Radiance temperatures (in the wavelength range 523–907 nm) of group IVB transition metals titanium,zirconium, and hafnium at their melting points by a pulse-heating technique

The melting-point radiance temperatures (at six wavelengths in the range 523–907 nm) of the Group IVB transition metals titanium, zirconium, and hafnium were measured by a pulse-heating technique. The method is based on rapid resistive self-heating of the specimen from room temperature to its melting point in less than 1 s and on simultaneously measuring the specimen radiance temperatures every 0.5 ms with a high-speed six-wavelength pyrometer. Melting was manifested by a plateau in the radiance temperature-versus-time function for each wavelength. The melting-point radiance temperatures for a given specimen were determined by averaging the measured temperatures along the plateau at each wavelength. The melting-point radiance temperatures for each metal were determined by averaging results for several specimens at each wavelength as follows: Based on estimates of the random and systematic errors arising from pyrometry and specimen conditions, the combined uncertainty (95% confidence level) in the reported values is about ±8K at each wavelength.     

Radiance temperatures (in the wavelength range 525 to 906 nm) of vanadium at its melting point by a pulse-heating technique

The radiance temperatures (at six wavelengths in the range 525 to 906 nm) of vanadium at its melting point were measured by a pulse-heating technique. The method is based on rapid resistive self-heating of the specimen from room temperature to its melting point in less than 1 s and on simultaneously measuring the specimen radiance temperatures every 0.5 ms with a high-speed six-wavelength pyrometer. Melting was manifested by a plateau in the radiance temperature-vs-time function for each wavelength. The melting-point radiance temperatures for a given specimen were determined by averaging the measured temperatures along the plateau at each wavelength. The melting-point radiance temperatures for vanadium as determined by averaging the results at each wavelength for 16 specimens (standard deviation in the range 0.3 to 0.4 K. depending on the wavelength) are 2030 K at 525 nm, 1998 K at 622 nm, 1988 K at 652 nm, 1968 K at 714 nm, 1935 K at 809 nm, and 1900 K at 906 nm. Based on estimates of the random and systematic errors that arise from pyrometry and specimen conditions, the resultant uncertainty (2 SD level) in the reported values is about ±7 K at each wavelength.     

Radiance Temperatures (in the Wavelength Range 530 to 1500 nm) of Nickel at Its Melting Point by a Pulse-Heating Technique

The radiance temperatures (at seven wavelengths in the range 530 to 1500 nm) of nickel at its melting point were measured by a pulse-heating technique. The method is based on rapid resistive self-heating of the specimen from room temperature to its melting point in less than 1 s and on simultaneously measuring specimen radiance temperatures every 0.5 ms. Melting of the specimen was manifested by a plateau in the radiance temperature-versus-time function for each wavelength. The melting-point radiance temperatures for a given specimen were determined by averaging the measured temperatures along the plateau at each wavelength. The melting-point radiance temperatures for nickel, as determined by averaging the results at each wavelength for 25 specimens, are: 1641 K at 530 nm, 1615 K at 627 nm, 1606 K at 657 nm, 1589 K at 722 nm, 1564 K at 812 nm, 1538 K at 908 nm, and 1381 K at 1500 nm. Based on uncertainties arising from pyrometry and specimen conditions, the combined uncertainty (two standard-deviation level) is about ± 6 K for the reported values in the range 530 to 900 nm and is about ± 8 K for the reported value at 1500 nm.     

Radiance temperatures (in the wavelength range 519–906 nm) of tungsten at its melting point by a pulse-heating technique

Radiance temperatures (at six wavelengths in the range 519–906 nm) of tungsten at its melting point were measured by a pulse-heating technique. The method is based on rapid resistive self-heating of the specimen from room temperature to its melting point in less than 1 s; and on simultaneously measuring the specimen radiance temperatures every 0.5 ms with a high-speed six-wavelength pyrometer. Melting was manifested by a plateau in the radiance temperature versus time function for each wavelength. The melting-point radiance temperatures for a given specimen were determined by averaging the measured temperatures along the plateau at each wavelength. The melting-point radiance temperatures for tungsten were determined by averaging the results at each wavelength for 10 specimens (standard deviation in the range 0.5–1.1 K, depending on the wavelength) as follows: 3319 K at 519 nm, 3236 K at 615 nm, 3207 K at 652 nm, 3157 K at 707 nm, 3078 K at 808 nm, and 2995 K at 906 nm. Based on estimates of the random and systematic errors arising from pyrometry and specimen conditions, the total uncertainty in the reported values is about ±7 K at 653 nm and ± 8 K at the other wavelengths.Paper presented at the Third Workshop on Subsecond Thermophysics, September 17–18, 1992, Graz, Austria.     

Radiance Temperatures (in the Wavelength Range 527 to 1500 nm) of Palladium and Platinum at Their Melting Points by a Pulse-Heating Technique

The radiance temperatures (at seven wavelengths in the range 527 to 1500 nm) of palladium and platinum at their respective melting points were measured by a pulse-heating technique. The method, based on rapid resistive self-heating of a specimen from room temperature to its melting point in less than 1 s, used two high-speed pyrometers to measure specimen radiance temperatures every 0.5 ms during the heating and melting period. Melting was manifested by a plateau in the radiance temperature-versus-time function for each wavelength. The melting-point radiance temperatures for a given specimen were determined by averaging the measured temperatures along the plateau at each wavelength. The melting-point radiance temperatures for each metal as determined by averaging the results for several specimens at each wavelength are as follows. Based on uncertainties arising from pyrometry and specimen conditions, the expanded uncertainty (two-standard deviation level) is about ±7 K for the reported values in the range 527 to 900 nm and about ±8 K for the reported values at 1500 nm.     

Radiance temperatures (in the wavelength range 522–906 nm) of niobium at its melting point by a pulse-heating technique

Radiance temperatures (at six wavelengths in the range 522–906 nm) of niobium at its melting point were measured by a pulse-heating technique. The method is based on rapid resistive self-heating of the specimen from room temperature to its melting point in less than 1 s and on simultaneously measuring the specimen radiance temperatures every 0.5 ms with a high-speed multiwavelength pyrometer. Melting was manifested by a plateau in the radiance temperatureversus-time function for each wavelength. The melting-point radiance temperatures for a given specimen were determined by averaging the measured temperatures along the plateau at each wavelength (standard deviation of an individual temperature from the mean: 0.1–0.4 K). The melting-point radiance temperatures for niobium were determined, by averaging the results at each wavelength for 10 specimens (standard deviation: 0.3 K), as follows: 2497 K at 522 nm, 2445 K at 617 nm, 2422 K at 653 nm, 2393 K at 708 nm, 2337 K at 809 nm, and 2282 K at 906 nm. Based on estimates of the random and systematic errors arising from pyrometry and specimen conditions, the total error in the reported values is about 5 K at 653 nm and 6 K at the other wavelengths.Paper presented at the Second Workshop on Subsecond Thermophysics, September 20–21, 1990, Torino, Italy.     

Radiance temperatures at 1500 nm of niobium and molybdenum at their melting points by a pulse-heating technique

Radiance temperatures at 1500 nm of niobium and molybdenum at their melting points were measured by a pulse-heating technique. The method is based on rapid resistive self-heating of the strip-shaped specimen from room temperature to its melting point in less than I s and measuring the specimen radiance temperature every 0.5 ms with a high-speed infrared pyrometer. Melting of the specimen was manifested by a plateau in the radiance temperature-versus-time function. The melting-point radiance temperature for a given specimen was determined by averaging the measured values along the plateau. A total of 12 to 13 experiments was performed for each metal under investigation. The melting point radiance temperatures for each metal were determined by averaging the results of the individual specimens. The results for radiance temperatures at 1500 nm are as follows: 1983 K for niobium and 2050 K for molybdenum. Based on the estimates of the uncertainties arising from the use of pyrometry and specimen conditions, the combined uncertainty (two standard-deviation level) in the reported values is ± 8 K.Paper presented at the Fourth International Workshop on Subsecond Thermophysics, June 27–29, 1995, Köln, Germany.     

Radiance Temperatures (in the Wavelength Range 521 to 1500 nm) of Rhenium and Iridium at Their Melting Points by a Pulse-Heating Technique

The melting-point radiance temperatures (at seven wavelengths in the range 521 to 1500 nm) of rhenium and iridium were measured by a pulse-heating technique. The method is based on rapid resistive self-heating of the specimen from room temperature to its melting point in less than 1 s and on simultaneously measuring the specimen radiance temperature every 0.5 ms with two high-speed pyrometers. Melting was manifested by a plateau in the radiance temperature-versus-time function for each wavelength. The melting-point radiance temperatures for a given specimen were determined by averaging the measured temperatures along the plateau at each wavelength. The melting-point radiance temperatures for each metal were determined by averaging results for several specimens at each wavelength. The results are as follows. Based on estimates of the random and systematic errors arising from pyrometry and specimen conditions, the expanded uncertainty (two standard-deviation level) in the reported values is ±8K.     

Radiance Temperature and Normal Spectral Emittance (in the Wavelength Range of 1.5 to 5 μm) of Nickel at its Melting Point by a Pulse-Heating Technique

The radiance temperature of nickel at its melting point was measured at four wavelengths (in the nominal range of 1.5 to 5 μm) by a pulse-heating technique using a high-speed fiber-coupled four-channel infrared pyrometer. The method was based on rapid resistive self-heating of a specimen from room temperature to its melting point in less than 1 s while simultaneously measuring the radiance emitted by it in four spectral bands as a function of time. A plateau in the recorded radiance-versus-time traces indicated melting of the specimen. The melting-point radiance temperature for a given specimen was determined by averaging the temperature measured along the plateau at each wavelength. The results for several specimens were then, in turn, averaged to yield the melting-point radiance temperature of nickel, as follows: 1316 K at 1.77 μm, 1211 K at 2.26 μm, 995 K at 3.48 μm, and 845 K at 4.75 μm. The melting-point normal spectral emittance of nickel at these wavelengths was derived from the measured radiance in each spectral band using the published value of the thermodynamic (true) melting temperature of nickel.     

Radiance temperatures (at 658 and 898 nm) of niobium at its melting point

Radiance temperatures (at 658 and 898 nm) of niobium at its melting point were measured by a pulse-heating technique. A current pulse of subsecond duration was imparted to a niobium strip and the initial part of the melting plateau was measured by high-speed pyrometry. Experiments were performed with two techniques and the results do not indicate any dependence of radiance temperature (at the melting point) on initial surface or system operational conditions. The average radiance temperature at the melting point of niobium is 2420 K at 658 nm and 2288 K at 898 nm, with a standard deviation of 0.4 K at 658 nm and 0.3–0.6 K at 898 nm (depending on the technique used). The total uncertainty in radiance temperature is estimated to be not more than ±6 K. The results are in good agreement with earlier measurements at the National Institute of Standards and Technology (USA) and confirm that both radiance temperature and normal spectral emissivity (of niobium at its melting point) decrease with increasing wavelength in the region 500–900 nm.Paper presented at the Third Workshop on Subsecond Thermophysics, September 17–18, 1992, Graz, Austria.     

Validation of the Infrared Emittance Characterization of Materials Through Intercomparison of Direct and Indirect Methods

A comparison of the spectral directional emittance of samples as a function of wavelength was performed at the Fourier Transform Infrared Spectrophotometry (FTIS) and the Advanced Infrared Radiometry and Imaging (AIRI) facilities at NIST. At the FTIS, the emittance is obtained indirectly through the measurement of near-normal directional-hemispherical reflectance (DHR) using an infrared integrating sphere. At the AIRI, the normal directional emittance is obtained directly through the measurement of the sample spectral radiance referenced to that from blackbody sources, while the sample is located behind a black plate of known temperature and emittance. On the same setup at the AIRI, the normal emittance at near ambient temperatures is also measured indirectly by a “two-temperature” method in which the sample spectral radiance is measured while the background temperature is controlled and varied. The sample emittance measurements on the comparison samples are presented over a wavelength range of 3.4 μm to 13.5 μm at several near-ambient temperatures and for near-normal incidence. The results obtained validate the two independent capabilities and demonstrate the potential of the controlled background methods for measurements of the radiative properties of IR materials.     

A transient (subsecond) technique for measuring heat of fusion of metals

A transient technique is described for measuring the heats of fusion of metals with melting temperatures above 1500 K. The specimen configuration consists of a strip of the metal under study sandwiched between two strips of another metal with a higher melting temperature. The basic method consists of rapidly heating the composite specimen by passing a subsecond-duration electrical current pulse through it and simultaneously measuring the radiance temperature of the containment metal surface, as well as the current through and voltage drop across the specimen. The melting of the metal under study is manifested by a plateau in the temperature versus time function for the containing metal surface. The time integral of the power absorbed by the specimen during melting yields the heat of fusion. Measurements on several tantalum-niobium-tantalum specimens yield a value of 31.5 kJ · mor^–1 for the heat of fusion of niobium, with an estimated maximum inaccuracy of ± 5%.     

Measurement of the heat of fusion of tantalum by a microsecond-resolution transient technique

The heat of fusion of tantalum was measured using a microsecond-resolution pulse-heating technique. The technique is based on rapid (about 100-s) resistive self-heating of a specimen by a high-current pulse from a capacitor discharge system and measuring the current through the specimen, voltage across the specimen, and radiance temperature of the specimen as functions of time. Melting of a specimen is manifested by a plateau in the radiance temperature versus time function. The time integral of the power absorbed by the specimen during melting yields the heat of fusion. Measurements gave a value of 34.8 kJ · mot^– for the heat of fusion of tantalum, with a total uncertainty of ±6%. Electrical resistivity of solid and liquid tantalum at its melting temperature was also measured.     

Temperature Dependence of the Density and Electrical Resistivity of Liquid Zirconium up to 4100 K

Experimental data on the temperature dependence of the density of liquid zirconium and its electrical resistivity are obtained under conditions of pulsed electric heating (for 5 to 10 s) of wire and foil zirconium samples. Samples in the form of a wedge-shaped blackbody model are prepared for use in temperature measurements. The thermal radiation from the model space is registered by a high-speed optical pyrometer at a wavelength of 855 nm. The temperature (up to 4100 K) is calculated by Planck's formula. The temperature plateau in the melting region of the blackbody model is used for calibration of the pyrometer. In so doing, it is assumed that this plateau has the equilibrium melting temperature of 2128 K. A digital oscilloscope is used for recording the current through the sample, the voltage across the sample, and the pyrometer signal. The density of zirconium is determined using the laser flash method while heating zirconium wires. The sample is illuminated by a Q-switched Nd-YAG laser. A CCD video camera is used for photographing. The experimental data on the density and electrical resistivity of liquid zirconium are essential for simulation of the behavior of nuclear power plants in the case of a serious emergency.     

A Fast Laser Polarimeter Improving a Microsecond Pulse Heating System

The microsecond pulse heating system has been used for more than 15 years to investigate thermophysical properties of solid and liquid metals and alloys. The only way to measure temperature in the time and temperature range of these experiments (duration of a few tens of microseconds, temperatures up to 7000 K) is optical pyrometry. The radiance temperature can be measured very accurately. However, to obtain true temperature from radiance temperature the normal spectral emissivity at the wavelength of interest of the material under investigation has to be known. Because normal spectral emissivity measurements on pulse heated liquid metals were not possible in the past, an assumption about the behavior of the emissivity in the liquid phase had to be made, which increased the uncertainty of the temperature determination. To overcome this limitation in temperature measurement, a microsecond division of amplitude polarimeter (µ-DOAP) was added to the pulse heating system. The normal spectral emissivity at 684.5 nm is derived from the measured change in the state of polarization of laser light that is reflected off the sample surface. The working principle of this polarimeter system is presented, and experimental results of the normal spectral emissivity at 684.5 nm as a function of radiance temperature at 650 nm are discussed.     

Design and Evaluation of Large-Aperture Gallium Fixed-Point Blackbody

To complement existing water bath blackbodies that now serve as NIST primary standard sources in the temperature range from 15 °C to 75 °C, a gallium fixed-point blackbody has been recently built. The main objectives of the project included creating an extended-area radiation source with a target emissivity of 0.9999 capable of operating either inside a cryo-vacuum chamber or in a standard laboratory environment. A minimum aperture diameter of 45 mm is necessary for the calibration of radiometers with a collimated input geometry or large spot size. This article describes the design and performance evaluation of the gallium fixed-point blackbody, including the calculation and measurements of directional effective emissivity, estimates of uncertainty due to the temperature drop across the interface between the pure metal and radiating surfaces, as well as the radiometrically obtained spatial uniformity of the radiance temperature and the melting plateau stability. Another important test is the measurement of the cavity reflectance, which was achieved by using total integrated scatter measurements at a laser wavelength of 10.6 μm. The result allows one to predict the performance under the low-background conditions of a cryo-chamber. Finally, results of the spectral radiance comparison with the NIST water-bath blackbody are provided. The experimental results are in good agreement with predicted values and demonstrate the potential of our approach. It is anticipated that, after completion of the characterization, a similar source operating at the water triple point will be constructed. Certain commercial equipment, instruments, or material are identified in this paper to specify the experimental procedures and result adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that material or equipment identified are necessarily the best available for the purpose.     

真空镓固定点黑体辐射源研制

为满足红外遥感载荷实验室辐射定标需求,实现红外遥感辐射量值溯源到ITS-90国际温标,研制了真空镓固定点黑体辐射源.黑体腔开口直径为25 mm,深度220 mm,内部喷涂高发射率涂层,通过仿真计算黑体腔的发射率优于0.9999.在真空下测试了镓固定点相变坪台的复现性为4.4 mK,坪台稳定性优于2 mK.测量了镓固定点...     

Normal Spectral Emissivity of Niobium (at 900 nm) by a Pulse-Heating Reflectometric Technique

The normal spectral emissivity of niobium strip specimens was measured using a new pulse-heating reflectometric technique. The hemispherical spectral reflectivity of the surface of a strip tangent to an integrating sphere is determined by a high-speed lock-in technique. At the same time, the radiance temperature of the strip is measured by high-speed pyrometry from approximately 1000K to the melting point. Details of the measurement method and of the related calibration techniques are reported. Results of the normal spectral emissivity of niobium at 900 nm from room temperature to its melting point are presented, discussing differences related to the heating rate and to surface conditions.     

A microsecond-resolution transient technique for measuring the heat of fusion of metals: Niobium

A microsecond-resolution pulse-heating technique is described for the measurement of the heat of fusion of refractory metals. The method is based on rapid resistive self-heating of the specimen by a high-current pulse from a capacitor discharge system and measurement of the current through the specimen, the voltage across the specimen, and the radiance temperature of the specimen as a function of time. Melting of the specimen is manifested by a plateau in the temperature versus time function. The time integral of the power absorbed by the specimen during melting yields the heat of fusion. Measurements gave a value of 31.1 kj · mol^–1 for the heat of fusion of niobium, with an estimated maximum uncertainty of ±5%. Electrical resistivity of solid and liquid niobium at its melting temperature was also measured.