Inorganic Materials

The effect of deposition conditions on the growth rate, crystal quality, surface morphology and concentration of growth defects of CdTe epitaxial layers obtained by MOCVD on GaAs (310), (100), (111) B substrates using dimethylcadmium and methylallyltellurium (MATe) was studied.The growth rate of CdTe layers under the studied conditions varied from 0.6 to 2.0 μm/h, and the apparent activation energy of the growth process at 300–350°C was in the range of 45.2–54.0 kJ/mol. It is suggested that the limiting stage of deposition in this temperature range is the adsorption stage of reagents (primarily MATe) on the surface. CdTe (100) layers grown at 300–350°C had the best crystal quality. The smoothest and most mirror-like surfaces were found in CdTe (100) and (111)B layers grown at temperatures of 330–350 and 330–370°C, respectively. The conditions for obtaining CdTe (100) layers with a concentration of growth defects (10–20 microns in size) on the surface of ≤150 cm^–2 have been established.

To produce a xerogel a two-stage sol-gel synthesis of silicon dioxide was carried out including acid hydrolysis of thetreathoxysilane in the presence of ethanol, followed by polycondensation of hydrolysis products. An aqueous solution of ammonia of various mass concentrations was used as a catalyst for the polycondensation reaction: 0.8, 1, 2, 3, 5%. The properties of the obtained xerogels, such as bulk density, specific surface area, particle size distribution, and porosity, have been studied. A decrease in the concentration of an aqueous ammonia solution leads to the formation of a microporous xerogel and the rise of the medium (100- 500 microns) and fine (<100 microns) powder fractions. Changing the concentration of ammonia during the sol-gel synthesis of silicon dioxide makes it possible to control the properties of the xerogel, increasing the proportion of the "working" fraction of the powder, which is used at subsequent stages of heat treatment and melting of quartz glass.

A method for preparation of high- purity molybdenum trioxide by desublimating its vapors from oxygen flow is proposed. X- ray diffraction analysis confirmed the formation of rhombic molybdenum trioxide (Pmna, a = 13.7690(4)Å b = 3.70318(10)Å c = 3.95972(10)Å Z = 4). Iodometric titration has shown that the resulting product possesses an increased content of oxygen atoms compared to stoichiometric one and corresponds to the MoO_3.0073 formula. The content of metallic elements impurities at the 1 - 10 ppm level was found by laser mass spectrometry. The low content of transition element impurities and the excess of oxygen atoms over the stoichiometric MoO₃ composition make us hopeful that the use of molybdenum trioxide deposited from the oxygen flow allows us to prepare glasses with high optical transparency.

The possibility of creating composite proton electrolytes with the addition of nanodiamond (ND) to caesium pentahydrodiphosphate has been studied. Changes in the structural properties of salt in the composite, morphology, and proton conductivity depending on the composition for (1 – x)CsH₃(PO₄)₂ – xND (x – mole fraction) in a wide range of compositions (x = 0 – 0.99) are considered. It is shown that there is no chemical interaction between the components and the structure of CsH₃(PO₄)₂ (P2₁/c) with an increase in the proportion of ND is preserved during the dispersion and partial amorphization of the salt. Using IR spectroscopy, information was obtained on the mechanism of formation of composite electrolytes due to partial binding of salt protons to surface OH^- ND's hydroxo groups. This leads to the formation of a weaker network of hydrogen bonds in CsH₃(PO₄)₂. A uniform distribution of salt particles in composites and a decrease in particle size as a result of the interfacial surface interaction of the components are shown. Melting enthalpy of CsH₃(PO₄)₂ decreases disproportionately to the salt content with an increase in the proportion of ND due to an increase in the proportion of the amorphous phase in the composites. There is a significant increase in the proton conductivity of CsH₃(PO₄)₂ in composites to two orders of magnitude with a maximum at x = 0.9 and a decrease at x > 0.95 due to the "percolation effect" of the "conductor-insulator" type. The activation energy of the conductivity of composites decreases slightly. The studied composites have a relatively high proton conductivity at medium temperatures and chemical stability, which creates prospects for their use as proton membranes of electrochemical devices.

The results of studies of the effect of natural deformation changes in milky-white quartz on its trace element composition and properties of deposited glasses are presented. It is shown that various stages of enrichment have a significant effect on the content of elements in quartz grains and are subsequently inherited by glass. It has been established that impurities are not only a source of defects in glass, but also increase the speed of the crystallization process, improving the quality of welded glasses.

The effect of transition metals Cr, Co, and Ni on the structure, thermal conductivity, and strength characteristics of WC-Cu composites with a copper mesh structure has been studied. It is shown that WC70Cu30 composites doped with Co or Cr have high thermal conductivity, hardness, and wear resistance. The method of synthesizing composites differs from the existing ones by the absence of precursor stages of the formation of a rigid frame of refractory particles, as well as the activation of physico-chemical processes in a melt with refractory particles by precrystallization low-frequency vibration (80 Hz, amplitude 0.5 mm, 10 min).

In order to determine the causes of the scattering of the impact toughness values of hot-rolled low-carbon low-alloy steel by optical microscopy, scanning electron microscopy and Electron Backscatter Diffraction, a comprehensive study of the mechanisms of sample fracture after multiple Charpy impact tests at a temperature of –60°C were carried out. It is established that the scattering of impact toughness values is determined by the formation of martensitic-bainitic interlayers in the axial region of rolled products with an increased concentration of both nonmetallic inclusions and Mn, S, P. On the one hand, they act as an origins of brittle macrofracture, on the other hand, they contribute to the formation of splits. The effect of brittle fracture on the main fracture surface prevails over the formation of splits in a plane parallel to the rolling plane. Even before the fracture, two groups of microcracks are formed in the plastic zone, oriented either parallel to the rolling plane or parallel to the propagation path of the main crack. The duality of the role of MnS in fracture process during Charpy impact tests is shown. The contributions of nonmetallic inclusions and martensiticbainitic interlayers on cleavage nucleation in samples without splittings are divided. The nature of splittings formation has been studied, and the absence of a correlation between the total length of splittings and impact toughness values has been shown. Fractures with the formation of main splitting can lead to a slight increase in impact toughness due to the shift of the focal facets sites from martensite-bainite interlayers into the ferritepearlite microstructure.