Reaction-bonded silicon nitride ceramic

Table 10 summarises all methods for the densification of Si3N4 used at present. The resulting Si3N4 ceramics classified according to the densification routes are also listed together with several remarks on manufacturing characteristics, properties and applications. For comparison with the sintered qualities, information on reaction bonded silicon nitride ceramics are also included but will be treated in more detail in Sect. 8. 

Pugh, M.D. and Gavoret, L. Nitridation of whisker reinforced reaction bonded silicon nitride ceramics , J. Mat. Sci., 35 (2000) 3257-3262. 

Metallurgical grade silicon is marketed in a coarsely crushed form or as a finely ground powder in different particle sizes. Powders with increased purity due to acid washing, particularly for the removal of metallic impurities, are specialty products. They are utilized, for example, in the manufacture of silicon nitride powder or reaction-bonded silicon nitride ceramic components and are therefore the starting materials for engineering ceramic specialties. 

Table 15.1 Values of the thermal shock resistance parameters R, R, R"" for a range of ceramic materials where HPSN is hot pressed silicon nitride and RBSN is reaction bonded silicon nitride (reprinted from Table 11.1 on p 213 of Ceramics Mechanical Properties, Failure Behaviour, Materials Selection by Munz and Fett, 1999, published with permission from Springer-Verlag GmbFI)...

Slip-casting of technical ceramics has been steadily introduced over the past 60 years or so, and now it is standard practice to cast alumina crucibles and large tubes. The process has been successfully extended to include silica, beryllia, magnesia, zirconia, silicon (to make the preforms for reaction-bonded silicon nitride articles) and mixtures of silicon carbide and carbon (to make the preforms for a variety of self-bonded silicon carbide articles). Many metallics and intermetallics, including tungsten, molybdenum, chromium, WC, ZrC and MoSi2, have also been successfully slip-cast. 

G. Morscher, P. Pirouz, and A. H. Heuer, Temperature Dependence of Interfacial Shear Strength in SiC-Fiber-Reinforced Reaction-Bonded Silicon Nitride, 7. Am. Ceram. Soc., 73[3], 713-720 (1990). 

A. S. Kobayashi, A. F. Emery, and B. M. Liaw Dynamic Fracture Toughness of Reaction Bonded Silicon Nitride, Journal of the American Ceramic Society, 66[2], 151-155 (1983). 

In some cases, the reaction between a gas and a solid gives a ceramic of interest, and this reaction can be used to densify the green body. The classic example is reaction sintered SisN4, also called reaction bonded Si3N4. The gas—solid reaction used to make reaction bonded silicon nitride [132] is between silicon metal powder and nitrogen ... 

Hackley, V.A. et al.. Aqueous processing of sintered reaction-bonded silicon nitride I. Dispersion properties of silicon powder, 7. Am. Ceram. Soc., 80, 1781, 1997. 

The tensile fracture strengths of three different structural ceramics are listed below hot-pressed silicon nitride (HPSN), reaction-bonded silicon nitride (RBSN), and chemical vapor-deposited silicon carbide (CVDSC), measured at room temperature. 

J.W. Lucek, G.A. Rossetti, Jr., and S.D. Haitline, Stability of Continuous Si-C (-0) Reinforcing Elements in Reaction-Bonded Silicon Nitride Process Environments, pp. 27-38 in Metal Matrix, Carbon, and Ceramic Matrix Composites 1985, NASA CP-2406, Edited by J.D. Buckley, NASA, Washington, B.C., 1985. 

OJ. Gregory and M.H. Richman, Thermal Oxidation of Sputter-Coated Reaction-Bonded Silicon Nitride, J. Amer. Ceram. Soc. 67, [5], pp. 335-340 (1984). 

J. Desmaison, N. Roels, and P. Belair, High-Temperature Oxidation-Protection CVD Coatings for Stmctural Ceramics Oxidation BehaviorofCVD-Coated Reaction-Bonded Silicon Nitride, Mater. Sci. and Eng., A121 441 47 (1989). 

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. 

Mayer, J.E. Jr., Fang, G.-P., and Edler, J.P., Grinding of reaction bonded silicon nitride (RBSN) ceramic. Manufacturing Science and Engineering, MED-Vol. 4, ASME, 1996, pp. 267-271. 

Since the 1970s, the search for improved materials has led to a better understanding of the role of additives in the densification and microstructural development of silicon nitride-based ceramics and the consequences for final properties [1, 6]. Improvements in powder manufacture and forming techniques and the development of alternative firing processes has led to a complete family of materials including RBSN, HPSN, sintered silicon nitride (SSN), sintered reaction-bonded silicon nitride (SRBSN), gas-pressure sintered silicon nitride (GPSSN), hot isostatically pressed silicon nitride (HIPSN) and silicon nitride alloys or solid solutions termed SiAlONs, based on their elemental components. 

Dalgleish, B.J., Pratt, P.L., 1973. The microstructure of reaction-bonded silicon nitride. Proc. British Ceram. Soc. 22, 923. 

Alternatively, Si3N4 can be manufactured as reaction bonded silicon nitride (rbsn). This process starts with silicon powder that reacts with nitrogen in a nitrogen atmosphere. This produces a somewhat porous ceramic, containing both a and (3 phase. The strength of this material is much smaller than that of sintered silicon nitride due to the different grains and the larger defect size caused by the increased porosity (see table 7.4). 

Haggerty, J.S., Garvey, G.J., Flint, J.H., Sheldon, B.W., Okuyama, M., Ritter, J.E. and Nair, S.V., Processing and Properties of Reaction Bonded Silicon Nitride and Sintered Silicon Carbide Made from Laser Synthesized Powders. In Cer. Trans. Vol 1. Ceramic Powder Science Messing, G.L., Fuller, E.R. Or. and Hausner, H. (Eds), p 1059-68, American Ceramic Society, (1988). 

The thermodynamics of the above-elucidated SiC/C and SijN Si composites are determined by the decomposition of silicon carbide and silicon nitride, respectively, into their elements. The chemistry of ternary Si-C-N composites is more complex. If producing Si-C-N ceramics for applications at elevated temperature, reactions between carbon and silicon nitride have to be considered. Figure 18.2, which exhibits a ternary phase diagram valid up to 1484°C (1 bar N2) displays the situation. The only stable crystalline phases under these conditions are silicon carbide and silicon nitride. Ceramics with compositions in the three-phase field SiC/Si3N4/N are unknown (this is a consequence of the thermal instability of C-N bonds). Although composites within the three-phase field SiC/Si3N4/Si are thermodynamically stable even above 1500°C, such materials are rare. The reasons are difficulties in the synthesis of the required precursors and silicon melting above 1414°C. The latter aspect is of relevance, since liquid silicon dramatically worsens the mechanical properties of the derived ceramics. 

The slopes of the lines in Figure 13.13, at > 0.75, are also typical for reaction-bonded silicon carbide [24, 28]. These data also indicate that over 75% of the measured axial tensile strain results from cavitation. The volumes generated by cavities are transferred primarily into axial tensile strain [25], which suggests that cavitation is the main creep mechanism of deformation in these ceramics. As the contribution of cavities to strain in SN 281 is dose to zero, creep in this material is fundamentally different from that of other grades of silicon nitride [15, 40, 41, 44]. The suppression of cavitation in SN281 is most likely the reason for its increased creep resistance. 

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