ADSORPTION OF WATER VAPORS ON MAGNETITE POWDERS PREPARED BY CHEMICAL PRECIPITATION AND THERMOLYSIS METHODS

Abstract

A comparative study of the morphology and physicochemical properties of magnetite synthesized by chemical precipitation for 5 min, 30 min, and 1 h and by thermolysis in nitrogen and hydrocarbon media was carried out. Regardless of the synthesis method, duration, and medium, the powders were found to be characterized by a spherical particle shape, uniform particle size distribution, and the ability to agglomerate. The chemical precipitation method allows producing powders in a narrower size range, namely up to 56 nm, compared to the thermolysis method, characterized by a particle size of up to 84 nm. Gravimetric analysis of the kinetic laws of adsorbing water vapors on the synthesized powders in an air flow with a relative humidity ranging from 60 to 100% showed that the adsorption process was most intensive in the initial stage (within 30 min). The adsorption of water vapors and the process speed depend significantly on the synthesis method, its duration, and thermolysis medium. Magnetite produced by chemical precipitation has more than an order of magnitude higher adsorption properties compared to powders produced by thermolysis. This is due not only to the specific surface area but also to the greater affinity of the material for water molecules. The hydrocarbon medium for thermolysis halves the adsorption properties of magnetite compared to nitrogen. This may be associated not only with potential passivation or catalytic poisoning of the powder surface but also with the influence of the carbon component on the reduction of pore volume and the formation of the adsorption capacity of magnetite to polar molecules of the gaseous water phase.