Analytical control of silicified graphite SG-P

An analytical scheme for the analysis of silicified graphite SG-P, a four-phase composite material consisting of silicon, carbon, silicon carbide and silicon dioxide, has been developed. The procedure can be successfully used in the quality control of raw materials and in the study of the phase composition of finished products The porosity and density of the graphite base, as well as the impurities contained in the base and silicon change the course of silicification and the properties of the finished product as well. The impurities are the main reason for the formation of delamination, swelling, cracking and light spots on the treated surfaces. It should be noted that the iron content 0.023 – 0.17 wt.% in the carbon material intended for silicification, leads to catalytic graphitization of the artificial graphite and dispersion in the silicon melt. Methods of rapid assessment of the quality of raw materials are to be used to provide quick understanding of their suitability for manufacturing final products on their base. Quality control of the silicified graphite produced at the JSC «Research Institute Graphite» is carried out by determination of the phase composition of the finished product by chemical and X-ray diffraction methods of analysis. The content of silicon carbide (not less than 45%), unbound silicon and carbon (not more than 20 and 35%, respectively) affects the corrosion resistance and thermal expansion of silicified graphite.

Effect of Argon Flow on Oxygen and Carbon Coupled Transport in an Industrial Directional Solidification Furnace for Crystalline Silicon Ingots

Transient global simulations were carried out to investigate the effect of argon flow on oxygen and carbon coupled transport in an industrial directional solidification furnace for quasi-single crystalline silicon ingots. Global calculation of impurity transport in the argon gas and silicon melt was based on a fully coupled calculation of the thermal and flow fields. Numerical results show that the argon flow rate affects the flow intensity along the melt–gas surface, but has no significant effect on the flow patterns of silicon melt and argon gas above the melt–gas surface. It was found that the evaporation flux of SiO along the melt–gas surface decreases with the increasing argon flow rate during the solidification process. However, the net flux of oxygen atoms (SiO evaporation flux minus CO dissolution flux) away from the melt–gas surface increases with the increasing argon flow rate, leading to a decrease in the oxygen concentration in the grown ingot. The carbon concentration in the grown ingot shows an exponential decrease with the increase of the argon flow rate, owing to the fact that the dissolution flux of CO significantly decreases with the increasing argon flow rate. The numerical results agree well with the experimental measurements.

Environment-Friendly Preparation of Reaction-Bonded Silicon Carbide by Addition of Boron in the Silicon Melt

Reaction-bonded silicon carbide ceramics were sintered by infiltration of Si and B–Si alloy under an argon atmosphere at different temperatures. The element boron was added to the silicon melt to form a B–Si alloy first. The mechanical properties of samples were improved by infiltration of the B–Si melt. The samples infiltrated with the Si-only melt were found to be very sensitive to experimental temperature. The bending strengths of 58.6 and 317.0 MPa were achieved at 1530 and 1570 °C, respectively. The sample made by infiltration of B–Si alloy was successfully sintered at 1530 °C. The relative density of the sample was more than 90%. The infiltration of B–Si alloy reduced the sintering temperature and the bending strength reached 326.9 MPa. The infiltration mechanism of B–Si alloy is discussed herein.

Механические свойства композитного покрытия SiC на графите, полученного методом замещения атомов

The mechanical properties of composite coatings made of silicon carbide on graphite are studied for the first time. For the deposition of coatings, a new method of annealing the initial graphite was used, which was in contact with a silicon melt in an atmosphere of carbon monoxide.The samples were studied by nanoindentation and scanning electron microscopy. It is shown that the formed coating consists of a continuous film of monocrystalline silicon carbide lying on the surface, dendrites and crystalline druses, with roots going deep into the sample through a system of pores. It is shown that the coating significantly increases the mechanical characteristics of the graphite surface, including the microhardness.