V. L. Ugolkov

Thermal expansion and phase transitions in K 1 − x Rb x BSi 2 O 6 leucite borosilicate solid solutions

Continuous solid solutions and the reversible phase transition from the I-43d cubic phase to the Ia-3d cubic phase are revealed in the borosilicate series K1 − xRbxBSi2O6. Samples in the KBSi2O6-RbBSi2O6 system are prepared by solid-phase synthesis and crystallization of glasses and investigated using the annealing and quenching technique, high-temperature X-ray diffraction, and dilatometry. The above polymorphic phase transition is observed in all solid solutions at temperatures in the range from 330 to 430°C depending on the composition: an increase in the rubidium content in the solid solution leads to a gradual decrease in the phase transition temperature. The linear thermal expansion coefficients α are determined for solid solutions of different crystalline modifications and glasses. The linear thermal expansion coefficients α for the I-43d low-temperature phase are equal to (20–23) × 10−6 K−1 according to the X-ray diffraction data and (21–24) × 10−6 K−1 according to the dilatometric data. The values of α for the Ia-3d high-temperature phase lie in the range (4–9) × 10−6 K−1 according to the X-ray diffraction data and in the range (6–9) × 10−6 K−1 according to the dilatometric data. The linear thermal expansion coefficients for both modifications decrease with an increase in the rubidium content in the solid solutions. The linear thermal expansion coefficients for glasses α = (10–11) × 10−6 K−1 are close to those for the high-temperature modification and virtually independent of the sample composition. The I-43d (cubic) ai I41/a (tetragonal) o Ia-3d (cubic) polymorphic phase transitions in the KBSi2O6 compound are revealed by differential scanning calorimetry (DSC) and dilatometry. Their reversibility is confirmed by the DSC data.

Preparation and thermal transformations of nanocrystals in the LaPO4-LuPO4-H2O system

Powders of nanosized particles of individual and mixed lanthanum and lutetium orthophosphates are synthesized. The grain growth process is studied in the temperature range of 200–1100°C. Temperature and concentration regions of existence of the solid solutions based on hexagonal and monoclinic forms of LaPO4 as well as on tetragonal LuPO4 are determined.

Thermal expansion and polymorphism in a series of rubidium cesium boroleucites

The crystal structure of the boroleucite solid solution Rb0.40Cs0.54B0.94Si2.06O6 is refined in space group I-43d by the Rietveld method with the use of the X-ray powder diffraction data. The refinement data complement the available crystal chemical characteristics of Rb1−xCsxBSi2O6 solid solutions. The thermal expansion and phase transformations of Rb1−xCsxBSi2O6 borosilicates are investigated in parallel by high-temperature X-ray diffraction with conventional powdered samples and by the dilatometric method with samples in the form of pressed pellets. It is demonstrated that the thermal expansion coefficients, as well as the temperatures and sequence of polymorphic transitions, which are determined from the data obtained by two methods are in close agreement. The temperature curve of the I-43d ⇄ Ia3d phase transition for the Rb1−xCsxBSi2O6 solid solution system is constructed from the data obtained by both methods. It is shown with the use of the structural data obtained by the Rietveld method that, at temperatures above 800°C, rubidium-cesium boroleucites undergo decomposition due to the release of alkali cations.

Glass formation region and order of formation of crystalline phases in the SrO-B2O3-SiO2 system

The glass formation region in the SrO-B2O3-SiO2 system has been refined. The order of formation of crystalline phases in the system has been investigated at SrO contents of 50–75 mol %. It has been demonstrated that, at low temperatures, the 2SrO · SiO2 and 3SrO · B2O3 phases crystallize first irrespective of the composition. The congruent melting temperature of the 3SrO · B2O3 · SiO2 compound is determined to be 1180 ± 10°C. The triangulation previously performed for the SrO-B2O3-SiO2 system in the concentration range 50–75 mol % SrO has been confirmed.

Formation of organic-inorganic composite materials based on cellulose Acetobacter xylinum and calcium phosphates for medical applications

The formation of composites based on the cellulose Acetobacter xylinum and calcium phosphates has been investigated using X-ray diffraction, electron diffraction, electron microscopy, energy-dispersive analysis, and differential scanning calorimetry. It has been demonstrated that the planar morphology of calcium phosphate nanoparticles capable of interacting with nanofibrils of the cellulose matrix is an important factor providing interfacial contacts in the formation of organic-inorganic composite materials. It has been established that magnesium-containing calcium phosphates represent two-phase systems consisting of calcium magnesium phosphate Ca2.6Mg0.4(PO4)2 (whitlockite) and hydroxyapatite Ca5(PO4)3(OH). The biocompatibility of the composite materials based on two-phase calcium phosphate systems and the temperature range of their stability (∼20–250°C) determined by the thermal stability of the organic component have been investigated.

Synthesis, mutual solubility, and thermal behavior of nanocrystals in the LaPO4-YPO4-H2O system

Nanopowders of lanthanum and yttrium orthophosphates have been synthesized. The growth of nanocrystals has been investigated in the temperature range 200–1100°C. The temperature-concentration limits of the existence of the solid solutions have been determined. The thermal behavior of the orthophosphates has been studied over the entire range of lanthanum and yttrium concentrations.

Thermal expansion and phase transitions in K1 − xCsxBSi2O6 borosilicate solid solutions

AbstractSolid solutions K1 − xCsxBSi2O6 (x (atomic fraction) = 0.00, 0.20, 0.30, 0.35, 0.40, 0.80, 0.90,1.00) have been prepared by solid-phase synthesis and crystallization of glasses in the KBSi2O6-CsBSi2O6 borosilicate series. The thermal behavior of the solid solutions has been investigated using the annealing and quenching techniques, dilatometry, and high-temperature X-ray powder diffraction. It has been shown that solid solutions with x = 0.00–0.35 and 0.40–1.00 correspond to space groups I

The influence of the particularities of synthesis on the physicochemical properties of nanosized powders and ceramic samples of REE orthophosphates

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