Mechanochemical Synthesis and Characterization of Silver (Ag<SUP>+</SUP>) and Tantalum (Ta<SUP>5</SUP><SUP>+</SUP>) Doped Calcium Silicate Nanopowders

Abstract

Calcium silicate (CS) nanopowders doped with monovalent (Ag + ) and pentavalent (Ta 5+ ) cations were successfully synthesized via a mechanochemical method. This technique consisted of milling mixtures of calcium oxide, silicon dioxide and variable amounts of silver nitrate as a source of Ag + or tantalum pentoxide as source of Ta 5+ , respectively, using a high-energy planetary ball mill for 3 h. To investigate the influence of subsequent annealing on the phase evolution, the mechanosynthesized powders were annealed at 1000 � C for 2 h. The results from the structural investigation confirmed that the synthesized doped and undoped powders crystallized in both � -CS (Parawollastonite, monoclinic crystal system) and � -CS (Cyclowollastonite, anorthic crystal system). With increasing the degree of Ag substitution, no obvious phase changes were observed in the synthesized powders; however, the presence of 5 wt% of Ta source led to a significant volume of phase changes. The results of EDX analysis showed that the stoichiometric doped and undoped CS powders were in good agreement with the literature data for crystalline CS. From TEM observations, the doped nanopowders annealed at 1000 � C for 2 h entailed polycrystalline nanoparticles with an average length of around 1 � m and mean width of about 200 nm.