磁场作用下镁合金纳米颗粒增强转化膜形成过程的同步辐射实时成像与扫描微电极原位监测

Chemical conversion coating technique is widely used in magnesium alloy protective method，however, there are a large number of microcrack in the magnesium alloy conversion coating obtained by current technology, which makes the corrosion resistance of conversion coating is not perfect and its difficult to meet the need of practical engineering. Recently, the applicant added alumina nanoparticles in phosphate solution to accelerate the conversion coating nucleation and growth and controlled particle distribution in solution by external magnetic fields, which produced crack free alumina nano particle reinforced conversion coating. Whereas，the solution becomes opaque when nanopartcle is added to the solution,which is not conducive to the real time imaging of particle behavior and conversion growth. The varity, low concentration，evanescence of reaction ion in solution obstructed in situ monitoring of reaction ion at magnesium alloy/solution interface.Therefore, the formation process of nano particle reinforced conversion coating under magnetic field is unknown.In this project, the characteristics nanoparticle migration at magnesium alloy/solution interface and the growth of conversion coating under magnetic field will be observed in real time by synchrotron radiation technique. The reaction ion transportation rule at magnesium alloy/solution interface will be monitored in real time by scanning microelectrode.These studies may provide insight into the conversion coating growth without hypothesis, which can elucidate the formation mechanism of nano alumina particle reinforced conversion coating on magnesium alloy under magnetic field. Moreover, those results can provide a theoretical basis for new magnesium alloy conversion coatings design and production.

化学转化膜技术是广泛应用于镁合金的防护方法，但当前技术制备的转化膜存在大量微裂纹，耐蚀性能不理想，难以满足实际工程需要。近期，申请人在磷酸盐溶液中添加氧化铝纳米颗粒促进镁合金转化膜形核与生长，加磁场调控氧化铝纳米颗粒分布，制备了无微裂纹缺陷的氧化铝纳米颗粒增强转化膜。然而，添加纳米颗粒降低了溶液透明特性，制约了颗粒行为和转化膜生长的实时观察；反应离子的多样性、微弱性和瞬时性阻碍了镁合金/溶液界面反应离子行为的原位监测；因而，磁场作用下纳米颗粒增强转化膜形成过程的所知甚少。本项目拟采用同步辐射成像技术，实时观察磁场作用下镁合金／溶液界面纳米颗粒的迁移特点和转化膜形核及生长过程；采用扫描微电极实时监测磁场作用下镁合金／溶液界面反应离子的传输规律，为转化膜生长过程提供直接无假设的实验结果；阐明磁场作用下镁合金氧化铝纳米颗粒增强转化膜的形成机制；为新型镁合金转化膜的设计与制备提供理论依据。

现有技术制备的转化膜存在大量微缺陷限制其在工程领域的广泛应用，在成功研发同步辐射成像实验装置的基础上，本项目施加磁场作用于化学转化过程, 采用同步辐射成像技术实时观察磁场作用下镁合金／溶液界面纳米颗粒的迁移特点和转化膜形核及生长过程；采用扫描微电极实时监测磁场作用下镁合金／溶液界面反应离子的传输规律。研究表明，磁场将导致镁合金/溶液界面反应离子传输过程呈现弱磁流体效应、磁流体效应增强和强磁流体效应的阶段特征；磁流体效应能抑制处理液中米氧化铝纳米颗粒的团聚，在转化膜生长过程中氧化铝颗粒被捕获,可以有效促进磷酸盐转化膜的形核；此外，磁场能有效调节镁合金/溶液界面反应离子分布，改变镁合金化学转化膜的形成过程，从而形成致密的转化膜。结合模拟磁场与晶界结构对反应离子行为的耦合作用，揭示了磁场作用下镁合金/溶液界面反应离子分布规律，丰富了合金/溶液界面电化学理论。根据磁场对镁合金化学转化膜形成的影响机制，成功研发了基于磁场调控技术制备的镁合金磷酸盐/氮化硅复合膜、磷酸盐/脂肪酸盐复合膜等新型的转化膜技术，有效促进了新型化学转化膜可控制备技术的发展，为转化膜技术的复合功能化开辟了新的领域。