Infrared Emission Measurements Research Articles

Study on the Thermal Control Performance of Mg-Li Alloy Micro-Arc Oxidation Coating in High-Temperature Environments

This paper reports on the successful preparation of a low absorption–emission thermal control coating on the surface of LAZ933 magnesium–lithium alloy using the micro-arc oxidation method. This study analyzed the microstructure, phase composition, and thermal control properties of the coating using Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), UV–visible near-infrared spectroscopy (UV-VIS-NIR) and infrared emissivity measurements. The results indicate that the hemispherical emissivity of the coating remains unaffected with an increase in temperature and holding time, while the solar absorption ratio gradually increases. The thermal control performance of the coating after a high-temperature experiment was found to be related to the diffusion of the Li metal element in the magnesium lithium alloy matrix, as determined by X-ray photoelectron spectroscopy (XPS), flame graphite furnace atomic absorption spectrometry (GFAAS) and Glow Discharge Optical Emission Spectroscopy (GD-OES). As the holding time is extended, the coating structure gradually loosens under thermal stress. The Li metal element in the substrate diffuses outward and reacts with O2, H2O and CO2 in the air, forming LiO2, LiOH, Li2CO3 and other products. This reaction affects the coating’s solar absorption ratio in the end.

Infrared emissivity measurement methods considering target reflective characteristics

Emissivity measurements are of great significance for infrared thermal radiation and infrared remote sensing. However, traditional methods often face challenges such as difficulties in non-contact measurement, small measurement areas, and unsuitability for non-Lambertian surfaces. To address these issues, we propose the reflective distribution model integral method (RDMIM). This method is based on a reflective distribution model using the scattering-reflective deviation angle (SRDA). By regressing and integrating the object’s reflective distribution model, it achieves accurate non-contact measurement of non-Lambertian surfaces under normal temperature conditions. Additionally, the measurement scheme has been further optimized to improve measurement efficiency while ensuring the accuracy of the model regression. Finally, the proposed RDMIM method has been validated through experimental measurements. The results have shown that this method has advantages in non-contact and large-area measurements. Moreover, the systematic error is smaller when the reflective characteristics of the reference body and the target are relatively similar.

Normal spectral emissivity measurement of thermal management materials for electronic components in the 2–14 μm range

Reducing the operating temperature of electronic components is an effective method for enhancing their performance. Selecting suitable thermal management materials is crucial for optimizing cooling efficiency. Normal spectral emissivity, a dimensionless physical quantity, is key in assessing a material’s capability for radiative cooling. This paper outlines the construction of a reflective infrared emissivity measurement apparatus using the IS-50 Fourier Transform Infrared Spectrometer. A gold-coated diffuse integrating sphere was strategically placed in the spectrometer’s sample chamber. By ingeniously leveraging the spectrometer’s original optical path, a dual-sided gold-coated mirror was employed to capture both incident and reflected light, enabling accurate measurements of the normal spectral emissivity of materials used for cooling electronic components. The measurement results for typical materials were consistent with those reported in the literature, satisfyingly so. The uncertainty of the measurement setup was thoroughly evaluated, achieving a combined uncertainty of better than 1 %. This experimental study measured the normal spectral emissivity of various thermal management materials and analyzed the influence of temperature on normal spectral emissivity. These results provide crucial data support for thermal design, simulation analysis, and temperature monitoring in the development of thermal structures for electronic components.

Fabrication of thermal insulation sodium alginate/SiO2 composite aerogel with superior radiative cooling function for firefighting clothing

Purpose This study aims to evaluate the thermal performance of sodium alginate (SA) aerogel attached to nano SiO2 and its radiative cooling effect on firefighting clothing without environmental pollution. Design/methodology/approach SA/SiO2 aerogel with refractory heat insulation and enhanced radiative cooling performance was fabricated by freeze-drying method, which can be used in firefighting clothing. The microstructure, chemical composition, thermal stability, and thermal emissivity were analyzed using Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analyzer and infrared emissivity measurement instrument. The radiative cooling effect of aerogel was studied using thermal infrared imager and thermocouple. Findings When the addition of SiO2 is 25% of SA, the prepared aerogel has excellent heat insulation and a high radiative cooling effect. Under a clear sky, the temperature of SA/SiO2 aerogel is 9.4°C lower than that of pure SA aerogel and 22.1°C lower than that of the simulated environment. In addition, aerogel has more exceptional heat insulation effect than other common fabrics in the heat insulation performance test. Research limitations/implications SA/SiO2 aerogel has passive radiative cooling function, which can efficaciously economize global energy, and it is paramount to environment-friendly cooling. Practical implications This method could pave the way for high-performance cooling materials designed for firefighting clothing to keep maintain the wearing comfort of firefighters. Originality/value SA/SiO2 aerogel used in firefighting clothing can release heat to the low-temperature outer space in the form of thermal radiation to achieve its own cooling purpose, without additional energy supply. Graphical abstract

Infrared emissivity measurement based on polarized reflection characteristics of non-transmissive insulators

Infrared emissivity measurement based on polarized reflection characteristics of non-transmissive insulators

A Proposition to Correct Infrared Emissivity Measurements for Curved Surface Targets Based on the Irradiation Reflection Method

In this paper, a measurement correction method is proposed to correct the error of the irradiation reflection method when measuring the emissivity of curved surface targets. First, by introducing an angle parameter related to the target surface shape, the formulas of emissivity measurements for curved surface targets under various types of radiation sources were obtained. Then, the variation law of these emissivity measurement formulas was analyzed, the concept of the measurement correction factor was proposed, and then a unified correction measurement formula was obtained. Finally, a scene of measuring the emissivity of a curved surface target based on the irradiation reflection method was simulated. Different target emissivities and different distances between the radiation source and target were set, and the errors between the measured and corrected emissivities were compared. The results revealed that the proposed method could effectively correct the error caused by the curvature of the target surface when measuring its emissivity by the irradiation reflection method. This is of great significance to expanding the application scope of the irradiation reflection method and improving the measurement accuracy.

Development of a novel probe for measuring emissivity and temperature during Raman spectroscopy

Abstract In this work, an innovative tool to perform real-time measurements of emissivity and temperature of a given material surface under CW laser irradiation was developed. In the radiative energy balance, the emissivity represents the complementary component of the reflectance, thus, its measurement can be exploited to calculate the temperature at the target surface from infrared emission measurements provided by a suitable sensor. A miniaturized photothermal sensing line was designed as an accessory of Raman probes for driving thermal control loops in order to prevent overheating during the spectroscopic acquisition. To demonstrate its effectiveness and reliability, it was integrated with in a home-made Raman instrument (exc. 1064 nm) and associated software to achieve an automated online thermal control. Temperature rise during Raman spectroscopy can induce chemical alterations of the material under analysis and seriously affect its original spectral features. In several applications, such photothermal side effects can represent a serious problem to be carefully controlled in order to safeguard the integrity of the material and its spectral fingerprint. A thorough experimentation of the novel tool was carried out on photothermally sensitive materials such as red lead and massicot powders, traditionally used as pigments since ancient times. Finally, the compactness of the components and the fast response time made this system particularly suitable for nondestructive in-situ investigations.

An Experimental Study of Thermochemical Nonequilibrium

An experimental study of flows subjected to expanding conditions relevant to Mars entry is presented. A condition with a nominal velocity of was generated in the X2 expansion tunnel. Midwavelength infrared emission measurements of the 4.3 and bands were made over both a two-dimensional wedge model and for the freestream. Consistent results in the characterization of the freestream were obtained from pressure and spectroscopic measurements. The rotational and vibrational temperatures estimated in the wedge flow using the band were consistent with those estimated from the band. The difference between the translational–rotational temperature and the vibrational temperature was shown to be small in the freestream and expanding flow over the wedge model: less than 10%. Using vibrational relaxation rates tuned for postshock conditions, computational fluid dynamics simulations significantly overestimated the thermal nonequilibrium in the expanding flow, but not in the postshock (compressive) flow. This observation is consistent with past results for and CO, as well as at lower temperatures.

Spectroscopy, gas kinetics, and opacity of thermospheric nitric oxide and implications for analysis of SABER infrared emission measurements at 5.3 µm

The spectroscopy of the υ = 1 → υ = 0 fundamental vibration-rotation band of nitric oxide (NO) in Earth's atmosphere is examined in depth in order to further assess the long-running dataset of infrared radiative cooling rates in the thermosphere from the SABER instrument on the NASA TIMED satellite. The fundamental band at 5.3 µm is shown to be almost solely responsible for the cooling by NO. The distribution of line strength in this band and the concentration of NO in the atmosphere are such that NO is remarkably transparent in Earth's atmosphere. Every fundamental band photon emitted in the nadir direction by NO in the thermosphere has a nearly 100% chance of hitting the Earth's surface before being absorbed by another NO molecule. The mean free paths of these photons exceed 5000 km. Vertical optical depths of the strongest NO absorption lines in 2 km thick layers in the thermosphere are less than 10−4 even during geomagnetically disturbed conditions. Consequently, nearly all of the radiation emitted by thermospheric NO escapes to space or to the lower atmosphere. Radiative excitation of thermospheric NO by upwelling infrared radiation (“earthshine”) from the troposphere is accurately assessed using measurements of infrared spectra made by the IASI instruments on the METOP satellites. Earthshine and solar excitation of NO are shown to compete with collisional excitation of NO by atomic oxygen below 110 km in polar regions and below 115 km in tropical regions. Therefore, NO 5.3 µm energy loss rates currently derived below ~ 115 km from measurements made by the SABER instrument on the NASA TIMED satellite are not representative of radiative cooling. Consequently, the current values of SABER-derived daily global power radiated from the thermosphere by NO are 5% to 15% too large. Approaches to further improve the SABER radiative cooling dataset are presented.

Investigation of infrared spectral emissivity of low emittance functional coating artefacts

Accurate infrared spectral emissivity measurements play a vital role in many thermal and optical applications of high value industries. In this paper, we report the experimental investigation of the infrared spectral emissivity of low emittance functional coating artefacts. The functional coating uses 35% aluminum particles as filler to reduce the surface emissivity. Fourier transform infrared spectrometer based infrared emissivity measurement systems, developed by NIM, were used in this investigation. The normal spectral emissivity of the coating was investigated both at NIM and BIAM in the spectral infrared range 3–14 μm, and the temperature range 300–600 °C. The artefacts’ stability and the infrared emittance scale comparison between BIAM and NIM are reported in this paper. An indirect comparison between NIM and CCT was also carried out using the CVD-SiC sample that was used to validate the uncertainty claimed by NIM. The infrared emittance scales’ comparison results demonstrate the scales are clearly in agreement well within the overall comparison uncertainty.

Isothermal oxidation kinetics of nitrided Ti-6Al-4V studied by infrared emissivity

The oxidation kinetics of Ti-6Al-4V samples nitrided in forming gas (N2+5%H2) between 520 and 805 °C is investigated using infrared emissivity measurements. Several kinetic exponents have been observed depending on temperature and time. The activation energy corresponding to the main parabolic rutile growth stage is 223 ± 10 kJ/mol. This value is significantly higher than that corresponding to TiN oxidation, which suggests that it is not the rate-limiting step. The protective role of the nitridation is attributed to the internal Ti2N layer. The microstructural characterization reveals a reduction in the oxygen-diffusion depth compared to non-nitrided Ti-6Al-4V, and a multi-layered Al2O3-TiO2 oxide.

Machine learning applied to retrieval of temperature and concentration distributions from infrared emission measurements

Inversion of temperature and species concentration distributions from radiometric measurements involves solving nonlinear, ill-posed and high-dimensional problems. Machine Learning approaches allow solving such highly nonlinear problems, offering an alternative way to deal with complex and dynamic systems with good flexibility. In this study, we present a machine learning approach for retrieving temperatures and species concentrations from spectral infrared emission measurements in combustion systems. The training spectra for the machine learning model were synthesized through calculations from HITEMP 2010 for gas mixtures of CO2, H2O, and CO. The method was tested for different line-of-sight temperature and concentration distributions, different gas path lengths and different spectral intervals. Experimental validation was carried out by measuring spectral emission from a Hencken flat flame burner with a Fourier-transform infrared spectrometer with different spectral resolutions. The temperature fields above the burner for combustion with equivalence ratios of ϕ = 1, ϕ = 0.8, and ϕ = 1.4 were retrieved and were in excellent agreement with temperatures deduced from Rayleigh scattering thermometry.

Preparation and performance of low-emissivity Al-doped ZnO films for energy-saving glass

Low-emissivity Al-doped ZnO films were deposited on the surface of glass by direct current magnetron sputtering method. The infrared emissivity of sample was focused on. The structural characteristics were investigated by the X-ray diffractometry and scanning electron microscopy, while the properties were measured by a four-point probe, an infrared emissivity measurement instrument and an UV–Vis spectrophotometer. The results show that the infrared emissivity of the AZO film is affected by substrate temperature, working pressure and sputtering power. The film deposited at 200 °C, 1.0 Pa and 80 W possesses the lowest emissivity, 0.41. There is a very strong correlation between emissivity and resistivity. When the resistivity is low, the infrared emissivity increases with the increase of resistivity, following the Hagen-Rubens relationship. When the resistivity is high, the correlation between them decreases.

Effect of boron on enhancing infrared emissivity of Ni-Cr system coating

High infrared emissivity coating possesses great value in practical application, whether in the military or civilian areas. In this study, B-NiCr precursor powder containing NiO, Cr2O3 and ZrB2 was calcined at 1300 °C and then used to prepare a high infrared emissivity B-NiCr coating via atmospheric plasma spraying. A large number of test methods were employed to analyze the powder and coating, including TG-DSC, XRD, FE-SEM, infrared spectrometer and so on. The result of infrared emissivity measurement indicates that the coating possesses maximum infrared emissivity of 0.908 at 1000 °C while the infrared emissivity is 0.901 after thermal shock test. Comparing with NiCr coating, Ni2CrO2(BO3) formed during calcination may be the main factor to improve the infrared emissivity of B-NiCr coating. The B-NiCr coating possesses good thermal shock resistance and can withstand 50 times thermal shock at least without falling off, from 800 °C to room temperature.

In Situ Optical Investigations of Contaminants in Operating Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) can generate electricity efficiently and with broad fuel flexibility, but practical applications require them to be more durable and resistant to degradation when subjected to impurities. In order to better understand poisoning mechanisms and guide strategies for developing more durable materials and devices, we have used operando optical methods combined with electrochemical measurements to investigate the effects of sulfur (170 ppm H2S) on SOFC Ni/YSZ anodes operating on methane at high temperature (700 °C). There is clear evidence of reduced anode catalytic activity based on near infrared thermal imaging which shows not only that the cooling associated with endothermic methane cracking is reduced but also that an elevated temperature is observed that is temporally correlated with drastic electrochemical changes indicative of substantial anode degradation. Mid infrared emission measurements indicate less fuel consumption and fewer oxidation products in agreement with the trend of suppressed anode activity. The effects are compared to similar studies of chlorine contamination where reversibility and degradation mechanism have been mapped out more extensively to show they depend sensitively on temperature and type of fuel; the effects are more pronounced and seem to be promoted in electrochemically active regions for sulfur.

Fabrication of copper and titanium coated textiles for sunlight management

Copper (Cu) and titanium (Ti) films with a thickness of 200 nm are deposited onto cotton and polyester fabrics respectively by magnetron sputtering technology and systematically investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), infrared emissivity measurements and Fourier transform infrared (FTIR) spectroscopy. The physical properties of the coated fabrics that are evaluated include the infrared emissivity, reflection rate, contact angle (CA) and ultraviolet protection factor (UPF) value. It is found that the Cu coated fabric samples have an infrared reflection rate of 20–30%, infrared emissivity of about 0.7 and UPF value of 273. The Cu coated fabric samples therefore provide excellent UV radiation protection and good infrared shielding, which make them promising materials for sunlight management textiles.

Application of indium tin oxide (ITO) thin film as a low emissivity film on Ni-based alloy at high temperature

Indium tin oxide (ITO) films as the low emissivity coatings of Ni-based alloy at high temperature were studies. ITO films were deposited on the polished surface of alloy K424 by direct current magnetron sputtering. These ITO-coated samples were heat-treated in air at 600–900°C for 150h to explore the effect of high temperature environment on the emissivity. The samples were analyzed by X-ray diffraction (XRD), SEM and EDS. The results show that the surface of sample is integrity after heat processing at 700°C and below it. A small amount of fine crack is observed on the surface of sample heated at 800°C and Ti oxide appears. There are lots of fine cracks on the sample annealed at 900°C and a large number of various oxides are detected. The average infrared emissivities at 3–5μm and 8–14μm wavebands were tested by an infrared emissivity measurement instrument. The results show the emissivity of the sample after annealed at 600 and 700°C is still kept at a low value as the sample before annealed. The ITO film can be used as a low emissivity coating of super alloy K424 up to 700°C.

Effects of varying environmental conditions on emissivity spectra of bulk lunar soils: Application to Diviner thermal infrared observations of the Moon

Currently, few thermal infrared measurements exist of fine particulate (<63 µm) analogue samples (e.g. minerals, mineral mixtures, rocks, meteorites, and lunar soils) measured under simulated lunar conditions. Such measurements are fundamental for interpreting thermal infrared (TIR) observations by the Diviner Lunar Radiometer Experiment (Diviner) onboard NASA's Lunar Reconnaissance Orbiter as well as future TIR observations of the Moon and other airless bodies. In this work, we present thermal infrared emissivity measurements of a suite of well-characterized Apollo lunar soils and a fine particulate (<25 µm) San Carlos olivine sample as we systematically vary parameters that control the near-surface environment in our vacuum chamber (atmospheric pressure, incident solar-like radiation, and sample cup temperature). The atmospheric pressure is varied between ambient (1000mbar) and vacuum (<10−3mbar) pressures, the incident solar-like radiation is varied between 52 and 146mW/cm2, and the sample cup temperature is varied between 325 and 405K. Spectral changes are characterized as each parameter is varied, which highlight the sensitivity of thermal infrared emissivity spectra to the atmospheric pressure and the incident solar-like radiation. Finally spectral measurements of Apollo 15 and 16 bulk lunar soils are compared with Diviner thermal infrared observations of the Apollo 15 and 16 sampling sites. This comparison allows us to constrain the temperature and pressure conditions that best simulate the near-surface environment of the Moon for future laboratory measurements and to better interpret lunar surface compositions as observed by Diviner.

Flat mid-infrared composite plasmonic materials using lateral doping-patterned semiconductors

We demonstrate lateral control of carrier concentration in doped Si for mid-infrared plasmonic applications. Using commercially available spin-dopants, we show that doped silicon can act as a plasmonic material at mid-infrared wavelengths, and that control of the doping pattern allows for the development of flat, single-material plasmonic composites. Our materials are characterized by infrared spectroscopy and microscopy, surface profilometry and infrared emissivity measurements. We demonstrate the ability to fabricate subwavelength doped features and show distinct diffraction from one-dimensional arrays of ‘metal’ lines patterned in our material system.

Infrared Emissivity Measurements of Building and Civil Engineering Materials: A New Device for Measuring Emissivity

The knowledge of the infrared emissivity of materials used in buildings and civil engineering structures is useful for two specific approaches. First, quantitative diagnosis of buildings or civil engineering infrastructures by infrared thermography requires emissivity values in the spectral bandwidth of the camera used for measurements, in order to obtain accurate surface temperatures; for instance, emissivity in the band III domain is required when using cameras with uncooled detectors (such as micro-bolometer arrays). Second, setting up accurate thermal balances by numerical modeling requires the total emissivity value for a large wavelength domain; this is, for instance, the case for computing the road surface temperature to predict ice occurrence. Furthermore, periodical surveys of emissivity variations due to aging or soiling of surfaces could be useful in many situations such as thermal mapping of roads or building insulation diagnosis. The use of portable emissivity measurement devices is required for that purpose. A device using an indirect measurement method was previously developed in our lab; the method uses measurement of the reflectivity from a modulated IR source and requires calibration with a highly reflective surface. However, that device uses a low-frequency, thermal modulation well adapted to laboratory measurements but unfit for fast and in situ measurements. Therefore, a new, portable system which retains the principle of an indirect measurement but uses a faster-frequency, mechanical modulation more appropriate to outdoor measurements was developed. Both devices allow measurements in the broad \((1\,\upmu \)m to \(40\,\upmu \)m) and narrow \((8\,\upmu \)m to \(14\,\upmu \)m) bands. Experiments were performed on a large number of materials commonly used in buildings and civil engineering structures. The final objective of this work is to build a database of emissivity of these materials. A comparison of laboratory and on-site measurements of emissivity values obtained in both spectral bands will be presented along with an estimation and an analysis of measurement uncertainties.