| 1. |
- Bauhn, Lovisa, 1981, et al.
(författare)
-
The fate of hydroxyl radicals produced during H2O2 decomposition on a SIMFUEL surface in the presence of dissolved hydrogen
- 2018
-
Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115. ; 507, s. 38-43
-
Tidskriftsartikel (refereegranskat)abstract
- Over geologic timescales hydrogen peroxide will be one of the most important radiolytic oxidants challenging the spent fuel integrity in a deep repository. Consequently, the reaction between hydrogen peroxide and different kinds of UO 2 based materials has been the subject of several studies over recent decades. Parts of these studies have investigated the effect of dissolved hydrogen on this reaction, as large amounts of hydrogen are expected to be produced by anoxic corrosion of iron in the deep repositories. In some of the studies hydrogen has been shown to offset the radiolysis-driven oxidative dissolution of the fuel despite the expected inertia of hydrogen at repository temperatures. However, the underlying mechanism is primarily based on the effect of the metallic particles contained in the spent fuel. One clue to the mechanistic understanding is whether or not a reaction takes place between dissolved hydrogen and hydroxyl radicals adsorbed to a fuel surface resulting from the decomposition of H 2 O 2 . In the study presented here this reaction could be confirmed in an autoclave system with SIMFUEL, a hydrogen peroxide spiked solution, and deuterium gas. The results show that the studied reaction does not only occur, but accounts for a substantial part of the hydrogen peroxide consumption in the system. Only a very minor part, 0.02%, of the total consumed hydrogen peroxide caused oxidative dissolution of the SIMFUEL. The conclusion is supported by quantitative measurements of HDO, dissolved U in solution and O 2 in the gas phase.
|
|
| 2. |
- Alnegren, Patrik, 1988
(författare)
-
Corrosion of Ferritic Stainless Steel Interconnects for Solid Oxide Cells – Challenging Operating Conditions
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Solid oxide cells (SOC) have the potential to revolutionize electricity production by being able to both produce electricity with very high efficiency from a variety of fuels or to produce fuels from electricity and abundant raw materials such as water or carbon dioxide. Some material challenges remain to be solved before large-scale commercialization can be achieved. Interconnects made from ferritic stainless steels are key components in solid oxide cells, but the conditions within the cells cause them to degrade from high temperature corrosion. This thesis seeks out the potentially demanding operating conditions for solid oxide cells and focuses on investigating the effect of changing the environment on the degradation of ferritic stainless steels. Tests in which steel coupons were exposed to different atmospheres were performed to simulate the degradation of an interconnect inside an operating solid oxide cell. The effect of operating solid oxide fuel cells in electrolysis mode was specifically investigated, which means that interconnects were exposed to pure oxygen instead of ambient air and higher steam content on the fuel side. It was found that at 850 °C, ferritic stainless steels with 18-26% chromium content did not oxidize faster when the oxygen pressure was increased. However, the microstructure of the formed oxide scales on the steels was found to depend on oxygen concentration which caused oxide spallation for some steels at lower oxygen pressures. Experiments in hydrogen with high steam content, representing the other side of the interconnect, revealed an increase in the oxidation rate of the steel if the chromium content in the steel was too low, due to a change of the oxidation mechanism. Dilution of the same atmosphere with argon changed the oxidation mechanism to more protective behavior, which led to new insights in designing relevant simulated solid oxide cell fuel side conditions. It was also found that the oxidation rate of ferritic stainless steels in fuel side atmosphere can be significantly reduced by the physical vapor deposition (PVD) of cerium onto the surface. Even with applied cerium, however, steels with lower chromium content might still be at risk of rapid oxidation due to iron-rich oxide formation. A close-to-reality atmosphere was also simulated by exposing a ferritic steel simultaneously to air on one side and hydrogen on the other, which resulted in severely accelerated corrosion at 600 °C. Areas of up to 30 µm thick iron oxide were formed on the air side after 1000 h and grew to cover most of the surface after 3000 h. This dual atmosphere effect was concluded to have an inverse relation to temperature since accelerated corrosion was not observed at 700 and 800 °C. In addition, it was found that the corrosion resistance could be improved if the steel was pre-oxidized in air before exposure to dual atmosphere.
|
|
| 3. |
- Andersson, Viktor, 1983, et al.
(författare)
-
Alkali-wall interactions in a laboratory-scale reactor for chemical looping combustion studies
- 2021
-
Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820 .- 1873-7188. ; 217
-
Tidskriftsartikel (refereegranskat)abstract
- Alkali metal-containing compounds are readily released during thermal conversion of solid fuels, and may have both detrimental and beneficial effects on chemical looping combustion. Here, we characterize alkali interactions with the inner walls of a laboratory-scale reactor under oxidizing, reducing and inert conditions at temperatures up to 900 °C. KCl aerosol particles are continuously introduced to the stainless steel reactor and the alkali concentration is measured on-line with a surface ionization detector. Aerosol particles evaporate at temperatures above 500 °C and KCl molecules rapidly diffuse to the reactor wall. Up to 92% of the alkali reaching the wall below 700 °C remains adsorbed, while re-evaporation is important at higher temperatures, where up to 74% remains adsorbed. Transient changes in alkali concentration are observed during repeated redox cycles, which are associated with changes in chemical composition of the wall material. Metal oxides on the reactor wall are partially depleted under reducing conditions, which allow for the formation of a new potassium-rich phase that is stable in a reducing atmosphere, but not under inert conditions. The observed wall effects are concluded to be extensive and include major transient effects depending on gas composition, and the implications for laboratory studies and improved experimental methodology are discussed.
|
|
| 4. |
- Chyrkin, Anton, 1984, et al.
(författare)
-
Effect of Hydrogen on the Internal Oxidation of a Pd–Cr Alloy in Dual-Atmosphere Conditions
- 2022
-
Ingår i: Oxidation of Metals. - : Springer Science and Business Media LLC. - 1573-4889 .- 0030-770X. ; 97:5-6, s. 527-538
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of hydrogen on oxygen permeability has been studied in a diluted Pd–Cr alloy in dual- and single- atmosphere conditions between 600 and 950 °C. The 0.3 mm thick Pd–1.5Cr foil was exposed in dry and humid air as well as in dual-atmosphere conditions, with one sample surface being exposed to air and one to hydrogen, as encountered in solid oxide fuel cells. At all temperatures, Cr oxidized internally forming internal oxidation zones which were measured in metallographic cross sections. Below 800 °C, an external layer of PdO formed on the surface decreasing the internal oxidation kinetics. No measurable effect of hydrogen on the internal oxidation of Cr in Pd has been detected.
|
|
| 5. |
- Gagliani, Luca, 1991, et al.
(författare)
-
The Influence of Humidity Content on Ferritic Stainless Steels Used in Solid Oxide Fuel Cell under Dual Atmosphere Conditions at 600 C
- 2021
-
Ingår i: ECS Transactions. - : The Electrochemical Society. - 1938-5862 .- 1938-6737. ; 103:1, s. 1809-1815
-
Konferensbidrag (refereegranskat)abstract
- In Solid Oxide Fuel Cells (SOFC), interconnects are simultaneously exposed to dual atmosphere conditions in a range of temperature between 600 and 900 C. The presence of dissolved hydrogen in the steel can cause accelerated corrosion on the side exposed to air compared to exposures in air only. Moreover, the interconnect is subject to different humidity levels on the fuel side depending on fuel utilization. It has been already observed that a protective layer of chromia (Cr2O3) at the fuel side can mitigate the dual effect at the airside acting as a barrier for hydrogen permeation into the material. In this work, AISI 441 and Crofer 22 APU samples were exposed to dual atmosphere at 600 C under controlled humidity levels at the fuel side (20% vs. dry). Analysis performed showed how the humidity content on the fuel side largely affects the breakaway corrosion of the samples at the airside.
|
|
| 6. |
- Goebel, Claudia, 1988
(författare)
-
Corrosion of Ferritic Stainless Steels Used in Solid Oxide Fuel Cells
- 2018
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Solid oxide fuel cells (SOFC) are energy conversion systems with clean emissions (depending on the fuel used) and high electrical efficiencies, which could potentially replace conventional conversion systems such as combustion engines. However, other issues, such as high costs and limited lifetime, must be resolved before widespread commercialization of SOFCs can be achieved. One of the major cost factors and the component that reduces the lifetime of SOFCs immensely, is the interconnect, which electrically connects multiple fuel cells to form a stack. Interconnects are typically made of ferritic stainless steels, and, due to high temperatures (600 °C – 900 °C) and the aggressive environments prevalent in fuel cells, the interconnects corrode over time. The protective Cr2O3 that forms on ferritic stainless steels at high temperatures mitigates the corrosion process to a certain extent. However, this oxide layer leads to two other issues: (i) vaporization of hexavalent Cr species, which leads to cathode poisoning and (ii) an increase in the electrical resistance of the interconnect caused by a continuously growing oxide layer. Both these problems can be reduced to a certain extent with coatings. Especially spinel coatings have been proven highly effective at decreasing Cr-evaporation. The first part of this work examines the influence of the Co3O4 spinel coating on area specific resistance (ASR). It was found that the Co3O4 thickness of Crofer 22 APU, which was exposed in air for 500 h at 600 °C, did not significantly impact the ASR, and, instead, the main contributor to overall resistance was the thermally grown Cr2O3. The second part of this work focuses on the long-term stability of Ce/Co-coated (10 nm Ce/640 nm Co) AISI 441. Coated AISI 441 was exposed by AB Sandvik Materials Technology for up to 37 000 hours at 800 °C in laboratory air. Subsequent analysis showed very low Cr-evaporation rates compared to uncoated AISI 441, and ASR values below 40 mΩcm2, suggesting that, under these conditions, the coating is effective in reducing Cr-evaporation rates and Cr2O3-growth rates even after long exposure times. The last part of the work analyzes the influence of pre-oxidation on the dual atmosphere effect at 600 °C with regard to two parameters: the pre-oxidation time and the pre-oxidation location. It was demonstrated that longer pre-oxidation times for AISI 441 result in extended resistance against dual atmosphere corrosion on the air-facing side. It was also found that the pre-oxidation layer on the hydrogen-facing side is more important for corrosion resistance in dual atmosphere than the pre-oxidation layer on the air-facing side.
|
|
| 7. |
- Lehmusto, Juho, et al.
(författare)
-
Should the oxygen source be considered in the initiation of KCl-induced high-temperature corrosion?
- 2021
-
Ingår i: Corrosion Science. - : Elsevier BV. - 0010-938X. ; 183
-
Tidskriftsartikel (refereegranskat)abstract
- The role of two oxygen sources, oxygen and water vapor, in the initiation of KCl-induced high-temperature corrosion was addressed by studying two high-alloyed commercial materials at 550 °C. The differentiation between the two oxygen sources was implemented with 18O-enriched water and 16O2. Based on the results, the solid-solid reaction between KCl(s) and the protective oxide on the alloy surface appeared to be more responsible for corrosion than the gas-solid reaction between KCl(g) and the protective oxide. Water was more involved in the abovementioned reactions than O2: 18O was the main oxygen isotope found in the formed surface oxides and intermediates.
|
|
| 8. |
- Engkvist, Josefin, 1972, et al.
(författare)
-
The initial effect of KCl deposit on alumina scales characterized by ToF-SIMS and AES
- 2013
-
Ingår i: Surface and Interface Analysis. - : Wiley. - 1096-9918 .- 0142-2421. ; 45:1, s. 445-448
-
Tidskriftsartikel (refereegranskat)abstract
- A FeCrAl alloy was preoxidized to form a protective alumina scale, and the effect of KCl deposits on the alumina scale was investigated while exposed during 1 and 24 h at 600 degrees C. However, impurity concentrations in the alumina scale change the ion conductivity and hence affect its protective properties. Therefore, Auger electron spectroscopy and time-of-flight secondary ion mass spectrometry were used to characterize the alumina scales and detect traces of K and Cl. The results showed that K and Cl existed as large sharp-edged crystals surrounded by a dendritic network after 1 h. However, after 24 h, those were dissolved, and K together with Cl was detected only in the outer layer of the duplex alumina scale, which was formed during preoxidation.
|
|
| 9. |
- Wang, Di, et al.
(författare)
-
In-situ coating wear condition monitoring based on solid-liquid triboelectric nanogenerator and its mechanism study
- 2023
-
Ingår i: Nano Energy. - : Elsevier Ltd. - 2211-2855 .- 2211-3282. ; 112
-
Tidskriftsartikel (refereegranskat)abstract
- Various more or less wear-resistant coatings have been developed and used to protect metal substrates. However, the damage caused by wear is still a problem for most coatings. It is of great importance to monitor the wear of coatings in real-time during the applications. Recently reported wear monitoring methods (image processing, luminescent layers and the use of a sensing underlayer) require complex external equipment or additional coating preparation process steps, which limit their applications. As an emerging technology, a triboelectric nanogenerator (TENG) can convert mechanical energy into electricity, and it has been applied as a self-powered sensor. In this study, a new coating wear monitoring method is developed based on a solid-liquid TENG. The developed TENG generates electric signals corresponding to different wear states, which facilitates easy monitoring of the coating’s wear conditions. The results show that the surface composition change caused by wear is the main reason affecting the TENG signal output. The coating-liquid contact-separation motion generates real-time output signals that directly reflect the coating wear states without the need of any additional equipment. This study provides a promising new technology for in-situ coating wear monitoring.
|
|
| 10. |
- Kharazmi, Parastou, 1977-
(författare)
-
Durability study of reinforced polyester composite used as pipe lining under artificial aging conditions
-
Tidskriftsartikel (refereegranskat)abstract
- The aging of sewer infrastructure is an ongoing problem. As a result, different materials and methods are being used in alternative sewer rehabilitation approaches. This work was conducted to study one pipe lining, namely the reinforced polyester composite, under artificial aging; this was done to provide a better understanding of the material’s performance under operating conditions, where it is regularly exposed to degrading factors such as heat and water. Aging of the material was monitored by means of several tests, including thermal and mechanical analyses, water absorption and microscopy. The results showed that the combination of aging in water and at high temperatures resulted in greater effects on the material compared to aging at high temperatures in dry conditions. Although the measured properties were affected significantly when immersed in water at high temperatures, the material showed acceptable properties at lower exposure temperatures close to the expected temperature inside sewer systems.
|
|
