鐵鈷鎳基等莫耳合金之高溫硫化行為研究

High-temperature Sulfidation of FeCoNi-base Equal-molar Alloys

本研究探討FeCoNi(H3)、FeCoNiCr(H4Cr)及FeCoNiCrCu(H5Cr)三種鐵鈷鎳基等莫耳合金於500～800℃分別在兩種H2/H2S/Ar混合氣氛(含80/20/0 17/2/81vol.%)下之高溫硫化行為研究。而本實驗之等莫耳合金依等莫耳配比經真空電弧熔煉而得，包含FeCoNi、FeCoNiCr及FeCoNiCrCu等三種（以下分別簡稱H3、H4Cr及H5Cr），切好之試片在其一端以放電加工機打孔以利實驗時試片之掛取，所有試片皆以砂紙研磨至800號後，再分別置於丙酮及酒精中以超音波震盪機反覆清洗並吹乾備用。研究結果顯示三種等莫耳合金的腐蝕動力學皆遵守拋物線型定律，且腐蝕速率隨溫度的上升而增加，其中H4Cr及H5Cr合金在部分溫度呈現兩動力學表現，H3則皆為一段式。而腐蝕生成物方面H3合金生成單一(Ni,Co,Fe)9S8腐蝕層；H4Cr則在外層生成(Ni,Co,Fe)9S8，內層則為Cr2S3及NiCr2S4；而H5Cr合金硫化後在外層生成(Ni,Co,Fe)9S8及Cu5FeS4，內層則為CuCrS2；整體而言，等莫耳合金在高硫分壓下(80/20/0)的硫化速率皆較低硫分壓下快。

The high-temperature sulfidation of FeCoNi-base equal molar alloys (EMA's) containing FeCoNi(H3), FeCoNiCr(H4Cr), and FeCoNiCrCu(H5Cr) has been studied over the temperature range 500~800℃ in H2/H2S/Ar gas mixtures containing two different ratios of 80/20/0 and 17/2/81(in vol.%). The results indicated that the sulfidation kinetics of all the alloys followed the parabolic rate law, and the corrosion rate constants increased with increasing temperature. The scales formed in the H2/H2S/Ar gas mixtures were heterophasic and composition-dependent, consisting of single (Ni,Co,Fe)9S8 layer for FeCoNi. Duplex scales formed on the quaternary alloy consisted of (Ni,Co,Fe)9S8 in the outer layer, and Cr2S3/Cr3S4, NiCr2S4 in the inner layer. The scales formed on the quinary alloy consisted of (Ni,Co,Fe)9S8, Cu5FeS4 in the outer layer and CuCrS2 in the inner layer. In general, all the EMA's existed faster sulfidation rates in the higher sulfur partial-pressure (80/20/0 case).