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Solution-based synthesis of AgI coatings for low-friction applications
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
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2013 (English)In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 48, no 5, 2236-2244 p.Article in journal (Refereed) Published
Abstract [en]

Thin films of AgI have been synthesized from Ag surfaces and elemental I-2 using a rapid and simple solution-based method. The effect of using ultrasound during the synthesis was studied, as well as the influence of the nature of the solvent, the I-2 concentration, the time, the temperature, and the sonication power. The films were characterized using X-ray diffraction, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy, and found to consist of beta-AgI, possibly along with some gamma-AgI. It was found that sonication increases the film thickness and grain size. The nature of the solvent has a profound effect on the film growth, with mixtures of water and ethanol leading to thicker coatings than films synthesized using either component in its pure form. Selected coatings were tribologically tested, and the AgI coating was seen to lower the friction coefficient significantly compared to a reference Ag surface under otherwise identical conditions. Long lifetimes (over 30000 cycles) were seen against a Ag counter surface. Tracks and wear scars were studied using SEM and Raman spectroscopy, and it was found that the friction level remains low as long as there is AgI in the points of contact. This method is found to be a simple and fast way to deposit AgI on Ag with large possibilities of tuning the thickness and grains sizes of the resulting films, thereby optimizing it for the desired use.

Place, publisher, year, edition, pages
2013. Vol. 48, no 5, 2236-2244 p.
National Category
Natural Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Materials Science
Identifiers
URN: urn:nbn:se:uu:diva-193479DOI: 10.1007/s10853-012-6999-5ISI: 000312906400043OAI: oai:DiVA.org:uu-193479DiVA: diva2:603294
Available from: 2013-02-05 Created: 2013-02-04 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Synthesis, Characterization, and Evaluation of Ag-based Electrical Contact Materials
Open this publication in new window or tab >>Synthesis, Characterization, and Evaluation of Ag-based Electrical Contact Materials
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Ag is a widely used electrical contact material due to its excellent electrical properties. The problems with Ag are that it is soft and has poor tribological properties (high friction and wear in Ag/Ag sliding contacts). For smart grid applications, friction and wear became increasingly important issues to be improved, due to much higher sliding frequency in the harsh operation environment. The aim of this thesis is to explore several different concepts to improve the properties of Ag electrical contacts for smart grid applications.

Bulk Ag-X (X=Al, Sn In) alloys were synthesized by melting of metals. An important result was that the presence of a hcp phase in the alloys significantly reduced friction coefficients and wear rates compared to Ag. This was explained by a sliding-induced reorientation of easy-shearing planes in the hexagonal structure. The Ag-In system showed the best combination of properties for potential use in future contact applications. 

This thesis has also demonstrated the strength of a combinatorial approach as a high-throughput method to rapidly screen Ag-based alloy coatings. It was also used for a rapid identification of optimal deposition parameters for reactive sputtering of a complex AgFeO2 oxide with narrow synthesis window. A new and rapid process was developed to grow low frictional AgI coatings and a novel designed microstructure of nanoporous Ag filled with AgI (n-porous Ag/AgI) using a solution chemical method was also explored. The AgI coatings exhibited low friction coefficient and acceptable contact resistance. However, under very harsh conditions, their lifetime is too short. The initial tribotests showed high friction coefficient of the n-porous Ag/AgI coating, indicating an issue regarding its mechanical integrity.

The use of graphene as a solid lubricant in sliding electrical contacts was investigated as well. The results show that graphene is an excellent solid lubricant in Ag-based contacts. Furthermore, the lubricating effect was found to be dependent on chemical composition of the counter surface. As an alternative lubricant, graphene oxide is cheaper and easier to produce. Preliminary tests with graphene oxide showed a similar frictional behavior as graphene suggesting a potential use of this material as lubricant in Ag contacts.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. 98 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1517
Keyword
electrical contact, bulk, coating, Ag-based alloys, Ag-based delafossite, AgI, graphene, graphene oxide, combinatorial material science, dc magnetron sputtering, friction, wear, hardness, contact resistance
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-320235 (URN)978-91-554-9915-0 (ISBN)
Public defence
2017-06-08, Room 2001, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2017-05-18 Created: 2017-04-18 Last updated: 2017-06-07

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Sundberg, JillMao, FangWiklund, UrbanJansson, Ulf

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