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Co-precipitation synthesis of Y<inf>2</inf>W<inf>3</inf>O<inf>12</inf> submicronic powder

Abstract:

Synthesis of negative and near-zero thermal expansion powders with low degree of agglomeration is one of the major challenges in their applications. In this research, Y2W3O12 was synthesized via two soft-chemical approaches, co-precipitation by mixing reactants and modified reverse strike co-precipitation, to assess the effect of these methods on the agglomeration degree of powders. Chemical composition of amorphous precursors was estimated based on charge neutrality principle, carbon-hydrogen-nitrogen (CHN) and thermogravimetric analyses. It was demonstrated that both precursors are oxyhydroxynitrate compounds, determined as Y2W3Oy(OH)z(NO3)x·nH2O. Both co-precipitation methods presented similar particle sizes and agglomeration degrees. The applied calcination conditions caused the formation of necks and hard agglomerates and were critical factors for the final agglomerated state of the Y2W3O12 powders. The formation of Y2W3O12 submicronic powders in the range of 0.60–0.70 µm was verified by laser diffraction and field-emission scanning electron microscopy analyses. X-ray powder diffraction patterns, at room temperature, of hydrated Y2W3O12 revealed predominantly the presence of monoclinic phase, while the monoclinic to orthorhombic phase transition was detected by dilatometry.