A Model for Calculating Hydrogen Solubility in Liquid Transition Metals
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INTRODUCTION
HYDROGEN has high solubility in most liquid metals, which can usually induce defects in the solidified metal as porosity, property reduction structure (e.g. hydrogen brittleness), etc.[1] Recently, the high solubility of hydrogen is being used positively to produce an ordered porous new material called GASAR.[2–5] So, the solubility of hydrogen in liquid metals is an interesting problem. Commonly, this solubility CH(at pct) is ruled by the Siverts’ law[1,6]: pffiffiffiffiffiffiffiffiffiffiffiffiffiffi ½1 CH ¼ pH2 =p0 exp DH0 RT þ DS0 R where DH0 and DS0 are the change of enthalpy and entropy of hydrogen during solution, which are determined by the interaction between hydrogen and liquid metal; pH2(Pa) is the partial pressure of hydrogen on the liquid metal; p0(Pa) is the standard pressure and is usually set to be 0.1 MPa; and T(K) is the temperature of the liquid metal. Until now, however, no strict theory exists to determine the DH0 and DS0 for different metals,[1,7,8] which partly results from the muddy understanding of the structure and properties of liquid metals[9–11] and partly from the scatter of experimental results.[1,12,13] Chen[1] compiled several documented hydrogen solubility data in iron and its alloys, in which the existing form of hydrogen in metals was also discussed. Manchester[13] collected abundant information on metal–hydrogen systems in the form of periodic table, which implied the relationship between the properties of
GUANGRUI JIANG, Ph.D. Candidate, is with the Department of Mechanical Engineering, Tsinghua University, Beijing 100084, P.R. China. YANXIANG LI, Professor, is with the Key Laboratory for Advanced Materials Processing Technology, China, and the Department of Mechanical Engineering, Ministry of Education, Tsinghua University, Beijing 100084, P.R. China. Contact e-mail: yanxiang@ tsinghua.edu.cn Manuscript submitted January 14, 2010. Article published online November 2, 2010 1038—VOLUME 42A, APRIL 2011
metal–hydrogen system and the position of metallic element in the Periodic Table. Fromm and Hoerz[14] reviewed the interaction of hydrogen with metals, in which the DH0 and DS0 values were plotted as a function of the position of the metallic element in the Periodic Table. The author summarized the documented results of hydrogen solubility in some liquid metals by statistical analysis to obtain more accurate values.[15] Unfortunately, until now, no work has been done to check out the predominant factor in determining the hydrogen solubility in liquid metals. In the current study, it is supposed that the electron interaction between hydrogen and atoms of the liquid metal is the major factor in determining hydrogen solubility in the liquid metal. Based on this consideration, a model was proposed for characterizing electron interaction and calculating the hydrogen solubility in different liquid metals according to the nearly freeelectron theory. For the convenience of comparison with the documented hydrogen solubility results, the temperature T is fixed at the melting point Tm and the hydr
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