Chemical mechanism of precipitate formation and pH effect on the morphology and thermochemical co-precipitation of W–Cu nanocomposite powders

Abstract

W–25%Cu composite powder was produced via thermochemical procedure. Copper nitrate and sodium tungstate salts were used as Cu and W containing precursors, respectively. Aqueous solutions of these salts were reacted under several different pH conditions. It was found that the products of all stages involving Cu 2WO 4(OH) 2 and CuWO 4·2H 2O as raw precipitates, CuWO 4− x , CuO, and WO 3 as calcined powders, and W–Cu reduced composite powders possessed similar compositions in different pH conditions. But changing the reaction pH in the range of 3–13 was found to markedly influence the microstructure of the products. At low and medium pH precipitates were in the form of large monolithic agglomerates while in high pH smaller cotton like agglomerates were formed. At low and medium pH conditions simple ion replacement was found to be dominant mechanism of precipitation while in high pH Cu(NH 3) 4 2+ complex ion was formed and ligand exchange was the dominant mechanism of precipitation.