Melting of metals during rapid bulk heating.

Autor: Chekhovskoi, V., Tarasov, V.
Zdroj: Russian Metallurgy (Metally); Aug2009, Vol. 2009 Issue 4, p297-302, 6p
Abstrakt: The melting of metals is studied during electric-current pulse heating at high rates (106−109 K/s). This process is found to be nonequilibrium: it proceeds with the overheating of the onset and end of melting and is nonisothermal. The experimentally measured enthalpies of nonequilibrium melting are used to calculate the nonisothermicity of nonequilibrium melting δ T and nonisothermicity factor δ T/ T m, where δ T reflects the increase or decrease in the temperature of the end of nonequilibrium melting with respect to equilibrium melting temperature T m. For many metals with a melting temperature of 500–3695 K, melting factor of nonisothermic melting δ T/ T m ranges from 0.8–4.6% to −(0.2–5.1)% and depends on the relation between homogeneous and heterogeneous nucleation. The nonisothermicity of melting is confirmed by direct temperature measurements during melting of hafnium and zirconium. The contribution of the energy consumed for heating of a two-phase solid metal-melt system during nonisothermal melting in the course of pulsed heating to the melting heat is estimated. The relaxation times of equilibrium melting of some metals are estimated using nonequilibrium pulsed measurements. The role of the melting nonisothermicity factor in increasing the melting temperature of a graphite sample placed in a closed volume and heated with an electric current pulse at a rate of 5 × 109 K/s is determined. [ABSTRACT FROM AUTHOR]
Databáze: Complementary Index
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