Ceramics, sintered composites

Infiltration (67) provides a unique means of fabricating ceramic composites. A ceramic compact is partially sintered to produce a porous body that is subsequently infiltrated with a low viscosity ceramic precursor solution. Advanced ceramic matrix composites such as alumina dispersed in zirconia [1314-23-4] Zr02, can be fabricated using this technique. Complete infiltration produces a homogeneous composite partial infiltration produces a surface modified ceramic composite. 

Ceramic matrix composites are produced by one of several methods. Short fibers and whiskers can be mixed with a ceramic powder before the body is sintered. Long fibers and yams can be impregiated with a slurry of ceramic particles and, after drying, be sintered. Metals (e.g., aluminum, magnesium, and titanium) are frequently used as matrixes for ceramic composites as well. Ceramic metal-matrix composites are fabricated by infiltrating arrays of fibers with molten metal so that a chemical reaction between the fiber and the metal can take place in a thin layer surrounding the fiber. 

Nygren, M., Shen, Z.J., On the preparation of bio-, nano- and structural ceramics and composites by spark plasma sintering, Solid State Sciences, 2003, 5(1) 125. 

The modem technological needs of stmctural materials are not fulfilled entirely by these two types of materials. There is also a need for materials that exhibit properties in between cement and sintered ceramics. That need can be met by CBPC matrix composites—materials that are produced like cements at ambient or at slightly elevated temperatures, but exhibit properties of ceramics. These composites are attractive for many stmctural applications, including architectural products, oil-field drilling cements, road repair materials that set in very cold environments, stabilization of radioactive and hazardous waste streams, and biomaterials. 

FIGURE 12.11 Improvements of the mechanical properties of three-dimensional reinforced CMCs by hybrid infiltration routes (a) R.T. flexural stress-strain plots for a three-dimensional carbon fiber reinforced composite before and after cycles of infiltration (comparison between eight cycles with zirconium propoxide and fonr cycles pins a last infiltration with aluminum-silicon ester (b) plot of the mechanical strength as a fnnction of the final open porosity for composites and matrix of equivalent porosity, before and after infiltration (Reprinted from Colomban, R and Wey, M., Sol-gel control of the matrix net-shape sintering in 3D reinforced ceramic matrix composites, J. Eur. Ceram. Soc., 17, 1475, 1997. With permission from Elsevier) (c) R.T. tensile behavior (d) comparison of the R.T. mechanical strength after thermal treatments at various temperatures. (Reprinted from Colomban, R, Tailoring of the nano/microstructure of heterogeneous ceramics by sol-gel routes, Ceram. Trans., 95, 243, 1998. With permission from The American Ceramic Society.)... 

Cylindrically converging shock waves on powders were used to make mixtures of diamonds and hBN. BN fiber reinforced Zr02 was described . A nanostructured composite of magnetic particles of FOj N in a nonmagnetic matrix of BN is made via an inorganic geP. Fabrication of BN-B4 composites was reported . Consolidation of novel sintered composites formed from high pressure crystallization of amorphous ceramics was also described. The literature discusses other ceramics reinforced with BN fibers, as welF . ... 

Fig. 19. Creep behavior of silicon nitride ceramics. The composition of this ceramic contains 7 vol % Y3A15Oi2 as a sintering aid. The specimens were hot-pressed at 1750°C under a pressure of 20 Mpa. The holding times are marked on the curve. This curve indicates that crystallization of the grain-boundary phase improves the creep resistance. Garnet crystals were observed at the grain boundaries after annealing [3/]. , Sample A60 , Sample B60 A, Sample B150, x, failure.

Recently, a modified small punch testing (MSP) method has been developed for mechanical evaluation of ceramic and ceramic/metal composite materials used in FGMs [5]. In the present study, the MSP method was applied to evaluate TiC-based ceramics, which are employed as ceramic-side materials in a TiC/Ni3Al FGM. Because the TiC/Ni3Al FGMs apparently show different damage behavior at temperatures from 1208 to 1373 K, the fracture strength and deformation of TiC-based ceramics were measured at these two critical temperatures. The differences in the behaviors of different TiC sintered bodies and their... 

Ceramic parts are often made from finely powdered components which are shaped by a pressure agglomeration technique and then sintered by the application of heat. In some cases this simple technique is not applicable because the powders may not sinter together, the sintering temperature or atmosphere requirements may be impractical or uneconomic, or a base material may not be readily available or may decompose under normal sintering compositions. In some of these cases, reaction sintering may offer the possibility of making sound ceramic bodies, often also with high density, which are impossible or at least difficult to produce by other methods [B.12c]. 

Sacks, M. D., Scheiffele, G. W., Bozkurt, N., and Raghunathan, R., Fabrication of ceramics and composites by viscous sintering of composite particles, Ceram-... 

Due to the tailored properties of liquid phase sintered silicon carbide (LPSSiC) it is used as dewatering elements in the paper machinery and as rings for highly stressed gas seals. It is a price competitive alternative to silicon nitride materials and outperforms alumina and tungsten carbide materials. In addition, LPSSiC is proposed as neutral matrix in ceramic matrix composites containing plutonium to burn the world s stockpiles of military plutonium in thermal or fast reactors [278]. 

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