High-Temperature Heat Capacity and Thermal Extension of FeTa2O6

Physics of the Solid State - The heat capacity of synthesized iron tantalate FeTa2O6 was measured in the temperature range of 323–1103 K by the ratio method using a thermal analyzer combining...     

Thermochemical properties of MnNb<Subscript>2</Subscript>O<Subscript>6</Subscript>

Homogeneous manganocolumbite (MnNb₂O₆) was synthesized from Nb₂O₅ and MnO oxides. Powder sample was orthorhombic with unit cell parameters: α = 0.5766 nm, b = 1.4439 nm, c = 0.5085 nm and V = 0.4234 nm³. Heat capacity over the temperature range of 313–1253 K was measured in an inert atmosphere with combined thermogravimetry and calorimetry using NETZSCH STA 449C Jupiter thermoanalyzer. Melting point was 1767 ± 3 K, enthalpy of melting was 144 ± 4 kJ mol⁻¹. Experimental heat capacity of MnNb₂O₆ is fitted to polynomial C _pm = 221.46 + 3.03 · 10⁻³ T + −39.79 · 10⁵ T ⁻² + 40.59 · 10⁻⁶ T ².     

Formation of an eutectic structure in Al-Mo-Zr alloy crystallization

A eutectic structure has been obtained in crystallization of an Al-Mo-Zr alloy. This structure is represented by lamellar eutectic colonies, consisting of Mo₃Al₈ and Al₂Zr solid solution, between which more disperse triple and double eutectics with Mo₃Al and Mo₂Zr are crystallized.     

Effect of tantalum on phase formation in the Fe-S system

Phase formation in the Fe_{1 ? x} -Ta _x -S system with 0 < x < 0.5 has been studied at temperatures up to 1273 K using X-ray diffraction. When the constituent elements are heated to 823 K, troilite (Tr), pyrrhotites (PoI, PoII, and Po_m), and pyrite (FeS₂) are formed. Tantalum at these temperatures only insignificantly dissolves in iron sulfides. In the range 823–1273 K, tantalum reacts with pyrrhotites PoII and Po_m and pyrite to yield PoI, FeTa₃S₆, and α-Fe. The solubility limit of tantalum in PoI is near Fe_0.98Ta_0.02S. The initiation temperature of the reaction between troilite and tantalum producing FeTa₃S₆ and α-Fe is 873 K. The unit cell parameters of tantalum change at 500 K, presumably due to the dissolution of iron and possibly sulfur (iron sulfide).     

Effect of Phase Composition on Sulfuric Acid Leaching of Tantalum-containing Alloys

Phase composition of iron-based tantalum-niobium alloys (Ta 2-5, Nb 3-6, Si up to 12, C 1.4-2.4%) was studied. The kinetics of leaching of ferroalloys with H₂SO₄ aqueous solutions and with mixtures of sulfuric and hydrofluoric acids was considered. The conditions of hydrochemical treatment of the alloys, which make it possible to concentrate niobium and tantalum in the solid residue through dissolution of up to 94% of Fe, 90% of Mn, and 70% of Si, were found.