Low-temperature synthesis of some orthosilicates

Crystalline and amorphous orthosilicates of magnesium, zinc, cadmium and copper were prepared by non-traditional sol-gel schemes connected with the use of high-boiling chemically active (HBCA) additives to prevent the polycondensation of silicate anions at early synthesis stages. Metal acetates and nitrates were used as the metal oxide precursors, tetraethoxysilane and γaminopropyltriethoxysilane - as the SiO2 precursors, resorcinol and triethanolamine - as the HBCA additives, water and dimethyl formamide - as the solvents. Gelation and drying of the precursor solutions were carried out at 20° or 120°C, the further thermal treatment of samples were performed in three stages up to 900°C. Chemical evolution of the systems during the thermal treatment, was controlled using TGA-DTA and XRD techniques, the kinetic molybdate method, FTIR and UV-VIS spectrophotometry. The use of high-boiling chemically active additives was shown to reduce the content of free metal oxides in the synthesis products, as well as to suppress the formation of high-polymerized silicate species that could complicate the further formation of orthosilicates. The formation of amorphous Cu2SiO4 is particularly complicated by thermodynamic instability of the corresponding crystalline silicate and needs of quaternary ammonium hydroxide a the highly basic agent.