The article discussed the problem of manufacturing boron carbide ceramics with high physical and mechanical characteristics. The problem of choosing raw powders and ceramic manufacturing technology is considered. The paper presents the results of research of domestic and imported boron carbide powders and shows the differences in their structure and properties. The results of domestic and imported boron carbide powders studies are presented; the differences in their structure and properties are shown. It is also shown that the grain shape and granulometric composition of the powders have a significant impact on the density of the blanks and the silicon content after reaction sintering, and the chemical composition of the powders affects the structure of the ceramics. The comparison of the structure and physical-mechanical properties of boron carbide ceramics based on domestic and imported powders showed the advantage of using powders produced by JSC “UNICHIM & EP” in most of physical-mechanical properties.
This paper presents the results of investigation on obtaining ZrB2-based ceramic by the method of slip casting followed by pressureless sintering. Optimal parameters for forming complex-shaped blanks were determined. The influence of the maximum by pressureless sintering temperature on the microstructure, physical and mechanical properties of ZrB2-based ceramic were investigated. Thermal physical properties of the developed material were studied in a wide temperature range.
The influence of ceria (CeO2: 0…3,56 wt. %) and sintering method (pressureless sintering in air, hot pressing in Ar) on the phase composition, microstructure, and properties of alumina-zirconia ceramics was investigated. The sintering method was found to determine the dual role of CeO2. Hot pressing facilitated the reduction of Ce4+ до Ce3+ and the formation of plate cerium hexaaluminate CeAl11O18, identified by XRD and EDS. Pressureless sintering led to the stabilization of the cubic ZrO2 phase (c-ZrO2). Hot pressing achieved high relative density (>99 %) and practically no open porosity, while pressureless sintering resulted in porosity up to 5 %. Hardness decreased with increasing CeO2 content for both methods. Fracture toughness in pressureless sintered ceramics was primarily controlled by porosity. In contrast, KIC increased with CeO2/CeAl11O18 content in hot-pressed materials, reaching a maximum of 7,5 ± 0,2 MPa·m1/2, demonstrating the effectiveness of CeAl11O18 as a toughening phase. The results indicate that hot pressing is the preferred method for producing CeAl11O18-toughened Al2O3–ZrO2 ceramics.
This article presents a review of the available scientific and technical information on conductive metallization pastes used in the production by low-temperature co-fired ceramic (LTCC) multilayer electronic components. The influence of the main components of metallization pastes on their rheological properties, sintering temperature, and electrical resistance of the conductive elements of multilayer ceramic boards is examined. It is established that the composition and amount of inorganic and organic components significantly affect the rheological and thixotropic properties of metallization pastes. The size and shape of the metal filler particles have the greatest impact on the sintering temperature and electrical resistance of the conductive elements. The composition and properties of borosilicate glasses and refractory metal oxides in the pastes influence the adhesion of the conductive layer to the glass-ceramic material and the conformity of paste and glass-ceramic shrinkage during the co-firing of the multilayer package.
It is known that the introduction of small Na2O additives (up to 5 mol. %) into the glass composition of the ZnO–MgO–Al2O3–SiO2 (ZMAS) does not interfere with the production of zinc spinel (ZnAl2O4) based glass-ceramic and allows the usage of ion exchange for further improve their mechanical properties. In this work, the submicrostructure of ZMAS glass-ceramic with sodium oxide additives in a transparent state and at the initial stages of opalescence and opacity was studied using the TEM method using XRD data. The main crystalline phase, zinc spinel, embedded in the glass-ceramic, does not contain sodium cations: they remain in the residual glass phase, creating favorable conditions for the strengthening of the material by ion exchange. After heat treatment of glass for 10 h in the temperature range 770…790 °C, in addition to zinc spinel, zinc-magnesium silicate (Zn, Mg)2SiO4 crystallizes, the particle sizes of which reach 15…20 nm, while the sizes of ZnAl2O4 crystals do not exceed 6 nm, and therefore it is the silicate phase that limits the conditions of crystallization and prevents the improvement of strength properties and preservation of transparency.
Ceramic materials based on silicon carbide were synthesized using reaction sintering with the introduction of a reactive component – technical carbon black – into the starting mixture at varying concentrations (5, 15, and 30 % by weight). The tribological characteristics of the resulting ceramic materials were determined in a friction pair with a VT6 structural titanium alloy under friction conditions in air and water at room temperature. It was determined that the best antifriction properties (µ = 0.17 in water) are observed during contact interaction between the titanium alloy and silicon carbide material obtained from a mechanical mixture containing the highest amount (30 % by weight) of technical carbon black.
Fe-substituted ceramic materials of the NASICON family, corresponding to the generally accepted formula Na3+yМ(III)yZr2–ySi2PO12, with a dopant concentration from 5 to 20 mol. % were studied. Doping changes the morphology and phase composition of ceramics. Electron paramagnetic resonance spectra indicate the presence of Fe3+ atoms both in the crystalline phase (with g ~ 2.0) and in disordered phases with a strong rhombic component of the crystal field on impurity ions (with g ~4.3 and ~4.2). A quantitative analysis of the distribution of paramagnetic centres in ceramics was performed. It was noted that the dopant is predominantly found in the crystalline phase of the sample. It was shown that Fe-substituted NASICON complexes correspond to the composition Na3М(III)yZr2–ySi2–yP1+yO12. The Fe3+ content in the crystalline phase of these complexes is 36% higher than in samples obtained in accordance with Na3+yМ(III)yZr2–ySi2PO12.
To produce Al–Al2O3 cermet with a heterogeneous granular-layered structure, mixing of flake aluminum powder of the PAP-2 brand with the plasma-chemical alumina powder (PCAP) consisting of nano-thick lamellar agglomerates in a planetary ball mill in the mechanical alloying mode was carried out. The resulting charge, consisting of layered granules containing alternating alumina and aluminum layers, was compacted under a pressure of 700 MPa. Sintering of green samples was carried out in a vacuum (10–5 mm Hg) at a temperature of 650 ? for 1 hour. The content of the alumina component in the cermet composition in the amount of 15% by weight ensured a combination of low density – 2.54 g/cm3 with significant indicators of its mechanical properties (flexural strength – 280 MPa, axial compression strength – 350 MPa, crack resistance – 8.5 MPa?m1/2, microhardness – 1070 MPa) as a result of achieving a compromise between the plasticity of this composite and its hardness. Cermet can be used as lightweight armor protection elements, wear-resistant elements and special abrasive tools.
The adhesion properties of polyurethane- and polyurea-based polymer coatings designed to protect concrete were studied under the climatic conditions of Yakutia. Coated concrete samples were exposed to outdoor conditions for two years, where temperatures ranged from +20 °C in summer to –42.8 °C in winter. The results showed that climatic factors primarily affect the surface layers. During the first year, coating adhesion decreased approximately equally for all samples. However, as the testing period increased, the decrease in adhesion properties became more pronounced and uneven. This is presumably due to moisture absorption by the polymer and concrete, the intensity of which depends on the coating thickness. Freezing of moisture leads to the formation of internal stresses and microcracks, weakening the bond between the coating and concrete. Frequent temperature fluctuations accelerate this process. It was established that the physical and mechanical properties of the coatings are determined by the composition of the original components and the nature of the chemical bonds, while curing temperature has a significant impact on their mechanical characteristics.
In this paper the experience of using regular and specially developed resistive pastes for resistors compatible with LTCC substrates is reviewed. Characteristics of surface, buried, and 3D resistors manufactured using DuPont, Ferro, Shoei, and ESL pastes on ceramics from various manufacturers are examined. Results of a study of the resistors' microstructure, phase and elemental composition, sheet resistance, tolerance, hot (HTCR) and cold (CTCR) temperature coefficient of resistance, frequency behaviour, noise indices, gauge factors, as well as their performance after thermal aging, laser trimming, and high-voltage pulse loads are presented. The influence of process conditions, resistor dimensions and the physicochemical interactions of the materials on these characteristics is assessed.
