Abstract In the present studies, the Al coating deposited by arc thermal spraying process was treated with different concentrations of ammonium phosphate mono basic ((NH4)H2PO4) and caesium nitrate (CsNO3) to improve the morphology and corrosion characteristics of the coating. As coated (AC) sample exhibits pores and defects onto the surface but once the treatment was carried out, the coating shows reduction in porosity as observed by scanning electron microscopy (SEM). The treated coatings contain caesium aluminum oxide (CAO: Cs2Al2O3) and ammonium aluminum hydrogen phosphate hydrate (AHP: (NH4)3Al5H6(PO4)8.18H2O) as composite oxides identified by X-ray diffraction (XRD). Electrochemical impedance spectroscopy (EIS) results reveal that as the exposure periods are increased, the resistance to coating/treatment (Rc/t) and charge transfer resistance (Rct) of AC and 0.5 M NH4H2PO4 and 0.0025 M CsNO3 (CN2) are increased with exposure periods in artificial ocean water solution. The improvement in total impedance values at 0.01 Hz of AC sample is attributed to formation of corrosion products which fill the pores/defects of coating while CN2 sample owing to the treatment film i.e. AHP and CAO and transformation of AHP into stable form. As the amount of NH4H2PO4 and CsNO3 is increased up to 1 M and 0.005 M i.e. CN3, the AHP film dissolved and enhances the corrosion reaction. Thus, cracking is observed in corrosion products. The enhancement in corrosion resistance of CN2 sample is attributed to the formation of α-Al(OH)3 (bayerite) and Al3(PO4)2(OH)3(H2O)5 (Aluminium hydroxide phosphate hydrate: AHPH) in greater amount as corrosion products. These corrosion products of CN2 sample are stable, sparingly soluble and protective.

中文翻译：

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电弧热喷涂法沉积磷酸铵和硝酸铯处理的铝涂层的形貌和腐蚀研究

摘要 在目前的研究中，采用不同浓度的磷酸铵一碱((NH4)H2PO4)和硝酸铯(CsNO3)对电弧热喷涂工艺沉积的Al涂层进行处理，以改善涂层的形貌和腐蚀特性。由于涂层 (AC) 样品在表面上显示出孔隙和缺陷，但一旦进行处理，涂层显示出通过扫描电子显微镜 (SEM) 观察到的孔隙率降低。处理过的涂层含有氧化铝铯（CAO：Cs2Al2O3）和磷酸氢铵铝水合物（AHP：（NH4）3Al5H6（PO4）8.18H2O）作为通过X射线衍射（XRD）鉴定的复合氧化物。电化学阻抗谱 (EIS) 结果表明，随着暴露时间的增加，AC 和 0.5 M NH4H2PO4 和 0.0025 M CsNO3 (CN2) 的涂层/处理电阻 (Rc/t) 和电荷转移电阻 (Rct) 随暴露在人工海洋水溶液中的时间而增加。AC 样品在 0.01 Hz 下总阻抗值的改善归因于腐蚀产物的形成，这些腐蚀产物填充了涂层的孔隙/缺陷，而 CN2 样品由于处理膜，即 AHP 和 CAO，以及 AHP 转化为稳定形式。随着NH4H2PO4 和CsNO3 的量增加到1 M 和0.005 M，即CN3，AHP 膜溶解并增强了腐蚀反应。因此，在腐蚀产物中观察到裂纹。CN2 样品耐腐蚀性的增强归因于 α-Al(OH)3（三羟铝石）和 Al3(PO4)2(OH)3(H2O)5（磷酸氢氧化铝水合物）的形成：AHPH) 作为腐蚀产物的量更大。CN2 样品的这些腐蚀产物是稳定的、微溶的和保护性的。