苯乙炔衍生物對碳鋼在鹽酸中酸洗 腐蝕行為之抑制

Corrosion inhibition of Steel in hydrochloric acid by Phenylacetylene derivatives

周建毅(chien yi chou)

指導教授 ： 林景崎

國立中央大學/工學院/機械工程學系/碩士(2008年)

摘要

本論文探討碳鋼於90℃2M鹽酸酸洗液中，以苯乙炔衍生物作為腐蝕抑制劑之可行性。衍生物選用苯乙炔(Phenylacetylene. PE)、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-bromophenylacetylene,PEBr)等衍生物。論文中採用重量損失、線性極化、Tafel極化、交流阻抗等方法進行研究；試片表面則採用SEM、FTIR、XPS等來觀察分析；抑制劑與鋼鐵之吸附模擬，則採用電子密度泛函理論商用軟體B3LYP 6-311G(d)來進行。
重量損失法及各種電化學法之實驗結果均顯示:苯乙炔衍生物之腐蝕抑制效率(%) 依次為: PEBr (82%) > PECl (78%) > PE (47%) > PEF (20%) > PEC (9%)。隨著酸液溫度上升，各種抑制劑之抑制效率皆下降。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等溫吸附模式之吸附。根據Arrhenius 方程式求出:不含抑制劑時鋼鐵遭受腐蝕之活化能(kJ/mol)為243.8，一旦鹽酸中添加抑制劑後，其活化能下降, 分別為: 240.4 (PEC) > 215.8 (PEF) > 198.4 (PE) > 174.1 (PECl) > 167.1 (PEBr)，顯示此類型抑制劑屬於化學吸附。
由FTIR分析顯示: 苯乙炔衍生物吸附於鋼片表面來成腐蝕抑制劑作用，此等抑制劑之存在，可由苯環及C≣C光譜判知。XPS分析C 1S之鍵結能發現: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；XPS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，最容易提供電子給予鋼材以便形成鍵結，達最高抑制效果；苯乙炔衍生物抑制劑中，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。

關鍵字

苯乙炔 ； 最高佔據軌道能量(HOMO) ； 交流阻抗法 ； Tafel極化法 ； 線性極化法

並列摘要

The corrosion inhibition of low steel in 2M hydrochloric acid at 90℃ by derivatives of phenylacetylene, such as phenylacetylene (PE), p-Tolyacetylene (PEC), 4-fluorophenylacetylene (PEF), 4-chlorophenylacetylene (PECl) and
4-bromophenylacetylene (PEBr) has been investigated. The corrosion rate of the steel was estimated by weight loss measurement, linear polarization resistance, Tafel extrapolation and electrochemical impedance spectroscopy. The surface morphology was observed using scanning electron microscope (SEM). The surface film was analyzed with Fourier-transformed infrared spectrometer (FTIR) and X-ray photoelectron spectroscopy (XPS). Based on the data of corrosion and analysis results, a mechanism is proposed to delineate the corrosion inhibition of this system. The commercial software B3LYP 6-311(G) based on quantum chemical approach was used to correlate the experimental results with electron density distributed on the inhibitor molecules to evaluate the adsorption strength between the inhibitor and the steel.
The inhibition efficiency decreases in the order PEBr (82%) > PECl (78%) > PE (47%) > PEF (20%) > PEC (9%) and it decreases with increasing the environmental temperature. Resultant from Tafel extrapolation, both PECl and PEBr are surmised as cathodic inhibitors due to their negative shift in the corrosion potential. The inhibitors adsorbed onto the metal surface were found to obey Langmuir’s adsorption isotherm. The activation energies (kJ/mol) were estimated via Arrhenius plots and they decrease in order: 243.8 (without inhibitors) > 240.4 (PEC) > 215.8 (PEF) > 198.4 (PE) > 174.1 (PECl) > 167.1 (PEBr). Obviously, a higher efficient inhibitor reveals lower activation energy. This implies the adsorption of inhibitors onto steel belongs to chemisorption.
The results of FTIR analysis confirmed the presence of inhibitors on the steel surface. Analysis of XPS depicted an increase in peak intensity for C–H and C–C peaks but a decrease for both FeCl2 and FeCl3 species. This reflects that a higher extent adsorption of inhibitors onto the surface tends to depress the steel corrosion.
The simulation result of the software B3LYP 6-311(G) based on quantum chemistry showed that the high inhibition efficiency could be expressed by greater highest occupied molecular orbital (HOMO) and electron density, which often associated with the electron donating ability of a molecule.

並列關鍵字

Phenylacetylene ； linear polarization resistance ； Tafel extrapolation ； electrochemical impedance spectroscopy ； highest occupied molecular orbital (HOMO)

參考文獻

2. 王俊堯，”炔醇類有機物對碳鋼高溫酸洗腐蝕抑制作用”，中央大學96年碩士論文。

Corrosio Sci, Vol4,1987,p.421

Corrosion for students of Science and Engineering,1988

9.An Introduction to Corrosion and Protection of Materials,

13. W.S.Tait,”An introduction to electrochemical corrosion