鎳鐵合金微柱（Ni41Fe59、Ni55Fe45、Ni71Fe29及Ni86Fe14）之製作及其在1 M KOH及0.5 M NaCl混合溶液中之電化學行為

On the fabrication of nickel-iron alloy microcolumns (Ni41Fe59, Ni55Fe45, Ni71Fe29, and Ni86Fe14) and their electrochemical behavior in a mixing solution of 1 M KOH and 0.5 M NaCl

本研究以影像監控微陽極導引電鍍法（Micro anode-guided electroplating, MAGE），電鍍出表面平滑緻密的鎳鐵合金微柱，並研究其在含0.5 M NaCl與1 M KOH鹼性溶液中之腐蝕特性。在MAGE製程中，微陽極為白金圓形電極，陰極為銅柱，浸泡在含鎳、鐵之硫酸鹽鍍浴中（其中離子濃度比設定在[Ni2+]:[ Fe2+] = 10），陰極電位控制在-1.10 V （vs. Ag/AgCl, 3 M KCl），兩極間距則分別為45、60、75、90μm進行定電位析鍍。SEM之結果顯示:當兩極間距在45、60、75μm時，析鍍所得微柱之平均柱徑為67 ~ 92μm，所得微柱呈現圓柱形且柱徑均勻；當間距在90μm時，所得微柱呈現圓錐體形貌。鎳鐵合金微柱之組成由EDS分析，當兩極間距增加（由45逐漸增至90μm），微柱中之鎳含量隨之增高（依序為41、55、71增至86 at. %），並將試片標示為：Ni41Fe59、Ni55Fe45、Ni71Fe29及Ni86Fe14。XRD分析顯示：兩極間距較大時（如在75及90μm）電鍍所得之鎳鐵微柱（Ni71Fe29及Ni86Fe14）為具有fcc結構之富鎳合金，在間距縮小時，合金中之鐵濃度逐漸上升，此時圖譜中之鎳主峰因合金化逐漸往低角度偏移，峰值強度也逐漸下降。鎳鐵合金微柱浸泡在含0.5 M NaCl之1 M KOH鹼性溶液中時，其電化學行為隨合金組成顯示如下：鐵含量由14 at. %增加至59 at. %，開路電位由0.18 V下降至-0.10 V （vs. Ag/AgCl, 3 M KCl）。塔弗曲線之結果：鐵含量在14 at.%時具有最低的腐蝕電流密度9.86μA/cm2，當含鐵量增加至59at.%則表現出最高的腐蝕電流密度為497μA/cm2，結果顯示鹼性電解液中含氯離子及鎳鐵微柱中鐵含量增加將加劇鎳鐵合金之腐蝕速率。

Microanode-guided electroplating (MAGE) was used to fabricate Ni-Fe alloy microcolumns in this work. The corrosion behavior of the alloy microcolumns in the alkaline saline solutions (a mixture of 0.5 M NaCl and 1 M KOH) were then investigated. The MAGE process was conducted in a sulfate bath wherein [Ni2+]/[Fe2+] fixed at 10/1. A constant potential of -1.10 V (vs. Ag/AgCl, 3 M KCl) was applied and the gap between the Ptmicro anode and Cu-cathode was varied at 45, 60, 75, and 90 μm. Cylindrical microcolumns in a uniform diameter of 67 ~ 92 μm were fabricated while the electrode gap was controlled at 45, 60, and 75 μm. On the other hand, conical ones were formed as the gap was fixed at 90 μm. Through analysis of EDS, the chemical composition of microcolumns (i.e., Ni41Fe59, Ni55Fe45, Ni71Fe29, and Ni86Fe14) varies depending upon the change of electrode gaps. Evidently, the Ni-content (at. %) increases from 41, 55, 71 to 86 with increasing the gap from 45 to 90 μm. XRD spectra of the columns revealed that Ni-enriched microcolumns (Ni71Fe29 and Ni86Fe14) were in fcc structure. The position of the major Ni-peak shifts to lower angles and its intensity decreases as the Fecontent increases. The corrosion behavior of Ni-Fe microcolumns in an alkaline saline solution (1.0 M KOH + 0.5 M NaCl) was studied and the results are cited below: the OCP of the microcolumns moves more negatively from 0.18 V to -0.10 V (vs. Ag/AgCl, 3 M KCl) with increasing the Fe-content from 14 at. % to 59 at. %. Resulting of Tafel polarization, the Ni86Fe14 microcolumn demonstrates the lowest corrosion current density (at 9.86 μA/cm2) as compared to Ni41Fe59 (whose corrosion current density is at 497 μA/cm2). Apparently, the Nienriched Ni-Fe microcolumn (containing less Fe-content) fabricated by MAGE is more resistant to corrosion in the alkaline saline solution.