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 transformation of melamine at high pressure and temperature

Pyrolysis experiments of melamine were carried out under high pressure of 5 GPa and different temperatures. The crystal structure, chemical bonding, and composition of the melamine pyrolysate were studied by X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray energy-dispersive analysis (EDX), and combustion elemental analysis. A new C–N–H phase was found in the pyrolysate at 5 GPa and 800 °C. The structure is tentatively indexed as a monoclinic symmetry, with the following lattice parameters: a = 8.5368 (±0.0009)Å, b = 9.1153 (±0.0010)Å, c = 10.2440 (±0.0011)Å, α = γ = 90°, and β = 95.5696 (±0.0016)°. The photoluminescence behavior of the pyrolysates was investigated. A blue emission at 421 nm for the C–N–H phase was observed under the ultraviolet light excitation of 365 nm.     

Preparation, thermal expansion, high pressure and high temperature behavior of Al2(WO4)3

The titled compound Al₂(WO₄)₃ was synthesized by a conventional solid state reaction and characterized by powder XRD. It crystallizes in an orthorhombic (Pbcn, No. 60) lattice, with unit cell parameters as 12.582(2), 9.051(1), 9.128(2) Å, and V = 1039.5(3) (Å)³. The compound was found to show negative thermal expansion (NTE) behavior in the temperature range of 25 to 850°C. The average linear NTE coefficient (₁), in this temperature range, was –1.5 × 10^–6 K^–1. The effect of pressure at ambient temperature, was studied by a Bridgman Anvil (BA) apparatus, to reveal that there is no irreversible phase transition up to 8 GPa. The effect of high pressure and high temperature on this compound was studied by a Toroid Anvil (TA) apparatus. This compound has a limited stability under high pressure and temperature, as it undergoes a decomposition to AlWO₄ and WO_3–x with a partial oxygen loss. As an off-shoot of this work, certain new modifications of WO_3–x under pressure and temperature were observed, viz., monoclinic, tetragonal and an orthorhombic modifications at 5 GPa/1400°C, 3 GPa/900°C and 1.8 GPa/1030°C, respectively. The detailed XRD studies of the products are presented here.     

Interactions between chemical evolution (hydration) and physical evolution (setting) in the case of tricalcium silicate

This paper describes recent experimental results concerning investigation of the parameters which determine, on the one hand, the kinetics of hydration of tricalcium silicate and the thermodynamic, morphological and structural characteristics of C-S-H and, on the other hand, the evolution of the particle interactions at the origin of setting. It is shown that, in both cases, lime concentration in solution is the most important parameter. As a consequence, the chemical evolution of the system, which controls the lime concentration in solution, determines the nature of particle interactions and the physical evolution of the suspension or paste. In return, the contacts, between particles, resulting from the coagulation of the suspension, seem to have a role in the kinetics of the chemical reaction.     

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.     

Two-step precipitation preparation and self-setting properties of tricalcium silicate

Tricalcium silicate (Ca₃SiO₅) powders were synthesized by a novel precipitation method with Ca(NO₃)₂·4H₂O, Na₂SiO₃·9H₂O and Na₂CO₃ as the starting materials. Pure Ca₃SiO₅ was obtained at 1400 °C for 8 h. The characteristics of tricalcium silicate powders prepared by this method were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and laser particle size analyzer, and compared with the powders prepared by the sol–gel method reported in a previous study. The effects of the size of the powder on the self-setting properties of Ca₃SiO₅ were also investigated. The result showed that the size of Ca₃SiO₅ powders prepared by the two-step precipitation method was 1–10 μm and less than that of Ca₃SiO₅ powders prepared by sol–gel method. The results showed that the reduction of the particle size accelerated the setting and hardening of the cement and resulted in a significant increase of the compressive strength of the cement.     

含Ni单矿C3S晶型及早期水化特性研究

以Ca(OH)2、SiO2化学纯为原料,分别掺入不同质量分数的Ni2O3制备不同晶型的C3S相,运用化学分析、XRD、DTA、SEM、水化热测试方法,研究了掺Ni2O3后C3S矿物相形成、晶型及其水化特性变化趋势。结果表明,Ni2O3促进C3S形成效应一般,掺量大于2%后促进效应增强;且掺量大于2%时,Ni2O3可稳定单斜型C3S存在;含Ni的C3S具有一定的活性点或活性面,水化后会导致液相呈现较高的Ca2+浓度,轻微地加快了C3S水化速率,且水化产物颗粒较小,分散度和水化程度高。     

TiO2对高C3S熟料水化的影响

为了探讨TiO2在高C3S熟料水化过程中的作用机制,分析了TiO2对水泥水化组成和抗压强度的影响,并借助微量量热法和熟料矿物的高分辨图像分析了熟料的早期水化与抗压强度之间的关系。结果发现:0.5%TiO2虽延缓熟料的初始水化,但缩短了诱导期,提高了3天抗压强度,而掺量超过2.0%后,熟料的诱导期变长和3天强度降低,即诱导期的长短会影响到强度的变化。此外,TiO2对晶格缺陷增加的贡献并没有引起天强度的提高。     

Nanosilica effects on composition and silicate polymerization in hardened cement paste cured under high temperature and pressure

Cement pastes of water to cement ratio (w/c) of 0.45 with and without nanosilica are hydrated under two conditions, room condition (20 °C with 0.1 MPa pressure) and an oil well condition (80 °C with 10 MPa pressure) for 7 days. For the cement pastes with nanosilica, 1% and 3% of cements weights were replaced by nanosilica. The composition of the hardened cement pastes is investigated using X-ray diffraction (XRD). Nuclear magnetic resonance (NMR) experiments are used to quantify the silicate polymerization in hydrated cement paste. Microstructural phases are identified according to the corresponding mechanical property using nanoindentation. The results showed that under room curing conditions, hardened cement paste with 1% nanosilica has the highest level of calcium silicate hydrate (C–S–H) polymerization. However, under high temperature and pressure curing conditions, hardened cement paste with 3% nanosilica has the highest level of C–S–H polymerization. A new relatively stiff microstructural phase is observed in cement pastes incorporating nanosilica and cured under elevated pressure and temperature conditions. The significance of curing conditions and nanosilica content on the polymerization and stiffness of hydrated cement pastes are discussed.     

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.     

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.     

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.     

The microstructure and infra-red spectra of hydrated tricalcium silicate containing phosphate

The influence of phosphate, in the concentration range 0.7 to 4.5%, on the hydration reaction of tricalcium silicate was examined with a scanning electron microscope and an infra-red spectrometer. Correlation between the morphology and infra-red vibrations, on the one hand, and the free lime content dependence on the phosphate concentration, on the other, is discussed.This paper is in partial fulfilment of the MSc degree of Y. Rubinsztain, at the Hebrew University.     

AsNCa3 at high pressure

A constant pressure optimization scheme is applied to the study of ternary calcium nitrides under pressure. The enthalpy is minimized with respect to the electronic configuration, the positions of the atoms and the cell metric (i.e. the lattice parameters). Symmetry corrections can be performed during the relaxation towards the equilibrium structure in order to be able to investigate the compound in a certain proposed symmetry. We obtain excellent agreement with experiment for the zero-pressure structural parameters of the cubic anti-perovskite structure BiNCa₃ and of the distorted anti-perovskite structures AsNCa₃ and PNCa₃. For AsNCa₃ the structural parameters, band gap energies, etc. are investigated as a function of the pressure. A new cubic phase is predicted to have a lower enthalpy than the orthorhombic phase for pressures above 59 GPa.     

High temperature and pressure preparation and properties of iron carbides Fe7C3 and Fe3C

The formation regions of Fe₇C₃ and Fe₃C were determined at high temperature and high pressure in the iron-graphite system. Fe₇C₃ formed at relatively higher pressures and Fe₃C at lower pressures. Both Fe₇C₃ and Fe₃C were isolated from coexisting excess carbon powders by a magnetic method. Fe₇C₃ had a Curie point of 250° C and a saturation magnetization of 120 emu g^–1 at room temperature and Fe₃C had those of 210° C and 125 emu g^–1. Fe₇C₃ decomposed to Fe₃C and carbon at 600° C, but to -Fe and carbon at 700° C at atmospheric pressure, and Fe₃C to -Fe and carbon at 700° C. The substitution of other metals (Cr, Mo and W) for iron in these carbides leads to changes in the thermal stabilities and the magnetic properties.