Application of the cluster variation method to interstitial solid solutions

Application of the cluster variation method to interstitial solid solutions

Pekelharing, M.I.

Thijsse, B.J. (promotor)
Böttger, A.J. (promotor)

Applied Sciences

2008-01-08

A thermodynamic model for interstitial alloys, based on the Cluster Variation Method (CVM), has been developed, capable of incorporating short range ordering (SRO), long range ordering (LRO), and the mutual interaction between the host and the interstitial sublattices. The obtained cluster-based model is applied to describe phase equilibria between iron nitrides in order to compare quantitative analysis of CVM calculations directly to experimental MÖssbauer data, resulting in good agreement between the CVM predictions and the fractional occurrences of specific iron atom surroundings in terms of the number of neighboring nitrogen atoms. Furthermore, analysis of the order-disorder transitions demonstrates that phase transitions on the sublattices are coupled. Not only the induction of SRO on both the metal and the interstitial sublattices following the introduction of a second metal atom type is demonstrated, preferential grouping of metal atoms with specific interstitials is observed as well. The ideas and methods explored in this thesis combined with ab initio calculations create an environment which supports design and development of interstitial alloys exhibiting specific desirable properties and stabilities in a finite range of temperatures for practical industrial applications. Currently, this approach is used to improve the efficiency and life span of hydrogen gas separation membranes.

cluster variation method
iron nitrides
long range ordening
short range ordening
solid solution
interstitial alloy
lattice frustration

http://resolver.tudelft.nl/uuid:abb8c554-5668-4742-a724-f9c951df2a82

978-90-8559-304-1

Institutional Repository

doctoral thesis

(c) 2008 M.I. Pekelharing