Dissertations / Theses on the topic 'Powder'

Additive  manufacturing  technologies  are  widely  used  in  aerospace,  space,  and  turbine industries. Parts can be manufactured directly by selectively adding materials layer-by-layer. A key aspect that is critical to the quality of the final component being manufactured is the powder characteristics. The prevailing powder characterisation techniques help in predicting the flowability of powders but do not relate to the spreading nature of the powder. To create high-quality thin layers of metal powder, it is essential to understand powder spreadability in powder bed-based additive manufacturing processes. The objective of this study was to create spreadability metrics using image analysis, mass analysis, and density analysis. A lab-scale experimental setup was constructed to replicate the powder bed-based additive manufacturing process. The impact of spreading speed and layer thickness on five different steel powders were studied using the suggested metrics. The metrics obtained powder rheometry and revolution powder analysis. The flowability parameters were compared to the spreadability analysis. Image analysis was shown to be efficient to predict the spreading nature of the powder when the processing parameters are varied. One metric, the convex hull ratio, was found to be high for  free-flowing  powders.  The  spread  area  of  free-flowing  powders  was  higher  than  the powders with poor flow properties. A mass-based analysis procedure shows that the ratio of mass deposited to the theoretical mass fluctuated in a systematic manner as a function of testing parameters  and  for  different  powders,  suggesting  that  the  mass  analysis  might  be  another potential   metric   to   assess   spreadability.   The   density-based   analysis   was   effective   in differentiating the layer density of different powders under various experimental conditions. It   is   expected   that   the   proposed   metrics   will   be   a   beginning   for  developing   further characterisation techniques. For example, the layer thickness could be studied by creating a homogenous  layer.  We  anticipate  these  metrics  to  be  used  to  develop  standardisation techniques for defining and quantifying powder spreadability, and thereby improve quality ofadditive manufacturing processes.
Additiv  tillverkning  är  teknologier  som  har  stor  uträckning  inom  flyg-,  rymd  och  turbin industrier. Delar kan bli tillverkade direkt genom att lagervis addera material på varandra. En nyckelaspekt som är kritisk till kvalitén av den slutgiltiga komponenten är egenskaperna hos pulvret. De allmänna teknikerna för pulverkarakterisering hjälper till att förutspå flytförmågan hos pulver men relaterar ej till dess spridningsförmåga. För att kunna skapa högkvalitativa skikt av  metallpulver  är  det  nödvändigt  att  förstå  pulvrets  spridningsförmåga  inom  pulverbädds baserade additiva tillverkningsprocesser. Målet  med denna studie var  att skapa ett mått för spridningsförmågan  genom  bild-  och  massanalys.  Ett  experimentellt  upplägg  i  labbskala konstruerades för att efterlikna en pulverbädds baserad additiv tillverkningsprocess. Effekten av bladets hastighet och lagrets tjocklek på fem olika pulver studerades genom användandet av de  föreslagna  mätetalen.  De  framtagna  mätetalen  jämfördes  sedan  med  existerande  pulver karakteriseringsmetoder  såsom  FT-4  Rheometer  och  pulver  analys  med  hjälp  av  roterande trumma. Slutligen så jämförs flytbarhets parametrarna med spridbarhets mätetalen. Det visar sig att bildanalysen är tillräckligt bra på att förutspå spridningsförmågan hos pulvret när  processparametrarna  låtes  vara  varierande.  Mer  specifikt  så  var  förhållandet  mellan pulvrets yta och det konvexa höljet stort för pulver som visar bra spridning. De framtagna procent  värden  från  massanalysdiagrammen  fluktuerar  vid  olika  processparametrar  hos  de olika  pulvren,  vilket  kan  betyda  att  massanalys  kan  vara  ett  potentiellt  sätt  för  att  mätta spridningsförmågan hos pulver. Det är förväntat att dessa föreslagna mätetal kommer vara början för utveckling av ytterligare karakteriseringstekniker. Till exempel, för att studera densiteten och tjockleken hos ett lager skulle man kunna skapa homogena lager. Vi förutser att dessa mätetal kommer att bli använda för att skapa standardiseringstekniker för att definiera och kvantifiera spridningsförmågan hos ett pulver och genom detta förbättra kvaliteten av den additiva tillverkningsprocessen.

Electroplating is a common method of obtaining metallic coatings on a surface. Generally, the metal salt is introduced into solution and a direct current is applied to the material that is to be coated. In this thesis, an alternative approach is investigated, namely the metal is introduced onto the metal surface as a powder and a pulsed current is applied to firstly dissolve some of the powder and the polarity is reversed so that the metal is then deposited. This fuses the powder to itself and to the substrate. In the current study, deep eutectic solvents were used as the electrolytes and two metals were chosen; zinc and copper. Initially the dissolution and deposition of the pure metals were investigated. It was found that far from being simple dissolution and deposition processes insoluble films were formed on the electrode surface during both deposition and dissolution for zinc and during dissolution for copper. Powder pulse plating was successfully demonstrated if the current pulse characteristics were kept within a window of size and duration which avoided these insoluble films. It was found that large metallic particles could be used when the substrate was held in a horizontal orientation and small particles were best when the electrode was held vertically. For both metals it was demonstrated that super-efficient deposition could be obtained (Faradaic current efficiency in the cathodic pulse > 100%). It was also shown that composite materials could be produced by mixing inert particles with the metallic powder.

Additive manufacturing is an increasingly popular industry that has gained significant traction in the last decade. Today there exists no way to predict how a powder will spread in a powder bed additive manufacturing machine or how well it will form into thin layers. This is important because major costs can be saved by using a test that predicts the spreading behaviour of powder. This ability to be spread will be given the name spreadability. To test the spreadability of powder, a machine that mimicked the pushing of the powder in powder bed additive manufacturing was used. Since there exist no metric for spreadability, the study decided to attempt to quantify the spreadability with the help of image analysis. In the image analysis the area of the powders was measured, and through a comparison of the area against a bounding geometry, a measurement for spreadability can theoretically be attained. To further validate the results and simultaneously search for possible correlations, the experimental data was compared against flowability data obtained from angle of repose and Hall flowmeter. The results showed that the method of choice worked well for measuring the area and gave data that could be used to interpret spreadability. The data also showed what seems to be a correlation with the flowability data. While no definitive conclusions could bedrawn due to a small sample size, the collected data does seem promising for future work.
Additiv tillverkning är en alltmer populär industri som har fått stor uppmärksamhet under det senaste decenniet. Idag så finns det inga sätt som man kan förutse hur ett pulver kommer att bredas ut i en pulverbädds additiv tillverkningsmaskin eller hur bra den är på att bilda tunna lager. Detta är en viktig kunskap att förstå då stora kostnader kan sparas in genom att använda ett test som förutser utbredningsförmågan av pulver. Denna förmåga får namnet spridbarhet. För att kunna testa spridbarheten hos pulver, används en maskin som härmar puttandet av pulver i en pulverbädds additiv tillverkningsmaskin. Eftersom det inte finns någon metod att mäta spridbarhet med, så valde denna studie att försöka kvantifiera spridbarheten via en bildanalys. Med denna bildanalys kunde arean av pulver mätas och genom att jämföra denna mot en avgränsande geometri kan mätdata för spridbarheten teoretiskt fås fram.För att kunna validera resultatet, och samtidigt se om det finns en korrelation, jämfördes det med flytbarhetsdata från rasvinkelmätare och Hall flödesmätare. Resultaten visade att metoden klarade av att mäta arean, och gav resultat som kan användas för att tolka spridbarhet. Den data som framtogs visade också att det möjligtvis kan finnas en korrelation mellan spridbarhet och flytbarhet. Även om något klart svar inte kan ges på grund av en liten provstorlek, så verkar resultaten vara lovande för framtida arbeten.

A novel powder processing technique has been developed by combining conventional powder injection moulding with polymer co-injection moulding, to permit the in-situ surface engineering of metal or ceramic components as an integral step within the processing cycle. The new technique has been used to produce surface engineered iron based components with either corrosion resistant or wear resistant surfaces, and to produce alumina based components with toughened surfaces. The most critical factor for the feasibility of surface engineered components is that the sintering profiles of the skin and core materials must be well matched or differential shrinkage or delamination will result. A particular requirement of surface engineering is the ability to control the surface engineered skin profile. Polymer injection moulding modelling software was applied to predict the surface engineered skin profiles of the surface engineered metal/ceramic components. Successful skin profile prediction is dependent on the characterisation of the feedstock materials being injection moulded. Several feedstocks have been characterised for their material properties and first pass models developed to predict the feedstock material properties as a function of their individual material properties and mass or volume ratios. It has been demonstrated that the design of the feedstock composition and injection moulding process conditions can be optimised by the use of computer-based injection moulding modelling software to achieve the desired surface engineered skin profile. A methodology has been developed that outlines all the stages necessary for successful powder co-injection moulding.

This dissertation explores the extent to which dynamical information is preserved in neutron powder diffraction data. Total scattering data collected on the GEM instrument in ISIS have been used as input for the reverse Monte Carlo (RMC) method to generate large ensembles of independent atomistic configurations consistent with the data. A method of analysing these configurations for evidence of correlated atomic motion has been developed. The method is based on a similar technique originally used to analyse molecular dynamics (MD) configurations. It has been extended further in the dissertation to account for lattice symmetry, allowing unambiguous assignment of the normal modes at each wavevector. The theory has also been used to show that phonons are determined uniquely by first- and second-order displacement correlation functions alone, and should consequently be fixed by diffraction data. The impact of various restraints and constraints in the RMC method on the dynamical information stored within configurations has been systematically studied and used to develop a new constraint (the DW constraint) that helps prevent the incorporation of damaged regions into RMC configurations without affecting the form of the phonon dispersion curves obtained. The phonons-from-diffraction approach, implemented in the program PHONON, has been applied to MgO and SrTiO₃. Calculated phonon dispersion curves resemble those obtained independently in spectroscopic experiments in the low-frequency region; however, the higher-frequency modes were generally not well preserved. Temperature-dependent mode softening of the R₂₅ and Γ₁₅ modes in SrTiO₃ could be observed, and the mode displacement vectors used to characterise the atomic translations involved in the 105 K displacive phase transition.

Compaction of powders followed by sintering is a convenient manufacturing method for products of complex shape and components of materials that are difficult to produce using conventional metallurgy. During the compaction and the handling of the unsintered compact, defects can develop which could remain in the final sintered product. Modeling is an option to predict these issues and in this thesis micromechanical modeling of the compaction and the final components is discussed. Such models provide a more physical description than a macroscopic model, and specifically, the Discrete Element Method (DEM) is utilized. An initial study of the efect of particle size distribution, performed with DEM, was presented in Paper A. The study showed that this effect is small and is thus neglected in the other DEM studies in this thesis. The study also showed that good agreement with experimental data can be obtained if friction effects is correctly accounted for. The most critical issue for accurate results in the DEM simulations is the modeling of normal contact between the powder particles. A unified treatment of this problem for particles of a strain hardening elastic-plastic material is presented in Paper B. Results concerning both the elastic-plastic loading, elastic unloading as well as the adhesive bonding between the particles is included. All results are compared with finite element simulation with good agreement with the proposed model. The modeling of industry relevant powders, namely spray dried granules is presented in Paper C. The mechanical behavior of the granules is determined using two types of micromechanical experiments, granule compression tests and nanoindentation testing. The determined material model is used in an FEM simulation of two granules in contact. The resulting force-displacement relationships are exported to a DEM analysis of the compaction of the granules which shows very good agreement with corresponding experimental data. The modeling of the tangential forces between two contacting powder particles is studied in Paper D by an extensive parametric study using the finite element method. The outcome are correlated using normalized parameters and the resulting equations provide the tangential contact force as function of the tangential displacement for different materials and friction coefficients. Finally, in Paper E, the unloading and fracture of powder compacts, made of the same granules as in Paper C, are studied both experimentally and numerically. A microscopy study showed that fracture of the powder granules might be of importance for the fracture and thus a granule fracture model is presented and implemented in the numerical model. The simulations show that incorporating the fracture of the granules is essential to obtain agreement with the experimental data.

QC 20150122

The mechanisms involved in the production of chromate-phosphate conversion coatings on aluminium have been investigated. A sequence of coating nucleation and growth has been outlined and the principle roles of the constituent ingredients of the chromate-phosphate solution have been shown. The effect of dissolved aluminium has been studied and its role in producing sound conversion coatings has been shown. Metallic contamination has been found to have a dramatic influence on chromate-phosphate coatings when particular levels have been exceeded. Coating formation was seen to be affected in proportion to the level of contaminaton; no evidence of sudden failure was noted. The influence of substrate and the effect of an acidic cleaner prior to conversion coating have been studied and explained. It was found that the cleaner ages rapidly and that this must .be allowed for when attempting to reproduce industrial conditions in the laboratory. A study was carried out on the flowing characteristics of polyester powders of various size distributions as they melt using the hot-stage microscopy techniques developed at Aston. It was found that the condition of the substrate (ie extent of pretreatment), had a significant effect on particle flow. This was explained by considering the topography of the substrate surface. A number of 'low-bake' polyester powders were developed and tested for mechanical, physical and chemical resistance. The best formulation had overall properties which were as good as the standard polyester in many respects. However chemical resistance was found to be slightly lower. The charging characteristics of powder paints during application by means of electrostatic spraying was studied by measuring the charge per unit mass and relating this to the surface area. A high degree of correlation was found between charge carried and surface area, and the charge retained was related to the powder's formulation.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1998.
Includes bibliographical references (leaves 138-142).
This thesis describes an experimental program aimed at the development of elastic-plastic constitutive relations for cold compaction of ANCOR MH-100 iron powder. A systematic experimental program consisting of triaxial compression, torsion ring shear, uniaxial strain compression, and simple compression test systems has been conducted to investigate the room temperature deformation response of powders ranging from a relative density of n = 0.4 - 0.9. A torsion ring shear apparatus has been designed and fabricated to investigate the frictional behavior of iron powder. The torsion ring shear apparatus is also used to examine the important interface frictional behavior between the powder compact and confinement dies.
by Michael Kim.
S.M.

Les contributions de cette thèse de doctorat sont focalisées sur les développements de formulations à base de polymères bio sourcés et déliantable à l’eau basés sur l’emploi d’acétate butyrate de cellulose (CAB) et de polyéthylène glycol (PEG). Ces nouvelles formulations ont été appliquées sur différentes nuances de poudres métalliques (invar) et céramiques (zircones). Ces matériaux possèdent une bonne stabilité dimensionnelle sous une large gamme de température imposée et possèdent de très bas coefficients d’expansion thermique.L’objective est l’étude et la compréhension du comportement des liants à base de CAB et PEG quand ils sont utilisés dans les variantes du procédé MIP (étapes de moulage avec ou sans pression, conditions particulières liées à la micro-injection, …) réalisées avec différentes nuances de poudres et différentes granulométries.Les caractéristiques intrinsèques de chaque CAB, leurs interactions avec le PEG et les poudres, l’influence de la nuance de poudre employée, ainsi que la granulométrie et la morphologie des poudres employées ont été étudiées et analysées en fonction du comportement final de la formulation développé et des taux de charges obtenues.L’homogénéité des mélanges développés, leurs taux de charge critique et maximal, ainsi que leurs comportements mécaniques, thermiques et rhéologiques ont été analysés et investigués par différentes études mécaniques, thermo et physico-chimiques. De nouvelles analyses chimiques et physiques ont été introduites par accroitre les connaissances sur les formulations développées. Les formulations optimales ont été validées pour différentes applications et avec l’emploi de différentes variantes du procédé MIP conduisant à l’élaboration de composants et de micro-composants PIM obtenus sans défauts et possédant d’excellentes propriétés fonctionnelles. L’étape de déliantage ainsi que l’étape de densification ont été optimisées en termes de cinétique et d’atmosphère aboutissant aux propriétés physiques et mécaniques escomptées pour l’ensemble des nuances de poudres considérées dans cette étude.En conclusion, les formulations développés des liants basées sur l’emploie de CAB et PEG sont exploitable au niveau de la recherche et au niveau industriel dans le procédé MIP. Elles apportent des améliorations par rapport aux liants conventionnels grâce à un procédé plus écologique. Cette première contribution représente une avancée significative dans l’émergence d’un procédé MIP plus écologique mais d’autres travaux futurs sont encore possibles
This PhD Thesis studied the use of binders based on cellulose acetate butyrate (CAB) andpoly(ethylene glycol) (PEG) in different type of materials, including a ceramic, the zirconiumsilicate, and a metallic alloy, the Invar 36. These materials share their low dimensionalstability with temperature with low coefficients of thermal expansion.The scope of this work is the study and comprehension of the behaviour of the mentionedbinder systems when they are employed in different PIM processes and under differentconditions and powder-types. With regard to this matter, different formulations were designedwith several types of PEG and CAB. These formulations were compared with commercialones. The intrinsic characteristics of each CAB were linked with the behaviour of the differentfeedstock also containing PEG and powder particles. The mixtures homogeneity, the optimumand critical solid loading and its flowability were assessed by torque and capillary rheology.Other complementary techniques such as electronic and light microscopy or the measurementof the mixtures densities by pycnometry were carried out to contrast rheology results. Thecompatibility between the feedstocks’ components and their thermal behaviour were analysedby calorimetry and thermogravimetry techniques. These methods were employed by the firsttime to determine the optimal solid loading.The optimal compositions were injected by using low or high pressures or by a micro injectionmoulding process. The debinding and sintering stages were optimised using severalatmospheres. Finally, the physical and mechanical properties of the final consolidated partswere measured.It could be concluded that the studied binder systems based on PEG and CAB presentedsuitable characteristics for PIM, providing improvements with respect to conventional bindersystems and by a more environmental friendly processing. However, that doctoral work wasjust a first approach to the use of these types of binder systems in PIM. Along this workseveral issues were detected and some topics regarding the processing should be furtherinvestigated to obtain the best of these binder systems

Additive manufacturing (AM) shows great promise for the manufacturing of next-generation engineering structures by enabling the production of engineered cellular structures, overhangs, and reducing waste. Melt-pool geometry prediction and control is critical for widespread implementation of laser powder bed processes due to speed and accuracy requirements. The process mapping approach used in previous work for different alloys and additive manufacturing processes is applied to the selective laser powder bed process for IN625 and 17-4 stainless steel alloys. The ability to predict the resulting steady state melt-pool geometry in terms of process parameters, specifically power and velocity, is explored in detail numerically and experimentally verified. A finite element model was created that simulates powder at the macro scale. This model correlates well with current experiments in showing that small amounts of powder relative to melt-pool depth have negligible effects on resulting geometry. Results indicate that the effect of powder may be negligible when comparing steady state widths of the no powder and one layer of powder cases. The work in this thesis investigates the effect of powder on the resulting steady-state melt-pool geometries for IN625 and 17-4 alloys. This analysis has been extended to the production of overhanging and cellular structures. The successful analysis will allow for better predictions and possible correction for cellular structure production issues as well as overhanging features.

In this thesis, experimental investigations into powder-die friction and powder yielding measurement techniques, and numerical modelling work on powder-die friction mechanisms are presented. The experimental friction work explores the use of a shear-plate technique to measure the frictional characteristics between a compacted powder and a target surface. The study confirms that the shear-plate technique is valid to measure these frictional characteristics. Surface roughness and hardness was explored fully for both Iron and an Alumina power. This confirmed the major impacts of surface hardness, roughness and roughness orientation on the friction coefficient. With regard to static friction, benefit may be obtained by using a very smooth surface finish, however, the minimum level of dynamic friction coefficient is not always associated with the smoothest surface. Comparisons between different experimental techniques for characterising the yielding of powders are presented. Three techniques were compared using an iron powder: triaxial testing, instrumented die testing and shear-box testing. The techniques were compared with a particular view to measuring the applicability of the less well recognised experiments with the more established triaxial experiment. Predicted yield surfaces from a single instrument die test compared very well with the yield surfaces obtained triaxial tests. Results from shear-box experiments show that it defines the region in which it is appropriate to use the yield surfaces obtained from the instrumented die, for modelling purposes. Beyond this limit yielding of the powder is achieved by a shearing mechanism.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2011.
ENGLISH ABSTRACT: The purpose of this study is to investigate the machinability of commercially pure (CP) titanium, manufactured using the press-and-sinter PM process. To this end, CP titanium powder (-200 mesh) was compacted and sintered in vacuum (10-4 torr) for two hours at 1200°C. Small cylindrical samples were compacted at pressures varying from 350 to 600 MPa in order to determine the compressibility of the powder. Following these tests, four larger stepped-cylinder samples were compacted at pressures close to 400 MPa and sintered under similar conditions. These samples had sintered densities varying between 3.82 and 4.41 g/cm3. They were used to evaluate the machinability of the sintered titanium using face turning machining tests. The samples were machined dry, using uncoated carbide (WC-Co) cutting tool. Cutting speeds between 60-150 m/min were evaluated while keeping the feed rate and depth of cut constant at 0.15 mm/rev and 0.5 mm, respectively. The final machined surface finish and the tool wear experienced during the face turning machining tests were monitored in order to evaluate PM titanium’s machining performance. This study showed that it is possible to use the press-and-sinter PM process with CP titanium powder, with a particle size of less than 75 μm (-200 mesh), to manufacture sintered titanium. However, particle shape influences the compressibility of the powder and pressing parts of larger volume, such as the machining test sample shape, is challenging when using such small particle size powder. Processing conditions, such as compaction pressure, sintering temperature and sintering time, influence the sintered density. Results from the machinability tests show that tool wear increases with a decrease in the porosity of the sintered titanium. A more porous sintered material has both lower strength and thermal conductivity. As these factors have opposing effects on the machinability of materials, it is concluded that the strength of the sintered titanium has a stronger influence on its machinability than the thermal conductivity. The cutting tool wear was uniform but showed indications of crater wear. The machined surface of the denser parts had minimal defects compared to less dense parts. Chip shape is long for the dense parts, and spiral for the less dense parts. The chips formed were all segmented, which is typical for titanium. The machinability of the sintered CP titanium was compared to that of wrought titanium alloys. As expected, it was found that the machinability of the sintered titanium was poor in comparison.
AFRIKAANSE OPSOMMING: Die doel van hierdie studie is om die masjineerbaarheid van kommersieel suiwer (KS) titaan, wat deur die pers-en-sinter poeiermetallurgie (PM) metode vervaardig word, te ondersoek. Om hierdie doel te bereik, is KS titaan poeier (-200 ogiesdraad) gekompakteer en gesinter in ‘n vakuum (10-4 torr) teen 1200°C vir 2 ure. Klein silindriese monsters is tussen drukke van 350en 600 MPa gekompakteer om die samedrukbaarheid van die poeier te bepaal. Na aanleiding van hierdie toetse, is vier groter trapvormige-silinder monsters by drukke naby aan 400MPa gekompakteer en onder soortgelyke omstandighede gesinter. Hierdie monsters het gesinterde digthede tussen 3.82 en 4.41 g/cm3 gehad. Hulle is gebruik om die masjineerbaarheid van die gesinterde titaan te ondersoek deur middel van vlak-draai masjineringstoetse. Die monsters is sonder smeermiddel gemasjineer met onbedekte karbied (WC-Co) snygereedskap. Snysnelhede tussen 60 – 150 m/min is geëvalueer terwyl die voertempo en diepte van die snit konstant by 0.15 mm/rev en 0.5 mm, onderskeidelik, gehou is. Die finale gemasjineerde oppervlak afwerking en gereedskapsslytasie tydens die vlak-draai masjinering toets is van die faktore wat gemonitor is sodat PM titaan se optrede tydens masjinering geëvalueer kan word. Hierdie studie wys dat diepers-en-sinter metode wel met KS titaan poeier, met ‘n partikel grootte van minder as 75 μm (-200 maas), gebruik kan word om gesinterde titaan te vervaardig. Die partikelgrootte beïnvloed wel die samedrukbaarheid van die poeier. Die samedrukking van parte met groter volume, soos bv die masjinerings toetsmonster, is uitdagend wanneer klein partikelgrootte poeier gebruik word. Proses omstandighede, soos kompaksie druk, sinteringstemperatuur en sinteringstyd, beïnvloed die gesinterde digtheid. Resultate van die masjineerbaarheidstoetse wys dat beitelslytasie toeneem met ‘n afname in porositeit van die gesinterede titaan. ‘n Meer poreus gesinterde materiaal het beide laer sterkte en termiese geleidingsvermoë. Aangesien hierdie faktore teenoorgestelde uitwerkings op masjineerbaarheid het, word dit dan afgelei dat die sterkte van gesinterde titaan ‘n groter invloed het op sy masjineerbaarheid as die termiese geleidingsvermoë. Die beitel se slytasie is hoofsaahlik, maar het tekens van kraterslytasie getoon. Die gemasjineerde oppervlak van die meer digte onderdele of toetsmonters het min gebreke gehad in vergelyking met die minder digte dele. Die vorm van die spaanders is lank vir digte parte, en spiraalvormig vir minder digte toetsmonsters. Die spaanders wat gevorm het, was almal gesegmenteerd, wat tipies is vir titaan. Die masjineerbaarheid van die gesinterde KS titaan is met dié van gesmede titaanallooie vergelyk. Soos verwag is, is gevind dat die masjineerbaarheid van die gesinterde titaan in vergelyking swak is.

The aim of this study was to develop blueberry powder via foam-mat freeze-drying (FMFD) and to investigate the foam and powder properties. The spray-drying (SD) method was also carried out as a comparison to foam-mat freeze-drying. Foam-mat freeze-drying of blueberry juice was conducted using constant temperature (-55 0C) and vacuum pressure (0.04 mbar) for 24 h, while spray-drying was tested using two feed flow rates, 180 (SD 180) and 360 (SD 360) mL h-1, and other conditions of spray-drying were kept constant. Foam properties were compared amongst foam made with ratio 2.8 of maltodextrin/whey protein isolate (M3W1), trehalose/β-lactoglobulin (T3BL1), and trehalose/bovine serum albumin (T3A1). The M3W1 foam was found less stable than those with T3BL1 and T3A1 since the M3W1 gave high foam density. FMFD powder made with M3W1 had higher moisture content (3.5%), longer rehydration time (90 s), and lower bulk density (0.32 g cm-3) over the T3BL1 and T3A1. The FMFD powders made with trehalose/pure proteins generated pores and ordered structures, while the M3W1 powder had broken glass-like structures. The M3W1 reconstituted powder gave high a*/redness which was probably attributed to high total monomeric anthocyanins (TMA) content (8.5 mg Cyn3Gl g-1 solids). The MD/WPI as matrices had reduced losses in the total phenolic content (TPC) and individual anthocyanin than T3A1 or T3BL1. The TPC and TMA retention of M3W1 reconstituted powder were recorded as 73 and 95%, respectively. FMFD and SD powders made with MD/WPI 0.4-3.2 were also compared. The FMFD had a higher yield, lower moisture content, longer rehydration time and lower bulk density compared to those of spray-dried (SD) powders. The FMFD samples were purple powders and flake-like shaped of particles, while SD samples were bright pink powders. The SD powder particles were smooth, spherical and smaller sized than the FMFD powder. The TMA of FMFD powders showed higher levels than those of SD samples. Delphinidin-3-glucosiede (Del3Gl), Cyanidin-3-glucoside (Cyn3Gl), and Malvidin-3-glucoside (Mal3Gl) retentions were greater, in the order: FMFD > SD.

Dry powder inhalers (DPIs) are used for delivering drugs to the airways. In addition to the drug, the formulations often contain a coarse carrier, most commonly alpha lactose monohydrate. The presence of fine lactose particles in the formulation is known to improve the formulation performance. The active site, drug-fines agglomeration and increased cohesion theories have been suggested to explain improved DPI performance upon addition of fine excipient particles. This project aimed to investigate the validity of those theories. The viability of the active sites theory in explaining the improved DPI performance was investigated by studying the impact of loaded drug dose on the in vitro performance for formulation series prepared with coarse carriers with different surface characteristics. The formulations prepared with the rougher lactose carrier were seen to outperform the formulations prepared with the smoother carrier at all drug concentrations. These findings were concluded to be non-compatible with the active sites theory. The impact of addition of lactose fines with different size distributions on powder flow and fluidisation properties and in vitro performance was studied. Powder cohesion increased independent of size distribution of the fines, but did not necessarily correspond to improved performance. Therefore, the increased cohesion theory was concluded not to be the sole explanation for the improvement in DPI performance in the presence of lactose fines. Instead, the increase in performance could be preliminarily attributed to the formation of agglomerated systems. The formation and co-deposition of drug-fines agglomerates, and consequential improvement in the DPI performance was proved using morphologically directed Raman spectroscopy. The project also aimed to develop a universal model for predicting DPI performance based on the lactose properties for a wide range of carriers with different properties. No simple linear correlations between any the lactose properties and the final DPI performance were found. Therefore no single parameter can be used as a universal predictor for DPI performance. To establish more complex relationships, artificial neural networks were used for modelling the importance of different lactose properties in determining DPI performance. The proportion of fine lactose particles (<4.5 μm) was identified as the most important parameter. However, this parameter was capable of explaining only approximately half of the variation seen in the formulation performance. The current study showed that to obtain more accurate predictions for the purposes of quality-by-design approach, also other lactose properties need to be characterised.

We study the problem of packing spheres of different radii into a rigid container. The spheres are packed as densely as possible so they neither overlap nor cross the boundaries of the container. The packed spheres are then meshed in preparation for finite element analysis. The spheres are meshed individually (separately) without taking care of the contact surface between spheres or containers wall. The last step is the hydrostatic pressing of the spheres made of elastic-plastic materials and with simplified contact conditions. Such simulations are of interest to the metallurgist because they can show differences in structure between grain surfaces and centres.

Sintering at high-pressure improves the properties of the material, either through new sintering aids becoming available or through improving intergranular bonding. This gives the manufactured products potential advantages like faster cut rates, and more precise and cleaner production methods that add up to cost efficiency and competitive edge. The production of synthetic diamond products demands tooling that can achieve high pressures and deliver it with a high degree of certainty. The common denominator for almost all high-pressure systems is to use capsules where a powder material encloses the core material. Numerical analysis of manufacturing processes with working conditions that reach ultra high pressure (above 10 GPa) requires a constitutive model that can handle the specific behaviours of the powder from a low density to solid state. The work in this thesis deals with characterization and simulation of the material behaviour during high-pressure compaction in powder pressing. Some of the work was focused on investigating the material when used as compressible gasket in high-pressure systems. The aim was to increase the knowledge of the high-pressure pressing process. This includes a better understanding of how mean stress develops in the compact during pressing and an insight into the development material models concerning highpressure materials. Both experimental and numerical investigations were made to gain knowledge in these fields. The mechanical behaviour of a CaCO3 powder mix was investigated using the Brazilian disc test, uniaxial compression testing and closed die experiments. The aim of the experimental work was to provide a foundation for numerical simulation of CaCO3 powder compaction at higher pressures. Friction measurements of the powder were also conducted. From the experimental investigations, density dependent material parameters were found. An elasto-plastic Cap model was developed for ultra high-pressure powder pressing. To improve the material model, density dependent constitutive parameters were included. The model was implemented as a user-defined material subroutine in a nonlinear finite element program. The model was validated against pressure measurements using phase transitions of Bismuth. The measurements were conducted in a Bridgman anvil apparatus. The simulations showed that thin discs with small radial extrusion generate a plateau at a low-pressure level, while thick discs with large radial extrusion generate a pressure peak at a high-pressure level. The results showed that FE-results can be used to engineer pressure peaks needed to seal HPHT-systems. For compressible gaskets, it was found that diametral support increases the phase transformation load. Higher initial density of the powder compact and diametral support generate higher pressure per unit thickness. The results from the validation using pressure measurements showed that the simulation model was indeed capable of reproducing load–thickness curves and pressure profiles, up to 9 GPa, close to the experimental curves.
Godkänd; 2011; 20111020 (bersve); DISPUTATION Ämnesområde: Hållfasthetslära/Solid Mechanics Opponent: Professor Javier Oliver, Dept of Strength of Materials and Structural Analysis, Technical University of Catalonia, Barcelona, Spain, Ordförande: Bitr professor Pär Jonsén, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Tid: Torsdag den 15 december 2011, kl 09.00 Plats: E246, Luleå tekniska universitet

The MAX phases constitute a group of ternary ceramics which has received intense attention over the last decade due to their unique combination of properties. The Ti3SiC2 is the most well studied MAX phase to date and it has turned out to be a promising candidate for high temperature applications. It is oxidation resistant, refractory and not susceptible to thermal shock, while at the same time it can be machined with conventional tools which is of great technological importance. Most attempts to synthesize bulk Ti3SiC2 have involved pure titanium in the starting powder mixtures, but Ti powder is oxidising and requires an inert atmosphere throughout the synthesis process which makes the procedures unsuitable for large scale production. The aim of the first part of this study was to delineate the influence of sintering time and temperature on the formation of Ti3SiC2 from a starting powder which does not contain pure titanium. Titanium silicon carbide MAX phase was synthesised from ball milled TiC/Si powders, sintered under vacuum for different times and temperatures. After heat treatment the samples were evaluated using scanning electron microscopy (SEM) and x-ray diffraction (XRD). This study showed that TiC was always present in the final products whereas TiSi2 was an intermediate phase to the Ti3SiC2 formation. The highest amount of Ti3SiC2 was achieved for short holding times of 2-4 hours, at high temperatures, 1350-1400¢ªC. More elevated temperatures or extended times resulted in silicon loss and decomposition of Ti3SiC2. In the second part of this study the sintering reactions and the mechanisms of formation of Ti3SiC2 were investigated by x-ray diffractometry, thermodilatometry, thermogravimetry, differential scanning calorimetry and mass spectrometry. TiC/Si powders of the different ratios; 3:2 and 3:2.2, were heated to different temperatures under flowing argon gas in a dilatometer and examined by XRD. The TiC/Si powder samples of the ratio 3:2 were further investigated by the other thermal analysis methods. The results confirmed the presence of the intermediate phase TiSi2. From 1500¢ªC silicon evaporation and MAX phase decomposition were observed, and the results show that the MAX phase formation may be concurrent with the melting of silicon. TiC was always present in the final products, either as a reactant or as a decomposition product. The extra silicon of the 3:2.2 TiC/Si powder significantly increased the Ti3SiC2 conversion and no intermediate phases were observed for this powder mixture. The Si of these samples did not melt or evaporate, and only minor decomposition was observed even at 1700¢ªC. These results indicate that the silicon content of the initial powder mixture is decisive to the reaction mechanisms of the sintering process.

Godkänd; 2007; 20070523 (ysko)

Skim milk powder (SMP) is a widely used commodity in the food industry; hence its physical and chemical characteristics should be controlled for ensuring the successful functionality of the powder in the end product. An important characteristic of SMP is its heat stability. The current study involved a thorough examination of heat stability and other characteristics of low-heat and high-heat SMP. The main differences between these two powders were related to a lower pH, smaller particle size and a lower level of denatured whey proteins in the low-heat SMP.

This thesis describes measurements, primarily of velocity and turbulence, taken within a laboratory-scale nickel carbonyl decomposer. These measurements are part of a research programme intended to provide a fuller understanding of the formation of nickel powder by the thermal decomposition of nickel tetracarbonyl. The Laser Deppler technique was used as the only practical method available of obtaining quantitative information concerning the motion of nickel particles within the reactor. A one-component of velocity system was designed and built for this purpose and was subsequently used with a Burst Spectrum Analyzer for signal processing, to produce a map of the velocity and turbulence within the decomposer under three sets of operating conditions. Techniques for the analysis of the velocity measurements for investigating turbulent phenomena by spectral methods were also explored. Nickel powder particles generated by the reaction provided ample seeding for laser anemometry and under some operating conditions it was found that the Doppler signal quality deteriorated because the seeding density was so high. Some correlation was found between signal quality and powder properties. The measurements have highlighted the importance of turbulence, particularly in the decomposer inlet and have indicated that the flow in much of the decomposer is dominated by large scale flow structures.

This thesis aims to improve the understanding of the factors that determine the performance of baghouses used for milk powder collection. The research focuses specifically on the similarities and differences between milk powder collection and other common baghouse applications. The thesis also aims to demonstrate the value of recent developments in computational fluid dynamics in developing predictive models of baghouse performance. It is hoped that the findings of the thesis may find application in the New Zealand dairy industry, where such baghouses are commonly used to collect milk powder after spray drying. The effect of operating temperature and humidity on the performance of baghouses was investigated by examining both the forward filtration process and pulse cleaning process. Forward filtration was examined in a series of bench scale experiments, then scaled up to the pilot scale to confirm the findings. The effect of humidity on the pulsing performance was then investigated at the pilot scale. The importance of pulse system design was investigated at the pilot scale in a separate set of experiments. Pulse nozzle position, pulse pressure, and pulse duration were varied and the effect on the baghouse pressure differentials was measured. A computational fluid dynamics (CFD) filter model designed for membrane filtration was adapted with some success to simulate a milk powder baghouse. The model was successful in predicting the length of the low pressure zone at the top of the bag, and the general trends in overpressure associated with changes to the pulse system geometry. The model was not successful in predicting the acceleration of the filter bag during the pulse. The model was used to simulate both forward filtration and pulsing, to extend the results of the experimental investigation. The effects of changes in the pulse nozzle height, pulse nozzle diameter, and pulse pressure were simulated, as well as the effect of gravitational settling during forward filtration, to extend the results of the previous experiments. There is a clear opportunity remaining for further work to extend the basic model developed here and to adapt the model to simulate large industrial baghouses. Experiments on the bench scale and pilot scale indicated that increased cohesive forces between particles improve the performance of milk powder baghouses by lowering the resistance of the filter cake during forward filtration and aiding cake removal during pulse cleaning. Under the conditions typical of industrial milk powder baghouses, cohesive forces are governed primarily by liquid bridging between particles, due to melted fat (particularly at high temperatures) and softened lactose (at high humidity levels). As a range of milk powders with different compositions are produced commercially, the relative importance of lactose-based and fat-based cohesion differs between powder types. Cohesion promotes the formation of porous structures in the filter cake, improving the cake permeability. In skim milk powder (SMP), particle cohesion is dominated by softened lactose, and is highly moisture dependent. In the bench scale experiments conducted here, increasing the relative humidity from 6% to 17% decreased the specific cake resistance from 1.69x10⁹ m.kg¯¹ to 8.23X10⁸ m.kg¯¹, and decreased the proportion of powder adhering to the filter from 14% of the total supplied powder to 3%. The combination of these effects decreased the total resistance over the filter from 1.09X10⁹m¯¹ to 1.89X10⁸; m¯¹, an 83% reduction. The low deposition at high humidity suggested that the porous cake structure formed at high humidity levels was fragile, so that deposited particles were prone to subsequent dislodgement, especially in areas where the shear velocity near the filter surface was high. In pilot scale experiments, the porous cake structure formed at high humidity was more easily removed from the filter bag, resulting in more effective pulse cleaning. It was concluded that particle cohesion promoted cake filtration over depth filtration, as particles tended to adhere to the cake surface immediately upon contact. As depth filtered particles are more difficult to remove, the shift toward cake filtration at high humidity improved the pulse cleaning performance. A high-fat milk protein concentrate (MPC) powder was also filtered on the bench scale apparatus. Particle cohesion in the MPC powder was dominated by liquid fat, and showed a clear dependence on temperature but not on humidity. Increasing the temperature from 30°C to 90°C caused the specific cake resistance of the MPC to decrease from 1.06x10⁸ m⁻¹ to 3.94x10⁷m⁻¹, a 63% decrease. The deposition of MPC powder was unaffected by either temperature or humidity. Gravitational settling of particles in large baghouses was found to produce significant variations in the properties of the filter cake throughout the baghouse. Experimental results with the pilot scale baghouse found a strong decreasing trend in the particle size with increasing height in the baghouse, with the mean particle size decreasing from 117 μm at the bottom of the baghouse to only 31 μm near the top of the filter bag. The filter cake thickness also decreased sharply with height. Results from the CFD simulations indicated that in the pilot scale baghouse particles larger than 120 μm in diameter tend to fall out of the air flow and collect in the bottom of the baghouse, instead of depositing on the filter. While industrial baghouses tend to have a higher elutriation velocity than the pilot scale baghouse used in this study, the large size of industrial baghouses provides ample opportunity for particles to segregate on the basis of size. In addition, bench scale results indicated that high air velocities near the filter surface may cause particles to rebound from the filter. This may occur in industrial baghouses in the region near the inlet, where the air velocity is highest. The reverse pressure differential induced in the filter bag by a cleaning pulse was found to increase with distance from the cell plate. Positioning the nozzle too close to the bag opening created a low pressure zone just beneath the cell plate, where the pressure remained lower inside the bag than outside throughout the pulse. This may lead to poor cleaning at the top of the bag. In the pilot scale baghouse, positioning the nozzle at least 0.7 m from the bag opening eliminated the low pressure zone. The optimum distance of 0.7 m is is dependent on the nozzle type and bag diameter, but can be directly applied to recent industrial baghouse designs in the NZ dairy industry, which have the same nozzle type and bag diameter as the pilot scale baghouse. The design of the pulse cleaning system is important in achieving good baghouse performance. Increasing the pulse tank pressure on the pilot scale baghouse from 3.5 bar to 6.5 bar caused a 30% reduction in the forward pressure differential after the pulse, while decreasing the pulse pressure below 3.5 bar caused the pressure differentials to increase indefinitely. Altering the nozzle position had no effect on the overall pressure differentials, but did alter the local acceleration at different points on the filter bag during a pulse. CFD simulations indicated that decreasing the distance between the nozzle and the bag opening from 0.7 m to 0.1 m increased the overpressure at the bottom of the bag from 770 Pa to 3500 Pa, but this was offset by the appearance of the low pressure zone at the top of the bag as mentioned above. CFD simulations indicated that the diameter of the pulse nozzle altered both the mean bag overpressure generated by the pulse, and the distribution of the overpressure over the bag surface, with the low pressure zone at the top of the bag becoming longer at large nozzle diameters. The pulse duration was found to be unimportant, with experiments on the pilot scale baghouse finding that this had no effect on either the overall baghouse pressure differentials or the length of the low pressure zone at the top of the bag. The project has extended the understanding of milk powder baghouse performance by relating the moisture-dependent properties of lactose and the temperature-dependent melting of dairy fats to baghouse performance. The project has also provided a useful design tool in the form of the CFD model. The project demonstrates an opportunity for further CFD research into baghouse design, as the basic model developed here could now be modified to directly simulate large industrial baghouses. It is hoped that the results from this thesis will find application in the New Zealand Dairy Industry.