Papers by Keyword: Liquid Phase

Abstract: The effects of 3Z2B addition on the microwave dielectric properties and the microstructures of (1-x)(Mg_0.95Co_0.05)TiO₃-xCa_0.6La_0.8/3TiO₃ ceramics prepared with conventional solid-state route have been investigated. Doping with 3Z2B can effectively promote the densification and the microwave dielectric properties of (1-x)(Mg_0.95Co_0.05)TiO₃-xCa_0.6La_0.8/3TiO₃ ceramics. It was found that (1-x)(Mg_0.95Co_0.05)TiO₃-xCa_0.6La_0.8/3TiO₃ ceramics can be sintered at 1150°C due to the liquid phase effect of 3Z2B additions observed by SEM. The Q×f value of (1-x)(Mg_0.95Co_0.05)TiO₃-xCa_0.6La_0.8/3TiO₃ ceramics decreased with increasing 3Z2B content. At 1150°C, 0.9(Mg_0.95Co_0.05)TiO₃-0.1Ca_0.6La_0.8/3TiO₃ ceramics with 1.0wt% 3Z2B addition possesses a ε_r value of 22.6, a Qf value of 49,000 (GHz) and a τ_f value of-10.7 ppm/°C.

Abstract: A set of experimental system was self-designed and made for liquid phase catalytic oxidation of gas to methanol. It was used to investigate the impacts of catalyst and reaction conditions on catalytic oxidation of gas to methanol in acetic acid solution, and to analyze its reaction mechanism. It has been showed that the yield of the methanol is 1840 μmol under the catalysis of 0.5 g of 0.5% Pd-CuPc/Y and the following conditions: CH3COOH:H2O = 4:1 (v/v), 1000 μmol of p-benzoquinone; reaction time, 3 h; reaction temperature, 150°C; gas composition, 2.5MPa CH4+0.4MPaO2 +0.4MPa N2; in acetic acid solution, catalytic oxidation of mine gas to methanol follows mechanisms of electrophilic substitution and oxidation of reactive oxygen species (ROS).

Abstract: β-Tricalcium phosphate (β-TCP) ceramics are of interest for bone requirements implants due to resoption behavior. The mechanical properties of β-TCP, however, are not yet sufficient to allow load bearing application of implants. The aim of this work was to investigate the effect of Mg²⁺ substitution on the strength sintered TCP. Due to promotion of a liquid phase at 1200°C, Calcium pyrophosphate (CPP-C₂P₂O₇) was used to improve the sintering of the samples. The introduction of CPP was promoted by use of a Ca/P molar ratio of 1.45. The powders were synthesized using a mixture of Ca (OH)₂ suspension and diluted H₃PO₄ with addition of MgO and calcined at 750 °C, 900 °C and 1050 °C. The cold isostatic pressing compacts were sintered at 1200 °C and 1300 °C, respectively.It was shown that a small Mg content (1.5 mol%) increased both compressive strength and fractional density of the TCP material sintered at 1200 °C from 132 ± 39 MPa at 92.1 % of fractional density to 193 ± 29 MPa at 94.5 % of theoretical density. Higher amounts of Mg inhibited the grain growth provoking a increase of the boundary mobility activation energy. Abnormal grain growth (AGG) was observed after sintering at 1300°C, as result CPP - liquid phase formation. Increase of Mg content promoted AGG, due to inhibition of grain growth during normal grain growth resulting in a increase of the residual elastic energy of the system.

Abstract: The densification of α-SiC occurred by liquid-phase sintering mechanism with AlN-RE₂O₃ (RE=Nd, Gd, Y, Lu) was studied. The total additive content was fixed at 15 wt%. Cold isostatically pressed samples were sintered at 1800-1950 °C under N₂ atmosphere for 1 h. The linear shrinkage and weight loss of the samples were about 17-20% and 2-5%, respectively. The mechanical properties and microstructure of sintered samples were investigated. The experimental results showed that the fracture toughness of samples was 6-8 MPa·m^1/2, the hardness was in the range of 18-21 GPa and the bending strength was in the range of 400-500 MPa. It was found that a decrease in the cationic radius of the rare-earth oxides was accompanied by an increase in hardness and flexural strength of the SiC ceramics, whereas the fracture toughness was improved by incorporating rare-earth oxides of larger cationic radius. The morphology (SEM) of sintered sample showed a fine grained microstructure with equiaxed grains. Fracture mode was intergranular fracture.

Abstract: The speeds of sound in near saturated and subcooled liquid phases of R-1234yf have been measured using a ultrasonic sensor. The measurements were conducted at the temperature range from 0 to 80 °C, and the pressure range from 0.316 to 2.52 MPa. In order to validate the ultrasonic sensor, the measurement in pure water at the temperature range from 0 to 80 °C was also performed. The measurement result of water was compared with those calculated from REFPROP (based on IAPWS-95) and PROPATH (based on IAPWS-IF97). The result of water agrees well with that calculated from REFPROP within a maximum deviation of 0.28%, except for that at temperature of 80 °C. And it agrees well also with that calculated from PROPATH within a maximum deviation of ±0.2%. The measurement results for near saturated and subcooled liquid phases of R-1234yf were compared with those calculated from REFPROP and JSRAE thermodynamic table.

Abstract: The production and pyrophorisity of iron sulfur compounds in liquid phase were studied in order to get the spontaneous combustion rules of iron sulfur compounds producted by different ways. In the experiment, FeSO₄·7H₂O, FeCl₂·4H₂O, Fe (NO₃) ₃·9H₂O react with (NH₄)₂S_x and Na₂S·9H₂O respectively,then the pyrophorisity were analyzed by the exothermic oxidation process of sulfuration productions. The results show that, the pyrophorisity of sulfuration productions formed from (NH₄)₂S_x and dissolvable iron salt is obviously higher than formed from Na₂S and the same dissolvable iron salt. With the increase of dissolvable iron salt concentration, the oxidation pyrophorisity of sulfuration productions formed from (NH₄)₂S_x also increases. There is some pyrophorisity of sulfuration productions formed from Na₂S and dissolvable iron salt. But the pyrophorisity is faint relatively.

Abstract: Particle reinforced SiC composites with the addition of TiB2 were fabricated in range of 1750°C to 1950°C by pressureless sintering by utilizing liquid phase with AlN-Y2O3 as sintering additives. The effective of sintering aids in densification, the mechanical properties of sintered sample and the microstructure had been investigated in this paper. The results showed that the best densification behaviors occurred in AlN:Y2O3 at 60 :40%mol ratio not at eutectic point. Adding TiB2 to SiC matrix increase the toughness and decreased the hardness. Microstructure analysis showed that the increasing of toughness was due to the crack deflection with some contribution intergranular fracture mechanism.

Abstract: Abstract. In this paper, conditions for obtaining high growth rate during epitaxial growth of SiC by vapor-liquid-solid mechanism are investigated. The alloys studied were Ge-Si, Al-Si and Al-Ge-Si with various compositions. Temperature was varied between 1100 and 1300°C and the carbon precursor was either propane or methane. The variation of layers thickness was studied at low and high precursor partial pressure. It was found that growth rates obtained with both methane and propane are rather similar at low precursor partial pressures. However, when using Ge based melts, the use of high propane flux leads to the formation of a SiC crust on top of the liquid, which limits the growth by VLS. But when methane is used, even at extremely high flux (up to 100 sccm), no crust could be detected on top of the liquid while the deposit thickness was still rather small (between 1.12 μm and 1.30 μm). When using Al-Si alloys, no crust was also observed under 100 sccm methane but the thickness was as high as 11.5 µm after 30 min growth. It is proposed that the upper limitation of VLS growth rate depends mainly on C solubility of the liquid phase.

Abstract: Phase transitions can be usually observed in nature and technology which effectively utilize certain types of these transitions. An approach to modeling phase transition processes on the basis of the mathematical theory of growing solids is developed. Liquid-solid and gas-solid phase transitions are under consideration. Main attention is paid to the processes of solid phase growth and deformation.

Abstract: We have discussed the origin of the attractive interactions between like charged ions in the liquid phase, by using the theoretical formula, which explains an anomalous diffusion mechanism of positrons in the liquid phase. It is suggested strongly that the attractive interactions are attributed to exchange interactions of the massive gauge fields between like charged ions.