Thermodynamic evaluation of pure Co for the third generation of thermodynamic databases

Abstract

An updated thermodynamic description of pure Co was obtained by applying new models for the third generation of Calphad databases. In these models, different contributions to the heat capacity, especially the vibrational part, were treated separately, each with a clear physical meaning. More importantly, the phase stabilities of the various allotropes are now physically well defined. Thus, the derived thermodynamic properties vary more reasonably and smoothly from 0 K and up. Calculated thermodynamic properties were compared with experimental data and good agreement was obtained.

Thermodynamic Modeling of Pure Co Accounting Two Magnetic States for the Fcc Phase

“…Some assessments of the elements have been performed based on these models. [5,6,8] The Einstein model lays the foundation of the framework. The heat capacity of a solid substance can be described by its combination with the polynomials (see Eq 1).…”

“…[11,12] The details of this modified model could be found in the literature. [4,6] The Gibbs energy could be calculated from the heat capacity correspondingly (see Eq 2).…”

“…The The experimental results accepted in the assessment [6] were also adopted in the present work except for (1) the value of the magnetic moment of each phase (2) the range of the hcp/fcc transition enthalpy and fcc/liquid transition enthalpy (3) the Curie temperature of the hcp phase. In this work, the value of beta for all stable phases of pure Co (hcp, fcc and liquid-amorphous phase) are set to 1.7 which fall within the range of magnetization measurement results.…”

“…[1][2][3][4] The descriptions of the pure elements, as the basis of the databases, have been evaluated using a combination of the Einstein/Debye model and polynomials or the segmented models. [5][6][7][8][9][10] The transition metals such as Fe, Co, Mn who occupy the center position of the periodic table are of special interest because many of them have intriguing magnetic properties. The magnetic heat capacity and magnetic Gibbs energy of most elements could be well described by the widely used Inden-Hillert-Jarl (I-H-J) model [11,12] while a few exceptional cases may not be.…”

A New Description of Pure C in Developing the Third Generation of Calphad Databases

“…One approach based on this suggestion, [2] that is currently possible to implement in the Calphad software Thermo-Calc is the one suggested by Chen and Sundman in 2001 [3] for modelling thermodynamic properties of pure Fe. Although this model is simple, it has so far proven to describe Ni, Cr, [4] Mn, [5,6] Co [7] and Pb. [8] In the present article unary carbon, C, is reassessed.…”