No abstract

No abstract

The thermal diffusivity and heat capacity of uranium dioxide have been measured from 500 to 2900 K with an advanced laser-flash technique. These two quantities were determined simultaneously by means of an accurate numerical fitting of the experimental thermograms. At high temperatures the precision of the method used is much better than that associated with conventional laser-flash measurements. It was found that the heat capacity continues to increase even at temperatures above the expected lambda transition (2670 K). The inverse of the thermal diffusivity increases linearly with temperature up to 2600 K, whilst at higher temperatures the slope markedly decreases. A new expression for the thermal conductivity as a function of temperature is proposed, which is corroborated by some theoretical considerations on the underlying heat transport mechanisms.

Despite large commercial production of MgO-based ceramics for a wide gamut of applications, the melting point of magnesia remained uncertain for almost one century. This article shows that a number of problems must be solved to attain experimental conditions where the solid–liquid phase transition of magnesia can be unambiguously detected, and the temperature be measured with sufficient accuracy. The method adopted in the reported work is based on controlled laser pulse heating. The solidification point was measured by the thermal arrest occurring during cooldown from the melt. The measurement of temperature, a most delicate problem for pyrometry applications in semitransparent materials, was obtained by using combined brightness and spectral pyrometers. The experimental and analytical methods are described in some detail. The resulting melting point of MgO is 3250±20 K, which is approximately 150 K higher than the value currently recommended.

No abstract