Recent Development in the Investigation on Thermal Conductivity of Silicate Melts

Abstract

Accurate values of thermal conductivity of the silicate melts systematically measured as a function of chemical composition are necessary to understand a mechanism of heat transfer in the silicate melts. Hot wire method and laser flash methods have been used to measure thermal conductivity or thermal diffusivity of oxides melts at high temperatures. Laser flash method has been improved to measure thermal diffusivity of oxides melts with high accuracy. However the effects of radiative heat transfer and low electrical resistivity of samples have been made it difficult to derive precise values. To over come these difficulties, a frontheating frontdetection laser flash method with use of high time resolution detec tor has been proposed. The temperature response at the bottom surface of thin platinum cell containing sample irradiated by pulse laser is measured. The measurement techniques used for measurement oxide melts are com pared. Then, thermal conductivity of Al 2 O 3 Na 2 OCaOSiO 2 silicate melts was measured at temperature up to 1830 K. Thermal conductivity of the molten silicate shows insig nificant temperature dependence for all investigated melts. A fairly good correlation has been found between the thermal conductivity and the value of NBO/T (NonBridging Oxygen ions/Tetrahedrally coordinated cation) calculated from the chemical composition. The thermal conductivity increases with decrease of NBO/T for small NBO/T value and becomes constant for larger NBO/T value.

Thermal Conductivity of Molten Slags: A Review of Measurement Techniques and Discussion Based on Microstructural Analysis

“…Moreover, Hasegawa et al have pointed out that the influence of bubbles in the sample can be eliminated, thanks to the absence of a top plate on the surface of the sample. 20) Various types of laser flash methods are schematically described in Fig. 2.…”

“…21) Menashe and Wakeham investigated the effect of radiation absorption and emission on heat conduction during measurement of thermal conductivity using the hot wire (c) front-heating and front-detection. 20) method. 22) According to their simulation, the relative contribution of absorption into a sample was considered to be negligible compared to that of emission.…”

“…Recently, Hasegawa et al pointed out that even in case of a molten CaO-Al2O3-SiO2 slag, current leakage may occur during thermal conductivity measurements using the hot wire method. 20,39) To elucidate the possibility of current leakage from a Pt-Rh hot wire during thermal conductivity measurement of various molten slags, the resistivity of the Pt-Rh wire has been estimated at their respective measurement temperatures. 40) In spite of the low resistivity of molten slag (0.01-0.05 Ohm·m), 41) the current passing through the slag sample is expected to be much less than that through the hot-wire (resistivity of 5.0-6.0 × 10 -7 Ohm·m).…”

“…20,39) According to several previous researches using the laser flash method, the negligible temperature dependence of thermal conductivity of molten silicate was attributed to the constant mean free path, which will be equal to the unit cell size in fully depolymerized structure. In the laser flash method, however, the radiation effect on the heat transfer might be underestimated, resulting in the considerable difference in the temperature dependence.…”

On the Heat Flux Vector and Thermal Conductivity of Slags: A Brief Review

“…Brackbill et al [49] used the volume of the fluid model and the continuum surface force model for the slag surface tension to find the free surface of the slag flow using the CFD approach. Hasegawa et al [50] reviewed the measurement techniques for the thermal conductivity of molten silicate at high temperatures.…”