Normal Spectral Emissivity Research Articles

Modeling the Normal Spectral Emissivity of Aluminum 1060 at 800-910 K During the Growth of Oxide Layer

This work strives to model the normal spectral emissivity of aluminum 1060 during the growth of oxide layer in air over the temperatures ranging from 800 to 910 K. For this reason, the normal spectral emissivity of aluminum 1060 has been measured over a 6 h heating period at a definite temperature. In our experiment, the radiance coming from the specimen is received by an InGaAs photodiode detector, which works at 1.5 μm with the bandwidth of 20 nm. The temperature of specimen surface is measured by averaging the two platinum-rhodium thermocouples, which are symmetrically welded in the front surface of specimen near the measuring area viewed by the detector. The strong oscillations of normal spectral emissivity have been observed and discussed, which are affirmed to be connected with the thickness of oxide layer on the specimen surface, and originate from the interference effect between the radiation coming from the oxide layer on the specimen surface and the radiation stemming from the substrate. The uncertainty of normal spectral emissivity contributed only by the surface oxidization is about 4.6-10.6%, and the corresponding uncertainty of temperature contributed only by the surface oxidization is about 3.5-8.4 K. The analytical model between the normal spectral emissivity and the heating time is evaluated at a definite temperature. A simple functional form with the exponential and logarithmic functions can be employed to reproduce well the variation of normal spectral emissivity with the heating time at a definite temperature, including the reproduction of strong oscillations.

Effect of Surface Oxidization on the Normal Spectral Emissivity of Straight Carbon Steel at 800–1100 K in Air

Effect of Surface Oxidization on the Normal Spectral Emissivity of Straight Carbon Steel at 800–1100 K in Air

Modeling the Normal Spectral Emissivity of Red Copper T2 at 800–1,100 K During the Growth of Oxide Layer

This paper strives to model the normal spectral emissivity of red copper T2 during the growth of oxide layer at 800–1,100 K. For this reason, the normal spectral emissivity of red copper T2 specimens is evaluated at the sixteen definite temperatures during a 6-h heating period. In experiment, the normal radiance is measured using an InGaAs photodiode detector at 1.5 μm, which is perpendicular to the surface of specimens as accurately as possible. The temperature of specimen surface is obtained by averaging the two platinum–rhodium thermocouples, which are welded symmetrically and tightly in the front surface of specimens near the measuring area viewed by the detector. The strong oscillation of normal spectral emissivity occurs only during the initial heating period at each definite temperature, which has been affirmed to be connected with the thickness of oxide layer on the specimen surface. The interference effect between the radiation coming from the oxide layer on the specimen surface and the radiation stemming from the substrate is discussed, which is responsible to the strong oscillations of normal spectral emissivity. The uncertainty of normal spectral emissivity contributed only by the surface oxidization is estimated to be 3.3–10.0 %, and the corresponding uncertainty of temperature is estimated to be about 3.2–10.0 K. The analytical models between the normal spectral emissivity and the heating time are evaluated in detail. A simple functional form with the exponential and logarithmic functions has been found to reproduce well the variation of normal spectral emissivity with the heating time, including the fundamental reproduction of strong oscillation occurring during the initial heating period.

The application of the fast pulse heating method for investigation of carbon-rich side of Zr–C phase diagram under high temperatures

The microsecond technique of electrical pulse heating which gives rather uniform energy input into a film specimen is considered. ZrC+C specimens in the form of a thin layer (4.9μm) sputtered on isolating substrates by magnetron sputtering technique were used. Specimens contained (in at.%): Zr – 17.88; C – 67.69; N – 8.13; O – 5.98.It was measured: the imparted energy; the normal spectral emissivity; specific heat; resistivity (referred to the initial size of a specimen); specimen temperature from 2100 to 4500K. To obtain true temperature of the specimen the blackbody design was used. The temperature of the beginning and completion of phase transition (solid–liquid) is determined. The obtained results are considered together with the equilibrium Zr–C phase diagram.

New experimental device for high-temperature normal spectral emissivity measurements of coatings

A new experimental device for normal spectral emissivity measurements of coatings in the infrared spectral range from 1.38 μm to 26 μm and in the temperature range from 550 K to 1250 K is presented. A Fourier transform infrared spectrometer (FTIR) is used for the detection of sample and blackbody spectral radiation. Sample heating is achieved by a fiber laser with a scanning head. Surface temperature is measured by two methods. The first method uses an infrared camera and a reference coating with known effective emissivity, the second method is based on the combination of Christiansen wavelength with contact and noncontact surface temperature measurement. Application of the method is shown on the example of a high-temperature high-emissivity coating. Experimental results obtained with this apparatus are compared with the results performed by a direct method of Laboratoire National d’Essais (LNE) in France. The differences in the spectra are analyzed.

Metrology for New Generation Nuclear Power Plants–MetroFission

Metrology for New Generation Nuclear Power Plants–MetroFission

Traceability Improvement of High Temperature Thermal Property Measurements of Materials for New Fission Reactors

New metrological facilities for high temperature measurements of thermophysical properties have been recently developed by European National Metrology Institutes (NMIs). This work, performed in the framework of the joint research project “MetroFission”, aims to provide reliable measurements up to 2000 for materials having thermal properties similar to those required for design of new generations of fission reactors. This will enable to improve the traceability to the International System of Units (SI) of measurements performed by nuclear research laboratories. The validation of these reference apparatuses was done at high temperature by measuring the thermal diffusivity and normal spectral emissivity of an isostatic graphite and pure tungsten.

Enhanced infrared emissivity of MAO coatings formed on Ti2AlNb alloy

In order to improve infrared emissivity property, microarc oxidation (MAO) ceramic coatings have been fabricated on Ti2AlNb alloy by adding NH4VO3 and Cr2O3 into a Na2SiO3 electrolyte. Microstructure and chemical compositions of MAO ceramic coatings are investigated by X-ray diffraction and scanning electron microscopy equipped with energy dispersive X-ray spectroscopy. Normal spectral emissivity values of both coated and bared Ti2AlNb samples are measured at 600°C in the infrared wavelength range of 3–20 μm. The infrared emissivity of MAO ceramic coatings has been improved by different additives of NH4VO3 and Cr2O3. Microarc oxidation coating with NH4VO3 has a high emissivity of 0·7 in short wavebands, while Cr2O3 additive increases the emissivity value up to 0·9 in the waveband of 10–20 μm. Furthermore, the S–10Cr–6V ceramic coating exhibits the best infrared emission property due to the synergistic effects of NH4VO3 and Cr2O3.

Thermophysical properties of solid phase rhodium measured by the pulse calorimetry technique over a wide temperature range

AbstractThis paper presents experimental results on four thermophysical properties of pure polycrystalline rhodium samples over a wide temperature range. Specific heat capacity and specific electrical resistivity were measured from 300 to 2 200 K, while hemispherical total and normal spectral emissivities were measured from 1 200 to 2 200 K. All the properties were obtained by means of the electrical pulse calorimetry technique using specimens in the form of a thin rod, of about 2 mm in diameter and 200 mm in length. For necessary corrections, literature data on thermal linear expansion have been used. All the results are compared with available literature data and discussed.

Microstructure and high temperature properties of two-step voltage-controlled MAO ceramic coatings formed on Ti2AlNb alloy

• MAO coatings on Ti 2 AlNb alloy consist of Al 2 TiO 5 , R-TiO 2 , Al 2 O 3 and Nb 2 O 5 . • Two-step voltage technique enhances the densification of MAO coatings. • MAO coating improves the thermal radiation property of Ti 2 AlNb alloy. • MAO coatings protect Ti 2 AlNb substrate from the high temperature oxidation. • Two-step MAO coatings exhibit better high temperature properties. A two-step voltage-controlled microarc oxidation (MAO) method has been used to produce ceramic coatings (NA-2st) on Ti 2 AlNb alloy. For a comparative study, one-step voltage-controlled MAO ceramic coatings (NA-1st) were also formed on Ti 2 AlNb alloy. The NA-2st coating with a relatively compact microstructure is composed of Al 2 TiO 5 , R-TiO 2 , α-Al 2 O 3 and γ-Al 2 O 3 phases. The adhesive strength of MAO coatings was tested by a direct pull-off method. Isothermal oxidation tests were carried out at 800 °C in a muffle furnace in air. Normal spectral emissivity of MAO coatings was measured at 600 °C in the infrared wavelength range of 3–20 μm. High temperature tribological properties of MAO coatings were evaluated by using a ball-on-disc friction and wear tester at 600 °C. Due to its compact microstructure and high content of Al 2 TiO 5 phase, the NA-2st coating exhibits better high temperature properties, such as good oxidation resistance, high infrared emissivity, low friction coefficient and small wear rate.

Melting point determination of uranium nitride and uranium plutonium nitride: A laser heating study

Understanding of the behaviour of nuclear material in extreme conditions is essential for the analyses of the operation limits of nuclear fuels, and prediction of possible nuclear reaction accidents. In this context, the high temperature behaviour of uranium nitride and mixed uranium–plutonium nitrides has been studied in the present work by laser heating under controlled atmosphere coupled with fast multi-wavelength pyrometry. Such an approach has allowed performing a thermal arrest analysis and establishing the solid–liquid phase boundaries in the investigated compositions, whereby non-congruent vaporisation was avoided by setting a suitable nitrogen overpressure. In addition, the normal spectral emissivities of the current samples were determined by radiance spectroscopy. Besides revealing a slightly more metallic optical behaviour in plutonium-containing compositions, this latter characterisation led to the determination of the real melting/solidification temperatures of the investigated nitrides. It is confirmed that UN melts congruently at (3120±30) K in a nitrogen pressure of 0.25MPa (2.5bar). The melting/solidification temperatures decrease in plutonium containing samples, reaching (3045±25) K for x(PuN)=0.2, a composition of interest for potential applications of this material as a nuclear fuel. Besides their fundamental importance, the current results are useful for a deeper understanding of the nitride fuel behaviour under accidental conditions, whereby uncontrolled thermal excursions might occur in the nuclear reactor core.

Preparation and performance evaluation of Er2O3 coating-type selective emitter

An Er2O3 coating-type selective emitter for themophotovoltaic application was prepared by plasma spray technology. The test results show that plasma spray technology could be used to prepare the Er2O3 coating-type selective emitter with good stability at 1400°C. Based on the measurements of the high temperature normal spectral emissivity and the spectral hemispherical emissivity of the samples at room temperature, the influence of the coating thickness was discussed, and the selective emission performance of the sample was evaluated using radiative efficiency as the criterion. The results demonstrate that the emission of substrate could not be neglected unless the coating thickness would be larger than the penetration depth, which is around 100 μm. The selective emission peak of the Er2O3 coating occurs at 1550 nm, matching well with the GaSb cells. However, the radiative efficiency is not larger than that of the SiC emitter, because the non-convertible emission of 1.725–5 μm accounts for a large proportion of the total radiation power, especially at high temperature. Effective suppression of this band emission is essential to the improvement of the radiation efficiency of the emitter.

Infrared optical properties of α-alumina with the approach to melting: γ-like tetrahedral structure and small polaron conduction

The normal spectral emittance of α-Al2O3 single crystal has been measured from room temperature up to the liquid state and from 20 cm−1 up to 10 000 cm−1, in two polarization configurations. The spectra were fitted with a semi-quantum dielectric function model. AlO4 structure units are revealed within the phonon spectral range more than a hundred degrees below the melting point when heating from the solid state. In parallel, the anomalous increase of emittance observed within the transparency spectral range with the approach to melting appears strongly correlated. Implications on the electronic structure are discussed: the existence of small polaron conduction is suggested which has never been mentioned before.

Direct Measurements of Infrared Normal Spectral Emissivity of Solid Materials for High-Temperature Applications

A new facility for the measurement of the normal spectral emissivity of solid materials for high-temperature applications in the thermal steady state was developed at the Bundeswehr University of Munich. The measurements are performed under atmospheric conditions. The facility covers the temperature range between \(500\,^{\circ }\hbox {C}\) and \(1350\,^{\circ }\hbox {C}\) and wavelengths between \(0.6\,\upmu \hbox {m}\) and \(15\,\upmu \hbox {m}\). The principle of operation involves the spectral comparison of a test sample with a reference blackbody and the sample surface temperature determination with a numerical spectral ratio calculation. The optical characteristics of the blackbody and the sample surface temperature determination are discussed in detail. Furthermore, measurement results of the quasi-reference material silicon-carbide under steady-state conditions are presented to validate the measurement method.

Thermophysical properties of solid phase palladium over a wide temperature range

AbstractThis paper presents experimental results of a range of thermophysical properties of pure polycrystalline palladium samples over a wide temperature range. Specific heat capacity was measured from 250 to 1 770 K, specific electrical resistivity from 250 to 1 800 K, hemispherical total emissivity from 1 100 to 1 800 K, normal spectral emissivity from 1 340 to 1 720 K, and thermal diffusivity in the range from 200 to 1 540 K. From the measured data, the thermal conductivity and Lorentz function were computed in the range from 250 to 1 540 K. Specific heat capacity, electrical resistivity, and both emissivities were measured by means of subsecond pulse calorimetry, while the thermal diffusivity was obtained using the laser flash technique. The first method used specimens in the form of a thin rod, of about 2 mm in diameter and 200 mm in length, and the second disk specimens of about 3 mm in thickness and 10 mm in diameter. For necessary corrections, literature data on thermal linear expansion have been used. All the results are compared with available literature data and discussed.

Microstructure, thermal shock resistance and thermal emissivity of plasma sprayed LaMAl11O19 (M = Mg, Fe) coatings for metallic thermal protection systems

LaMAl11O19 (M=Mg, Fe) ceramic coatings were plasma-sprayed on nickel-based superalloy with NiCoCrAlYTa as the bond coat. The microstructure, thermal shock resistance and thermal emissivity of these two ceramic coatings were investigated. LaMAl11O19 coatings exhibit a characteristic of stacked lamellae, and consist mainly of a magnetoplumbite-type hexaaluminate phase and an amorphous phase. During thermal cycling, the amorphous phase disappears and a LaAlO3 phase is formed at temperatures of both 1000 and 1200°C. The thermal cycling numbers of LaMgAl11O19 coating are 102 at 1000°C and 42 at 1200°C; LaFeAl11O19 has a thermal cycling lifetime of 87 at 1000°C and 30 at 1200°C, respectively. Normal spectral emissivity of nickel-based superalloy is about 0.2 over the whole wavelength range of 3–14μm. However, the emissivity of LaFeAl11O19 coating is about 0.7 at short wavelengths and above 0.9 in the wavelength range of 7–14μm.

The ZrC–C eutectic structure and melting behaviour: A high-temperature radiance spectroscopy study

Abstract A fast spectro-pyrometer has been employed for radiance measurements of zirconium carbide samples laser-heated to very high temperature, for compositions 0.7 ≤ C/Zr ≤ 2.61 and in a spectral range 0.550 μm ≤ λ ≤ 0.900 μm. The ZrC–C eutectic temperature has been taken as the radiance reference. The measured normal spectral emissivity (NSE) ɛ λ of solid zirconium carbide is close to 0.6 at 0.650 μm, in agreement with previous literature. Its high-temperature behaviour, value in the liquid, carbon-content and wavelength dependences in the visible-near infrared range have been determined here for the first time. Liquid zirconium carbide seems to interact with electromagnetic radiation in a more metallic way than the solid. A considerable NSE increase has been observed at increasing carbon content, which can be interpreted on the basis of preferential growth along the “c” plane of the carbon lamellae in the eutectic structure.

Prediction of the radiative properties of reconstructed alpha-SiC foams used for concentrated solar applications

ABSTRACTA SiC-based ceramic foam applied in solar thermal processes was characterized in detail in terms of its textural parameters and its radiative properties. Scanning electron microscopy and x-ray µ-tomography were first performed to investigate the 3D texture of the sample at several length scales. Infrared reflectance microscopy was also applied to probe the local optical responses on the struts constituting the foam. Based on the whole set of experimental data, a numerical tool (C++) was implemented to reconstruct virtual SiC foams. A Monte Carlo Ray Tracing code (iMorphRad, C++) was then used to compute the normal spectral emittance for the real SiC foam and for another reconstructed SiC foam with similar textural features. The two numerically determined emittances were then compared with previous infrared spectroscopy experimental measurements. This numerical procedure enables us to propose a methodology for the design of SiC foams with prescribed radiative properties.

Software solution for control and data acquisition in the pulse calorimetry method

This work presents a software solution for adjusting, controlling, displaying, and acquiring parameters and data in the pulse calorimetry experimental technique for specific heat capacity, electrical resistivity, total hemispherical emissivity, and normal spectral emissivity measurements. The software has been developed under the LabVIEW platform, V.7.11, and an example of its application with measurement results is presented in a separate section. The total expanded uncertainty of obtained results for the specific heat capacity and electrical resistivity of palladium was 5% and 1 - 2%, respectively.

Normal spectral emissivity measurement of molten copper using an electromagnetic levitator superimposed with a static magnetic field

The normal spectral emissivity of molten copper was determined in the wavelength range of 780–920 nm and in the temperature range of 1288–1678 K, by directly measuring the radiance emitted by an electromagnetically levitated molten copper droplet under a static magnetic field of 1.5 T. The spectrometer for radiance measurement was calibrated using the relation between the theoretical blackbody radiance from Planck's law and the light intensity of a quasi-blackbody radiation source measured using a spectrometer at a given temperature. As a result, the normal spectral emissivity of molten copper was determined as 0.075 ± 0.011 at a wavelength of 807 nm, and it was found that its temperature dependence is negligible in the entire measurement temperature range tested. In addition, the results of the normal spectral emissivity and its wavelength dependence were discussed, in comparison with those obtained using the Drude free-electron model.