Sains Malaysiana 43(7)(2014):1069–1075

Effect of High Temperature Corrosion on

Austenitic Stainless Steel Grade 304 in CO2 Gas at 700ºC

(Kesan Kakisan Suhu Tinggi Terhadap Keluli Tahan Karat Austenit Gred 304 Dalam Persekitaran Gas CO2 Pada Suhu 700^oC )

NURUL ATIKAH SHARIFF, AZMAN JALAR, MUHAMAD IZHAR SAHRI & NORINSAN KAMIL OTHMAN*

School of Applied Physics, Faculty of Science and Technology, Universiti Kebangsaan Malaysia

43600 Bangi, Selangor, Malaysia

Diserahkan: 27 Mac 2013/Diterima: 24 Februari 2014

ABSTRACT

Austenitic stainless steels of grade 304 were exposed to dry (Ar-75%CO₂) and wet (Ar-75%CO₂-12% H₂O) environments at 700^oC. This experimental setup involved horizontal tube furnace connected to CO₂ gas and water vapour facilities. X-ray diffraction (XRD) technique, variable pressure-scanning electron microscope (VP-SEM) and optical microscope techniques were used to characterize the products of corrosion. The results of XRD showed that the phase of oxide layers consists of Cr₂O₃ and NiCr2O₄ in dry CO₂, meanwhile Fe₂O₃, Cr₂O₃, Fe_0.56Ni_0.34, Fe₃O₄ were identified in wet condition after 50 h. Adding 12% H₂O in Ar-75%CO₂ leads significantly in weight change occurred at 10 h exposure. However, after 20 h, the weight gain was decreased due to spallation of the oxide scale. The addition of water vapour accelerates the oxidation rate on the steel than that in dry condition. Morphologies and growth kinetics of these oxides vary with reaction condition. The oxidation behaviour at different times of exposure and the effect of water vapour were discussed in correlation with the microstructure of the oxides.

Keywords: Austenitic stainless steel; oxidation; water vapour

ABSTRAK

Keluli tahan karat Austenit gred 304 telah didedahkan dalam persekitaran kering (Ar-75% CO₂) dan basah (Ar-75% CO₂-12%  H₂O) pada suhu 700^oC. Kajian ini telah menggunakan relau melintang yang dilengkapi dengan aliran gas CO₂ dan kemudahan penghasilan wap air. Teknik pembelauan sinar-X (XRD), mikroskop elektron imbasan pelbagai tekanan (VP-SEM) dan mikroskopi optik (OM) telah digunakan untuk pencirian hasil produk kakisan. Hasil keputusan XRD menunjukkan fasa lapisan oksida Cr₂O₃ dan NiCr₂O₄ terbentuk dalam persekitaran kering CO₂, sementara itu Fe₂O₃, Cr₂O₃, Fe_0.56Ni_0.34, Fe₃O₄ telah dikenal pasti dalam persekitaran basah selepas 50 jam pendedahan. Penambahan 12% H₂O dalam Ar-75% CO₂ membawa kepada perubahan berat yang ketara pada pendedahan selama 10 jam. Walau bagaimanapun, selepas 20 jam, pertambahan berat menurun disebabkan oleh pengelupasan lapisan oksida. Kehadiran wap air mempercepat kadar pengoksidaan terhadap keluli berbanding dalam keadaan kering. Morfologi dan pertumbuhan kinetik lapisan oksida adalah berbeza mengikut keadaan tindak balas. Perilaku pengoksidaan pada masa pendedahan yang berbeza dan kesan wap air telah dibincangkan dengan menghubungkait mikrostruktur oksida.

Kata kunci: Keluli tahan karat Austenit; pengoksidaan; wap air

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*Pengarang untuk surat-menyurat; email: insan@ukm.edu.my