Silicon sintered reaction-bonded

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. 

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... 

Figure 14.3 Microstructure of sintered reaction-bonded silicon nitride.

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

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. 

Properties of Dense Silicon Carbide. Properties of the SiC stmctural ceramics are shown in Table 1. These properties are for representative materials. Variations can exist within a given form depending on the manufacturer. Figure 2 shows the flexure strength of the SiC as a function of temperature. Sintered or sinter/HIP SiC is the preferred material for appHcations at temperatures over 1400°C and the Hquid-phase densified materials show best performance at low temperatures. The reaction-bonded form is utilized primarily for its ease of manufacture and not for superior mechanical properties. 

Fig. 4. Thermal diffusivity of silicon-based stmctural ceramics (a) reaction-bonded SiC (b) hot-pressed and sintered SiC (c) hot-pressed (1% MgO,...

Reaction bonded silicon carbide (RBSiC) or self sintered silicon carbide (SSSiC)—see API Standard 682 for SiC application guidelines in mechanical seals... 

Sintered silicon carbide retains its strength at elevated temperatures and shows excellent time-dependent properties such as creep and slow crack growth resistance. Reaction-bonded SiC, because of the presence of free silicon in its microstructure, exhibits slightly inferior elevated temperature properties as compared to sintered silicon carbide. Table 2 (11,43) and Table 3 (44) show selected mechanical properties of silicon carbide at room and elevated temperatures. 

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 ... 

Impermeable silicon carbides of both types, sintered and reaction bonded, perform generally better than the permeable refractories as shown in Table 19-3 Both reaction bonded and sintered products can be exposed to higher temperature for longer periods of time with lower weight loss than the oxide, Si3N4 or Si20N2 bonded refractories. This is due to the lower surface area available for reaction and to the greater relative inertness of their bond phases. 

A rather different approach has been developed for reaction sintered silicon carbide (RSSC), first developed in the former Soviet Union. In this process a powder preform of mixed graphite and silicon carbide is immersed in a liquid bath of molten silicon. The silicon wets and infiltrates the preform, reacting with the finely-divided graphitic component (carbon black). In the best case, all graphite is reacted and the residual sihcon content is no more than a few percent. The product of the reaction, silicon carbide, firmly bonds the silicon carbide preform powder... 

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... 

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