The powders of electrical-engineering periclase obtained from natural brucite mainly meet the specifications of the second and the third classes according to GOST 13236-83. The reason for the poor quality of the powders is their high calcium oxide content and this owes to its presence in large quantities in the original brucite (exceeds 2.0~ in the calcined substance). This fact made it necessary to carry out additional and more detailed studies on the properties of the periclase powders having a high calcium oxide content.Moisture (water) absorption is one of the most important parameters determining the service characteristics of the periclase powders in TEN [i, 2]. Calcium oxide has a considerable hydration ability [3] and, consequently, it can make periclase powders highly prone to moisture absorption.It was established [4] that the change in the weight content of calcium oxide in a periclase powder from 0.75 up to 2.20~ does not have a significant effect on its moisture absorption. We note that in these experimental powders, calcium oxide was present in the form of silicate compounds.However, in periclase powders, calcium oxide can be present in free state (besides calcium silicates).This paper deals with a study of the aspects concerning the hydration activity of a periclase powder, pure magnesium and calcium oxides, and the calcium-containing compounds present in periclase in the form of additional (impurity) phases. Imported periclase powders were also studied for the purpose of comparison.The granulometric composition of the experimental periclase powders that were obtained from brucite met the specifications concerning the 'fine grade' according to GOST 13236-83. Pure magnesium and calcium oxides and silicate compounds (monticellite CaO'MgO'SiO 2, mervinite 3CaO-MgO'2SiO2, and dicalcium silicate 2CaO'SiOe) had a grain (particle) size less than 0.063 mm.The powders were calcined at 1000~ and were held in the medium of air having a humidity of 97-98~ at 20-25~The duration of holding varied from i up to 50 days. Hydration activity of the powders was evaluated on the basis of the change in their weight during calcination at 1000~In view of the fact that the processes of moisture adsorption and subsequent hydration occur mainly at the surface of the grains, it is necessary to take the specific surface of the powders into account. The data presented in Table I show that the powders of calcium and magnesium oxides and the impurity-phase are characterized by uncomparable (widely differing) values of the specific surface. Therefore, in order to evaluate their hydration activity, we used the parameter of weight change during calcination (recalculated) per unit surface area (Table 2).It was established that the hydration activity (ability to hydrate) of calcium oxide exceeds that of magnesium oxide by approximately 8 times. Monticellite, mervinite, and dicalcium silicate hydrate very strongly as compared to pure calcium oxide.Thus, calcium oxide present in the periclase powders in free state must have a signific...

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Exhaustion of deposits of ore and nonore minerals, the increase in costs for mineral raw materials, and increasing ecological problems have created an increasing interest in recent years in secondary resources, composite processing of raw material, and the development and introduction of low-waste and waste-free methods.The use of secondary resources makes it possible to solve problems of providing raw materials, to reduce costs for their extraction and processing, and to reduce industrial discharges into the atmosphere and hydrosphere. In addition, processing of spent materials accelerates recultivation of disturbed lands and return of them to agriculture. These are obvious advantages of use of secondary resources.For production of refractories there is interest in metallurgical industry wastes, particularly in slags formed in production of ferroalloys, which at present in many plants are shipped to the slag dump.We will present the results of a technical, economic, and ecological evaluation of methods of production of periclase-spinellide-forsterite refractories with use of magnesiasilicate slags of Serov Ferroalloy Plant, of production of high-alumina cement and dry concrete mixtues and compounds from Klyuchevsk Ferroalloy Plant, and of production of periclasechromite unfired ladle parts with use of steel plat refractory scrap.The slags formed in melting of high-carbon ferrochrome at Serov Ferroalloy Plant have a magnesia-silicate composition and include forsterite (65%), aluminomagnesia spinel (24%), glassy phase of melilite composition (5%), and ferrochrome (6%). The refractoriness of the slags is 1700~This indicates the desirability of their use as raw material for magnesia refractories [i].In Eastern Refractory Institute a method of production of periclase-spinellide-forsterite (PShF) parts, forsterite-spinellide (FSh) refractories, and unfired periclase-spinellide (PShBS) and forsterite-spinellide (FShBS) nozzles and inserts ((PShBV, FShBV) has been developed [2,3]. The experimental lots of PShF parts were produced at Panteleimonovka Refractory Plant.Tests of PShF parts in the lining of an anodic furnace of Kyshtym Electrolytic Copper Plant showed life of them equal to that of chromite-periclase parts. Forsterite-spinellide refractories (FSh) and steel pouring nozzles (FShBS) were prepared at Magnesite Compound using high-carbon ferrochrome slag with addition of sintered periclase powder to eliminate the negative influence of the glassy phase of the slag. Therefore the positive results of tests of forsterite-spinellide parts with use of Serov Ferroalloy Plant magnesia-silicate slags in different steel production equipment indicates that the refractories developed are at least as good as chromite-periclase parts and in a number of cases exceed them in life.All-Union Refractory Institute.

One of the indices for evaluating the quality of GOST 13236-73 electrical periclase is the particle-size composition [i]. The standard covers production of two types of periclase, "fine" and "coarse," differing in the ratio of the fractions. The periclase produced by foreign firms differs significantly in particle-size composition from domestic.* A comparative analysis of the periclase produced by firms in Japan, West Germany, and England shows that its particle-size composition is close to the requirements of GOST 13236-73 for the "fine" type (Table i).In investigations conducted earlier the influence of the particle-size composition of periclase on its electrical resistance was studied. However, attempts to find a correlation relationship between particle-size composition, electrical resistance, and dielectric strength did not lead to any conclusion, The statistically treated lots were obtained from different raw materials and differed in chemical composition, To reveal the influence of particle-size composition among a large number of relationships was impossible.In Eastern Refractory Institute an investigation has been made of the influence of particle-size composition on the electrical resistance of periclase with the use of methods of experiment planning. For the investigation periclase of a single lot but differing in fraction in accordance with GOST 13236-73 was taken, The influence of the content of fractions coarser than 0.4, 0,25, 0.16, 0,063, and 0,04 mm and finer than 0.04 mm was studied. Since 6 the weight portions of the fractions are not independent values (~=I), methods for investii=J gating multicomponent mixtures similar to those presented in [2] were used, A simplex-lattice plan of the second order was taken as the experiment plan. In accordance with the matrix of this plan periclase samples of individual fractions and combinations of them were prepared and the electrical resistance at 600, 800, and 1000~ was determined.The highest values of electrical resistance were obtained for compositions containing the fractions from 0.4 to 0.063 mm. Compositions of fractions finer than 0.063 mm are characterized by lower values of electrical resistances. This may be explained by the content in the fine fractions of a large quantity of iron and calcium oxide impurities, which have a negative influence on the electrical resistance of periclase,

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