Academic literature on the topic 'Hybrid layer degradation'

There is a consensus that dentine/resin bonding deteriorates over time, and such degradation is one of the main reasons for limiting adhesive restoration longevity. Enzymes known as matrix metalloproteinases (MMPs) are responsible by enzymatic degradation of collagen fibrils without protection, which are present in the resin-dentine interface. Therefore, these enzymes are involved in the process of adhesive interface degradation. Currently, studies point out chlorhexidine digluconate has antiproteolytic function by inhibiting the action of MMPS. Thus, it is thought this substance application prior to the use of bonding agents could slow the process of degradation of the tooth-restoration interface, resulting in longevity. Objective: To review the literature on the influence of chlorhexidine application on the stability of the adhesive interface. Literature review: Chlorhexidine digluconate proprieties and its application in Dentistry were discussed. Next, hybrid layer formation and degradation was discussed and the mechanism of action of chlorhexidine on preserving this layer was detailed. Finally, scientific studies from the last six years were analyzed on the performance of adhesive systems after chlorhexidine application. Results: Considering the results of reviewed studies, it can be concluded that chlorhexidine application did not interfere on the immediate bond strength to dentin and hybrid layer degradation over time occurred later and/or with lower intensity. Conclusion: Chlorhexidine application interferes positively when incorporated into the adhesion protocols, by promoting hybrid layer stability over time.

The effects of IrO2/Pt layered hybrid bottom and/or top electrode structures on the leakage current density versus voltage (J–V), polarization versus voltage (P–V), ferroelectric imprint, and fatigue properties of chemical-solution-derived Pb(ZrxTi1−x)O3 (PZT, Zr/Ti = 35/65) thin films were investigated. The best P–V and J–V performances were obtained from a capacitor with nonhybrid electrodes (Pt/PZT/Pt capacitor). However, the poor fatigue performance of the capacitor required the adoption of hybrid electrode structures. A thin IrO2 layer, as thin as 6 nm, which was inserted between top Pt electrode and PZT layer was sufficient for improving the fatigue performance without any degradation of the other ferroelectric properties. However, the same layer adopted on the bottom Pt electrode was not effective in improving the fatigue performance with degradation in P–V and J–V properties. This was ascribed to IrO2 layer dissolution into the PZT layer during the crystallization annealing of the PZT thin film. A thicker IrO2 layer resulted in more serious degradation.

This paper proposes hybrid methods using physics-informed (PI) lightweight Temporal Convolution Neural Network (PITCN) for bearings’ remaining useful life (RUL) prediction under stiffness degradation. It includes three PI hybrid models: a) PI Feature model (PIFM) — constructing physics-informed health indicator (PIHI) to augment the feature space, b) PI Layer model (PILM)—encoding the physics governing equations in a hidden layer, and c) PI Layer Based Loss model (PILLM)—designing PI conflict loss, taking into account the difference before and after integration of the physics input-output relations involved module to the loss function. We simulated 200 different bearing stiffness degradations, using their discrete monitored vibration signals to verify the effectiveness of the proposed method. We also investigate their inference process through feature heat map analysis to interpret how the models melt physics knowledge to assist in capturing the degradation trend. The physics knowledge considered in this paper is the dynamic relationship between vibration amplitude and stiffness in a damped forced vibration model. The results show that all three PITCN models effectively capture degradation-related trend information and perform better than the vanilla lightweight TCN. Furthermore, the visualization of the feature channels highlights the important role of physics information in model training. Channels containing physics information demonstrate higher correlation with results as they significantly dominate the heat map compared to other channels.

We have shown that admixtures of 5CB and SWCN accelerate the degradation of l,d-PLA in the composite layer due to hydrophilic/hydrophobic interface in the layer and act as plasticizers. The mechanism of the degradation process is also discussed.

Despite the remarkable progress in perovskite solar cells (PSCs), their instability and rapid degradation over time still restrict their commercialization. A 2D capping layer has been proved to overcome the stability issues; however, an in-depth understanding of the complex degradation processes over a prolonged time at PSC interfaces is crucial for improving their stability. In the current work, we investigated the stability of a triple cation 3D ([(FA0.83MA0.17)Cs0.05]Pb(I0.83Br0.17)3) and 2D/3D PSC fabricated by a layer-by-layer deposition technique (PEAI-based 2D layer over triple cation 3D perovskite) using a state-of-art characterization technique: electrochemical impedance spectroscopy (EIS). A long-term stability test over 24 months was performed on the 3D and 2D/3D PSCs with an initial PCE of 18.87% and 20.21%, respectively, to suggest a more practical scenario. The current-voltage (J-V) and EIS results showed degradation in both the solar cell types; however, a slower degradation rate was observed in 2D/3D PSCs. Finally, the quantitative analysis of the key EIS parameters affected by the degradation in 3D and 2D/3D PSCs were discussed.

Loss of hybrid layer integrity compromises resin-dentin bond stability. Matrix metalloproteinases (MMPs) may be partially responsible for hybrid layer degradation. Since chlorhexidine inhibits MMPs, we hypothesized that chlorhexidine would decelerate the loss of resin-dentin bonds. Class I preparations in extracted third molars were sectioned into two halves. One half was customarily restored (etch-and-rinse adhesive/resin composite), and the other was treated with 2% chlorhexidine after being acid-etched before restoration. Specimens were stored in artificial saliva with/without protease inhibitors. Microtensile bond strengths and failure mode distribution under SEM were analyzed immediately after specimens’ preparation and 6 months later. With chlorhexidine, significantly better preservation of bond strength was observed after 6 months; protease inhibitors in the storage medium had no effect. Failure analysis showed significantly less failure in the hybrid layer with chlorhexidine, compared with controls after 6 months. In conclusion, this in vitro study suggests that chlorhexidine might be useful for the preservation of dentin bond strength.

Organic-inorganic hybrid halide perovskite solar cells (PSCs) have been a trending topic in recent years. Significant progress has been made to increase their power conversion efficiency (PCE) to more than 20%. However, the poor stability of PSCs in both working and non-working conditions results in rapid degradation through multiple environmental erosions such as water, heat, and UV light. Attempts have been made to resolve the rapid-degradation problems, including formula changes, transport layer improvements, and encapsulations, but none of these have effectively resolved the dilemma. This paper reports our findings on adding inorganic films as surface-passivation layers on top of the hybrid perovskite materials, which not only enhance stability by eliminating weak sites but also prevent water penetration by using a water-stable layer. The surface-passivated hybrid perovskite layer indicates a slight increase of bandgap energy (Eg=1.76 eV), compared to the original methylammonium lead iodide (MAPbI3, Eg=1.61 eV) layer, allowing for more stable perovskite layer with a small sacrifice in the photoluminescence property, which represents a lower charge diffusion rate and higher bandgap energy. Our finding offers an alternative approach to resolving the low stability issue for PSC fabrication.

2012/2013
The subject of this thesis is the stability of the adhesive interface in dentistry. Success in adhesive dentistry means long lasting restorations. However, there is substantial evidence that this ideal objective is not achieved. Current research in this field aims at increasing the resin-dentin bond durability. This doctoral research examines the fundamental processes responsible for the aging mechanisms involved in the degradation of resin-bonded interfaces, as well as some potential approaches to prevent and counteract this degradation. Resin-dentin bond degradation is a complex process that is not completely understood, involving the hydrolysis of both the resin and the collagen component of the hybrid layer. The hydrophilic and acidic characteristics of current dentin adhesives have made hybrid layers highly prone to water sorption, which causes polymer degradation and results in decreased resin-dentin bond strength over time. These unstable polymers inside the hybrid layer may result in an incomplete encapsulation of collagen fibers, which become vulnerable to mechanical and hydrolytical fatigue, as well as degradation by host-derived proteases with collagenolytic activity. These enzymes, such as matrix metalloproteinases (MMPs) and cysteine cathepsins, have a crucial role in the degradation of type I collagen, the organic component of the hybrid layer. The first part of this thesis aims to review the current knowledge regarding adhesion to the tooth substrate (Chapter 1), focusing on the fundamental processes that are responsible for the degradation of the adhesive interface (Chapter 2). Since the permeability of adhesives to water is particularly evident in simplified adhesive formulations, the research activity was focused on self-etch and universal adhesive systems’ behavior. Thus, the research study reported in Chapter 3 showed that the bond strength and nanoleakage expression of two-step and one-step self-etch tested bonding systems were affected by storage for 6 month and 1 year in artificial saliva. Although it is generally accepted that the permeability of adhesives to water is particularly evident in simplified adhesive formulations, the stability over time was not related to the number of steps of bonding systems, but to their chemical formulations. The performance of a new universal (or multi-mode) adhesive system through storage in artificial saliva was also investigated. The original results presented in Chapter 4 found that improved bonding effectiveness of the tested universal adhesive system on dentin was obtained when the adhesive was applied with the self-etch approach. Indeed, the etch-and-rinse approaches tested (both on wet and dry dentin) resulted in immediate bond strength comparable to the self-etch mode but expedited long-term aging resulted in reduced bond strength and increased nanoleakage expression, irrespective of dentin wetness. Moreover, the results of the zymographic analysis showed evident changes in dentinal MMP-2 and -9 enzyme activities after the application of the tested adhesives, revealing differences in the extent of enzyme activation. These findings exhibit that the activation of endogenous MMPs is not related to the adhesive system or the strategy employed. Thus, regardless of the approach and the material used in bonding procedures, a stable and durable bond is not achieved. Therefore, experimental strategies that aim to enhance the adhesive interface, particularly improving the durability of the resin-dentin bond strength by inhibiting intrinsic collagenolytic activity and increasing the resistance of dentin collagen matrix to enzymatic degradation are needed. The last part of the thesis is focused on both the strategies to inhibit the proteolytic and collagenolytic activity of the endogenous proteases and the methods to increase the mechanical strength of collagen network and its resistance to enzymatic degradation (Chapter 5). Chlorhexidine (CHX) has been used as a non-specific MMP inhibitor to prevent degradation of hybrid layers. However, CHX is water-soluble and may leach out of hybrid layers, compromising its long-term anti-MMP effectiveness. An entirely different approach is to treat the acid-etched dentin containing activated matrix-bound MMPs with cross-linking agents that inactivate the catalytic site of proteases. In particular, the ability of a cross-linker agent, 1-ethyl-3-(3-dimethylamino-propyl) carbodiimide (EDC), to prevent collagen degradation was evaluated under occlusal cycle loading. Previous research successfully utilized EDC to increase the durability of resin-dentin bonds by increasing the mechanical properties of the collagen matrix; however, the 1 to 4 hrs required for that procedure was clinically unacceptable. For this reason, the purpose of the last part of the research, presented in Chapter 6, was to evaluate the ability of 0.5 M EDC short-time (1 min) pre-treatment to improve the stability of demineralized dentin collagen matrices by quantifying the release of telopeptide fragments over time. The results showed that EDC application for 1 min may be a clinically relevant and effective means for stabilizing the collagen network not only by strengthening the fibrils, but also by reducing the enzymatic degradation rate. Thus, dentin collagen reinforcement and strengthening through EDC cross-linking might be of importance to improve the bond strength and structural integrity of the resin-dentin interface over time against the enzymatic and hydrolytic degradation.
La tesi qui presentata riguarda la stabilità dell'interfaccia adesiva in odontoiatria. Il successo delle moderne terapie conservative è rappresentato dalla longevità dei restauri adesivi. Tuttavia, vi è una sostanziale evidenza che questo obiettivo ideale non sia raggiunto. La stabilità dell’interfaccia adesiva dipende dalla formazione di uno strato ibrido, compatto e omogeneo, durante l’impregnazione del substrato dentinale da parte dei monomeri adesivi. Poiché lo strato ibrido rappresenta un’entità complessa, in cui interagiscono componenti biologiche diverse (matrice dentinale collagenica e cristalli d’idrossiapatite residui) e non (monomeri resinosi e solventi), i fenomeni d’invecchiamento interessano in maniera sinergica sia la porzione resinosa che quella dentale. L’articolato processo che porta alla degradazione dell’interfaccia adesiva coinvolge infatti la componente resinosa, attraverso l’idrolisi della resina negli spazi interfibrillari, e quella organica, attraverso la disorganizzazione delle fibre collagene dovuta ad un incompleto incapsulamento delle stesse, nonché alla degradazione da parte di proteasi intrinseche con attività collagenolitica. È stato dimostrato come questi enzimi, le metalloproteinasi della matrice (MMP) e le catepsine, abbiano un ruolo cruciale nella degradazione del collagene di tipo I, la principale componente organica dello strato ibrido. Inoltre le caratteristiche idrofile e acide degli attuali sistemi adesivi dentinali hanno reso lo strato ibrido molto suscettibile all'assorbimento di acqua, comportando, attraverso l’idrolisi, la degradazione dello stesso e andando così a contribuire ad una diminuzione della forza di legame nel tempo. Attualmente l’interesse della comunità scientifica mira ad aumentare la durata del legame adesivo con il substrato dentinale. Dopo un’attenta analisi delle attuali conoscenze riguardanti adesione al substrato dentale (Capitolo 1), la prima parte della tesi si propone di valutare i processi fondamentali che sono responsabili della degradazione dell'interfaccia adesiva (Capitolo 2). Poiché la permeabilità all’acqua degli adesivi è particolarmente evidente nelle formulazioni semplificate, l'attività di ricerca si è concentrata sull’analisi del comportamento dei sistemi adesivi self-etch e dei recenti sistemi adesivi universali. I risultati riportati nel Capitolo 3 ha dimostrato come la forza di legame e l’espressione del nanoleakage dei sistemi adesivi self-etch two-step e one-step testati sia negativamente influenzata dall’invecchiamento in saliva artificiale per 6 mesi e 1 anno. Sebbene sia generalmente accettato che la permeabilità degli adesivi all'acqua è particolarmente evidente in formulazioni di adesivi semplificati, la stabilità nel tempo non è stata correlata al numero di passaggi dei sistemi adesivi, bensì alle loro composizioni chimiche. Sono state in seguito analizzate anche le prestazioni di un nuovo sistema adesivo universale (o multimodale). I risultati presentati nel Capitolo 4 hanno stabilito una migliore efficienza adesiva del sistema universale, testato sul substrato dentinale, quando l'adesivo è stato applicato con l'approccio self-etch. Infatti, la tecnica etch-and-rinse, testata sia su dentina umida che secca, ha comportato una forza di adesione immediata paragonabile alla modalità self-etch, ma a tempi di invecchiamento incrementali si è evidenziata una diminuzione della forza di legame e una maggiore espressione del nanoleakage, a prescindere dalla condizione di umidità dentinale. Inoltre, i risultati dell'analisi zimografica hanno mostrato evidenti variazioni dell’attività enzimatica delle metalloproteinasi MMP-2 e -9 dopo l'applicazione degli adesivi testati. Questi risultati dimostrano come l'attivazione delle MMP endogene non sia correlata al sistema adesivo o alla strategia adottata. Ne evince che, indipendentemente dal metodo e dal materiale utilizzato nelle procedure adesive, non si è in grado di stabilire un legame affidabile e duraturo. Pertanto si avverte l’esigenza di strategie sperimentali che mirino a migliorare la stabilità dell’interfaccia adesiva, in particolare incrementando la durata della forza di legame in dentina inibendo l'attività collagenolitica intrinseca e aumentando la resistenza del collagene alla degradazione enzimatica. L'ultima parte della tesi è focalizzata quindi sulle strategie per inibire l'attività proteolitica e collagenolitica delle proteasi endogene e sui metodi per aumentare la resistenza meccanica del collagene alla degradazione enzimatica (Capitolo 5). Un potente agente antibatterico, la clorexidina (CHX), è stato usato come inibitore non specifico delle MMP al fine di impedire la degradazione dello strato ibrido. Tuttavia la CHX, essendo solubile in acqua, può dissolversi nello strato ibrido, compromettendo la sua efficacia anti-MMP a lungo termine. Un approccio completamente diverso è quello di trattare la dentina mordenzata con agenti cross-linker. In particolare, simulando il carico occlusale, è stata valutata la capacità di un agente cross-linker, l’1-etil-3-(3-dimetilammino-propil) carbodiimmide (EDC), per prevenire la degradazione del collagene. Precedenti ricerche hanno utilizzato con successo l’EDC con lo scopo di aumentare la durata dell’interfaccia adesiva, aumentando le proprietà meccaniche della matrice di collagene; tuttavia, il tempo necessario (da 1 a 4 ore) richiesto per tali procedure è clinicamente inaccettabile. Per questo motivo, lo scopo dell’ultima parte della ricerca, presentata nel Capitolo 6, è stato quello di valutare la capacità di 0,5 M EDC nel breve periodo di pretrattamento (1 min), andando a quantificare il rilascio di frammenti di telopeptidi di collagene nel corso del tempo. I risultati hanno dimostrato che l'applicazione di EDC per 1 min può essere un approccio clinicamente rilevante ed efficace nello stabilizzare il collagene, non solo rafforzando le fibrille, ma anche riducendo la velocità di degradazione enzimatica. Di conseguenza, l’utilizzo di questo cross-linker può garantire una valida strategia per migliorare la forza di legame e l'integrità strutturale dell'interfaccia adesiva nel tempo contro l’attività enzimatica intrinseca del collagene e la degradazione idrolitica.
XXVI Ciclo
1985

Nanotechnology has drawn the attention of many researchers for the delivery of therapeutics used in various medical applications. Liposomes and polymeric nanoparticles represent promising nanocarriers that efficiently encapsulate drugs, which prevents their degradation along with the control and sustained drug release. Despite the many advantages of these formulations, some of the drawbacks associated with them limit their application to a certain extent. Therefore, there is need for a novel nanocarrier that possesses all of their individual advantages and excludes their drawbacks. Currently, researchers are focused on developing a novel platform that is a hybrid of a polymeric and liposomal-based carrier that combines the peculiarity of both and excludes their shortcomings. Lipid hybrid polymer nanoparticles (LPNs) contain the hydrophobic biodegradable polymeric core surrounded by a lipid layer for intensification of biocompatibility. This chapter includes an introduction of LPNs along with their advantages, composition, and method of preparation.

Nanotechnology has drawn the attention of many researchers for the delivery of therapeutics used in various medical applications. Liposomes and polymeric nanoparticles represent promising nanocarriers that efficiently encapsulate drugs, which prevents their degradation along with the control and sustained drug release. Despite the many advantages of these formulations, some of the drawbacks associated with them limit their application to a certain extent. Therefore, there is need for a novel nanocarrier that possesses all of their individual advantages and excludes their drawbacks. Currently, researchers are focused on developing a novel platform that is a hybrid of a polymeric and liposomal-based carrier that combines the peculiarity of both and excludes their shortcomings. Lipid hybrid polymer nanoparticles (LPNs) contain the hydrophobic biodegradable polymeric core surrounded by a lipid layer for intensification of biocompatibility. This chapter includes an introduction of LPNs along with their advantages, composition, and method of preparation.

Over the last few years, due to its exceptional two-dimensional (2D) structure, graphene has played a key role in developing conductive transparent devices and acquired significant attention from scientists to get placed as a boon material in the energy industry. Graphene-based materials have played several roles, including interfacial buffer layers, electron/hole transport material, and transparent electrodes in photovoltaic devices. Apart from charge extraction and electron transportation, graphene protects the photovoltaic devices from atmospheric degradation through its 2D network and offers long-term air or environmental stability. This chapter focuses on the recent advancements in graphene and its nanocomposites-based solar cell devices, including dye-sensitized solar cells (DSSCs), organic solar cells (OSCs), and perovskite solar cells (PSCs). We further discuss the impact of incorporating graphene based materials on the power conversion efficiency for each type of solar cell. The last section of this chapter highlights the potential challenges and future research scope of graphene-based nanocomposites for solar cell applications.

The degradation of silicon nanostructure / poly(3,4-ethylenedioxylthiophene : poly(styrenesulphonic acid) (SiNS/PEDOT:PSS) hybrid solar cell due to the moisture is investigated with an environmental chamber. The unencapsulated devices were tested under different relative humidity (RH) varied from (15% to 100%). Under different RH, the devices show various degradation trends. After 3hrs of storage under 100% RH, the average device power conversion efficiency (PCE) drops from 6.52% to 1.27%. While the device is stored under 15% RH, the averaged PCE just drop from 6.40% to 5.49% and the device at 60% RH degrades from 5.97% to 3.12%. To understand the cause of the device degradation, we compare the ITO conductivity and apply tunneling electron microscopy (TEM) to study the growth of the silicon dioxide layer on the silicon nanostructures. We confirmed that the major cause of the PCE drop in the current devices are due to the decrease of the PEDOT:PSS conductivity and the increase of the interface resistances. By re-depositing the PEDOT:PSS layer onto the degraded device and recycling the Si (and fresh ITO), we demonstrated that the efficiency of the device can be partially recovered (to fully recovered). The current work not only highlighted the importance of the humidity control in these SiNS/PEDOT:PSS hybrid solar cells, but also identified the major causes of the device degradation. The observation has been re-confirmed by recovering the PCE of the degraded device with a fresh PEDOT:PSS layer and a fresh ITO.

A hybrid oxide ceramic matrix composite (CMC) outer combustor liner was tested in a Solar Turbines Incorporated Centaur® 50S engine between 2003 and 2006, accumulating >25,000 hours of field exposure. The hybrid CMC liner, which was ∼76 cm in diameter, had an alumina matrix with a Nextel 720 fiber-reinforcement (A/N720). The CMC, produced by ATK-COI Ceramics, Inc., was coated with a ceramic insulation layer known as FGI (Friable Graded Insulation) developed by Siemens Energy Incorporated. Post-test microstructural and mechanical evaluation was conducted on the field-exposed liner at Oak Ridge National Laboratory (ORNL) to determine the types of surface and structural damage that occurred to the combustor liner during engine exposure to elevated temperatures (>1200°C), thermal cycling (stop-start cycles), and combustion gases (especially water vapor). In this study, numerous sections were cut from the liner for mechanical and microstructural characterization that exhibited varying amounts of FGI and/or CMC degradation. In this way, damage accumulation was assessed (1) within the CMC and FGI layers, both on the gas-path surface and below the surface and (2) as a function of liner position (fore-to-aft) in the engine. The amount and type of damage observed was directly related to the starting CMC and FGI microstructures. The tensile strength of the hybrid liner after field exposure was found to be 19 MPa. The FGI layer remained well bonded to the CMC and the fracture surface of the CMC exhibited scissor-like features, which is typical of composites with ±45° fiber architecture. The stress acting on the CMC at failure was 53 MPa.

Electromagnetic (EM) waves, such as electronic noise and radio frequency interference can be regarded as an invisible electronic pollution which justifies a very active quest for effective electromagnetic interference (EMI) shielding materials. Highly conductive materials of adequate thickness are the primary solutions to shield against EMI. Equipment cases and basic structure of space aircraft and launch vehicles have traditionally been made of aluminum, steel and other electrically conductive metals. However, in recent years composite materials have been used for electronic equipment manufacturing because of their lightweight, high strength, and ease of fabrication. Despite these benefits, composite materials are not as electrically conductive as traditional metals, especially in terms of electrical grounding purposes and shielding. Therefore, extra effort must be taken to resolve these shortcomings. The present work demonstrates a study on developing hybrid composites based on fiberglass with surface grown carbon nanotubes (CNTs) for EMI applications. The choice of fiberglass is primarily because it naturally possesses poor electrical conductivity, hence growing CNTs over glass fiber surface can significantly improve the conductivity. The fabrics were sputter-coated with a thin layer of SiO2 thermal barrier prior to growing of CNTs. The CNTs were grown on the surface of woven fiberglass fabrics utilizing a relatively low temperature technique. Raw fiberglass fabric, SiO2 coated fabric, and SiO2 coated fabric which was subjected to the identical heat treatment as the samples with CNTs were also prepared. Two-layers composite specimens based on different surface treated fiberglass fabrics were fabricated and their EMI shielding effectiveness (SE) was measured. The EMI SE of the hybrid CNT-fiberglass composites was shown to be 5–10 times of the reference samples. However, the tensile mechanical properties of the composites based on the different above mentioned fibers revealed significant degradation due to the elevated CNT growth temperature and the addition of coating layer and CNTs. To further probe the structure of the hybrid composites and the inter-connectivity of the CNTs from one interface to another, sets of 20-layers composites based on different surface treated fabrics were also fabricated and characterized.

Abstract Increasing turbine inlet temperature (TIT) of recuperated gas turbines would lead to simultaneously high efficiency and power density, making them prime candidates for low-emission aeronautics applications, such as hybrid-electric aircraft. The Inside-out Ceramic Turbine (ICT) architecture achieves high TIT by using compression-loaded monolithic ceramics. To resist inertial forces due to blade tip speed exceeding 450 m/s, the shroud of the ICT is made of carbon-polymer composite, wound around a metallic cooling ring. This paper demonstrates that it is beneficial to use a titanium alloy cooling ring with a thermal barrier coating (TBC), rather than nickel superalloys, for the interstitial cooling ring protecting the carbon-polymer from the hot combustion gases. A numerical Design of Experiments (DOE) analysis shows the design trade-offs between the minimum safety factor and the required cooling power for multiple geometries. An optimized high-pressure first turbine stage of a 500 kW microturbine concept using ceramic blades and a titanium cooling ring in an ICT configuration is presented. Its structural performance (minimum safety factor of 1.4) as well as its cooling losses (2% of turbine stage power) are evaluated. Finally, a 20 kW-scale prototype is tested at 300 m/s and a TIT of 1375 K during 4hrs to demonstrate the viability of the concept. Experiments show that the polymer composite was kept below its maximum safe operating temperature and components show no early signs of degradation.

Abstract In comparison to various other materials, carbon fiber, specifically carbon fiber reinforced polymers (CFRP) remains pre-eminent amongst other materials for use on aeronautical systems. Due to its high specific strength (strength-to-weight ratio), CFRP has been able to carry heavy loads while maintaining a lightweight build. This strength and weight efficiency has allowed for commercial airplanes such as the Airbus A350 and the Boeing-787 Dreamliner to greatly outperform common aluminum frame airplanes. Despite its extraordinary strength and light weight efficiency, when influenced by heat resulting from air resistance, CFRP is known to undergo serious degradation that would significantly decrease the effectiveness of the polymers. To prevent this degradation and maintain the strength of the CFRP, thermal protective layers (TPLs) are designed to shield the CFRP from heat exposure. This research is focused on the examination of the effectiveness of TPLs, that are hybrid compositions of epoxy resins and buckypaper (carbon nanotubes) for 3K 2 × 2 twill carbon-fiber, through experimental methods. Experimental thermal analysis of the CFRP is performed at 225 °C for hot plate testing and 650 °C for heat gun testing. The results show that the addition of buckypaper in the thermal protective layer seemed to detect nearly 48°C less heat on average of the four measured intervals in hot plate tests. From heat gun tests, moreover, it was clearly seen that the carbon fiber TPL that contains the epoxy and buckypaper is dominant in terms of heat dispersion. The anisotropic thermal transport property of nanostructured carbon is expected to spread heat accumulated in hot spots efficiently, preventing the heat from being propagated into the CFRP body material. In the near future, the authors will use analytical method and FEA simulations to explain this heat dissipation phenomena.

A novel technique to grow carbon nanotubes (CNTs) on the surface of carbon fibers in a controlled fashion using simple lab set up is developed. Growing CNTs on the surface of carbon fibers will eliminate the problem of dispersion of CNTs in polymeric matrices. The employed synthesis technique retains the attractive feature of uniform distribution of the grown CNTs, low temperature of CNTs’ formation, i.e. 550 °C, via cheap and safe synthesis setup and catalysts. A protective thermal shield of thin ceramic layer and subsequently nickel catalytic particles are deposited on the surface of the carbon fiber yarns using magnetron sputtering. A simple tube furnace setup utilizing nitrogen, hydrogen and ethylene (C2H4) were used to grow CNTs on the carbon fiber yarns. Scanning electron microscopy revealed a uniform areal growth over the carbon fibers where the catalytic particles had been sputtered. The structure of the grown multiwall carbon nanotubes was characterized with the aid of transmission electron microscopy (TEM). Dynamical mechanical analysis (DMA) was employed to measure the loss and storage moduli of the hybrid composite together with the reference raw carbon fiber composite and the composite for which only ceramic and nickel substrates had been deposited on. The DMA tests were conducted over a frequency range of 1–40 Hz. Although the storage modulus remained almost unchanged over the frequency range for all samples, the loss modulus showed a frequency dependent behavior. The hybrid composite obtained the highest loss modulus among other samples with an average increase of approximately 25% and 55% compared to composites of the raw and ceramic/nickel coated carbon fibers, respectively. This improvement occurred while the average storage modulus of the hybrid composite declined by almost 9% and 15% compared to the composites of reference and ceramic/nickel coated samples, respectively. The ultimate strength and elastic moduli of the samples were measured using standard ASTM tensile test. Results of this study show that while the addition of the ceramic layer protects the fibers from mechanical degradation it abolishes the mechanisms by which the composite dissipates energy. On the other hand, with almost no compromise in weight, the hybrid composites are good potential candidate for damping applications. Furthermore, the addition of CNTs could contribute to improving other mechanical, electrical and thermal properties of the hybrid composite.

Chemo-thermal micro-machining is a hybrid method of micro fabrication achieved by integrating laser based thermal ablation and chemical etching. Material removal in this process involves focussing laser beam on a glass specimen submerged in aqueous sodium hydroxide (NaOH) solution that causes chemical degradation of glass along with thermal ablation at the laser target point. Though laser by itself is capable of machining numerous materials, it often causes micro fractures radially along the machined surface, especially when used on glass. In the proposed process, continuous waves of carbon dioxide laser (10.6 μm wavelength) with varying power are irradiated on the surface of borosilicate glass slide immersed in 1M NaOH solution for varying duration of exposure. This resulted in smaller hole diameter and better surface finish in the micro machining of glass, as compared to machining by laser beam alone.