K2ZrF6含量对ZrH1.8表面微弧氧化阻氢膜层的影响

采用微弧氧化技术在ZrH_1.8表面制备阻氢膜层,研究在Na₅P₃O₁₀-NaOH-Na₂EDTA电解液体系中K₂ZrF₆含量对膜层组织结构和阻氢性能的影响。借助场发射扫描电子显微镜(FESEM)和X射线衍射仪(XRD)分析膜层的微观结构和物相组成。采用涂层测厚仪对膜层的厚度进行测量,通过真空脱氢实验表征膜层的阻氢性能。相比未加入K₂ZrF₆时,电解液中添加适量K₂ZrF₆有助于改善膜层的表面质量,减少膜层中微孔和裂纹等缺陷的出现。XRD分析表明,不同K₂ZrF₆浓度时ZrH_1.8表面微弧氧化制备的膜层均主要由m-ZrO₂,t-ZrO₂和少量c-ZrO₂相组成。膜层厚度和氢渗透降低因子(PRF)随K₂ZrF₆浓度的增加均呈先增大后减小趋势,当K₂ZrF₆为4g·L^-1时,膜层的厚度最大为68.7μm,PRF最大为13.1,且膜层中大尺寸缺陷较少,添加K₂ZrF₆制备的陶瓷膜的阻氢性能均得到提高。K₂ZrF₆添加剂的加入可以使ZrH_1.8表面微弧氧化膜层的厚度增大,致密性增强,进而阻氢性能提高,膜层表面质量也得到改善。

Micro-arc Oxidation and Hydrogen Resistance Film on ZrH1.8 Surface with K2ZrF6 Concentration

Zirconium hydride was regarded as an ideal solid neutron moderator and shielding material for space nuclear reactors.The high temperature hydrogen loss phenomenon of zirconium hydride was a problem that researchers had been paying attention to.Using micro-arc oxidation technology to prepare a hydrogen resistance film on the surface of zirconium hydride could effectively slow down the hydrogen precipitation.Studies had shown that the type and content of additives in the micro-arc oxidation electrolyte would affect the structure and performance of the hydrogen barrier film on the surface of zirconium hydride.The hydrogen barrier film was prepared on the surface of ZrH_1.8by micro-arc oxidation technique.The experiment process mainly included pretreatment of the sample such as cutting,grinding,degreasing,electrolyte preparation and micro-arc oxidation treatment.The effect of K2Zr F6content on the microstructure and properties of the film in Na₅P₃O₁₀-NaOH-Na₂EDTA electrolyte system was studied.The microstructure and phase composition of the film were analyzed by field emission scanning electron microscopy(FESEM)and X-ray diffraction(XRD).The thickness of the film was measured by a coating thickness gauge,and the hydrogen barrier performance of the film was characterized by vacuum dehydrogenation experiments.When K₂ZrF₆ was not added to the electrolyte,there were large pores on the surface of the micro-arc oxidation film on the surface of ZrH_1.8,and many cracks were distributed discretely.Compared with the absence of K2Zr F6,the addition of an appropriate amount of K₂ZrF₆ helped to improve the surface quality of the film and reduce the occurrence of defects such as micropores and cracks in the film.With the increase of the concentration of K₂ZrF₆ in the electrolyte(<4 g·L^-1),the number of micropores on the surface of the film increased,the size of the micropores decreased significantly,and the number of cracks decreased.The surface of the film gradually became flat.When the K₂ZrF₆ concentration was 4 g·L^-1,there were almost no large-size defects in the film,and the surface quality was further improved.This was mainly because the K₂ZrF₆ in the electrolyte had a significant modulation effect on the surface morphology of the micro-arc oxidation film,which improved the surface quality.K₂ZrF₆ generated Zr(OH)4 solid particles in the alkaline solution,which was oxidized in the micro-arc.During the process,the negatively charged Zr(OH)4 particles in the solution tended to accumulate in the discharge micropores under the action of the electric field force,and dehydration and sintering occurred under the thermochemical action of the micro-arc discharge,and the Zr(OH)4transformed into ZrO₂,Thus filling and repairing the micro-holes and cracks of the micro-arc oxide film.At the same time,adding K₂ZrF₆ could provide F-1,and F-1 could improve the uniformity of the film during the micro-arc oxidation process.The cross-sectional morphology showed that the film layer was composed of an inner dense layer and an outer loose layer.The side close to the substrate was a dense layer and the outside was a loose layer.When K₂ZrF₆ was not added to the electrolyte,the size of the micropores in the loose layer of the membrane was larger,and the average thickness of the membrane was 51.5μm.It could also be seen from the cross-sectional morphology of the film that when the K₂ZrF₆concentration was 4 g·L^-1,the boundary between the loose layer and the dense layer was not obvious.The overall thickness of the film was relatively dense,with the maximum thickness of 68.7μm.The PRF(permeation reduction factor)was the maximum value of 13.1.It showed that the hydrogen barrier performance of the film was better at this concentration.As the concentration of K₂ZrF₆ increased,the thickness and PRF of the film were both reduced.In an electrolyte containing a higher concentration of K2Zr F6,a more violent spark arc would be generated at a lower voltage,which would cause a certain damage to the film,that was,micropores and thermal cracks appeared in the cross section,making the film looser.The thickness of the film was also reduced.In turn,the hydrogen barrier performance was reduced,so the PRF value was reduced.XRD analysis showed that the films prepared by micro-arc oxidation on the surface of Zr H1.8 at different K₂ZrF₆ concentrations were mainly composed of monoclinic-ZrO₂(m-ZrO₂),tetragonal-Zr O2(t-ZrO₂) and a small amount of cubic-ZrO₂(c-ZrO₂).Different concentrations of K₂ZrF₆ were added to the phosphate electrolyte system,and a hydrogen barrier film with a certain thickness could be prepared on the surface of the Zr H1.8substrate through the micro-arc oxidation technique.Adding the additive K₂ZrF₆ to the micro-arc oxidation electrolyte could effectively improve the structure and hydrogen barrier properties of the micro-arc oxidation film on the surface of ZrH_1.8.The addition of K₂ZrF₆ could increase the thickness of the microarc oxidation film on the surface of ZrH_1.8 and enhance the compactness,so the hydrogen barrier performance and surface quality of the film were improved.