Phase transformation and indentation response in the surface of MoSi2 exposed to vacuum at high temperature

A MoSi₂ sample contains a small amount of Mo₅Si₃C phase was exposed to vacuum at 1300 °C for 100 h. The surface of the sample was examined by XRD, SEM and indention test. Two layers were revealed in the surface of the MoSi₂ sample. The outer layer consists of (002) textured Mo₅Si₃ phase and porosities. The Mo₅Si₃ phase is formed through the decomposition of the MoSi₂ phase. The Mo₅Si₃C phase, which is a constituent phase in the matrix, disappears in the inner layer. The phase transformation process was analyzed in the light of assuming that silicon is the predominant diffuser. Indentation test on the surface revealed that the fracture mode of Mo₅Si₃ is completely transgranular.     

Capillary ion chromatography at high pressure and temperature

The application of high pressure and temperature in ion chromatography (IC) can significantly improve the efficiency and reduce the analysis time. In this work, the kinetic-performance limits of capillary IC columns with inner diameters of 400 μm packed with 4 and 7 μm macroporous anion-exchange particles were investigated employing a capillary ion-exchange instrument allowing column pressures up to 34 MPa and column temperatures up to 80 °C. Plate heights below 10 μm could be realized using capillary columns packed with 4 μm particles. Compared to conventional IC using 7 μm particles and pressures up to 21 MPa, a 40% improvement in plate number could be achieved when working at the kinetic performance limits at 34 MPa and using columns packed with 4 μm particles. Using coupled columns with a total length of 400 mm, a mixture of seven anions was separated within 7.5 min while yielding 20?000 plates. Increasing the temperature improved the performance limits when operating in the C-term region (for fast IC separation using columns <75 cm). Temperature also affected the retention properties and hence the selectivity. At higher temperature, retention for monovalent ions was mainly governed by ion diameter. An increase in retention with temperature was observed for small ions, and there was a decrease for ions having a larger diameter. The retention factor for divalent and trivalent anions increased with temperature.     

Crystallization of amorphous carbon at high static pressure and high temperature

Amorphous carbons prepared from furfuryl alcohol resin have been studied in a high-pressure apparatus of octahedral anvil type at pressures up to 18 GPa and at temperatures up to 2000° C. The amorphous carbons, when heated under pressure, crystallized first into graphite at 450 to 600°C and then into diamond at 1120 to 2000° C. The temperatures for the onset of these crystallizations,T ₉ andT _d, were determined by a simple technique. As the temperature for the preparation of the amorphous carbons was raised from 700 to 1000° C,T ₉ at 15 GPa increased slightly whereasT _d at the same pressure turned from a decrease into an increase beyond 750° C for the preparation temperature. For amorphous carbon prepared at 850° C,T _g increased a little whileT _d decreased markedly with increasing pressure.     

Phase stability of SiC against Ti at high temperature

SiC to SiC were reacted by Ti foil at high temperature of 1673 K in vacuum. Ti reacted with SiC, and formed many reaction phases between SiC and Ti. At 1673 K SiC reacted at a reaction time of 0.5 ks or longer. From the SiC many reaction zones of Ti₃SiC₂, Ti₅Si₃C_X, Ti₅Si₃C_X + TiC, and TiC + Ti were formed. Ti binary compound of TiC and Ti ternary compounds of Ti₃SiC₂, and Ti₅Si₃C_X, were formed. The principle of the reaction zones was thermodynamically discussed by the corresponding chemical potential diagram.     

Thermal conductivity of liquid propionates at high temperature and pressure

Experimental data on thermal conductivity of octyl- and heptylpropionate over a wide range of temperature and pressure are presented.Notation T_b boiling point at atmospheric pressure - n_C number of carbon atoms per molecule Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 4, pp. 654–657, October, 1980.     

NbRu合金室温马氏体的相变和显微组织

利用示差扫描量热分析、X射线衍射分析、透射电子显微分析和高分辨电子显微分析研究了等原子比NbRu合金室温马氏体的相变和显微组织．确定了其在一个冷热循环中发生两步相变时不同的相变温度，研究了其室温热马氏体组织的微观组织及其亚结构，实验结果表明：该合金的马氏体为热弹性马氏体；马氏体变体间界面呈现典型的自协作组态；变体内部存在大量的(101)I型孪晶亚结构，孪晶亚结构板条间界面平直、清晰。     

Sintering behaviour of the diamond-cobalt system at high temperature and pressure

A powder mixture of diamond—8.9 vol % Co was consolidatedin situ on a WC-10 wt % Co base at temperatures of 1300 to 1500° C under a pressure of 5.8 GPa. The sintered body obtained at 1300° C, which is below the diamond—cobalt eutectic point, was not hard, and the surface of the diamond particle was partially graphitized. On the other hand, the sintered body obtained at 1400 to 1500° C was fairly hard. A strong correlation was also observed between hardness and the cobalt content found in the sintered body. The cobalt content in the harder sintered body was clearly lower compared with that of the softer one. The surface graphitization of the diamond particles is necessary to the transfer of cobalt during the sintering of diamond. In sintering the diamond-cobalt system, the sinterability of diamond was closely related to the feasibility of transformation from diamond to graphite.     

Phase transformation of high aluminium fly ash in carbothermal reduction–nitridation at high temperatures

Abstract

Sialons (Si₅AlON₇, Si₄Al₂O₂N₆, Si₃Al₃O₃N₅ and SiAl₄O₂N₄) were synthesised from high aluminium fly ash by using a carbothermal reduction–nitridation process. The effects of temperature and the addition of carbon black on the phase compositions and morphologies have been investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Thermodynamic analysis has been used to study phase transformations. For the sample with the stoichiometric carbon black content, the product formed at 1500°C was single phase short prismatic Si₃Al₃O₃N₅. The products at 1600°C were Ca–α-Sialon accompanied by AlN, whereas at 1700°C, Si₄Al₂O₂N₆ and SiAl₄O₂N₄ formed. Increasing the carbon black at 1500°C, Si₃Al₃O₃N₅, β-SiC, 15R and Fe_xSi were produced as reaction products.     

The stability of yttrium α-SiAlON and β-SiAlON at high pressure and high temperature

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Hydration of tricalcium silicate (C3S) at high temperature and high pressure

Hydration products of tricalcium silicate (C₃S) are the calcium silicate hydrates (C-S-H) and Portlandite. Silica fume, added to anhydrous cement in industrial formulations reacts with Portlandite and leads to C-S-H different from the previous one. C₃S hydration with and without silica fume has been studied under high pressure (1000 bar) and high temperature (160°C) by numerous techniques (²⁹Si and ¹H NMR, XRD, Thermal analysis, SEM) for different hydration times. In these conditions, high temperature more stable crystalline phases are formed and their kinetics of formation is dependent on pressure. Besides, electrical conductivity measurement on hydrating cement under pressure have been carried out in order to evidence the great dependence of hydration kinetics with pressure. This study proposes a practical phase diagram which allows on a thermodynamical base to understand the change of equilibrium temperature with pressure. The kinetics of reaction has been studied and mechanisms of reaction proposed to explain the results.     

Growth of diamond microcrystals by the oriented attachment mechanism at high pressure and high temperature

For the first time it has been experimentally shown that a powder of detonation nanodiamonds (DND) and a saturated acyclic hydrocarbon, mono- or dibasic alcohol, used as the reaction mixture after treatment at high pressures (5–8 GPa) and high temperatures (1300–1800°C) results in the formation of diamond single crystals up to 15 micron in size. The Raman spectrum indicates that the diamonds have a perfect of crystal structure. It has been suggested that the oriented attachment mechanism is responsible for growth of micrometer-size diamond single crystals out of DND particles with sizes of about 5 nm under these technological conditions.     

Behaviour of B-N-Si under high pressure and high temperature

The phase relations of the B-N-Si system have been studied using a quenching method up to 10GPa and 2000 °C using a high-pressure apparatus of the octahedral anvil type. Pressure-temperature conditions for obtaining z-BN (diamond analogue of boron nitride) were delineated for turbostratic BN (t-BN), t-BN/amorphous Si₃N₄ and t-BN/-Si₃N₄. These conditions shift toward higher regimes of temperature as amorphous Si₃N₄ or -Si₃N₄ is incorporated into t-BN. Spontaneous sintering occurringin situ at high pressure yields z-BN-based composite compacts.     

Sintering behaviour of the diamond-super invar alloy system at high temperature and pressure

In the diamond-super invar alloy system, effect of the grain size of the starting diamond powder on the sintering behaviour was investigated at 5.8 G Pa and 1300 to 1500 ° C for 30 to 60 min. Abnormal grain growth was often observed in the sintered diamond using fine diamond powder, but a homogeneous sintered diamond was easily synthesized using 5 to 10m diamond. By the rigorous control of sintering conditions, a 3m grain size homogeneous sintered diamond was synthesized under conditions of 5.8 G Pa and 1350 ° C for 30 min. The Vickers hardness and thermal resistance of the fine grained sintered diamond was examined.     

Alternating sequence of ring and chain structures in sulphur at high pressure and temperature

Sulphur is the subject of a renewed intensive research effort aiming at characterizing its complex phase diagram. Nonetheless, on reading recent literature on its high-pressure phases, a confused picture emerges where different techniques obtain different results. We have investigated the phase diagram of sulphur by X-ray diffraction at high pressures and temperatures (6-11 GPa and 300-1,000 K), and have observed a new occurrence of a molecular S6 phase, in addition to the previously described polymeric helical trigonal and tetragonal phases. The stability regime of the S6 phase has been defined through the observation of coexistence points with each of the polymeric phases and the trigonal-S6-tetragonal triple point. The existence of these high-pressure phases allows us to define a framework that reconciles the apparently contradictory results existing in the literature. Moreover, the classic idea that pressure induces polymerization in sulphur is refined by the direct observation of an alternating sequence of molecular and polymeric phases that we report here.     

Phase transformation of calcium phenyl phosphate in calcium hydroxyapatite using alkaline phosphatase at body temperature

Layered calcium phenyl phosphate ((C₆H₅PO₄)_0.92(HPO₄)_0.08Ca·1.3H₂O: CaPP), which is composed of a multilayer alternating bimolecular layer of phenyl groups and amorphous calcium phosphate phase, was treated in aqueous media including different amounts of enzyme such as alkaline phosphatase (ALP) at pH = 9.6 and 37 °C for 48 h. Treating the CaPP in the absence of ALP took place only the dissolution of this material. When the CaPP particles were treated in the presence ALP, calcium hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂: Hap) was formed. The yielded Hap contained no phenyl group and the molar ratio Ca/P of this material was 1.66, almost corresponding to 1.67 of the stoichiometric Ca/P ratio of Hap. TEM observation revealed that the irregular-shaped CaPP particles disappeared and rod-shaped Hap nano-particles were generated. The particle length and crystallite size of Hap were slightly increased on increasing the additive amount of ALP. These facts allow us to infer that the CaPP particles are dissolved, hydrolyzed and recrystallized to Hap by treating with ALP in aqueous media at body temperature of 37 °C and that the ALP plays as a catalyst for hydrolysis of phenyl phosphate ions. This phase transformation of CaPP in Hap in the presence of ALP resembles to the formation mechanism of Hap in animal organism.     

Behavior of the refractive index of lithium disilicate glass ceramic processed at high pressure and high temperature

The aim of this work was to investigate the effect of high pressure and high temperature on the refractive index of lithium disilicate glass ceramic with the stoichiometric composition Li₂O·2SiO₂ (LS₂). A first group of monolithic LS₂ glass samples were processed at 2.5 GPa, 4 GPa and 7.7 GPa at room temperature and a second group was submitted to high pressure and, simultaneously, to heat treatments for nucleation and growth of the crystalline phases. For comparison, samples submitted to the same heat treatments at 1 atm were also investigated. The refractive index of the samples was obtained by spectral ellipsometry and the results were clearly dependent on the particular pressure and temperature conditions. The crystallization of the samples was investigated by X-ray diffraction. For the samples processed under high temperature at 1 atm and at 2.5 GPa a fraction of the originally amorphous glass was transformed to a monoclinic phase of lithium disilicate. For the samples processed under high temperature and at 4 GPa, a large fraction of the originally amorphous glass transformed to an orthorhombic phase while, at 7.7 GPa, it was observed the formation of lithium metasilicate.     

Stress and dislocations in diamond–SiC composites sintered at high pressure,high temperature conditions

Diamond–silicon carbide composites were sintered at 10 GPa and three different temperatures: 1600, 1800, and 2000 °C. Distributions of residual surface stresses in diamond crystals were obtained by the analysis of Raman band shifts and splitting. It was noted that stresses concentrate around points of contacts between diamond crystals. Average stress increase with increasing sintering temperature. Complementary information on average sizes of crystallites, concentration of stacking faults, and population of dislocations in both diamond and SiC were obtained from X-ray diffraction profile analysis. It was observed that for both diamond and silicon carbide phases the average crystallite sizes decrease. The population of dislocations in the diamond phase increases with increasing sintering temperature and the population fluctuates in the SiC phase. Concentration of stacking faults was significant only in SiC.