Deformation of graphite at high pressures

In high pressure experiments, it is shown that the compression stress-strain curve of a porous polycrystalline graphite depends markedly on the confining pressure in the range 1–8 kb and that considerable volume changes occur during the deformation as well as during application of the pressure. There is also an almost complete recovery of both length and volume during release of the pressure after strains of up to 20 per cent. After allowing for the interaction with the stress-strain behaviour of the work associated with volume changes, it is concluded that, in addition to basal slip, frictional sliding on internal surfaces is an important mechanism of deformation, especially at the lower pressures, and that the deformation is accompanied by some process such as flexure of platelets which introduces the internal stresses responsible for the recovery effects.     

Coal pyrolysis at high temperatures and pressures

At high temperatures (s> 1100°C), pyrolysis of coal plays an increasingly important role in the overall coal conversion process. This Paper presents experimental data on the extent of pyrolysis of coal at 800–1600°C. In addition, the effects of the following parameters are examined: gaseous environment (N₂, CO₂ and H₂O), pressure (1–20 atm), particle size, moisture content and type of coal. Previous data on some of these parameters are non-existent. A unique TGA apparatus constructed for this work allows high heating rates (10²–10³°Cs^?1) due to the direct radiation heating. In all the gaseous environments, a plateau in per cent pyrolysis is noticed at 1200–1400°C followed by a sharp increase in the amount of pyrolysis as the temperature is raised. This is found consistent with the three-stage mechanism proposed for the evolution of volatiles. In CO₂ and steam environments, there is slightly less pyrolysis than in pure nitrogen, while considerably more pyrolysis is noted for predried coal and for smaller particle sizes. The results suggest a strong influence of secondary volatile reactions on the extent of pyrolysis. Pyrolysis in steam at 800–900°C shows an increase with pressure similar to that reported for pyrolysis in hydrogen. Finally, gasification rates of chars immediately following the pyrolysis are found to be much higher than those of chars prepared separately and then reacted. These results suggest morphological rearrangements and crystallization effects.     

Nitrogen solubilities in low-density polyethylene at high temperatures and high pressures

An apparatus for the determination of the solubility of gases in polymers at high pressure and high temperature is described. The solubilities of nitrogen in low-density polyethylene (PE800E) at 394–450 K at pressures between 10 and 125 atm are reported. Empirical correlations are obtained which represent the Flory–Huggins interaction parameter χ, solubility coefficient K_H, and activity coefficient of dissolved gas Ω₂ as functions of temperature and pressure for the above system. © 1995 John Wiley & Sons, Inc.     

高纯氧化镁-元明粉联产新工艺研究

以硫氢化钠与运城盐湖的高镁卤水为原料,制取高纯氧化镁,并副产无水硫酸钠,为运城盐湖资源的综合利用提供了新思路.工艺条件:硫氢化钠过量2%;镁离子质量浓度25 g/L;硫氢化钠质量浓度350 g/L;反应温度80～90 ℃;搅拌转速50 r/min;加料速度20 L/min;反应时间1 h;洗水量为氧化镁质量的60倍.生产的高纯氧化镁纯度达98%以上;反应后的母液经过蒸发,所得无水硫酸钠纯度可达99%.每30 t高镁卤水可生产1 t高纯氧化镁,副产元明粉10.87 t.     

Gas cleaning at high temperatures and high pressures: A review

This is a review of gas cleaning methods to be used for particulate removal from the gases emerging from pressurized coal gasifiers or fluid bed combustors at high temperature and high pressure. References are given (collected in tables) for the emissions of these processes, the inlet requirements if the hot gas is to pass a turbine and all cleaning methods that have been proposed in this context, including the removal of gaseous alkalis.

The design feasibility and available performance data for high temperature, high pressure applications of cyclones, electrostatic precipitators, barrier filters (using fibre, felt and sintered filter elements) and various types of granular bed filters, are discussed in some detail and suggestions are made for the further research and development. The theory of capture mechanisms is reviewed in so far as relevant in the present context. Turbulent flow, electrostatic forces, and re-entrainment are the phenomena that require special attention in almost all applications.     

氟硅酸、氧化镁制无水氟化氢联产优质硫酸镁工艺研究

无水氟化氢作为氟化工的基础原料,传统工艺多为萤石硫酸法制备,随着萤石资源日益匮乏和国家对萤石资源的限制开采,如何大力开发低品位氟资源、实现高效循环利用成为氟化工面临的重要问题。对此,重点研究了磷肥行业副产氟硅酸制备高附加值无水氟化氢并联产优质硫酸镁的工艺方法,详细剖析了实验过程各关键控制参数的影响,包括原料浓度、原料配比、反应温度、反应时间等,完成了副产低品位氟硅资源的循环高效开发,解决了制约相关行业发展的瓶颈问题,其经济效益、环保效益和社会效益显著。     

一氧化碳还原硫酸镁制备氧化镁的工艺研究

应用热力学原理计算并分析了一氧化碳还原无水硫酸镁制备氧化镁反应的可能性;研究了反应温度、加热时间和样品粒径对无水硫酸镁分解率的影响; 并且通过正交设计与实验,给出了制备氧化镁的优化工艺条件：反应温度为973.15 K、加热时间为30 min、样品粒径为106 μm。采用此工艺,硫酸镁的分解率达到99.3%。得到的氧化镁晶型单一,呈多孔形貌,符合HG/T 2573-2006《工业轻质氧化镁》标准规定的I类优等品质量指标。     

Corrosion of zirconia ceramics in acidic solutions at high pressures and temperatures

Changes in microstructure and phase composition of ceria stabilized tetragonal zirconia polycrystals (Ce-TZP), magnesia and yttria partially stabilized zirconia [(Mg,Y)-PSZ] and magnesia partially stabilized zirconia (Mg-PSZ) were studied in diluted aqueous HCl, H₂SO₄ or H₃PO₄ solutions at a temperature of 390° C and a pressure of 27 MPa. Ce-TZP is corrosion resistant under these conditions in HCl, while Mg-PSZ is attacked severely and (Mg,Y)-PSZ undergoes a surface tetragonal to monoclinic phase transformation. All investigated zirconia ceramics suffer severe weight losses and transformation to the monoclinic phase on the surface in H₂SO₄. Only a small weight gain and a slight increase of m-phase on the surface of the ceramics is found in H₃PO₄.     

Impurity diffusion and microstructure in diamonds deformed at high pressures and temperatures

Results of a comprehensive study of the influence of deformation at high-pressure and high-temperature conditions on diamond microstructure and nitrogen diffusion are presented. Selection of the pressure medium allows the introduction of different types of extended defects (dislocations, mechanical twins). Despite clear differences in microstructure of diamonds deformed in variable pressure mediums, the relationship between the deformation and the rate of aggregation of the C to A nitrogen defects is still not clear. In some cases the deformation apparently increases the aggregation rate; in others no effect or even a decrease in the conversion rate was observed.     

Conversion of polycyclic aromatic hydrocarbons to graphite and diamond at high pressures

The polycyclic aromatic hydrocarbons (PAH): naphthalene, anthracene, pentacene, perylene, and coronene were submitted to temperatures up to 1500 °C at 8 GPa. To avoid catalytic action of metals on thermal conversion, graphite was used as container material. Moreover, graphite is very permeable to the gaseous products of thermal decomposition of PAH. The resulting thermal transformations and their evolution were studied by X-ray diffraction, Raman spectroscopy and scanning electron microscopy as a function of temperature for 60-s treatments. The nature of the initial compounds clearly affects the products of the different stages of carbonization and the first steps of graphitization. This becomes hardly discernible in the final stages of graphitization above 1000 °C. Above 1200 °C, graphite with high crystallinity forms in all cases. The temperature of the beginning of diamond formation does not seem to be influenced by the nature of the initial PAH and is equal to ∼1280 °C for all investigated compounds. Diamonds formed from the PAH are high-quality 5-40 μm single crystals. The p,T values of diamond formation here obtained are significantly lower than those previously known for direct graphite-diamond transformation.     

Calculation of the state parameters of condensed substances at high pressures and temperatures

A universal two-term equation of state is proposed for solids and liquids; it contains three parameters, two of which are known for the majority of substances, while the third can be determined from a small segment of the experimental isotherm or from a single experimental point on the shock adiabat. The parameters of the proposed equation of state are given for several dozen compounds from all classes of solids and liquids.Odessa. Translated from Fizika Goreniya i Vzryva, Vol. 27, No. 4, pp. 39–46, July–August, 1991.     

Solubility of isobutane and propane in polyethylene at high temperatures and low pressures

A novel procedure was developed to measure the solubility of isobutane and propane in both low and high-density polyethylene at temperatures to 500°F (260°C) and vapor pressures from 1 to 1500 torr (33 psia). These measurements represent the first known solubility measurements at these combined extremes of pressure and temperature. Excellent agreement was found when our data were extrapolated to higher pressures and compared with data from another source. In the temperature and pressure regions of interest in this work, the linear isotherms were fit with a form of the Flory–Huggins equation. With the equation in that form we can now estimate the ratio of solubilities of two solutes in a given polymer from pure solute data only. We can also predict the absolute solubility of nonpolar solutes in polyethylene at various temperatures and pressures using only critical temperatures and acentric factors of the solutes.     

An apparatus for the measurement of surface tensions at high pressures and temperatures

An apparatus for the measurement of surface tensions of organic liquids in contact with a gas has been developed which is capable of operation to 400°C and to 14 MPa. It is based on the maximum bubble pressure technique, modified for hydrocarbon oils at high pressures and temperatures. Accuracy of measurement is of the order of ±3% for non‐aqueous systems for values down to 5 mN/m. Only a 20 to 30 mL liquid sample is required, and small gas volumes. In practice, it was found that measurements with most organic liquids could only be made to a maximum of about 350°C because of the thermal instability of most of these compounds, in particular, for hydrocarbon liquids. Any thermal decomposition or coke deposition leads to inaccurate results. Results obtained for known liquids are compared with values given in the literature.     

The gasification of carbon by carbon dioxide at high temperatures and pressures

Presented is the analysis of experimental data on the interaction of carbon with CO₂ + N₂ mixtures at temperatures up to 3400 K and pressures up to 40 atm. The influence of pressure and roles of different stages of the reaction multistage mechanism are determined.