Papers by Keyword: Refining

Abstract: The study of the silicon crystallization mechanism by standard analytical methods is difficult since the temperature of liquid silicon in the ladle during oxidative refining is quite high rising to 1500-1600 °C. Therefore, the method of mathematical modelling was used. To understand the mechanism of inclusions formation in silicon the authors applied a method of computer-generated state diagrams of three-component systems using the soft package Diatris. The package allows one to study the behavior of components involved in various physical and chemical transformations, and the interaction of elements with each other during the crystallization of the silicon melt. This work studies the behavior of such impurities as Fe, Ti, B, and C. To achieve the set goals, the ternary diagrams were constructed and analyzed for the Si-Ti-Fe, Si-Ti-B, Si-Ti-C, Si-Fe-B, Si-Fe-C, and Si-B-C systems. To characterize the increase in the number of crystals when a multicomponent alloy passes the crystallization interval, the crystallization rate was calculated. It is established that the most probable impurity compounds in crystalline silicon are SiFe_0.4B_0.06, FeTiSi₅, SiB_0.06Ti_0.33, and SiTi_0.4C_0.1.

Abstract: The paper investigates the technology of refining primary aluminum from vanadium impurities, based on flux treatment with boron-containing fluxes. In the Pavlodar region of the Republic of Kazakhstan, on the basis of local enterprises, the production of primary aluminum and products based on local raw materials is developing. The main problem in the production of primary aluminum on the basis of JSC “Kazakhstan Electrolysis Plant” is the presence of undesirable vanadium impurities, which pass into metal during electrolysis from baked anodes based on calcined coke (vanadium content up to 800 ppm) of the local enterprise LLP UPNK-PV (Pavlodar, Kazakhstan). The authors investigated the process of ladle refining of aluminum from vanadium using the Al-B (3% B) alloy. Laboratory and industrial tests have shown a decrease in the vanadium content by an average of 78% in the bulk of the metal, with an increase in its content in volume up to 5-10% of the ladle capacity. It was found that mixing leads to a certain averaging of the vanadium content in the ladle volume.

Abstract: Rice straw, an abundant agricultural waste, is shown to be a promising resource for pulp and paper packaging manufacturing. In this study, rice straw pulps or cellulose fibers were extracted using a soda-AQ process and then the rice straw pulp slurries were refined by a Valley beater. The effect of refining time (15-60 min) on the pulp fiber characteristics was studied. It was found that both initial fiber length and width were decreased with refining time. The refined fibers became fibrillated, finer, and also more uniform in size confirmed by SEM. The pulp freeness (CSF) was reduced with increasing refining time as expected due to higher water-holding capacity of more fibrillated pulps. Then, the molded sheets were formed from the prepared rice straw pulps and examined. From tensile testing, the results indicated that the tensile properties of the molded sheets from the refined pulps were significantly enhanced (p < 0.05), thanks to an increase in fibrillated fiber surface area and inter-fiber bonding degree. The Valley beater refined rice straw pulp provided the molded sheet with the highest tensile index of 51.96 ± 4.08 Nm/g which are comparable to that of the sheets prepared from PFI mill refining process. The tensile properties of the current refined sheets were also in the acceptable range for typical commercial molded pulp packaging. In addition, the freeness values of the optimal Valley beater refined pulps are relatively high (348-423 ml), implying a benefit in forming process and manufacturing of pulp products.

Abstract: Centrifuging is one of the most complicated technological processes, and centrifuges are the ones of the most complex technological machines. Not all the questions of the theory of centrifuges have been sufficiently developed, in particular, there is no reliable description of hydrodynamic flows in the process of centrifugation, resulting in the impossibility of an accurate prediction of the separation of heterogeneous systems. Circulation and stagnant (“dead”) zones often appear in centrifuge casings, which lead to uneven residence time of the fluid flow and reduced productivity of the centrate. To improve the construction of these machines, as well as to substantiate the technological mode of their operation, experimental studies were conducted, aimed at identifying the dependence between a proportion of the stagnant zones and the rotor speed. Determination of proportion ofthe stagnation zones was carried out by processing and analyzing the response curves obtained at the centrifuge output, after creating a pulsed input disturbance. Studies have shown that an increase in the rotor speed from 350 to 750 rpm leads to a decrease in proportion of the stagnation the stagnation zones in the centrifuge from 12% to 4.5%, thereby contributing to the intensification of the centrifugation process.

Abstract: The article deals with technologies of refining and inoculating casting alloys with the use of nanostructured diamond powder, as well as stimulation technique on molten metal including processing of the liquid alloy with nanosecond electromagnetic pulses. The developed method of cast iron inoculation allows to eliminate the flare and to increase the physical and mechanical properties of the castings through the grain refining and the decrease of chilling tendency during crystallization of the liquid alloy. Inoculating of aluminium alloys by high-melting particles of a nanostructured diamond powder leads to the grinding of structural constituents, including conditions for dispersing hardening intermetallics during postbaking of such castings. As a result, foundry and physicomechanical properties of castings are significantly improved.

Abstract: Electro-slag re-melting (ESR) is a process that combines all important elements of steel melting conversion. JSC “RPA “CNIITMASH” continuously developed ways to use ESR to manufacture critically important parts for power engineering, including nuclear power engineering, heavy-duty machine engineering and other machine building industries. Enhanced performance of product is an important competitive advantage that ESR provides in comparison to other metallurgical processes. Present report reflects results of the latest research work aimed at resolving issues related to control and management of refining and crystallization processes, cost reduction for ESR products. Practical relevance of developed approach to control of ESR metal quality is revealed by data of achieved parameters which characterize properties of pipes and pipeline elements in energy and nuclear power industries which rely on ESR ingots as work-piece blanks.

Abstract: Within the researches made, the establishment of the processing with synthetic slag decreasing possibilities, of the sulphur and oxygen contents, from the steel made in electric arc ovens, of 100 t ladle capacity oven (LF) - (EBT) type, was taken into account. For the formation of the synthetic slag, reducing mixing made of lime, fluorine, bauxite and aluminum slag. The experiments we performed consisted in adding the waste mechanical mixture at the bottom of the ladle, its melting leading to the formation of synthetic slag. The obtained data was processed in the EXCEL program, obtaining correlation equations between the desulphuration, deoxidation and the addition of a reducing mixture, respectively the treatment duration.

Abstract: A YAG continue-wave laser has been used to refine the surface of silicon wafers in this study. During laser scanning, the irradiated region of the surface of the wafer experienced melting and subsequent recrystallization, which results in a redistribution of metal impurities in the molten pool along the depth direction. Cross-sectional micrographs of irradiated wafers have a clear boundary, which confirms the process of recrystallization, and the depth of molten region depends on the scanning parameters and the size of wafer. Secondary ion mass spectrometry measurements have been carried out to characterize the concentration of metal impurities. After redistribution of metal impurities, a final relative purity region was formed close to the surface. SIMS measurements demonstrate that the metal impurity concentration of the purity region has significantly reduced. The mechanism of the redistribution process of metal impurities in the molten pool has been qualitatively analyzed. All of the experimental results support that the CW laser scanning technology can effectively refine the specific surfaces of silicon wafers, and this technology has a great potential in the field of solar cells.

Abstract: Metallic mould properties are influenced by the technological process used on casting. The mechanical properties of aluminium castings can be affected by dissolved gases, heterogeneous impurities or shrinkage remaining in casting after solidification. Dissolved gases and oxide inclusions in aluminium all have a deleterious effect on casting quality. The treatment of molten aluminium using vibrations and salts was found to be highly efficient in refining the microstructure of the alloy. The main objective of the paper is to understand the effects of vibrations and salts treatment on the final microstructure and changes that take place and influences aluminium alloy properties used in mould manufacture. The microstructural changes have a great significance in improving the properties of aluminium alloy castings. Understanding this effects and the modification mechanism can undoubtedly be of great significance for improving casting quality. Fluxes based on a KCl-NaCl mixture may be used to cover and protect the metal from oxidation. Most fluxes are based on a mixture of KCl and NaCl, which forms at low-temperature (665 °C) eutectic.

Abstract: Diffusion phenomena are of great importance in materials processing wherein atomic, molecular or ionic species are distributed within a phase or among different phases. Though the phenomenological equation describing the diffusion phenomena including the bulk flow arising out of diffusion in fluid and the phenomena of Kirkendall shift in substitutional solids are the same, these processes are often treated independently. Some discussion on this aspect is presented in the theoretical aspects of diffusion. Owing to the complexity of atomic interactions, prediction of diffusion coefficients in condensed systems from first principles may not be that reliable; Experimental determination of diffusion coefficients is essential. In the second section, some novel experimental techniques developed recently to measure diffusion coefficients in the solid state as well as liquid systems including those in slags are described. In the last section, two case studies on application of diffusion phenomena in process metallurgy are presented emphasizing the importance of these in metallurgical processing.