Analysis of corrosion of Al in thermal storage Na2HPO4·12H2O by molecular dynamics

Abstract

Molecular dynamics is employed to analyze the corrosion of aluminum in molten sodium hydrogen phosphate dodecahydrate (Na2HPO4·12H2O) hydrate salt phase-change material and the inhibition effect of 3·25% sodium metasilicate nonahydrate (Na2SiO3·9H2O) and 1% sodium chromate tetrahydrate (Na2CrO4·4H2O) additions. The corrosion of aluminum in a dilute solution of 3% sodium hydrogen phosphate is calculated comparatively. The results show that the diffusion coefficients of hydrogen phosphate (HPO4 2−) and water (H2O) in the pure molten sodium hydrogen phosphate dodecahydrate are 4·65 × 10−9 and 1·80 × 10−8 m2/s, respectively. When 3·25% sodium metasilicate nonahydrate and 1% sodium chromate tetrahydrate are added to the molten sodium hydrogen phosphate dodecahydrate, the coverage degrees of metasilicate (SiO3 2−) and chromate (CrO4 2−) are 78 and 84% in molten sodium hydrogen phosphate dodecahydrate solution, the diffusion coefficients of hydrogen phosphate reduce to 1·34 × 10−9 and 1·01 × 10−9 m2/s, and the corresponding diffusion coefficients of water are 4·35 × 10−9 and 1·05 × 10−8 m2/s, respectively. This indicates the obvious inhibition effect of the additions of sodium metasilicate nonahydrate and sodium chromate tetrahydrate. Comparatively, the reduction of diffusion coefficients of hydrogen phosphate and water in the similar cases is not too much.