Preparation and properties of uniform coated inorganic colloidal particles. 12. Tin and its compounds on hematite

Abstract

Colloidal spherical particles of tin hydroxide of narrow size distribution were obtained by heating acidic solutions of stannous sulfate and urea at elevated temperatures over a range of experimental conditions. The original particles were amorphous, which on calcination at 750°C converted into crystalline SnO₂, without a change in their morphology. The same tin compound was also precipitated in the form of uniform coatings on ellipsoidal hematite particles by heating dispersions of the latter in acidified solutions of stannous sulfate and urea at 80°C for 1 h. The size of the shell could be altered over a broad range by adjusting several experimental parameters. The amorphous coating was converted into crystalline SnO₂ by heating the composite powders at 750°C, without interaction with the cores. On heating at 350°C in the flow of hydrogen, the calcined coated particles were reduced to metals, composed of Fe, Sn, and Fe₃Sn₂. In contrast, under similar conditions SnO₂ particles could not be changed to metallic tin. A mechanism involved in the reduction process is offered.

Supported by the NSF grant CHE-9423163