The effect of iron phosphate, alumina and silica coatings on the morphology of carbonyl iron particles

摘要

Carbonyl iron powders were coated with iron phosphate using phosphating method and boehmite (γ-AlOOH) or silicon hydroxide (Si(OH)_4) nanoparticles derived from the hydrolysis of tri-sec-butoxide (Al(OC _4H_9)_3) or tetramethylsilane (Si(OCH _3)_4) using sol-gel method. The coated powders were dried and calcined at 400 ° C for 3 h in air. Cross-section morphology of coated carbonyl iron powders were investigated by scanning electron microscopy energy dispersive X-ray analysis. Coated Fe micro-particles were spherical in shape with 'shell/core' structures. The shells consisted of an amorphous layer with varying thickness (100-800 nm) and the core represented a carbonyl iron. Gelatinous morphology of dried FePO_4 coating composed from nanoparticles of iron oxyhydroxides and hydrated iron phosphate with a shell thickness of ～100 nm around iron particles was observed. In coatings based on alumina or silica xerogels with a thickness of ～100-150 nm or ～200-500 nm, the coatings were composed of iron oxyhydroxides and γ-AlOOH or Si(OH)_4. The resulting XRD diffractograms revealed the hematite (α-Fe_2O_3)and magnetite (Fe _3O_4) that were formed in phosphated and sol-gel coated iron powders. The X-ray diffraction patterns did not verify the presence of phosphates, alumina or silica and indicate the amorphous or nanocrystalline structure of FePO_4, γ-Al_2O_3 and SiO _2.