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Nanoscale characterisation of crystallinity in DSA coating
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.ORCID iD: 0000-0001-9137-3440
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
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2008 (English)In: PROCEEDINGS OF THE 17TH INTERNATIONAL VACUUM CONGRESS/13TH INTERNATIONAL CONFERENCE ON SURFACE SCIENCE/INTERNATIONAL CONFERENCE ON NANOSCIENCE AND TECHNOLOGY, Institute of Physics (IOP), 2008, Vol. 100, no 052026, 4-4 p.Conference paper, (Refereed)
Abstract [en]

Dimensionally Stable Anodes (DSA (R)) are used for industrial production of e. g. chlorine and chlorate. It is known that the superior electrocatalytical properties of DSA (R) is due to the large effective area of the porous coating. However, this knowledge is mainly found from in situ electrochemical measurements. Here, we used ex situ methods, AFM, TEM and gas porosimetry, for characterization at the nanoscale. The DSA (R) coating was found to consist of mono-crystalline grains with a size of 20-30 nm and with pores of about 10 nm in diameter. Using a simple geometrical model an effective area was calculated. For a typical coating thickness, an increase of about 1000 times in the effective surface area was found, which is consistent with in situ estimations. These results suggest that the dominating source of surface enlargement is due to nano-crystallinity.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2008. Vol. 100, no 052026, 4-4 p.
Series
Journal of Physics Conference Series, ISSN 1742-6588 ; 100
Keyword [en]
nanoteknik nanotechnology
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:miun:diva-4291DOI: 10.1088/1742-6596/100/5/052026ISI: 000275655200122Local ID: 5088OAI: oai:DiVA.org:miun-4291DiVA: diva2:29323
Conference
17th International Vacuum Congress/13th International Conference on Surface Science/Internatinal Conference on Nanoscience and Technology, Jul 02-06, 2007, Stockholm, Sweden
Available from: 2008-09-30 Created: 2009-03-19 Last updated: 2016-09-22Bibliographically approved
In thesis
1. Nanoscaled Structures in Ruthenium Dioxide Coatings
Open this publication in new window or tab >>Nanoscaled Structures in Ruthenium Dioxide Coatings
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

An essential ingredient in the generation of environmentally compatible pulp bleaching chemicals is sodium chlorate. Chlorate is produced in electrochemical cells, where the electrodes are the key components. In Sweden the so-called DSA !R electrodes with catalytic coatings have been produced for more than 35 years. The production of chlorate uses a large amount of electric energy, and a decrease of just five percent of this consumption would, globally, decrease the consumption of electrical energy corresponding to half a nuclear power reactor. The aim of this project is to improve the electrode design on the nanoscale to decrease the energy consumption. The success of the DSA!R depends on the large catalytic area of the coating, however, little is known about the actual structure at the nanometer level. To increase the understanding of the nanostructure of these coatings, we used a number of methods, including atomic force microscopy, transmission electron microscopy, X-ray diffraction, porosimetry, and voltammetric charge. We found that the entire coating is built up of loosely packed rutile mono-crystalline 20 − 30 nm sized grains. The small grain sizes give a the large area, and consequently, lower cell-voltage and reduced energy consumption. A method to control the grain size would thus be a way to control the electrode efficiency. To alter the catalytically active area, we made changes in the coating process parameters. We found a dependency of the crystal-grain sizes on the choice of ruthenium precursor and processing temperature. The use of ruthenium nitrosyl nitrate resulted in smaller grains than ruthenium chloride and lowering the temperature tended to favour smaller grains. A more radical way would be to create a totally different type of electrode, manufactured in another way than using the 1965 DSA !R recipe. Such new types of electrodes based on, for example, nanowires or nanoimprint lithography, are discussed as future directions.

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University, 2009
Series
Mid Sweden University licentiate thesis, ISSN 1652-8948 ; 36
Keyword
Bleaching chemicals, sodium chlorate, ruthenium dioxide, electrodes, crystallites, nanowires, microscopy, diffraction, electrocatalytic area, reduced energy consumption
National Category
Natural Sciences
Identifiers
urn:nbn:se:miun:diva-8728 (URN)978-91-86073-33-6 (ISBN)
Presentation
(English)
Supervisors
Available from: 2009-03-19 Created: 2009-03-19 Last updated: 2013-11-01Bibliographically approved
2. Nanoscaled Structures of Chlorate Producing Electrodes
Open this publication in new window or tab >>Nanoscaled Structures of Chlorate Producing Electrodes
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Sodium chlorate is mainly used for production of chlorine dioxide (a pulp bleaching agent). Sodium chlorate is produced by an electrochemical process where chloride ions (from sodium chloride dissolved in water) are oxidized to chlorine on the anodes and hydrogen is evolved on the cathodes. The anode of this process consists of a metal plate coated with a catalytically active metal oxide film. The electrocatalytic properties of the anode coating film have been widely investigated due to the great importance of these electrodes in the electrochemical industry. The material properties are, however, not as well investigated, and the studies described in this thesis are an attempt to remedy this.

Several standard material characterization methods were used, such as SEM, TEM, AFM, EDX, XRD, porosimetry and DSC. Also, a novel model system based on spin coated electrode films on smooth substrates was developed. The model system provided a way to design samples suitable for e.g. TEM, where the sample thickness is limited to maximum of 100 nm. This is possible due to the ability to control the film thickness by the spinning velocity when using the spin coating technique.

It was shown here that the anode coating has a nanostructure. It consists of grains, a few tens of nanometers across. The nanostructure leads to a large effective area and thus provides an explanation of the superior catalytic properties of these coatings. The grains were also shown to be monocrystalline. The size of these grains and its origin was investigated. The calcination temperature, the precursor salt and (if any) doping material all affected the grain size. A higher calcination temperature yielded larger grains and doping with cobalt resulted in smaller grains and therefore a larger real area of the coating. Some preparation conditions also affected the microstructure of the coating; such as substrate roughness. The microstructure is for example the cracked-mud structure. A smoother substrate gave a lower crack density.

The cathode of chlorate production is usually an uncoated metal plate, therefore 'less catalytically active'. It is, however, possible to activate the cathode by for example in situ additions to the electrolyte. It was shown here that sufficient addition of molybdate to the electrolyte resulted in a molybdenum film deposited on the cathode and thereby an increase of its surface area and an activation the hydrogen evolution reaction.

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University, 2012
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 134
National Category
Natural Sciences
Identifiers
urn:nbn:se:miun:diva-17206 (URN)978-91-87103-35-3 (ISBN)
Public defence
2012-11-09, M102, 13:15 (Swedish)
Opponent
Supervisors
Available from: 2012-10-18 Created: 2012-10-17 Last updated: 2012-11-30Bibliographically approved

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Malmgren, ChristineHummelgård, MagnusBäckström, JoakimOlin, Håkan
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