Thermal Expansion of Molten Materials by the Gamma Attenuation Technique

Abstract

An apparatus was constructed for measurement of the density and volumetric thermal expansion of high temperature molten materials using the gamma attenuation technique. It was found that significant improvements in overall experimental precision could be realized by employing an automatic gain control in the linear section of the gamma counting system. This device reduced errors due to system gain shifts and thereby increased the precision of the gamma counting. Corrections were also made for the dead time of the electronics system. A preliminary experimental investigation of the precision of the method was made by measuring small dimensional steps of a tool steel block at a single temperature. A fractional length increment Δℓ/ℓ of 1% was. determined to 1%, equivalent to a length change precision of 10^-4 cm/cm. In addition, the precision of the experimental technique was analytically examined for both absolute and relative density determinations. Three analytical expressions used to reduce data for liquid density determinations were evaluated for their precision. Each allows use of a different set of input data parameters, which can be chosen based on experimental considerations. Using experimentally reasonable values for the precision of the parameters yields a similar resultant density precision from the three methods, on the order of 0.2%.

This work supported by the U.S. Department of Energy.