Thermophysical properties of zinc gallate

Complex spinel oxides AB₂O₄ are inorganic materials, which, due to their refractoriness and a whole range of functional properties, are widely in demand in various fields of the power industry and electronics. This paper reports on the results of an experimental study of the thermophysical properties of zinc gallate, which is a promising material for optoelectronics, solid-state lighting and catalytic and biomedical applications. Highly dispersed single-phase ZnGa₂O₄ powder was synthesised by gel combustion. As a result of high-temperature sintering of pressed powder blanks, ZnGa₂O₄ ceramics (≈95% of the theoretical) were produced. According to SEM, the material has a dense microstructure consisting of micron-sized spinel grains. The heat capacity of the material produced was investigated by relaxation, adiabatic and differential scanning calorimetry. By combining experimental data in the range of 8.7–1276 K, a single consistent temperature dependence of ZnGa₂O₄ heat capacity was obtained for the first time. The analysis of the curve obtained showed no signs of phase transitions in the studied temperature range. Based on the results of calorimetric measurements within the range 0 K–1276 K, the temperature dependences of heat capacity, entropy, enthalpy change and Gibbs energy function were calculated. The absolute entropy of ZnGa₂O₄ spinel at 298.15 K was 120.23 J/(K·mol). The thermal diffusivity of ZnGa₂O₄ ceramics measured by laser flash method was 2.6 mm²/s at 300 K, decreasing to 0.46 mm²/s at 1174 K. Its thermal conductivity calculated using experimental data on heat capacity and thermal diffusivity at room temperature was 7.6 W/(m·K). The obtained data are of interest in terms of improving materials based on ZnGa₂O₄, which are promising for use in light-emitting diodes and new-generation power semiconductor devices.     

Thermophysical properties of heat-insulating materials

The paper concerns a study of the thermophysical properties and electron-microscopic data for mullite-silica and carbon fibers operating in vacuum and in air at various heating rates.     

Thermophysical properties of Devonian shales

A detailed study of the thermophysical properties of Devonian shales from the central and eastern United States has been carried out. Thermal conductivity, thermal diffusivity, specific heat and dielectric constant data are presented. A Michigan shale sample with an oil yield of 28 litres per metric ton (1 t^?1) and a Kentucky shale (oil yield: 52 l t^?1) were selected. The specific heats of these shales are in the range 0.20–0.30 cal gm^?1 °C^?1, and increase with increasing temperature. The thermal conductivity (κ) of the two shale samples are comparable (ca. 1 W m^?1 °C^?1). The κ values show only a weak temperature dependance. The thermal diffusivity (α) of these shales range from 0.3–0.5 × 10^?2 cm² s^?1 and tend to decrease with increasing temperature. The dielectric constants show anomalously high values at temperatures above 200 °C. This effect is indicative of interfacial polarization mechanisms presumably arising from loss of water and onset of pyrolysis of the shale organic matter. Comparison of the trends in thermophysical behaviour of Devonian shales with data obtained previously on Green River oil shales is presented. The importance of thermophysical measurements in on-field applications in oil shale technology is highlighted.     

焦炉荒煤气物性参数的研究

为了解决焦炉荒煤气显热回收传热计算中物性参数缺乏的问题,在简单介绍了焦炉煤气的实际组成和热工计算用焦炉煤气组成的前提下,研究了常压下焦炉煤气黏度、导热系数和比热容3个物性参数。采用热工计算用煤气组分,分别选用合适的数学模型对焦炉煤气的物性参数进行分析与计算,推导出焦炉煤气物性参数的计算公式。结果表明:焦炉煤气黏度、导热系数、比热容这三者的计算值与文献值最大偏差分别为-4.02%,-4.88%,-4.89%,表明数学模型可以用在工程计算中。     

Thermophysical properties of rare earth barium aluminates

The super low thermal conductivity and ultrahigh thermal expansion of Ba₆Ln₂Al₄O₁₅ (Ln = Gd, Dy, Er, and Yb) compounds with one‐sixth of the oxygen vacancy have been synthesized by the solid‐state reaction method. The lowest thermal conductivity of Ba₆Yb₂Al₄O₁₅ was found to be 0.98 W/(m.K) at 1073 K. The large concentration of oxygen vacancies in Ba₆Ln₂Al₄O₁₅ compounds leads to low elastic modulus and loose chemical bonds. The average thermal expansion coefficients of Ba₆Ln₂Al₄O₁₅ compounds was 11.8 × 10^?6 ? 13.6 × 10^?6 · K^?1. The loose chemical bonds with Young's moduli were in the range of 102.8 ? 135.9 GPa.     

Thermophysical properties of polyamide yarn-air composite systems

Conclusions By use of methods of nonstationary heat flow, thermophysical characteristics (thermal conductivity, , thermal diffusivity,a, and specific heat capacity, C) have been obtained and the character of the temperature dependence, =f(T), has been established for a yarn-air composite system with a parallel disposition of elementary filaments.The character of the temperature dependence, =f(T), is supported by the results of studies of PA yarn-air composite systems having an unordered disposition of the elementary filaments, which were obtained by the method of a stationary heat flux.The dependence of the change in specific heat capacity coefficient of a composite system with an unordered disposition of elementary filaments on temperature, C = f(T), has been determined by the nonstationary heat flux method.Equations for the temperature dependences of the coefficient of specific heat capacity and the thermal conductivity coefficient of PA complex yarns have been obtained in the temperature range from 300 to 423 K.Translated from Khimicheskie Volokna, No. 4, pp. 46–48, July–August, 1987.     

Evaluation of the effect of dispersion of fillers on the properties of carbon-filled fibre materials

The spinnability of filled spinning compositions with different dispersion of the filler was investigated. The effect of the dispersion of the filler on the performance characteristics of carbon-filled fibre materials was assessed.     

Thermophysical properties of polymer-probe pairs by gas chromatography

The chromatographic technique of measuring thermophysical parameters at infinite dilution is applied for polyisobutylene (PIB), antishock polystyrene (high-impact polystyrene) and styrene-butadiene rubber (SBR) using benzene, cyclohexane, n-hexane and n-pentane as probes. The experiments were performed for antishock polystyrene in the temperature range of 313.3 to 402.3 K, for SBR in the temperature range of 343.3 to 363.2 K and for PIB at 313.1 and 323.1 K. The chromatographic retention data obtained at these temperatures were used to determine the Flory-Huggins interaction parameter, weight fraction infinite dilution activity coefficient and diffusion coefficient. In addition, the glass transition temperature of antishock polystyrene was estimated.     

Shielding effectiveness of carbon-filled nylon 6,6

Electrically conductive resins can be made by adding electrically conductive fillers to typically insulating polymers. Resins with an electrical resistivity of approximately 10⁰ ohm-cm or less can be used for electromagnetic and radio frequency interference shielding applications. This research focused on performing compounding runs followed by injection molding and shielding effectiveness testing of carbon filled nylon 6,6 based resins. The three carbon fillers investigated included an electrically conductive carbon black, synthetic graphite particles, and a surface-treated polyacrylonitrile (PAN)-based carbon fiber. Conductive resins were produced and tested that contained varying amounts of these single carbon fillers. In addition, combinations of fillers were investigated by conducting a full 2³ factorial design and a complete replicate. The objective of this paper was to determine the effects and interactions of each filler on the shielding effectiveness properties of the conductive resins. Carbon fiber caused the largest increase in shielding effectiveness. Also, all the single fillers and combinations of fillers were statistically significant at the 95% confidence level, except the composite containing carbon black and synthetic graphite particles tested at 800 MHz. Polym. Compos. 25:407–416, 2004. © 2004 Society of Plastics Engineers.     

Thermophysical properties of polyurethane foams and their melts

The thermal conductivity (λ) and the specific heat (c_p) of seven polyurethane foam formulations and their melts are obtained using a transient plane source technique called the Hot Disk experiment. In the experiment, the Hot Disk sensor is sandwiched by the samples and acts as both a heat source and a temperature sensor. The fundamental assumption is that throughout the experiment, the heat from the sensor does not penetrate beyond the boundaries of the sample. The suitable sample dimensions and sensor radius are determined from the preliminary calculations. Through sensitivity analysis, the appropriate measuring time and output power for the experiments are established. For polyurethane foams, λ ranges from 0.048 to 0.050 W/m K, and c_p ranges from 2359 to 2996 J/kg K. For melts, λ ranges from 0.186 to 0.200 W/m K, and c_p ranges from 1958 to 2076 J/kg K. When foam decomposes into melts, the changes in thermophysical properties shows λ increases by approximately 300%, whereas c_p decreases by approximately 20%. On the basis of these changes, the collapse of the foam structure into melt appears to improve the heat transfer through the material. Copyright © 2013 John Wiley & Sons, Ltd.     

HFE7100和HFE7500的热物理性质

为了获得氢氟醚HFE7100、HFE7500的热物理性质参数,补充现有数据不足,为其作为电子元器件的冷却介质、工业清洗剂等工程应用提供技术支持,利用瞬态热线法测量了常压下HFE7100和HFE7500的热导率,并用表面光散射法测量了HFE7100和HFE7500的液相黏度和表面张力。HFE7100和HFE7500的热导率和液相黏度均关联成温度的多项式函数,HFE7100热导率和黏度的实验值和关联式的平均绝对偏差分别为0.37%和1.19%,HFE7500热导率和黏度的实验值和关联式的平均绝对偏差分别0.08%和1.10%。利用改进的van der Waals关联表面张力和温度的关系,HFE7100和HFE7500的表面张力的实验值和关联式的平均绝对偏差分别为0.03 mN·m^-1和0.02 mN·m^-1。获得的HFE7100和HFE7500的热导率、黏度和表面张力实验数据及方程,可为其工程应用提出数据支持。     

Thermophysical and electrical properties of rare-earth-cerate high-entropy ceramics

A new series of rare-earth-cerate high-entropy ceramics with compositions of (La_0.2Nd_0.2Sm_0.2Gd_0.2Dy_0.2)₂Ce₂O₇ (HEC1), (La_0.2Nd_0.2Sm_0.2Gd_0.2Yb_0.2)₂Ce₂O₇ (HEC2), (La_0.2Nd_0.2Sm_0.2Yb_0.2Dy_0.2)₂Ce₂O₇ (HEC3), (La_0.2Nd_0.2Yb_0.2Gd_0.2Dy_0.2)₂Ce₂O₇ (HEC4), (La_0.2Yb_0.2Sm_0.2Gd_0.2Dy_0.2)₂Ce₂O₇ (HEC5) as well as a single component of Nd₂Ce₂O₇ are fabricated via sintering the corresponding sol–gel-derived powders at 1600°C for 10 h. HEC1–5 samples exhibit a single-cerate phase with fluorite structure and high configurational entropy. Compared with Nd₂Ce₂O₇, HEC1–5 samples have a lower grain growth rate owing to the sluggish diffusion effect. The chemical compositional uniformity of HEC1–5 as well as Nd₂Ce₂O₇ does not apparently change after annealing at 1500°C for different time intervals (1, 6, 12, and 18 h). Compared with 8YSZ, HEC1–5 samples display the decreased thermal conductivity and increased thermal expansion coefficient. The lattice size disorder parameter of HEC1–5 is negatively related to the thermal conductivity in 26–450°C. Furthermore, HEC1–5 and Nd₂Ce₂O₇ exhibit lower oxygen-ion conductivity, meaning an increased resistance to oxygen diffusion.     

Production of Polikon carbon-filled conducting materials

The effect of disperse graphite on the kinetics and thermodynamics of formation of an ion-exchange matrix was investigated and the basic parameters for production of Polikon K carbon-filled material were selected. The effect of the filler on crosslinking and the yield of finished oligomer was established. Incorporation of colloidal graphite changes the dielectric properties of Polikon K material by increasing its conductivity. __________ Translated from Khimicheskie Volokna, No. 1, pp. 52–54, January–February, 2008.