| 1. |
- Elwinger, Fredrik, et al.
(författare)
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Diffusive Transport in Pores. Tortuosity and Molecular Interaction with the Pore Wall
- 2017
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 121:25, s. 13757-13764
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Tidskriftsartikel (refereegranskat)abstract
- The self-diffusion of neat water, dimethyl sulfoxide (DMSO), octanol, and the molecular components in a water-DMSO solution was measured by H-1 and H-2 NMR diffusion experiments for those fluids imbibed into controlled pore glasses (CPG). Their highly interconnected structure is scaled by pore size and shows invariant pore topology independent of the size. The nominal pore diameter of the explored CPGs varied from 7.5 to 72.9 nm. Hence, the about micrometer mean-square diffusional displacement during the explored diffusion tithes was much larger than the individual pore size, and the experiment yielded the average diffusion coefficient Great care was taken to establish the actual pore: volumes of the CPGs. Transverse relaxation experiments processed by inverse Laplace transformation were performed to verify that the liquids explored filled exactly the available pore volume. Relative to the respective diffusion coefficients obtained in bulk phases, we observe a reduction in the diffusion coefficient that is independent of pore size for the larger pores and becomes stronger toward the smaller pores. Geometric tortuosity governs the behavior at larger pore sizes, while the interaction with pore walls becomes the dominant factor at our smallest pore diameter. Deviation from the trends predicted by the Renkin equation indicates that the interaction with the pore wall is not a just simple steric one but is in part dependent on the specific features of the molecules explored here.
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| 2. |
- Elwinger, Fredrik, et al.
(författare)
-
Diffusive transport in pores. Tortuosity and molecular interaction with the pore wall
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The self-diffusion of neat water, dimethylsulfoxide (DMSO), octanol and the molecular components in a water-DMSO solution were measured by 1H and 2H NMR diffusion experiments for those fluids imbibed into Controlled Pore Glasses (CPG). Their highly interconnected structure is scaled by pore size and shows the some pore topology independently of the size. The nominal pore diameter of the explored CPGs varied from 7.5 nm to 72.9 nm. Hence, the ∼μm mean-square diffusional displacement during the explored diffusion times was much larger than the individual pore size. Great care was taken to establish the actual pore volumes of the CPGs. In addition, transverse relaxation experiments processed by Inverse Laplace Transformation were performed to verify that the liquids explored filled exactly the available pore volume. Relative to the respective diffusion coefficients obtained in bulk phases, we observe a reduction in the diffusion coefficient that is independent of pore sizes for the larger pores and becomes larger towards the smaller pores. Geometric tortuosity governs the behavior at larger pore sizes while the interaction with pore walls becomes the dominant factor at our smallest pore diameter. The interaction with the pore wall is not just simple steric one but must in part be dependent on the specific features of the molecules explored here.
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| 3. |
- Koemmling, Anja, et al.
(författare)
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Analysis of O-Ring Seal Failure under Static Conditions and Determination of End-of-Lifetime Criterion
- 2019
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Ingår i: Polymers. - : MDPI. - 2073-4360. ; 11:8
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Tidskriftsartikel (refereegranskat)abstract
- Determining a suitable and reliable end-of-lifetime criterion for O-ring seals is an important issue for long-term seal applications. Therefore, seal failure of ethylene propylene diene rubber (EPDM) and hydrogenated nitrile butadiene rubber (HNBR) O-rings aged in the compressed state at 125 degrees C and at 150 degrees C for up to 1.5 years was analyzed and investigated under static conditions, using both non-lubricated and lubricated seals. Changes of the material properties were analyzed with dynamic-mechanical analysis and permeability experiments. Indenter modulus measurements were used to investigate DLO effects. It became clear that O-rings can remain leak-tight under static conditions even when material properties have already degraded considerably, especially when adhesion effects are encountered. As a feasible and reliable end-of-lifetime criterion for O-ring seals under static conditions should include a safety margin for slight dimensional changes, a modified leakage test involving a small and rapid partial decompression of the seal was introduced that enabled determining a more realistic but still conservative end-of-lifetime criterion for an EPDM seal.
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| 4. |
- Kömmling, Anja, et al.
(författare)
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Influence of Ageing on Sealability of Elastomeric O-Rings
- 2017
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Ingår i: MACROMOLECULAR SYMPOSIA. - : Wiley-VCH Verlagsgesellschaft. - 1022-1360.
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Konferensbidrag (refereegranskat)abstract
- At BAM, which is the federal institute for materials research and testing in Germany, it is one of our tasks to evaluate the safety of casks designed for transport and/or storage of radioactive material. This includes the assessment of the service lifetime of elastomeric seals that are part of the container lid system with regard to the requirements for long-term safety (40 years and more) of the containers. Therefore, we started an accelerated ageing programme with selected rubbers often used for seals (HNBR, EPDM and FKM) which are aged at four different temperatures (75 degrees C, 100 degrees C, 125 degrees C and 150 degrees C) up to 1.5 years. In order to assess sealability, O-rings are aged in compression by 25% (corresponding to the compression during service) between plates as well as in flanges that allow leakage rate measurements. For comparison, uncompressed O-rings are aged as well. Further methods characterising seal performance are compression stress relaxation (CSR) reflecting the loss of sealing force of a compressed seal over time, and compression set (CS) which represents the recovery behaviour of a seal after release from compression. Additionally, hardness is measured for information about the change of mechanical properties. The experimental results indicate that while hardness, CSR and CS show considerable degradation effects, the leakage rate stays relatively constant or even decreases until shrinkage combined with the loss of resilience of the aged seal leads to leakage. This demonstrates that static leakage rate, which is the only available direct seal performance criterion, has only limited sensitivity towards the degradation of the seal material. CS data is extrapolated using time-temperature shifts and Arrhenius graphs. An exemplary CS of 50% would be reached after approx. 1.2, 17 and 29 years at 60 degrees C for HNBR, EPDM and FKM respectively.
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| 5. |
- Linde, Erik, et al.
(författare)
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Non-destructive condition monitoring of aged ethylene-propylene copolymer cable insulation samples using dielectric spectroscopy and NMR spectroscopy
- 2015
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Ingår i: Polymer testing. - : Elsevier. - 0142-9418 .- 1873-2348. ; 46, s. 72-78
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Tidskriftsartikel (refereegranskat)abstract
- The causes of changes in dielectric response as a result of thermal and irradiative ageing of cable insulation of ethylene propylene copolymer rubber containing 38 wt.% filler were investigated. Samples were aged in three different combinations of irradiation dose rate and temperature, 0.42 kGy h(-1) at 85 degrees C, and 1.58 kGy h(-1) at 55 and 85 degrees C, and subsequently studied by dielectric spectroscopy, NMR spectroscopy using a portable spectrometer, and tensile testing. The extractable mass fraction and density were determined and related to the imaginary part of the dielectric permittivity at 100 kHz. The ageing led to an increase in the dielectric permittivity, stiffness, density and degree of oxidation, together with a decrease in both strain-at-break and relaxation time, as revealed by NMR spectroscopy. Except for the strain-at-break, the properties changed in a linear fashion with increasing imaginary part of the dielectric permittivity at 100 kHz, with particularly good agreement with respect to the density. As these properties are affected by the degree of oxidation, the results show that both NMR using a portable spectrometer and dielectric spectroscopy can be used as condition monitoring techniques to detect the degree of oxidation in complex systems such as filled copolymers.
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| 6. |
- Linde, Erik, et al.
(författare)
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Non-destructive condition monitoring of aged ethylene-propylenecopolymer cable insulation samples using dielectric spectroscopy and NMR spectroscopy
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The causes of changes in dielectric response as a result of thermal and irradiative ageingof a cable insulation of ethylene propylene copolymer rubber containing 38 wt.% filler wereinvestigated. Samples were aged in three different combinations of irradiation dose rate andtemperature, 0.42 kGy h–1 at 85 °C, and 1.58 kGy h–1 at 55 and 85 °C, and subsequentlystudied by dielectric spectroscopy, NMR spectroscopy using a portable spectrometer andtensile testing. The extractable mass fraction and density were determined, and related to theimaginary part of the dielectric permittivity at 100 kHz. The ageing led to an increase in thedielectric permittivity, stiffness, density and degree of oxidation, together with a decrease inboth strain-at-break and relaxation time, as revealed by NMR spectroscopy. Except for thestrain-at-break, the properties changed in a linear fashion with increasing imaginary part ofthe dielectric permittivity at 100 kHz, with a particularly good agreement with respect to thedensity. As these properties are affected by the degree of oxidation, the results show that bothNMR using a portable spectrometer and dielectric spectroscopy can be used as conditionmonitoring techniques to detect the degree of oxidation in complex systems such as filledcopolymers.
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| 7. |
- Pourmand, Payam, et al.
(författare)
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Assessment of moisture protective properties of wood coatings by a portable NMR sensor
- 2011
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Ingår i: JCT Research. - : Springer Science and Business Media LLC. - 1547-0091 .- 2168-8028. ; 8:5, s. 649-654
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Tidskriftsartikel (refereegranskat)abstract
- We have evaluated the potential of nuclear magnetic resonance (NMR) spectroscopy based on small portable magnets for in situ assessment of moisture protective properties of wood coatings. Low field (1)H NMR with a unilateral permanent magnet was used to monitor and map the local moisture content (MC) of wood specimens uncoated or coated with various types of commercial paint systems. The MC beneath a coating layer was measured with a penetration depth up to 5 mm and with a depth resolution of 0.2 mm. The method is quick, noninvasive, simple to perform, and does not require removing wooden parts from the structure.
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| 8. |
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| 9. |
- Pourmand, Payam, et al.
(författare)
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Deterioration of highly filled EPDM rubber by thermal ageing in air : Kinetics and non-destructive monitoring
- 2017
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Ingår i: Polymer testing. - : ELSEVIER SCI LTD. - 0142-9418 .- 1873-2348. ; 64, s. 267-276
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Tidskriftsartikel (refereegranskat)abstract
- The effects of air ageing at different temperatures between 110 and 170 degrees C on cable transit seals based on highly filled EPDM rubber used in nuclear power plants were studied. The changes of the macroscopic mechanical properties (Young's modulus, indentation modulus and strain-at-break) were in accordance with the Arrhenius equation with an activation energy of 110 kJ mol(-1). Profiling to assess the structure and property gradients within aged blocks was performed via IR spectroscopy, micro-indentation, gravimetric analysis of n-heptane-extracted samples and non-invasive portable NMR spectroscopy. A previously developed methodology was used to separate the deterioration into three different processes: polymer oxidation that was diffusion-limited at all temperatures, migration of low-molar-mass species to the surrounding media and anaerobic changes to the polymer network. The methodology allowed the assessment of the kinetics (rate as a function of time and temperature) of the different processes. It was noticed that polymer oxidation yielded more crosslinking at higher temperatures than at lower temperatures. The data obtained by both the portable NMR (a non-invasive method) and the indentation modulus profiling showed correlations with strain-at-break data, indicating their usefulness as condition monitoring methods.
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| 10. |
- Pourmand, Payam, et al.
(författare)
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Deterioration of highly filled EPDM rubber exposed to thermal ageing in air: kinetics and non-destructive monitoring
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The effects of thermal ageing on EPDM cable transit seals were investigated. Samples were aged in air at 110, 120, 150 and 170 °C, and evaluated with tensile testing, indenter modulus profiling, oxidation profiling (using IR spectroscopy), nuclear magnetic resonance (NMR) spectroscopy profiling. The ageing resulted in an increase in the indenter modulus, the degree of oxidation and in a decrease in the NMR transverse relaxation time, T2. Diffusion-limited oxidation (DLO) occurred with a large oxidation gradient close to the sample surface. The portable NMR MOUSE (non-invasive method) was used to obtain detailed degradation profiles, up to a depth of 5 mm of the aged samples. The results indicated a deterioration process that was attributed to several mechanisms, i.e. oxidation, anaerobic crosslinking and migration of oil extender. By combining the data acquired from the profiling, separation and quantification of these three contributing mechanisms was determined. Additionally, it was shown that the portable NMR data correlated well with the strain at break data, highlighting the potential use of the portable NMR for condition monitoring.
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