Spectral-Directional Emittance of 99.99% Aluminum, Thermally Oxidized Below Its Melting Point

Spectral-directional emittance measurements for 99.99% aluminum, thermally oxidized in air, were performed using a radiometric technique. The apparatus is comprised of a Fourier transform infrared spectrometer and a blackbody-radiating cavity. The sample holder is held on a slotted arc rack, which allows directional measurements from normal to grazing angles. The aluminum sample was heated for an extended period of time (150 h) at high temperature below its melting point prior to performing measurements. The data presented here cover the spectral range between 3 and 14 μm, directional range from surface normal to 72° polar angle, and temperatures from 673 to 873 K. The complex index of refraction is also reduced from emittance data. Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and Auger depth profiling were used as surface techniques to characterize the thickness and composition of aluminum oxide film that formed on the metallic surface.     

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.     

Spectral and directional emittance of alumina at 823 K

Spectral–directional emittance measurements of aluminum oxide (99.5% pure), in air, were performed at 823 K using an apparatus comprised of a Fourier Transform Infrared (FTIR) spectrometer, a blackbody radiating cavity (hohlraum), and a sample holder which allows directional measurements. The data cover a wide spectral range between 2 and 25 μm, and a directional range from a surface normal to a 72° polar angle. The aluminum oxide sample used in the experiment had a nominal surface roughness of 1 μm determined by a profilometer. Directional emittance shows no departure from dielectric behavior.     

Temperature-Resolved Infrared Spectral Emissivity of SiC and Pt–10Rh for Temperatures up to 900°C

This article reports the first comprehensive results obtained from a fully functional, recently established infrared spectral-emissivity measurement facility at the National Institute of Standards and Technology (NIST). First, sample surface temperatures are obtained with a radiometer using actual emittance values from a newly designed sphere reflectometer and a comparison between the radiometer temperatures and contact thermometry results is presented. Spectral emissivity measurements are made by comparison of the sample spectral radiance to that of a reference blackbody at a similar (but not identical) temperature. Initial materials selected for measurement are potential candidates for use as spectral emissivity standards or are of particular technical interest. Temperature-resolved measurements of the spectral directional emissivity of SiC and Pt–10Rh are performed in the spectral range of 2–20 μm, over a temperature range from 300 to 900°C at normal incidence. Further, a careful study of the uncertainty components of this measurement is presented.     

Normal and Directional Spectral Emittance Measurement of Semi-Transparent Materials Using Two-Substrate Method: Alumina

The normal and directional spectral emittance of alumina is measured using a Fourier transform infrared spectrometer. A new measurement method, called the two-substrate method, is developed to measure infrared optical properties of semi-transparent materials, which comes over the limitations of the substrate heating method. The uncertainty of the emittance is evaluated with the calibration method (black surroundings), phase correction, temperature measurement, background radiation reflection by the sample surface, and the size-of-source effect. The maximum relative combined relative uncertainty (k = 1) is less than 4.3 % at 4 μm, and the minimum value is less than 0.57 % at 10 μm in the case of an alumina sample at 300 °C. The directional spectral emissivity of alumina is successfully measured in semi-transparent and opaque regions, showing a typical behavior of dielectric materials.     

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.     

Spectral-directional emittance of thermally oxidized 316 stainless steel

The spectral-directional emittance of thermally oxidized stainless steel is measured for angles from normal to grazing, wavelengths between 2 and 10m, and temperatures between 773 and 973 K. The oxide is grown by holding the steel substrate at a high temperature over a long period while exposed to normal atmospheric conditions, until the measured emissive power of the surface achieves an asymptotic level. It is found that the emittance decreases with angle away from the surface normal at the lower end of the measured spectral range and increases with angle at the higher end. The emittance decreases with wavelength, although there is evidence of a peak near 2 pill. The variation with temperature within the measured range is insignificant. Overall higher values for the oxidized steel are measured than those reported in previous work.     

Measurement of Infrared Spectral Directional Hemispherical Reflectance and Emissivity at BNM-LNE

An infrared reflectometer has been designed by BNM-LNE (Bureau National de Métrologie–Laboratoire National d’Essais) to measure the spectral directional hemispherical reflectance of solid materials at ambient temperature. For opaque materials, the spectral directional emissivity can be calculated from the measured reflectance. The reflectance can be measured from 0.8 to 14 μm in five directions with an angle of 12°, 24°, 36°, 48°, and 60° with respect to the normal to the surface of the sample. The optical arrangement to collect the reflected flux is based on the Coblentz arrangement (hemispherical mirror). In fact, four mirrors cut in an hemisphere are used to collect the flux reflected by the sample. This optical arrangement was chosen to limit the angle of incidence of rays on the detector (38° instead of 90° for the Coblentz arrangement). The final expanded uncertainty (level of confidence 95%) of the reflectance is estimated to be about ±0.03 for wavelengths between 0.8 and 10 μm and ±0.04 for wavelengths over 10 μm. The values of the spectral reflectance measured on a black paint and on a white ceramic tile are compared to those measured by the two laboratories PTB (Physikalisch Technische Bundesanstalt) and NIST (National Institute of Standards and Technology). The results validate the measurements performed at BNM-LNE. Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22–27, 2003, Boulder, Colorado, U.S.A.     

Spectral Emissivity of Surface Blackbody Calibrators

The normal spectral emissivity of commercial infrared calibrators is compared with measurements of anodized aluminum samples and grooved aluminum surfaces coated with Pyromark. Measurements performed by FTIR spectroscopy in the wavelength interval from 2 to 20 μm and at temperatures between 5 and 550°C are presented with absolute uncertainties from 0.25% to 1% in spectral regions with sufficient signal and no significant atmospheric gas absorption. A large variation in emissivity with wavelength is observed for some surfaces, i.e., from 1% to 3% to more than 10%. The variation in emissivity using similar materials can be reduced to 0.5–1% by optimizing the coating process and the surface geometry. Results are discussed and an equation for calculation of the equivalent blackbody surface temperature from FTIR spectra is presented, including reflected ambient radiation. It is in most cases necessary to correct temperature calibration results for calibrators calibrated at 8–14 μm to obtain absolute accuracies of 0.1–1°C in other spectral regions depending on the temperature. Uncertainties are discussed and equations are given for the correction of measured radiation temperatures.     

Measurement and Modeling of the Emittance of Silicon Wafers with Anisotropic Roughness

The unpolished surface of crystalline silicon wafers often exhibits non-Gaussian and anisotropic roughness characteristics, as evidenced by the side peaks in the slope distribution. This work investigates the effect of anisotropy on the emittance. The directional-hemispherical reflectance of slightly and strongly anisotropic silicon wafers was measured at room temperature using a center-mount integrating sphere. A monochromator with a lamp was used for near-normal incidence in the wavelength region from 400–1000 nm, and a continuous-wave diode laser at the wavelength of 635 nm was used for measurements at zenith angles up to 60°. The directional emittance was deduced from the measured reflectance based on Kirchhoff’s law. The geometric-optics-based Monte Carlo model that incorporates the measured surface topography is in good agreement with the experiment. Both the experimental and modeling results suggest that anisotropic roughness increases multiple scattering, thereby enhancing the emittance. On the other hand, if the wafer with strongly anisotropic roughness were modeled as a Gaussian surface with the same roughness parameters, the predicted emittance near the normal direction would be lower by approximately 0.05, or up to 10% at a wavelength of 400 nm. Comparisons also suggest that the Gaussian surface assumption is questionable in calculating the emittance at large emission angles with s polarization, even for the slightly anisotropic wafer. This work demonstrates that anisotropy plays a significant role in the emittance enhancement of rough surfaces. Hence, it is imperative to obtain precise surface microstructure information in order to accurately predict the emittance, a critical parameter for non-contact temperature measurements and radiative transfer analysis.     

Preparation and characterization of NIC thermistors based on Fe2+δMn1−x−δNixO4

Single-phase nickel manganese ferrites, Ni_xMn_1−xδFe_2+δO₄, have been prepared by mild heating of solid solutions of nickel-manganese-iron formates obtained by coprecipitation. Dilatometric and X-ray diffraction studies were conducted at different temperatures, showing the different stages of the sintering process of highly densified nickel manganese ferrite ceramics (density, 94%–96%). Granulometric and SEM studies showed that the oxide particles formed agglomerates of 4 μm, with a narrow size distribution. XPS studies showed that Fe²⁺ was oxidized to Fe³⁺ on the ceramic surface. Finally, electrical measurements showed that Fe_2.16Mn_0.074Ni_0.10O₄ presented the minimum resistivity (1340 Ωcm). The sensitivity indices were around 4000 K.     

Radiation Thermometry and Emissivity Measurements Under Vacuum at the PTB

A new experimental facility was realized at the PTB for reduced-background radiation thermometry under vacuum. This facility serves three purposes: (i) providing traceable calibration of space-based infrared remote-sensing experiments in terms of radiation temperature from  −173 °C to 430 °C and spectral radiance; (ii) meeting the demand of industry to perform radiation thermometric measurements under vacuum conditions; and (iii) performing spectral emissivity measurements in the range from 0 °C to 430 °C without atmospheric interferences. The general concept of the reduced background calibration facility is to connect a source chamber with a detector chamber via a liquid nitrogen-cooled beamline. Translation and alignment units in the source and detector chambers enable the facility to compare and calibrate different sources and detectors under vacuum. In addition to the source chamber, a liquid nitrogen-cooled reference blackbody and an indium fixed-point blackbody radiator are connected to the cooled beamline on the radiation side. The radiation from the various sources is measured with a vacuum infrared standard radiation thermometer (VIRST) and is also imaged on a vacuum Fourier-transform infrared spectrometer (FTIR) to allow for spectrally resolved measurements of blackbodies and emissivity samples. Determination of the directional spectral emissivity will be performed in the temperature range from 0 °C to 430 °C for angles from 0° to ±70° with respect to normal incidence in the wavelength range from 1 μm to 1,000 μm. References to commercial products are provided for identification purposes only and constitute neither endorsement nor representation that the item identified is the best available for the stated purpose.     

Gas Pressure Dependence of the Heat Transport in Porous Solids with Pores Smaller than 10 μm

To elucidate the gaseous heat transfer in open porous materials with pore sizes below 10 μm, an experimental setup for hot-wire measurements at high gas pressures was designed and tested. The samples investigated were organic, resorcinol–formaldehyde-based aerogels with average pore sizes of about 600 nm and 7μm. The range in gas pressure covered was 10 Pa to 10 MPa. To avoid effects due to mass transport along the inner surface of the porous backbone of the samples, He and Ar, i.e., gases with very low interaction with the sample surface at ambient temperature, were chosen. The study reveals a significant contribution of coupling effects to the thermal transport in nanoporous media. A model has been developed that qualitatively describes the observed gas pressure dependence of the heat transport.     

Visible photoluminescence of zinc oxide films electrochemically deposited on silicon substrates

Continuous crystalline films of zinc oxide (ZnO) with thicknesses of 6–10 μm were obtained by electrochemical deposition from aqueous zinc nitrate solutions on silicon substrates with a buffer nickel layer. X-ray diffraction measurements showed that the polycrystalline films possess a hexagonal crystal lattice with predominant (0002) orientation. The obtained ZnO films exhibit strong photoluminescence in the visible spectral range at room temperature.     

The ductile to brittle transition of ultrafine-grained Armco iron: an experimental study

Fracture toughness measurements on bcc iron (Armco-iron), which is subjected to severe plastic deformation (SPD), were performed. Through high pressure torsion, an ultrafine grain structure was obtained and with subsequent heat treatments the grain size varied between 300 nm and 5 μm. The combination of SPD and individual heat treatments allows for a systematic study of the ductile to brittle transition (DBT) in the fracture behaviour as a function of grain size. Additionally, the influence of different crack plane orientations was taken into account. The results show that the DBT moves for smaller grain sizes (<1 μm) to higher transition temperatures. Furthermore, large differences in the absolute toughness values for a given temperature for the different crack plane orientations and grain sizes were determined. The findings can be related to a change in the crack path from transcrystalline fracture for grain sizes larger than 1 μm to intercrystalline-dominated fracture for grain sizes smaller than 1 μm.     

An investigation of oxidation effects on hysteresis heating of nickel particles

The oxidation kinetics of nickel particles with approximate diameters of 79 nm, 0.7 micron, and 3 micron, at temperatures between 250°C and 350°C in air were investigated. Thermogravimetric measurements indicated a diffusion-controlled mechanism for the oxidation of spherical metal particles. Deviation of the oxidation kinetic rate from the diffusion-limited model was found in the case of Ni 3 micron and Ni 79 nm. The oxidation rate constant is governed by an Arrhenius equation as expected. Apparent activation energies are approximately 1.55 eV, 1.32 eV and 1.12 eV for Ni 79 nm, Ni 0.7 m and Ni 3 m, respectively. The exponential factor is found to be a function of particle size. Oxidation maps were constructed to relate the degree of oxidation to time and temperature. The oxide formed on the surface of the particles significantly modified the magnetic properties of the nickel particles by changing both the magnetization and the coercivity. The measured properties of oxidized particles were used to construct magnetic property maps to help determine appropriate processing conditions and predict oxidation effects on hysteresis heating performance.     

Mixed manganese spinel oxides: optical properties in the infrared range

Spinel oxides in manganite family are studied in terms of optical properties in the infrared range (3–12 μm). The reflectivity is measured on sintered pellets. The complex refractive index is estimated by fitting hemispherical directional reflectance in both polarizations, perpendicular and parallel. The influence of different metallic cations (Ni, Co, Fe, Cu) is compared. In particular, in the case of manganese nickel copper oxides, the impact of variations in copper and nickel contents is evaluated. Cationic distribution is determined and correlated to the optical characteristics. These materials, usually used for NTC thermistor applications, are investigated for IR charges in coating.     

Ultrasonic Nondestructive Evaluation of Cylindrical Samples with Surface Acoustic Waves

The paper reports experimental methodology and results of nondestructive evaluation and flaw imaging in cylindrical samples using surface acoustic waves (SAW) generated with conventional longitudinal wave transducers attached to the sample surface. A very thin layer of couplant (or even dry coupling) was used to provide efficient SAW generation in the direction normal to a cylinder element in the frequency range 5—15 MHz. A single B-scan mode was sufficient to inspect a total surface of cylindrical shafts of ceramic and metal engine valves. A delay of the processing time gate allowed us to analyze any of the successive SAW revolutions implementing a specific ``transmission B-scan' with a single probe. Amplitude and phase contrast of the B-scans obtained demonstrate the system capability to detect valve radius deviations of 1 μm and cracked flaws with sizes down to 30 μm.     

Synthesis of isotopically-labeled graphite films by cold-wall chemical vapor deposition and electronic properties of graphene obtained from such films

We report the synthesis of isotopically-labeled graphite films on nickel substrates by using cold-wall chemical vapor deposition (CVD). During the synthesis, carbon from ¹²C- and ¹³C-methane was deposited on, and dissolved in, a nickel foil at high temperature, and a uniform graphite film was segregated from the nickel surface by cooling the sample to room temperature. Scanning and transmission electron microscopy, micro-Raman spectroscopy, and X-ray diffraction prove the presence of a graphite film. Monolayer graphene films obtained from such isotopically-labeled graphite films by mechanical methods have electron mobility values greater than 5000 cm²·V⁻¹·s⁻¹ at low temperatures. Furthermore, such films exhibit the half-integer quantum Hall effect over a wide temperature range from 2 K to 200 K, implying that the graphite grown by this cold-wall CVD approach has a quality as high as highly oriented pyrolytic graphite (HOPG). The results from transport measurements indicate that ¹³C-labeling does not significantly affect the electrical transport properties of graphene.     

Spectral Emissivities and Emissivity X-Points of Pure Molybdenum and Tungsten

Prediction methods for thermophysical properties of metals and alloys such as emissivity are of great interest not only for science but also for the metal working industry as time-consuming and often expensive measurements may not be required. As recent results have shown, an assumed Hagen–Rubens relation for the prediction of emissivity based on electrical resistivity results was not found in the visible spectra. Within this work normal spectral emissivity results obtained with two complete different techniques are presented. On one hand, a multi-wavelength-pyrometry (MWLP) approach has been used to obtain emissivity as a function of temperature at 684.5, 902, and 1570 nm, and on the other hand, a radiance-comparison method was used to obtain emissivity isotherms as a function of wavelength for a range starting from 1 to 24 μm. From results of the radiance-comparison measurements an intersection of the isotherms, often referred to as the emissivity x-point, was found for both investigated materials, tungsten and molybdenum. According to these results, the x-point wavelengths are given by λ _x = 1.41 μm for tungsten and λ _x = 1.55 μm for molybdenum. Based on these x-points and the MWLP measurements, a new prediction method for the liquid-phase behavior of emissivity is developed and discussed. Paper presented at the Seventh International Workshop on Subsecond Thermophysics, October 6–8, 2004, Orléans, France.