Sains Malaysiana 40(9)(2011): 1013–1018

Curcuminoid Compounds Isolated from Curcuma domestica Val. as Corrosion

Inhibitor Towards Carbon Steel in 1% NaCl Solution

(Pengasingan Sebatian Kurkuminoid daripada Curcuma domestica Val. sebagai Perencat Pengaratan Aloi Karbon dalam 1% Larutan NaCl)

Dias Kandias*, Bunbun Bundjali & Deana Wahyuningrum

Chemistry Study Program, Faculty of Mathematics and Natural Sciences, Bandung

Institute of Technology, Jl. Ganesha 10, Bandung 40132, Indonesia

Diserahkan: 16 Jun 2010 / Diterima: 3 Januari 2011

ABSTRACT

The corrosion inhibitor of carbon steel in 1% NaCl solution by curcuminoids has been studied at 27oC using weight loss and electrochemical method. The determination of corrosion inhibition efficiency (%eff) utilising weight loss method at the concentration of 80 ppm showed the best result of 78.70% for third isolated fraction. Further determination utilising Tafel method showed the following results: raw pure extract of curcuminoid gave 89.88% at 50 ppm; the first isolated fraction gave 46.50% at 80 ppm; the second isolated fraction gave 44.83% at 30 ppm; and the third isolated fraction gave 92.44% at 70 ppm. Based on the analysis of Tafel extrapolation curve, the raw pure extract and the third fraction of curcuminoid acted as anodic inhibitor, whereas the first and the second fraction performed as cathodic inhibitors. The evaluations of synergism parameter (Sθ) indicate that the enhancement in inhibition efficiency towards raw pure extract was caused by the presence of second and third fractions as cathodic and anodic inhibitors. The contribution of steric hindrance of methoxy groups in curcuminoid structure causes the decrease in curcuminoid activity to be adsorbed on the electrode (carbon steel) surface.

Keywords: Anodic inhibitor; cathodic inhibitor; corrosion inhibitor; Tafel

ABSTRAK

Perencat kakisan daripada kumpulan kurkuminoid terhadap aloi karbon dalam larutan NaCl 1% telah dikaji pada suhu 27oC menggunakan kaedah hilang-berat dan elektrokimia. Penentuan kecekapan perencat kakisan (%eff) menggunakan kaedah kehilangan berat pada kepekatan 80 ppm menunjukkan hasil terbaik 78.70% untuk fraksi ketiga hasil pemencilan. Penentuan lebih lanjut menggunakan kaedah Tafel menunjukkan hasil seperti berikut: ekstrak kasar kurkuminoid tulen memiliki kecekapan perencat kakisan 89.88% pada 50 ppm; peringkat pemisahan pertama 46.50% pada 80 ppm; peringkat pemisahan kedua 44.83% pada 30 ppm; dan peringkat pemisahan ketiga 92.44% pada 70 ppm. Analisis terhadap lengkung ekstrapolasi Tafel menunjukkan bahwa ekstrak kasar tulen dan peringkat pemisahan ketiga kurkuminoud bertindak sebagai inhibitor anodik, sedangkan peringkat pemisahan pertama dan kedua berfungsi sebagai inhibitor katodik. Parameter sinergisme (Sθ) menunjukkan bahawa peningkatan kecekapan perencat pemangkinan dalam ekstrak kasar tulen disebabkan oleh adanya peringkat pemisahan kedua dan ketiga sebagai inhibitor katodik dan anodik. Sumbangan halangan sterik daripada kumpulan metoksi dalam struktur kurkuminoid menyebabkan penurunan keaktifan kemampuan kurkuminoid untuk terjerap pada permukaan elektrod (aloi karbon).

Kata kunci: Perencat anodik; perencat katodik; perencat pengaratan; Tafel

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*Pengarang untuk surat-menyurat; email: diaskandias@yahoo.co.id