SOFC不锈钢连接体用Nb掺杂NiFe2O4涂层的制备与高温性能

Cr2O3-forming ferritic stainless steels have been considered as the most promising materials for the interconnects of intermediate-temperature solid oxide fuel cell. However, the main obstacles for using ferritic stainless steel interconnects are the increase of area specific resistance due to the growth of oxide scales and the poisoning of cathodes due to volatile Cr. Applying oxidation resistant and electrically conductive coatings is an effective method to overcome these problems. In view of the fact that n-type NiFe2O4 spinel oxide is nonvolatile, has a similar thermal expansion coefficient to ferritic stainless steels and high electronic conductivity, it is proposed in this project that high-valence Nb5+ is introduced to prepare Nb-doped NiFe2O4, with an attempt to increase its electronic conductivity and protective performances. Thereby, NiFe-Nb composite coatings will be prepared on a type 430 ferritic stainless steel, followed by heat treatment in a low oxygen pressure environment and in air to obtain Nb-doped NiFe2O4 spinel coatings. Furthermore, the high temperature oxidation behavior and area specific resistance of the alloy with and without coatings will be investigated in both simulated cathode and anode atmosphere at 700-800℃, and its microstructures will also be examined, in an attempt to understand the mechanism of the spinel coatings and Nb in improving the oxidation resistance and electronic conductivity.This investigation is of great significance to the development of oxidation resistant and electrically conductive coatings for stainless steel interconnects of solid oxide fuel cell.

铁素体不锈钢被认为是最有希望的中温固体氧化物燃料电池(SOFC)连接体材料。然而，应用铁素体不锈钢连接体面临的主要障碍是合金表面氧化物的生长而导致的面比电阻的增加和Cr挥发导致的电池阴极中毒。施加抗氧化、导电涂层是解决上述问题的一种有效途径。鉴于n-型NiFe2O4尖晶石氧化物是非挥发性的，与铁素体不锈钢具有相近的热膨胀系数和高的电导率，本项目拟通过掺杂高价态的Nb5+来提高其电导率与保护性能，制备Nb掺杂的NiFe2O4尖晶石涂层。为此，采用复合电镀技术在430铁素体不锈钢表面制备NiFe-Nb复合镀层，通过高温氧化处理使合金镀层转化为Nb掺杂的NiFe2O4尖晶石涂层。研究合金/涂层在700-800℃模拟SOFC阴、阳极气氛中的高温氧化行为及面比电阻，表征合金/涂层的微观结构，阐明涂层与Nb的作用机制。本项研究对于推动SOFC不锈钢连接体表面防护涂层的发展与应用具有积极的意义。

铁素体不锈钢被认为是最有希望的中温固体氧化物燃料电池(SOFC)连接体材料，但它也面临着因氧化物的生长而导致的面比电阻的增加和Cr挥发导致的电池阴极中毒等问题。施加抗氧化、导电涂层是解决上述问题的一种有效途径。n-型NiFe2O4尖晶石氧化物是非挥发性的，与铁素体不锈钢具有相近的热膨胀系数和高的电导率，是一类有希望的涂层。本项目拟通过掺杂高价态的Nb5+来提高其电导率与保护性能，制备Nb掺杂的NiFe2O4尖晶石涂层。为此，项目采用复合电沉积NiFe-Nb涂层及高温氧化处理在430铁素体不锈钢表面制备了Nb掺杂NiFe2O4尖晶石涂层，并研究了其高温氧化与导电性能，阐明了涂层与Nb的作用机制。. 通过电沉积Ni-Fe涂层与高温氧化在430不锈钢(430SS)表面制备了均匀、致密、与基体结合良好的NiFe2O4尖晶石涂层。涂层显著提高了合金在高温潮湿空气中的抗氧化性能,降低了其面比电阻，有效地抑制了Cr的外扩散。然而，沿氧化膜/基体界面形成了孔洞，影响了涂层的长期抗氧化性能。. 通过电沉积NiFe-Nb复合涂层与高温氧化制备了Nb改性NiFe2O4尖晶石涂层。适量加入Nb有助于提高NiFe2O4尖晶石涂层的抗高温氧化性能，并降低面比电阻。Nb改变了Ni-Fe合金涂层表面氧化膜的生长机制，即从外扩散生长为主转变为内扩散生长为主，减少了界面孔洞的形成，提高了氧化膜的粘附性。同时Nb掺杂于有助于抑制氧的内扩散，促进保护性Cr2O3膜的形成。. 采用复合电沉积方法在430SS表面制备了NiFe-CeO2复合涂层。在氧化过程中涂层转变为外层为NiFe2O4尖晶石、内层为Cr2O3的双层结构氧化膜。CeO2有效地降低了Cr2O3的生长速度，减少了氧化膜/基体界面的孔洞，进一步提高了NiFe2O4的抗氧化性能，并降低其面比电阻。. 研究了多弧离子镀CrN扩散障对Ni-Fe合金涂层的高温性能的影响。双层结构的CrN/Ni-Fe涂层在氧化过程中能转变为致密、粘附性良好的外层为NiFe2O4尖晶石和内层为Cr2O3的氧化物涂层。CrN扩散障提高了Ni-Fe合金涂层的抗氧化性能，抑制了Cr2O3膜的生长与界面孔洞的形成，减小了面比电阻。. 本项研究对于SOFC不锈钢连接体表面防护涂层的发展与应用具有积极的意义。