- 學位論文
三價鉻電鍍膜於900℃之抗高溫氧化及耐腐蝕性質研究
High-temperature oxidation at 900℃ and corrosion resistance of Cr-based coating electroplated in trivalent chromium baths
摘要
本實驗研究三價鉻鍍膜之抗高溫氧化性質及耐蝕性。抗高溫氧化實驗，鍍膜於22MnB5先進高強度鋼，並藉由SEM、EDS、XRD、TEM、TGA及AES檢測高溫氧化前後之膜層的改變。結果顯示，有機硫化物的添加，能將含有殘留應力之非晶Cr-C膜層轉變為結晶的Cr-C-S膜層，但使電流效率大幅降低，膜層厚度有明顯變薄的趨勢。高溫氧化後之結果顯示，長時間電鍍之Cr-C-S膜層，因膨脹係數與基材有所差異，導致應力的產生，而應力會集中於膜層微裂紋的位置，最終造成膜層由內部裂開。長時間電鍍之Cr-C膜層，因含有許多粗大的裂紋，因此無法有效抑制高溫氧化。相反的，短時間電鍍Cr-C膜層，其膜層厚度約為1 μm，並伴隨著細小的裂紋，此裂紋能有效釋放熱膨脹所造成的應力，且細小的裂紋會於高溫氧化期間被氧化鉻所填滿，進而抵抗高溫氧化的侵襲。 耐蝕性實驗，是將三價鉻電鍍於SS304不鏽鋼上，並使用SEM、EDS、XRD、PDP及EIS檢測膜層性質。結果顯示出，Cr-C膜層之耐蝕性不佳，因此無法用於雙極板之保護膜層。相反的，Cr-C-S膜層之耐蝕性於0.5 M硫酸之腐蝕溶液中，腐蝕電流密度皆達到10-7 A/cm2級數，並以脈衝電鍍50 ASD Cr-C-S膜層有最佳耐蝕性，達到1.61 x 10-7 A/cm2。介電阻抗結果顯示，以50 ASD電鍍之Cr-C-S膜層，於壓力達到120 N以上時，阻抗值皆小於30 mΩ•cm2。綜合耐蝕性及介電阻抗結果得知，以脈衝電鍍50 ASD Cr-C-S膜層，不僅擁有極佳耐蝕性，也展現出低的介面阻抗值，因此較適用於雙極板之保護鍍膜。
並列摘要
This investigation studies the high temperature oxidation resistance and corrosion resistance of trivalent chromium coatings. High temperature oxidation resistance test, coating on 22MnB5 advanced high strength steel, and analyze the changes of the film before and after high temperature oxidation by SEM, EDS, XRD, TEM, TGA and AES. The results showed that the addition of organic sulfide could change the amorphous Cr-C film containing residual stress to crystalline Cr-C-S film, but the current efficiency was significantly reduced and the film thickness tended to be significantly thinner. The result of high temperature oxidation shows that the Cr-C-S layer plated for a long time has a different expansion coefficient from that of the substrate, resulting in the generation of stress, which is concentrated in the location of microcracks in the layer and eventually causes the layer to crack from the inside. The Cr-C film that is electroplated for a long time contains many coarse cracks, so it cannot effectively inhibit high-temperature oxidation. On the contrary, the short-time electroplating Cr-C film has a thickness of about 1 μm and is accompanied by small cracks. This crack can effectively release the stress caused by thermal expansion, and the small cracks will be filled up with oxide during high temperature oxidation. The corrosion resistance test is to electroplate trivalent chromium on SS304 stainless steel, and use SEM, EDS, XRD, PDP and EIS to analyze the properties of the film. The results show that the corrosion resistance of Cr-C film is poor, so it cannot be used for protective film of bipolar plate. On the contrary, the corrosion resistance of Cr-C-S films with 0.5 M sulfuric acid as corrosion solution, the corrosion current density is 10-7 A/cm2, and 50 ASD Cr-C-S film has the best corrosion resistance by pulse electroplating which is 1.61 x 10-7 A/cm2. The interfacial contact resistance results show that the Cr-C-S film electroplated with 50 ASD, when the pressure reaches 120 N or more, the resistance is less than 30 mΩ•cm2. Comprehensive corrosion resistance and interfacial contact resistance results show that pulse plating 50 ASD Cr-C-S film not only has excellent corrosion resistance, but also exhibits low interfacial contact resistance, so it is more suitable for protective coating of bipolar plates.
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