The properties and the structure of colloid agregates of the silver besilcate Ag6Si2O7 in water medium

TL;DR

This study investigates the properties, structure, and formation conditions of silver besilicate Ag6Si2O7 colloids in water, revealing morphology dependence on growth conditions, elemental composition, vibrational spectra, and the presence of a silicon acid shell.

Contribution

It provides new insights into the morphology, crystallinity, and structural features of Ag6Si2O7 colloids, including the existence of a silicon acid shell, under various synthesis conditions.

Findings

Slow growth yields quasi-crystalline whiskers.

High precursor concentration leads to quasi-amorphous aggregates.

Silicon acid shell around colloids confirmed by electron microscopy.

Abstract

The paper describes the investigation of the properties of silver besilicate salt colloids in water medium. Ag6Si2O7 was obtained in a soft conditions, in water medium, at temperatures and pressure close to room ones. The morphology and crystallinity of matter under investigations appear to depend on the growth conditions. Slow growth resulted in quasi-crystalline yellowish whiskers, while high concentration of precursors led to fast formation of the quasi-amorphous aggregates. The elemental constitution of object under study was determined with the help of Comebax-INCA set-up, and was then proved by chemical analysis. The ratio of elements was close to Ag6Si2O7, and depended a little whether the sample was taken from the sediments of reaction or from dried residue of a liquid medium. The experiments in Raman technique revile several well-resolvable bands in whisker-like samples, but only few of them were able to detect in quasi-amorphous material. In the last case the bands were broader, but the positions of weak broad bands were close to the positions of corresponding bands in whiskers. We can suggest, that the bands, common in two former cases, are due to oscillation in bepyramidal molecules of Ag6Si2O7, and the bands, seen only at whiskers, are due to long-rang order. The very special peculiarity was observed under chemical test with hydrochloric acid. The white flakes sedimentation appeared after addition of NaCl but do not appeared when HCl was added. This result can be explained if to assume the existence of silicon acid shell around the colloidal particles of silver besilicate. The model of silicon acid shell around colloids was proved by high resolution electron microscopy.