A review of dielectric materials with high (exceeding 10,000) values of relative permittivity is presented. Most of the compositions of these materials are based on systems that include ferroelectric and non-ferroelectric components, as well as solid solutions based thereon. Various approaches to increasing the permittivity of materials are considered, including doping, sintering atmosphere, grinding time, sintering temperature, and grain size. The effect of dopants and the synthesis method on the characteristics of capacitor ceramics that can be used in the low-frequency and high-frequency range are compared.

Ceramic materials based on cordierite Mg2Al4Si5О18, their different compositions and methods of preparation are considered. The results of tests of thermal shock resistance of ceramic samples of different compositions are presented. The thermal shock resistance of the obtained samples is more than 15 heat changes (1000 °C ‒ 15 °C running water). This cordierite material, in the production of which it is supposed to use only native raw materials, has good prospects when used as a thermo stable catalyst carrier for controlling industrial emissions, as well as car exhaust gases.

The results of studies on the preparation of highly dispersed bimetallic materials based on platinum with chromium, molybdenum, and tungsten under autoclave conditions at 190°C are summarized in this report. The thermodynamic and chemical features of the interactions between [Pt(NH3)4]Cl2 and (NH4)2CrO4, (NH4)2MoO4 and (NH4)2WO4 are considered. Solid products (powders) are represented by two phases—Pt and disordered solid solutions based on platinum. The morphology of powders has been studied—spherical particles with a diameter of 300–700 nm form agglomerates up to 2 µm. A route for the reduction of platinum (II) and oxometalate anions to the corresponding metals with intrasphere ammonia is proposed. The results of this work can form the basis for the synthesis of catalysts that are widely used in a number of industrially important reactions.

The paper presents the results of studies of porous composite materials based on CaCu3Ti4O12 (CCTO) obtained by ceramic technology. Samples of ceramics based on CCTO demonstrate very high values of relative permittivity (ε > 10000). CCTO material was used both as a binder and as a filler for the production of ceramic composites with a porous permeable structure. For the samples under consideration, there was a several-fold decrease in the value of the dielectric constant and an increase in the electrical resistivity compared with the corresponding parameters of CCTO ceramics. The open porosity of ceramic samples was 30–54

Исследованы структура и морфология мелкокристаллического титаната бария, синтезированного в докритическом водном флюиде при температуре 230 °С и давлении 2,9 МПа с использованием различные исходныгх реагентов: оксида бария BaO., октагидрата гидроксида бария Ba(OH) • 8HO и двух модификаций оксида титана (рутил и анатаз). Установлена связь между составом и свойствами реагентов и характеристиками получаемого из них титаната бария, свидетельствующая о твердофазном механизме формирования структуры BaTiO в докритическом водном флюиде. The structure and morphology of fine-crystalline barium titanate synthesized in a subcritical water fluid at 230 °C and 2.9 MPa were studied. Barium oxide, barium hydroxide octahydrate Ba(OH) • 8HO and two modifications of titanium dioxide (rutile and anatase) were used as starting reactants . Relationships between the composition and properties of the reactants and the characteristics of the product (barium titanate) were revealed. They indicate that the product structure in the subcritical water is formed via a solid-phase mechanism.

The possibility of obtaining samples of lead-free piezoceramic by vibromolding under pressing pressure < 0.3 MPa is studied. The experiments were performed on the material K 0.49 Na 0.49 Sr 0.02 NbO 3 synthesized by the standard ceramic technology of solid-phase synthesis. The samples of the piezoceramic fabricated by vibromolding are similar in terms of their properties to those obtained by static pressing under pressure 100 – 150 MPa. The advantages of the vibrocompaction process are: lower expenditures on tooling and equipment, smaller elastic deformation, and higher product density.

The dependence of dielectric and piezoelectric properties of lead-free piezoceramics on fractional composition of initial powders has been investigated. The material on the basis of solid solutions of potassium and sodium niobates doped with strontium is considered. Piezoceramic samples with different porosity values (from 4% to 36%) were obtained using powders of piezoceramic material of different granulometric composition. For these samples, the dielectric constant decreased monotonically with increasing porosity from 600 to 300, while the value d(33) (80-90pC/H) varied slightly.

Barium titanate is a prominent ferroelectric which has wide industrial applications as a material for base-metalelectrode capacitors, piezoelectric actuators, thermistors and electro-optic devices [1,2]. The progress in this field requires submicron-grained ceramics produced from fine-crystalline BaTiO3 powders. A perfect powder for microelectronics production should perform high purity, homogeneous composition, uniformity of particles and weak agglomeration of crystals [3]. Recently, a novel method of synthesis based on the use of suband supercritical water was successfully used for nanocrystalline BaTiO3 preparation [4-6]. The current study is to perform the connection between the conditions of synthesis in water medium and the capability of BaTiO3 powders to be used as raw material for high-density dielectric ceramics. The proposed method of synthesis operates with barium and titanium oxides as reagents and subcritical vapor or supercritical water as a reaction medium. It was reported [6,7] that during the synthesis in these conditions water molecules provided hydration and hydroxylation of the starting metal oxides accompanied by breaking of metal – oxygen bonds and formation of metal – hydroxyl bonds. These processes led to a dramatic increase of solid-state mobility and facilitated solid-state diffusion of barium ions into TiO2 structure followed by the formation of BaTiO3 structure. This reaction between BaO and TiO2 had a similar mechanism in suband supercritical water. Nevertheless, H2O molecules in supercritical region possessed more degrees of freedom than in subcritical state and their reactivity towards oxides was higher. Due to this the reaction in supercritical water yeilded nearly full conversion while in subcritical medium it reached only about 80%. Besides, the contents of volatile admixtures in the product obtained in supercritical water was nearly four times lower (0.241 mass.%) than in case of synthesis in subcritical vapor (0.884 mass.%).

The results have been described of experimental studies of the influence of vibrocompaction modes, shape of particles and their size distribution on the relative package density. The glass spheres with diameters distributed from 0.4 to 0.9 mm and from 0.63 to 0.8 mm, containing a fraction of nonspherical particle inclusions of about 30 % have been taken as the research object. Also in the experiments the powder was used of electrocorundum with particle size of 0.63-0.8 mm. This choice was aimed at bringing the particles characteristics to those of a real granular material and no separation of particles into spherical and non-spherical was planned. The experiments on vibrating packing have been performed with the help of dynamic "Revolution" powders rheometer. The modes of compaction vibration varied over a wide range of frequencies and amplitudes: from 5 to 475 Hz and from 106 to 1062 µm, respectively. The vibration frequency has shown to exert a greater effect on relative density as compared to that of the amplitude. The dependence of relative density on vibration frequency exhibits several local maxima for all vibration amplitudes. The maximum relative packing density of 0.64 ... 0.65 is achieved at a combination of high amplitude (850, 1062 µm ) and high frequency (300 ... 350 Hz). Effect of granulometric composition on relative packing spheres density is less pronounced than that of the vibration frequency and approximately equals to than of the amplitude. Increasing the deviations of the particles size is accompanied by increasing frequencies leading to maximum packing density. The particles shape affects the level of packing density, thereby remaining the same character of dependence of relative density on vibration frequency for both spherical and non-spherical particles of similar particle size distribution.

BaTiO3 powders synthesized by two different methods based on the solid-state mechanism of formation were studied as raw materials for ferroelectric ceramics production. Fine-crystalline BaTiO3 obtained by reaction between BaO and TiO2 in supercritical water at 400 degrees C and 26 MPa had superior properties to the powder obtained by conventional high-temperature synthesis in air at 1100-1300 degrees C. Quasi-reversible interaction of water molecules with solid oxides in supercritical region had beneficial effect on morphology and phase purity of BaTiO3. Ceramics manufactured from the powders synthesized in supercritical water possessed uniform microstructure and narrow grain size distribution. This ceramic material performed ferroelectric phase transition at temperature of about 130 degrees C and possessed dielectric permittivity up to 8650 and the loss tangent lower then 0.02 at 1 kHz. BaTiO3 powder synthesized in supercritical conditions appeared to be an affordable and high quality raw material for ferroelectric ceramics compared to the powder obtained by high-temperature solid-state method.

The current status of theoretical research on close-packed systems of hard spheres is reviewed. The basic models of regular and random close-packings of hard spheres are described. Examples are presented of the application of modeling of the close packing of hard spheres for solving applied problems in the development of promising materials made from ceramics, including refractories.

The paper is aimed to perform and compare the capabilities of the solid state technology and a new method of synthesis in supercritical water for the production of barium titanate powder. This material is of interest for applications such as dense piezoceramics. The new method of synthesis in an aqueous medium allowed obtaining barium titanate of higher phase purity and with a narrow crystal size distribution compared to the solid state method. The ceramics manufactured from the barium titanate powder synthesized in supercritical water possessed a consistently high dielectric constant (2400-2600) and a low loss tangent (∼ 10−2) at low and medium frequencies.

Anomalous thermal expansion of the pressed mixture of initial reactants is observed in solid-phase synthesis of piezoceramic materials based on complex oxides with perovskite structure. Under certain conditions the magnitude of this expansion can be an indicator of the degree of completion of the solid-phase reactions. The thermal expansion of the pressed mixture of powders of potassium and sodium carbonates and niobium oxide in the synthesis of the complex oxide potassium niobate and sodium niobate KNN is analyzed. It is shown that the temperature and completeness of the synthesis reaction can be determined on the basis of this analysis. The obtained material was used to prepare samples of piezoceramic with density to 92% of the theoretical value and piezoelectric modulus d33 to 1.0 × 10–10 C/N.

Fine-crystalline barium titanate was synthesized by a new method using supercritical water and examined as a raw material for dielectric ceramics preparation by semidry pressing and further high-temperature sintering. The nature of temporary technological binder utilized at the stage of pressing significantly affected the structural, mechanical and electro-physical properties of BaTiO3 ceramics. Ceramics prepared from BaTiO3 powder synthesized in supercritical water possessed necessary applied characteristics: the dielectric permittivity as high as 2819 and loss tangent as low as 0.012.

One the main issues in the chemical engineering is to evaluate the grinding procedure powders for pizoceramic materals, which has gained attention in industry with valuables applications. It was demonstrated that the grinding of precursor powders for the PCM synthesis based on sodium and potassium niobates can be carried out using both spherical, and planetary mill. However, this process for niobium oxide is the most efficient if a planetary mill is used.: The coarse grinding should be carried out in a fluid medium, thereby typical dimension of grinding bodies should be decreased with decreasing powder size. Thus, by means of two sets of grinding bodies having a size of 6mm and 2mm it was possible to produce Nb2O5 powder with a mean particle size of about 1μm. The use of an ultrasonic disperser at the final stage of grinding makes it possible to disperse about 5 % wt. of nanoparticles. This significantly increases the specific surface area of these components substantively affecting their reactive activity.

The results of theoretical and experimental studies of methods for obtaining bitstone powder with relative density greater than 0.50 for subsequent sintering of high-density, aluminum oxide based, ceramic samples are presented. The indicated pressing density was achieved by picking the spherical fractional composition of corundum power based on known theoretical models of close regular and random packing of spheres of different size. The prospects for using the described methods in ceramic part fabrication technology are evaluated.

The structure and morphology of fine-crystalline barium titanate synthesized in a subcritical water fluid at 230°C and 2.9 MPa were studied. Barium oxide, barium hydroxide octahydrate (Ba(OH)2 · 8H2O), and two modifications of titanium oxide (rutile and anatase) were used as starting reactants. Relationships between the composition and properties of the reactants and the characteristics of the product (barium titanate) were revealed. They indicate that the product structure in the subcritical water is formed via a solidphase mechanism.

Kinetics experimental results of the interaction of an aluminum alloy D16 with a sodium hydroxide aqueous solution under the alternating electric current are presented. It is stated that the reaction rate under the AC is much larger than the reaction rate without applying an electric current. The use of an alternating electric current makes it possible to obtain smaller particles of Al(OH)3 with a narrower particle size distribution range.

The paper reviews the state of art in the development of new lead-free piezoelectric ceramic materials. Piezoceramic materials are used in a wide field of applications, most of them are based on lead titanate-zirconate. However, modern human health and environmental requirements make necessary the use of alternative lead-free materials. Advantages and drawbacks of perspective piezoceramics are discussed, possible approaches to increase their piezoelectric properties (texturing and template grain growth method) are considered.

Results are given for studying electrophysical properties of ceramic materials based on powders prepared by chemical dispersion of aluminum-magnesium alloys. The possibility is demonstrated of using these materials as UHF-energy bulk absorbents. It is shown that good test material thermal stability makes it possible to use it as heat insulation and refractory material in systems requiring protection from UHF-energy.