High temperature corrosion of stainless steel AISI 316L in molten nitrate salts based thermofluids for concentration solar plants

ABSTRACT With the recent boom of environmentally friendly energies, the demand for materials capable of resisting certain working conditions demanded by these processes arises, for example, the obtaining of energy from sunlight, in which the Thermal storage is vital during the operation of the plant. In the present work, the reaction of AISI 316L steel in contact with molten nitrate salts (Ca (NO3)2 + NaNO3 + KNO3 and LiNO3 + KNO3 + NaNO3) was evaluated, gravimetric tests were carried out with Two types of ternary salts of nitrates at a temperature of 600°C, evaluating the gain of mass in the steel, in turn, were carried out metallographic studies, in order to evaluate the damage of the microstructure. By means of SEM and optical micrographs, the morphology of the layer and the damage caused to the steel was observed. The surface where the greater aggressiveness of damage by the ternary salt in the steel was evidenced is the surface of the steel exposed to the lithium salt. The results of DRX yielded Fe0.612Ni0.388 and CrNi, as the main steel corrosion products, demonstrating that the salt fused with the calcium component is less harmful to the steel used in this project.

摘要
随着近年来环保能源产业的蓬勃兴起，适配此类工艺特定服役工况的抗蚀材料需求日益迫切。以太阳能发电为例，其电站运行过程中，热能存储（Thermal storage）环节至关重要。
本研究针对AISI 316L钢与两类熔融硝酸盐盐（Ca(NO₃)₂ + NaNO₃ + KNO₃与LiNO₃ + KNO₃ + NaNO₃）的接触反应展开评估：于600℃下针对两类三元硝酸盐盐开展重量法测试，以表征钢材的质量增益；同时开展金相分析，以评估其微观结构损伤情况。
借助扫描电子显微镜（SEM）与光学显微图像，观测了腐蚀层的形貌以及钢材所受的损伤。实验结果表明，与锂基盐接触的钢表面所受三元盐侵蚀损伤最为严重。
X射线衍射（DRX）测试结果显示，钢材的主要腐蚀产物为Fe₀.₆₁₂Ni₀.₃₈₈与CrNi，由此证实，含钙组分的熔融盐对本研究所用钢材的腐蚀性更弱。