| 1. |
- Berendson, Jaak
(författare)
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Electrochemical methods
- 2007
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Ingår i: Surface Characterization. - Weinheim, Germany : Wiley-Blackwell. - 9783527612451 ; , s. 590-606
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 2. |
- Gil, Harveth, et al.
(författare)
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Electrochemical reduction modeling of copper oxides obtained during in situ and ex situ conditions in the presence of acetic acid
- 2009
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Ingår i: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 54:20, s. 4676-4681
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Tidskriftsartikel (refereegranskat)abstract
- We used the potentiodynamic reduction technique to study the mechanism of copper oxide formation inthe presence of acetic acid.We performed all reductions under neutral conditions (0.1MKCl) until hydrogenevolution. We produced the copper oxides in an environment containing 0, 500, and 800 ppb aceticacid at high relative humidity. We then compared experimental results between electrochemically producedoxide films obtained by imposing anodic potentials to copper specimens in several concentrationsof pure acetic acid (1, 0.1, 0.01 and 0.001 M). We found that, as the concentration of the acid decreases,the formation of the copper oxide (I) increases.We also found the same peaks in samples produced underthe synthetic environment.We modeled the curves, taking into account the electrochemical reduction ofcopper (II) oxide (CuO), amorphous cuprite (Cu2O)am, intermediate cuprite (Cu2O)in, crystalline cuprite(Cu2O)cr, and hydrogen. These oxides have been previously detected in similar conditions. We found noevidence of copper carboxylate founding samples produced by the electrochemical method.
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| 3. |
- Goidanich, S., et al.
(författare)
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Effect of the environment on the metal release and corrosion behaviour of different copper-based alloys : Field exposures at 5 different test sites in Europe
- 2008
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Ingår i: 17th International Corrosion Congress 2008. - 9781615674251 ; , s. 102-115
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Konferensbidrag (refereegranskat)abstract
- Diffuse emissions and dispersion of metals from different sources in the society have lately received an increased concern from an environmental perspective. Large research efforts have been initiated and undertaken by the division of Corrosion Science at KTH to fill knowledge gaps on corrosion-induced metal release from external constructions and buildings. The generation of such data is of paramount importance for the on-going assessment of flows and potential adverse environmental effects caused by released metals. Generated information is also essential for an improved understanding of prevailing atmospheric corrosion processes of importance for the preservation of our cultural heritage, e.g. bronze statues exposed to the atmosphere. This paper summarizes and compares long-term metal release data from pure copper, bronze (6%wt Sn) and brass (20%wt Zn) exposed at unsheltered conditions in five European environments of significantly different climatic and pollutant conditions; three urban sites (Stockholm-Sweden, Milan-Italy and Madrid-Spain) and two marine sites (Brest-France, Cadiz-Spain). Generated data are interpreted with respect to parallel multi-analytical studies of changes in patina characteristics, corrosion rates and differences in prevailing environmental conditions.
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| 4. |
- Henderson, Pamela
(författare)
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Högtemperaturkorrosion i barkpannor : Del 1
- 2007
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Ingår i: Nordisk Papper & Massa. - Stockholm : Conventus Communications AB. - 1652-9995. ; :2, s. 58-59
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Forskningsöversikt (populärvet., debatt m.m.)abstract
- Ökad eldning av retur- och avfallsbränslen i barkpannor har medfört att alltfler har fått problem med avlagringar och korrosion. Det finns ett stort intresse att minska kostnader för högtemperaturkorrosion genom att förlänga livslängden och att minska risken för oplanerade stopp. Samtidigt finns det starka drivkrafter att förbättra anläggningarnas elverkningsgrad genom högre ångdata.
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| 5. |
- Henderson, Pamela
(författare)
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Högtemperaturkorrosion i barkpannor : del 2
- 2007
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Ingår i: Nordisk Papper & Massa. - Stockholm : Medact Press AB. - 1652-9995. ; :3/4, s. 83-85
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Forskningsöversikt (populärvet., debatt m.m.)abstract
- Ökad eldning av retur- och avfallsbränslen i barkpannor har medfört att alltfler har fått problem med avlagringar och korrosion. Det finns ett stort intresse att minska kostnader för högtemperaturkorrosion genom att förlänga livslängden och att minska risken för oplanerade stopp. Samtidigt finns det starka drivkrafter att förbättra anläggningarnas elverkningsgrad genom högre ångdata.
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| 6. |
- Henderson, Pamela, et al.
(författare)
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In-situ fireside corrosion testing of superheater materials with coal, wood and straw fuels for conventional and asvanced steam temperatures
- 2005
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Ingår i: VGB PowerTech. - Essen, Germany : VGB PowerTech eV. - 1435-3199. ; 84:6, s. 53-59
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Tidskriftsartikel (refereegranskat)abstract
- An increase in the steam temperature of a power station increases the electrical efficiency of the turbine. This in turn leads to a reduction in the cost of electricity and in environmental emissions produced per unit of electricity generated. However, higher steam temperatures give rise to more aggressive corrosive environments and the choice of material becomes more important. In addition, the aggressiveness of the fuels also depends on their chemical compositions. As part of a European research programme (COST 522) fireside corrosion tests of superheater and waterwall materials have been performed in-situ in industrial boilers or combustion test facilities, simulating conventional and higher steam temperatures. The fuels used were, straw, wood (logging residues) and coal. Goals were set at different maximum steam temperatures and lifetimes according to the fuel. The targets were: coal 650°C/100,000 h, wood 580°C/40,000 h and straw 580°C/20,000 h .A wide range of materials was tested. An overriding constraint was that the materials must be economically viable and not impose exceptional fabrication requirements. Some materials were tested in a number of combustion environments, allowing useful comparisons to be made. The results showed that for a given superheater alloy, temperature and fuel, the corrosion rate depended on the alloy’s position in a superheater bank. Tubes on the outside, exposed to the flue gas, corroded faster than those positioned deeper in a bank. Tubes experiencing a greater heat flux will corrode more rapidly. Poorly controlled combustion will also increase corrosion. Straw was much more corrosive than wood (logging residues). The difference in corrosiveness increased with increasing temperature above a metal temperature of about 520°C. The corrosion rates of the alloys tested during wood-firing were only a little higher than those from firing coal with a medium to high chlorine content. Straw and wood are often collectively known as “biomass”, but the corrosion they cause can vary by a factor of 5 or more. No difference could be found in the fireside corrosion rates of the steels TP 347H and TP 347HFG, when tested under similar conditions. Esshete 1250 also showed similar fireside corrosion rates to347 instraw and wood boilers and at temperatures below 650°Cin coal boilers. Several alloys were identified to resist corrosion in coal-fired plant at metal temperatures of680°C(steam temperatures650°C) and high heat fluxes. Adequate high temperature creep strength remains more problematic. At lower heat fluxes (resulting in lower corrosion rates) more candidate alloys exist. It is expected that the goals set can be achieved with the use of suitable alloys in the case of wood, waste and coal. For wood (logging residues) TP347, Esshete 1250 and 50Ni50Cr coatings showed sufficient corrosion resistance at the target temperatures. In the coal case HR3C fulfills the requirements of strength and corrosion resistance with a high heat flux and Super 304H and SAVE 25 if the heat flux is low. HR11N and IN671 are suitable for use as claddings on a substrate with the appropriate creep strength. The goal set for straw firing was ambitious, a steam temperature of580°C, and in this case a combination of material, combustion technology and boiler design are needed.
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| 7. |
- Henderson, Pamela, et al.
(författare)
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Reducing superheater corrosion in wood-fired boilers
- 2008
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Ingår i: Novel approaches to improving high temperature corrosion resistance. - : Woodhead Publishing Limited. ; , s. 428-444
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Bokkapitel (refereegranskat)abstract
- In the last few years, there has been a move away from burning fossil fuels through the co-utilisation of biomass and coal and finally to 100% biomass such as wood and waste wood products. Unfortunately, burning of biomass causes widespread fouling of superheater tubes and corrosion can occur rapidly under the sticky alkali chloride deposits. Even at today's maximum steam temperatures of 500 to540°C there are some severe corrosion problems when burning 100% wood-based fuel. It is also desirable to be able to burn other environmental fuels such as straw, demolition wood or other wood-waste products, to reduce production costs and avoid dumping waste at landfill sites. This, however, makes the corrosion and fouling problems even more serious. A complete set of superheaters for a 100 MW combined heat and power boiler costs in excess of 1 MEuro. The durability of superheaters is thus an important factor in determining the long-term production costs. Unplanned outages due to leaking superheaters are also very expensive. As well as causing corrosion problems, the build-up of deposits reduces the heat uptake to the superheaters which leads to lower efficiency. Consequently, ways are being sought to reduce superheater corrosion.Most biomass fuels have a high content of alkali metals and chlorine, but they contain very little sulphur compared to fossil fuels. Potassium chloride, KCl, is found in the gas phase, condenses on the superheater tubes and forms complex alkali salts with iron and other elements in the steels. These salts have low melting points and are very corrosive. Vattenfall has developed and patented an instrument for in-situ measurement of gaseous alkali chlorides which gives an indication of how corrosive the flue gases are. This instrument is called an in-situ alkali chloride monitor (IACM). Vattenfall has also developed and patented a concept with a sulphate containing compound called “ChlorOut” , which is sprayed into the flue gases after combustion is complete, but before the flue gases reach the superheaters, and effectively converts KCl into potassium sulphate, K2SO4. This compound much less corrosive than KCl. In the experiments reported here the sulphate used in ChlorOut was ammonium sulphate. This is also used for the reduction of NOx. This study reports on measures taken to reduce superheater corrosion in two fluidised bed boilers burning wood-based fuels, using the ChlorOut additive to control the KCl levels and by using more corrosion-resistant steels.
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| 8. |
- Henderson, Pamela, et al.
(författare)
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Reducing superheater corrosion in wood-fired boilers
- 2006
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Ingår i: Materials and corrosion - Werkstoffe und Korrosion. - : Wiley-VCH Verlagsgesellschaft. - 0947-5117 .- 1521-4176. ; 57:2, s. 128-134
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Tidskriftsartikel (refereegranskat)abstract
- One of the major drawbacks to the combustion of 100% biomass in power station boilers is the increase in the fouling and corrosion of superheaters. Experience shows that conventional superheater steels last no more than 20 000 h or four operating years before they must be replaced, if 100% wood-based fuel is used and the steam temperature is higher than 480C. Rapid corrosion of superheaters leads to increased maintenance costs while widespread deposit formation gives rise to a decrease in efficiency of the turbine and an increase in unplanned outages. This paper reports on measures taken to reduce superheater corrosion. Most biomass fuels have a high content of alkali metals and chlorine, but they contain very little sulphur compared to fossil fuels. Potassium chloride, KCl, is found in the gas phase, condenses on the superheater tubes and forms complex alkali salts with iron and other elements in the steels. These salts have low melting points and are very corrosive. The corrosion can be mitigated by use of an instrument for in-situ measurement of alkali chlorides in the flue gases, in combination with the addition of ammonium sulphate. An ammonium sulphate solution, specially developed for the reduction of corrosion was sprayed into the flue gases and effectively converted KCl into potassium sulphate, K2SO4, much less corrosive than KCl. Deposit probe tests and long-term corrosion probe tests have been performed in-situ in two biomass-fired fluidised bed boilers. One boiler, 105 MW tot, 540C steam, is the CHP plant in Nyköping,Sweden. The other producing 98 MWtot, 480C steam, is a bark-fired boiler at a pulp and paper mill in Munksund, also in Sweden. Tests have been performed with a range of steel types, ferritic and austenitic, with ammonium sulphate additive and under normal conditions (no additive). Corrosion rates have been measured, deposit chemistry analysed and flue gas chemistry and KCl content measured. The structure and composition of the oxide with and without ammonium sulphate has been investigated. The results show that ammonium sulphate reduced the KCl levels in the flue gases, removed the chlorides from the deposits and the metal/oxide interface, greatly reduced the deposition rates and halved the corrosion rates for superheater materials. The alkali chloride measuring system and the use of ammonium sulphate for the reduction of corrosion have now been patented.
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| 9. |
- Herting, Gunilla, et al.
(författare)
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Corrosion-induced release of Cu and Zn into rainwater from brass, bronze and their pure metals. A 2-year field study
- 2008
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Ingår i: Environmental Monitoring & Assessment. - : Springer Science and Business Media LLC. - 0167-6369 .- 1573-2959. ; 144:1-3, s. 455-461
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Tidskriftsartikel (refereegranskat)abstract
- A 2-year field study has been conducted in an urban environment to provide annual release rates of copper and zinc from brass (20 wt% Zn) and copper and tin from bronze (6 wt% Sn) compared to sheets of their pure alloy constituents, copper and zinc. Despite relatively low nominal bulk alloy content, substantially more zinc was released from brass compared to copper. Both metals were released at a significantly slower rate from the brass alloy, compared to the pure metals. The proportion of release rates of copper and zinc from the alloy differed significantly from their proportions in the bulk alloy. Bronze showed relatively constant release rates of copper, being similar to that of pure copper sheet. The release of tin from bronze was negligible. The results clearly show that alloys and the pure metals behave very differently when exposed to rainwater. Accordingly, release rates from pure metals cannot be used to predict release rates of individual constituents from their alloys. Generated data are of importance within REACH, the new chemical policy of the European commission, where metal alloys erroneously are being treated as mixtures of chemical substances.
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| 10. |
- Hultquist, Gunnar, et al.
(författare)
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Effects of hydrogen on the corrosion resistance of metallic materials and semiconductors
- 2006
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Ingår i: High-Temperature Oxidation And Corrosion 2005. - 087849409X ; , s. 139-146
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Konferensbidrag (refereegranskat)abstract
- For long time it is known that protons in aqueous solutions have a detrimental effect on metallic materials. Relatively recently, it has also been observed in aqueous solution that the pitting corrosion resistance of Cr, stainless steel 304 and 310 decreases and the anodic dissolution rate increases due to the presence of hydrogen in the metal. In gas phase a high oxidation rate has been observed for hydrogen containing Cr and Fe. Hydrogen in the substrate can also enhance the oxidation of Fe in SS 316 and As in GaAs. All these results suggest enhanced dissolution in aqueous solution and enhanced oxide growth at the oxide/gas interface in gas phase oxidation due to hydrogen promoted outward-transport of substrate components. A possible mechanism for such out-transport is an increased metal ion diffusivity in the metal-oxide due to a high abundance of metal ion vacancies generated by hydrogen. In contrast to all the above examples, also positive effects of hydrogen have been identified under certain conditions. In an attempt to understand both the negative and the positive effects the concept of a beneficial, balanced oxide growth is used. In this concept a certain amount of hydrogen can be beneficial in the oxidation by improving the balance between oxygen-ion and metalion transport, leading to more dense and protective oxides. Depending on the temperature, H(2) in air is considered as either a sink or a source for hydrogen in materials.
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