Phase Dependence (Liquid/Solid) of Normal Spectral Emissivities of Noble Metals at Melting Points

Normal spectral emissivities of liquid and solid Cu, Ag, and Au have been determined at their melting (freezing) points in the visible region using a cold crucible as the heating method. The use of the cold crucible enables the solidification front to be moved on the molten metal surface slowly enough to measure the emissivities of liquid and solid phases separately at the freezing point. Combined standard uncertainties of the spectral emissivities and wavelengths have been estimated. In silver, the spectral emissivity obtained for the liquid is systematically larger than that for the solid over the visible region, which is consistent with the prediction from a classical free-electron model. In copper and gold, the spectral emissivities at wavelengths around their absorption edges do not change for the solid-to-liquid transition. The wavelength range where the emissivity of copper is independent of the phase is unexpectedly broad (the width is greater than 40 nm), which differs significantly from classical experimental studies on the so-called X-point in the emissivity of copper. A qualitative explanation is provided for the difference in the phase dependence (liquid/solid) of the emissivity between copper and gold.     

Phase (Liquid/Solid) Dependence of the Normal Spectral Emissivity for Iron, Cobalt, and Nickel at Melting Points

Normal spectral emissivities of liquid and solid Fe, Co, and Ni have been determined at their melting points at wavelengths from 650 to 800 nm and from 1000 to 1900 nm using an apparatus that consists of a cold crucible and diffraction grating spectroscopes. For all three metals, the emissivities of the liquid phases are slightly larger than those of the solid phases both in the visible and near-infrared regions. For iron, the near-infrared emissivities decreased progressively with each additional measurement series and settled down after three series. A possible explanation to this behavior is offered. The present results for iron were assessed by comparisons with previously reported results and with predictions based upon the Hagen–Rubens relation for the ratio of the emissivity of the liquid to that of the solid ( _Liquid/ _Solid). The measured emissivities for all three metals are in good agreement with previous results at and near the melting point. The results for _Liquid/ _Solid in the near-infrared region demonstrate that the phase (liquid/solid) dependence of the infrared emissivity is consistent with that of the dc resistivity for all the metals at their melting points.     

Emissivity modeling of metals during the growth of oxide film and comparison of the model with experimental results

Emissivity modeling of metals has been developed to elucidate behavior during the growth of oxide film, and the modeling results have been compared with experimental results. To express emissivities, pseudo-optical constants of a bare metal and of an oxide film obtained by an elipsometer are substituted into the model equations. Emissivity behavior during the growth of an oxide film upon the surface of a specimen is shown in terms of spectral, directional, and polarized characteristics, and it coincides with the experimental results, both quantitatively and qualitatively. The modeling is simple and provides useful guidance for the development of emissivity-compensated radiation thermometry.     

Evaluation of effective emissivities of nonisothermal cavities

Local effective spectral and total emissivities of nonisothermal cavities having diffuse surfaces are evaluated. The effective emissivity of the cavity wall around the half-depth of a cylinder is little affected by a linear decrease or increase of temperature along the cavity axis because of a compensation effect. The nonisothermal effect on the integrated cavity emissivity changes considerably with cavity geometry for a given temperature distribution.     

Determination of boron in high-aluminum semiproduct by inductively coupled plasma atomic emission spectroscopy

A method to determine boron in a high-aluminum semiproduct by ICP-AES is described. The detection limit is 0.012 wt %. The iron and chromium spectral noise affecting the most sensitive boron lines is studied. It is shown that the Al₂O₃ matrix does not influence the intensity of the analytical signal. The ways to decompose a probe by melting together are compared.     

Near-Infrared Spectral Emissivity of Cu, Ag, and Au in the Liquid and Solid States at Their Melting Points

Normal spectral emissivities of liquid and solid Cu, Ag, and Au have been determined at their melting points over a wavelength range 1000 to 2500 nm using an apparatus that consists of a cold crucible and a diffraction grating spectrometer. For the noble metals, the emissivities of liquid phases are systematically larger than those of solid phases over the measured wavelength range, and the wavelength dependence of the liquid is similar to that of the solid. The measured emissivities for the liquid metals are compared with those deduced from the optical constants measured by Miller and Krishnan et al. The present results for liquid Cu and Au are in good agreement with the data of Krishnan et al., but not with those of Miller for Cu, which suggests that the optical constants measured by Krishnan et al. for liquid Cu are more accurate than those of Miller. The present data for liquid Ag and Au are in excellent agreement with all previously reported data. For the solid metals at their melting point, a semi-empirical estimation of the emissivity was carried out based upon the Drude model incorporating the effects of interband absorption and a frequency-dependent scattering rate, ^–1()= ^–1 ₀+b ². The values of ^–1 ₀ and b at the melting point are obtained by fitting the modified Drude model to the measurement results for the solid noble metals.     

Texture and Porosity Effects on the Thermal Radiative Behavior of Alumina Ceramics

Thermal and optical properties of ceramics are dependent on radiation scattering and cannot be determined by a knowledge of their chemical composition alone, as for single crystals. In this paper, extrinsic effects, such as roughness, porosity, and texture, on the spectral emissivity of alumina ceramics are investigated. Roughness effects have an influence mainly in the opaque zone; an important porosity dependence and the presence of a critical porosity threshold were observed in the semitransparent zone. Furthermore, it was shown that two ceramics with similar total porosities, but with different textures, possess radically different emissivities, showing that grain size, pore size, and spatial repartition of the grains are also crucial for an understanding of the thermal properties of the ceramics. This study was performed at CEMTHI laboratory.     

Portable Fourier transform infrared spectroradiometer for field measurements of radiance and emissivity

A hand-held, battery-powered Fourier transform infrared spectroradiometer weighing 12.5 kg has been developed for the field measurement of spectral radiance from the Earth's surface and atmosphere in the 3-5-μm and 8-14-μm atmospheric windows, with a 6-cm(-1) spectral resolution. Other versions of this instrument measure spectral radiance between 0.4 and 20 μm, using different optical materials and detectors, with maximum spectral resolutions of 1 cm(-1). The instrument tested here has a measured noise-equivalent delta T of 0.01 °C, and it measures surface emissivities, in the field, with an accuracy of 0.02 or better in the 8-14-μm window (depending on atmospheric conditions), and within 0.04 in accessible regions of the 3-5-μm window. The unique, patented design of the interferometer has permitted operation in weather ranging from 0 to 45 °C and 0 to 100% relative humidity, and in vibration-intensive environments such as moving helicopters. The instrument has made field measurements of radiance and emissivity for 3 yr without loss of optical alignment. We describe the design of the instrument and discuss methods used to calibrate spectral radiance and calculate spectral emissivity from radiance measurements. Examples of emissivity spectra are shown for both the 3-5-μm and 8-14-μm atmospheric windows.     

六方氮化硼的剥离及其在导热复合材料中的应用

六方氮化硼(h-BN)是一种石墨烯类二维材料,具有很高的导热性。当将其剥离成二维氮化硼纳米片(BNNSs)时,因其层状材料特殊的电子性能和高比表面积,使其制备技术受到很多研究人员的关注,其剥离方法以机械球磨和液相超声为主。综述了氮化硼二维纳米材料的几种剥离方法、原理及其优缺点,将在塑料导热材料中呈现较好的应用前景。     

Bandpass-resampling effects for the retrieval of surface emissivity

The retrieval of surface emissivity in the 8-14-microm region from remotely sensed thermal imagery requires channel-averaged values of atmospheric transmittance, path radiance, and downwelling sky flux. Band-pass resampling introduces inherent retrieval errors that depend on atmospheric conditions, spectral region, bandwidth, flight altitude, and surface temperature. This simulation study is performed for clear sky conditions and moderate atmospheric water vapor contents. It shows that relative emissivity retrieval errors can reach as much as 3% for broadband sensors (1-2-microm bandwidth) and 0.8% for narrowband instruments (0.15 microm), even for constant surface emissivity. For spectrally varying surface emissivities the relative retrieval error increases for the broadband instrument by approximately 2% in channels with strong emissivity changes of 0.05-0.1. The corresponding retrieval errors for narrowband sensors increase by approximately 3-4%. The channels in the atmospheric window regions with lower transmittance, i.e., 8-8.5 and 12.5-14 microm, are most sensitive to retrieval errors.     

High-Accuracy Emissivity Data on the Coatings Nextel 811-21, Herberts 1534, Aeroglaze Z306 and Acktar Fractal Black

The Physikalisch-Technische Bundesanstalt determined the directional spectral emissivities of several widely used black coatings: Nextel 811-21, Herberts 1534, Aeroglaze Z306 and Acktar Fractal Black. These are and were often applied in different industrial and scientific applications. The measurements are taken angularly resolved over a range from \(10{^{\circ }}\) to \(70{^{\circ }}\). They cover the temperature range typical for the application of the respective coating and a wide wavelength range from \(4~\upmu \hbox {m}\) to \(100~\upmu \hbox {m}\). The respective directional total emissivities and hemispherical total emissivities are given as well. The measurements were taken under vacuum at the reduced background calibration facility to achieve low uncertainties and avoid atmospheric interferences. Additionally, some measurements were taken with the emissivity measurement setup in air.     

Fe304／Au复合纳米材料的制备及SERS研究

采用化学共沉淀法制备Fe3O4,通过对Fe3O4的表面处理后,将纳米金组装在Fe3O4表面,制备Fe3O4／Au复合磁性纳米材料。利用透射电子显微镜（TEM）对复合磁性纳米材料的形貌进行了表征,通过紫外一可见吸收光谱和拉曼光谱仪对磁性纳米材料的表面增强拉曼散射光谱进行表征研究,采用铷硼磁铁对磁性纳米材料的磁性进行初步研究。实验结果表明：复合磁性纳米颗粒既具有磁性又具有贵金属光谱特性;纳米金能很好地改善Fe3O4磁性纳米颗粒的表面增强拉曼散射活性。     

Peak-Wavelength Method for Temperature Measurement

Based on measurements of the spectrum emitted by a target, a new method for measuring temperature, the peak-wavelength method (PWM), is proposed and evaluated in this paper. The uncertainty and resolution of this method have been estimated theoretically, and it is shown that this method offers high resolution and accuracy. Moreover, several analyses have been done for various surfaces (non-blackbody) with a series of assumed spectral emissivities. The results show that better accuracy can also be obtained in these cases. Finally, an experimental setup using a Fourier transform infrared spectrometer was built and tested in our lab. Several experiments have been carried out that show the peak-wavelength method is feasible and practical.     

Boron segregation on a vicinal Si(1 0 0) surface

Energetics of boron on a Si(1 0 0) stepped surface has been studied quantum mechanically at semi-empirical level. The step is represented by a cluster of silicon atoms and the boron impurity is moved in the step in substitutional and interstitial positions. The optimal configuration of the step with the impurity is evaluated from the minimization of the total energy. It has been found that, similarly to the known behavior in the flat surface, the boron impurity segregates below the surface. However the preferred adsorption sites have also a remarkable dependence on the distance from the step-edge. We illustrate the dependence of these sites on the step geometry.     

Application of band-target entropy minimization to infrared emission spectroscopy and the reconstruction of pure component emissivities from thin films and liquid samples

Thermal emission spectral data sets were collected for a thin solid film (parafilm) and a thin liquid film (isopropanol) on the interval of 298-348 K. The measurements were performed using a conventional Fourier transform infrared (FT-IR) spectrometer with external optical bench and in-house-designed emission cell. Both DTGS and MCT detectors were used. The data sets were analyzed with band-target entropy minimization (BTEM), which is a pure component spectral reconstruction program. Pure component emissivities of the parafilm, isopropanol, and thermal background were all recovered without any a priori information. Furthermore, the emissivities were obtained with increased signal-to-noise ratios, and the signals due to absorbance of thermal radiation by gas-phase moisture and CO2 were significantly reduced. As expected, the MCT results displayed better signal-to-noise ratios than the DTGS results, but the latter results were still rather impressive given the low temperatures used in this study. Comparison is made with spectral reconstruction using the orthogonal projection approach-alternating least squares (OPA-ALS) technique. This contribution introduces the primary equation for emission spectral reconstruction using BTEM and discusses some of the unusual characteristics of thermal emission and their impact on the analysis.     

Research on the Temperature and Emissivity Measurement of the Metallic Thermal Protection Blanket

The temperatures and emissivities of the metallic thermal protection blanket at (900–1,300) °C are investigated experimentally by using a multi-wavelength pyrometer. A linear relation between the emissivity and true temperature at different wavelengths is assumed. Based on this assumption, the true temperatures and spectral emissivities of the metallic thermal protection blanket at the two temperature measurement points can be calculated simultaneously. Some experimental results for the practical data processing of measurements performed on the metallic thermal protection blanket show that the difference between the calculated temperature and the temperature measured by a standard thermocouple is within  ±  10°C.     

The Influence of Crucible Material on Aluminum Composition

The freezing point of aluminum is one of the ITS-90 defining fixed points widely used for thermometer calibration. However, long-term investigations have revealed slow temperature depressions of the aluminum freezing temperature and alterations of the metal structure that are probably due to metallic contamination caused by the partial dissolution of crucible material. The objective of this work was to study the interaction of liquid aluminum with graphite and boron nitride in order to select a nonreactive material. Two crucibles made of high purity graphite and boron nitride were filled with Al of 6N5 purity; then, 40 melting-freezing cycles were carried out. The total time of contact between aluminum in the liquid phase and the crucible was 240 h. After that, the composition of Al, graphite, and boron nitride was studied and the results were compared with the analysis of the initial samples. The Al ingot in contact with boron nitride was found to be contaminated by boron.     

Use of superconductors in thermal insulations

A suggestion is made for using superconductors as thermal radiation shields at or below liquid helium temperatures. Calculations are described which predict total emissivities for niobium of 10^?4–10^?5 at 4K and 10^?8–10^?7 for temperatures of 1–2 K.     

Simultaneous measurements of normal spectral emissivity by spectral radiometry and laser polarimetry at high temperatures in millisecond-resolution pulse-heating experiments: Application to molybdenum and tungsten

Spectral radiometry and laser polarimetry are two independent techniques for the measurement of spectral emissivity of materials. In this paper, a high-speed system is described for the rapid measurement of normal spectral emissivity of a specimen based on the simultaneous utilization of the two techniques. One of the goals of this work to ascertain the accuracy of the laser polarimetry technique in measurement of normal spectral emissivity at high temperatures. To accomplish this goal, the normal spectral emissivities, in the vicinity of 0.633m, of molybdenum and tungsten were measured by the two techniques over the temperature range 2000 to 2600 K. The results obtained by the two techniques are in agreement within 1%. The total uncertainty (two-standard deviation level) in measurement of emissivity by either spectral radiometry or laser polarimetry technique is estimated to be not more than + 2%.     

Surface Tension of Liquid Alumina from Contactless Techniques

New data for the surface tension of liquid alumina from 2300 to 3200 K are reported. Aerodynamic levitation of CO₂ laser-heated liquid drops allowed contactless measurement of vibration frequencies directly related to surface tension. Consistent data were obtained on drops of different mass ranging from 20 to 160 mg. It was also shown that the oxydo-reducing character of the atmosphere does not modify the results within experimental uncertainty.