【作者】 王丽；

【导师】 陈砺；

【作者基本信息】 华南理工大学 ， 化学工艺， 2010， 博士

【摘要】 可开发能源和矿产资源日益短缺的问题,迫使人们必须把提高材料和能源利用率放在研究的首要位置。等离子体电解氧化(PEO)技术为轻金属材料表面改性提供了新思路,利用该技术制得的膜层兼具阳极氧化膜及陶瓷膜的性能,拓宽了轻金属材料的使用领域。目前国内外对于PEO膜层性能做了大量的研究工作,而PEO技术的重要特征之一是其击穿放电现象,这是PEO的基础问题。鉴于此,本论文以AZ31镁合金为工作电极,围绕介质阻挡层特性对击穿放电的影响、电解液离子性质对等离子体场放电火花特性的影响、PEO膜层击穿放电机理和阴阳离子对PEO过程贡献等方面进行研究。(1)以第二三周期元素组成的含氧酸盐碱性电解液为对象：研究电解液中阴离子性质对介质阻挡层组分性质的影响；对介质阻挡层的致密性或绝缘性做了定性评价；通过放电前后的电流密度来验证介质阻挡层的质量好坏,研究生成的介质阻挡层的质量对击穿放电及后续膜层成膜能力的影响。(2)选取氟锆酸盐系列酸性电解液为研究对象,研究电解液阴离子的稳定性对放电特性及膜层性能的影响。研究表明：(1)阴离子通过自身形成氧化物成膜或者与基体离子结合形成化合物成膜而形成介质阻挡层。介质阻挡层组分性质越稳定、介质阻挡层越致密,则介质阻挡层质量越好,在稳定放电阶段平衡电流越小。(2)介质阻挡层的形成以及膜层击穿放电之后电解液中阴离子的后续成膜是PEO过程顺利进行的两个必要条件。(3)膜层组分溶度积<10-10时,生成的介质阻挡层较稳定且质量好,PEO过程放电特性较好,放电稳定,放电平衡电流密度约为15-40 mA／cm2。膜层组分溶度积>10-10时,生成的介质阻挡层质量较差,放电不稳定,放电平衡电流密度约为300-700 mA／cm2。膜层组分性质可溶时,不能放电。(4)添加剂可以改善氟锆酸盐系列电解液阴离子的稳定性,继而改善放电性能及膜层各方面性能,膜层耐腐蚀性能相比于基体而言提高了3-4个数量级。利用光发射光谱对上述电解液在PEO过程的不同阶段进行了研究：(1)分析在放电之前电极表面的能量状态及物种分布。研究放电之后等离子体场放电火花的特性(2)分析阴阳离子对等离子体成分及PEO过程的贡献。(3)对等离子体场内活性物种的来源、能级跃迁过程及归属进行分析。(4)探讨了PEO过程击穿放电、生长过程的理论模型及等离子体场内传热及物种传递的理论模型。(5)在特定Na2SiO3电解液中对PEO生长过程进行研究,验证PEO膜层生长模型及物质传递过程模型。研究表明：(1)光谱在PEO过程不同阶段呈现不同特性,阳极氧化阶段光谱为钝峰,由热致辐射引起发光；过渡阶段气体鞘层被离子化而发光,随后气体鞘层被击穿,接着发生介质阻挡层的击穿；在放电阶段,等离子体场内放电火花活性物种主要由阳离子和来自H20分解的气体及其元素组成。在放电阶段,电解液中离子的移动,主要是由于等离子体场作用产生的离子加速和由于气泡破裂所产生的离子气泡的吸附和迁移。(2)阴离子对等离子体场放电火花活性物种组成无影响,但可以形成氧化物而影响膜层组分；阳离子可为等离子体场提供高温能量环境。(3)活性物种被激发顺序只与等离子体场能量状态有关,与浓度无关。单个活性物种浓度在PEO过程随时间的变化与电极表面的能量状态有关。等离子体场内各活性物种经历了激发、解离和离子化的过程。等离子体场内电子温度可达103-104K。(4)在Na2SiO3电解液中的膜层生长特性较好地验证了PEO膜层生长过程模型及物质传递过程模型。更多还原

【Abstract】 The shortage of energy and mineral resources force people to improve the materials and energy’s using efficiency. Plasma electrolytic oxidation (PEO) technology provides a new platform for surface modification of light-metallic materials. The films formed by PEO combine the performance of both anodic oxide films and ceramic films, which broadens the application field of light-metallic materials. Many researches related to the PEO films’ properties have been down at home and abroad. The breakdown discharge phenomenon, which is the basic problem of PEO, is one of the most important characteristics of the PEO technology. Based on this, the AZ31 magnesium alloy was used as the working electrode. The influence of the dielectric barrier layer’s (DBL) characteristics on the breakdown discharge, the influence of the electrolytes’ ion nature on the characteristics of the micro-discharge in the plasma field, the mechanism of the breakdown discharge and the contribution of cations and anions to the PEO process were investigated.(1) the oxygen-containing alkaline electrolytes composed by the second and third cycle elements were the objects of the study:the influence of anion nature on the properties of the DBL’s composition was investigated. The compactness and insulation of the DBL were evaluated qualitatively. The current densitis before and after the discharge were used to verify the quality of the DBL. The influence of the quality of the DBL on the breakdown discharge and follow-up the film forming ability was studied. (2) fluorozirconate series acidic electrolytes were selected as the research objects; the influence of the electrolyte anions’ stability on the discharge characteristics and the films’performance were investigated.It was found that:(1) the anions formed the DBL through their own by forming the oxide or combining with the substrate ions to form the compounds. The more stable the DBL’s composition, the more compact the DBL, the better the quality of the DBL, thus the stable equilibrium current density could be got at the stable discharge stage. (2) DBL’s formation and the anions’s film-forming after breakdown discharge were two necessary conditions for the PEO process been carried out smoothly. (3) if the solubility product of the film composition is smaller than 10-10, the formed DBL exhibits good stability and quality, the discharge characteristics are better with stable micro-discharges and the equilibrium current density is about 15-40 mA/cm2; if the solubility product of the film composition is larger than 10-10, the formed DBL has a poor quality with unstable micro-discharges, the equilibrium current density is about 300-700 mA/cm2; if the film composition is soluble, the discharge can not happen. (4) the additives could improve the stability of the anions in the fluorozirconate series electrolytes, followed by improving the discharge quality and the performance of the films. The corrosion resistance of the films increased 3-4 orders of magnitude compared to the substrate.The optical emission spectroscopy(OES) was used to investigate the different stage characteristics during the PEO process:(1) the energy status on the electrode surface before discharge and the reasons for the formation of species’distribution were studied. The characteristics of micro-discharge in the plasma filed were also analyzed. (2) the contribution of cations and anions to the plasma’s composition and the PEO process were analyzed. (3) the source, energy level transition process and attribution of active species in the plasma field were investigated. (4) the breakdown discharge and growth mechanism during the PEO process, the heat and species’transfer mechanism in the plasma field were discussed. (5) the PEO growth process in the particular Na2SiO3 electrolyte was studied to verify the PEO film growth model and the species transfer process model.The results indicated that:(1) the spectra showed different characteristics at different PEO stages. At the anodic oxidation stage, the spectra has blunt peak caused by heat radiation which resulted in the luminescence; at the transition stage, the gas envelop was ionized and emitting light, followed by the breakdown of the gas envelop and DBL; at the discharge stage, the plasma active species were mainly composed of metal cations, the gases and its elements produced by water decomposition. The transfer of the electrolyte ions was mainly due to the ion acceleration, the adsorption and migration of ion bubbles, which resulted from the plasma field and the rupture of bubbles, respectively. (2) the anions in the electrolyte had little influence on the composition of the plasma active species, but they could affect the film composition by forming oxide; the cations could provide high energy environment for the plasma field. (3) the excited order of the plasma active species depended on the energy that the orbit transition of the species needed. It was not related to the ion’s concentration. The concentration variation of each special active species with time during the PEO process was related to the energy status on the electrode surface. The active species in the plasma field were found to undergo dissociation, ionization and excitation. The electron temperature of the plasma field was between 6×103 and 3×104 K. (4) the PEO growth process in the Na2SiO3 electrolyte verify the PEO film growth model and the species transfer process model well.更多还原