Low-temperature synthesis of some orthosilicates

Crystalline and amorphous orthosilicates of magnesium, zinc, cadmium and co pper were prepared by to non-traditional sol-gel schemes connected with the use of high-boiling chemically active (HBCA) additives to prevent the poly condensation of silicate anions at early synthesis stages. Metal acetates a nd nitrates were used as the metal oxide precursors. tetraethoxysilane and gamma -aminopropyltriethoxysilane - 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 o ut at 20 degrees or 120 degreesC, the further thermal treatment of samples were performed in three stages up to 900 degreesC. Chemical evolution of th e systems during the thermal treatment, was controlled using TGA-DTA and XR D techniques, the kinetic "molybdate" method, FTIR and UV-VIS spectrophotom etry. The use of high-boiling chemically active additives was shown to redu ce the content of free metal oxides in the synthesis products, as well as t o suppress the formation of high-polymerized silicate species that could co mplicate the further formation of orthosilicates. The formation of amorphou s Cu2SiO4 is particularly complicated by thermodynamic instability of the c orresponding crystalline silicate and needs addition of quaternary ammonium hydroxide as the highly basic agent.