Addition Of PTFE Research Articles

Reactive Sensor for Investigation of Gas Diffusion Layer Hydrophobicity in PEM Fuel Cells

In an effort to develop methods for spatial characterization of the active interface (catalyst/polymer electrolyte/carbon fiber) in polymer electrolyte membrane fuel cell (PEMFC) gas diffusion electrodes, the present work investigates the effect of the hydrophobic agent [0-20 wt % Teflon poly(tetrafluoroethylene) (PTFE)] and Nafion loading on the properties of the carbon fiber gas diffusion layer (GDL). The reduction of O 2 in 0.1 M H 2 SO 4 on various uncatalyzed carbon fiber papers (two-electron process) was chosen as the additive-sensitive electrochemical reaction. The oxygen electro-reduction on the carbon fiber paper was a strong function of PTFE and Nafion content, as revealed by both cyclic voltammetry and electrochemical impedance spectroscopy. The changes in charge-transfer resistance can be used as a quantitative measure of both PTFE and Nafion content. The addition of PTFE increased while the presence of Nafion decreased, in a sensitive fashion, the charge-transfer resistance of the two-electron O 2 reduction as determined by impedance spectroscopy. Hence, oxygen electroreduction could be used as an electrochemical sensor for the nondestructive analysis of the GDL properties. The electrochemical studies were corroborated by cross-sectional scanning electron microscopy and mercury intrusion porosimetry investigation of PTFE penetration in the carbon fiber paper.

Influence of the Nb 2O 5 distribution on the electrochemical hydrogenation of nanocrystalline magnesium

Nanocrystalline Mg powder without and with 2 mol% Nb 2O 5 catalyst was studied as an electrode material for electrochemical hydrogen charging in a 6 M KOH electrolyte. A strong influence of the compaction parameters, the current density and the catalyst on the hydrogenation behavior was observed. The addition of graphite and PTFE to the Mg/Nb 2O 5 electrodes improves the charging kinetics as well as the hydrogen content. The hydrogen contents achieved in Mg with Nb 2O 5, however, show a broad scatter. It was concluded that the catalyst distribution influences the upper limit of the storage capacity as well as the oxidation process at the surface during preparation. Since the addition of Nb 2O 5 was observed to reduce the hydrogen overpotential of Mg depending on the catalyst distribution, it is assumed that the catalyst influences the electrode reactions. Therefore, hydrogenation was investigated for different Nb 2O 5 distributions at different current densities in detail.

Electrophoretic deposition (EPD) of hydrous ruthenium oxides with PTFE and their supercapacitor performances

The effect of PTFE addition was investigated for the electrophoretic deposition (EPD) of hydrous ruthenium oxide electrodes. Mechanical stability of electrode layers, together with deposition yield, was enhanced by using hydrous ruthenium oxide/PTFE dispersions. High supercapacitor performance was obtained for the electrodes prepared with 2% PTFE and 10% water. When PTFE content was higher, the rate capability became poor with low electronic conductivity; higher water content than 10% resulted in non-uniform depositions with poor cycleability and power capability. When electrodes were heat treated at 200 °C for 10 h, the specific energy was as high as 17.6 Wh/kg based on single electrode (at 200 W/kg); while utilizable energy was lower with heat treatment time of 1 and 50 h, due to the high resistance and gradual crystallization, respectively. With PTFE addition and heat treatment at 200 °C for 10 h, the specific capacitance was increased by 31% (460 → 599 F/g at ca. 0.6 mg/cm 2) at 10 mV/s, and the deposition weight was increased up to 1.7 mg/cm 2 with initial capacitance of 350 F/g.

The friction and wear of electroless Ni–P matrix with PTFE and/or SiC particles composite

In this paper, the friction behaviour and wear mechanism of electroless Ni–P matrix with PTFE and/or SiC particles composite coating are investigated by virtue of ring-on-disk wear machine at a high load of 150 N. The worn surface, wear debris and the composition changes after wear were characterized using scanning electron microscopy (SEM) and energy-dispersive analysis of X-ray (EDAX). By comparison with Ni–P and Ni–P–SiC coatings, the results indicated that the combination of a PTFE-rich mechanical mixed layer (PRMML) formed on the worn surface and hard SiC were responsible for the good tribological properties of the hybrid Ni–P–PTFE–SiC composites at high load. After heat treatment at 400 °C for 1 h, the wear rate of Ni–P matrix composites decreased with corresponding increase in microhardness. During sliding, an obvious decrease in the temperature rise with PTFE addition was attributed to the good anti-friction of PTFE.

Influence of PTFE content in PEEK–PTFE blends on mechanical properties and tribo-performance in various wear modes

Few papers are available on the optimum composition of PEEK–PTFE blends for the best possible combination of mechanical and tribological properties in the adhesive wear mode. Nothing is reported in this context on low amplitude oscillating/fretting wear mode. Moreover, the influence of increasing amounts of PTFE in the blend on abrasive wear behaviour along with a correlation with strength properties is not reported. Hence, in this work, five injection-moulded blends of PEEK with PTFE (in the range of 0–30 wt.%) were evaluated on a pin-on-disc configuration on an SRV Optimol Tester for their tribo-behaviour in the low amplitude oscillating wear mode. The data in the abrasive wear mode were generated by abrading a pin loaded against an abrasive paper fitted on the rotating disc. Data on neat PTFE were also included for comparison. It was observed that inclusion of PTFE affected the adhesive wear and low amplitude oscillating wear (LAOW) in a beneficial way. With an increase in PTFE contents, coefficient of friction in both the wear modes (adhesive and low amplitude oscillating) decreased but the trends in wear performance differed. In the adhesive wear mode, the specific wear rate showed minima for 7.5% PTFE inclusion followed by a slow increase for further PTFE addition. In the case of LAOW mode, on the other hand, the wear rate continuously decreased for the selected compositions. The 30% PTFE blend showed excellent combination of μ, wear rate and limiting pressure–velocity (PV) values. Unfilled PEEK proved to be fairly good wear-resistant material but exhibited high μ, a stick-slip tendency and a low PV limit value. Abrasive wear performance of the blends on the other hand, deteriorated with increasing amount of PTFE. Fairly good correlation was observed between the wear rate and product of H and S ( H-hardness and S-ultimate tensile strength) rather than Ratner–Lancaster plot (product of S and e, where e is elongation to break). Thus, with increase in PTFE contents, though adhesive and LAOW performance increased substantially, it was at the cost of deterioration in all mechanical properties (except impact strength) and abrasive wear performance.

Hydrogenation of nanocrystalline Mg-based alloys

ABSTRACTDesirable properties of hydrogen storage in materials include mainly, high hydrogen capacity, high number of hydride / dehydride cycles, low temperature of dissociation and microstructural stability. Hydrogen storage can proceed from the gas phase as well as during cathodic charging.The use of nanocrystalline Mg powder without and with 2 mol% Nb2O5 catalyst as an electrode material for electrochemical hydrogen charging processes in a 6M KOH electrolyte was studied. A strong influence of the compaction parameters and the current density but no influence of the catalyst on the hydrogenation behavior was observed. However, a strong influence of the catalyst on the hydrogen overpotential was observed and is assumed to result into a change of the electrochemical surface reaction. The addition of graphite and PTFE to the Mg/Nb2O5electrodes improves the charging kinetic as well as the hydrogen content up to 1 wt.% hydrogen.

?-Irradiated poly(tetrafluoroethylene) particle-filled low-density polyethylene. I. Effect of silane coupling agents on mechanical, thermal, and morphological properties

Poly(tetrafluoroethylene) (PTFE) scraps were recovered as a filler material for low-density polyethylene (LDPE) after they were degraded by Co-60 γ-rays under atmospheric conditions to make small-size powder. The powder PTFE, which was called secondary PTFE (2°-PTFE), was melt mixed with LDPE and then extruded to obtain 200 µm films. The mechanical and thermal properties and also the morphology of the fractured surface of these 2°-PTFE–filled LDPE were studied. It was found that the addition of 2°-PTFE resulted in thermofilm property of LDPE but it slightly decreased the thermal oxidative temperature of LDPE. The tensile strength and ultimate elongation of LDPE were found to decrease with the addition of 2°-PTFE. However, when it is compared to the addition of virgin PTFE into LDPE, 2°-PTFE shows better mechanical properties due to the presence of oxy groups which are capable of interacting with the main matrix. A further improvement in mechanical properties was achieved by silane coupling agent treatment of 2°-PTFE. Silane coupling agents were found to enhance the interfacial adhesion between 2°-PTFE and LDPE. The study on the fractured surfaces by scanning electron microscope revealed this adhesion between these two polymers. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 866–876, 1999

Study of the determination of trace amounts of chromium by electrothermal atomic absorption spectrometry with a poly(tetrafluoroethylene) slurry as a chemical modifier

Using poly(tetrafluoroethylene) (PTFE) slurry as a chemical modifier, the process of vaporization and atomization of Cr in a graphite furnace for electrothermal atomic absorption spectrometry was investigated. It was shown that PTFE could react with Cr to form chromium fluoride and suppressed the formation of refractory metal carbides. The addition of PTFE clearly enhanced the analytical sensitivity of Cr and significantly reduced the interferences of a 103–104-fold excess of matrix elements. The detection limit (DL) and characteristic mass (mch) of the conventional method are 9.6 and 24.5 pg (Cr), respectively, whereas with PTFE the best DL and mch values of the proposed method are 2.73 and 10.0 pg (Cr), respectively. The calibration graph is linear in the range 5–80 ng ml–1 (Cr) with RSDs of 1.1–6.6%. The method was applied to the determination of trace amounts of Cr in surface water and copper chloride samples. The Cr recoveries from the samples were 96.4–103.7%.

The growth and bonding of transfer film and the role of CuS and PTFE in the tribological behavior of PEEK

Sliding experiments on the PEEK composites filled with CuS and PTFE powders while rubbing against tool steel surfaces were performed under ambient conditions in a pin-on-disk configuration. A constant sliding velocity of 1 m s −1 and a contact pressure of 0.654 MPa were used in all experiments. The steel counterfaces were finished by abrasion to a surface roughness of 0.11 μm R a. The optimum CuS proportion for minimum wear rate as determined experimentally was 35 vol.%. With the addition of CuS, the coefficient of friction increased. The addition of PTFE to these composites reduced both the wear rate and the coefficient of friction. The wear rate of the different compositions depended upon their ability to form transfer films on the steel counterfaces. The study of the transfer film growth by scanning electron microscopy revealed that it was a mechanical process in which the fragments of the material removed were locked into the crevices of counterface asperities. The compositional changes in the transfer film were studied by XPS analysis of the top surface of the transfer film and also closer to the steel substrate. It was found that Cu ions and the compounds of FeF 2, FeSO 4 and FeS were formed near the interface of the transfer film with its steel substrate. These compounds contributed to enhanced bonding between the transfer film and the counterface. Of the various mechanisms of wear, the cracking and delamination of the transfer film will also be affected by the bonding of transfer film to the counterface.