Glass-ceramic matrices

Many researchers have used glass and glass-ceramic matrices for reinforcing with high-modulus graphite fibres [1, 2], silicon carbide fibres and silicon carbide mono-filaments [3-7], Very strong, tough and refractory composites were obtained from these efforts. 

A range of glass-ceramics, each having different crystalline phases, has been used as the matrix material. The most widely used matrices are based on the lithium aluminosilicate (LAS) system. The constituents of typical glass-ceramic matrices are given in Table 3.12. 

Whisker-reinforced glass-ceramic matrices are expected to find several applications in automotive components, metal forming, cutting tools, etc., due to their low thermal expansion, high thermal shock resistance, high reliability and low material and processing costs. Some industrial applications for continuous fibre-reinforced ceramic matrix composites (CMCs) are listed below. 

The fabrication of glass or glass ceramic matrices by hot pressing is outlined at moderate temperatures and pressures, but they are sufficiently high to cause formation of interphases between SiC-fibers - namely NICALON and TYRANNO - their coatings and the matrix. Formation of very complex... 

The use of glass and glass-ceramic matrices for CMC fabrication aroused considerable interest and support in the 1970s and 1980s. Efforts to commercialize this technology were unsuccessful, however, because the market base was too small and there were no viable commercial suppliers. Nevertheless, numerous gas turbine engine component demonstrations... 

TABLE 1. Glass and glass-ceramic matrices of interest for fiber-reinforced composites [1-2]. Reprinted with kind permission of Kluwer Academic Publishers... 

The use of fibre reinforcement in silicate glass and glass-ceramic matrices started at the end of the decade after 1960 [1, 2]. A great variety of composite systems has been developed since then employing numerous matrix compositions and many types of ceramic... 

The biomedical field offers another potential area for broader application of composites with biocompatible glass and glass-ceramic matrices. Fibre reinforcement could be used to enhance the mechanical properties of components made of bioctive glass with the aim of fabricating load-bearing implants [25, 26). Although fibre reinforcement may provide the necessary structural integrity, the biocompatibility of the composite must equally be achieved [27]. 

TABLE 1. Some glass and glass-ceramic matrices commonly used to fabricate fibre-reinforced... 

Researchers at NASA Lewis Research Centre have used SiC monofilaments for the reinforcement of glass-ceramic matrices of refractory compositions, including strontium aluminosilicate (SAS) [82] and barium aluminosilicate (BAS) [83], with temperature capability of up to 1600°C. 

J. Vicens, G. Farizy, J.-L. Chermant, Microstmcture of Ceramic Composites with Glass-ceramic Matrices Reinforced by SiC-Based Fibres, Aerospace Sci. Technol. 7, 135-146 (2003). 

Ceramic particles, chopped fibres, whiskers and platelets have been used as discontinuous reinforcement in glass and glass-ceramic matrices. 

Ceramic matrix composites (CMCs), in which carbon or ceramic fibers are embedded in a ceramic matrix, have been designed to overcome the intrinsic brittleness of monolithic ceramics with a view toward structural uses at extremely high service temperatures. The most commonly used are carbon (C/C) and SiC matrix composites (C/SiC and SiC/SiC). Ceramic matrix composites with a silica based glass or glass-ceramic matrices have also been studied [12] [53-56]. 

Oxynitride glass ceramic matrices ean be prepared by introducing the nitrogen in the form of Si3N4 or AIN, which can be ineorporated into an oxide based glass ceramic to give p -sialon, an oxynitride glass ceramie [81], when erystallized ... 

Other work reviewed by Prewo and co-workers [105-108] includes the development of glass ceramic matrices with significantly improved properties. 

The recovery of U and Pu in the closed nuclear fuel cycle usually produces an high level waste (HLW) stream containing high concentration of fission/activation products (e.g., U, Pu, Am, Eu, Sr) and process/structural materials (Fe, Ni, Cr, etc.). This concentrated HLW is typically submitted to immobilization in glass/ceramic matrices, followed by their disposal in geological repositories. Considering the half-lives of the fission products (in the range of hundred-millions years) this solution result is unsustainable. The treatment of HLW by SLM represents a possible alternative. 

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