Melting behavior and thermal conductivity of solid sodium-concrete reaction product

Abstract

ABSTRACT This study revealed melting behavior and thermal conductivity of four samples generated by sodium-concrete reaction (SCR). We prepared the samples using two methods such as firing mixtures of sodium (Na) and grinded concrete powder, and sampling depositions after the SCR experiments. In the former, the mixing ratios were determined from the past experiment. The latter simulated the more realistic conditions such as the temperature history and the distribution of Na and concrete. The thermogravimetry-differential thermal analyzer (TG-DTA) measurement showed the temperatures of the onset of the melting (solidus temperatures) were 865–942°C, but those of the samples containing metallic Na could not be clarified. In the two more realistic samples, the compression moldings in a furnace were observed. The observation revealed the softening temperature was 800–840°C and the solidus temperature was 840–850°C, which was 10–20°C lower than the TG-DTA results. The thermodynamics calculation of FactSage 7.2 revealed the solidus temperature was caused by melting of the some components such as Na2SiO3 and/or Na4SiO4 and NaAlO2. Moreover, the thermal conductivity was λ ~ 1–3 W/m-K, which was comparable to xNa2O - (1 - x)SiO2 (x = 0.5, 0.33, and 0.25), and that at 700°C was explained by NBO/T of Equation (1).