No abstract

At the present time a range of technological processes connected with heat treatment are carried out in electric furnaces with a hydrogen atomsphere.The linings of such furnaces have special demands placed on them: adequate resistance to the action of the hydrogen atmosphere at high temperatures~ minimum moistening of the hydrogen by the refractories as a result of the reduction of oxides in them, desorption, and diffusion of gases.Chemical processes and certain structural changes taking place in the refractories under the action of hydrogen and moistening of the atmosphere during reaction of hydrogen with the refractory were studied previously* [1][2][3]. On the basis of these investigations, Soviet and foreign authors recommend refractories with a high A1203 concentration for such duties. The present authors studied the behavior in hydrogen of refractories of those grades that are often used in Soviet hydrogen electric furnaces at temperatures of operation in air conditions. The technical properties and chemical compositions are shown in Table i.The factors characterizing the behavior of refractories in hydrogen atmospheres were selected as follows:the changes in the mass and linear dimensions of the specimens afte~ soaking them in hydrogen; the external appearance and compressive strength, and the phase composition.The moistening capacity of the hydrogen atmosphere on the refractory was not examined.The specimens were tested in a vacuum electric furnace SShVL-I.2.5/25 MO4 reequipped for working with hydrogen.The furnace is fitted with a temperature control system in the working region (tungsten--rhenium thermocouple TVR-229, arranged between the specimens and leading to the potentiometer), a vacuum creating system and one for measuring the depth using the ionization-thermocouple vacuum meter VIT-3, a system for feeding hydrogen and blowing inert gas, apparatus for registering the pressure (manometer TNM-PI) and gas consumption (rotameter RS-3A), and also instruments for measuring the atmospheric moisture (IG-I) oThe dimensions of the specimens were chosen on the basis of the measurements of the working zone of the furnace and the results of mechanical tests, and equaled 40 • 40 • 40 mm. Specimens had a smooth surface without scaling or cracks, and with cavities measuring not more than 5 mm; the opposite faces of the cubes were made parallel with each other.Specimens were prepared from the standard articles in lots of 7-10 items of each grade: 4-7 specimens were kept in hydrogen, and the remainder were kept as controls and tested for compressive strength.Before determining the strength the specimens were dried in air at I00-200~ for 2-10 h.

No abstract

The crucibles containing a significant amount of crystalline graphite as one of the refractory components are used in a number of induction crucible furnaces [I]. The produc tion technology of the crucibles involves maxing of the initial (raw) components, shaping the body using one technique or other, and firing [2].The composition and the dispersion of the original body, its moisture content, and the production technology of the crucibles (the mode of compaction and the firing conditions) determine the structure of the material of the crucibles and the degree of uniformity (homogeneity) throughout the volume which, in turn, determine the properties.In order to calculate the thermal and electrical parameters, to determine the main parameters of the induction crucible furnaces, and to evaluate the structuraluniformity of the crucibles, it is necessary to study the properties of the material (such as density, thermal conductivity, and electrical resistance) in different parts (zones).In view of this, we studied the properties of three types of graphite-containing crucibles. Table i gives the basic information regarding these crucibles.According to the data of x-ray structural analysis* of the specimens subjected to technological heat treatment and subsequently used for determining the property indices, the material of the TKG crucible contains graphite and silicon carbide B-SiC as the main components, the material of the TGG crucible contains graphite, ~-cristobalite, and mullite, and the material of the TGN crucible contains graphite and silicon.In order to evalaute the effect of structural nonuniformity of the material of the crucible on its properties, specimens were taken from different parts (zones) of the crucibles (Fig. i) and their thermal conductivity and electrical resistance were measured.For carrying out thermal conductivity measurements, 10-mm-thick plate-specimens in the form of squeres having a side of 85 mm were cut out parallel to the working surfaces of the crucible: from the side walls, specimens were taken in the immediate vicinity of the external surface after removing the glaze layer and from the base, specimens were taken in the regions close to the internal surface.In order to conduct the measurements of electrical resistance, specimens were cut out in the form of prisms having a cross section of I0 • i0 mm and a height of 25-30 mm in the directions perpendicular to the side wall and the base of the crucible.

No abstract