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Journal of Phase Equilibria and Diffusion

, Volume 40, Issue 1, pp 104–114 | Cite as

A Modified Neumann–Kopp Treatment of the Heat Capacity of Stoichiometric Phases for Use in Computational Thermodynamics

  • Michael Schick
  • Andy WatsonEmail author
  • Moritz to Baben
  • Klaus Hack
Article
  • 21 Downloads

Abstract

Since the early days of phase diagram calculation, the CALPHAD community has accepted a method of data assessment that is based on using Gibbs energy expressions for stoichiometric compounds that consist of a part that represents the contributions of the reference components, the so-called Neumann–Kopp sum, and a part that represents the Gibbs energy of formation. Usually, the latter consists only of a simple A + B * T term, which implies on the one hand that enthalpy and entropy of formation of a compound are temperature independent, and on the other, that the heat capacity of the respective compound is given by the Neumann–Kopp sum of the Cps of the constituents. In most cases this method yields acceptable results, also for the heat capacity. However, if certain elementary components are involved, this is not so. The paper highlights the problem outlining a remedial treatment that can be applied to problematic heat capacity functions present in pre-existing assessments, and thus giving a suggestion of how to prevent the problem in the future.

Keywords

heat capacity Neumann–Kopp CALPHAD thermodynamics phase diagram 

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Copyright information

© ASM International 2019

Authors and Affiliations

  • Michael Schick
    • 1
  • Andy Watson
    • 2
    Email author
  • Moritz to Baben
    • 1
  • Klaus Hack
    • 1
  1. 1.GTT TechnologiesHerzogenrathGermany
  2. 2.Centre for the Built and Natural Environment, Faculty of Engineering and ComputingCoventry UniversityCoventryUK

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