Study on a Thermal-diffusivity Standard for Laser Flash Method Measurements

The National Metrology Institute of Japan (NMIJ) of AIST has been studying the laser flash method in order to establish an SI traceable thermal- diffusivity standard. Key technologies have been developed to reduce the uncertainty in laser flash measurements. In the present study, an uncertainty evaluation has been carried out on the laser flash measurement method in order to determine the thermal diffusivity value of IG-110, a grade of isotropic high-density graphite, as a candidate reference material. The thermal diffusivity measured by the laser flash method is derived from a specimen thickness and a heat diffusion time. And a laser flash measurement is carried out at a given temperature. The measurement system is composed of three sections corresponding to each measured quantity: length, time, and temperature. Therefore, we checked and calibrated our measurement system, and estimated the uncertainty of measurement results for the case of a grade of isotropic graphite.Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak Republic.     

Evaluation of the Effective Sample Temperature in Thermal Diffusivity Measurements Using the Laser Flash Method

In the measurement of thermal diffusivity by the laser flash method, a temperature rise occurs in the sample as a pulsed laser hits on the sample surface. Due to the temperature dependence of thermal diffusivity of the sample, the thermal diffusivity corresponds to a temperature that is larger by T _eff than the temperature before laser irradiation is applied. This effective temperature rise, T _eff, has been investigated by using a numerical simulation. The results indicate that the effective temperature rise is almost equal to a maximum temperature rise, T _M, of the back surface of the sample in cases where both linear and nonlinear temperature variations of thermal diffusivity are considered.     

Thermal Diffusivity Measurements on Insulation Materials with the Laser Flash Method

An iterative approach is adopted to determine the thermal diffusivity of the xonotlite-type calcium silicate insulation material with very low thermal conductivity. The measurements were performed with a conventional laser flash apparatus by rear-face detection of the temperature response of the three-layered sample, where the insulating material is sandwiched between two iron slices. In the evaluation of the thermal conductivity, the theoretical curve is fitted to the complete temperature–time curve, instead of just using the t _1/2 point. The theoretical model is based on the thermal quadrupole method. The nonlinear parameter estimation technique is used to estimate simultaneously the thermal diffusivity, heat transfer coefficient, and absorbed energy. Based on experimental results, the optimal thickness range of the insulation material in the sample is indicated as 1.6 to 1.9 mm. The effects of the uncertainties of the thicknesses, contact resistance, and thermophysical properties of the three layers on the measurement uncertainty are estimated, giving an overall uncertainty in the thermal conductivity of approximately 7.5%.Paper presented at the Seventh Asian Thermophysical Properties Conference, August 23–28, 2004, Hefei and Huangshan, Anhui, P. R. China.     

Thermal-Diffusivity Measurements of Conductive Composites Based on EVA Copolymer Filled With Expanded and Unexpanded Graphite

In this research, the thermal diffusivity of composites based on ethylene- vinyl acetate (EVA) copolymer filled with two kinds of reinforcement graphite materials was investigated. The reinforcement graphite fillers were untreated natural graphite (UG) and expanded graphite (EG). Composite samples up to 29.3 % graphite particle volumetric concentrations (50 % mass concentration) were prepared by the melt- mixing process in a Brabender Plasticorder. Upon mixing, the EG exfoliates in these films having nanosized thicknesses as evidenced by TEM micrographs. Thus, the thermal diffusivity and electrical conductivity of composites based on the ethylene-vinyl acetate matrix filled with nanostructuralized expanded graphite and standard, micro-sized graphite were investigated. From the experimental results it was deduced that the electrical conductivity was not only a function of filler concentration, but also strongly dependent on the graphite structure. The percolation concentration of the filler was found to be (15 to 17) vol% for micro-sized natural graphite, whereas the percolation concentration of the filler in nanocomposites filled with expanded graphite was much lower, about (5 to 6) vol%. The electrical conductivity of nanocomposites was also much higher than the electrical conductivity of composites filled with micro-sized filler at similar concentrations. Similarly, the values of the thermal diffusivity for the nanocomposites, EG-filled EVA, were significantly higher than the thermal diffusivity of the composites filled with micro-sized filler, UG-filled EVA, at similar concentrations. For 29.3 % graphite particle volumetric concentrations, the thermal diffusivity was 8.23 × 10^?7 m² · s^?1 for EG-filled EVA and 6.14 × 10^?7 m² · s^?1 for UG-filled EVA. The thermal diffusivity was measured by the flash method.     

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.     

Thermal-Diffusivity Measurements of Mexican Citrus Essential Oils Using Photoacoustic Methodology in the Transmission Configuration

Photoacoustic methodology in the transmission configuration (PMTC) was used to study the thermophysical properties and their relation with the composition in Mexican citrus essential oils providing the viability of using photothermal techniques for quality control and for authentication of oils and their adulteration. Linear relations for the amplitude (on a semi-log scale) and phase, as functions of the sample’s thickness, for the PMTC was obtained through a theoretical model fit to the experimental data for thermal-diffusivity measurements in Mexican orange, pink grapefruit, mandarin, lime type A, centrifuged essential oils, and Mexican distilled lime essential oil. Gas chromatography for distilled lime essential oil and centrifuged lime essential oil type A is reported to complement the study. Experimental results showed close thermal-diffusivity values between Mexican citrus essential oils obtained by centrifugation, but a significant difference of this physical property for distilled lime oil and the corresponding value obtained by centrifugation, which is due to their different chemical compositions involved with the extraction processes.     

激光闪光法测量材料热扩散率标准装置的研制

介绍了材料热扩散率测量标准装置的研制和实验方法,采用参考样品进行了比对,其测量扩展不确定度优于5%.     

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.     

The Effect of the Surrounding Medium and Its Pressure on Data Obtained in Thermal Diffusivity Measurements Using the Flash Method

This work describes experimental measurements made with a high temperature–high pressure flash thermal diffusivity instrument, using nitrogen, argon, and helium as environment. Data was generated using pressures from vacuum to 30 bar in the temperature range of ambient to 1000°C. NIST SRM 8425 (Poco AXM 5Q, fine grain graphite) was used for the tests. A total of 2.970 data points were obtained, showing a clear and prominent shift in the data, depending on the pressure and the thermal properties of the surrounding gas. Preliminary conclusions drawn from the work indicate the influence of heat conduction, convection, and diffusion through the environmental gas, on the thermal diffusivity results.     

International Intercomparison of Laser Power Measurements in the Visible Region

In this paper we describe results of the international intercomparison of He-Ne and Ar-ion laser power measurements. The intercomparison measurements were of He-Ne laser power of 3 mW at the wavelength of 633 nm and Ar-ion laser power of 200 mW at 488 nm and 515 nm. The participating laboratories coincided within deviation from the average of 0.6 percent at 633 nm, 0.8 percent at 488 nm, and 0.9 percent at 515 nm.     

Analysis of Parameter Estimation Possibilities of the Thermal Contact Resistance Using the Laser Flash Method with Two-Layer Specimens

The paper presents a curve-fitting-based calculation of the thermal contact resistance and other parameters (absorbed energy and material properties) from laser flash measurements considering a two-layer specimen (aluminum substrate and stainless-steel film). Sensitivity analysis of different cases was used to examine the sensitivities of the unknown parameters: thermal contact resistance, absorbed energy, specific heat of the film, and thermal conductivity of the film. A nonlinear curve-fitting method was applied to perform the estimation of the unknown parameters using simulated measurements generated by the solution of the direct problem. An extensive analysis was performed to examine which parameters might be estimated simultaneously with the contact resistance for different noise levels of the simulated measurement. It was concluded that in the noiseless case all four unknown parameters can be estimated simultaneously with high accuracy. The noise has a significant effect on the accuracy of the parameter estimation, but even when a reasonable noise level is present, it is still possible to accurately estimate one or two parameters together with the thermal contact resistance.     

Techniques for Accurate Resistance Measurement in the Transient Short-Hot-Wire Method Applied to High Thermal-Diffusivity Gas

The accuracy of high-speed transient resistance measurements is an important issue particularly for measuring the thermal conductivity of high thermal-diffusivity (low-density) gases. This is because the hot-wire temperature rise against the logarithm of time is non-linear and can approach a steady state within the typical measurement time of 1 s. Two types of voltmeters are compared for use in the transient short-hot-wire method. Details of suitable procedures for taking accurate transient resistance measurements with either a two-channel high-speed analog/digital converter or a pair of integrating digital multimeters are presented.     

A Method of Estimating the Accuracy Characteristics of Radio Rangefinder Measuring Instruments Using Precision Laser System Measurements

A new method of estimating the accuracy characteristics of radio rangefinder measuring instruments using laser system measurements is proposed. Smoothed results of laser system measurements, reduced to the same coordinates and to the same instant of time with measurements of the radio systems, are used as standards.     

应用于激光闪光法测量热扩散率装置的微弱信号放大调理技术研究

针对激光闪光法热扩散率测量装置中光伏型探测器输出信号微弱、易受干扰的问题,设计了微弱信号放大调理电路。应用输入保护环技术增强抗干扰能力,精选电子元器件提高测量准确度,应用开尔文开关技术实现自动切换功能避免导通电阻的干扰。经实验证明,本文研制的微弱信号放大调理电路具有较好的重复性、较小的波动度和长期稳定性,为激光闪光法热扩散率测量装置的应用提供了重要技术保障。     

火花放电原子发射光谱法测定球化铁水中C,S元素的制样方法研究

用发射光谱仪精准测定球化铁水C元素一直是铸造行业的一大难题,由于样品制备误差具有显著性,测定用的科学仪器校准好,不等于测定的产品成分真实客观。国标GB/T 20066-2006《钢和铁化学成分测定用试样的取样和制样方法》对球化铁水测定未给出明确的制样方法,应用企业无法按统一方法进行生产过程控制,精准诊断产品化学成分可以降低可疑品数量和质量控制成本。本文介绍用发射光谱仪精准测定球化铁水化学成分样品制备方法认证,可以解决用发射光谱仪精准测定球化铁水化学成分技术难题。     

Phase Diagram and Melting Curve of Iron Obtained Using the Data of Static and Shock-Wave Measurements

Interest shown by geophysicists in the Earth's core has stimulated numerous investigations of the phase diagram of iron and its melting curve in the pressure range up to several megabar and temperature range up to several thousand degrees. The development of new investigation methods involving the use of laser heating and in situ diagnostics with the aid of X-radiation has promoted the studies into the solid phase structure under conditions of static compression in diamond anvils. The results obtained by different research teams, though differing in details, have made it possible to determine the position of the phase boundaries in the phase diagram and make estimates of the density dependence of the Grueneisen coefficient for the main phases of iron, which correlate in varying degrees with the data on the melting curve. In this paper, shock-wave and static data for iron available in the literature are analyzed, as well as the parameters of the equation of state for the and phases obtained using the experimental data on isentropic expansion from the state of shock compression.     

Systematic Errors in Laser Gain, Saturation Irradiance, and Cavity Loss Measurements and Comparison with a HCN Laser.

A pair of laser parameters of considerable practical interest are the small signal gain and saturation irradiance of the gain medium. These are commonly measured by observing the dependence of the output power on some adjustable cavity loss parameter and comparing the measured data with the predictions of a suitable laser model. Because of the inevitable approximations in this model the resulting estimates of gain and saturation irradiance are always affected to some extent by systematic errors. The small-gain, plane-wave, mean-field, and pure homogeneous or inhomogeneous line-broadening approximations are considered, with estimates of the magnitudes of these errors being presented for the case in which the gain, the saturation irradiance, and the cavity loss are fitted to the data. It is shown that these errors can be quite substantial, and therefore accurate absolute measurements of the three laser parameters can be quite difficult to obtain using the variable loss method. As an illustration of these errors, a comparison between the measured output power from a HCN laser and the power predicted using experimentally measured gain and saturation irradiance values is shown. The poor quality of these predictions illustrates the serious effects that the systematic errors can have, although an alternative analysis in which the cavity loss is supplied and only the gain and saturation irradiance fitted is also shown and gives good predictions despite inaccuracies in the model.