Diboride powders

The densification under high pressure of titanium diboride powder with different particles size (400 nm, 5 pm and 50 pm) has been investigated. It has been shown that powder with mean particles size of 400 nm demonstrates the best intensity of densification at low sintering temperatures. Samples sintered from the powder with mean particles size of 5 pm have the highest density (about 99%) and modulus of elasticity ( 500 GPa), at the same time samples sintered from the powder with mean particles size 50 pm have the highest microhardness ( 37 GPa). 

S.M. Zhu, W.G Fahrenholtz, et al., Pressureless Sintering of Carbon-coated Zirconium Diboride Powders, Maler. Sci. Eng. A-Siruct. Mater. Prop. Microstruct. Process., 459 1-2, 167-171 (2007). 

Carbide and nitride powders are conventionally prepared by the carboreduction of oxide powder with subsequent nitridation in a nitrogen atmosphere or carborization in an inert gas. Diboride powders are synthesized by carbothermal reduction, where boron needs to form the boride and carbon aids in the removal of oxygen. These processes require a high temperature and a long heating time. Fine powders of these compounds are prepared by the thermite method by reduction with Mg. 

Let us consider the various plasma processes for producing powders. One process involves the reaction between metal halides and reactive gases, which have been widely used in ordinary CVD processes. The compositions of the products are controlled linearly by those of the reactants (6). Titanium diboride powder consisting of submicrometer-sized crystals of equiaxed and tabular forms with only small amounts of crystal intergrowth was produced in an arc plasma... 

JD Casey, JS Haggerty. Laser-induced vapor-phase syntheses of boron and titanium diboride powders. J Mater Sci 22 737, 1987. 

Khanra, A. K., Pathak, L. C., Mishra, S. K., Godkhindi, M. M. (2005). Sintering of ultrafine zirconium diboride powder prepared by modified SHS technique. Advances in Applied Ceramics, 104 6), 282-284. doi 10.1179/174367605X52077. 

Yan, Y, Huang, Z., Dong, S., Jiang, D. (2006). New route to synthesize ultra-fine zirconium diboride powders using inorganic- organic hybrid precursors. Journal of the American Ceramic Society, S9(ll), 3585-3588. doi 10.1111/j.l551-2916.2006.01269.x. 

Zhu, S., Fahrenholtz, W. G., Hilmas, G. E., Zhang, S. C. (2007b). Pressureless sintering of carbon-coated zireonium diboride powders. Materials Science and Engineering A, 459,167-171. doi 10.1016/j.msea.2007.02.116. 

Mishra, S. JC, Das, S., Pathak, L. C. (2004). Defect structures in zirconium diboride powder prepared by self-propagating high-temperature synthesis. Materials Science and Engineering A, 364(1-2), 249—255. doi 10.1016/j.msea.2003.08.021. 

Different methods used to prepare titanium diboride have been reviewed by Samsonov et al. (1975). At present, it is mainly produced as a powder by thermochemical reduction of boron and titanium oxides followed by hot pressing and sintering to process the final product. The less costly alternative appears to be to coat suitable substrate materials with TiB2 or TiB2-based composites by hot pressing, plasma spraying, chemical vapor deposition, etc. 

Among the systems of alkali metal fluorides containing boron oxide, the melts of the system LiF-KF-B203-Ti02 were tested as possible electrolytes in the electro-chemical synthesis of titanium diboride, especially when well-dispersed powders should be... 

Hafnium-like boron is known to be a neutron absorber or neutron moderator element, and, therefore, composites of boron carbide, B4C, and hafnium diboride, HfB2, can be considered as nuclear materials. These boron compounds after sintering and °B/"B isotopic ratio adapting are found to be heterogeneous polyphone cermets useful for nuclear applications (Beauvy et al. 1999). Boron acid obtained from the °B enriched boron trifluoride also was used in nuclear reactors (Shalamberidze et al. 2005). Amorphous boron powders enriched both in °B and "B, boron carbide, and zirconium diboride (ZrB2) powders and pallets labeled with °B isotope And applications in nuclear engineering too. The °B enriched Fe-B and Ni-B alloys are useful for the production of casks for spent nuclear fuel transfer and storage. 

Tani and Wada [154] fabricated optimized SiC-TiB2 composites by reactive sintering starting from an intimate mixture of SiC, Ti02, B4C, and C powders. The mixture was either hot pressed or pressureless sintered and post-HIPed at temperatures of > 1900°C. Titanium diboride was formed in situ according to the reaction... 

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. 

---