T. V. Vakalova

Caky character and plasticity of refractory clays from the Troshkovo deposit

A model is developed to represent the structure of the mineral component of Troshkovo refractory clays. According to it, a refractory clay particle is an aggregate composed of a crystalline core and an amorphized film around it. Such refractory clays owe their caky character to the colloidal mineral shells that bond the particles into strong aggregates. Mechanical working breaks up the aggregates into a finely divided material and improves the plastic and bonding properties of kaolinite clays.

A new raw material for aluminosilicate ceramics for refractory and engineering use

Topaz-containing raw materials from the Kopna deposit are analyzed for chemical and mineral composition. Beneficiated rocks with different contents of topaz and topaz concentrates are classified as commercially promising for the manufacture of aluminosilicate refractories such as heat insulators and general-purpose products. The role of topaz in the quality improvement of clay-topaz compositions and processes of sintering and phase formation is discussed.

Argillaceous Materials in the Siberian Region

The results of integrated studies of argillaceous materials of the Siberian Region are considered and recommendations are issued for evaluation of the quality of materials, which make it possible to identify the means of control of the main technological properties of argillaceous rocks with the aim of bringing then to the required level.

Alumosilicate ceramic proppants based on natural refractory raw materials

The sintering-strengthening effect of the additions of the highly ferrous bauxite (with Fe2O3 content of 20-25 % in the calcined state) in the compositions with refractory clays was established. It was found that in the temperature range 1350-1500°C the additions of bauxite in amounts of 10-40% have a fluxing effect due to the iron oxide introduced with bauxite in compositions with clay. An increasing the bauxite additive in the amount of 50-70% ensures its strengthening effect by increasing the total content of the mullite of the prismatic habit in the firing products of composites with clay. Preliminary clay and bauxite calcination at 900 °C and an increase in the content of bauxite additive up to 50-70% in compositions with clay allow to produce aluminosilicate proppants with a bulk density of 1.62-1.65 g/cm3 and compressive strength up to 52 MPa.

Heat-Insulating Ceramics which Have a Nanoporous Structure and are Made with the Use of Ash-Bearing Wastes from Power Plants

It is determined that the pore-forming effect exhibited by ash and ash microspheres in compositions with clayey rocks is due not only to certain structural features (the presence of spherical hollow particles) and the makeup of the ash components (the presence of residual fuel in the ash) but also to physico-chemical processes (the synthesis of anorthite and mullite) which take place in clay – ash-and-clay – ash- microsphere systems and prevent shrinkage during sintering.

Physico-Chemical Features of the Synthesis of Mullite in Mixtures of Quartz-Pyrophyllite Rock with a Fluoride-Forming Component

It is established that the use of an ammonium fluoride treatment on quartz-pyrophyllite rock (45% pyrophyllite and 53% quartz) at 650°C changes the traditional mechanism by which mullite is synthesized; it is formed not from metapyrophyllite but from fluoridated pyrophyllite, with the formation of aluminum trifluoride and topaz being intermediate stages of the synthesis process. The optimum ratio of quartzpyrophyllite rock to ammonium hydrodifluoride is 1:1.6, which at 1300°C increases the yield of acicular mullite (with particles 20 – 30 μm long and 3 – 5 μm in cross section) from 12 to 68 wt.%. The content of residual quartz in the mullite is no greater than 15 – 18 wt.%.

Refractory ceramics for aluminum electrolyzes based on clay raw material

The results of integrated studies of clay raw material of the Siberian Region are considered and recommendations are issued for evaluation of the quality of materials, which make it possible to identify the means of control of the main technological properties of clay rocks with the aim of bringing then to the required level. The results of developing compositions and technologies for barrier materials based on the products of concentration of refractory clay for cathode lining in aluminum electrolyzes are described. High-density dry barrier mixtures with different Al2O3-SiO2 ratios (from 0.42 to 0.76) have been obtained, which can be used in two-layer linings for aluminum electrolyzers (in the high-alumina and silica layers).

Influence of kaolin ignition temperature changes on the strength qualities of proppants

The article describes investigation of the influence of kaolin ignition temperature of 900°C, 980°C and 1100°C on the strength of proppants. It was established that the ignition temperature of kaolin has a significant influence on the strength of the proppant. It was revealed that the ignition of kaolin at a temperature of 980°C and higher temeperatures causes the appearance of poorly crystallized defective mullite - imperfection of the crystal structure. The presence of defective mullite activates the sintering process (consolidation and hardening) of proppant granules, which provides a proppant with higher strength at the same temperatures (1450°C). In this case the active crystallization of cristobalite from the melt during the sintering roasting reduces the total amount of glass phase in the material, which in its turn is beneficial to increase the strength of the proppants.

Structural-Phase Transformations in Firing of a New Ceramic Material: Topaz-Bearing Rock

The specifics of the chemicomineralogical composition of the topaz-bearing raw material from the Kopna deposit and the phase-formation process in thermal treatment of topaz-bearing rocks with different ratios between the topaz and quartz components are considered. The expedience of using this material in the technology of refractory and engineering aluminosilicate ceramics is established. Owing to the good reinforcing properties, the needle-shaped and filament mullite formed in decomposition of topaz can be used in various composite materials based on glass, ceramics, polymers, etc.

Specifics of Phase Formation in Refractory Clay in the Presence of Topaz

The processes of phase formation in refractory clay in the presence of topaz-bearing rock additives are investigated. It is established that the effect of topaz proper is determined by its quantity. Topaz in low quantities (up to 0.5 – 1.0%) intensifies the formation of primary and secondary mullite of prismatic habitus, lowers the temperature of mullite synthesis, and improves the mullite structure. An increase in the topaz content over 25% is accompanied by the formation of mullite of needle-shaped habitus, in addition to prismatic mullite.