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An entirely aqueous solution-gel route has been developed for the synthesis of zirconium carbide, hafnium carbide and their ternary carbide powders. Zirconium oxychloride (ZrOCl₂.8H₂O), malic acid (MA) and ethylene glycol (EG) were dissolved in water to form the aqueous zirconium carbide precursor. Afterwards, this aqueous precursor was gelled and transformed into zirconium carbide at a relatively low temperature (1200 °C) for achieving an intimate mixing of the intermediate products. Hafnium and the ternary carbide powders were also synthesized via the same aqueous route. All the zirconium, hafnium and ternary carbide powders exhibited a particle size of ∼100 nm.

Submicrometer (200-800 nm) ZrB2 powders have been successfully prepared via a new ZrO2-C- BN precursor powder system at a relatively low temperature (1550°C) for 1.5 h. As a moderate cost boron source, BN has a well-defined stoichiometry and low impurity. Both thermodynamic and experimental results indicated that ZrC was formed below 1300°C, a temperature required for ZrB2 formation. Moreover, the reaction of ZrC- BN mixture at 1300°C indicated that the ZrC acted as an effective direct reducing reagent for BN to form ZrB2, indicating that the pathway involving the formation of intermediate phase ZrC determined the formation mechanism. [ABSTRACT FROM AUTHOR]

Abstract: Three-dimensional (3D) silicon carbide fiber reinforced silicon carbide matrix (SiCf/SiC) composites, employing KD-1 SiC fibers (from National University of Defense Technology, China) as reinforcements, were fabricated by a combining chemical vapor infiltration (CVI) and vapor silicon infiltration (VSI) process. The microstructure and properties of the as prepared SiCf/SiC composites were studied. The results show that the density and open porosity of the as prepared SiCf/SiC composites are 2.1g/cm3 and 7.7%, respectively. The SiC fibers are not severely damaged during the VSI process. And the SiC fibers adhere to the matrix with a weak interface, therefore the SiCf/SiC composites exhibit non-catastrophic failure behavior with the flexural strength of 270MPa, fracture toughness of 11.4MPa·m1/2 and shear strength of 25.7MPa at ambient conditions. Moreover, the flexural strength decreases sharply at the temperature higher than 1200°C. In addition, the thermal conductivity is 10.6W/mk at room temperature. [Copyright &y& Elsevier]