RBSN

Reactive Hquid infiltration (45,68,90,93,94) is similar to the CVI process used to make RBSN. Driven by capillarity, a reactive Hquid infiltrates a porous preform and reacts on free surfaces. Reactive Hquid infiltration is used to make reaction bonded siHcon carbide (RBSC), which is used in advanced heat engines and as diffusion furnace components for semiconductor wafer processing. 

ESR spectrum of the RjSn radical (R = 2,4,6-triisopropylphenyl), spontaneously generated upon dissolving distannane RBSn-SnRj in deoxygenated toluene, revealed at -140°C in the solid state the Sn hfcc of 163 Such a radical is more planar than the PhjSn radical ( Sn hfcc = 186.6mT) but less planar than the MejSn radical C Snhfcc = 161.1 mT)3° ... 

Morscher, G, Pirouz, P. and Hener, A.H. (1990). Temperature dependence of interfacial shear strength in SiC-fiher-reinforced RBSN. J. Am. Ceram. Soc. 73, 713-720. 

Rubidium combines with hydrogen and nitrogen forming hydride, RbH and nitride, RbsN, respectively. 

This compd was found to be sensitive to impact by drop hammer (Ref 8), but stable to heat and light at RT (Ref 3). During electrolysis of its solns Nt is liberated in an active form (Ref 4). In the thermal de-compn of Rb azide, the residue contains the nitride, RbsN, which is a grn grey pdr extremely sensitive to moisture (Ref 11). The structure of Rb azide was detd by Pauling (Ref 10) and by Biissen et al (Ref 12) its diffraction data tabulated by Frevel et al (Ref 16) and the Raman Effect of both crystn pdr and in soln was reported by Kahovec Kohlrausch (Ref 17)... 

Post sintered RBSN Gas pressure Sintering (GPSN)... 

Material SSN GPSN HPSN HIP-SSN, Sinter-HIP-SN HIP-SN RBSN SRBSN, HIP-SRBSN... 

By a post sintering process including additional sintering aids RBSN can densified to porosities of about 0-5% [538-540] This material, SRBSN, is applied for different wear parts [540]. A comparison of the production and material properties is given in Table 10. 

The production of RBSN starts from Si powder (mean grain size 3-40 pm), which is shaped to parts and then nitrided [541]. The nitridation of the shaped... 

Table 15. Influence of processing variables during nitridation on the conversion rate, microstructure and properties of RBSN [541-546, 549, 550]...

In inert atmospheres the mechanical properties of RBSN are constant up to 1200-1400 °C because of the absence of a glassy grain boundary phase, which is also the reason for the excellent thermal shock and creep behaviour. The thermal shock resistance, hardness and elastic constants depend on the microstructural parameters but are much lower than for dense Si3N4 ceramics [539]. 

In air, the mechanical properties are influenced by the oxidation processes [543], In materials with a fine overall porosity the oxidation at > 1100 °C closes the pores with the help of an Si02 surface layer. This layer protects the material from further oxidation and heals surface defects. This and the formation of compressive stresses due to the different thermal expansion coefficients between Si02 and RBSN are the reasons for strength increase after oxidation. Materials with a high amount of macropores (>1 pm) oxidise not only at the surface but also inside the volume due to longer closing times of the surface pores. In consequence these oxidation mechanisms result in more intensive oxidation at low temperatures < 1100 °C, due to the slow rate of pore closure and higher internal oxidation. 

Growing market, RBSN is more and more replaced by low cost SSN [636, 637], [640]... 

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)...

Si3N4 (RBSN) A400 C750 (air) C1000 (air) C500 C500 C800... 

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