High temperature erosion behavior and microstructure of metallic materials in molten salt of sodium cyanate
The high-temperature reaction kettle for sodium cyanide molten salt is usually made of 316L stainless steel,but its lifespan is insufficient due to high-temperature corrosion failure.In order to improve the lifespan of the sodium cyanide molten salt reactor,this article studied the corrosion resistance of five metal materials,namely 316L,C-2000,C-276,high-purity Ni,and high-purity Cu,in sodium cyanide molten salt.The erosion rate was measured using the differential method,and the macroscopic and microscopic morphology before and after erosion were observed using a stereomicroscope and SEM.The phases and compositions of the erosion products were analyzed using XRD and EDS.The research show that the erosion rates,from lowest to highest,are Ni＜Cu＜C-276＜C-2000＜316L.From the perspective of erosion rate,high-purity Ni has the best corrosion resistance,but there are products distributed in a dotted pattern on the subsurface of the sample.Macroscopically,the 316L,C-2000,and C-276 samples exhibits surface blackening after high-temperature erosion by sodium cyanide molten salt,while the surface color of high-purity Ni and high-purity Cu samples do not show significant changes.After high-temperature erosion,the surface compound layer of 316L is composed of NiO,Cr2O2 4,and CrO3 phases.The surface compound layer and diffusion layer of C-2000 are both composed of CrN phase.The surface compound layer of C-276 contains CrN and NiO phases,while the diffusion layer exists in the form of NiO phase.The analysis shows that the main erosion mechanisms of sodium cyanate high-temperature molten salt on metals are nitridation and oxidation.The use of high-purity copper or high-purity nickel instead of 316L stainless steel for the preparation of sodium cyanide molten salt in reaction reactors is expected to improve its lifespan.
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