Dense boron carbide

Attempts have been made to produce hard, dense boron carbide coatings by air plasma and low pressure plasma spray (LPPS) processes, but all techniques have so far proved unsuccessful. 

Sdicon carbide, hot pressed Alumina, dense sintered Boron nitride, hot pressed Sdicon nitride, hot pressed Boron carbide, hot pressed... 

The microstructure of a pure B4C layer of three-layered B4C/B4C-30wt%SiC laminate with 4% porosity is presented in Fig. 7.20. The three-layered B4C/ B4C-30wt%SiC tiles tested as armor material had the same microstructure and porosity level as the material shown in Fig. 7.20. As one can see, the porosity at the grain boundary of the ceramics might be a reason why threelayered laminates have not outperformed the dense monolithic boron carbide tiles. A different set of ballistic experiments are required in which fully... 

Finally, two other characteristics of hard materials are important their density and their chemical stability. The importance of these properties depends on the application. Oxides are chemically more stable than nitrides, which are in turn more stable than borides or carbides. The susceptibility to oxidation of boron carbide prevents its application at high temperatures, but for ballistic protection, where hardness, rigidity and low density take precedence, boron carbide is unparalleled. Tungsten carbide, on the other hand, is the material of first choice for cutting tools, because of its high hardness and stiffness, and high-temperature oxidation resistance, but is far too dense for application in which weight or inertial forces are important. Its use for ballistic protection is therefore out of the question. 

The only technically important sintering additive for boron carbide is carbon, as discovered almost simultaneously by Schwetz and Vogt [189], Henney and Jones [190], and Suzuki et al. [191], which today allows the routine production of dense parts. An amount ranging from 1 to 6 mass-% is sufficient to obtain almost theoretical density. Schwetz and Grellner [192] added phenolic resin (corresponding to 1-3 mass-% C) to a submicron B4C powder and obtained >98% density at 2150°C. The resins are pyrolized at temperatures up to 1000°C and they leave a... 

In the past, different routes have been utilized to produce dense B4C-TiB2 composite materials, differing in starting powder mixtures. Two main methods can be distinguished (i) to use B4C and TiB2 and (ii) to make use of the reactions building up the final components of boron carbide and titanium diboride. 

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

Figure 15.5 Macroscopic neutron absorption cross-section for some common compounds. B4C boron carbide is calculated for natural boron ( B/B = 0.198) and fiiUy dense material.

By using a boron-nitride powder barrier (hot pressed or deposited onto graphite mold and punches), it is possible to prepare dense and pure boron and boron-rich phases, especially carbides (between B,o.4C and B4C) by hot pressing in graphite dies " . 

As with silicon nitride, solid forms of silicon carbide are made by one of three processes sintered, hot-pressed, or reaction-sintered. Sintering requires use of an additive such as alumina, carbon, or boron to promote liquid-phase sintering. Hot pressing is done at 2000°C and results in a very hard, dense material. Reaction sintering occurs when a mixture of SiC powder and carbon is heated in contact with molten silicon. The reaction results in a nearly complete conversion to SiC, although according to Schwartz, most materials made by this process contain an excess of carhon or silicon. ... 

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