Sains Malaysiana 39(2)(2010): 249–259

Kesan Wap Air Terhadap Pengoksidaan Berkitar pada Aloi Fe-Cr

(Water Vapour Effects of Cyclic Oxidation on Fe-Cr Alloys)

N.K. Othman*

Fakulti Sains dan Teknologi, Universiti Kebangsaan Malaysia

43600 Bangi, Selangor D.E., Malaysia

N.Othman

Bahagian Teknologi Industri, Agensi Nuklear Malaysia Bangi

43000 Kajang, Selangor D.E., Malaysia

J. Zhang & D.J. Young

School of Materials Science & Engineering

University of New South Wales, 2052, Sydney Australia

Received: 28 May 2009 / Accepted: 25 August 2009

ABSTRAK

Aloi Fe-Cr (Cr: 9-30 brt%) telah dikenakan pengoksidaan berkitar dalam Ar-20%O2, Ar-20%O2-5%H2O dan Ar-10%H2-5%H2O (tekanan separa oksigen, pO2 = 1.1 ¥ 10-16atm), pada suhu 950oC. Pengukuran perubahan berat pengoksidaan menunjukkan secara umunnya bahawa peningkatan kandungan Cr dalam aloi akan mengurangkan kadar pengoksidaan. Untuk aloi Cr≤17%, ‘pengoksidaan pemecahan’ telah dapat diperhatikan. Untuk aloi Cr≥25%, penambahan berat adalah sangat rendah disebabkan oleh pembentukan lapisan Cr2O3. Penambahan 5%H2O kepada Ar-20%O2 dapat mempercepatkan lagi kadar pengoksidaan pada aloi yang mempunyai Cr≤20%. Walau bagaimanapun, kesan pencepatan ini tidak berlaku pada aloi yang mempunyai kandungan Cr yang tinggi. AnalisisXRD menunjukkan aloi yang mempunyai kandungan Cr≤20%, wustit dan spinel terbentuk pada pO2 yang rendah, manakala pada pO2 yang tinggi, hematit, oksida besi dan spinel didapati terbentuk. Untuk aloi yang mempunyai kandungan Cr yang tinggi, hanya Cr2O3 dapat dikesan. Analisis keratan rentas menunjukkan bahawa spinel terbentuk melalui pengoksidaan dalaman. Ketebalan dan saiz zon oksida dalaman bertambah dengan bertambahnya kandungan Cr. Lapisan kromium oksida tunggal yang tumpat dapat diperhatikan apabila kandungan Cr melebihi 25%. Kerak oksida yang terbentuk di dalam wap air adalah lebih poros dan kurang padat berbanding kerak yang terbentuk dalam keadaan oksigen kering. Kesan wap air ke atas peningkatan pengoksidaan aloi Fe-Cr telah dibincangkan daripada aspek interaksi gas-pepejal.

Kata kunci: Aloi Fe-Cr; Cr2O3; pengoksidaan berkitar; wap air

ABSTRACT

Fe-Cr alloys (Cr: 9-30 wt%) were subjected to cyclic oxidation in Ar-20%O2, Ar-20%O2-5%H2O and Ar-10%H2-5%H2O (partial pressure of oxygen, pO2 = 1.1 ¥ 10-16atm). Oxidation weight change measurement showed that in general, increasing Cr content reduced the oxidation rate. At Cr < 17%Cr, breakaway oxidation was observed. However, for Cr > 25%, the weight gain became very low due to formation of Cr2O3 layer. Adding 5%H2O to Ar-20%O2 accelerated the oxidation rate of alloys with Cr < 20%. However, this accelerating effect did not appear in high chromium content alloys. XRD analysis showed that for alloys with Cr < 20%, wustite and spinel were formed at low pO2, while at high pO2, hematite, iron oxide and spinel were formed. For high Cr content alloy only Cr2O3 was detected. Cross-section analysis showed that the spinel was formed by internal oxidation. The thickness and size of this internal oxide zone increased with increasing Cr content. A dense chromia layer was observed when the Cr content was above 25%. The oxides scales formed in water vapour were more porous and less compact than the scale formed in dry oxygen. The accelerating effect of water vapour on Fe-Cr oxidation is discussed in terms of gas-solid interactions.

Keywords: Cr2O3; cyclic oxidation; Fe-Cr alloy; water vapour

REFERENCES

Asteman, H., Svensson, J.E., Johansson, L.G., & Norell, M. 1999. Indication of chromium oxide hydroxide evaporation during oxidation of 304L at 873 K in the presence of 10% water vapor. Oxidation of Metals 52: 95-111.

Asteman, H., Svensson, J.E., Norell, M., Johansson, L.G. 2000. Influence of water vapor and flow rate on the high-temperature oxidation of 304L; Effect of chromium oxide hydroxide evaporation. Oxidation of Metals 54: 11-26.

Asteman, H., Segerdahl, K., Svensson, J.E. & Johansson, L. G. 2001. The influence of water vapour on the corrosion of chromia forming steels. Materials Science Forum 369-372: 277-286.

Asteman, H., Svensson, J.E. & Johansson, L.G. 2004. Effect of Water-Vapor-Induced Cr Vaporization on the Oxidation of Austenitic Stainless Steels at 700 and 900¡C. Journal of the Electrochemical Society 151(3): B141-B150

Asteman, H., Svensson, J.E. &. Johansson, L.G. 2002. Evidence for chromium evaporation influencing the oxidation of 304L: The effect of temperature and flow rate. Oxidation of Metals 57: 93-216.

Ehlers, J., Young, D.J., Smaardijk, E.J., Tyagi, A.K., Penkalla, H.J., Singheiser, L. & Quaddakers, W.J. 2006. Enhanced oxidation of the 9% Cr steel P91 in water vapour containing environment Corrosion Science 48: 3428-3454.

Evans, H.E., Donaldson, A.T. & Gilmour, T.C. 1999. Mechanisms of breakaway oxidation and application to a chromia-forming steel. Oxidation of Metals 52: 379-402.

Fuji, C.T & Meussner, R.A. 1964. The mechanisms of the high-temperature oxidation of iron-chromium alloys in water vapour. Journal of the Electrochemical Society 11: 1215-1218.

Henry, S., Galerie, A. & Antoni, L. 2001. Abnormal oxidation of stabilized ferritic stainless steels in water vapour. Materials Science Forum 369-372: 353-360.

Ikeda, Y. & Nii, K. 1978. Microcrack generation and its healing in the oxide scale formed on Fe-Cr alloys. Oxidation of Metals 12(6): 487-502.

Jonsson, T., Canovic, S., Liu, F., Asteman, H., Svennson, J.E., Johansson, L.G. & Halvarsson, M. 2005. Microstructural invenstigation of the water vapour on the oxidation of alloy 353 MA in oxygen at 700 and 900oC. Materials at High Temperature. Science Reviews 22(3/4): 231-243.

Lide, D.R. 1997. CRC Handbook of Chemistery and Physics. 78th Florida: CRC Press

Monteiro, M.J & Rizzo, F.C. 2006. Effect of chromium content on the oxidation behaviour of high-speed steels under dry and moist air environments. Materials Science Forum 522-523: 171-180.

Moon, C.O & Lee, S.B. 1993. Analysis on failures of protective-oxide layers and cyclic oxidation. Oxidation of Metals 39: 1-13.

Nickel, H., Wounters, Y., Thiele, M., Quadakkers, W.J. & Fresenius. 1998. The effect of water vapor on the oxidation behavior of 9%Cr steels in simulated combustion gases. J. Anal. Chem. 361: 540-544.

Peraldi, R. &. Pint, B.A. 2004. Effect of Cr and Ni contents on the oxidation behavior of ferritic and austenitic model alloys in air with water vapor. Oxidation of Metals 61: 463-483.

Poquillon, D. & Monceau, D. 2003. Application of a simple statistical spalling model for the analysis of high-temperature, cyclic-oxidation kinetics data. Oxidation of Metals 59: 409-431.

Rahmel, A. & Tobolski, J. 1965. Influences of water vapor and carbon dioxide on the oxidation of iron in oxygen at high temperature. Corrosion Science 5: 333-346.

Stanislowski, M., Wessel, E., Hilpert, K., Markus, T. & Singheiser, L. 2007. Chromium Vaporization from High-Temperature Alloys I. Chromia-Forming Steels and the Influence of Outer Oxide Layers. Journal of the Electrochemical Society 154(4): 295-306.

Surman, P.L. & Castle, J.E. 1969. Gas phase transport in the oxidation of Fe and steel. Corrosion Science 9: 771-777.

Young, D.J & Pint, B.A. 2006. Chromium volatilization rates from Cr2O3 scales into flowing gases containing water vapour. Oxidation of Metals 66: 137-153.

Zurek, J., Michalik M., Schmitz, F., Kern, T.U., Singheiser, L. & Quadakkers, W.J. 2005. The effect of water-vapor content and gas flow rate on the oxidation mechanism of a 10%Cr-Ferritic steel in Ar-H2O mixtures. Oxidation of Metals 63(5/6): 401-422.

*Corresponding author; email: insan@ukm.my