Sains Malaysiana 37(2):  155-160(2008)

Electrochemical Study of Stainless Steel Corrosion

by Marine Sulphate-Reducing Bacteria

(Kajian Elektrokimia Terhadap Kakisan Keluli Kalis

Karat oleh Bakteria Penurun-Sulfat)

Fathul Karim Sahrani, Zaharah Ibrahim, Madzlan Aziz & Adibah Yahya

School of Environment and Natural Resource Sciences

Faculty of Science and Technology, Universiti Kebangsaan Malaysia

43600 UKM Bangi, Selangor, Malaysia

Received : 25 May 2007 / Accepted: 6 November 2007

ABSTRACT

Corrosion caused by sulphate-reducing bacteria (SRB) isolated from seawater nearby to Pasir Gudang has been studied. The test coupon was a AISI 304 stainless steel. Potential and corrosion rate measurements were carried out in various types of culturing solutions, with SRB1, SRB2, combination of SRB1 & SRB2 and without SRBs inoculated (sterilized).  From Tafel plots a higher corrosion rate has been found in medium inoculated with SRBs than that of the sterilized medium (control). When SRBs were present in the medium, the Tafel plot shifted towards more negative values (E_corr was shifted to much less anodic values) and increase in current density compared to that of the sterilized medium (control). Localized corrosion was observed on the metal surface, and it was associated to the SRB activity. X-ray analysis (EDAX) showed that the corrosion product has higher content of sulphur for medium containing SRBs than that of the sterilized medium. X-Ray Diffraction analysis carried out on corrosion products which showed the presence of iron sulphide. This indicates the influence of the presence of SRB in corrosion process.

Keywords:  sulphate-reducing bacteria; stainless steel; electrochemical test

ABSTRAK

Kajian mengenai kakisan oleh bakteria penurun-sulfat (SRB) dipencilkan dari air laut berhampiran Pasir Gudang telah dilakukan. Kupon ujian adalah keluli kalis karat AISI 304.  Pengukuran keupayaan dan kadar kakisan dijalankan dalam pelbagai keadaan iaitu dalam medium yang mengandungi SRB1, SRB2, kombinasi SRB1 & SRB2 dan tanpa kultur SRB (steril). Daripada plot Tafel, didapati kadar kakisan tinggi pada medium yang mengandungi kultur SRB berbanding medium steril. Pada medium yang mengandungi kultur SRB, keupayaan kakisan berubah ke arah nilai yang lebih negatif (E_corr berubah kearah anodik dengan nilai yang semakin berkurangan) dan meningkatkan ketumpatan arus berbanding medium kawalan. Kakisan setempat diperhatikan berlaku pada permukaan keluli yang dikaitkan dengan aktiviti SRB. Analisis sinar-x (EDAX) menunjukkan produk kakisan mengandungi kandungan sulfur yang tinggi bagi medium yang mengandungi kultur SRB berbanding medium steril (kawalan). Selanjutnya analisis belauan sinar-x (XRD) terhadap produk kakisan menunjukkan kehadiran sebatian besi sulfida. Ini menunjukkan pengaruh SRB dalam proses kakisan.

Kata kunci: bakteria penurun-sulfat; keluli kalis karat; ujian elektrokimia; plot Tafel

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