Effect of certain factors on the process of hot pressing parts from silicon-carbide based materials

Conclusions The effect of friability of the starting materials on the microstructure, phase composition and physicomechanical properties of products made from alloy S-8 was studied. The optimum temperature of the process was determined for alloy S-8. The conditions were found at which it is possible to obtain articles from alloy S-8 of uniform density over the volume.     

Study of Adsorption of TiO Nanoclusters on a TiS 2 Single Layer via the ab initio Random Structure Searching

The adsorption of TiO nanoclusters onto a TiS2 single layer surface is investigated via the density functional theory in combination with random structure searching algorithms. The nanoclusters are Ti—O dipoles and their orientation in the electrostatic field is induced by S atoms near the TiS2 single layer surface. The binding energy of nanoclusters with a TiS2 single layer surface is found to be 4.713 eV. Another curious observation is the creation of a nanocluster with an S–S–S–O anionic tetrahedron by Ti atoms, where the O anion is located at the maximum distance from the surface.     

Production of Chemically Pure Zirconia-Based Nanoceramics in the ZrO2(Y2O3)–Al2O3 System for Restorative Dentistry

Theoretical Foundations of Chemical Engineering - The synthesis technology of a chemically pure nanodisperse precursor powder (10–12 nm) based on a tetragonal solid zirconia (t-ZrO2) solution...     

Silicon core–iron siloxane shell nanoparticle polymer composites with multiferroic properties

Multiferroic (MF) composites based on nanoparticles consisting of a silica core and a shell of spin-variable Fe(III) complexes in a polymer matrix (polystyrene) were synthesized and characterized by different methods. The nanoparticles had the formula 80SiO₂·20{Fe[OSi(Me)(OEt)₂]₃}, and their particle size was on the order of 5–7 nm. Dielectric and electron spin resonance studies showed the presence of two types of Fe ions in the nanocomposite. Iron ions in the low-spin state [Fe(III)-LS] and iron ions in the high-spin state [Fe(III)-HS], which were bound by indirect exchange interactions through oxygen and silicon atoms {[Fe(III)-LS]─O─Si─O─[Fe(III)-HS]} were responsible for the MF properties of the composites with core–shell nanoparticles. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47681.     

Ultrasonic disintegration of tungsten trioxide pseudomorphs after ammonium paratungstate as a route for stable aqueous sols of nanocrystalline WO<Subscript>3</Subscript>

A new facile method is proposed for the preparation of aqueous sols of highly crystalline tungsten trioxide with a particle size of 60–150 nm, containing no organic stabilizers/surfactants. These sols possess high sedimentation stability, which is quite unusual for inorganic colloidal systems containing relatively large particles, with a rather high density (ρ _c(WO₃) = 7.3 g/cm³). The method is based on the thermal decomposition of ammonium paratungstate, followed by dispersing the resulting powders in water under ultrasonic treatment. Thermal decomposition of ammonium paratungstate, and the composition and structure of the resulting tungsten trioxide and its aqueous dispersions, were investigated with thermal analysis combined with the mass spectrometry of gaseous thermolysis products, powder X-ray diffraction, scanning electron microscopy, low-temperature nitrogen adsorption, IR spectroscopy and dynamic light scattering. It has been demonstrated that the high sedimentation stability of WO₃ results from electrostatic stabilization, which might be caused by the formation of tungstic acid on the surface of WO₃ particles when they come into contact with water. The nanocrystalline WO₃ obtained can be used to produce gas sensors for ammonia.     

Influence of cryochemical and ultrasonic processing on the texture and thermal decomposition of xerogels and properties of nanoceramics in the ZrO<Subscript>2</Subscript>〈Y<Subscript>2</Subscript>O<Subscript>3</Subscript>〉–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> system

We have studied the influence of cryochemical and ultrasonic processing on the formation, structure, particle size, and thermal decomposition of xerogels in the ZrO₂〈Y₂O₃〉–Al₂O₃ (20 wt %) system. Nanopowders of tetragonal-zirconia-based solid solutions with a high degree of tetragonality (c/a = 1.4366) have been synthesized. Al₂O₃ has been shown to slow down t-ZrO₂ crystallite growth in the temperature range 600–1400°C. We have optimized nanopowder consolidation conditions, obtained nanoceramics stable to low-temperature “aging” in a humid medium, and investigated their physicochemical and mechanical properties.     

Synthesis and Physicochemical Properties of Nanopowders and Ceramics in a CeO<Subscript>2</Subscript>–Gd<Subscript>2</Subscript>O<Subscript>3</Subscript> System

Nanopowders with a composition of (СeO₂)_1–x(Gd₂O₃)_x (x = 0.03, 0.05, 0.07, and 0.10) are synthesized by the coprecipitation method using cryotechnologies. The coherent scattering region (CSR) of the powders is 10–14 nm and the specific surface area is 70–81 m²/g. Based on the powders, ceramic nanosized materials with CRS of 64–71 nm are obtained. The dependence of the phase composition, microstructure, and electrical transport properties of the obtained samples on the Gd₂O₃ content is established. In a CeO₂–Gd₂O₃ system, a solid solution with the composition of (CeO₂)_0.90(Gd₂O₃)_0.10 has the highest ionic conductivity with the transfer number of ions of t_i = 0.74 at a temperature of 700°C. It is shown that ceramics of this composition can be used as a solid electrolyte of intermediate-temperature fuel cells due to their physicochemical characteristics.     

Structure and conductivity of yttria and scandia‐doped zirconia crystals grown by skull melting

In this paper a detailed study of the (ZrO₂)_1‐x(Y₂O₃)_x (x=0.025–0.15), (ZrO₂)_1‐x(Sc₂O₃)_x (x = 0.06 – 0.11) and (ZrO₂)_1‐x‐y(Sc₂O₃)_x(Y₂O₃)_y (x=0.07 – 0.11; y=0.01 – 0.04) solid solution crystals grown by skull melting technique is presented. The structure, phase composition, and ion conductivity of the obtained crystals were investigated by X‐ray diffraction, transmission electron microscopy, Raman scattering spectroscopy, and impedance spectroscopy. Maximum conductivity as (ZrO₂)_1‐x(Y₂O₃)_x and (ZrO₂)_1‐x(Sc₂O₃)_x solid solution crystals is observed for the compositions containing 10 mol% stabilizing oxide, and the conductivity of 10ScSZ is ~3 times higher than for 10YSZ. Experiments on crystal growth (ZrO₂)_1‐x‐y(Sc₂O₃)_x(Y₂O₃)_y solid solutions showed that uniform, transparent crystals 7Sc3YSZ, 7Sc4YSZ, 8Sc2YSZ, 8Sc3YSZ, 9Sc2YSZ, 9Sc3YSZ, 10Sc1YSZ, and 10Sc2YSZ are single phase crystal containing t″ phase. It is established that a necessary condition of melt growth of (ZrO₂)_1‐x‐y(Sc₂O₃)_x(Y₂O₃)_y single‐phase crystals is the total concentration of the stabilizing oxides from 10 to 12 mol%. The addition of Y₂O₃ affects the (ZrO₂)_1‐x‐y(Sc₂O₃)_x(Y₂O₃)_y solid solution conductivity different ways and depends on the Sc₂O₃ content in the starting composition. The effects of structure, phase composition, concentration, and type of stabilizing oxides on the electrical characteristics of obtained crystals are discussed.