Hysteretic anelasticity of graphitehalogen residue compounds at high temperatures

The internal friction and dynamic elastic modulus of graphite-halogen residue compounds have been investigated between 280 and 660 K. The host material for intercalation was a high purity reactor-grade graphite. Graphite-bromine residue compounds show a thermal hysteresis in the dynamic modulus (resonant frequency) vs temperature plot, corresponding to the finding of Miyauchi-Takahashi on interplanar spacing and electrical resistivity. On the other hand, internal friction is almost independent of temperature above 400 K. These results have been discussed in terms of the modified Granate-Lücke theory; bromine clusters function as a pinning agent for dislocations, while single molecules and small complexes as a viscous drag. The hysteresis is concluded to come from the delay of bromine redistribution in the cooling process. No hysteresis was observed of iodine-monochloride compounds in this temperature range, leaving a problem for further study.     

Defect structure of metal oxides at high temperatures

High temperature oxidation of some metals contained in special alloys has been studied. Defect models for pure an doped CoO and pure NiO were developed and fitted to electrical conductivity data. The models involve different kinds of theoretically possible complex defects with different numbers of vacancies and interstitials forming a cluster. Equilibrium constants for defects formation have been estimated using an algorithm based on the constrained variation method that allows fitting of data to implicit models involving errors in all the measured variables. Results indicate the presence of a significant concentration of complex defects in CoO at high temperatures, while confirming the rather small concentration of these defects in NiO.     

Thermal properties of gypsum plasterboard at high temperatures

Light timber frame wall and floor assemblies typically use gypsum‐based boards as a lining to provide fire resistance. In order to model the thermal behaviour of such assemblies, the thermo‐physical properties of gypsum plasterboard must be determined. The relevant literature and the chemistry of the two consecutive endothermic dehydration reactions that gypsum undergoes when heated are reviewed. The values determined for the thermo‐physical properties are modified to create smooth enthalpy and thermal conductivity curves suitable for input into a finite element heat transfer model. These values are calibrated within a reasonable range and then validated using furnace and fire test data. The type of plasterboard used in these tests is an engineered product similar to the North American type C board. The temperature at which the second dehydration reaction occurs is altered to be consistent with later research with little apparent affect on the comparison with test results. Values for specific heat, mass loss rates and thermal conductivity for gypsum plasterboard that are suitable for use in finite element heat transfer modelling of light timber frame wall and floor assemblies are recommended. Copyright © 2002 John Wiley & Sons, Ltd.     

Physical properties of graphite-nitrate residue compound

Thermal expansion, specific heat and magnetic properties of the “residue” compounds of graphitenitrate were measured at low temperatures between 1.5 and 300 K. Metallic behaviour of the compound is confirmed from high density of state at Fermi level which was evaluated from specific heat data and from magnetic susceptibility measurements. The effective modulation of structural parameters and of properties with doping of nitrate ions is shown. Phase transitions of the compound are found to occur at ca. 320 and 230 K.     

Performance and structure evolution of fluoindinate glass at high temperatures

Fluoindinate glass (FIG) is considered an ideal material for fiber laser devices and mid-infrared bulk optics components owing to its ultra-low phonon energy and broad transparency window. However, the heat generated by devices fabricated with FIG during their operation limits its application. Therefore, there is an urgent need to study its high-temperature properties. In this study, the thermal properties, microstructure, crystal phase behaviors, and optical and luminescent properties of high-temperature FIG were comprehensively evaluated. We also attempted to reveal the changes in its structure at high temperatures using variable-temperature Raman spectroscopy. We first found that the stretching vibration intensity of nonbridging F(F_nb) decreases, and the bending vibration of FIG increases with an increase in temperature, indicating that high temperatures could lead to the fracture of bridge bonds between some [InF₆]³⁻ octahedrons. Certainly, this will lead to glass structural instability, which will further increase the tendency of FIG to undergo devitrification in high-temperature conditions. We believe that this work will provide a reference for the performance improvement and application of fluoride glass at high temperatures.     

Change in structure and some properties of industrial aluminosilicate refractories under prolonged anneals at high temperatures

Conclusions A study was made of the change in the structure and some properties of aluminosilicate refractories after prolonged heat processing at 1350–1500°C. The changes in the structure of the refractories occur mainly after heating at 1500°C, and consist in the redistribution of the glassy phase and some increase in the mullite crystals. In the fireclay refractories there was an increase in the quantity of glass phase, because of which its porosity sharply diminished.The change in the structure in aluminosilicate refractories is much lower than in pure-oxide materials, so the properties of these refractories after prolonged heating hardly change.Translated from Ogneupory, No. 6, pp. 27–30, June, 1970.     

高温作用下角砾岩动态力学特性研究

为了解高温作用下角砾岩动态力学特性,开展了不同温度、不同加载速率下的角砾岩动态冲击实验.试样为取自云南卡房地区的天然角砾岩,将试样加热到200、400、600、800℃并采用3种加载速率(7.8、9.8、11.8 m/s)进行霍普金森冲击实验,结果表明:随着温度的升高,温度对于角砾岩动态抗压强度有着先强化后弱化的作用,...     

高温处理粉煤灰的理化特性研究

为多元化、高附加值利用粉煤灰,以朔州电厂粉煤灰为例,进行了X射线衍射测试、粒度测试和热重分析。结果表明,朔州电厂粉煤灰的w(Al2O3)=41. 09%、w(CaO)=4. 64%,属于高铝低钙型,其平均粒径为108. 1μm;未煅烧的朔州电厂粉煤灰矿物组成为莫来石、石英、石膏;质量损失主要发生在570~750℃和1 100~1 280℃。然后称取未筛选经105℃烘干后的粉煤灰制成Φ40 mm×8. 8 mm的试样,经1 200~1 550℃热处理后,进行劈裂强度试验、XRD分析等。结果表明,随热处理温度升高,试样的强度和密度增大,莫来石含量逐渐增多,1 400℃时性能达到最佳。     

Physicochemical properties and structural evolutions of gas-phase carbonization chars at high temperatures

The gas-phase carbonization chars from hydrocarbons with low molecular weight (anthracene oil and petroleum ether) were prepared using a drop tube reactor at 1000-1200 °C, and their physicochemical properties and structural evolutions (elemental composition, carbon crystallite structure, surface morphology, pore structure and chemical composition of volatile matters) were mainly investigated. The chars obtained in the high temperature region, which appeared with high C/H atomic ratio and poor carbon crystallite structure far from natural graphite, could be used as high carbonaceous materials. The chars were composed of uniform spherical particles with a continuous pore size distribution. The average pore diameters of the chars were much smaller and in the rage of 5.0-8.7 nm. The increasing carbonization temperature led to an initial increasing and a sequent decreasing of specific surface areas from mico-meso-pores and an increasing of those from meso-macro-pores in the chars. The volatile matters in the chars were composed of an easily-extracted fraction (CS₂-soluble compounds with three to six aromatic rings) and a hard-extracted fraction (CS₂-insoluble compounds with higher aromaticity). The elevated carbonization temperature led to diminish the two volatile fractions. A liquid core formation mechanism was proposed to explain the gas-phase carbonization process of hydrocarbons.     

Sintering boron nitride by hot pressing and its properties at high temperatures

Conclusions During hot pressing only powders of BN synthesized at low temperatures are sintered. The high dispersion of the powder, and the imperfect structure of the crystals lead to its recrystallization and sintering at high temperatures.The optimum conditions for hot pressings BN are: temperature 1800C, soak 10 min, pressure 300 kg/cm². The apparent porosity of the specimens obtained under these conditions is 0–0.1%, apparent density 2.06–2.08 g/cm³.In the hot-pressed specimens we detected substantial growth of the crystals of BN.The properties of the hot-pressed articles made from low-temperature BN suggest that they can be considered as constructional refractory materials capable of operating at high temperatures.Translated from Ogneupory, No. 3, pp. 48–54, March, 1967.     

Thermal and electrical properties of epoxy composites at high alumina loadings and various temperatures

Epoxy microcomposites with high loading micro alumina (Al₂O₃, 100–400 phr) were prepared by casting method and their thermal and electrical properties were studied at temperatures from 25 to 150 °C. The electric resistance device and the dielectric electrode device were designed to measure the electrical properties of the composites. Thermogravimetric analysis (TGA) and scanning electron microscopic proves the homodispersion of Al₂O₃ microparticles in epoxy. TGA indicates that the temperature of 5 % weight loss of epoxy/Al₂O₃ (100 phr) composite is 366 °C, 34 °C higher than that of pure epoxy. Differential scanning calorimetry shows that the glass transition temperature of epoxy/Al₂O₃ composite (400 phr) increases to 114.7 °C, 9.2 °C higher than that of pure epoxy. Thermal conductivity test demonstrated that with increasing Al₂O₃ content at 25 °C, thermal conductivity of epoxy/Al₂O₃ composites increased to 1.382 W/(m K) which is 5.62 times that of pure epoxy. Electrical tests demonstrate that by increasing of Al₂O₃ content and temperature, the electric resistance and dielectric properties of the composites show great dependencies on them. Resistivities of all the specimens decreased with the increasing of temperature owing to the increasing molecular mobility in the higher temperature. Resistivity of pure epoxy at 25 °C is about 9.56 × 10¹⁶ Ω cm, about one order of magnitude higher than that of pure epoxy at 125 °C and two orders of magnitude higher than that of pure epoxy at 150 °C. These results can give some advice to design formulations for practical applications in power apparatus.     

Permeation properties of hydrogen and water vapor through porous silica membranes at high temperatures

Silica and cobalt‐doped silica membranes that showed a high permeance of 1.8 × 10^?7 mol m^?2 s^?1 Pa^?1 and a H₂/N₂ permeance ratio of ～730, with excellent hydrothermal stability under steam pressure of 300 kPa, were successfully prepared. The permeation mechanism of gas molecules, focusing particularly on hydrogen and water vapor, was investigated in the 300–500°C range and is discussed based on the activation energy of permeation and the selectivity of gaseous molecules. The activation energy of H₂ permeation correlated well with the permeance ratio of He/H₂ for porous silica membranes prepared by sol–gel processing, chemical vapor deposition (CVD), and vitreous glasses, indicating that similar amorphous silica network structures were formed. The permeance ratios of H₂/H₂O were found to range from 5 to 40, that is, hydrogen (kinetic diameter: 0.289 nm) was always more permeable than water (0.265 nm). © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Thermal and mechanical properties of fiber reinforced high performance self-consolidating concrete at elevated temperatures

This paper presents the effect of temperature on thermal and mechanical properties of self-consolidating concrete (SCC) and fiber reinforced SCC (FRSCC). For thermal properties specific heat, thermal conductivity, and thermal expansion were measured, whereas for mechanical properties compressive strength, tensile strength and elastic modulus were measured in the temperature range of 20–800 °C. Four SCC mixes, plain SCC, steel, polypropylene, and hybrid fiber reinforced SCC were considered in the test program. Data from mechanical property tests show that the presence of steel fibers enhances high temperature splitting tensile strength and elastic modulus of SCC. Also the thermal expansion of FRSCC is slightly higher than that of SCC in 20–1000 °C range. Data generated from these tests was utilized to develop simplified relations for expressing thermal and mechanical properties of SCC and FRSCC as a function of temperature.     

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.     

Evolution of the structure and mechanical behaviour of a carbon foam at very high temperatures

Mechanical behaviour of a low density carbon/carbon composite at very high temperature is studied in relation with its microstructure. This composite is a syntactic foam made of carbon microbeads with a binder and voids. The resulting geometrical density is 0.3 g cm⁻³. Compressive tests from room temperature up to 3100 °C with a very high heating rate (180 °C s⁻¹) have been conducted. Intermediate temperature tests have also been performed and show an obvious modification of mechanical behaviour from around 2000 °C. This result is related to a sudden modification of structure and texture of the carbonaceous matter during the high temperature mechanical test. A strong plastic deformation occurs when the mechanical experiment is performed at 3100 °C whereas the material elastically deforms at room temperature.     

硫化温度对白炭黑配方胎面胶性能的影响

本文通过对不同硫化温度下白炭黑配方胎面胶料性能差异进行实验研究,实验结果表明,随着硫化温度的提高,胶料的综合物理机械性能下降明显,而动态力学性能中,损耗因子随温度的上升有增大的趋势。