Effects of dissolved hydrogen on high temperature corrosion resistance of chromia scale /
Fe-Cr alloy is commonly being used as boiler tube's material. It is subjected to prolonged exposure to water vapor oxidation. The ability to withstand high temperature corrosion can normally be attributed to the formation of a dense and slow growing Cr-rich-oxide scale known as chromia (Cr2O3)...
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| Main Author: | |
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| Format: | Thesis |
| Language: | English |
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Kuala Lumpur :
Kulliyyah of Engineering, International Islamic University Malaysia,
2018
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| Subjects: | |
| Online Access: | http://studentrepo.iium.edu.my/handle/123456789/4731 |
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| Summary: | Fe-Cr alloy is commonly being used as boiler tube's material. It is subjected to prolonged exposure to water vapor oxidation. The ability to withstand high temperature corrosion can normally be attributed to the formation of a dense and slow growing Cr-rich-oxide scale known as chromia (Cr2O3) scale. This scale protects Fe-Cr from further high temperature corrosion. However, oxidation may limit the alloy's service lifetime due to the declining of its protective capability. One of the factor to this issue is hydrogen induced cracking which paradoxically, water vapor dissociates to dissolved H2. But to date, this claim has not being fully studied systemically. Thus, these led to the need of studying the effect of dissolved H2 on high temperature corrosion resistance of chromia scale. This work focus on the effect of dissolved H2 to Cr2O3 protectiveness and its surface bond. To observe the protectiveness capability, Cr2O3 pellet has been examined its mass change by thermo gravimetric analysis. A dense sintered Cr2O3 was being exposed to dry (Ar) and wet (Ar-5%H2) environment for 172.8 ks (48 h) at 1073 K. By ratio, the mass change different between these conditions is at 1.2. It could be presumed that exposure time of 27.5 h is the critical time where Cr2O3 in wet condition loss its protectiveness based on thermodynamic calculation. FT-IR result confirms that dissolved H2 affect the chemical bonding of Cr2O3 and thus later promotes volatilization of protective Cr2O3 scale. Further observation has been done to determine the effect of dissolved H2 on electrolyte (water vapor) conductivity which led to gas phase conductivity analysis. The result provides an indication to corrosiveness of Cr2O3 scale. It was found that resistivity ratio value Rwet/Rdry is around 1.4. It is substantiated that the presence of dissolved H2 contributes to 40% higher corrosivity. |
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| Physical Description: | xx, 62 leaves : colour illustrations ; 30cm. |
| Bibliography: | Includes bibliographical references (leaves 57-61). |