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Nanocrystalline chromium disilicide was synthesized by co-reducing anhydrous chromium trichloride and sodium fluorosilicate with metallic potassium at 650 °C in an autoclave. X-ray powder diffraction pattern indicated that the product was hexagonal CrSi2. Transmission electron microscope images showed that the sample consisted of particles with the diameters of 20–50 nm and an average diameter of about 35 nm. TGA and DTA indicated that the oxidation of CrSi2 began to proceed at 700 °C in air, and only about 8.6 wt.% of the sample was oxidized in the surfaces of the particles below 1000 °C. It had high thermal oxidation stability due to the formed protective layer. [Copyright &y& Elsevier]

Nanocrystalline hafnium diboride (HfB2) has been prepared by the reaction of HfCl4 with NaBH4 at 600 °C in an autoclave. The X-ray powder diffraction (XRD) pattern can be indexed as hexagonal HfB2 with the lattice constants of a=3.146 and c=3.456 A˚. The transmission electron microscopy (TEM) image shows a particle morphology with an average size of 25 nm. The selected area electron diffraction (SAED) pattern confirms the presence of hexagonal HfB2. The oxidation behavior of HfB2 is studied by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). [Copyright &y& Elsevier]