Proving the contact rules for phase regions: Implications to phase diagrams of metal-hydrogen systems

The rule of triple joints has recently been proved for two-dimensional phase diagrams and two-dimensional sections of phase diagrams of a higher dimension (Antonov, 2013). The present paper is extending this rule to phase diagrams of binary metal-hydrogen systems composed of a metal immersed in a hydrogen gas. The rule is shown to be valid for every triple point in the temperature-pressure phase diagrams of these systems, including the points with the intersecting boundary lines tangent to each other. The paper also considers the sufficient conditions for the application of the rule to triple points in the projections of phase diagrams onto the temperature-concentration plane. (C) 2015 Elsevier B.V. All rights reserved.