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標題: | AZ31鎂合金檸檬酸鹽化成處理 Citrate Conversion Coating on AZ31 Magnesium Alloys |
作者: | Yu-Ren Chu 褚喻仁 |
指導教授: | 林招松(Chao-Sung Lin) |
關鍵字: | 鎂合金,檸檬酸鹽,聚醯胺醯亞胺,化成處理,電化學交流阻抗分析, Magnesium,Citrate,Polyamide-imide,Conversion Coating,EIS, |
出版年 : | 2015 |
學位: | 博士 |
摘要: | 鎂合金具有良好的比強度、比剛性與生物相容性,然而當暴露於腐蝕環境時,鎂合金的腐蝕速率極高,大大限制了鎂合金的工程應用。本研究以檸檬酸鹽為主要反應物種,嘗試建立一可應用於鎂合金之無鉻環保鈍化系統,以調控鎂合金之腐蝕速率及腐蝕行為。實驗包含三個部分:第一部分包含在水溶液與甘油溶液系統中以輥塗製程進行檸檬酸鹽化成處理,藉此探討鎂合金上檸檬酸鹽化成皮膜之成長機制;第二部分藉由添加銅離子與硫酸根離子,探討不同添加物在水溶液與甘油溶液系統中對檸檬酸鹽化成皮膜之影響;第三部份則是透過一後處理製程,在檸檬酸鹽化成皮膜上披覆一以檸檬酸基聚醯胺醯亞胺為主結構之高分子,以嘗試更進一步提升其抗蝕能力。
實驗發現,不論是水溶液或甘油溶液,檸檬酸鹽化成處理可以在AZ31鎂合金表面形成一層具有獨特微結構特徵的化成皮膜,且此化成皮膜可以降低AZ31鎂合金於動電位極化曲線中的腐蝕電流,並提高電化學交流阻抗分析中的阻抗值。在添加物的方面,硫酸根有抑制檸檬酸鹽化成皮膜成膜的傾向;在甘油溶液系統中添加銅離子時,可以觀察到富含銅的顆粒在鎂合金表面析出,且動電位極化曲線中的腐蝕電位也會隨之提高,而在水溶液中添加銅離子時,則會析出銅氧化物顆粒,造成動電位極化曲線中的腐蝕電流大幅提升。在電化學交流阻抗測試評估中,檸檬酸鹽化成處理可將AZ31鎂合金之阻抗值自5,000 Ωcm2左右提升至約10,000 Ωcm2, 當再披覆檸檬酸基聚醯胺醯亞胺之高分子作為後處理時,更可進一步提升至約20,000 Ωcm2。 Magnesium alloys are known for their high specific strength, high specific stiffness, and good biocompatibility. However, their engineering applications are still limited, due to their extremely high corrosion rate when exposed in corrosive environment. In order to develop an environmental friendly passivation process for magnesium alloys, a citrate conversion coating system has been developed in this study. To investigate the formation mechanism of the citrate conversion coating on AZ31 magnesium alloy, the conversion coating process is performed in both aqueous and glycerin solutions. As the result, citrate conversion coatings formed in aqueous and glycerin solutions are similar in both microstructure and corrosion properties, which includes the reduced corrosion current density in potentiodynamic polarization and the elevated total impedance in electrochemical impedance measurement. Despite the similarity of pure citrate conversion coating, the effect of cupric ion shows significant difference in aqueous and glycerine solutions. In glycerin solution, the copper-rich clusters are formed on the citrate conversion coating with cupric ion added, and an apparently higher corrosion potential in potentiodynamic polarization can be observed. On the other hand, oxide particles are formed with cupric added in aqueous solution, which leads to an intense increase in corrosion current density. A post treatment using a citrate-based polyamide-imide (PAI) is also proposed in this study. It was found that the impedance of the AZ31 in EIS increases from around 5,000 to 10,000 Ωcm2 after citrate-based conversion coating, and can be further elevated to near 20,000 Ωcm2 with the PAI post treatment. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/4443 |
全文授權: | 同意授權(全球公開) |
顯示於系所單位: | 材料科學與工程學系 |
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