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Synthesis, Characterization, and Evaluation of Ag-based Electrical Contact Materials
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
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 [en]
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: urn:nbn:se:uu:diva-320235ISBN: 978-91-554-9915-0 (print)OAI: oai:DiVA.org:uu-320235DiVA: diva2:1089132
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
List of papers
1. Tuning tribological, mechanical and electrical properties of Ag-X (X=Al, In, Sn) alloys
Open this publication in new window or tab >>Tuning tribological, mechanical and electrical properties of Ag-X (X=Al, In, Sn) alloys
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(English)Manuscript (preprint) (Other academic)
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:uu:diva-320227 (URN)
Available from: 2017-04-18 Created: 2017-04-18 Last updated: 2017-04-18
2. The Influence of Chemical and Phase Composition on Mechanical, Tribological and Electrical Properties of Ag-Al Alloys
Open this publication in new window or tab >>The Influence of Chemical and Phase Composition on Mechanical, Tribological and Electrical Properties of Ag-Al Alloys
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(English)Manuscript (preprint) (Other academic)
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:uu:diva-320229 (URN)
Available from: 2017-04-18 Created: 2017-04-18 Last updated: 2017-04-18
3. Combinatorial Study of Gradient Ag-Al Thin Films: Microstructure, Phase Formation, Mechanical and Electrical Properties
Open this publication in new window or tab >>Combinatorial Study of Gradient Ag-Al Thin Films: Microstructure, Phase Formation, Mechanical and Electrical Properties
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2016 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 8, no 44, 30635-30643 p.Article in journal (Refereed) Published
Abstract [en]

A combinatorial approach is applied to rapidly deposit and screen Ag-Al thin films-to evaluate the mechanical, tribological, and electrical properties as a function of chemical composition. Ag-Al thin films with large continuous composition gradients (6-60 atom % Al) were deposited by a custom-designed combinatorial magnetron sputtering system. X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), scanning and transmission electron microscopy (SEM and TEM), X-ray photoelectron spectroscopy (XPS), nanoindentation, and four-point electrical resistance screening were employed to characterize the chemical composition, structure, and physical properties of the films in a time-efficient way. For low Al contents (<13 atom %), a highly (111)-textured fcc phase was formed. At higher Al contents, a (002)-textured hcp solid solution phase was formed followed by a fcc phase in the most At-rich regions. No indication of a mu phase was observed. The Ag-Al films with fcc-Ag matrix is prone to adhesive material transfer leading to a high friction coefficient (>1) and adhesive wear, similar to the behavior of pure Ag. In contrast, the hexagonal solid solution phase (from ca. 15 atom %Al) exhibited dramatically reduced friction coefficients (about 15% of that of the fcc phase) and dramatically reduced adhesive wear when tested against the pure Ag counter surface. The increase in contact resistance of the Ag Al films is limited to only 50% higher than a pure Ag reference sample at the low friction and low wear region (19-27 atom %). This suggests that a hcp Ag Al alloy can have a potential use in sliding electrical contact applications and in the future will replace pure Ag in specific electromechanical applications.

Keyword
Ag-Al alloy, combinatorial approach, low friction, adhesive wear, hexagonal phase, electrical contact
National Category
Materials Chemistry Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-310756 (URN)10.1021/acsami.6b10659 (DOI)000387737200089 ()
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage, 38432-1Knut and Alice Wallenberg FoundationSwedish Foundation for Strategic Research
Available from: 2016-12-20 Created: 2016-12-19 Last updated: 2017-04-18Bibliographically approved
4. Combinatorial magnetron sputtering of AgFeO2 thin films with the delafossite structure
Open this publication in new window or tab >>Combinatorial magnetron sputtering of AgFeO2 thin films with the delafossite structure
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2016 (English)In: Materials & Design, ISSN 0261-3069, Vol. 91, 132-142 p.Article in journal (Refereed) Published
Abstract [en]

The main objective of this study is to demonstrate the strength of the combinatorial approach to rapidly and effectively identify suitable process parameters for the synthesis of AgFeO2 filmswith layered delafossite structure. (00l)- textured delafossite AgFeO2 thin films have been successfully deposited for the first time without post-annealing by magnetron sputtering from elemental silver and iron targets in a reactive Ar-O-2 atmosphere. Gradient filmswith a wide composition range were deposited on singlewafers and subsequent screenings of phase- and chemical compositions were employed to optimize process parameters. The optimum deposition temperature for single-phase AgFeO2 growth was 450 degrees C using a Ag target powered at 15 W with a pulsing frequency of 150 kHz and a Fe target powered at constant 120 W at a total pressure of 4 mTorr and a O-2 partial pressure of 0.8 mTorr. Selected films were studied with scanning electron microcopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The optical band gap for the indirect transition in the AgFeO2 film was determined to 1.7 +/- 0.1 eV, and the band gap for the direct transition was 2.5 +/- 0.1 eV. The film showed insulating electrical properties.

Keyword
Combinatorial sputtering, Delafossite, Thin film, AgFeO2
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-274897 (URN)10.1016/j.matdes.2015.11.092 (DOI)000367235400016 ()
External cooperation:
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy StorageKnut and Alice Wallenberg FoundationSwedish Research Council
Available from: 2016-02-02 Created: 2016-01-26 Last updated: 2017-04-18Bibliographically approved
5. Solution-based synthesis of AgI coatings for low-friction applications
Open this publication in new window or tab >>Solution-based synthesis of AgI coatings for low-friction applications
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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.

National Category
Natural Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-193479 (URN)10.1007/s10853-012-6999-5 (DOI)000312906400043 ()
Available from: 2013-02-05 Created: 2013-02-04 Last updated: 2017-04-18Bibliographically approved
6. Graphene as a lubricant on Ag for electrical contact applications
Open this publication in new window or tab >>Graphene as a lubricant on Ag for electrical contact applications
2015 (English)In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 50, no 19, 6518-6525 p.Article in journal (Refereed) Published
Abstract [en]

The potential of graphene as a solid lubricant in sliding Ag-based electrical contacts has been investigated. Graphene was easily and quickly deposited by evaporating a few droplets of a commercial graphene solution in air. The addition of graphene reduced the friction coefficient in an Ag/Ag contact with a factor of similar to 10. The lubricating effect was maintained for more than 150,000 cycles in a pin-on-disk test at 1 N. A reduction in friction coefficient was also observed with other counter surfaces such as steel and W but the life time was strongly dependent on the materials combination. Ag/Ag contacts exhibited a significantly longer life time than steel/Ag and W/Ag contacts. The trend was explained by an increased affinity for metal-carbon bond formation.

National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-260595 (URN)10.1007/s10853-015-9212-9 (DOI)000358149600028 ()
Funder
Knut and Alice Wallenberg FoundationSwedish Foundation for Strategic Research
Available from: 2015-08-25 Created: 2015-08-21 Last updated: 2017-04-18Bibliographically approved
7. The influence of oxygen in TiAlOxNy on the optical properties of colored solar-absorbing coatings
Open this publication in new window or tab >>The influence of oxygen in TiAlOxNy on the optical properties of colored solar-absorbing coatings
2012 (English)In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, Vol. 98, 179-184 p.Article in journal (Refereed) Published
Abstract [en]

Low cost and ease of fabrication are important factors for solar-thermal applications in energy-efficient buildings. This contribution reports the influence of oxygen on structure, optical properties and chromaticity of TiAlOxNy thin films prepared by DC magnetron sputtering. It is an extension of a previous study on colored solar-thermal absorbers based on titanium-aluminum nitride. The purpose is to investigate the possibility of using TiAlOxNy as middle layer to achieve a gradient effect. The results reveal that the structure and optical properties of the TiAlOxNy coatings are sensitive to the oxygen content under certain sputtering conditions.  The ratio of oxygen/nitrogen of 0.7:10 is the most appropriate to form the crystalline structure of TiAlON.  The optical constants of TiAlN and TiAlON were deduced by fitting the experimental data. It shows that both the refractive index (n) and the extinction coefficient (k) are decreased when oxygen is introduced to form titanium-aluminium nitro-oxide. The gradient effect can be achieved and controlled by adjusting the ratio of oxygen/nitrogen flow during the process to enhance solar absorptance while keeping the desired color appearance.

Place, publisher, year, edition, pages
Amsterdam: Elsevier, 2012
Keyword
Titanium-aluminum nitride/nitro-oxide; colored solar-thermal absorber; optical properties; chromaticity.
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-164134 (URN)10.1016/j.solmat.2011.11.001 (DOI)000300536500023 ()
Available from: 2011-12-19 Created: 2011-12-16 Last updated: 2017-04-18Bibliographically approved
8. Deposition and characterization of reactive magnetron sputtered zirconium carbide films
Open this publication in new window or tab >>Deposition and characterization of reactive magnetron sputtered zirconium carbide films
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2013 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 232, 876-883 p.Article in journal (Refereed) Published
Abstract [en]

Zirconium carbide films have been deposited on silicon (100) substrates using direct current magnetron reactive sputtering using CH4 as a carbon source. The films exhibit a typical nanocomposite structure consisting of nanocrystalline ZrCx (nc-ZrC) grains embedded in a matrix of amorphous carbon (a-C) at low carbon content. Almost no crystalline phase can be found for carbon contents above 86 at.%. The mechanical, tribological and electrical properties of the films showed a significant dependency on the amount of the a-C in the nanocomposite structure. A larger amount of a-C gives rise to reduced hardness and higher resistivity of the film. However, both friction coefficient and wear resistance are improved by increasing the content of the surplus a-C. The influence of binding state of excess a-C phase on the properties has also been investigated. A larger sp(2)/sp(3) ratio was beneficial to relax the stress and improve the electrical properties. The Zr-based films exhibited lower friction coefficients than nanocomposites films based on e.g. Ti suggesting a potential application for this material in sliding contacts.

Keyword
Zirconium carbide, Mechanical properties, Friction and wear, Electrical resistivity, Magnetron sputtering
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-214005 (URN)10.1016/j.surfcoat.2013.06.116 (DOI)000327691300113 ()
Available from: 2014-01-06 Created: 2014-01-06 Last updated: 2017-04-18Bibliographically approved
9. Characterization of amorphous Zr-Si-C thin films deposited by DC magnetron sputtering
Open this publication in new window or tab >>Characterization of amorphous Zr-Si-C thin films deposited by DC magnetron sputtering
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2015 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 261, 227-234 p.Article in journal (Refereed) Published
Abstract [en]

Zr-x(SiyC1-y)(1-x) films with different Si/C atomic ratios and Zr contents were deposited using non-reactive dc-magnetron co-sputtering. All films exhibited an X-ray amorphous structure with a complex distribution of chemical bonds. The presence of Zr in the films reduced the amount of C-C and Si-C bonds but favored the formation of Zr-C and Zr-Si bonds. The mechanical and electrical properties were dependent on the bond distribution in the amorphous structure and a linear relationship between film hardness and the relative amount of Si-C bonds was observed. The addition of Zr in films also gave rise to an increase in metallic character resulting in a lower electrical resistivity. Analysis of the tribofilm showed that a low friction coefficient was favored by the formation of a lubricating a-C layer and that the formation of zirconium and silicon oxides in the more Zr-rich films has a detrimental effect on the tribological performance. (C) 2014 Elsevier B.V. All rights reserved.

Keyword
Zirconium silicon carbide, Chemical bond structure, Mechanical properties, Tribofilm, Electrical resistivity
National Category
Other Chemistry Topics
Identifiers
urn:nbn:se:uu:diva-245365 (URN)10.1016/j.surfcoat.2014.11.024 (DOI)000348255500031 ()
Available from: 2015-02-26 Created: 2015-02-26 Last updated: 2017-04-18Bibliographically approved
10. A polymer foil non-contact IR temperature sensor with a thermoresistor integrated on the back of a vertically configured thermopile
Open this publication in new window or tab >>A polymer foil non-contact IR temperature sensor with a thermoresistor integrated on the back of a vertically configured thermopile
2012 (English)In: Sensors and Actuators A-Physical, ISSN 0924-4247, Vol. 179, 56-61 p.Article in journal (Refereed) Published
Abstract [en]

A very thin non-contact IR temperature sensor has been fabricated in a polymer foil. A thermoresistor was placed in the isothermal back-layer of a vertical configured IR-sensor. The IR-sensor is a thermopile consisting of through-the-foil thermocouple legs in a flexible polyimide foil, and the integration of a thermoresistor to one of its surfaces enables use of the sensor for non-contact temperature measurements. The size of the sensor is 3 mm x 3 mm and the thickness is less than 0.2 mm. The sensor can easily be surface mounted to printed circuit boards. An ion track technique followed by lithographically controlled electroplating of nanowires and thin film deposited interconnects are used to fabricate the infrared sensor. The thin film nickel thermoresistor was fabricated using evaporation. Layers of Parylene C was used for electric insulation and protection to improve environmental stability. In the temperature range of 20-55 degrees C, the thermoresistor shows good linearity. Some initial decrease in resistance was seen at 105 degrees C whereafter the resistance stabilized. The IR temperature sensor was characterized, and for temperatures near room temperature a simple linear equation using the voltage response and temperature of the thermoresistor as the only input parameters was curve fitted to the experimental data. The difference between the measured and the calculated object temperature is less than 0.5 degrees C using a confidence level of 95%.

Keyword
Non-contact IR sensor, Polyimide, Thermopile, Thermoresistor
National Category
Engineering and Technology Inorganic Chemistry
Research subject
Engineering Science with specialization in Microsystems Technology; Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-175607 (URN)10.1016/j.sna.2012.03.022 (DOI)000304077100009 ()
Available from: 2012-06-13 Created: 2012-06-11 Last updated: 2017-04-18Bibliographically approved

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