The low temperature synthesis of metal oxides by novel hydrazine method

Abstract

The hydroxide, oxalate and citrate precursors of the metal oxides such as gamma-Fe2O3, (MnZn)Fe2O4, Cu(K)Fe2O4, BaTiO3, La(Sr)MnO3, La(Sr)AlO3, La/Gd(Ca/Ba/Sr)CoO3, and anatase TiO2 on modifications with the hydrazine decompose at low temperatures give single phase oxides of superior properties, while the complexes without such modification require higher temperatures for achieving the phases. The hydrazine released at lower temperatures reacts with the oxygen in the atmosphere, N2H4+O2 to N2+2H(2)O; Delta H=-625 kJ mol(-1), and liberates enormous energy that is sufficient for the oxidative decomposition of the complexes now devoid of hydrazine. Such extra energy is not available in the case of the precursors without such modifications. The reaction products of hydrazine oxidation provide desired partial pressure of moisture needed for the stabilization of gamma-Fe2O3. Also, the nitrogen that is formed in the reaction of hydrazine with oxygen gets trapped in the lattice of TiO2 giving yellow color nitrogen doped TiO2-xNx photocatalyst. Thus, hydrazine method of preparation has many advantages in the preparation of metal oxides of superior properties.