| 1. |
- Johansson, Pontus, et al.
(författare)
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Mechanisms behind the environmental sensitivity of carbon fiber reinforced polytetrafluoroethylene (PTFE)
- 2024
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Ingår i: Friction. - : Springer Nature. - 2223-7690 .- 2223-7704. ; 12:5, s. 997-1015
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Tidskriftsartikel (refereegranskat)abstract
- Carbon fiber reinforced polytetrafluoroethylene (CF/PTFE) composites are known for their exceptional tribological performance when sliding against steel or cast iron in inert gas environments. Compared to experiments in humid air, about an order of magnitude lower wear rate and several times lower coefficient of friction have been reported for tests conducted in dry nitrogen and hydrogen. Moreover, trace moisture has been shown to affect the friction and wear significantly of this tribosystem, although a possible effect of oxygen cannot be ruled out due to uncertainties regarding the oxygen concentrations. While several studies have pointed out the environmental sensitivity of CF/PTFE, the understanding of the underlying mechanisms are very limited. The objective of this research is to investigate the individual and combined effect of oxygen and moisture on the tribological behavior of CF/PTFE sliding against steel. Additionally, this study aims to elucidate the underlying mechanisms that govern the environmental sensitivity of the system. Climate-controlled three-pin-on-disc experiments were conducted in nitrogen atmospheres at various concentrations of oxygen and moisture. The tribological results clearly demonstrate that both moisture and oxygen contribute to increased friction and wear. However, the adverse effect was much more pronounced for oxygen than moisture. A qualitative method was developed to estimate the tribofilm coverage on the CF/PTFE surface. Results showed strong correlation between high coverage of strongly adhered tribofilm and low wear rate. Moreover, a loosely adhered tribofilm was observed on top of the CF/PTFE surface in presence of moisture. FTIR analysis indicated that the loosely adhered tribofilm found in the moisture-enriched environment contained a significant amount of adsorbed water, which may explain the lower coefficient of friction in presence of moisture compared to oxygen. The adsorbed water in the loosely adhered tribofilm could be an indication of moisture-driven lubrication by the non-graphitic carbon in the tribofilm.
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| 2. |
- Johansson, Pontus, et al.
(författare)
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Effect of Oxygen and Moisture on the Friction and Wear of Carbon Fiber-Reinforced Polymers
- 2023
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Ingår i: Lubricants. - : MDPI. - 2075-4442. ; 11:9
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Tidskriftsartikel (refereegranskat)abstract
- Carbon fiber-reinforced polytetrafluoroethylene (CF/PTFE) composites are frequently used in tribological dry gas applications, such as in dynamic seals in reciprocating hydrogen gas compressors and Stirling engines, due to their superior friction and wear. Due to the increasing concerns regarding fluoropolymers as possible pollutants of harmful per- and poly-fluoroalkyl substances (PFAS) emissions, replacements for PTFE should be investigated. The literature indicates that CF-reinforced polyetheretherketone (CF/PEEK) may have similar favorable tribological properties to CF/PTFE. However, the tribological behavior of CF/PEEK in dry gas is poorly understood, and no direct comparison has been made between the two materials. The aim of this study was to compare the effect of oxygen and moisture on the friction and wear of CF/PTFE and CF/PEEK. Tribological tests were carried out with a tri-pin-on-disc tribometer in a nitrogen environment with individually controlled contents of oxygen and moisture. The results showed that the effect of oxygen and moisture are distinctly different for CF/PTFE and CF/PEEK. While CF/PTFE performs best in oxygen-deficient environments, CF/PEEK performs best in moisture-enriched environments. Complementary tests with a PTFE composite filled with both CF and PEEK suggested that the environmental sensitivity can be significantly reduced by combining the two polymers.
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| 3. |
- Johansson, Pontus, et al.
(författare)
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Insights of the Ultralow Wear and Low Friction of Carbon Fiber Reinforced PTFE in Inert Trace Moisture Environment
- 2023
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Ingår i: Tribology letters. - : Springer. - 1023-8883 .- 1573-2711. ; 71:3
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Tidskriftsartikel (refereegranskat)abstract
- Ultralow wear rates and low friction have been observed for carbon fiber reinforced PTFE (CF/PTFE) when sliding against steel or cast iron in dry gas environments. Although the strong environmental sensitivity of this tribosystem is well known, the origin of the outstanding tribological performance in dry gas remains unanswered. Some researchers attribute the low friction and wear to the formation of carbon-rich surfaces in the absence of oxygen and moisture in the environment. However, low friction between carbon surfaces is generally dependent on moisture. In this paper, extensive analyzes are conducted on the tribofilms formed on the CF/PTFE surface and the steel counterface after sliding in a high-purity nitrogen environment. TEM analysis of a cross-section of the tribofilm on the steel surface reveals that the sliding surface consists mainly of iron (II) fluoride and not carbon, even though a significant amount of carbon was observed near the surface. XPS and TEM analysis further revealed that the tribofilm formed on the worn composite surface consisted of nanoparticle agglomerates, anchored to the PTFE matrix and to each other by carbon with turbostratic structure. Turbostratic carbon also formed an ultrathin and surface-oriented superficial layer on top of the agglomerates. Governing mechanisms of the low friction and wear of the CF/PTFE—steel tribosystem were investigated by complementary tribotests with pure graphite samples and MD simulations of the identified surfaces. These indicated that the low friction between the carbon and iron fluoride in the tribofilms is due to poor adhesion between the distinctly different surfaces.
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| 4. |
- Johansson, Pontus
(författare)
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Tribology of carbon fiber reinforced PTFE composites in dry gas environments
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With hydrogen being one of the key pillars of decarbonization, the reliability and efficiency of hydrogen applications become increasingly important. In applications such as oil-free reciprocating hydrogen compressors and Stirling engines, the self-lubricating pistonrings and other dynamic seals are critical components in terms of efficiency, service life and proper functioning. These components are commonly made from carbon fiber reinforced PTFE (CF/PTFE) composites, which need to work under very dry conditions. Up tothis day, the available literature on the tribology of CF/PTFE in dry gas environments is scarce and the fundamental understanding of the governing mechanisms behind its low friction and wear in such environments is limited. The main aim of this research project is to increase the fundamental understanding of the tribology of CF/PTFE in dry gas environments, focusing on how gas impurities and counterface properties affect the tribological performance, as well as to investigate the governing mechanisms behind the ultralow wear and low friction in inert gas atmosphere. Since fluoropolymers are potential emitters of harmful PFAS during their lifecycle, restrictions towards the use of fluoropolymers are currently considered by the European Chemical Agency (ECHA). Therefore, a secondary aim is to evaluate the tribological performance of other potential carbon fiber reinforced polymers in dry gas environments.To be able to study the tribology CF/PTFE composites in dry gas environments, a climate control system was developed to enable continuous monitoring and precise control of the moisture and oxygen content at ppm levels. Tribological investigations in gas environments with different levels of oxygen and moisture highlight the environmental sensitivity of CF/PTFE composites. CF/PTFE composites have superior tribological performance in high-purity gas environments, where small amounts of oxygen have a detrimental effect on friction and wear. Moisture also affects the tribological performance negatively. However, the effect of moisture is rather mild in comparison to oxygen and the coefficient of friction remain slow. Analysis of the tribofilms formed on the counterface and the CF/PTFE surface in high-purity and in moisture-enriched gas indicate that the mechanisms behind the low friction and wear are different for the two environments. In high-purity gas, the sliding takes place between an iron fluoride tribofilm on the counterface and a carbon-based tribofilm on the CF/PTFE surface. Molecular dynamics simulations corroborated this finding, where simulations showed a similar coefficient of friction between a non-graphitic carbonsurface and an iron fluoride surface as in the experiments. For the moisture-enriched environment, the low coefficient of friction could be related to the generation of carbon in the sliding interface, which becomes lubricious in the presence of moisture.CF/PEEK was selected as a potential replacement for CF/PTFE due to its reported low friction when sliding against steel in a dry gas environment. From the evaluation of the tribological performance of CF/PEEK in dry gas environments, it could be concluded that CF/PEEK may be an appropriate replacement for CF/PTFE in moisture-rich environments. However, in moisture-deficient environments, CF/PEEK wears excessively.The effect of counterface properties on the friction and wear of CF/PTFE composites has been studied by testing different materials, roughness and hardness individually. The counterface material had a distinct effect on friction and further changed the effect of the environment on friction and wear. Roughness only had a slight negative effect on the wear of the CF/PTFE composite during steadystate conditions for the tested range of roughness levels. Moreover, it was found that the coefficient of friction at steady-state conditions is unaffected by roughness, while the friction behavior during running-in varies significantly between a smooth and a rough countersurface. Furthermore, the transient wear of the PTFE composite was higher against a rough counterface than a smooth. Surface analysis from different stages of running-in was done to elucidate the formation of tribofilms and their different characteristics. For the rough counterface, a loosely adhered transfer film is transitionally formed at the beginning of sliding to enable the formation of a persistent transfer film. Contrarily, in the case of a smooth countersurface, the formation of a persistent transfer film is initiated from the start. Hardness did not show any significant effect on friction or wear during steady-state sliding.In summary, the superior tribological performance of CF/PTFE when sliding against a steel counterface in high-purity gas can be related to the beneficial mechanical and tribochemical degradation of PTFE and carbon fiber in the absence of oxygen and moisture. Since the defluorination of PTFE is key to the formation of robust tribofilms in high-purity gas, PTFE cannot be easily replaced by another polymer that does not contain carbon–fluorine bonds. Contrarily, the tribological performance of carbon fiber reinforced polymers in moisture-rich environments is governed by the carbonfibers, where formed carbon-based tribofilms become lubricious in the presence of moisture. Due to the strong link between tribochemical reactions and the tribological performance of CF/PTFE, the chemical composition of the counterface has a significant effect on the friction and wear of the system.
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| 5. |
- Johansson, Pontus, et al.
(författare)
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Effect of roughness on the running-in behavior and tribofilm formation of carbon fiber reinforced PTFE composite in trace moisture environment
- 2022
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Ingår i: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 500-501
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Tidskriftsartikel (refereegranskat)abstract
- Counterface roughness is known to affect the tribological behavior of carbon fiber reinforced PTFE. However, the effect of roughness in trace moisture environments has not yet been extensively investigated. In this study, the tribological behavior and tribofilm formation were evaluated for a carbon fiber reinforced PTFE composite sliding in a trace moisture environment against 34CrNiMo6 steel counterfaces with different roughness. Tribotests were conducted with a three-pin-on-disc tribometer at a sliding velocity of 2.2 m/s and in a nitrogen environment with moisture content controlled to 11 ppm. Generally, smoother counterfaces gave lower wear, both during running-in and steady-state. Contrarily, the coefficient of friction was only affected by roughness during running-in. Surface analysis from different stages of running-in were done to elucidate the formation of tribofilms and their different characteristics. For the rough countersurface, a loosely adhered transfer film is transitionally formed at the beginning of sliding to enable the formation of a persistent transfer film. Contrarily, for the case of a smooth countersurface, the formation of a persistent transfer film is initiated from the start. Similarly for the rough and smooth countersurface, a micrometer thick tribofilm with excellent low friction properties is observed on the PTFE composite after running-in.
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| 6. |
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| 7. |
- Johansson, Pontus, et al.
(författare)
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Effect of humidity and counterface material on the friction and wear of carbon fiber reinforced PTFE composites
- 2021
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Ingår i: Tribology International. - : Elsevier. - 0301-679X .- 1879-2464. ; 157
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Tidskriftsartikel (refereegranskat)abstract
- The tribological performance of PTFE composites is affected by both the composition of the counterface material and the sliding environment. However, no comprehensive investigation has been conducted on the combined effect of the humidity and counterface material on PTFE composites. This study investigates the tribological behavior of carbon fiber reinforced PTFE composites sliding in a dry nitrogen environment at different humidity levels. Experiments were conducted in an enclosed tri-pin-on-disc tribometer against two different metallic counterface materials. Tests in laboratory air were used for comparison. Results indicate that the tribological performance of carbon fiber reinforced PTFE composites are sensitive to environmental changes. The impact of humidity on both the coefficient of friction and specific wear rate was up to about 40%.
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| 8. |
- Johansson, Pontus, et al.
(författare)
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Precise control of operating conditions in tribotesting with respect to trace humidity and contact temperature
- 2021
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Ingår i: MethodsX. - : Elsevier. - 1258-780X .- 2215-0161. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Research in tribology are often connected to tribosystems operating in specific environments, where climate chambers are needed for tribotesting to resemble the environmental conditions in the real application. Although the effect of humidity on the tribological performance of many materials and lubricants is evident, many studies are conducted without sufficient systems to accurately monitor and control the humidity level throughout testing. In this paper, a humidity controlling system was developed to enable continuous monitoring and precise control of the humidity at trace moisture levels. The climate controller was validated in a tri-pin-on-disc tribometer with excellent performance and can be fitted to most climate chambers. To further improve the control of operating conditions during tribotesting, a thermodynamic simulation of the contact temperature was developed.• The developed climate controller is a simple and cost-effective method to accurately monitor and control the humidity in a climate chamber at trace moisture levels.• The portable design of the humidity controller enables use with most climate chambers and enclosed tribometers.• To have better control over the temperature in the sliding interface during testing, a thermodynamic simulation method was used to estimate contact temperature between sliding bodies from near-contact temperature measurements and the measured friction forces.
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| 9. |
- Johansson, Pontus, et al.
(författare)
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Blubblubblubb
- 2020
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Ingår i: Rampen, Bibliotek i Uddevalla.
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Konstnärligt arbete (övrigt vetenskapligt/konstnärligt)abstract
- Blubblubblubb är en konstgestaltning på ett nytt bibliotek i Uddevalla. Verket består av rumsskapande element, textila installationer, textila skulpturer, väggmålning, möbler, mattor, ljud, en saga samt en tanke om hur tematiken kan vara ett stöd och en inspriration i det dagliga arbetet. Målgruppen är främst barn och unga.
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| 10. |
- Graff, Pål, 1973-, et al.
(författare)
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Evaluating Measuring Techniques for Occupational Exposure during Additive Manufacturing of Metals : A Pilot Study
- 2017
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Ingår i: Journal of Industrial Ecology. - : John Wiley & Sons. - 1088-1980 .- 1530-9290. ; 21:Suppl. 1, s. S120-S129
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Tidskriftsartikel (refereegranskat)abstract
- Additive manufacturing that creates three-dimensional objects by adding layer uponlayer of material is a new technique that has proven to be an excellent tool for themanufacturing of complex structures for a variety of industrial sectors. Today, knowl-edge regarding particle emissions and potential exposure-related health hazards forthe operators is limited. The current study has focused on particle numbers, masses,sizes, and identities present in the air during additive manufacturing of metals. Mea-surements were performed during manufacturing with metal powder consisting es-sentially of chromium, nickel, and cobalt. Instruments used were Nanotracer (10 to300 nanometers [nm]), Lighthouse (300 nm to 10 micrometers), and traditional filter-basedparticle mass estimation followed by inductively coupled plasma mass spectrometry. Resultsshowed that there is a risk of particle exposure at certain operations and that particle sizestended to be smaller in recycled metal powder compared to new. In summary, nanosizedparticles were present in the additive manufacturing environment and the operators wereexposed specifically while handling the metal powder. For the workers’ safety, improvedpowder handling systems and measurement techniques for nanosized particles will possiblyhave to be developed and then translated into work environment regulations. Until then,relevant protective equipment and regular metal analyses of urine is recommended.
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