The preliminary exploration of composition origin of solid solution alloys used in thermocouple by cluster-plus-glue-atom model

Abstract

The chemical composition proportion of solid solution alloys in thermocouples (TCs) field is preliminarily explored by the cluster-plus-glue-atom (CPGA) model. CPGA clusters for face-centered cubic (fcc) and body-centered cubic (bcc) structure elemental metal are established, which are the cubic octahedron and rhombic dodecahedron respectively. With introducing the solute A element into solvent B matrix, the solute A atoms will prefer to the certain sites of solvent B atoms in CPGA cluster. Setting a CPGA cluster consisted of solute A and solvent B atoms as the central cluster, Friedel oscillation perturbation of central cluster on surrounding CPGA clusters will be totally shielded along radial at the position of 3 times of size of central cluster. Then, CPGA unit clusters for fcc and bcc structure solid solution alloys are established, which consist of the central, nearest neighbor, and glue clusters. Take K type TCs as an example. The nominal and theoretical stable composition proportion for Ni-Cr/Ni-Si solid solution alloys are Ni90Cr10/Ni97Si3 (wt. %) and Ni96.9Si3.1/Ni89.5Cr10.5 (wt. %), which correspond well with each other. Finally, CPGA unit clusters for most solid solution alloys in TCs field are analyzed, which display the better correspondence to the nominal composition proportion of them.

Keywords

• Thermocouple
• Solid solution alloy
• Cluster-plus-glue-atom model
• Stable composition proportion
• Coordinating polyhedron
• Phase diagram