Thermal Conductivity of Reference Solid Materials

The thermal conductivity of three thermal-conductivity reference materials, Pyrex 7740, Pyroceram 9606, and stainless steel AISI 304L, has been studied. The technique employed is the transient hot-wire technique, and measurements cover a temperature range from room temperature up to 570K. The technique is applied here in a novel way that eliminates all remaining contact resistances. This allows the apparatus to operate in an absolute way. The method makes use of a soft silicone paste material between the hot wires of the technique and the solid of interest. Measurements of the transient temperature rise of the wires in response to an electrical heating step in the wires over a period of 20s up to 20s allow an absolute determination of the thermal conductivity of the solid, as well as of the silicone paste. The method is based on a full theoretical model with equations solved by a two-dimensional finite-element method applied to the exact geometry. At the 95% confidence level, the standard deviation of the thermal conductivity measurements is 0.1% for Pyrex 7740, 0.4% for Pyroceram 9606, and 0.2% for stainless steel AISI 304L, while the standard uncertainty of the technique is less than 1.5%.     

Measurement of Selected Thermophysical Properties of the NPL Certified Reference Material Stainless Steel 310

Flash methods have become one of the most commonly used techniques for measuring the thermal diffusivity and thermal conductivity of various kinds of solids and liquids such as metals, carbon materials, ceramics, and polymers. Easy sample preparation, small sample dimensions, fast measurement times, and high accuracy are only some of the advantages of this non-destructive measurement technique. However, the accuracy of measurement and level of uncertainty of the resulting data are becoming increasingly important for countless industrial applications. Instruments must be checked to determine the uncertainty of the system at different temperature and application ranges. One way of checking the accuracy of the results is to cross-check the unit with certified reference materials. However, there is a lack of standard materials for thermal diffusivity/thermal conductivity all over the world. Furthermore, for some available standards, the thermophysical properties are known only over a limited temperature range. Presented in this work are thermophysical property measurements on a certified thermal conductivity standard, Stainless Steel 310. Tests were carried out between −125 and 1000°C.     

Thermal Diffusivity Measurements of Refractory Metals as Candidate Reference Materials by the Laser Flash Method

A working group for standardization has organized to establish the Japanese Industrial Standard (JIS) for thermal diffusivity measurements of metals in the temperature range of 300–1700 K by the laser flash method. As candidate reference materials with high purity, high-temperature stability, and easy-to-get on a commercial basis, tantalum, niobium, and molybdenum have been selected. Thermal diffusivity values of the specimens, cut out of these materials, have been measured independently by members of the working group. Comparisons of results have been performed for different high-temperature stabilities, repeatabilities, and manufacturers, as well as by different members. Comparisons show that the measured values agree within 10% for different specimens by different institutions, and no systematic differences have been observed for materials from different manufacturers. The measured results for molybdenum specimens agree well with the recommended values of thermophysical properties of matter from the TPRC data series, and the high-temperature stability is found to be the best. The results for tantalum and niobium, however, show significant differences with those of the TPRC data series in the high-temperature range, and some further study on the stability of these materials is needed for recommending these values. As a result, molybdenum can be recommended as a reference material for practical use of the laser flash method. Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22–27, 2003, Boulder, Colorado, U.S.A.     

Assessment of Uncertainties for the NIST 1016 mm Guarded-Hot-Plate Apparatus: Extended Analysis for Low-Density Fibrous-Glass Thermal Insulation

An assessment of uncertainties for the National Institute of Standards and Technology (NIST) 1016 mm Guarded-Hot-Plate apparatus is presented. The uncertainties are reported in a format consistent with current NIST policy on the expression of measurement uncertainty. The report describes a procedure for determination of component uncertainties for thermal conductivity and thermal resistance for the apparatus under operation in either the double-sided or single-sided mode of operation. An extensive example for computation of uncertainties for the single-sided mode of operation is provided for a low-density fibrous-glass blanket thermal insulation. For this material, the relative expanded uncertainty for thermal resistance increases from 1 % for a thickness of 25.4 mm to 3 % for a thickness of 228.6 mm. Although these uncertainties have been developed for a particular insulation material, the procedure and, to a lesser extent, the results are applicable to other insulation materials measured at a mean temperature close to 297 K (23.9 °C, 75 °F). The analysis identifies dominant components of uncertainty and, thus, potential areas for future improvement in the measurement process. For the NIST 1016 mm Guarded-Hot-Plate apparatus, considerable improvement, especially at higher values of thermal resistance, may be realized by developing better control strategies for guarding that include better measurement techniques for the guard gap thermopile voltage and the temperature sensors.     

材料热物性测试的研究现状及发展需求

材料热物性是对特定热过程进行基础研究、分析计算和工程设计的关键参数,是材料最基本的性能之一.在科学研究、工程设计、工业生产等领域应用十分广泛,也是各行业节能技术发展的基础.通过对材料热物性发展历史、国内外研究现状的分析,比较了我国与发达国家在防护热板法导热系数装置研究上的差距.阐明了热物性测试的重要意义及我国在材料热物性测试领域仍未建全量值传递体系的不足.     

A Novel Instrument for the Measurement of the Thermal Conductivity of Molten Metals. Part I: Instrument’s Description

The paper reports the design and construction of a new instrument for the measurement of the thermal conductivity of molten metals and salts. The apparatus is based on the transient hot-wire technique, and it is intended for operation over a wide range of temperatures, from ambient up to 1200 K. The present experimental technique overcomes problems of convection and thermal radiation, and it is demonstrated that it operates in accord with a theoretical model. The uncertainty of the thermal conductivity results is estimated to be ±2% which is superior to that achieved in most earlier work.     

Thermal Diffusivity Measurements of Candidate Reference Materials by the Laser Flash Method

The National Metrology Institute of Japan (NMIJ) in AIST has investigated the laser flash method in order to establish a thermal diffusivity standard for solid materials above room temperature. A uniform pulse-heating technique, fast infrared thermometry, and a new data analysis method were developed in order to reduce the uncertainty in thermal diffusivity measurements. The homogeneity and stability of candidate reference materials such as isotropic graphite were tested to confirm their qualification as thermal diffusivity reference materials. Since graphite is not transparent to both the heating laser beam and infrared light for thermometry, the laser flash method can be applied to graphite without black coatings. Thermal diffusivity values of these specimens with different thicknesses, were measured with changing heating laser pulse energies. A unique thermal diffusivity value can be determined for homogeneous materials independent of the specimen thickness, by extrapolating to zero heating laser pulse energy on the plot of apparent thermal diffusivity values measured with the laser flash method as a function of heating laser pulse energy.Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22--27, 2003, Boulder, Colorado, U.S.A.     

The Development of a Standard for Contact Transient Methods of Measurement of Thermophysical Properties

Contact transient methods, some of which are available as commercial forms, are now widely used worldwide for thermal properties measurements on broad ranges of materials used in physical, chemical, and medical applications. However, in many cases the claimed measurement uncertainty has not been substantiated while in others – especially for the multiproperty techniques – internal inconsistencies in measured and/or derived values are clearly apparent. Following recommendations of participants of two workshops held on the subject in Würzburg (1999) and Cambridge, Massachussetts (2001), NPL agreed to coordinate a task to develop a standard test-method for these techniques. This involved using inputs provided by a small group of individuals from organizations in several European countries and also taking note of comments from other interested parties via the internet during the course of the development. Details are provided on the resulting document, which takes the form of a generic standard containing appropriate details and related information common to all techniques. These sections include the scope, theory, summaries of method, basic apparatus and experiment, the influencing factors, specimen requirements, procedure, and recommended approach for analysis of the experiment and calculation of the results. In addition, there are six annexes, each of which contains additional information that applies to a specific technique. Finally, the document proposes a recommended approach for verification of a technique together with a list of appropriate reference materials having known values for one or more properties. The status of intercomparison studies will also be reported. Paper presented as the Fifteenth Symposium on Thermophysical Properties, June 22–27, 2003, Boulder.     

我国天然产物标准样品管理及技术体系发展现状

本文阐述了天然产物标准样品研制工作的背景和意义,介绍了我国天然产物标准样品研制工作的组织管理体系现状,重点对标准样品研制技术体系进行了描述,分析了构成技术体系的管理技术、信息技术和研制技术单元的特点,列举了标准样品示范性研制及技术规范工作的典型案例,探讨了如何解决标准样品分离纯化及定值等技术瓶颈问题。最后,汇总了标准样品研制工作的主要成果,并对我国天然产物研制工作的管理体系、技术体系建设,以及产业化发展前景进行了展望。