Thermodynamic analysis of interaction of components in the SIO2-C system: improvement of technical silicon production technological process

In order to identify ways to improve the technological process of smelting metallic (crystalline) silicon of technical purity, a thermodynamic analysis of the interaction of components in the SiO2-C system is carried out that reveals the main factor in obtaining high-quality technical silicon is the elimination of superposition of the silicon carbonization process that is possible by carrying out a two-stage carbothermal reduction reaction, in that firstly the incomplete reduction of silica (SiO2) by solid carbon (C) is provided, accompanied by the release of new reacting gas components - SiO and CO, the subsequent interaction of which leads to the formation of the target product - technical silicon that is suitable for the production of modern solar energy converters. It is determined that main condition for highly efficient reduction reactions is the fine fractionness (<1 mm) of the used quartzite ore with keeping of a rational temperature range for its carbothermal reduction (1688-2000 K). It has been shown experimentally that the optimal technical solution for the implementation of this reduction process is to performt melting in a special plasma-chemical furnace-reactor with one liquid-metal subconducting electrode, with a reverse vertical feed of the reaction gases released at the first stage. The degree of extraction of silicon was on average 95%, and the degree of its purity was 97.2%.

Rapid Synthesis and Chemical Durability of Gd2- x Nd x Zr2O7 (0.0 ≤ x ≤ 2.0) Sub-Micron Ceramics as Nuclear Waste Forms

In this work, Nd3+ was used as a surrogate and it was incorporated into Gd2Zr2O7 nanocrystalline ceramics to simulate the immobilization of trivalent actinide elements. A series of Gd2 − xNdxZr2O7 (0.0 ≤ x ≤ 2.0) nanocrystalline powders were fabricated by solvothermal method, and then Gd2 − xNdxZr2O7 sub-microncrystalline ceramics were prepared by sintering via self-propagating chemical furnace plus quick pressing (SCF/QP). All powders are in defective fluorite structure, and Nd doping hardly change the powder grain size. After analyzing the sintered ceramics, it can be found that the transition from defective fluorite structure to pyrochlore structure occurs when x ≥ 1.5. The sample density decreases with elevated Nd content, while the grain size gradually enlarges. Besides, the normalized release rates of Nd and Zr elements in the Nd2Zr2O7 waste form are kept in low values (below 10− 5 g•m− 2•d− 1), which exhibits its excellent aqueous stability.

Modeling of combustion synthesis in multilayer gasless system

A combustion model for a flat layered composition has been developed, where chemically active layers alternate with inert metallic layers with high thermal conductivity. The heat exchange between the layers was specified by the conjugate boundary conditions. A numerical study of gasless combustion of a multi-layer system with heat-conjugated layers of two types was performed. Optimal layer sizes and parameters of the layer system were obtained to provide the maximum burning rate of the layer package. The effect of increasing the burning rate was found to be associated with heat recovery and an increase in the effective thermal conductivity of the system. The concentration limits of combustion were determined depending on the volume content of the inert element. Replacing the system of inert layers with that of low-calorie mixture layers leads to a model for synthesis of inorganic materials in the "chemical furnace" mode.

Tungsten-Copper Composite Fabricated by Hot-Shock Consolidation

High-temperature shock consolidation and under-water shock wave are two effective methods to eliminate cracks generated when shock wave propagating the powder bed. In this work, a novel assembly consists of a chemical furnace and a water column was used to fabricate tungsten-copper composites. The heat released from the reaction of a SHS reaction mixture was used as chemical furnace to preheat the precursor powder. The water column as well as the explosive attached was detached from the furnace by a solenoid valve fixed on the slide guide. So the explosive and water column was kept cooling during the preheating process. The W-Cu powders with the grain size of 2μm were first blended with mass ratio of 9:1 by mechanically alloying in a planetary ball mill. Prior to application of shock wave, the elemental powders were preheated at different temperatures, i.e. the highest temperature up to 1000°C. The intensity of the shock wave loading was under 10GPa. The consolidated specimens were then characterized by microstructure analysis and micro-hardness testing. The different micromechanical behaviors of W and Cu phase in the consolidated sample were studied by using in situ high-energy X-ray diffraction technique. The result showed that a fine-grained 90W/10Cu composite with no cracks could be compacted to a density of 16.44g/cm3 by hot-shock consolidation at a preheating temperature of 970°C.