Pressureless boron carbides

It is technically easier to manufacture a molded component from SiC-powder by slip casting or dry pressing, working it mechanically and then sintering pressureless at 1950 to 2000°C. Due to the low sintering activity of silicon carbides, such processes have only been recently successfully carried out with the advent of fine particulate SiC-powders (specific surface area > 5 m /g) with low oxygen-contents (< 0.2%). Boron or aluminum and free carbon or boron carbide are added as sintering aids. 

S.C. Zhang, GE. Hilmas, et al.. Pressureless Densification of Zirconium Diboride with Boron Carbide Additions, J. zlm. Ceram. Soc., 89 5, 1544-1550(2006). 

Figure 36. Microstructure of boron carbide pressurelessly sintered with carbon black (after [197]).

Recently, boron carbide was successfully densified with TiC by pressureless sintering [207]. Since TiC reacts with B4C by the formation of TiB2 and free carbon. 

Campbell, J., Klusewitz, M., LaSalvia, J, et at (2008) Novel processing of boron carbide plasma synthesized nano powders and pressureless sintering forming of complex shapes. Proceedings 26th Army Science Conference, December 2008, Orlando, Florida,... 

Figure 83. Pressureless-sintered silicon carbide doped with boron carbide, BF. Etched by the Murakami method. Shown here are pores and elongated SiC grains and twins.

Figure 11.3 Results of pressureless sintering of boron carbide of different stoichiometric compositions (green density 60%, 1 h soaking time at final temperature, 1 bar argon atmosphere). The numbers in italics refer to percentage theoretical density.

ESK (Elektroschmelzwerk Kempten GmbH) (1995) Method of making polycrystalline dense shaped bodies based on boron carbide by pressureless sintering. European Patent EP 19940109275. 

Adrian Goldstein, Ygal Geffen, Ayala Goldenberg. Boron Carbide-Zirconium Boride In Situ Composites by the Reactive Pressureless Sintering of Boron Carbide-Zirconia Mixtures. Journal of the American Ceramic Society 2001 84 642. 

Zhang, S. C., Hilmas, G. E., Fahrenholtz, W. G. (2006). Pressureless Densifica-tion of Zirconium Diboride with Boron Carbide Additions. Journal of the American Ceramic Society, 89,1544-1550. doi 10.1111/j. 1551-2916.2006.00949.x. 

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