Vol 2019, No 3 (2019)

The mineralogical composition of the cobalt ore from the Dashkesan deposit is determined. The process of cobalt leaching with solutions of hydrochloric and sulfuric acids is studied. The leaching of cobalt with solutions of hydrochloric (7 and 20%) and sulfuric (up to 2 N) acids is incomplete, because the ore contains poorly soluble minerals of cobalt and silicate compounds (the recovery of cobalt with hydrochloric acid is 77.4% and that with sulfuric acid is 76.7%). Ore processing using sulfating roasting followed by leaching with water is proposed. The mechanism of sulfate formation, a sequence of the sulfation of the ore minerals at various temperatures, and the degree of recovery of the minerals are studied. The degree of recovery of cobalt reaches 85% for leaching of the ore sulfated at 700°C.

The conditions for the direct carbothermic reduction of metals from mixtures of sulfides Cu_1.96S and FeS with calcium oxide are studied using thermogravimetric and thermal analyses combined with mass spectrometry of the formed gases. The metal reduction in a mixture of FeS and CaO on heating to 1250°C is shown to occur with the formation of intermediate oxysulfide phases almost without the evolution of sulfur-containing gases. The formation of SO₂ is observed in a mixture of Cu_1.96S and CaO at temperatures higher than 550°C. The introduction of FeS into the reaction mixture of Cu_1.96S and CaO enhances the completeness of metal reduction by carbon, decreases the temperatures of the intense processes, and suppresses sulfur dioxide evolution.

The properties of a 49Ni–36Ti–15Hf (at %) high-temperature shape memory alloy (HTSMA) are studied comprehensively. Data on the elemental and phase compositions, the phase transformation temperatures, and the mechanical characteristics are obtained. The studies are carried out on samples cut from alloy ingots. The temperature range of the phase transformation of the alloy determined by differential thermal analysis is from M_f = 186.8°C to A_f = 275.2°C in the as-delivered state and from M_f = 188.1°C to A_f = 276.5°C after vacuum annealing. These values are suitable for designing of the required safety device. However, as-cast 49Ni–36Ti–15Hf (at %) alloy specimens undergo brittle fracture at stresses from 461 MPa (as-delivered state) to 514 MPa (after vacuum annealing at 700°C). In this connection, it is impossible to deform such samples in the afterelastic state, and the shape memory effect and the degree of shape recovery are zero in them; i.e., the as-cast 49Ni–36Ti–15Hf (at %) alloy is not suitable for designing an efficient safety device. To improve the thermomechanical characteristics, it is planned to change the HTSMA elemental composition, the conditions of deformation treatment (forging, rolling) or heat treatment of the as-cast alloy, or the deformation conditions of articles. The authors will take into account these results of studying the as-cast 49Ni–36Ti–15Hf (at %) alloy when designing various devices for nuclear power engineering.

The problems of estimating the corrosion resistance of novel multilayer metallic materials with an internal protector, where the principle of protector-assisted pitting protection is applied, are considered. An electron-microscopic method is used to experimentally substantiate the mechanism of corrosion damage of the material layers. Electrochemical and chemical methods are proposed for accelerated tests to determine the rate of corrosion damage. The electrochemical method can be used to reveal the rate-controlling step of the process, to calculate the mass corrosion index, and to substantiate the choice of a protector for a certain aggressive medium. The chemical method can quantitatively estimate the efficiency of an internal protector and can determine the relative corrosion resistance index of a multilayer material in comparison with the corresponding monometallic material.

The growth of a radiation-induced void after its nucleus has reached a critical size is described in terms of a point defect migration model. The void growth rate (conventional dd/dt and dose-controlled dd/dD) as a function of irradiation temperature T and the generation rate of atomic displacements G is investigated at the initial stage of the transient swelling in an EK164 steel used as the fuel cladding in fast neutron reactors.