Data are provided for laboratory studies of the resistance of aluminosilicate refractories to the action of commercial electrolyte. It is established that refractory ShPD M -45, prepared using a mullite-corundum chamotte, is most resistant to electrolyte action. Results are provided for studies in the change of mineral composition and phase transformations in aluminosilicate refractories during reaction with commercial electrolyte. It is shown that long-prismatic titanium-containing mullite is more resistant to the action of the fluoride ion than short-prismatic material.The service life of an aluminum electrolyzer is mainly governed by the resistance of refractory linings of the cathode assembly to the action of an incoming corrosive medium. There is information about tests of refractory materials for cryolite resistance. Different test procedures, their characteristics and comparisons are provided in [1,2].Data from laboratory studies are provided in this article for the resistance of aluminosilicate refractories ShA-5, ShPD-43 and ShPD M -45 [3] to the action of a commercial electrolyte with a cryolite ratio (c.r.) of 2.4. Tests were performed by a petrographic method in reflected and transmitted light in MBI-6 and MIN-8 microscopes respectively. The resistance of aluminosilicate refractories in contact with molten commercial electrolyte was determined with a steady-state method by heating test articles in a Tamman furnace followed by a study of the change in mineral and phase composition of the refractories. Cylindrical holes of identical diameter and depth were made in articles, and they were filled with a uniform amount of commercial electrolyte with c.r. of 2.4 containing, apart from the main components, calcium and magnesium fluorides. The prepared samples were placed in a hermetically sealed alundum crucible and heated in a Tamman furnace to 1000°C with isothermal soaking at 1000°C for 1 h. Cooling took place in the furnace.After testing refractory specimens changed in color. At the surface of specimens from the side of the opening reaction zones were seen in the form of concentric circles of different color. The diameter of the original hole increased (Fig. 1), and its relative increase for specimens of ShA-5, ShPD-43, and ShPD M -45 was 47.5, 33.3 and 16.1% respectively.A specimen of ShA-5 after testing had a dingy lilac color. Over its surface (at the top of the hole and over the side) glassy new formations were seen in the form of circles with a diameter of 4 mm and leakages from the direction of the depression (hole), i.e. coarse pores with a diameter of 1.0 -1.5 mm. The electrolyte was converted into glass. With separation over the length of the depression two zones seen: a working zone 5 -10 mm thick of green color, and a glassy and transition zone yellow in color. The base of the specimen was the least changed zone (Fig. 2a ).A specimen of ShPD-43 after testing had a gray color. At its surface from the direction of the hole in the form of circles there was a working zone green in color and then t...

The discovel 3, in 196 7 The application of SkIS processes for obtaining chromized coatings is based on the use of exothermic mixtures. The SHS consists in very intense exothermic interaction of chemical elements in condensed phase suitable for spontaneous propagation in the form of a combustion wave [I]. Enhancing the strength of material by SHS was carried out in the regime of combustion as well as in the regime of thermal self-ignition.The experiments were carried out with mild steel and steels with different carbon content ( Table 1). The microstructure of the hardened layers was investigated under an optical microscope Neophot-21. Phase analysis was carried out on an x-ray diffractometer Dron-2 and an x-ray microanalyzer Jeol Superprobe-733. Microhardness was measured on an instrument PMT-3 with a load of 1 N on the indentor.Thermoclaemical treatment (TCT) of the steels was carried out in an open-type reactor with an inert gas, viz., argon, blown through. The saturating medium was a mixture of powdered aluminum, aluminum oxide, trioxydichrome, metallic iodine. Saturation in the regime of combustion was initiated with the aid of an exothermic pellet or an electric coil. The combustion wave moved at a speed of 10 .3 m/sec. In distinction to the known chromizing methods [2] coating by SHS proceeds under nonisothermal conditions where chemical transport reactions play a considerable role. Such reactions occur on account of gas carriers in powder mixtures when there is a temperature gradient. Chemical transport in a combustion wave is possible because the combustion process entails a successive change of the thermal regimes. That means that at each point of the mixture the temperature changes from the initial value to the combustion temperature.On the basis of an analysis of the reactions accompanying the combustion of SHS mixtures, and also of the results of experiments and of metallographic investigations, we obtained a picture of the formation of a chromized layer in the regime of combustion. This process can be divided into three stages.Stage 1 is the heating of the object after the combustion front has passed through the charge; at that a coating does not form. On the object an unreacted layer forms, it is about 1 mm thick which is equal to the width of the heated zone. Iodine vapors diffuse from the charge into this layer. The iodine vapors react with the chromium reduced from the trioxydichrome, forming chromium iodine Crl 2.Stage 2 comprises the decomposition of CrI and deposition of chromium on the surface. The subsequent rise of the temperature leads to the formation of a modest diffusion zone. At that instant concentration of active chromium atoms on the surface is high. The high chenaical potential due to the concentration gradient dc/dx causes the formation of a diffusion layer which consists of the phase (Cr, Fe)7C 3, Calculations show that a layer with thickness of the order of 10 p,m forms.

Comparative analysis is provided for the structure and properties of aluminosilicate refractories grade ShPD. It is established that refractory ShPD M -45, produced with the use of an addition of mullite-corundum chamotte surpasses in all characteristics refractories prepared by the normal technology. Refractory ShPD M -45 may be recommended for use in aluminum electrolyzers.The service life of the lining of the cathode assembly of an aluminum electrolyzer is an important engineering parameter. In order to avoid penetration of subsidiary products of an electrolyzer into the lining a refractory layer is laid down under hearth blocks of the electrolyzer. Sodium vapor and fluorine compounds, diffusing into the refractory layer, lead to a change in its chemical-mineral and phase compositions and destruction of the refractory itself, as for the cathode lining of the aluminum electrolyzer as a whole, and therefore the question of selecting the grade of refractory remains important.There is currently use of aluminosilicate refractories for the refractory layer. The chemical and phase composition of chamotte refractories is determined by the raw material composition and properties. In turn the properties of the aluminosilicate articles depend not only on the Al 2 O 3 content within them, but also on the overall total sum of fluxes and often on their chemical nature [1]. The degree of mullitization, the composition of mullite, and the glassy phase in chamotte refractories, depend on the properties of the original raw material, firing temperature and duration.Properties are provided in the present communication for the characteristics and phase composition of chamotte dense articles of ShPD produced by traditional technology (ShPD-43), and with the use of addition of mullite-corundum chamotte (ShPD M -45). Studies were carried out petrographically in reflected and transmitted light in microscopes MBI-6 and MN-8 respectively. Articles made of ShPD M -45 with addition of mullite-corundum chamotte in production properties and phase composition somewhat exceed those for articles made of ShPD-43 prepared by normal technology. The physicochemical indices of ShPD, prepared by both production methods, are provided in Table 1.The average apparent density of specimens of the corresponding type of refractory was determined by hydrostatic weighing. Open porosity of ShPD M -45 articles was lower by a factor of 1.5, and the average density was higher by a factor of 1.1 than for articles without mullite-corundum chamotte. Since open porosity is connected with the nature of pores,

The compositions of glasses formed in the process of operation of an aluminum electrolyzer, the lowest content of aluminum at which the glass is separated into aluminosilicate and oxyfluoride components, and the temperatures of softening and of formation of drops of titanium-bearing glasses composition close to the glass in ShPD-45 refractory (with an additive of mullite-corundum chamotte) are determined. It is shown that the oxyfluoride glasses consist of both a silica skeleton and a corundum skeleton. The titanium-bearing glass phase can hinder penetration of aggressive gaseous byproducts of electrolysis.It is reported that the glass phase formed in operation of an aluminum electrolyzer plays a protective role. In accordance with the data of [1, 2] a high-viscosity vitreous mass based on albite is capable of hindering the penetration of electrolyte components into the lower layers of a lining. The exact chemical composition of the amorphous vitreous phase has not been determined [2]. It is only known that its primary component is silicon dioxide. It has been shown [3 -6] that the glass phase has a variable composition and is chiefly represented by oxyfluoride and aluminosilicate glasses. However, the element composition of the glass phase has not been determined.In the present study we made an attempt to decipher the glasses formed in the process of operation of an aluminum electrolyzer. We performed the study by the petrographic method in reflected and transmitted light using MBI-6 and MIN-8 microscopes. It is known that glass is an amorphous substance that cannot be deciphered by the method of x-ray diffraction analysis. For a chemical analysis we took samples of glasses with various refractive indexes under a binocular lens.The element composition of the common vitreous phase in ShA-5 refractories after service is as follows (in mass percent): 20.1 Sitot, 16.9 Altot, 8.86 Na, and 12.2 F. The density of this phase as determined by the method of hydrostatic weighing amounts to 2.37 g/cm 3 . It has also been determined that the prevailing kind of glass in the refractory layer after operation of an aluminum electrolyzer has an oxyfluoride composition consisting of (in mass percent) 3.92 Al, 20.65 Si, and 8.48 F at N = 1.33. Samples with a low total content of elemental silicon (due to its removal) are characterized by the presence of oxyfluoride glass with N = 1.362 and the following composition (in mass percent): 17 Al, 18.91 Na, 10.62 F, and traces of Si. Thus, the data of chemical and crystallographic analyses show that the oxyfluoride glasses consist of both a silica skeleton and a corundum skeleton.The authors of [5,7] have observed immiscibility of the oxyfluoride and aluminosilicate glasses. They detected pure aluminosilicate glass with N = 1.521 (nepheline glass with N = 1.51) containing 17.15% Al and 31.54% Si in a refractory layer. It was interesting to determine the critical content of aluminum at which the glasses separate into oxyfluoride and aluminosilicate components. An analysis of the glass phas...