Recovery characteristics of different tube materials in relation to combustion products

Abstract. Water molecules in vapor can exchange with gaseous water molecules sticking to surfaces of sampling tubing, and exchange rates are unique for each water isotopologue and tubing material. Therefore, water molecules on tubing walls take some time to reach isotopic equilibrium with a new vapor isotopic signal. This creates a memory effect that is observed as attenuation time for signal propagation in continuous stable water vapor isotope measurement systems. Tubing memory effects in δD and δ18O measurements can limit the ability to observe fast changes, and because δD and δ18O memory are not identical, this introduces transient deuterium excess (D-excess, defined as δD-8×δ18O) artifacts in time-varying observations. To our knowledge, a comprehensive performance comparison of commonly used tubing material water exchange properties in laser-based measurement systems has not been published. We compared how a large isotopic step change propagated through five commonly used tubing materials for water isotopic studies – perfluoroalkoxy (PFA), fluorinated ethylene propylene (FEP), polytetrafluoroethylene (PTFE), high-density polyethylene (HDPE), and copper – at two different temperatures and an airflow rate of 0.635 L min−1 through approximately 100 ft (30.5 m) of 1/4 in. (6.4 mm) outer diameter (o.d.) tubing. All commonly used tubing materials performed similarly to each other in terms of attenuation times, reaching δ18O-location-adjusted δD and δ18O 95 % completion in less than 45 s, with slight variations based on temperature. PFA does appear to perform slightly better than the other materials, although memory metric differences are small. A tubing material commonly used in the early 2000s but reported to have memory effects on δD, Dekabon, was also tested at ambient temperature and changing humidities. The Dekabon isotopic equilibrium was not reached until nearly an hour after source transition, much later than H2O mixing ratios equilibrated. Bev-A-Line XX (used in some soil O2 and CO2 gas studies) was also tested at ambient temperature, but it did not approach isotopic equilibrium until after nearly 6 h of testing. Therefore, we cannot recommend the use of Bev-A-Line XX or Dekabon in water vapor isotope applications. Source transition from heavy to light or from light to heavy affected isotopic transition speed only in experiments where H2O ppmv was changing. While a shorter tubing lengths and smaller inner diameters shorten the delay of signal propagation through the tubing, they did not greatly change the attenuation curves under these conditions for the current commonly used tubing materials tested. However, in Dekabon, attenuation curves were greatly extended with increased tubing length. Our results show that the commonly used plastic tubing materials tested were not inferior to copper in terms of isotopic memory under these conditions, and they are easier to work with and are less expensive than copper.

In this work, a novel fibre, fluorinated ethylene propylene (FEP) filament, was fabricated by melt-spinning. In addition, the properties of FEP fibres were investigated through apparent morphological observation, tensile testing, dry-hot shrinkage, differential scanning calorimetry, thermogramitric analysis (TGA) and Fourier transform infrared spectroscopy. Apparent morphological observation shows that FEP fibres present circular cross-sections and smooth surfaces. Just like the conventional fibres prepared by melt-spinning, such as poly (ethylene terephthalate) (PET) and polyamide 6, the stress–strain curves of FEP fibres show obvious stress yield points. The elastic recovery ratio of FEP fibres (80%) is much greater than that of polytetrafluoroethylene (PTFE) fibres (40%), endowing FEP textiles good wrinkle resistance. When FEP fibres are deposited in flame, smoke and droplets do not appear but shrinkage does occur. After treatment in hot air, the breaking strength of FEP fibres decreases, but the elongation at break increases. The melting temperature of FEP fibres is as closely high as that of the PET fibres, while the crystallization temperature is much higher, which puts forward greater challenges for FEP spinning. Compared with PTFE fibres, the crystallinity and the melting temperature of FEP fibres are much lower. TGA results demonstrate that FEP fibres present excellent thermal stability that is as stable as that of the PTFE fibres.

If the necessary infrastructure can be provided, a practical future electric vehicle will be an efficient hydrogen-powered hybrid operating on a polymer fuel cell. Light weight, lowest cost and high efficiency imply an atmospheric pressure, rather than a pressurized, system. Polymer fuel cells require humidification for ionic conductivity, which means that product water is normally rejected as liquid. Atmospheric pressure systems of this type are difficult to operate. A self-humidified atmospheric pressure system operating at higher temperature (about 75-80 °C) on oxygen-enriched air rejecting product water in the vapour phase is described. It combines the advantages of unpressurized operation with the higher power density of a pressurized system, but with much lower parasitic power requirements.

Poly Ether Ether Ketone (PEEK) is a very promising engineering thermoplastic material having capability to perform over wide service temperatures from cryogenic to around 300°C. Processing of PEEK is a challenging task, owing to its physical, thermo physical properties and chemical nature. The present paper envisages processing of PEEK by two different techniques viz, 3D printing and extrusion and assessment of properties of respective specimens at 30°C and −196°C. Thermal and mechanical properties and fracture morphological features of PEEK specimen, processed using these techniques are compared. Samples processed by extrusion possessed higher mechanical properties both at 30°C and −196°C. The 3D printed samples, though exhibited inferior strength and modulus, showed significantly higher elongation (150–250%) at 30°C. All samples showed ductile fracture behavior at 30°C. At −196°C, the fracture morphology got transformed in to a pattern typical of brittle materials, as expected. Extruded specimens showed lower thermal expansion coefficient compared to the 3D printed specimens. Thermal expansion characteristics were different in the X, Y and Z directions for 3D printed specimens due to the anisotropy resulting from printing direction which is corroborated by the morphological studies. The results of this investigation enable designing and fabrication of PEEK based structural components of desired geometries for various applications.

Five different types of tubing materials, namely, polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA), fluorinated ethylene propylene (FEP), high density polyethylene (HDPE), and polyvinyl chloride (PVC) were evaluated for ammonia adsorption at two nominal ammonia concentration values (1 and 10 ppm) at ~24C. All tubing sections were 2.5 m in length and 4.76 mm in i.d. except the HDPE which had an i.d. of 4.32 mm. Mass balance was used to determine ammonia (as ammonium-nitrogen (N)) adsorbed on the inside of the tubing versus the total N recovered in the tubing plus the gas scrubbers (primary and secondary). No tubing significantly differed in N adsorption. Averaged for both ammonia concentrations, N adsorption as percent of total N ranged from 0.15% (PVC) to 1.69% (FEP). Hence, the least expensive PVC tubing may represent the best option under conditions similar to those used in this study. The gas scrubber design used in this study had excellent trapping efficiency (>99%).

In May-June, 2020, a study was conducted to characterize the outgassing properties of a series PEKK (Poly(ether ketone ketone)) samples using cryo-GC/MS headspace analysis. Three sets of samples were interrogated: sample group 1 consisted of 2 additively manufactured PEKK samples (PEKK "ole and "New") prepared by KCNSC from powder material from Solvay Specialty Polymers USA, LLC. Sample groups 2 and 3 consist of 5 PEKK powder types (used as feedstock for additive manufacturing processes) and 4 additively-manufactured PEKK material lots, respectively. Contrary to expectations, all samples of PEKK material were observed to outgas sulfur-containing compounds. Other analyses (EDS/EMA, GC-TOF/MS of PEKK sample extractions) confirmed the presence of sulfur in the PEKK bulk material. Specifically, Diphenyl sulfone (used as a reagent or high-temperature solvent in the synthesis of Polyaryletherketone or PAEK polymers) was observed in three of the powders and in both the PEKK "Old" and "New" samples, suggesting that the source of the sulfur can be traced to impurities in the material left over from the synthesis process.

This paper delves into the application of nonmetallic (NM) materials in downhole environments, specifically assessing their use in Electric Submersible Pump (ESP) stages and components. This study reviews the current state of nonmetallic materials in ESP, highlighting technological advances and limitations. It critically evaluates nonmetallic alternatives' compatibility with ESP requirements in harsh environments, where corrosion and abrasion prevail. Synthesizing empirical findings and theory, this research informs innovation in ESP design and operation. A thorough literature review was conducted, analyzing recent studies and industry data on ceramic and polymer materials used in downhole applications. The review focused on evaluating the performance of specific materials, such as silicon carbide (SiC) ceramics, silicon nitride (Si3N4), graphite, and high-performance polymers like PEEK (Polyether ether ketone) and PTFE (Polytetrafluoroethylene), under high-temperature and high-pressure (HTHP) conditions. Sources included peer-reviewed journals, industry reports, and field test data to evaluate the mechanical, thermal, and chemical resistance of these materials. The review highlights that ceramic materials, such as silicon carbide (SiC), excel in high-temperature applications, tolerating up to 1,800°C, while silicon nitride (Si3N4) can withstand temperatures of up to 1,400°C. These materials demonstrate superior resistance to wear and corrosion due to their robust mechanical properties. Polymers, such as PTFE and PEEK, are more suited for moderate temperatures, showing mechanical integrity up to 260 and 250°C, respectively. PTFE offers exceptional chemical resistance, making it ideal for corrosive environments. PEEK and PTFE are more appropriate for wells with lower temperatures or chemically aggressive environments, where their flexibility and chemical resistance are advantageous. However, challenges such as hydrothermal cracking were noted in glass-fiber reinforced plastics (GRP) when exposed to high-temperature environments above 93°C. Graphite is suitable for extreme temperature conditions with careful consideration of oxidation risks. Nonmetallic seals faced reliability issues under extreme conditions, emphasizing the need for careful material selection. This review serves as a reference for selecting nonmetallic materials in ESP stages for downhole applications. Ceramic materials, such as silicon carbide (SiC) and silicon nitride (Si3N4), are recommended for their robust mechanical performance in HTHP wells. Polymers like PTFE and PEEK offer suitable alternatives for less severe conditions, leveraging flexibility and chemical resilience. Practical insights gleaned from this study enable optimized material selection, thereby boosting efficiency and extending the lifespan of ESP systems operating in diverse subsurface environments. Effective material choices facilitate reliable performance and reduce maintenance needs.

Wear resistance effects of alumina and carbon nanoscale fillers in PFA, FEP, and HDPE polymers

Thrombus formation in blood-contacting medical devices is a major concern in the medical device industry, limiting the clinical efficacy of these devices. Further, a locally formed clot within the device has the potential to detach from the surface, posing a risk of embolization. Clot embolization from blood-contacting cardiovascular devices can result in serious complications like acute ischemic stroke and myocardial infarction. Therefore, clot embolization associated with device-induced thrombosis can be life-threatening and requires an enhanced fundamental understanding of embolization characteristics to come up with advanced intervention strategies. Therefore, this work aims to investigate the adhesive characteristics of blood clots on common biocompatible materials used in various cardiovascular devices. This study focuses on characterizing the adhesion strength of blood clots on materials such as polytetrafluoroethylene (PTFE), polyurethane (PU), polyether ether ketone (PEEK), nitinol, and titanium, frequently used in medical devices. In addition, the effect of incubation time on clot adhesion is explored. Results from this work demonstrated strongest clot adhesion to titanium with 3h of incubation resulting in 1.06 ± 0.20kPa detachment stresses. The clot adhesion strength on titanium was 51.5% higher than PEEK, 35.9% higher than PTFE, 63.1% higher than PU, and 35.4% higher than nitinol. Further, adhesion strength increases with incubation time for all materials. The percentage increase in detachment stress over incubation time (ranging from 30min to 3h) for polymers ranged from at least 108.75% (PEEK), 140.74% (PU), to 151.61% (PTFE). Whereas, for metallic surfaces, the percentage rise ranged from 70.21% (nitinol) to 89.28% (titanium). Confocal fluorescence imaging of clot remnants on the material surfaces revealed a well-bounded platelet-fibrin network at the residual region, representing a comparatively higher adhesive region than the non-residual zone of the surface.

In order to study the tribological properties of PTFE modified by hard nanoparticles and soft polymer under dry friction conditions, the tribological properties of polytetrafluoroethylene (PTFE) filled with different volume contents of polyether ether ketone (PEEK) and nano-ZrO2 were investigated at a linear speed of 2 m/s, normal load of 200 N, and ambient temperature conditions for 60 min using a block-on-ring wear tester. A multiple-layer feedforward artificial neutral network (ANN) was used to simulate and analyze the friction coefficient and volume wear rate. The results showed that the friction coefficient and volume wear rate of PTFE composites were effectively reduced when nano-ZrO2 and PEEK were filled separately or simultaneously. The best tribological properties were obtained when the composites were filled with 5–8 vol% nano-ZrO2 and 20 vol% PEEK simultaneously; the volume wear rate was only 1.29 × 10−6 mm3/Nm and the friction coefficient was only 0.15. An ANN can accurately simulate and predict the friction coefficient and volume wear rate of composites, and the predicted results were consistent with the experimental results. A groove appeared in the volume wear rate simulation diagram when the volume content of nano-ZrO2 was about 7% with or without PEEK. This phenomenon indicates that the composites in this region had a lower volume wear rate. Therefore, the addition of nano-ZrO2 and PEEK can effectively improve the tribological properties of PTFE. As a simulation analysis method, an ANN can accurately analyze and predict the tribological properties of composites.

The present study investigates the wear and friction properties of Poly Ether Ether Ketone (PEEK) sliding against stainless steel. The materials are neat PEEK, PEEK with 10% Polytetrafluorethylene (PTFE), PEEK with 30% carbon fibers (CF) and PEEK with 30% glass fibers (GF). Adding fibers to PEEK (CF or GF) increased the wear by a factor of four. This may seem surprising but it is in accordance with the Ratner-Lancaster correlation which postulates that the wear rate is inversely proportional to the product of the strain and strength at break. Adding fibers may increase the strength but it decreases the strain at break even more. Water lubrication increases the wear by a factor of ten, except in the case of CF where the wear is halved. To investigate the influence of the polarity of the lubricant, the very polar water has been replaced by the quasi-nonpolar n-heptane. This decreases the wear significantly. The n-heptane lubricated PEEK with CF shows the lowest wear rate in the present study.In general the addition of a liquid lubricant decreases the friction whereas it is the opposite when fibers are added. But friction seems to be decoupled from the wear response in the present study.

Enhanced wear resistance of gamma-irradiated PTFE and FEP polymers and the effect of post-irradiation environmental handling

Ambient in situ measurements of the important sulfur gas carbonyl sulfide (OCS) very frequently rely on permeation devices based on weight loss measurements (gravimetry) as the method of calibration. Both time series studies as well as measurements of OCS sources and sinks typically employ this approach. Although this calibration approach is based upon fundamental quantities, its accuracy directly depends upon the purity of the permeating effluent. The present study describes a systematic investigation of four permeation wafers and their time history based on gravimetry, direct absorption spectroscopy employing a tunable diode laser absorption spectrometer (TDLAS), and two different ratio approaches. Gravimetric determinations for two of the devices, which employed fluorinated ethylene propylene (FEP) Teflon wafers as the permeating medium, indicated mass loss rates which decayed exponentially with time. This is in contrast to the direct absorption and ratio measurements, which were significantly lower at the start (37% in one case and 19% in the other) and displayed a small linear drop with time. We present evidence for the presence of a CO2 impurity in FEP permeation devices, either from the starting material or the breakdown of OCS. This impurity copermeates along with OCS but at a much faster rate, giving rise to an apparent exponential decay in the OCS rate. Calculations based on fundamental permeability parameters for CO2 in FEP Teflon and typical levels of CO2 impurity (0.1 to 2%) in the starting material yield results that are consistent with the present interpretation. Two other permeation wafers, which employed polytetrafluoroethylene (PTFE) Teflon membranes, exhibited completely different behavior; all the measurement methods indicated similar results and showed a linearly decreasing permeation rate with time. The CO2 impurity problem prevalent in FEP wafers is insignificant in PTFE wafers because the permeability of PTFE is at least 21 times higher. It is possible that the high pressure inside the membrane (POCS = 17.7 atm at 40°C) alters the crystalline PTFE structure with time, resulting in a real decrease in permeation rate. Although more studies are needed to further confirm and extend these findings, the effects observed here suggest that ambient OCS measurements could in some circumstances be systematically high by as much as 37%. Such errors can produce erroneous temporal trends and/or inconsistencies between ambient measurements carried out by different laboratories.

Remarkably low wear rates were observed in PTFE–PEEK and polytetrafluoroethylene (PTFE)-alpha-alumina composites when evaluated in a “self-mated” configuration, where a polymer pin is slid against a polymer countersample of the same composition. Each composite was tested in a controlled humidity environment on a linearly reciprocating tribometer on two different countersamples: a polymer countersample (self-mated) and a stainless steel countersample for comparison. For all the self-mated PTFE–PEEK composites [polyether ether ketone (PEEK) wt % 10, 20, 30, 40, and 50], the average friction coefficient was reduced, and the steady-state and total specific wear rates were improved when compared to testing against stainless steel. Self-mated PTFE–PEEK (wt % 10–40) achieved ultralow wear rates on the order of 10–9 mm3/Nm and friction coefficients of 0.08–0.14. When compared with samples slid against stainless steel, IR spectroscopy of the sliding surface showed that the self-mated PTFE–PEEK composites accumulate more PEEK at the sliding interface and more expression of a tribochemical carboxylate species, which have been linked with ultralow wear PTFE materials. The PTFE composites slid on steel rely on the formation of transfer films for ultralow wear performance. This is achieved by unidirectional increasing surface energy gradients from the polymer pin to the steel substrate, which dominate the transport and wear of PTFE composites slid on steel. However, the self-mated ultralow wear PTFE-based composites rely only on the formation and stability of tribofilms that consist of tribochemically altered PTFE with new carboxylate end groups as well as accumulated filler (i.e., PEEK or alumina). These films have self-regulating, minimal differences in surface energy. The close match of these low-energy surfaces contributes to low friction and ultralow wear. The self-mated PEEK-filled PTFE outperforms the alumina-filled PTFE primarily because of the ease at which PEEK accumulates at the surface. Additionally, the reinforcement and anchoring of the surface is better for a polymer blend than a particle-reinforced composite.

Fabrication of PEEK Ag/AgI mid-infrared hollow fiber and transmission reliability study for CO2 laser radiation