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本文利用非稳态卡计法精确地测定高度抛光的纯金属钨及镍在350—1000K的半球向全发射率。提出了一个修正公式,它不仅能消除非辐射热损对全热发射率的影响,而且能估计出因引进灰体假定而带来的误差。 测试结果表明,钨的全发射率的实测值与Drude自由电子模型的理论值相当符合。然而,镍则不同。它在居里温度附近,其冷却速率及全发射率都有严重畸变。只有在这个“临界温度”之外,其测定值与理论值才又趋向一致。发现镍的热发射率的这种特性恰恰与它的直流电阻率ρ的温度系数dρ/dT随温度变化的特性十分相似,从而可以设想,现有热辐射理论无法预言在临界点附近热发射率所产生的畸变,其原因可能是由于只考虑ρ,而完全忽略dρ/dT的缘故。
In this paper, the non-steady-state card counting method is used to accurately measure the hemispherical full emissivity of highly polished pure tungsten and nickel at 350-1000K. A correction formula is proposed, which can not only eliminate the influence of non-radiative heat loss on total emissivity, but also estimate the error caused by the introduction of gray body assumption. The test results show that the measured values of the total emissivity of tungsten are in good agreement with the theoretical values of the Drude free electron model. However, nickel is different. Near the Curie temperature, it has severe distortions in both cooling rate and total emissivity. Only in this “critical temperature”, the measured values and theoretical values and then tend to be the same. It has been found that this characteristic of the thermal emissivity of nickel is very similar to that of the temperature coefficient dρ / dT of its direct current resistivity ρ with temperature changes. Therefore, it can be assumed that the existing theory of thermal radiation can not predict the thermal emissivity near the critical point The resulting distortion may be due to the fact that only ρ is considered and dρ / dT is completely ignored.