EFFECT OF MoO₃ AND TiO₂ POWDER SIZES ON THE PHASE COMPOSITION  AND DENSITY OF DYSPROSIUM TITANATE PELLETS

Abstract

An important process task is to expand the range of raw materials applied for the synthesis of dysprosium titanate (neutron-absorbing material for VVER-1000 reactors), establish methods and optimize the manufacturing regimes for powders and pellets with characteristics that meet specific technical requirements, primarily those for the density and structural and phase composition of the materials. The influence of the MoO₃ as a doping element and TiO₂ powder with different particle sizes on the density and phase composition of dysprosium titanate (Dy₂O₃•TiO₂) pellets was experimentally studied. Titanium oxide powders of two grades were used: powder with spherical particles with a size of 10–30 μm (OSCh 7–3 grade as per TU 6–09–3811–79) and nanosized powder with an average particle size of~63 nm (produced by China Rare Metal Material Сo, China). The nanosized TiO₂ powder intensified the sintering of the pellets, which achieved a density of 6.9 g/cm³ and acquired a single-phase hexagonal structure at 1650 °C. The coarse TiO₂ powder does not promote high density of the sintered pellets or complete synthesis of dysprosium titanate since a significant amount of the intermediate compound of dysprosium dititanate (Dy₂Ti₂O₇) and initial dysprosium oxide (Dy₂O₃) remains in the synthesized material. The introduction of MoO₃ intensifies the sintering of pellets, increases the pellet density up to 6.7 g/cm³, and lead to the formation of a single-phase cubic structure of pyrochlore type, regardless of the grade of the TiO₂ powder used. The simultaneous use of the nanosized TiO₂ powder with the MoO₃ doping addition increases the density of sintered dysprosium titanate pellets to 7.1 g/cm³ and promotes the formation of a single-phase structure of pyrochlore type.