Sintered reaction-bonded silicon nitrides

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 range of applications for RBSN and sintered reaction-bonded silicon nitride has shrunk over the last few years. This is connected with the decreasing cost of silicon nitride powders, reducing the production costs of SSN and the lower strength and lifetime of RBSN in comparison to SSN in many applications. For this reason, these materials will not be explained in detail in this work reference is made to special reviews [6, 7]. The following paragraphs concentrate on dense silicon nitride materials made from silicon nitride powders. 

The experiments were conducted on a vertical rotary surface grinder with a 5.5 kW motor spindle. The feed can be continuously adjusted within a range. The workpieces were made from intered sintered reaction-bonded silicon nitride (SRBSN) and cast-and-sintered silicon nitride (Si3N4). The grain size was between 0.3 and 0.4 pm for SRBSN and between 0.6 and 0.8 pm for SiaN4. Cast-iron fiber-bonded diamond wheels of 200 mm diameter were used. A Noritake AFG-M grinding fluid at a rate of 20-30 L/min was used as electrolytic fluid. 

Figure 16.13 Relationship between thermal conductivity and four-point bending strength of various types of high-thermal conductivity Si3N4 fabricated by different routes. GPSN = gas-pressure-sintered silicon nitride SRBSN = sintered reaction-bonded silicon nitride [62].

Table 16.5 Characteristics of raw Si powders used for the preparation of sintered reaction-bonded silicon nitrides (SRBSN) and theirthermal conductivities (for comparison, the properties of normal sintered Si3N4 are also shown) [60].

Figure 16.15 Scanning electron microscopy images of polished and etched surfaces for (a) sintered reaction-bonded silicon nitride (SRBSN) from a fine silicon powder (b) SRBSN from a coarse Si powder (c) Sintered silicon nitride from a commercial fine-grained a-Si3N4 powder. All of the specimens were doped with...

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. 

Figure 14.3 Microstructure of sintered reaction-bonded silicon nitride.

Squint. A building brick with one end chamfered on both edges so that the brick can be used at an oblique quoin. SRBSN. Sintered Reaction-Bonded Silicon Nitride. 

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. 

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 ... 

Material type Reaction bonded silicon nitride (RBSN) Sintered RBSN (SRBSN) Sintered silicon nitride (SSN) Gas pressure sintered silicon nitride (GPSN) Hot-pressed silicon nitride (HPSN) Sinter HIP silicon nitride (Sinter-HIPSN) HIP-ed silicon nitride HIP-SN... 

Mechanical properties Symbol Units Silicon nitride, sintered Silicon nitride, reaction- bonded Silicon nitride, hot-pressed Silicon nitride, reaction- bonded Aluminium nitride... 

Silicon Nitride Compacts A flow chart of the production routes for porous reaction-bonded siUcon nitride (RBSN), dense sintered siUcon nitride (SSN), and sintered reaction-bonded siUcon nitride (SRBSN) is shown in Figure 11.15. 

Figure 11.16 Flexural strengths of reaction-bonded silicon nitride (RBSN) and dense sintered silicon nitride as a function of temperature. The strong deterioration of the strength of HT superalloys with temperature is given for comparison.

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 properties of a material may vary considerably depending on the sintering process. This is illustrated in the case of silicon nitride in Table 14.6.1 1 This table shows that both the sintered-reaction-bonded and the... 

RE, REL, REO, REOL, RER, RES, REX, REXH, REXR. Symbols for various shapes of ceramic wall tiles and fittings (see Fig. 7, p350). Reaction-bonding. The formation of a polycrystalline ceramic by a chemical reaction between the powder and a gas or a liquid. Cf. reaction sintering and see silicon nitride, silicon carbide. 

Silicon Nitride. SiUcon nitride is manufactured either as a powder as a precursor for the production of hot-pressed parts or as self-bonded, reaction-sintered, siUcon nitride parts. a-SiUcon nitride, used in the manufacture of Si N intended for hot pressing, can be obtained by nitriding Si powder in an atmosphere of H2, N2, and NH. Reaction conditions, eg, temperature, time, and atmosphere, have to be controlled closely. Special additions, such as Fe202 to the precursor material, act as catalysts for the formation of predorninately a-Si N. SiUcon nitride is ball-milled to a very fine powder and is purified by acid leaching. SiUcon nitride can be hot pressed to full density by adding 1—5% MgO. 

Self-baking electrodes, 12 305, 755 Self-bonded reaction-sintered silicon nitride, 17 210, 211 Self-catalyzed polyols, 25 464 Self-cleaning materials, 22 108-127 problems and outlook for, 22 123-124 surface characteristics of, 22 108-109... 

Silicon Nitride. Silicon nitride is manufactured either as a powder as a precursor for the production of hot-pressed parts or as self-bonded, reaction-sintered, silicon nitnde parts. 

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