Thermal operating conditions of an RKZ-4-0-Il furnace in melting corundum

Conclusions Investigations were conducted of the thermal operating conditions of an RKZ-4-0-ll furnace, and complete energy balances of its operation were calculated. The primary energy losses occur through the gas exhaust system (9–17%), the furnace roof (14–25%), and the side walls and bottom of the furnace (13–36%).To increase the efficiency of the installation it is necessary to optimize the gas exhaust conditions and the cooling water consumption with simultaneous solution of the problem of utilization of the thermal losses and to convert the furnace to single tappings of larger volumes of molten material (or to increase the rate of tappings).Translated from Ogneupory, No. 1, pp. 48–53, January, 1984.     

Glass melting in an electric direct-heated skull furnace

A fundamentally new process is proposed to make S88-5 glass. It involves the use of an electric direct-heated skull furnace. The furnace has a capacity of 200–250 kg/day. Translated from Steklo i Keramika, No. 5, pp. 6–7, May, 1997.     

Thermal behaviour of vitreous ceramic coatings obtained by electrophoretic deposition for furnace components

In this study, three different vitreous ceramic coatings have been designed to improve radiation heat transfer and thereby increase the thermal efficiency of fired heaters or furnaces working at high temperatures. The vitreous ceramic coatings were produced through Electrophoretic Deposition technique (EPD) of ceramic suspensions. These ceramic formulations were designed based on components which increase emissivity, such as SiO₂ and a Black dye (based on chromium, copper and iron oxides), added in 25 wt%. These coatings showed emissivity values around 0.89 at room temperature and around 0.82 at 550 °C in the middle infrared (MIR) spectral range, with slight differences between them. The SiO₂ and Black dye additions provide an important protective effect on the coatings’ thermal stability as it was proved by the absorbance level at long times, higher than 85% in the near infrared (NIR) spectral range. These results were also supported by microstructural characterisation, substrate-coatings adhesion strength and thermal stability tests.     

Thermal calculation of the water-cooled elements of the lining of an electric arc steel melting furnace

Conclusions A model and a computer program using it have been developed making it possible to evaluate the influence of the electrical conditions after melt-down in an electric arc steel melting furnace on the thermal operation of tubular water cooled elements of the lining.The calculation is made for steady and nonsteady thermal conditions and makes it possible to determine the following parameters of thermal operation of the element: the temperature distribution across the layer of lining slag and tube wall; the temperature losses with the water and the water temperature at the exit of the element; the equilibrium lining slag thickness for a specified arc radiant power and heat exchange conditions in the furnace space.The heat losses with the water of a tubular wall panel of a DSP-100I6 furnace (tube diam. 76 mm and wall thickness 12 mm, lining slag thickness 20 mm, water consumption 5 m³/h per m² of panel) after meltdown of the heat were calculated.The equilibrium thickness of the lining slag decreases with a reduction in its melting point and in increase in arc radiant power P_a.rad.Translated from Ogneupory, No. 6, pp. 40–43, June, 1988.     

Recent topics of research and development of catalysis by niobium and tantalum oxides

Current topics of catalysts containing niobium and tantalum, especially in the field of solid acid catalysis and selective oxidation of hydrocarbons are reviewed. Hydrated niobium oxide and hydrated tantalum oxide are highly acidic. Hydrated niobium oxide is active for the hydration of ethene to ethanol, and Nb–W mixed metal oxide is more active for the reaction. Acid properties of tantalum oxide are changed by being supported on SiO₂. Ta oxide/SiO₂, prepared by the chemical reaction between tantalum alkoxide and surface hydroxyl groups of SiO₂, is active and selective for the gas phase Beckmann rearrangement of cyclohexanoneoxime to caprolactam. Niobium oxide and tantalum oxide easily react with many other oxides to form mixed metal oxide phases with complex structure. Mixed metal oxide catalysts, containing molybdenum, vanadium, certain elements together with niobium are active for the selective oxidation of hydrocarbons. Especially, the selective oxidation of propane by such mixed metal oxide catalysts has been paid attention. Additionally, recent progress of environmental catalysts, promoted by niobium and tantalum compounds, namely catalysts for the pollution abatement is reviewed.     

Pressureless sintering of single-phase tantalum carbide and niobium carbide

This work presents the results of studies on the preparation of single-phase polycrystalline tantalum carbide and niobium carbide. It has been found that it is possible to obtain polycrystals with high density in the pressureless sintering process at temperatures up to 2000 °C and therefore relatively low temperatures such as for the compounds with one of the highest melting points; TaC – 3985 °C and NbC – 3600 °C. Only carbon as a sintering additive was used. The main role of carbon is to reduce of oxide contamination. It has been shown that the determination of the amount of carbon required to reduce oxide contamination is only possible through the experimental method.     

Extraction of tantalum, niobium, and antimony fluorides

This report deals with the effects of the HF and H₂SO₄ concentrations and the organic-to-aqueous phase ratio V _org: V _aq on the distribution of Ta, Nb, and Sb in their extraction with tributyl phosphate and n-octanol from model solutions that are similar in composition to those obtained in columbite-tantalite processing. The recovery of these elements decreases in the order Ta ? Sb ≥ Nb. Process conditions for efficient separation of Ta from Nb and Sb have been found.     

Heat-engineering study of the melting of magnesite in an electric-arc furnace

Conclusions In order to increase the productivity of the furnace and ensure better melting, it is necessary to exclude the energy-consuming, endothermic process of decomposition of magnesite beyond the limits of the melting furnace.The problem of improving the technology of obtaining periclase and increasing its quality requires the all-round solution of problems to do with optimizing the melting cycles, crystallization and cooling schedules.Translated from Ogneupory, No. 4, pp. 24–27, April, 1981.     

Isolation of niobium and tantalum from tails of Baddeleyite concentrate

We investigated the conditions of tantalum and niobium isolation from the tails of Baddeleyite concentrate by means of sequential sulfation, the leach of a sulfate roast, and hydrolysis. The addition of ammonium sulfate was shown to favor the sulfation step. Perspectives of the extraction isolation of niobium(V) and tantalum(V) by triisoamylphosphate from a fluoride sulfurous solution after the dissolving of the hydrolysis precipitate was also demonstrated.     

Ceramic materials for producing high-purity compounds of niobium and tantalum

Translated from Steklo i Keramika, No. 7, pp. 14–15, July, 1992.     

High niobium oxide content in germanate glasses: Thermal,structural, and optical properties

Niobium alkali germanate glasses were synthesized by the melt‐quenching technique. The ternary system (90‐x)GeO₂–xNb₂O₅–10K₂O forms homogeneous glasses with x ranging from 0 to 20 mol%. Samples were investigated by DSC and XRD analysis, FTIR and Raman spectroscopy, and optical absorption. Structural and physical features are discussed in terms of Nb₂O₅ content. The niobium content increase in the glass network strongly modifies the thermal, structural and optical properties of alkali germanate glasses. DSC, Raman and FTIR analysis suggest niobium addition promotes NbO₆ groups insertion close to GeO₄ units of the glass network. XRD analysis also pointed out that samples containing high niobium oxide contents exhibit preferential niobium oxide‐rich phase after crystallization after heat treatment, which is similar to orthorhombic Nb₂O₅. Absorption spectra revealed high transmission range between 400 nm to 6.2 μm, added to a considerably decreased hydroxyl group content as the addition of niobium in the alkali germanate network. The niobium oxide‐rich phase crystallization process was studied and activation energy was determined, as well as nucleation and crystal growth temperatures and time for obtaining transparent glass‐ceramics.     

The anodic oxidation of superimposed niobium and tantalum layers: theory

Perriere, Rigo and Siejka have investigated the anodization of superimposed layers of niobium and tantalum, and their results are interpreted here in terms of known processes for the individual metals. Niobium oxide is less resistive to the passage of anodizing current than tantalum oxide, and it can then be shown that, when the niobium layer is superimposed, the metal order will be conserved during anodization. When the tantalum layer is superimposed, however, a partial inversion occurs, with fingers of the substrate niobium oxide pushing their way through the tantalum oxide. The latter is thus converted to a mesh, whose holes are filled with niobium oxide; because the current flows preferentially through this niobium oxide, the tantalum oxide in the mesh is almost completely divorced from the anodizing process. It then acts as a good inert, immobile marker for the purpose of measuring the transport numbers of metal and oxygen, and thus confirms the immobility of the noble gas markers used previously. The tantalum oxide originally within the holes mixes with the niobium atoms pushing their way through; these tantalum atoms then migrate outwards with the niobium atoms, but at approximately two-thirds the rate. The observed movement of the tantalum atoms thus depends on their state of aggregation within the anodic film. The experiments of Perriere et al. with oxygen isotopes can be interpreted on the basis that the oxygen order is conserved throughout the migration process     

Slag resistance of refractories in the lining of an arc steel melting furnace

The interaction of refractories of various grades with liquid slags whose samples were taken in different stages of melting from an electric furnace are investigated by wetting for temperatures ranging from 20 to 1550°C. The compositions of the slags differed in the CaO/SiO₂ proportion and the content of chromium oxide. It has been established that the olivinite refractory has advantages under the conditions of electric melting, which seems to be explainable by its chemical composition and specific pore structure. The results of the investigation were used to develop compositions of gunite powders for torch guniting of linings of the slag belt of an arc steel melting furnace. Translated from Ogneupory, No. 9, pp. 18 – 20, September, 1995.     

Melting of magnesia refractory materials in an OKB-955N ore melting furnace

Conclusions The experinece in service of the IKB-955N furnace at Magnesite Plant in melting of different magnesia materials was summarized. The influence of a number of factors, including magnesium oxide content in the charge, on the indices of the melting process, was established.The optimum diameter of decomposition of the electrodes, diameter of reaction zone, and specific surface power in the molten material were determined for the different materials.On the basis of approximation equations of the experimental data a method of approximate evaluation of the basic production parameters of the melting process was proposed.Means of increasing the productivity of ore melting furnaces by selection of the optimum diameter of decomposition of the electrodes, adjustment of the automatic system, reduction of melting time, and increasing the average input power were shown.Translated from Ogneupory, No. 1, pp. 34–38, January, 1990.