红外陶瓷的研究进展及应用

红外陶瓷由于其良好的红外性能而受到越来越多的关注和研究。本文总结了近年来影响红外发射率的因素、改善和提高红外陶瓷的红外发射率的方法以及红外陶瓷材料的应用。     

Methodology for spectral emissivity measurement by means of single color pyrometer

The application of non-intrusive optical devices, such as infrared pyrometers able to measure the temperature of surfaces, makes possible the evaluation of emissivity curve of the tested materials at different temperature values. In this paper the authors propose a methodology for the spectral emissivity measurement by means of a single color pyrometer providing a semi-empirical formula, obtained experimentally at CIRA’s laboratory. The semi-empirical formula allows to know the actual emissivity value of the sample’s surface for whatever emissivity value set up on the pyrometer. The agreement between the experimental emissivity and the emissivity predicted by semi-empirical formula was verified.     

Studies on the effect of temperature and time on the SS 304 surface for the properties degradation of the solar collector

The properties of emissivity (?) and absorptivity (α) of the surface of the material is an essential output for the solar collector. This paper highlights the work based on the RSM design expert, to study the effect of parameters’ temperature and time when the surface is exposed to sunlight and absorbing the properties of emissivity and absorptivity of the material SS 304. The temperature range of the SS 304 varied from 20°C to 356°C for various time intervals from 90 to 1100?h. From this experimental work, it is clearly seen that the emissivity rate increased when the surface is focused onto sunlight beyond the saturated level. The absorptivity of the surface of SS 304 increases till the optimum level and reaches the saturated level. As a result, after the optimum level, emissivity rate of the surface increases, and absorptivity of the surface decreases when it is focused onto sunlight.     

Temperature behaviour of the substrate surface during growth of nanocrystalline silicon carbide films by deposition of 120 eV carbon and silicon ions

Changes in the temperature of nanocrystalline SiC film surface were measured during film growth by direct deposition of carbon and silicon ions onto substrates at ∼800 °С. It has been found that the initial stage of the film growth is characterized by uncontrolled variations of the surface temperature, which are observed for constant values of the deposition parameters. The energy components of the temperature balance on the film surface during its growth under conditions of direct ion deposition are analyzed. It is shown that magnitudes of temperature variations depend on the energy and current density of the deposited ions and on the ratio of the emissivity coefficients of the substrate material and silicon carbide. If this ratio is 1:6, the temperature rise at the initial growth stage reaches 160 °С when using 120 eV ion energy. For ion deposition onto silicon carbide substrates these uncontrolled temperature deviations at the initial stage of film growth were not observed.     

Effect of different parameters on the in situ thermal conductance evaluation

In the last years many studies have been carried out on the possible improvements of the in situ thermal conductance measurement; as well known, this has to be derived by recorded values of temperatures and heat fluxes. A big effort has been addressed in the implementation and comparison of different analysis methods. The aim of this paper is to widen the existent literature in the study of the influence of different kinds of input data on the final result. First the problem of analysing input data with significant drift in temperature is considered, adopting both nominal clean and noise affected data. Then the effect due to the presence of the Heat Flux Meter (HFM) on the thermal field of the testing element has been analysed, as well as the possibility of recording HFM surface temperature. These studies are based on Finite Element Method (FEM) simulations; both nominal clean and noise affected data have been considered as input. Finally, a difference in emissivity between the heat flux meter and internal plaster surface has been analysed by means of FEM simulations based on nominal clean data. An overall estimation of the occurred deviations in the different cases is shown.     

Measurement technology for material emissivity under high temperature dynamic heating conditions

The thermal dissipation of radiation is main heat shield mechanism for non-ablative thermal protection materials on hypersonic vehicles withstanding high temperature dynamic heating cycle during endo-atmospheric ascent, cruise and reentry. Therefore, it is necessary to know the thermal radiative properties of the material under the simulated high temperature dynamic heating conditions on the ground. The emissivity depends on the surface state and its temperature. A new simultaneous measurement technology of emissivity and varying surface temperature is proposed under high temperature dynamic heating conditions. This new technology solved synchronous measurement problems by utilizing spectral signal of Fourier transform infrared (FTIR) spectroscopy. The calibration of different temperature ranges, the background disturbances, the influences on temperature measurement by wavelength range and its corresponding fluctuations of measurement signal, were thoroughly investigated. The measured results of steel and graphite as reference materials proved the effectiveness of this simultaneous measurement technology and showed great potential in engineering applications under high temperature dynamic heating conditions.     

The surface tension of liquid silicon at high temperature

The measurement of the surface tension of liquid silicon has a long history with many results but no general agreement between them. Two values at the melting temperature are cited in reviews (749 and 827 mN/m [N. Eustathopoulos, E. Ricci, B. Drevet, Note Technique DEM No. 97/58, CEA, 1997]) but there are few arguments to determine the correct one. In the present study, new data for the surface tension obtained with the analysis of characteristic frequencies of a levitating drop are presented. The effect of oxygen and nitrogen are also considered. These data are compared with former data obtained with contactless techniques. The most recent surface tension values obtained with drop weights ranging on two orders of magnitude and environments of different natures (argon, hydrogen and vacuum) show excellent agreement (within a 1.5% margin) at temperatures between 1350 K and 2400 K. The comparison of these data to others obtained with different techniques, reveal a good agreement, except those obtained with the sessile drop technique on some supports like BN, SiO₂ and MgO. However, these special cases may be connected with the reactivity of silicon with these supports.     

Silver-based low-emissivity coatings for architectural windows: Optical and structural properties

Spectrally selective coatings are, nowadays, deposited onto architectural windows to be employed in commercial and residential buildings for the purpose of saving energy. In this work, the fundamental optical and structural properties of two types of low-emissivity silver-based coatings deposited onto glass, Ag and SnO₂/Ni-Cr/Ag/Ni-Cr/SnO₂ (Vitrage à couches avec une forte reflexion des rayonnements thermiques, European Patent EP 0 506 507 B1) are analyzed. It has been demonstrated that the silver-based multilayer coatings give an efficient heat isolation due to their low emissivity values, thus not deteriorating the optical properties in the visible range given by the glass substrate. From Atomic Force Microscopy measurements it has been determined that the Ag layer has a more homogeneous grain size when is deposited onto the Ni-Cr layer than when is deposited onto glass.     

Emissivity of substrate supported films

Results of experimental measurements of emissivity carried out on cobalt oxide and nickel sulphide films deposited on aluminum substrates are reported in this paper. Experimental results supported the general behaviour of variation of emissivity with film thickness as reported theoretically. The theoretical model is based on the interaction and attenuation of the emitted wavelengths from the substrate and film materials.     

应用于电子器件红外探测的发射率修正误差分析

器件表面温度是表征器件热性能的重要参数,应用红外热像法探测表面温度时,影响其测量结果准确性的关键因素是表面发射率的修正,通过对红外热像法发射率直接修正误差的统计分析,给出了不同条件下的发射率修正值标准差δ、误差ε的范围,提出了应用于电子器件的最小误差探测条件。