Corrosion Behavior Of Novel Ceramics Immersion In Flinak Molten Salt

Molten Salt Reactor （MSR） as one of six Gen-IV candidate nuclear systems is aliquid reactor which use fluoride molten salt as fuel carrier and coolant. The excellentthermal physical and chemical performance of molten fluoride brings MSR unparalleledadvantage in neutron economy, radioactive waste disposal, inherent safety and nuclearproliferation prevention. Accordingly, materials of an MSR will face more severechallenges which were caused by high operating temperature, high irradiation andcorrosive environments from molten fluoride salt, especially the corrosion of materials byhigh temperature molten fluoride. Alloy materials are substantially meet the requirementsof the MSR at lower temperatures; there are no corrosion problems between graphite andmolten fluoride, but the insufficient mechanical properties of graphite limit its applicationin the MSR. Ceramics of carbons, nitrides, borides, and intermetallic compounds havegood high temperature resistance and corrosion resistance, may be very likely to beapplied to MSR.Impurities in molten fluoride have an important effect on the corrosion of materials.Influencing factors and process to FLiNaK molten salt purification by vacuum dryingmethod was explored. The optimal pretreatment temperature is400℃, and time is6h; theoptimal preparation temperature is750℃, and time is8h.Since corrosion dates of ceramic materials in molten fluoride are very rare, Gibbs freeenergy （G） of dozens ceramics with F₂（g） were calculated by HSC Chemistry softwareto screen out the possible ceramics, which include carbides, nitrides, silicides, borides,oxides and intermetallic compounds. Under an argon cover gas, the selected ceramicswere performed in FLiNaK （LiF-NaF-KF:46.5-11.5-42mol%） molten salt at850℃for100h with the goal of obtaining corrosion data and verifying the calculation results.Corrosion performance and behavior of ceramics were evaluated by corrosion rate,surface morphology and scanning electron microscopy （SEM）. Corrosion resistance ofceramics in molten fluorides can judge initially based on itsâ–³G reaction with F₂（g）, butshould pay attention to the solubility of materials in molten salt. Corrosion resistance ofthe oxide ceramics are worst, carbide ceramics are better, and MoC exhibits bestcorrosion resistance with corrosion rate about0.26um/100h.Immersion corrosion of ZrC-SiC based ceramics was performed in molten fluoride saltFLiNaK, with the goal of assessing their suitability for candidate materials in moltenfluoride preparation, thermal storage and transfer application. The corrosion performances and mechanisms of these carbides at850℃for100h under argon gas wereinvestigated by weight change, scanning electron microscopy, X-ray diffraction andoxygen content analysis. The results indicate that zirconium and silicon carbides all loseweight under the conditions investigated. SiC exhibit better corrosion resistant than ZrC.In ZrC-SiC composites, ZrC was selectively attacked by molten salt, corrosion resistanceimproved as the SiC content increases. Carbide ceramics corrosion in molten fluoride ismainly due to the negative valence C^4-in ceramic materials oxidized to elemental C byoxidizing substances or impurities in the molten salt. Adding C can inhibit the molten saltcorrosion of carbide ceramic, and improve the corrosion resistance of the carbideceramic.