Solid state interactions in nano-sized oxides

Comparative study of reactivity of nano- and micro-sized alumina and nickel oxide, obtained by the electrical explosion of metal wires in oxidizing atmosphere, was carried out for the reactions NiO + MoO3, NiO + Al2O3, and Al2O3 + Bi2O3 by coupled anneals of ceramics, measurements of the conductivity of individual oxides and raw oxide mixtures, X-ray diffraction and differential thermal analysis. The total conductivity of nano-structured oxides was found lower than that of micro-structured ceramics. Mixing bismuth oxide with nano-structured alumina leads to stabilization of the low temperature polymorph α-Bi2O3 up to 780 °C. The diffusion permeability of NiMoO4 layer grown at the surface of NiO ceramics, having submicron grains, was found 2 times lower if compared to NiMoO4 grown at micro-sized NiO ceramics. NiO and Al2O3 nano-powders preserve the high reactivity even when heated up to 1000 °C. The results are discussed in terms of size effects on the solid state reactivity of oxides.