Thermographic investigation of the discrete fusion and crystallization supercooling of lead

Abstract

The kinetics of lead melting and solidification were studied by the method of ballistic thermal analysis (BTA). It was established for the first time that the melting process involves three stages of fusion at TL1, TL2, and TL3, with the temperature differences TL2-TL1=0.3±0.05 K and TL3-TL2=0.6±0.1 K. The corresponding specific enthalpies of fusion are H1=H2=(0.4±0.05)H and H3=(0.15±0.05)H, where H=H1+H2+H3. Crystallization always proceeds at a temperature equal to that of the first stage of fusion (Ts-TL1). Accordingly, the crystallization supercooling of the melt exhibits discrete variation: ΔT1−=0, ΔT2−=0.06±0.02 K, and ΔT3−=3±0.5 K after the first, second, and third stage, respectively. Overheating of the melt to ΔT+=22±2 K is accompanied by the maximum supercooling ΔT4−=4±0.2 K.