A method for processing of secondary tungsten-and cobalt-containing materials is suggested. The optimal parameters of the processes involved and the consumption of chemicals are determined.Processing of secondary tungsten-containing raw materials, and primarily the recovery of tungsten and cobalt from worn-out drilling and cutting tools, is an urgent problem.Hydrometalurgical, pyrometallurgical, physical, and electrochemical methods for processing of tungsten3cobalt alloys of the VK type are known [135]. These processes are low-intensive, have low selectivity, and involve discharge of noxious substances (nitrogen oxides, hydrogen fluoride) into the atmosphere. The existing techniques are mainly applicable to processing of lump scrap of cutting tools, but show low efficiency in recovery of tungsten and cobalt from worn-out roller drill bits used in mining and geological prospecting. Chemical and electrochemical methods performed in melts based on alkali metal hydroxides show promise for processing of raw materials of this kind [6 312].
038ChemInform Abstract The thermally induced reaction between KBF4 and Al2O3 is investigated by TG and X-ray phase analysis. The chosen ratio of the reactants varies from 2:1 to 10:1. The first product is KAlF4, which is converted to K3AlF6. Some possible mechanisms of the reactions, which assume elimination of BF3 or of (BOF)3, are discussed. The thermogravimetric characteristics of the decomposition of KBF4 and of its reaction with Al2O3 are presented. Mixtures of KBF4 and KF are used to purify metal surfaces. Hence, the reactions investigated are of practical interest.
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Dissolution of synthetic corundum in KBF 4 3NaBF 4 melts was studied as influenced by the composition of the salt mixture and temperature. The optimal parameters of the process for removal of synthetic corundum rods from internal channels of castings were determined.A severe difficulty encountered in fabrication of gas-turbine engines is removal of ceramic rods composed of the chemically inert aluminum oxide from internal cavities in blades, which are important elements of these devices [1].At present, industry uses for this purpose the method of dissolution of these rods in molten KHF 2 [2], which has a number of disadvantages: The process is performed at a temperature at which KHF 2 rapidly decomposes, the melt aggressively acts upon the alloy of castings, the quality of cleaning of channels in precision castings does not conform to the requirements imposed, and the expenditure of KHF 2 is too high (0.53 0.7 kg for removal of a rod with a mass of 123 15 g). EXPERIMENTALMolten alkali metal tetrafluoroborates (MBF 4 ) were used in the process under consideration. It was found in experiments on removal of ceramic rods from internal cavities in turbine blades that the rod dissolution rate in this method is comparable with that in the existing technique [2]. Therefore, it was necessary to find an additive to KBF 4 that would raise the etching rate of the ceramic by a factor of no less than 233. In addition, the advantageous effect of the additive might consist in that it would raise the flowability of the molten mixture and make higher the limiting solubility of aluminum oxide, i.e., improve the reactivity of the fluoroborate melt or diminish the specific expenditure of salts for blade cleaning and simplify removal of the residue of the fluoroborate fusion cake by washing from the internal cavities in castings.The experiments were performed using the procedure described in [3,4]. The reactivity of the melts was studied on planar rectangular samples of a virtually pore-free synthetic corundum. After being treated in the melts, the samples were washed to remove reaction products by prolonged boiling in distilled water with a short-time intermediate treatment with a 10% HCl solution. The samples were dried to complete removal of moisture and then weighed. The change in the sample mass was used to calculate the specific reaction rate. The dissolution experiments were carried out using corundum rods taken from internal cavities in turbine blades quantity-produced at an aviation plant. The porosity of the rods was 15318% at a grain size of 10 314 mm. KBF 4 and NaBF 4 of chemically pure grade were used. Thermogravimetric, X-ray phase, chemical, and microscopic analyses were made.As possible additives for improving the removal of rods in a melt based on KHF 2 were tested KF
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