Thermodynamic re-assessment of pure chromium using modified segmented regression model
A. Obaied, S. Zomorodpoosh, I. Roslyakova, L. Zhang.
CALPHAD XLVIII, Singapore, June 2nd - June 7th 2019, 71, (2019)
Chromium is an important addition element that is well known for its unique magnetic properties and high corrosion resistance. It is considered to be an essential part of the stainless steel and chrome plating industries. However, there is an ongoing debate regarding some of its properties, especially its melting point value. Multiple studies have reported different melting point values that can vary by a range of about 65 K, from 2115 K to 2180 K, but most of the recent studies seem to agree on the value of 2136 K, rather than the value, 2180 K, that is currently used in the SGTE description . Several attempts were made to improve the description of thermophysical properties of pure Cr [2,3,4]. One of the most recent re-assessment of pure Cr have been performed using the segmented regression (SR) model , which is valid from 0K up to the melting point. In order to expand the SR model beyond this region to high temperatures, a special logistic function has been utilized to modify the SR model without any additional fitting parameters. Such a modification of original SR model allows to change the melting point without the need for additional re-assessments. Moreover, in comparison to the recent SGTE description each phase would have a smooth description over the entire temperature range, even in regions where the phase might be metastable/unstable. Additionally, two machine learning methods were developed and applied to calculate weights of datasets involved in assessment and to detect possible outliers. These automated methods can improve a quality of thermodynamic assessments and give a hint to unexperienced researches which datasets should be validated more precisely. References  Dinsdale, A. SGTE data for pure elements, CALPHAD 15 (4) (1991) 317–425.  Thurnay, K. Thermal properties of transition metals. Forschungszentrum Karlsruhe GmbH Technik und Umwelt (Germany). Inst. fuer Neutronenphysik und Reaktortechnik (1998).  Pavlů, J. et al. Combined quantum-mechanical and CALPHAD approach to description of heat capacity of pure elements below room temperature, CALPHAD 51 (2015): 161-171.  Roslyakova, I., et al. Modeling of Gibbs energies of pure elements down to 0K using segmented regression, CALPHAD, 55 (2016): 165-180.
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