Particulate processes in freshly prepared silver iodide hydrosols Part I. Radiometric and electron-microscopic investigations

Abstract

Ageing of negative, stable AgI sols prepared in statu nascendi was investigated utilizing radiometric (heterogeneous exchange) and optical (electron microscopy) methods. AgI sols with different molar concentrations C o , of AgI have shown that the examined sols age by two processes of different speed. The duration interval Δt A , of the faster ageing process is approximately inversely proportional to the molar concentration of the sols. Results of a comparative analysis of the heterogeneous exchange process obtained by two different exchange procedures in identically prepared and aged sols revealed that primary particles of the sols approximately double their volume during the faster ageing process. This result is confirmed by analysing electron micrographs of differently aged stable sols. On the basis of data obtained by two different exchange procedures and the results of electron-microscopy analysis respectively, a new structural form of silver iodide is predicted. Such an up to now unknown form of silver iodide transforms spontaneously and gives a mixture of well-known cubic and hexagonal modifications of silver iodide during the aggregation of primary particles into secondary ones. This transformation is markedly accelerated during electrolytic coagulation of the sols.