The objective of this work was to study two-step sintering as a means of controlling the microstructure of coarse Al2O3 matrix composites containing submicrometric and nanometric inclusions of ZrO2 ranging from 0-30 wt. % by weight based on commercially available powders and evaluate its hydrothermal degradation as function of a water vapour pressure and its mechanical properties. The results showed that two-step sintering allowed a more efficient microstructural control than single-step sintering, resulting in good mechanical properties. The highest flexural strength was achieved for ZTA samples sintered in two-stage sintering conditions TSS2 with T1 = 1560 degrees C for 3 h, T2 = 1460 degrees C for 8 h. The studied composites showed good resistance to hydrothermal degradation compared to composites sintered in single step sintering conditions.

The research is relevant due to the need for the integrated use of magnesium materials, including mining waste. During the extraction of magnesia raw materials, as a refractory and strategic material, in some deposits the accompanying material is hydromagnesite rock, which is not used in classical magnesia technology. Simultaneously, it has characteristics that make it possible to obtain important products: fire retardants for various materials, a porous component in fire-resistant coatings, a feedstock for creating waterproof magnesia binders.The aim of the research is to determine the possibility and conditions of using the hydromagnesia formation of the Khalilovskoe field as a feedstock for obtaining water solution of magnesium bicarbonate - a mixing liquid of a waterproof magnesia binder.Materials: hydromagnesite rock accompanying magnesite of the cryptocrystalline structure of the Khalilovskoe deposit, Orenburg region. The studied rock consists of hydrocarbonate minerals: hydromagnesite, deepingite, nesvigonite, as well as admixture of clinochrysotile. The bicarbonate composition does not allow its use for molded fired magnesia products.Methods. The method of thermal activation of hydromagnesite rock makes it possible to produce a highly reactive defect structure; obtaining a solution of magnesium bicarbonate by artificial carbonization of a suspension of activated hydromagnesite material; thermal research methods - differential scanning calorimetry, thermogravimetry; X-ray phase analysis; titrometric method for determining the concentration of bicarbonate ions.Results. The possibility of using hydromagnesite formation to obtain water solution of magnesium bicarbonate with the bicarbonate ion concentration of up to 38 g/l was determined; the efficiency of heat treatment of hydromagnesites in the temperature range of 300-375 degrees C was established, that allows obtaining a highly defective product xMgCO(3)center dot yMg(OH)(2); thermal activation of hydromagnesites increases the efficiency of the transition of bicarbonate ions and magnesium cations into solution in the presence of CO2 at the low pressure of 0,2 MPa of the carbonization process; water solution of magnesium bicarbonate with high concentration of bicarbonate ions obtained at the low pressure of CO2 gas will make it possible to create hydraulic magnesia binders with high water resistance.

This study describes the synthesis of ceramics, in which a micrometre-sized Al2O3-ZrO2 nanopowder was used as an oxide base for the hardening of the materials. To a suspension of this mixed metal oxide, the pore-forming crystallisation additives camphor and carbamide were added to produce ceramics with thin permeable pores. Camphor crystallised in the oxide suspension in the form of single pentagonal stars and ?arbamide crystallised in the form of thin elongated needles. The use of the different crystallisation additives allowed the formation of ceramics after sintering that have both permeable and complex pore morphologies, where anisotropic properties were observed using carbamide as an additive but not when camphor was used. The total porosity of the resulting ceramics was 51.3%, with a compressive strength in the range of 17.3-92.3 MPa.

The effects of the ZrO2 content and the particle size of ZrO2 powders on the microstructure, phase composition, physical and mechanical properties, and the abrasion wear resistance of advanced Al2O3 ceramics and zirconiatoughened alumina (ZTA) composites containing 0 to 30 mass% yttria-stabilised zirconia (YSZ) were investigated. The composite with a ZTA content of 30 mass% of ZrO2 exhibited the greatest resistance to abrasion wear. alpha-Al2O3 reflex broadening (hid = 113) as a result of the microstresses in the Al2O3 crystal lattice during sandblasting decreased with increasing ZrO2 amount, where the ZrO2 particles located along the grain boundaries of Al2O3, hindering their growth and deformation. The use of nanodispersed ZrO2 powder produced by the plasma chemical technique led to a 1.5-fold increase in wear resistance in the resultant ZTA ceramic.

Results are provided for development of porous ceramic materials based on cordierite. The pore forming agents used are wood waste and carbamide in crystalline form. Analysis of the pore structure shows that all specimens have a complex pore space structure with a considerable number of elongated connected pores. The best porosity parameters are achieved using an organic crystalline pore former. It is shown that nano-dispersed aluminum metal has a strengthening effect during porous ceramic sintering. An organic clay suspension improves cordierite powder sintering capacity and leads to formation of additional nano- and micro-pores.

A fractional (rational) chemical analytical method is proposed by which the material composition of clay rocks can be quantified and the clay-forming minerals present can be characterised. Subjecting raw clay to this procedure allows for the determination of the chemical composition of its fine-grained fraction, the amount and composition of exchangeable cations, water-soluble salts, carbonates and colloidal minerals, and the amount of amorphous silica and free quartz. A new, effective method is proposed for the qualitative and quantitative evaluation of the amorphous component in clays. This involves extracting colloids by treating the clay fractions with Tamm's reagent, a buffer solution of oxalic acid and ammonium oxalate with a pH of 3.25. Additionally, through calculations based on the results of chemical analyses, the illite content (derived from the content of non-exchangeable potassium oxide) and the chemical composition of the clay residue are determined. This enables the rock-forming clay mineral to be characterised and its structural chemical formula to be determined. This allows prediction of the physico-chemical and technological properties of the clay.

The results of studying the effect of modifying additives LiF, ZnO, Ce 2 O 3 on the synthesis and properties of cordieritomullite ceramics from Kazakhstan raw materials are presented. It has been established that the additions of LiF, ZnO, and Ce 2 O 3 contribute to the activation of the synthesis of cordieritomullite ceramics based on natural raw materials. The addition of LiF reduces the temperature of the onset of the appearance of the eutectic melt, which contributes to the intensification of cordierite formation, and ZnO and Ce 2 O 3 act on a solid-phase mechanism. The addition of LiF, ZnO, and Ce 2 O 3 additives to the composition of cordieritommullite ceramics in the amount of 0,5‒2,0 % has made it possible to lower the temperature of its calcination and to increase the density, strength, chemical and thermal stability. Ill. 6. Ref. 11. Tab. 3.

The possibility is demonstrated of preparing porous ceramic based on zirconium dioxide micro- and nanopowder using crystallization of carbamide in a suspension. Different suspension cooling regimes are studied for oxide powders (in air, in a freezing chamber, in snow). It is shown that sintered ceramic porosity and pore size depend directly on suspension composition and cooling method. As a result of this ceramic is prepared with porosity of 30 – 60% with pore diameter of 0.2 – 200 μm.

The influence of additives of rare earth elements on the crystallization and properties of glassceramic materials such as coatings for metal crowns in prosthetic dentistry was studied. A material for coatings was synthesized from a mixture based on potassium feldspar with the addition of oxides of alkali metals in the form of carbonates and fluorides as well as salts and oxides of rare earth elements. The additives of rare earth elements were introduced to give the coatings natural color. It was shown that the additives influence both the color and the phase composition of a coating by impeding crystallization. Upon the increase in the content of additives by more than 0.5 wt %, the thermal expansion coefficient of glass-ceramic materials increases.

Results are given for a study of the effect of LiF, ZnO, and Ce2O3 modifying additions on synthesis and properties of cordierite-mullite ceramic from Kazakhstan resources. It is established that addition of LiF, ZnO, and Ce2O3 facilitates activation of synthesis for cordierite-mullite ceramic based on natural raw material. Addition of LiF reduces the temperature for the start of eutectic melt development, facilitating intensification of cordierite formation, and ZnO and Ce2O3 act by a solid-phase mechanism. Introduction of LiF, ZnO, and Ce2O3 into the composition of cordierite-mullite ceramic in an amount of 0.5 – 2.0% makes it possible to reduce its firing temperature and increase density, strength, and chemical and thermal stability.

The work presents the study of a ceramic material that would provide a satisfactory bond of the commercially available ceramics to Titanid alloy. Polished sections of Titanid alloy and ceramics supplied by various manufacturers were examined. The desired intermediate opaquer layer was fabricated from the following raw ingredients: potassium feldspar originating from Krasnoyarsk deposit and chemically pure barium oxide BaO, sodium carbonate Na2CO3, zinc oxide ZnO, hydroxyapatite Ca5(PO4)3(OH), and titanium oxide TiO2. The adhesion strength of Triceram dental ceramic to Titanid alloy with the use of the transitional ceramic opaquer appeared to be fairly high and ranged from 35 to 45 MPa.

The possibility of using tape casting to produce solid electrolyte films with a thickness of 100–300 μm from zirconia stabilized with oxides of scandium and cerium is considered. A method of slip casting onto a moving tape is used to produce rather thin ceramic sheets with a thickness of less than 1 mm. An organic slip based on azeotropic mixture of isopropyl alcohol and methyl ethyl ketone is used in the present work. The effect of solvents on the properties of the obtained film and sintered ceramic is analyzed. Dibutylphthalate, polyethylene glycol, and benzyl butylphthalate are used as plasticizers. The effectiveness of these plasticizers is based on the possibility of producing a slip with a viscosity of 2000–4000 mPa s by using them. Polyvinyl butyral appears to be the most optimal temporary binder, because it is satisfactorily removed in a continuous mode of annealing of plated ceramic blanks. The maximum density of ceramic plates is achieved at the annealing temperature of 1500°C. It is shown that the working range of the obtained solid electrolyte is 800–850°C, as the maximum ionic conductivity (more than 0.15 Ω−1 cm−1) is registered in it.

It was established that pore-forming effect of both fuel ash and ashy microspheres on clay rocks compounds is caused both by the structural features (the presence of the spherical shaped hollow particles), the ashy component composition, and the physical and chemical processes taking place in the clay ash and clay ashy microspheres systems, the latter processes preventing the shrinkage on sintering (owing to the anorthite and mullite synthesis occurring with molar volume increasing). Ill. 6. Ref. 14. Tab. 2.

The experimental studies were carried out for the influence of the dry axial compression process' parameters on the physical and mechanical properties of the composite ceramic material ZTA (Al 2 O 3 – ZrO 2 , ZrO 2 > 20 mass percent) with various nanosized ZrO 2 powder content (within the range of 0‒4 mass percent). The dependence was defined of both the compact density and general physical and mechanical properties of the sintered samples on the pressing force, as well as of the samples' linear contraction on the pressing force in both pressing and radial directions. It was established that the increasing of the nano-sized ZrO 2 powder amount in the initial batch mixture promotes the increasing both the compact's and sintered samples' densities, as well as it promotes the linear contraction decreasing of the samples in course of burning. Under the industrial production conditions the comparison of wear resistances was implemented for AL 2 O 3 ‒ ZrO 2 ceramic samples with various ZrO 2 content, as well as with nano-sized ZrO 2 additions. Ill. 7. Ref. 10.

In this paper porous ceramics on the base of ZrO2 nanopowders and micropowders has been developed by freeze-casting method. A zirconia/carbamide slurry was frozen in mold and dehydrated in CaCl2 at room temperature. This simple process enabled the formation of porous ceramics with highly aligned pores as a replica of the carbamide crystals. The samples showed higher porosity of 47.9%. In addition, these materials could be used as membrane for air cleaning.

Sintering of alumina ceramic with 95% Al2O3 [VK 95-1] content with additives of aluminum oxide nanopowder and without it is studied. The increase in strength by 32 ± 3% is ensured by additives of 1.5 ± 0.5 wt %. The strength reaches 170 ± 5 MPa, which allows it to be used as dental prosthesis forms in stomatology.

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.

We have investigated the processes of phase formation in the systems «cordierite-mullite» with a predominance of cordierite and «mullite-cordierite» with a predominance of mullite in the talc-kaolin-alumina mixtures and evaluated the possibility of activation of a small addition of topaz. It was confirmed that the synthesis of cordierite from stoichiometric talc-kaolin-alumina mixture flows through the formation of intermediate compounds clinoenstatite formed during the heat treatment of talc, and mullite, released from the structure of kaolinite. The activating effect of topaz on sintering cordierite-mullite compositions was established. This is caused by the action of gaseous fluoride released by thermal decomposition of topaz on lowering the high temperature viscosity of the melt formed during firing this compositions.

The effect of dry axial compaction process parameters on physicomechanical properties of ceramic composite material ZTA (Al2O3–ZrO2, ZrO2 > 20 wt.%) with a different content of nanosize ZrO2 powder (range 0 – 4 wt.%) is studied. The dependence of compact density is determined, and also the main physicomechanical properties of sintered specimens on compaction conditions, and linear specimen shrinkage on compaction pressure in the pressing direction and radial direction. It is revealed that an increase in the amount of nanosize ZrO2 in an original charge facilitates an increase in compact and sintered specimen density, and a reduction in specimen linear shrinkage during firing. Comparative evaluation is carried out under industrial production conditions for wear resistance of ceramic specimens based on Al2O3 and ZrO2 with a different ZrO2 content, and also addition of nanosize ZrO2.