No 4 (2025)

The importance of studying ceramic materials microstructure for controlling sintering processes which provide ceramic masses required performance characteristics is shown. The scanning electron microscopy (SEM) informativity in carrying out parametric structural analysis of building materials is noted. The physical principles that ensure electron microscopy high resolution and the various optical systems characteristics used in microscopic research methods are given. The samples prepared on modern equipment with application of a conductive layer on their surface were investigated, SEM and energy dispersive spectroscopy (EDS) were carried out using a KYKY EM 6900 electron microscope. Microstructure and features of pore space of the ceramic materials based on thermal power plant fly ash have been studied. A step-by-step procedure for setting up and conducting experiments is described, including study of the matrix structure at microscope resolution different limits, study of the matrix composite nuclei pore microstructure and the sample scanned surface elemental composition. The total elements concentration of EDS spectrum of the ceramic sample based on fly ash is presented. The SEM studies results are described indicating the peculiarities of the ceramic composite matrix structure formation that is a boundary layer forming a transition zone between the matrix and the core of the composite material. Features of the nuclei pore space fiber structure formation with fibers disorderly arrangement and abundance of air spaces between them.

Relevance of the research is conditioned by the necessity of raw material base search and development in the North Caucasus for the wide range of building ceramics production – ceramic bricks, large-size lightweighted ceramic stones, wall and road clinker bricks, clinker tiles. The aim of the work was to study the Lower Cretaceous mudstones of the Republic of Ingushetia (Assa River) material composition and ceramic properties as a raw material for the various types of construction ceramics production. The research objects were the Lower Cretaceous argillites surfacing along the Assa River and the road connecting the northern and southern parts of the Republic of Ingushetia between the village of Verkhny Alkun and the Tsarkh tract. Research methods: method of rocks quantitative chemical analysis, X-ray phase studies, optical and electron microscopy, electron probe studies, which provide the possibility of wide range elemental analysis, methods for the rocks physical and mechanical properties determining; methods for conducting technological tests on the relevant technologies for the building materials and products production. The study results of the Republic of Ingushetia Lower Cretaceous argillite deposits geological structure have shown an important feature – between the argillites layers with the 10–25 cm thickness there are argillite-like clays interlayers with the 5–10 cm thickness. The argillites suitability for the wide range of construction ceramics production was found. Their chemical and mineral composition, structural features and physical and technological properties have been determined. It was found that the sintering degree is significantly influenced by grain composition of crushed mudstones. The strength of argillites-based calcined samples is characterized by a small ratio of compressive strength to bending strength – 3.3–3.5 units, which is a positive property for the ceramic materials production. The obtained data lead to conclusions that the prospect of introducing Lower Cretaceous mudstones into the demanded building ceramics production not only in the Republic of Ingushetia, but also in the whole North Caucasus.

Data on changes in the physico-mechanical properties of wall ceramics, depending on the composition of the charge: density, strength, and water absorption, have been obtained. Based on the research results, an optimal composition has been developed using ash and slag waste in a composition with alumosilicate clay raw materials – loams from the Buguruslan deposit. The effect of silica gel on changes in the structure and physico-mechanical properties of wall ceramics of the «loam – ASW» type is presented. It was found that the use of ash and slag waste in the amount of 35% makes it possible to obtain ceramic bricks with a brand strength of at least M150, with the addition of 8 % silica gel. The paper also presents the results of experimental studies to identify optimal drying modes for ceramic raw materials. The most common causes of crack formation during drying are considered, as well as measures to increase the crack resistance of manufactured products using high-quality materials. The effect of the drying time on the firing properties of products with an ash and slag waste content of 35 % by weight, depending on the drying temperature, was revealed. The dependence of the shrinkage value on the moisture level of the ceramic raw material is determined. The developed approaches will make it possible to determine the optimal technological parameters for drying ceramic raw materials based on low-melting loams and ash-containing man-made waste molded by semi-dry pressing.

In recent years, soft molding method of ceramic face bricks production has been increasingly implemented. This method allows making bricks with special decorative effects that unattainable for other molding methods, which makes the products very popular on the market. The peculiarity of this method is the molding masses increased water content in comparison with the plastic method and reduced water content in comparison with identical mass composition casting. Conventionally four soft molding bricks manufacturing technological methods can be distinguished. These are the actual manual products molding, the workpiece casting or overclocking molding method, the crushing method and the vibration forming method. For selecting raw material compositions a special approach to their molding properties assessment is required, including the additional indicators determination: the samples deformation degree, the critical compression stress, adhesiveness, as well as the elastic-plastic-viscous characteristics (plasticity, elasticity, the true relaxation period, etc.). The structural and mechanical properties are determined by the chemical and mineralogical composition and the molding masses structure. There are still few practical developments in the field of the soft molding. The article presents the study results of the clay shales and quartz sand (as leaners) effect of various grain compositions on the ceramic masses molding properties of soft molding. It has been found that for typical polymineral clays, at optimal humidity (≈ 20-25%), the clay shales or quartz sand addition of up to 50% reduce the masses critical compression stress by 20 times. It makes possible to apply soft molding various methods and create a variety of the brick front faces reliefs without increasing the water content of the molding masses.

Nowadays, more and more attention is being paid to improving the aesthetic appeal of ceramic face bricks. It is the variety of appearance that influences a consumer’s choice of a face brick particular type. Different variations of the ceramic wall materials face surface are achieved by three main technological methods, which can be easily combined in one product: relief creation on the face surface --> coloring --> shotcreting. The technology of the first two techniques is well developed, but shotcrete causes certain difficulties. The problem is the lack of colored mineral chips. Natural quartz sand, which is white or grayish in color, and some industrial waste, which is gray and black in color, is often used for shotcrete for ceramic bricks. The authors propose to produce textured colored sands on the base of opal-cristobalite rocks – gaizes by saturating them with elements-chromophores salts solutions of different concentrations with the mineralizers introduction and subsequent burning. The gaizes microporous structure promotes gaize grains coloring throughout the entire volume during firing, while the salts and mineralizers introduction promotes intensive sintering. The conducted experiments allowed to obtain colored thermolite sands of different color and grain composition, which can be used not only for ceramic bricks texturing, but also for concrete products shotcreting, decorative plaster mixtures production, mosaic polymer floors, etc.