苯乙炔衍生物碳鋼在鹽酸中酸洗之腐蝕抑制行為

Corrosion Inhibition of Carbon Steels by Phenylacetylene Derivatives in Hydrochloric Acid

本文在探討碳鋼於90℃之2 M鹽酸酸洗液中，以苯乙炔衍生物為腐蝕抑制劑之可行性。苯乙炔衍生物包括甲苯乙炔（p-Tolyacetylene, PEC）、氟苯乙炔（4-fluorophenylacetylene, PEF）、氯苯乙炔（4-chlorophenylacetylene, PECl）、溴苯乙炔（4-bromo phenylacetylene, PEBr）等4種。採用重量損失法、線性極化、Tafel極化、交流阻抗等方法進行腐蝕評估，結果均顯示：苯乙炔衍生物之腐蝕抑制效率（%）依序為：PEBr （82%） > PECl （78%） > PEF （20%） > PEC（9%）。隨著酸液溫度上升，抑制劑之抑制效率下降。由Tafel極化法分析顯示：PECl、PEBr均屬於陰極型抑制劑，其餘三種則屬於混合型抑制劑。此類抑制劑在鋼鐵上呈現Langmuir等溫吸附模。根據Arrhenius作圖法求出：鋼鐵遭受腐蝕之活化能為243.8 kJ/mol，添加抑制劑後，活化能分別下降為240.4 （PEC） > 215.8 （PEF） > 174.1 （PECl） > 167.1 （PEBr）。
XPS分析C 1s鍵結能顯示：C-C、C-H的峰值面積增加，顯示鋼材表面吸附抑制劑量增加。分析Fe 2p 3/2之鍵結能顯示：FeCl2、FeCl3的峰值面積減少，顯示鋼材表面因吸附抑制劑而減少遭受氯離子之攻擊。採用電子密度泛函理論商用軟體B3LYP 6-311G（d）所做之模擬分析顯示：抑制劑之最高佔據軌道能量電子軌域（HOMO）以PEBr為最大值，最易提供電子給予鋼材以便形成鍵結，達最高抑制效果。苯乙炔衍生物中，在苯環上與C≣C對位（Para-position），由鹵素（-Br, -Cl, -F）或甲基（-CH3）取代，影響抑制劑的電子密度影響極大，因而導致其腐蝕抑制效率之差異。

Corrosion inhibition of carbon steels in 2 M hydrochloric acid at 90 ℃ by derivatives of phenylacetylene, such as p-Tolyacetylene (PEC), 4-fluorophenylacetylene (PEF), 4- chlorophenylacetylene (PECl) and 4-bromophenylacetylene (PEBr) was studied. According to the corrosion rate measurement of the steel estimated by weight loss, linear polarization resistance, Tafel extrapolation and electrochemical impedance spectroscopy, the inhibition efficiencies of these derivatives were in the order of PEBr (82%) > PECl (78%) > PEF (20%) > PEC (9%). The efficiency decreased with increasing environmental temperature. Due to negative shifts in corrosion potential, PECl and PEBr were identified as cathodic inhibitors. On the other hand, with no significant changes in corrosion potential, the others belonged to mixed type inhibitors. The Langmuir’s adsorption isotherm was followed in all systems. The activation energies (kJ/mol) were estimated via Arrhenius plots, and they decreased in the order of 243.8 (without inhibitors) > 240.4 (PEC) > 215.8 (PEF) > 174.1 (PECl) > 167.1 (PEBr). Accordingly, a more efficient inhibitor exhibited a lower activation energy.
Analyses of XPS on the steel depicted an increase in peak area for both C–H and C–C peaks but a decrease for both FeCl2 and FeCl3 peaks. This reflected that a larger amount of adsorption of inhibitors onto the surface tended to deter the corrosion rate of the steel. Simulations via the software B3LYP 6-311G(d), based on quantum mechanics, showed that the inhibitor showing a higher efficiency was ascribed to a stronger adsorption onto the steel. The higher electron density on the highest occupied molecular orbital (HOMO) of the inhibitor tended to form a stronger donating bond with the unfilled d-orbit of iron. The inhibitor with a functional group (such as an alkyl group) on the benzene ring at the para-position to C≣C substituted by a halogen atom became more efficient in terms of corrosion mitigation.