Petrographic methods are used to investigate concrete alumosilicate materials, produced by the Semiluki Refractory Works, on fireclay fill and an integral binder based on high-alumina cement. The microscopic investigations showed that as the result of heat treatment of concrete up to 380°C degradation processes are essentially completed in the binding substance, and formation of a glass phase, mullitization, and binder penetration into the fireclay fill are observed in samples calcined at 1000°C. After calcination the phase composition of the binder obtained from synthetic materials is similar to the composition of the clay binder used in conventional fireclay calcination materials.Alumosilicate fireclay refractories (the system Al 2 O 3 -SiO 2 ) are usually obtained by high temperature calcination of a grainy mixture of precalcined refractory clay or kaolin (fireclay) and plastic refractory clay. Most kaolins and refractory clays are kaolinite rocks whose main mineral component is hydrated silicon dioxide alumina -kaolinite and minerals come close to it, with the general formulaInvestigation of the solid phase of fireclay refractories showed that it consists of a mixture of mullite 3Al 2 O 3 × 2SiO 2 and crystalline modifications of silicacristobalite, tridimite, and quartz -products of the thermal regeneration of kaolinite in the process of technological calcination of the refractory [3]:The formation of the phase composition of fireclay material in the calcination process can be represented as follows.The kaolinite of the clay binder decomposes, on heating to 500 -600°C, with chemically bound water being released and after dehydration it exists, in the opinion of a number of investigators, in the form of the metakaolinite Al 2 O 3 -2SiO 2 up to the optimum temperature 800 -900°C [1] or it decomposes on dehydration into Al 2 O 3 and SiO 2 , present in a state of interpenetration [2].At a temperature of about 920 -940°C polymorphic transformations of amorphous alumina and formation of hidden crystalline mullite occur. At higher temperatures calcination of material begins as result of the appearance of a liquid phase (as a result the melting of the low-melting impurity minerals) and the interaction of impurities with the decomposition products of kaolinite -silica and alumina. At the same time, needle-shaped crystals of mullite grow and amorphous silica which is not bound in mullite transforms into cristobalite.The final calcination temperature of fireclay refractories usually is in the range 1350 -1400°C. At this temperature the crystallization of mullite in the form of individual crystals 2 -5 mm in size is completed and their clusters in a glassy, weakly crystallized (amorphous), substance containing silica and a negligible amount of flux. This is, in fact, the binding substance of conventional fireclay refractories.Fireclay refractory articles contain 35 -50% mullite and 50 -60% (by volume) and alumosilicate glass. Mullite is the predominant mineral and the carrier of the main properties of the refractory [4]...
When a lining consisting of large refractory parts is put into a working regime, it is important to know the increase in the temperature of the material in order to determine the assembly gaps and be confident that fracture as a result of structural transformations will not occur during operation when the temperature gradient over the thickness of a part increases. Comparative studies of the thermophysical properties of conventional fired fireclay materials (tamped beam for the bottom of the melt tank, semi-dry pressed ShSU beam) and low-cement concrete materials with VShS fireclay filler have been performed at the Semiluki Refractory Works. The materials BShBS and VShBO showed negligible change of the CLTE with increasing temperature in the operating range 600 -1300°C.There are indisputable advantages to using refractory concrete parts in the lining of commercial high-productivity furnaces for producing glass. First and foremost, these are great freedom in designing parts with different shapes and sizes, fewer seams in the refractory masonry because large beams are used, mechanization, and continuity of the assembly of the lining as a result of the accuracy of the geometric dimensions of even the largest parts.In spite of all this, however, the main user problem, which, as a rule, arises because of the properties of the binding system of composite materials such as low-cement concrete, is obtaining the correct setting of the apparatus governing the heat -moisture regime when a lining made of unfired concrete parts is put into and taken out of the working regime, since the heat-treatment temperature for such parts at the manufacturer does not exceed 400°C.Characteristically, when a refractory material is heated its volume changes: a temporary change, which vanishes on cooling, as a result of the thermal expansion of the material and a residual change which occurs as a result of chemical and physical transformations and, as a rule, happens when the operating temperature of the material is higher than the firing temperature of the material or when during firing of the part the required holding time at maximum temperature was not reached. The character of the volume changes depends on the nature of the refractory material. Thus, positive growth is characteristic for dinas-clay parts and negative growth is characteristic for fireclay parts.When equipment lined with large parts, such as the bottom beam in a glass-making furnace and the beam for the lining at the bottom of the tin melt tank, is put into a working temperature regime, it is very important to know the growth indicator for the material in all directions in order to determine the assembly gaps and be confident that the masonry will not fail as a result of structural transformations during operation with an increase of the temperature gradient over the thickness of the part. Conventionally, such parts have been made of fireclay by manual tamping or semi-dry pressing followed by firing up to a temperature of at least 1300°C.For refractory parts to be used in ...
Composition optimization and the areas of application of uncalcined refractory concretes dictate the need to study the structure-formation processes occurring in these concretes as temperature increases to the operational level. Methods for using IR spectroscopy to study structure-formation processes in refractory aluminosilicate concretes are examined.
Comprehensive studies of the phase composition of refractory concrete compositions heat-treated in different temperature intervals, including the operating range of glassmaking equipment, have been performed. The characteristic changes of the phase composition of unsintered concretes during the transformative heat-treatment have been established; a new phase appears after sintering at 1000°C -calcium aluminosilicate 2CaO × Al 2 O 3 × SiO 2 , which attests to the interaction in the sample of calcium aluminates with free silicamicrosilica or aluminosilicates.
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