Questions related to the preparation and control of the properties of raw materials from the standpoint of structural instability are considered. It is demonstrated that the use of the technology of artificial ceramic binders for the production of fine and technical ceramics and high-alumina refractories is showing promise.With the significant growth in the production of fine ceramic articles, the requirements that are imposed on the quality of the articles have now become more exacting. In addition, reserves of high-quality natural rawmaterials is being exhausted. The presence of soluble and insoluble impurities, structural irregularities and the instability of the properties of clay stock have together made the production process more complicated and led to a growth in production rejects.In a number of cases the influence of irregularities in the crystalline lattice and structural instability may become one of the most significant factors governing the rheotechnological properties of disperse systems and aspects of the formation of articles, and as a consequence, the quality of the ceramic. The degree of ordering of the crystalline structure of clay minerals plays an exceptionally important role in the manifestation of the physico-chemical properties of these minerals [1]. Thus, for example, irregularities in the crystalline lattice of Zhuravlinolog kaolin make it unstable in casting production procedures [2].Such imperfections may be eliminated with the use of various technological techniques that involve action in a disperse medium as well as the structure and phase composition of the solid phase. Thus, with the use of thermal and mechanical activation it becomes possible to substantially alter the properties of the rawmaterials and the behavior of these materials in the production cycle as well as the characteristics of the finished articles [3].The rate of structural changes is related to the mobility of defects and in the general case is a function of stresses and temperature. Stresses may be internal, associated with the concentration basically of nonequilibrium defects, or external, arising in the course of mechanical action (grinding, kneading, etc.). Structural changes accelerate with an increase in temperature as well as under conditions defined by the action of the Rebinder and Hedwall effects [3,4]. One of the most intensive methods of affecting the structure of clay is hydrothermal treatment of the material [5,6]. This method assures rapid stabilization of structure in the course of several dozen minutes, comparable with that achieved in months and years with natural treatment. It also makes it possible to reduce by nearly 90% the energy of the interaction between the particles in the suspensions and, as a consequence, achieve a high degree of yield of the casting slip practically without the use of addition agents or electrolytes. or with only minimal quantities of such agents and electrolytes [7].Wet grinding is another excellent and well-known method of stabilization of structure. The method lea...
The techniques examined in this article for controlling the structure and properties of materials and obtaining intermediate products make it possible to standardize individual features of even low-quality raw materials and increase the quality of the final product.As a result of the disordering of the crystal structure of clay raw materials their rheological properties are unstable and the formation process is more complicated [1]. It is precisely the preparation of clay that often determines the quality of the finished ceramic product. For example, in ancient China kaolins were placed in holes in the ground to age for decades and only after this aging period were they used to produce the best porcelain in the world. In Europe the system used to prepare clay made it possible to produce tiles which have a long life time. Elements of these technologies are still used today. All techniques for preparing ceramic raw material are based on stabilizing the properties of the raw material, and hence the change in the structure and texture of the materials, or on activation processes.The technological techniques for stabilizing or activating the phases of ceramic raw materials can be divided into two groups [1]:techniques which promote the removal of excess stresses in the material, decrease of the concentration of nonequilibrium defects, and ultimately stabilization of the structure and properties of the initial raw materials; activation techniques that increase the concentration of defects with nonequilibrium structure and produce materials with high reactivity.Techniques for stabilizing clay raw materials such as natural processing, mechanical action, and treatment with steam and silicate bacteria are distinguished by a low rate of structural changes. The most effective method could become hydrothermal modification of clays, which rapidly (within several tens of minutes) stabilizes and orders the structure, yielding a structure that is comparable to that obtained after months and year of natural processing [2]. In addition, steaming makes it possible to decrease by almost an order of magnitude the interaction energy between particles in suspensions and, in consequence, obtain casting slips with high fluidity without using electrolytes and eliminate slip aging from the technological process. In this process, the outflow time and yield stresses decrease substantially (Fig. 1).The introduction of hydrothermally modified clay materials into the casting suspension results in the formation of a high-quality intermediate product and increases the density of the casting. This is confirmed by photomicrographs of dry samples, obtained from suspensions of kaolins from the Prosyanovskoe and Zhuravlinyi Log deposits, before and after hydrothermal treatment (Fig. 2).The high quality of the intermediate product containing stabilized clays allows the calcination process to proceed for uniformly and, in consequence, obtain a defect-free, dense, and strong structure in sanitary ware and technical articles.
Ceramic bricks is one of the most popular architectural finishing and structural materials. It has high efficiency and decorative properties. Expanding the raw material base of clay deposits in the production of ceramic bricks is an urgent task. In order to assess the possibility of using clays from the Sazdinsky Deposit (Aktobe region) in the production of ceramic bricks. Studies are conducted on four sections of clays from this deposit. The chemical and mineralogical composition of clays is studied, and the rational composition of raw materials is calculated. It is revealed that the studied clays have a polymineral composition, the main rock-forming minerals are kaolinite, illite and montmorillonite. According to the classification of A. I. Augustinik, the technological purposes of the studied clays are evaluated. The phase composition of samples heat-treated at different temperatures is studied. Based on the data of chemical and mineralogical composition of raw materials, technological properties of clays, physical-mechanical and operational indicators, it is established that the clays of three sites are suitable for the production of ceramic bricks by plastic molding. Phase composition of the obtained ceramic materials based on clays of four sites at a firing temperature of 1050 ° C are represented by quartz, hematite, anorthite, mullite, hematite and cristobalite. The strength of the fired samples of all clays corresponds to the brand 150-200. It is found that a more frost-resistant brick is obtained from the clays of the second section.
The production of sanitary white wares traditionally uses multicomponent mixes, which is necessitated by a whole complex of properties: high density and low humidity of molding slurries with low thixotropic strengthening and good filterability of the slurry. However, modern understanding of the structure and properties of materials open opportunities for optimization of technological process and production of higher-quality articles. The implementation of activation technologies and replacement of traditional molding slurries by artificial ceramic binders will reduce the number of components in mixes and optimize the production of white wares. Since the achievement of working performance of ceramic materials substantially depends on the phase formation processes in a material during sintering. Current work analyses the phase transformations occurring at all stages of white ware production as per proposed technology.
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