickness of the "flakes" which is controlled by the time of BM. This strengthening was also attributed to the flake thickness, the refined microstructure and the hardening of the lamellar material.We showed also the possibility of fabrication of in-situ Ti/TiC laminated composite materials using BM (in the presence of stearic acid) and SPS sintering, with the possibility of the control of TiC content by controlling the BM conditions (BM time and stearic acid amount). This composite material exhibit improvement of the hardness and Young’s modulus, attributed to the TiC phase formed