Adsorption of Water Vapors on Magnetite Powders Prepared by Chemical Precipitation and Thermolysis Methods

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 atmospheres was conducted. Regardless of the synthesis method, duration, and atmosphere, the powders were found to have spherical particles, uniform particle size distribution, and ability to agglomerate. The chemical precipitation method produced powders within a narrower size range, specifically up to 56 nm, in contrast to the thermolysis method, characterized by a particle size of up to 84 nm. Gravimetric analysis of the kinetic laws of water vapor adsorption 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 were significantly influenced by the synthesis method and duration and by the thermolysis atmosphere. Magnetite produced by chemical precipitation exhibited adsorption properties more than an order of magnitude higher than those of the powders produced by thermolysis. This can be attributed not only to the specific surface area but also to the material’s greater affinity for water molecules. A hydrocarbon atmosphere for thermolysis reduced the adsorption properties of magnetite by half compared to nitrogen. This may be associated not only with the 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 promotion of magnetite adsorption capacity for polar molecules of the gaseous water phase.