Traceable Measurements of Seebeck Coefficients of Thermoelectric Materials by Using Noble Metal Thermocouples

The characterization of thermoelectric materials as reference materials for Seebeck coefficients at the Physikalisch-Technische Bundesanstalt (PTB) is based on the usage of gold/platinum differential thermocouples. In the case of thermoelectric materials containing silicon, the gold/platinum thermocouples are insufficient due to reactions with the silicon when the samples are at higher temperatures. To overcome this limitation and to expand the temperature range for the certification process, platinum/palladium thermocouples were incorporated in the measurement setup. This paper discusses the influence of the different differential thermocouples used for the measurement of the Seebeck coefficients. Results of a comparative investigation of Seebeck coefficient measurements of a metallic and two semiconducting reference materials in the temperature range from 300 K to 870 K are presented.     

Thermodynamic Temperature Measurements Traceable to Photometric Standards

The replacement of ITS-90 temperature measurements by direct thermodynamic temperature measurements based on radiometric techniques in the temperature range above 1000 °C has been proposed by many national measurement laboratories. This article reports on work at NMIA to develop a simple and robust traceability scheme for thermodynamic temperature, based on the use of photometers and a Thermogage furnace with a graphite tube element modified to improve its temperature uniformity and emissivity. A simple luminance meter was constructed using a commercial photometer and pairs of precision apertures to view the rear of the blackbody cavity. This photometer was calibrated against NMIA reference illuminance lamps, and relative spectral responsivity measurements were used to determine the color-temperature correction between the lamps and the Thermogage blackbody. Thermodynamic temperature determinations made using various combinations of apertures and photometers showed a range of less than 0.2 °C at 1700 °C, consistent with the calculated uncertainty of 0.29 °C (k = 2). ITS-90 measurements made by NMIA??s LP5 and HTSP primary radiation thermometers with an uncertainty of 0.16 °C (k = 2), are consistent with the thermodynamic measurements. It is suggested that routine thermodynamic temperature determinations can now be made with an effort comparable to that required to realize the ITS-90 above 1000 °C.     

Measurements of the Thermal Conductivity of HFC-125 in the Temperature Range from 300 to 515 K at Pressures up to 53 Mpa

Measurements of the thermal conductivity of HFC-125 that have been made by a coaxial cylinder cell operating in steady state are reported. The measurements of the thermal conductivity of HFC-125 were performed along several quasi-isotherms between 300 and 515 K in the gas phase and the liquid phase. The pressure range covered varies from 0.1 to 53 MPa. Based on the measurement of more than 600 points, an empirical equation is provided to describe the thermal conductivity outside the critical region as a function of temperature and density. A careful analysis of the various sources of error leads to an estimated uncertainty of approximately ± 1.5%.     

Measurements of the Thermal Conductivity of HFC-143a in the Temperature Range from 300 to 500 K at Pressures up to 50 MPa

Measurements of the thermal conductivity of HFC-143a that were made by a coaxial cylinder cell operating in steady state are reported. The measurements of the thermal conductivity of HFC-143a were performed along several quasi-isotherms between 300 and 500 K in the gas and liquid phases. The pressure range covered varies from 0.1 to 50 MPa. Based on the measurement of more than 600 points, an empirical equation is provided to describe the thermal conductivity outside the critical region as a function of temperature and density. A careful analysis of the various sources of error leads to an estimated uncertainty of approximately ±1.5%.     

Measurements of the Thermal Conductivity of HFC-134a in the Temperature Range from 300 to 530 K and at Pressures up to 50 MPa

Measurements of the thermal conductivity of HFC-134a made in a coaxial cylinder cell operating in steady state are reported. The measurements of the thermal conductivity of HFC-134a were performed along several quasi-isotherms between 300 and 530 K in the gas phase and the liquid phase. The pressure ranged from 0.1 to 50 MPa. Based on the experimental data, a background equation is provided to calculate the thermal conductivity outside the critical region as a function of temperature and pressure. A careful analysis of the various sources of errors leads to an estimated uncertainty of ±1.5%.     

Development of a Laser Interferometric Dilatometer for Measurements of Thermal Expansion of Solids in the Temperature Range 300 to 1300 K

A laser interferometric dilatometer has been developed for measuring linear thermal expansion coefficients of reference materials for thermal expansion in the temperature range 300 to 1300 K. The dilatometer is based on an optical heterodyne interferometer capable of measuring length change with an uncertainty of 0.6 nm. Linear thermal expansion coefficients of silicon were measured in the temperature range 700 to 1100 K. The performance of the present dilatometer was tested by a comparison between the present data and the data measured with the previous version of the present dilatometer and the data recommended by the Committee on Data for Science and Technology (CODATA). The present data agree well with the recommended values over all the temperature range measured. On the other hand, the present values at lower temperatures are in poor agreement with the previous experimental data. The combined standard uncertainty in the present value at 900 K is estimated to be 1.1×10^–8 K^–1.     

Measurements of the Thermal Conductivity of HFC-32 (Difluoromethane) in the Temperature Range from 300 to 465 K at Pressures up to 50 MPa

New measurements of the thermal conductivity of HFC-32, made in a coaxial cylinder cell operating in steady state, are reported. The measurements were performed along several quasi-isotherms between 300 and 465 K in both the liquid and the vapor phases. The pressure ranged from 0.1 to 50 MPa. Based on the experimental data, a background equation is provided to calculate the thermal conductivity outside the critical region as a function of temperature and density. A careful analysis of the various sources of experimental errors leads to an estimated uncertainty of ±1.5%. Comparisons between calculated and experimental values from the literature are presented.     

Determination of the Thermal Diffusivity of Electrically Non-Conductive Solids in the Temperature Range from 80 K to 300 K by Laser-Flash Measurement

The adoption of the popular laser-flash method at temperatures far below 300 K is restricted by the weak signal-to-noise ratio and the limited spectral bandwidth of the commonly used mercury cadmium tellurite (MCT) infrared (IR) detector used as a non-contacting temperature probe. In this work, a different approach to measure the temperature rise in pulse heating experiments is described and evaluated. This method utilizes the change of the temperature-dependent electrical resistance of a thin strip of sputtered gold for the detection of a temperature rise as it was proposed by Kogure et al. The main advantage of this method at lower temperatures is the significantly higher signal-to-noise ratio compared to the commonly used IR detectors. A newly developed laser-flash apparatus using this detection method for the determination of the thermal diffusivity in the temperature range from 80 K to 300 K is presented. To test the accuracy of the new detection method, the thermal diffusivity of a borosilicate crown glass (BK7) specimen at 300 K was determined and compared to results derived with a MCT detector. Good agreement of the derived thermal diffusivity values within 3 % was found. The thermal diffusivity of BK7 and polycrystalline aluminum nitride (AlN) was measured at temperatures between 80 K and 300 K by a laser-flash method to test the functionality of the apparatus. Finally, the thermal conductivity was calculated using values for the specific heat capacity determined by temperature modulated differential scanning calorimetry (MDSC). Comparisons with literature data confirm the reliability of the experimental setup.     

基于热电模块实验的低温下塞贝克系数的测量

利用热电发电器（TEG）进行温差发电是LNG冷能利用的方式之一,而目前低温下热电材料塞贝克系数（α）研究的缺失给低温TEG的设计带来了障碍。因此,本文提出一种通过TEG模块的实验得到低温下该模块所用热电材料α的测量方法,并测试了热电材料Bi2Te3在90~180 K温度范围内的α。结果表明：Bi2Te3在低温下的α随温度的降低而减小,温度从180 K降至90 K,塞贝克系数从124.6 μV/K降至49.3 μV/K,且与温度成二次函数关系。     

Reference Viscosity of Argon at Low Density in the Temperature Range from 290 K to 680 K

An all-quartz oscillating-disk viscometer of very high precision was used to measure the temperature dependence of the viscosity of argon in the limit of zero density. The measurements were based on a single calibration value at 298.15 K, which was calculated theoretically using an accurate ab initio pair potential for argon and the kinetic theory of dilute gases. The uncertainty of the experimental data is conservatively estimated to be 0.15 % temperature increasing to 0.2 % 680 K. The new data, as well as viscosities determined in 2007 at the National Institute of Standards and Technology in the range from 200 K to 400 K, agree excellently within ±0.1 % theoretically calculated viscosity of argon at zero density. On the contrary, the widely accepted viscosity data recommended by Kestin et al. (J Chem Phys 56:4119, 1972) deviate by as much as 0.9 %     

Laser Interferometric Dilatometer Applicable to Temperature Range from 1300 to 2000 K

A laser interferometric dilatometer has been developed for measuring the thermal expansion of high-temperature solids in the temperature range 1300 to 2000 K. The dilatometer consists of a double-path optical heterodyne interferometer, a spectral-band radiation thermometer, and a vacuum chamber with carbon-composite heaters. The performance of the dilatometer has been assessed on the basis of measurements of linear thermal expansion coefficients for glassy carbon. The relative standard deviation of the measured values from those calculated from the fitting polynomial is 0.63% over the temperature range investigated. The combined standard uncertainties in the measured values are estimated to be less than 1.3% over this range. The process of sample relocation predominantly affects the reproducibility of the experimental results.     

Determination of PRT Hysteresis in the Temperature Range from −50 °C to 300 °C

This paper discusses the contribution of hysteresis to the measurement uncertainty of industrial platinum resistance thermometers (IPRTs). Hysteresis is one of the sources of uncertainty that has so far not been sufficiently researched and documented. The term hysteresis applies to any system that is path dependent; the output depends on the history of the input. In our case, thermal hysteresis results in different resistance values at the same temperature point, depending on whether the temperature was increasing or decreasing. The reason for such behavior is related to the construction of the thermometer (strain due to thermal expansion and contraction) and also to possible moisture inside the encapsulation. In the process of evaluation of the calibration and measurement capabilities (CMCs) of IPRTs within Working Group 8, the Consultative Committee for Thermometry (CCT WG8) concluded that the uncertainty due to hysteresis is not uniformly defined and not always added to the total uncertainty of the resistance thermometer under calibration. In order to estimate the uncertainty contribution due to the hysteresis and compare different procedures, resistance measurements were carried out on a number of IPRTs of different qualities and tolerance classes. The temperature span was between ?50 °C and 300 °C, which is the most frequent temperature range in the practical use of IPRTs. The hysteresis was then determined in different ways (change of resistance at the ice point and at the midpoint temperature according to the ASTM International Standard E644 and according to the new version of IEC Standard 60751), and a comparison of results was made.     

ITS—90温标在83.8058—273.16K温区内温标的非唯一性研究

对ＩＴＳ＿９０温标在８３．８０５８－２７３．１６Ｋ温区内的温标的非唯一性进行了研究。在高精度低温恒温槽内对九支套管铂电阻温度计进行分度,分析其非唯一性,并研究此温区与１３．１８－２７３．１６Ｋ温区的非一致性。     

An Electronic Demagnetization Stage for the 0.5K to 1.8K Temperature Range

We have designed and built a demagnetization stage to operate between 1.8K and 0.5K, a somewhat unusual temperature range for adiabatic demagnetization refrigeration. The lower bound in temperature is dictated by the thermal performance of our ³ He gas heat switch, the upper by NASA specifications. We intend this demagnetization stage to be the fast stage of a proposed two-stage continuously operating adiabatic demagnetization refrigerator (ADR) which will operate between 1.8K and 50 mK. Here we discuss thermal, mechanical, magnetic and chemical considerations which led to novel features in our salt pill design.     

Installation of Relative Acoustic Gas Thermometry in the Low Temperature Range from 4.2 to 80 K

Measurement Techniques - A relative acoustic gas thermometry unit for reproducing and transmitting the unit of thermodynamic temperature, i.e., kelvin, in the low temperature range 4.2–80 K...     

铌酸锂在15至573K 温度范围内的电学性质

在15～573K 温度范围内测量了铁电相铌酸锂单晶沿 c 轴方向的体电阻、介电常数、和热释电系数。数据表明在88、139、166、226、352、408和549K 附近,晶体性质出现特殊的变化。精确到0.4%的热释电测量表明在79.60℃温度上,自发极化强度 P_(?)和热电系数 dP_(?)/dT 连续,但 P_(?)对温度 T 的二次微商不连续;这与晶体中氧八面体旋转角的突变有关。从热释电测量发现,当晶体由85℃急冷至0℃时,晶体的转变出现延续时间超过80h的驰豫效应。在74～130K 之间,热电系数比例于爱恩斯坦比热函数。     

Thermal Diffusivity of Aqueous Solutions of Magnesium Chloride in the Temperature Range from 294 to 371 K

The thermal diffusivity of aqueous solutions of magnesium chloride was determined in the temperature range 294 to 371 K and at atmospheric pressure. Using a noninvasive optical technique—laser-induced thermal grating (LTG)—the measurements were carried out in aqueous solutions of weight fractions of 5, 10, 15, and 20% magnesium chloride. The measurement results for the aqueous solutions are presented as a function of temperature and weight fraction.     

Measurement and Analysis of Thermophysical Properties of Diorites in the Temperature Range from 253 to 333 K

Thermal conductivity and thermal diffusivity are simultaneously measured for a collection of diorite samples taken from Shewa-Shahbaz Garhi volcanic complex near Mardan, Pakistan by using the transient plane source (TPS) technique. The temperature dependence of the transport properties of these samples is studied in the temperature range from 253 to 333 K. Different relationships for the temperature dependence of the thermal conductivity and thermal diffusivity are tested. The samples are also characterized by their chemical composition, density, porosity, and specific gravity at room temperature and atmospheric pressure. Theoretical calculation of the specific gravity parameter based on the chemical composition is in good agreement with the experimental observation. No correlation was found for the temperature dependence of the thermal transport behavior on porosity, chemical composition, and density.