超音波輔助後超臨界二氧化碳電鍍鎳鍍層之影響探討

後超臨界二氧化碳電鍍製程是將超臨界態的二氧化碳與鍍液混合後卸壓至常壓下，利用過飽和二氧化碳回復成氣態時所形成的微小氣泡混合於鍍液中，此氣泡微胞附著於電鍍基材表面，使附著部分絕緣，氣泡成長後離開基材表面，達到類似於脈衝電鍍的效果。由於常壓下鍍液中的二氧化碳氣泡會隨時間逐漸增大並散逸掉，因此藉由超音波激發微小二氧化碳氣泡並利用其增加類似脈衝電鍍之影響而得到更佳的鍍層品質。本實驗執行後超臨界電鍍，並將超音波喇叭錐置於鍍液中進行振動。電鍍過程中，藉由磁石攪拌、超音波攪拌與複合攪拌(磁石+超音波)三種不同攪拌方式以及超音波振動子之控制電壓，找出較佳之鍍層表面形貌與機械性質。實驗結果發現複合攪拌在電流密度為40 A/dm^2，可以得到較小的晶粒大小，表面粗糙度較平整，較薄的鍍層硬度提高至320 Hv以上而一般電鍍為160 Hv到300 Hv，但會產生較高的鍍層內應力約320 MPa；而控制電壓30-50 V對於後超臨界鍍液中二氧化碳微泡之激發狀態，隨著電壓的提高有逐漸劇烈的趨勢，在40 V和50 V製備的鍍層表面有鎳碎屑鍍散佈，對於表面粗糙鍍之改善有限，所得的晶粒大小也較大，但鍍層硬度值之變化較趨緩，過多的二氧化碳微泡容易造成鍍層包覆氣泡而內應力提高。

關鍵字

超音波；電鍍鎳；後超臨界電鍍

並列摘要

The process of post-supercritical CO2 electroplating uses the electrolyte solution left after being exposed to supercritical CO2 and released to atmospheric pressure. It utilizes the microbubbles that form when oversaturated CO2 in the electrolyte returns to gaseous state and adhere to the surface of the cathode; the adhered surface becomes insulated but after a certain time the bubbles will depart from the surface, which gives the similar effect of pulsed electroplating. Under atmospheric pressure the CO2 bubbles will gradually diffuse. Therefore, with the introduction of ultrasound we can excite the CO2 microbubbles to achieve an electroplated surface of even higher quality. For this experiment we implement post-supercritical electroplating, and place an ultrasonic horn in the electroplating solution to induce vibrations. During the electroplating process, we will use three different modes of agitation: magnetic stirrer agitation, ultrasonic agitation and a combined mode (magnetic + ultrasonic) and we will also control the voltage given to the ultrasonic agitator, in order to obtain an optimal surface morphology and mechanical properties for the electroplated surface. It is found that the combined agitation mode at a current density of 40 A/dm^2 can achieve the smallest grain size, a lower surface roughness, and produce a electroplated Ni layer that can achieve hardness of 320 Hv, much higher when compared with traditional methods, which achieve values in the range of 160 to 300 Hv. However, at the same time it will develop a higher internal stress of 320 MPa. As the excitation to the microbubbles in the post-supercritical CO2 electroplating solution is provided by a controlled voltage of 30 to 50 V, it is observed that when voltage increases there is gradually a more bubble agitation tendency. When the voltage is 40 V or 50 V, there is a distribution of nickel debris found all around the prepared electroplated surface. Thus, there is limited improvement to the surface roughness, and even bigger size grains, the hardness of the electroplated surface is gradually reducing as well. The increased number of microbubbles in the electrolyte makes it easier for some to be trapped in the surface and increase the internal stress. Therefore, it is proven through this experiment that the application of ultrasonic vibration in post-supercritical CO2 electroplating solution can improve the quality of the electroplating process.

並列關鍵字

Ultrasonic ； Nickel Electroplated ； Post Supercritical CO2 Process

參考文獻

[12] 陳黼澤，替代六價鉻製程研究，博士論文，國立台灣大學工學院機械工程學系，台北，2009。

[2] Perusich, S. A., Alkire, R. C., “Ultrasonically Induced Cavitation Studies of Electrochemical Passivity and Transport Mechanisms,” Electrochemical Society, vol. 138, no. 3, 1991, pp. 700-707.

[3] Hyde, M. E., Compton, R. G., “How Ultrasound Influences the Electrodeposition of Metals,” Electroanalytical Chemistry, vol. 531, no. 6, 2002, pp. 19-24.

[4] Walker, C. T., Walker, R., “Effect of Ultrasonic Agitation on Some Properties of Electrodeposits,” Electrodeposition and Surface Treatment, vol. 1, no. 6, 1973, pp. 457-469.

[5] Yoshida, H., Sone, M., Mizushima, A., Abe, K., Tao, X. T., Ichihara, S., Miyata, S., “Electroplating of Nanostructured Nickel in Emulsion of Supercritical Carbon Dioxide in Electrolyte Solution,” Chemistry Letters, vol. 11, 2002, pp. 1086.

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超音波輔助後超臨界二氧化碳電鍍鎳鍍層之影響探討

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