Vol 47, No 12 (2017)

Silicon production by the reduction of quartzite in furnaces is accompanied by copious dust emissions containing a high proportion of valuable silica (86%, on average). It is of great interest to capture that dust for reuse in the process. The dust captured in the gas-purification system consists of particles no larger than 120 μm, with a predominance of the 20–50 μm fraction. In order to use such dust in silicon production, it must be aggregated, so as to prevent its entrainment from the furnace by the gas fluxes. Since the batch pieces must be strong enough to withstand transportation, the binder employed is liquid glass with the addition of electrofilter dust from aluminum production, which contains tars (polyaromatic hydrocarbons). Strength tests of batch samples permit the recommendation of the following composition (by mass): 24–27% dust from silica production; 51–53% carbon reducing agent (a 1: 1 mixture of petroleum coke and charcoal); 4–5% silicon siftings; 14–15% binder (a 4:1 mixture of liquid glass and electrofilter dust from aluminum production). For such batch, the strength in drop tests is 82.5%, on average. Research shows that the batch pieces obtained by this method have a porous structure (45.5%) for the formation of a well-developed active surface and corresponding apparent density (1100 kg/cm³). That supports stable furnace operation. Trials in an HTF 17/10 high-temperature furnace yield an intermediate product containing more than 44 wt % silicon carbide. On that basis, such dust aggregates may be added to the main batch in silicon production.

Using the equations of physicochemical hydrodynamics and experimental results regarding the surface and interphase properties of metallic and oxide melts, the conditions in which metallic phase is formed in the bubbling of carbon monoxide through molten oxidized nickel ore are described. The critical dimensions of the gas bubble (R_b.cr) and the metal droplet (r_d.cr) moving in oxide melt without change in size are determined in the range 1550–1750°C. It is found that R_b.cr increases slightly from 6.35 × 10^–2 m at 1550°C to 6.58 × 10^–2 m at 1750°C. With change in the droplet composition and the temperature, r_d.cr varies from 2.1 × 10^–3 to 2.9 × 10^–3 m. The dimensions of the metal droplet formed at a single bubble during the reduction of nickel and iron from oxide melt are determined. As the content of nickel and iron oxides in the melt decreases with increase in the overall CO consumption, the nickel content in the ferronickel droplets falls from 89 to 18%, while the droplet diameter decreases from 1.4 × 10^–3 to 8.0 × 10^–4 m. The droplet mass falls correspondingly from 9.4 × 10^–5 to 1.6 × 10^–5 kg. The conditions in which the bubble–droplet system rises through the melt are determined. Over the whole range of temperature and Ni content, the bubble–droplet system begins to rise through the oxide melt when r_d/R_b is less than 0.68–0.78. To assess the stability of the bubble–droplet system, with the given bubble and droplet dimensions, the parameters determining their joint motion are calculated. It is found that breakaway of the metal droplet from the bubble is not possible in pyrometallurgical systems. The formation of metal phase as a result of the bubbling of carbon monoxide through the oxide melt is described. In this process, the interaction of the oxide melt with the gas is accompanied by the formation of metal droplets, which become attached to the surface of gas bubbles and move to the surface of the oxide melt. Metal with 80–90% Ni is formed at first. With decrease in the nickel content in the oxide melt, its content in the metal declines to 20%. At the surface of the oxide melt, the metal droplets coalesce. When their diameter is greater than 5 × 10^–3 m, they break away from the surface and fall to the bottom. If the falling drop collides with ascending bubble–droplet systems, they may coalesce with it or flow around it. On coalescence, the small droplets will be assimilated and rise to the surface. The breakaway force of the droplet from the bubble significantly exceeds the gravitational force on the droplet. Therefore, the bubble–droplet system is stable for all the size ratios considered.

TiC–Mo, TiC–Ni, TiB₂–Mo, and TiB₂–Ni coatings applied to the surface of Hardox 450 steel by electroexplosive sputtering are subjected to electron-beam treatment, After electroexplosive application, the surface relief of the coatings includes features such as deformed solidifying microglobules, buildup, microcraters, microcracks, and peeling. After electron-beam treatment, the microglobules, buildup, microcraters, and microcracks disappear from the coating surface. A polycrystalline structure containing cellular elements is formed. After electron-beam treatment, the surface roughness is 1.1–1.2 μm. The thickness of the layers modified by the electron beam in the electroexplosive coatings depends linearly on the surface energy density. The greatest coating thickness is observed when using the TiB₂–Mo system; the coating thickness is least for the TiC–Ni system. That may be attributed to the thermophysical properties of the coatings. The following substructures are observed in the coatings: cellular, striated, fragmented, and subgranular. Grains with chaotically distributed dislocations and reticular dislocations are also observed. Electron-beam treatment leads to the formation of composite filled structure over the whole cross section of the remelted layer. The structure formed in this layer is more disperse and uniform than in coatings formed without electron-beam treatment. The inclusions of titanium carbide or titanium diboride in the molybdenum or nickel matrix are 2–4 times smaller than immediately after electroexplosive sputtering. Within the molybdenum or nickel grains and at their boundaries, rounded particles of secondary phase (titanium carbide or titanium diboride) are observed. They may be divided into two classes by size: particles of the initial powder (80–150 nm) that have not dissolved on irradiation; and particles formed on solidification of the melt (10–15 nm). In the electroexplosive powder coatings, the structure is mainly formed by dynamic rotation of the sprayed particles, which form a vertical structure both in the coating and in the upper layers of the substrate. The coatings have excellent operational properties: nano- and microhardness, elastic modulus of the first kind, and wear resistance in dry slipping friction.

Global and Russian markets for polyvinylchloride (PVC) are compared and contrasted. The carbide technology used in PVC production may be competitive on the basis of cooperation between steel plants, coal mines, and power companies within a single region, thanks to logistical savings associated with lower costs of resource extraction and transportation. Potentially, there is considerable scope for Russian PVC production, with the corresponding decrease in imports. Vertical integration of steel plants with mining and processing enterprises in the Kuznetsk Basin provides new options for PVC production. Cost assessment of the options for acetylene production may be based on factorial analysis. Note that, rather than methane produced from coal beds and supplied in liquefied form, steel plants may use coke-oven gas from coke production as the raw material in PVC synthesis. Acetylene produced by the carbide technology may compete with ethylene as a raw material for PVC production if its cost does not exceed that of ethylene by more than 40%. Analysis in terms of coal chemistry facilitates the development of multistage synthesis of PVC on the basis of cooperation between chemical and steel enterprises. The organization of PVC production by means of coal-based technology may be a source of economic growth in the Kemerovo region, permitting diversification of steel production and expansion of the output of PAO Koks in terms of product range and exports.

In the development of conveyer roasting machines, heat and mass transfer in the bed must be simulated. In the present work, the results of calculations based on a thermal model of conveyer roasting machines developed at OOO NPVP TOREKS are presented for the MOK-1-592 system at PAO Mikhailovskii GOK. The thermal operation of the working zones in the pellet-roasting machine may be improved by taking account of the most significant factors affecting the physicochemical processes in those zones.

A control algorithm is proposed for the surface roughness of cold-rolled and tempered strip. The generalized functional structure of the automatic control system is presented.

Low-temperature plasma is used in the plasma-arc remelting of 55Kh20G9N4 steel. The plasmaforming gases employed are nitrogen and argon. The influence of the remelting parameters on the structure, the mechanical properties, the flexural strength, and the corrosion and wear resistance of the stainless steel is studied. When using nitrogen to form the plasma, its content in the steel increases. That increases the strength, crack resistance, and corrosion and wear resistance of the steel.