-
Details
-
Hits: 58
Presents the results of a study of PbZrO3 ceramics synthesized from nanodispersed PbO and ZrO2 powders with the addition of BaTiO3 nanoparticles with sizes of 50, 200 and 400 nm. It has been established that the addition of barium titanate BaTiO3 nanoparticles to lead zirconate PbZrO3-based ceramics promotes an expansion of the temperature range of the ferroelectric phase existence, right down to room temperature. With an increase in the BaTiO3 content, the maximum of the permittivity shifts to the region of lower temperatures, and the ?' values increase significantly, reaching a peak at a BaTiO3 concentration of 10 %, after which a decrease is observed.
-
Details
-
Hits: 69
A series of chromium-containing solid solutions CaCu3Ti4 – 4хСr4хO12 – ? (sp. gr. Im3) were obtained by the solid-phase synthesis method. The unit cell parameter of the solid solutions changed insignificantly from 7.3897 (х = 0.02) to 7.3866 ? (х = 0.06). Copper oxide was determined in the intergranular space in all samples. The samples were characterized by a low-porosity grain microstructure; with an increase in the chromium content in the samples from x = 0.01 to 0.06, the maximum longitudinal crystallite size, according to the scanning electron microscopy data, decreased from 16 to 10 ?m. Spectral studies of the charge state of chromium-doped titanium calcium copper CaCu3Ti4O12 cations were carried out using X-ray spectroscopy (XPS and NEXAFS). According to NEXAFS and XPS spectroscopy data, titanium cations have a charge state of +(4 – ?) in solid solutions of calcium-copper oxides, copper and calcium atoms have a charge state of +2, and doped chromium cations have a charge state of +3.
-
Details
-
Hits: 122
The chemical and mineralogical composition, grain structure and physicochemical properties of unenriched dune sands located in the Kushkupyr district of Uzbekistan were studied. Analysis of the granulometric composition indicates the predominance of particles with a size of at least 0.007 mm, while their fineness modulus does not exceed unity, which allows classifying these sands as fine-grained. Using scanning electron microscopy (SEM), the morphology of dune sand particles was studied and it was shown that its composition is mainly represented by irregularly shaped quartz grains. Compositions for obtaining sodium silicate in the microsilica – dune sand – caustic soda system are proposed.
-
Details
-
Hits: 120
The chemical and mineralogical compositions, physical and chemical characteristics and phase transformations of diabase rocks of the Uzunbulak deposit were studied. It has been shown that as a result of firing at a temperature of 1000 ?C, phase transformations occur in diabase samples, accompanied by the new formation of the minerals wollastonite, pyroxene and a small amount of high-temperature forms of quartz and cristobalite. The possibility of using this diabase rock as a raw material for producing acid-resistant materials for various purposes has been established.
-
Details
-
Hits: 100
This paper presents the results of annealing synthetic quartz glass of high purity at a temperature of 250 ?C and an elevated pressure of 7 MPa in an atmosphere of molecular hydrogen. Annealing under these conditions makes it possible to increase the transmission coefficient at a wavelength of 190 nm by 2 %. The absorption of quartz glass in the range from 238 to 254 nm corresponds to defects in the structural grid of quartz glass, namely, transitions of silicon oxygen-deficient centers of the non-bridge oxygen type, which are deactivated by atomic hydrogen to form stable Si–O–H hydroxyl groups, which in turn reduces absorption in the range from 238 to 254 nm. Using IR Fourier spectroscopy, it was found that the diffusion of molecular hydrogen produces a peak in the wavenumber range from 4200 to 4100 cm–1 and corresponds to molecular hydrogen dissolved in the structural grid of quartz glass.
-
Details
-
Hits: 96
The surfaces of lead-silicate glasses and non-etched blanks of microchannel plates after their mechanical processing are studied. It was found that exposure of the obtained samples in a 33 % H2O2 solution led to an increase in optical transparency with a corresponding decrease in their mass. The results obtained are explained by the removal of organic and organosilicon layers from the surface that arose during mechanical processing.
-
Details
-
Hits: 120
This study demonstrates the functional advantages of reaction-sintered diamond-silicon carbide (D–SiC) ceramics for armor applications compared to conventional materials including silicon carbide, boron carbide, and alumina. The ballistic performance of reaction-sintered D–SiC ceramics was experimentally evaluated according to protection class Br4 using prototype armor panels with varying ceramic plate thicknesses (6…10 mm) mounted on ultra-high-molecular-weight polyethylene (UHMWPE) flexible backing (8…10 mm). Ballistic tests confirmed complete resistance to penetration in all tested panel configurations.
-
Details
-
Hits: 128
Porous ceramic materials, including those with the addition of ?-Al2O3 of the order of 10 %, were obtained on the basis of yttrium oxide, which is inert to sintering and has cubic syngony. The characteristics of the porous structure and filtration properties of synthesized ceramics are revealed. The materials have also been tested under aggressive media (aqueous solutions of H2SO4 acid (20 wt. %) and KOH alkali (10 wt. %) and thermal cycling loads. The results of the studies have shown that the obtained materials are not subject to deformation and destruction in aggressive media. Thermal cycling tests have not revealed any degradation of the physical and mechanical characteristics of the samples. Experimental studies of the separation of solid and liquid components of suspensions on porous ceramic membranes have established the efficiency of rejection of model SiC particles with a size of D50 = 500 nm to be more than 99.9 %. The achieved performance characteristics in combination with the developed pore space of the synthesized materials allow their effective use for micro- and ultrafiltration of liquids, and catalysis processes under aggressive environments and high thermal loads.
-
Details
-
Hits: 103
Presents the results of the synthesis of mullite-silica ceramics with improved electrophysical characteristics based on natural kaolinite raw materials extracted in the Orenburg region. The main attention is paid to the study of the effect of heat treatment and the degree of dispersion of the starting material on the formation of the phase composition. Methods of differential thermal analysis, modeling of thermal processes during firing, as well as X-ray phase analysis for phase identification were used for the analysis. It is shown that the choice of the optimal temperature regime and preliminary mechanical (grinding) and chemical (oxalic acid) activation make it possible to stabilize the mullite phase and reduce the maturation of residual silica. This ensures low dielectric losses in a wide frequency range, as well as increased heat resistance and thermal insulation properties of the material. The obtained samples not only meet, but also exceed the requirements of GOST 20419–83 in key parameters such as thermal conductivity and dielectric losses, which confirms their promise for use in electrical insulation structures and thermal barriers in the energy and mechanical engineering.
-
Details
-
Hits: 145
The possibility of using waste from the enrichment of ferruginous quartzites of KMA and waste from vanadium production for the plasma synthesis of marblite and structural elements of a plasma glass furnace is considered. The operational parameters of marblite, such as water resistance, frost resistance, microhardness, and phase composition, have been studied. The color characteristics of marblite are determined in the CIE L*a*b* system.
