The research is of aluminide and silicide coating layer on 310 stainless steel by the pack cementation method. We use TEM,SEM,OM,X-ray instruements to analysis the coating layer.We find the aluminide layer good to protect substrate. The aluminide layer to resist oxidiation is better than silicide.We believe the method of the pack cementation will be developed very well in the future

Au cours de ce travail, des revêtements intermétalliques TiAlx (x=1,2,3) ont été élaborés sur des substrats à base titane : le titane pur et l’alliage commercial, TA6V. L’objectif était de réaliser des revêtements d’aluminiure en surface et d’étudier le comportement des matériaux revêtus vis-à-vis de l’oxydation à haute température sous air, sous air enrichi en vapeur d’eau et en présence de soufre. Les matériaux revêtus ont été testés à trois températures : 700°C, 800°C et 900°C. Les revêtements ont été réalisés à 1000°C par la méthode de cémentation en caisse. Les revêtements réalisés par ce procédé sont toujours adhérents au substrat. Pendant la réaction d’oxydation, l’existence d’un processus de rétrodiffusion de l’aluminium modifie la nature des phases et l’organisation du revêtement. Les phases TiAl et TiAl2 ne sont pas suffisamment riches en aluminium pour promouvoir la formation d’une couche d’alumine protectrice quelle que soit la température d’oxydation. Lorsque ce sont ces phases qui sont à la surface du revêtement, on assiste toujours à la formation d’une couche superficielle de rutile TiO2. Quand elle constitue la sous-couche externe du revêtement, la phase TiAl3 est assez riche en aluminium pour former une couche d’alumine -Al2O3 couvrante, compacte et protectrice. / During this study, intermetallic coatings TiAlx (x=1,2,3) were performed on titanium substrates: pure titanium and the commercial alloy, TA6V. The aim of this study was to elaborate aluminiure coatings on the surface and characterize the behaviour of these coated materials in oxidation at high temperature under air laboratory, under air enriched with water vapour and with sulfur. The coated materials were tested at three temperatures: 700°C, 800°C and 900°C. The coatings were realized at 1000°C by the pack-cementation process. The coatings realized are always adherent to the substrate. During oxidation the retrodiffusion of aluminium changes the nature of the phases and the organisation of the coating. TiAl and TiAl2 phases are not enough rich in aluminium to promote the formation of a protective alumina layer, whatever the temperature. When these phases are present on the surface of the coating, we always observe the formation of a TiO2 rutile top layer. When TiAl3 is the external sub-layer of the coating, this phase is rich enough in aluminium to form an -Al2O3 alumina layer, which is covering, compact and protective.

Novas demandas de aplicação tem sido a principal motivação para a produção de materiais estruturais associando boas propriedades mecânicas e baixo custo de fabricação. A indústria aeroespacial vem desenvolvendo estudos com titânio e suas ligas, devido, a sua elevada resistência mecânica e baixa massa específica. Alguns estudos afirmam que, em temperaturas acima de 500°C as ligas de titânio possuem baixa resistência à oxidação restringindo a sua aplicabilidade. Localizada na parte inferior das turbinas em aviões comerciais, a liga Ti ?-21S tem mostrado bom desempenho em até 700°C com grande potencial para substituir alguns componentes, diminuindo os gastos com manutenção e aumentando a autonomia das turbinas a gás. Diante desse cenário, o objetivo deste trabalho foi desenvolvimento de revestimentos visando o aumento da resistência a oxidação na liga Ti ?-21S mantendo as suas características iniciais. O processo de revestimento foi feito em diferentes condições de temperatura × tempo via HAPC (CVD in situ). A faixa de temperatura analisada foi de 560 à 760°C entre 1 à 25h. A microestrutura de todos os coupons (não revestidos, revestidos e oxidados) foram caracterizados por difração de raios X (DRX) e microscopia eletrônica de varredura (MEV). A cinética de crescimento aparente da camada de revestimento foi feita medindo a espessura de revestimento nas condições analisadas e a cinética de oxidação foi feita através da variação de massa superficial dos coupons. Os resultados do DRX e MEV mostraram que os revestimentos produzidos foram monofásicos com composição química TiAl3. A cinética de crescimento entre 660 à 760°C apresentou energia de ativação de 108 kJ/mol e constante pré-exponencial de 1,21 × 10-3 cm²/s, esses resultados sugerem que a cinética de crescimento é controlada pela difusão dos átomos de alumínio no volume da liga Ti ?-21S formando a camada de TiAl3. Os coupons revestidos foram oxidados à 750 e 850°C por 100, 200 e 300h, os resultados da caracterização microestrutural mostrou que nos coupons revestidos foi formada uma camada de Al2O3 e a variação de massa superficial após 300h à 850°C foi de 0,60 mg/cm². Portanto, após a oxidação dos coupons revestidos, foi observado que o revestimento promoveu a formação de óxidos protetores como Al2O3 aumentando a resistência a oxidação da liga Ti ?-21S revestida. / New application demands have been the main motivation for the production of structural materials associating good mechanical properties and low manufacturing cost. The aerospace industry has been developing studies with titanium and its alloys, due to its high mechanical strength and low specific mass. Some studies report that, at temperatures above 500°C, titanium alloys have low oxidation resistance, restricting their applicability. Located at the bottom of turbines in commercial aircraft, the Ti ?-21S alloy has shown good performance up to 700°C with great potential to replace some components, reducing maintenance costs and increasing the autonomy of gas turbines. In view of this scenario, the objective of this work was the development of coatings aiming at increasing the resistance to oxidation in the Ti ?-21S alloy while maintaining its initial characteristics. The coating process was done at different temperature × time conditions via Pack Cementation (CVD in situ). The temperature range analyzed was 560 - 760°C between 1 - 25h. The microstructure of all coupons (uncoated, coated and oxidized) were characterized by XRD and SEM. The kinetics of apparent growth of the coating layer were made by measuring the coating thickness under the analyzed conditions and the oxidation kinetics was done by varying the surface mass of the coupons. The results of the DRX and MEV showed that the coatings produced were monophasic with TiAl3 chemical composition. The kinetics of growth between 660 - 760°C showed activation energy of 108 kJ/mol and pre-exponential constant of 1.21 × 10-3 cm²/s, these results suggest that the kinetics of growth is controlled by the diffusion of atoms of aluminum in the volume of the Ti ?-21S alloy forming the TiAl3 layer. The coated coupons were oxidized at 750 and 850°C for 100, 200 and 300h, the results of the microstructural characterization showed that in the coated coupons an Al2O3 layer was formed and the surface mass variation after 300h at 850°C was 0.60 mg/cm². Therefore, after oxidation of the coated coupons, it was observed that the coating promoted the formation of protective oxides like Al2O3 increasing the oxidation resistance of the coated Ti ?-21S alloy.

No description available.

Energy storage provides sustainability when coupled with renewable but intermittent energy sources such as solar, wave and wind power, and electrochemical supercapacitors represent a new storage technology with high power and energy density. For inclusion in supercapacitors, transition metal oxide and sulfide electrodes such as RuO2, IrO2, TiS2, and MoS2 exhibit rapid faradaic electron–transfer reactions combined with low resistance. The pseudocapacitance of RuO2 is about 720 F/g, and is 100 times greater than double-layer capacitance of activated carbon electrodes. Due to the two-dimensional layered structure of MoS2, it has proven to be an excellent electrode material for electrochemical supercapacitors. Cathodic electrodeposition of MoS2 onto glassy carbon electrodes is obtained from electrolytes containing (NH4)2MoS4 and KCl. Annealing the as-deposited Mo sulfide deposit improves the capacitance by a factor of 40x, with a maximum value of 360 F/g for 50 nm thick MoS2 films. The effects of different annealing conditions were investigated by XRD, AFM and charge storage measurements. The specific capacitance measured by cyclic voltammetry is highest for MoS2 thin films annealed at 500°C for 3h and much lower for films annealed at 700°C for 1 h. Inclusion of copper as a dopant element into electrodeposited MoS2 thin films for reducing iR drop during film charge/discharge is also studied. Thin films of Cu-doped MoS2 are deposited from aqueous electrolytes containing SCN-, which acts as a complexing agent to shift the cathodic Cu deposition potential, which is much more anodic than that of MoS2. Annealed, Cu-doped MoS2 films exhibit enhanced charge storage capability about 5x higher than undoped MoS2 films. Coal combustion is currently the largest single anthropogenic source of CO2 emissions, and due to the growing concerns about climate change, several new technologies have been developed to mitigate the problem, including oxyfuel coal combustion, which makes CO2 sequestration easier. One complication of oxyfuel coal combustion is that corrosion problems can be exacerbated due to flue gas recycling, which is employed to dilute the pure O2 feed and reduce the flame temperature. Refractory metal diffusion coatings of Ti and Zr atop P91 steel were created and tested for their ability to prevent corrosion in an oxidizing atmosphere at elevated temperature. Using pack cementation, diffusion coatings of thickness approximately 12 and 20 µm are obtained for Ti and Zr, respectively. The effects of heating to 950°C for 24 hr in 5% O2 in He are studied in situ by thermogravimetric analyses (TGA), and ex situ by SEM analyses and depth profiling by EDX. For Ti-coated, Zr-coated and uncoated P91 samples, extended heating in an oxidizing environment causes relatively thick oxide growth, but extensive oxygen penetration greater than 2.7 mm below the sample surface, and eventual oxide exfoliation, are observed only for the uncoated P91 sample. For the Ti- and Zr-coated samples, oxygen penetrates approximately 16 and 56 µm, respectively, below the surface. In situ TGA verifies that Ti-and Zr-coated P91 samples undergo far smaller mass changes during corrosion than uncoated samples, reaching close to steady state mass after approximately four hours.

No description available.

L'amélioration du rendement des turboréacteurs requiert un accroissement de leur température de service. Le développement de nouveaux alliages, issus du système Nb-Si, permet d'envisager des températures de fonctionnement de 200°C supérieures à celles offertes par les superalliages base nickel utilisés actuellement. La première partie de ce manuscrit rappelle les principaux résultats scientifiques ayant menés à la sélection des alliages composites à base de siliciures de niobium (Nbss-Nb5Si3). La microstructure de ces alliages associe une matrice ductile de niobium pouvant solubiliser de nombreux éléments d'addition à une dispersion de siliciures durs et fragiles conférant aux alliages leurs bonnes propriétés en fluage et une meilleure résistance à l'oxydation à haute température. Malheureusement, ces alliages sont caractérisés par une récession rapide du métal associée au développement d'oxydes non protecteurs. L'oxygène réagit rapidement avec le substrat, se dissout dans la solution solide de niobium et y diffuse rapidement. L'effet des éléments Al, Si et Ti a été étudié en considérant à la fois les modifications microstructurales et les propriétés en oxydation lors de ces additions. Bien que ces optimisations de compositions conduisent à une amélioration significative de la résistance à l'oxydation des alliages Nbss-Nb5Si3, certaines nuances souffrent d'une résistance à l'oxydation catastrophique vers 800°C. L'ajout graduel d'étain au sein des alliages permet de modifier foncièrement la microstructure, notamment en initiant le développement d'une phase de type A15-Nb3Sn. A 800°C, l'étain supprime la dissolution de l'oxygène au sein de Nbss responsable du comportement en oxydation catastrophique rencontré par les nuances sans étain. Malgré ces progrès, la résistance à l'oxydation de ces alliages reste insuffisante et le développement de revêtements protecteurs contre l'oxydation a été nécessaire. Dans ce sens deux familles de siliciures Nb3X3CrSi6 et Nb4X4Si7 (X = Fe, Co ou Ni) ont été sélectionnées et leur stabilité thermodynamique ainsi que leur comportement en oxydation ont été évaluées. Ces phases se sont avérées capables de résister à l'oxydation à des températures d'exposition allant jusqu'à 1300°C. Le mécanisme d'oxydation de chacun de ces siliciures a été déterminé. Finalement, le dépôt de ces siliciures à la surface des alliages Nbss-Nb5Si3 via le procédé de pack cémentation s'est révélé possible. Les alliages revêtus par les siliciures choisis présentent des durées de vie pouvant aller jusqu'à 3000 cycles d'oxydation d'une heure à 1100°C / The improvement of the efficiency of turbine engine can be achieved by increasing the working temperature. The development of new alloys based on Nb-Si system allows a jump of 200°C of the operating temperature in comparison to that offered by current nickel based alloys. The first part of this manuscript focuses on the evolutions which have led to the development of niobium silicide in situ composites (Nbss-Nb5Si3). The microstructure of these alloys consists in a ductile niobium matrix where number of alloying elements can solubilise and of strengthening niobium silicides which are intended to provide creep and oxidation resistance at high temperature. Unfortunately, these alloys exhibit a poor oxidation resistance characterised by a high metal recession rate and the formation of non-protective oxide scale. Thus, oxygen can easily react with the substrate, dissolve in Nbss and diffuse quickly through this phase. The effect of Al, Si and Ti additions on both microstructure and oxidation resistance were investigated. Although, these composition optimisations lead to a significant enhance of oxidation resistance, some compositions still suffers from catastrophic oxidation behaviour around 800°C. In these alloys tin additions involve high microstructural changes, especially by initiating the formation of A15- Nb3Sn phase. At 800°C, Sn additions suppress oxygen dissolution in Nbss responsible of the catastrophic oxidation behaviour of these alloys. Nevertheless, the oxidation resistance of these alloys remains too low for the foreseen applications and protective coatings are required. Thermodynamic stability and oxidation resistance of two silicide families (Nb3X3CrSi6 and Nb4X4Si7 (X = Fe, Co or Ni)) were investigated. These silicides have exhibited a high oxidation resistance up to 1300°C by the formation of a protective silica layer. Finally, these silicides were deposited on Nbss-Nb5Si3 substrate by using the pack cementation process. Some coated alloys have then exhibited lifetime going up to 3000 one hour cycle at 1100°C

No description available.

<p>The introduction of metal supported cells may be a key innovation in the development of solid oxide fuel cell (SOFC) technology. The objective of this study was to develop a process of co-firing the ceramic layers of a solid oxide fuel cell attached to their porous metal support. This is a major departure from the traditional fuel cell architecture where the support layer is a ceramic composite made of YSZ and NiO.</p> <p>The problems to be eliminated during the fabrication process include the warping, cracking and delamination of the cell during the co-sintering process.</p> <p>In this study, the porous metal layer was produced by the freeze tape casting process. During co-sintering, it is necessary to match the relative shrinkage between the metal and ceramic layers. Different parameters which can influence the relative shrinkage were explored, including the heating rate, sintering temperature, sintering time, cell thickness, solid loading of the green tapes, applications of wet and dry hydrogen in the sintering atmosphere, as well as a change of the electrolyte material. Specifically, GDC was tested as an alternative electrolyte to YSZ.</p> <p>Since the porous metal substrate is exposed to air during fuel cell operation, it must be protected from oxidation. Therefore, the pack cementation method was used to apply a layer of aluminum onto the metal substrate. Variables such as temperature and exposure time of the coating materials were investigated in this thesis.</p> / Master of Applied Science (MASc)

Aluminium smelting is a high temperature electrometallurgical process, which suffers considerable inefficiencies in power utilization and equipment maintenance. Aluminium smelting cell works in the extreme environments that contain extraordinarily aggressive gases, such as HF, CO and SO2. Mild steel used as a structural material in the aluminium industry, can be catastrophically corroded or oxidized in these conditions. This project was mainly concerned with extending the lifetime of metal structures installed immediately above the aluminium smelting cells. An aluminium-rich coating was developed on low carbon steel A06 using pack cementation technique. Yttria (Y2O3) was also used to improve the corrosion resistance of coating. Kinetics of the coating formation were studied. XRD, FESEM and FIB were employed to investigate the phase constitution and the surface morphology. Together with other potentially competitive materials, aluminium-rich coating was evaluated in simulated plant environments. Results from the long time (up to 2500h) isothermal oxidation of materials at high temperature (800??C) in air showed that the oxidation resistance of coated A06 is close to that of stainless steel 304 and even better than SS304 in cyclic oxidation tests. Coated A06 was also found to have the best sulfidation resistance among the materials tested in the gas mixture contains SO2 at 800??C. Related kinetics and mechanisms were also studied. The superior corrosion resistance of the coated A06 is attributed to the slow growing alpha-Al2O3 formed. Low temperature corrosion tests were undertaken in the gas mixtures containing air, H2O, HCl and SO2 at 400??C. Together with SS304 and 253MA, coated A06 showed excellent corrosion resistance in all the conditions. The ranking of the top three materials for corrosion resistance is: 253MA, coated A06 and SS304. It is believed that aluminised A06 is an ideal and economical replacement material in the severe corrosive aluminium smelting cell environment.