Silicon toughened alumina

The ceramic materials investigated in this paper are hot-pressed silicon nitride (HPSN), reaction-bonded silicon nitride (RBSN), zirconia-toughened alumina (AI2O3), and porous SiC. The available material properties for these ceramics are given in Table 4.3. The HPSN and zirconia-toughened alumina ceramics were in the shape of flexural strength test bars cut from billets. The RBSN ceramic was molded into bars of the shape of flexural test specimens. The porous SiC ceramic was provided in the shape of flexural test specimens. 

Values for ceramics range from below 1 for glasses and most single crystals 1 to 3 for glass-ceramics, clay-based ceramics and MgO 2.5. to 4 for early engineering ceramics (alumina, boron carbide, silicon carbides, RBSN) 4 to 6 for hot-pressed silicon nitride and SRBSN and for transformation-toughened alumina... 

Toughened Alumina. Numerous researchers have reported that the addition of a second phase, a process referred to as toughening, can increase the strength and toughness of alumina. Schwartz discusses the properties of alumina toughened by additions of various forms of zirconia, and by additions of silicon carbide. Saito discusses alumina toughened by addition of titanium carbide, TiC. 

There are three t5q)es of ceramics that are cUiucally relevant to contemporary total hip replacement, including alumina, zirconia, and zirconia-toughened alumina composites. A fourth ceramic biomaterial, oxidized zirconium, is a ceramic-metal composite with a surface layer of zirconia. A fifth biomaterial, silicon nitride, is in advanced stages of commerciahzation for hip arthroplasty. 

Campbell, G.H., Rilhle, M., Dalkgleish, B.J. and Evans, A.G., (1990), Whisker toughening a comparison between alumina and silicon nitride toughened with silicon carbide , J. Am. Ceram. Soc., 73(3), 521. 

As mentioned previously, the main body of research on whisker-reinforced composites was concerned with alumina, mullite, and silicon nitride matrix materials. None the less, selected work examined zirconia, cordierite, and spinel as matrix materials.16-18 The high temperature strength behavior reported for these composites is summarized in Table 2.5. As shown, the zirconia matrix composites exhibited decreases in room temperature strength with the addition of SiC whiskers. However, the retained strength at 1000°C, was significantly improved for the whisker composites over the monolithic. Claussen and co-workers attributed this behavior to loss of transformation toughening at elevated temperatures for the zirconia monolith, whereas the whisker-reinforcement contribution did not decrease at the higher temperature.17,18... 

This chapter discusses the behavior, under thermal shock conditions, of epoxy resins toughened with ceramic particulates. Alumina Al203 and silica Si02, which are usually used as filler for insulation materials, and the new ceramic materials silicon carbide SiC and silicon nitride Si3N4 are employed. For these toughened epoxy resins, the thermal shock resistance is evaluated by using fracture mechanics. The difference between experimental and calculated values of the thermal shock resistance is discussed from a fractographic point of view. 

The effects of ceramic particles and filler content on the thermal shock behavior of toughened epoxy resins have been studied. Resins filled with stiff and strong particles, such as silicon nitride and silicon carbide, show high thermal shock resistance, and the effect of filler content is remarkable. At higher volume fractions (Vf > 40%), the thermal shock resistance of these composites reaches 140 K, whereas that of neat resin is about 90 K. The highest thermal shock resistance is obtained with silicon nitride. The thermal shock resistance of silica-filled composites also increases with increasing filler content, but above 30% of volume fraction it comes close to a certain value. On the contrary, in alumina-filled resin, the thermal shock resistance shows a decrease with increasing filler content. 

Ceramic-matrix composites are utilised to overcome the inherent brittleness of ceramics. The reinforcement consists of fibres or particles. The materials used include silicon carbide and alumina. The toughening comes about because the fibres or particles deflect or bridge cracks in the matrix. 

Becher, P. F., Heueh, C., Angellita, P., and Tiegs, T. N. (1988). Toughening behavior in whisker-reinforced ceramic matrix composites. / Am. Ceram Soc. 71 1051-1061. Homeny,J., Vaughn, W. L., and Ferber, M. K. (1990). Silicon carbide whisker/alumina matrix composites effect of whisker surface treatment on fracture toughness./ Am Ceram. Soc. 73 394-402. 

Ceramics as Valves Alumina or silicon carbide is fhe material for valves. Gate valves used in an irrigation ditch are made of metal or concrete. Slide-gate valves in ladles holding molten steel are made of ceramics. Alumina is the material used to make oxygen valves of respirators used in hospitals. Ball-and seat valves, made of WC-Co, transformation-toughened zirconia, or silicon nitride, are used in downhole pumps required for deep oil wells. 

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