Synthesis and properties of nanocomposites based on zinc phosphate and fumed silica

Abstract

The aim of the work was to synthesize nanocomposites based on pyrogenic silica and zinc phosphate by a simple method without using a large amount of solvent and to study the characteristics and properties of the obtained materials. The dual systems of zinc phosphate/pyrogenic silica with the different ratio of components were synthesized via mechanical grinding in a porcelain drum ball mill of fumed silica (Orysyl A-380), zinc acetate (Zn(CH3COO)2·2H2O) and phosphoric acid with distilled water, followed by air-drying in an oven at 125 °C (2 h) and calcination in a muffle oven at 450 °C for 2 h. The zinc phosphate content was 0.1, 0.2, and 0.3 mmol per 1 g of SiO2. The control sample (ZP-K) was synthesized by thermal treatment of the precipitate, formed after mixing on a magnetic stirrer an aqueous solution of zinc acetate with the addition dropwise of phosphoric acid, without the use of SiO2. X-ray diffraction studies of the nanocomposites confirmed the formation of the crystalline phase of Zn3(PO4)2·4H2O (orthorhombic modification) both in the silica-containing and control ZP-K samples after air drying at 125 °C, while heat treatment at 450 °C leaded to the formation of the anhydrous monoclinic Zn3(PO4)2 phase. The content of the zinc phosphate in the dual composites was 0.1, 0.2, and 0.3 mmol per 1 g of SiO2. The IR spectra of the nanocomposites indicated the presence of absorption bands in the range of 3760-3600 cm-1, which were attributed to the unequal structural ‒OH groups of silicon and phosphorus atoms. It was found that the presence of zinc phosphate on the SiO2 surface does not cause the chemical interaction with silica during heat treatment of composites in air even at 900-1000 °C. It was shown that the ability of Zn3(PO4)2/SiO2 composites to adsorb water vapor decreases with increasing amount of modifying compound. The effect of the obtained phosphorus-containing nanocomposite on the thermal stability of an alkyd polymer matrix was considered.