Plastic and nonmetallic article shaping or treating: processes – Including step of generating heat by friction
Patent
1989-11-16
1992-03-24
Derrington, James
Plastic and nonmetallic article shaping or treating: processes
Including step of generating heat by friction
501 97, 501 98, C04B 3558
Patent
active
050986236
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for producing ceramic composite materials containing silicon oxynitride and zirconium oxide, starting from ceramic powder materials containing silicon and/or silicon nitride powder and zirconium silicate powder In the method of preparation, use is made of a high-temperature reaction between silicon nitride and zirconium silicate which are reacted to form silicon oxynitride and zirconium oxide in connection with the sintering of compacts to the desired density.
Composite materials containing silicon oxynitride and zirconium oxide according to this invention should primarily be considered to belong to the group of high-performance ceramics which are distinguished inter alia by high strength, fracture toughness, wear, corrosion and thermal shock resistance also at high temperatures. However, advanced applications in the refractory field are also conceivable for this type of composite materials. An increase and extension of the use of the above-mentioned composite materials is however affected/hampered to a significant extent by the relatively high costs for the powder raw material and the costs for so-called sintering aids, which must be supplied to achieve the desired sintering qualities and qualities of the material. This applies especially to rare earth metal oxides. Another limiting factor is the need for an advanced furnace equipment to be able to sinter powder compacts to the desired density. The generally high degree of shrinkage in connection with sintering (densification) is another process engineering drawback. For composites containing true non-oxidic components, such as silicon nitride, there is often the additional problem of chemical incompatibility with respect to zirconium oxide which may result in the formation of secondary phases, such as zirconium nitride or zirconium oxynitride, which have an adverse effect on the thermomechanical properties. By using the method according to this invention, several of the above-mentioned drawbacks will be overcome in a composite material where the raw material powder consists to an essential part of ZrSiO.sub.4 and Si powder of a particle size substantially within the submicron range. As will be described further on, such a powder mixture can be obtained by concurrent milling and blending of the components, and the cost of this powder mixture is estimated at about one tenth of the current cost. The amount of necessary sintering aids from the group of rare earth oxides can be reduced by half at the same time as the sintering temperature can be below about 1650.degree. C., which thus makes it possible to use a more conventional furnace equipment. Further, the linear shrinkage in connection with sintering (densification) to almost full density can also be minimized to about 12% or less because of the increase of the internal volume on account of nitridation of Si to Si.sub.3 N.sub.4 and the reaction between ZrSiO.sub.4 and Si.sub.3 N.sub.4 to ZrO.sub.2 and Si.sub.2 N.sub.2 O. By the nitridation step, a bond is also produced in the material, resulting in fully sufficient strength to permit machining the nitrided material, if desired, before the final sintering step. After completed sintering, the included main components ZrO.sub.2 and Si.sub.2 N.sub.2 O will exhibit good compatibility with respect to the formation of undesirable secondary phases. In the scientific/technical literature, ZrSiO.sub.4 and Si.sub.2 N.sub.2 O materials are described separately and do not seem to have been tested as components in a composite material However, ZrSiO.sub.4 is mentioned by Rice et al (Refs. 1,2) as a desirable grain boundary phase in connection with the sintering of Si.sub.3 N.sub.4. This is so because of its high liquids temperature, high E-modulus and low thermal expansion coefficient. The latter two properties are close to those of Si.sub.3 N.sub.4, but also for the so-called sialons (.beta.'-phase) or Si.sub.2 N.sub.2 O (O'-phase), such as represented in the known compatibility diagram Si.sub.3 N.sub.4 --SiO.sub.2 --AlN--Al.
REFERENCES:
patent: 3839540 (1974-10-01), Arrol et al.
patent: 4069059 (1978-01-01), McDonough
M. B. Trigg et al., Proc. Int. Symp. Ceramic Comp. for Engines, 1983, pp. 199-207, Japan.
Rice et al., Progr. Rep. NRL, Dec. 1979, pp. 18-20.
Derrington James
Svenska Keraminstitutet
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