沃斯田不銹鋼常被用作核電廠乾式貯存容器的基材，因其具有優異的耐腐蝕性和機械性能。乾式貯存容器常暴露於靠近海岸的含氯環境中，這可能導致沃斯田不銹鋼在焊接區域的發生局部應力腐蝕開裂。乾式貯存容器的腐蝕劣化不僅可能導致容器內的放射性同位素釋放到環境中，還會因容器更換造成高額成本支出。本研究的目的是在304L不銹鋼基材上施加多層二氧化鈦複合塗層，例如掺雜鈰、鐵的二氧化鈦塗層和純二氧化鈦塗層，並評估塗層在紫外光照射下對容器材料抗腐蝕能力的影響。實驗內容是在不同退火溫度下對不同塗層樣品進行熱處理，接著通過電化學極化分析和開路電位測量，評估紫外光照射下塗層樣品的腐蝕行為和光催化反應。此外，本研究也利用掃描式電子顯微鏡、能量散射X射線光譜和X射線繞射分析樣品的表面形貌和晶體結構。

研究結果發現，在紫外光照射下，掺雜其他元素和純二氧化鈦的複合塗層不僅顯示出明顯的陰極保護作用，在紫外光停止照射後，還能維持高還原性的負開路電位數小時。電化學極化掃瞄分析的結果進一步證實了塗層樣品在紫外光照射下具有優異的抗腐蝕性。更重要的是，經過特殊處理的二氧化鈦複合塗層，經紫外光照射後，在沒有接受照射情況下，仍能持續展現優異的抗腐蝕能力。

Austenitic stainless steels are commonly used as the base materials for dry-storage canisters in nuclear power plants because of their excellent corrosion resistance and mechanical properties. Dry-storage canisters are often exposed to chloride containing atmospheres near seashores that could induce localized stress corrosion cracking in these stainless steels near the welded regions. Failure of a dry storage canister not only would release radioactive isotopes into the environment, but would also lead to a costly replacement of the cracked one. The primary objective of this study is to develop a multilayered titanium dioxide (TiO2) composite coating on a 304L stainless steel substrate. Doped (TiO2) coatings (Ce, Fe) and plain Titanium dioxide TiO2 coatings applied on stainless steel substrates (e.g. Type 304L stainless steels) along with ultraviolet (UV) irradiation have been proposed as a mitigation measure against corrosion in canister materials. The coated samples were then thermally treated at different annealing temperatures. Corrosion behavior and photocatalytic responses of the coated samples with and without UV illumination was evaluated by electrochemical polarization analyses and open-circuit potential measurements. Surface morphologies of the samples and crystal structures were studied by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD).
It was found that the both doped and plain TiO2 coating not only showed markedly enhanced photo-cathodic protection on 304LSS during UV illumination, but could also maintain more active open circuit potentials for several hours after the cutoff of UV. Results from electrochemical polarization analyses further supported the superior corrosion resistance of the coated samples under UV illumination. More importantly, the specifically processed TiO2 coatings applied on the samples, once irradiated with UV, would exhibit a prolonged corrosion resistance that could last for hours in the absence of UV.
Keywords: Dry storage canister, 304L stainless steel (304LSS), Titanium dioxide (TiO2), cerium doping, iron doping, photo-cathodic protection

Abstract
Acknowledgements
Chapter 1: Introduction………………………………………………………1
1.1 Outline of the problem………………………………………………….2
1.2 Motivation ……………………………………………………………...4
Chapter 2: Literature Survey…………………………………………………8
Chapter 3: Mechanism……………………………………………………….15
3.1 In-situ Fe doped TiO2 coating over 304LSS at high temperature……..15
3.2 Amorphous TiO2/ Ce doped TiO2 coatings on a 304LSS substrate…...19
3.3 Amorphous TiO2/ Fe doped TiO2 coatings on a 304LSS substrate……22
Chapter 4: Experimental…………………………………………………….25
4.1 In-situ Fe doped TiO2 coating over 304LSS at high temperature…….25
4.1.1 TiO2 solgel preparation………………………………………….25
4.1.2 Fe-doped TiO2 solgel preparation……………………………….25
4.1.3 Plain TiO2 solgel preparation……………………………………25
4.1.4 Substrate sample preparation…………………………………….26
4.1.5 Analytical measurements on coating properties…………………27
4.1.6 Electrochemical analyses…………………………………………27
4.2 Amorphous TiO2/ Ce doped TiO2 coatings on a 304LSS substrate………..30
4.2.1 TiO2 sol-gel preparation…………………………………………..30
4.2.2 Ce-doped TiO2 sol-gel preparation……………………………….30
4.2.3 Plain amorphous TiO2 sol-gel preparation……………………….30
4.2.4 Substrate sample preparation………………………………………31
4.2.5 Analytical measurements of the coating properties……………….32
4.2.6 Electrochemical analyses………………………………………….32
4.3 Amorphous TiO2/ Fe doped TiO2 coatings on a 304LSS substrate………35
4.3.1 Sol-gel preparation………………………………………….35
4.3.2 Plain TiO2 coating…………………………………………..35
4.3.3 Fe-doped TiO2 coating……………………………………..35
4.3.4 Substrate preparation………………………………………..36
4.3.5 Electrochemical analyses…………………………………….36
Chapter 5: Results and Discussion………………………………………………39
5.1 In-situ Fe doped TiO2 coating over 304LSS at high temperature………….39
5.1.1 Determination of optimal calcination temperature by TGA………….39
5.1.2 Optical absorption properties of the TiO2 coatings……………………40
5.1.3 Surface Morphologies of the Coatings……………………………….41
5.1.3.1 Surface analysis…………………………………………….41
5.1.3.2 Depth profile analysis……………………………………….43
5.1.3.3 XRD analysis……………………………………………… 44 5.1.4 OCP responses of TiO2 Coated Samples to UV illumination………..45
5.1.4.1 Variations in OCP of ITO substrates coated with plain TiO2………………………………………………………………….47
5.1.4.2 OCP responses to UV illumination of samples coated with Fe-doped TiO2………………………………………….49
5.1.5 Corrosion rates of the TiO2 coated samples…………………….51
5.2 Amorphous TiO2/ Ce doped TiO2 coatings on a 304LSS substrate…………..55
5.2.1 Optical absorption properties of the TiO2 Coatings……………………..55
5.2.2XRD analysis…………………………………………………………56
5.2.3 X-ray photoelectron spectroscopy analysis………………………….58
5.2.4 Surface analysis………………………………………………………60
5.2.5 Photo-electrochemical responses of TiO2-coated samples to
stimulated UV illumination………………………………………………….62
5.2.5.1 Variations in OCP responses of ITO substrates coated with Ce-doped TiO2 and plain TiO2 coating………………………………..62
5.2.5.2 Variations in OCP responses of 304LSS substrates coated with Ce-doped TiO2 and plain TiO2 coating……………………. …..64
5.2.6 Corrosion Rates of TiO2-coated samples………………………………66
5.3 Amorphous TiO2/ Fe doped TiO2 coatings on a 304LSS substrate……71
5.3.1 Variations in OCP responses of ITO substrates coated with Fe- doped TiO2 …………………………………………………………………..71
Chapter 6: Conclusions……………………………………………………………..75
References…………………………………………………………………………..77

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