Addition Of PTFE Research Articles

The effect of in‐situ fibrillated polytetrafluoroethylene on the rheological, mechanical, and foaming properties of polystyrene based nanocomposite foams

AbstractPolystyrene/polytetrafluoroethylene (PS/PTFE) in‐situ fibrillated nanocomposites were prepared by melt blending using a HAAKE torque rheometer, and the effects of different contents of in‐situ nanofibrillated PTFE on the properties of PS/PTFE nanocomposites were studied. The results showed that PTFE was in‐situ nanofibrillation in the composites, and the toughness, energy storage modulus and complex viscosity of PS/PTFE nanocomposite are all improved. When the content of PTFE was 3 wt%, the elongation at break was the highest, which was three times that of neat PS. What is more, the addition of PTFE significantly improved the cell morphology of PS/PTFE nanocomposite foams by supercritical fluid foaming. The cell structure and morphology of PS/PTFE (3 wt%) nanocomposite foam was the best under 110°C foaming temperature, and the cell diameter and cell density were 3.27 μm and 1.11 × 1010 cells/cm3, respectively. In addition, the tensile strength of PS/PTFE nanocomposite foams increased from 35.4 MPa of neat PS foam to 39.6 MPa of PS/PTFE (3 wt%) foam.

Wettability and Frictional Studies of PEEK Composites against Co-Cr Alloys with Surface Textures.

With the aim of promoting the qualities for total hip joint replacement, the wettability and tribological behaviors of PEEK composites pins with two sets of different fillers (PEEK/CF or PEEK/CF/PTFE/graphite) against Co-Cr alloy discs with five categories of surface textures (polished, orthogonal, spiral, r-θ, and orthogonal combined with spiral) were explored. It is revealed that the existence of CF in PEEK matrix increases the hydrophilicity in addition to the strength of PEEK, while the addition of PTFE increases the hydrophobicity of PEEK. The Co-Cr alloy discs with hydrophilic properties can be adjusted as hydrophobic, with the depth of textured grooves exceeding the critical sag height determined by the contact angle and the groove width. It can be concluded that PEEK/CF/PTFE/graphite composite has a lower wear rate than PEEK only reinforced with CF against Co-Cr alloy, both without surface texture and with shallow or deep grooves. The existence of shallow grooves on the disc surface could help the PEEK blends to achieve a steady friction against Co-Cr alloy in addition to collecting the worn debris. PEEK blend pins with 10 vol% CF, 10 vol% PTFE and 10 vol% graphite can achieve a lower friction coefficient of no more than 0.2 against Co-Cr alloy discs with shallow grooves around 3.5 μm in orthogonal or spiral textures.

Hydrophobic, anti-ice, wear- and corrosion-resistant C-(Ti)-PTFE coatings on Ti obtained by electrospark deposition using PTFE-impregnated graphite electrode

Titanium parts for marine and coastal infrastructure require protection from aggressive environment that lead to increased wear, corrosion and icing. To address these important issues, graphite-based coatings reinforced with titanium carbide and containing PTFE have been developed. Composite coatings were obtained by vacuum electrospark deposition using either a pure graphite (G) electrode or a porous graphite electrode impregnated with PTFE powder using both cathodic and anodic polarity. At cathodic polarity, the upper coating layer consists of mixtures of G + TiC (G electrode) and G + TiC + CF2 (G / PTFE electrode) phases. When changing polarity, coatings are obtained based on mixtures of Ti + TiC (G electrode) and Ti + TiF3 + −CF − (G + PTFE electrode) phases with a small amount of amorphous carbon on the surface. The as-deposited coatings were tested under conditions of simultaneous wear and corrosion in artificial seawater. The combination of G and TiC resulted in a hydrophobic (water contact angle (WCA) of 99°) corrosion-resistant (open circle potential (OCP) of 0.2 V versus −0.8 V for Ti) coating with a low coefficient of friction (0.1) and relatively low wear (2 × 10−5 mm3/Nm). The addition of PTFE increases hydrophobicity (WCA = 130°), significantly increases the freezing time of a water drop from 23 to 65 s, and reduces the ice adhesion strength from 0.52 to 0.38 MPa while maintaining tribocorrosion characteristics. The results obtained are important for the further development of wear-, corrosion-resistant, and anti-ice protective coatings.

Research on Energy and Economics of Self-Made Catalyst-Coated Membrane for Fuel Cell under Different Oxidants.

In the context of global warming, clean energy represented by fuel cells has ushered in a window period of rapid development; however, most research mainly focuses on the improvement of catalysts and performance, and there is very little research on the performance differences and energy consumption between different oxidants. In this paper, the performance differences of fuel cells with different oxidants (air and oxygen) are studied using a self-made CCM, and the economic aspect is calculated from the perspective of power improvement and energy consumption. Firstly, the CCM and GDL are prepared, and the hydrophilicity and hydrophobicity of GDL are realized by the addition of PTFE and SiO2, respectively. Secondly, through the experiment, it is found that the fuel cell can achieve the best comprehensive performance at 60 °C, and the use of oxygen can achieve the highest power increase, 117.1%, compared with air. Finally, from the perspective of economics, after excluding the power consumed for preparing oxygen, the use of oxygen as an oxidant still achieved a net power increase of 29.512%. The research in this paper clearly shows that using oxygen instead of air can greatly improve performance and is good economically, which makes it a useful exploration for the research of fuel cells.

Unexpected exfoliation and activity of nano poly(tetrafluoroethylene) particles from magnetic stir bars: Discovery and implication

Magnetic stir bars are routinely used by most of researchers in the fields of chemistry, biology and environment etc. An incredible phenomenon, in which the magnetic stirring increased reaction rate by tens of times under ultrasound irradiation, impelled us to explore roles of magnetic stirring. Unexpectedly, the thimbleful nano PTFE particles, from shell of magnetic stir bar, were exfoliated during magnetic stirring and account for ultrahigh tribocatalytic and piezocatalytic activities under ultrasonic irradiation. Reactive oxygen species (ROS), such as hydroxyl radical (OH), superoxide radicals (O2−) and singlet oxygen (1O2) were generated in the present of PTFE under ultrasound irradiation, which is desired in the pollution control. The newly discovered PTFE activity, against the conventional wisdom that PTFE is inert, which also reminds the researchers that the trace amount of PTFE ground during magnetic stirring may inadvertently botch our experiments and introduce false positive results, especially involving routine magnetic stirring and ultrasound irradiation operation in laboratory. In addition, the safety and inertness of PTFE may require further review in PTFE-based commercial, industrial and biomedical settings.

Effects of nano-Al2O3 and PTFE fillers on tribological property of basalt fabric-reinforced epoxy composites

ABSTRACT Effects of nano-Al2O3 and PTFE fillers on tribological behaviour of basalt fabric reinforced epoxy composite (BFRC) produced with a combination of molding and mixing method were studied by Taguchi L9 design. Microstructures and worn surfaces of composites were investigated by scanning electron microscopy. Regression equations were also developed for predicting wear and coefficient of friction. The results indicated that specific wear rate increased with increasing load and decreasing speed, but friction coefficient decreased with increasing speed, PTFE addition and medium load. In addition, wear rate of nano-PTFE was lower than that of nano-Al2O3 because of its microstructure. PTFE decreased the friction about 17%. Load was effective on the wear rate while speed was dominant on the friction. Moreover, multiple fiber fractures and large numbers of debris were dominated for BFRC while fiber debondings, fiber removals and debris agglomerations were effective for Al2O3, but fiber fractures and flake types of debris were responsible for PTFE.

Reactive Ni–Al-Based Materials: Strength and Combustion Behavior

The effect of PTFE, continuous boron, and tungsten fibers on the combustion behavior and strength of reactive Ni–Al compacts was examined in this study. The introduction of continuous fibers into Ni–Al compacts according to the developed scheme was found to increase the flexural strength from 12 to 120 MPa. Heat treatment (HT), leading to chemical interaction of the starting components, increases the strength of compacts at temperatures not exceeding 550 °C. The combination of reinforcement and HT significantly increases the strength without reducing reactivity. Experimental results showed that strength and combustion rate increase with the reduction in PTFE to 1 wt % in Ni–Al compacts. A favorable effect of the addition of PTFE from 5 to 10 wt % on the reduction of the threshold for the shock-wave initiation of reactions in Ni–Al was established. The obtained results can be used to produce reactive materials with high mechanical and energy characteristics.

Effects of PTFE on operational characteristics and diffusible H and O contents of weld metal in underwater wet welding

For this paper, oxidizing rutile type tubular wires were developed by using polytetrafluoroethylene (PFTE) as a flux ingredient in concentrations up to 21 %. The welds were carried out in a flat position at a depth of 0.5m by using both negative (DCEN) and positive electrodes (DCEP). Welding electrical signals were acquired and processed to determine process characteristics voltages, and quantify the occurrence of short-circuit and arc extinction. The influence of flux composition on weld bead shape and its hydrogen and oxygen contents were also evaluated. For both polarities, welding current increased with the addition of PTFE to the flux probably because it required more energy to melt and dissociate. The additions of PTFE also increased bead penetration and reinforcement and reduced the width as well as the H and O contents in the weld metal. These results were more pronounced with DCEN. Weld porosity was not observed for all formulations. Therefore, tubular wires with PTFE additions to the flux may have potential operational advantages for underwater welding including the reduction of weld metal oxygen and diffusible hydrogen contents particularly when used with DCEN.

Effect of Antifriction Solid Additives on the Temperature Stability of Bentonite Greases

The temperature stability of bentonite greases based on petroleum (I-40A) and synthetic (PAO-10) oils with the addition of PTFE, molybdenum disulfide, and boron nitride were evaluated. It was found that bentonite lubricants prepared on the basis of industrial oil I-40A have a higher lubricating ability than compared greases based on polyalphaolefine oil PAO-10.

Formation of zirconium silicide–Al2O3 composites from PTFE-assisted ZrO2/Si/Al combustion synthesis

Zirconium silicide–Al2O3 composites were fabricated from PTFE-assisted ZrO2–Al–Si combustion systems. PTFE acted as a reaction promoter to initiate and sustain combustion. Reactant mixtures were based on stoichiometries of 3ZrO2 + 4Al + xSi with x = 1.5, 3.0, and 6.0. With the addition of PTFE at 3 wt% of the powder mixture, self-sustaining combustion was established upon ignition. The effect of gas-phase diffusion transport induced by PTFE on the SHS process was confirmed. The composites synthesized from powder compacts of x = 1.5 and 3.0 were composed of ZrSi, ZrSi2, ZrC, and Al2O3. Formation of ZrSi2–Al2O3 composites with a trivial amount of ZrC was obtained from the Si-rich sample of x = 6.0. The microstructure of as-synthesized products exhibits a granular morphology and constituted particles have a size range of 1–2 μm.

PTFE as a toughness modifier of high‐performance PEI/PBT blends: Morphology control during melt processing

High‐performance PEI/PBT blends are brittle because of phase distribution and blends densification. New morphologies developed by adding PTFE to PEI matrix during melt processing favor the toughness improvement of PEI/PBT blends. Ternary PEI/PBT/PTFE processability is not compromised by PTFE addition, and miscibility study by modulated differential scanning calorimetry and harmonic mean method shows that PTFE does not interfere with PEI and PBT interaction. Dual‐phase and spore‐like morphologies are formed for both PEI/PBT and PEI/PBT/PTFE blends, and they strongly influenced their mechanical performance. Although tensile strength of ternary blends does not decrease by PTFE addition, elongation at break deteriorates for blends with PEI concentrations <70 wt%. Nevertheless, blends with 80 wt% increase their ductility, and a synergic effect is observed in impact resistance results. PTFE acts as an impact modifier of PEI/PBT blends due to its distribution in the PEI matrix as debonded spheres and nanoparticles well‐embedded in PEI matrix.Highlights Step‐by‐step melt processing enhances PTFE powders spheroidization Complete wetting of PTFE in PEI matrix PTFE do not interfere in partial miscibility of PEI/PBT blends Nanosized PTFE droplets inhibits PEI densification PTFE improves elongation at break and toughness of PEI/PBT blends

Prediction of Electrolyte Distribution in Technical Gas Diffusion Electrodes: From Imaging to SPH Simulations

The performance of the gas diffusion electrode (GDE) is crucial for technical processes like chlorine–alkali electrolysis. The function of the GDE is to provide an intimate contact between gaseous reactants, the solid catalyst, and the liquid electrolyte. To accomplish this, the GDE is composed of wetting and non-wetting materials to avoid electrolyte breakthrough. Knowledge of the spatial distribution of the electrolyte in the porous structure is a prerequisite for further improvement of GDE. Therefore, the ability of the electrolyte to imbibe into the porous electrode is studied by direct numeric simulations in a reconstructed porous electrode. The information on the geometry, including the information on silver and PTFE distribution of the technical GDE, is extracted from FIB/SEM imaging including a segmentation into the different phases. Modeling of wetting phenomena inside the GDE is challenging, since surface tension and wetting of the electrolyte on silver and PTFE surfaces must be included in a physically consistent manner. Recently, wetting was modeled from first principles on the continuum scale by introducing a contact line force. Here, the newly developed contact line force model is employed to simulate two-phase flow in the solid microstructures using the smoothed particle hydrodynamics (SPH) method. In this contribution, we present the complete workflow from imaging of the GDE to dynamic SPH simulations of the electrolyte intrusion process. The simulations are used to investigate the influence of addition of non-wetting PTFE as well as the application of external pressure differences between the electrolyte and the gas phase on the intrusion process.

Cold sintering of ZnO-PTFE: Utilizing polymer phase to promote ceramic anisotropic grain growth

Densification of ZnO-PTFE (polytetrafluoroethylene) composites is permitted by the Cold Sintering Process, having no effect on the stability of both materials. Highly dense samples can be obtained by this technique at extremely low temperatures in just a few minutes. Interestingly, the obtained samples show an anisotropy impacting: crystalline, microstructural and electrical properties. While the Wurztite ZnO crystals show a preferential growth along (00l) direction, microstructure observations show a grain growth along the in-plane (perpendicular to pressure application direction) up to 240%. Electrical conductivity is also influenced and is related to microstructure. In this situation, the addition of PTFE insulating phase allows to increase the conductivity in plane compared to the pure cold sintered ZnO sample. A mechanism is proposed to explain this phenomenon which involves PTFE transient distribution competing with the transient liquid driving densification and grain growth associated with cold sintering. This is further confirmed by the observation of a curvature of microstructure direction while approaching die edges. These observations offer a large variety of designs for further orientation driven properties.

Preparation of high-performance PEEK anti-wear blends with melt-processable PTFE

High-performance anti-wear polyetheretherketone/polytetrafluoroethylene (PEEK/PTFE) blends have drawn much attention over the past few years, owing to their wide range of potential applications. However, a convenient and effective method to prepare such blends with superior mechanical and tribological properties is still lacking. In this work, we propose a promising approach that uses melt-processable PTFE (MP PTFE), instead of conventional PTFE, to prepare anti-wear blends. MP PTFE, with melt flow abilities under appropriate conditions, can disperse homogeneously in PEEK, enhancing both the mechanical and tribological properties of the PEEK/PTFE blend. To prove this postulation, in this work, both MP PTFE and commercial PTFE were blended with PEEK, separately, and the effects of PTFE type and content on the tensile and tribological properties of the blends were studied. The results showed that, although the addition of commercial PTFE to PEEK could increase the wear resistance, it decreased the tensile strength of PEEK significantly. Compared to the blends with commercial PTFE, the blends with MP PTFE exhibited better tribological performance and higher tensile strength for PTFE content below 10 wt%. It was confirmed that the better dispersion of MP PTFE in PEEK endowed the blends with higher tensile strength. The surface analysis indicated that the MP PTFE could readily migrate to and enrich the surfaces of the blends. The relatively high PTFE content on the surface favored the formation of tribo-films, enhancing the tribological properties of the blends.

Preparation and Electrochemical Properties of Zinc Electrode for Alkaline Manganese Batteries Containing Ultrafine Zinc Powders

Submicron spherical zinc powders with high surface area, activity and low cost were prepared by DC arc plasma evaporation method. Based on the characterization of morphology, particle size and composition of ultrafine zinc powder, the effects of addition amount of PTFE and compounding of PTFE with PAAs and CMCs, electrolyte addition amount, compound mass ratio of flake and spherical zinc powder on the discharge performance of zinc electrode had been systematically studied. The results showed that ultrafine zinc powder was polycrystalline, spherical and its purity reached 99.96wt%. Under 0.2C, the discharge capacity reached 577.5mAh when addition of PTFE was 10wt.%. When 2.5wt.% PTFE was compound with 6.5wt.%(PAAs: CMCs = 2:1), the discharge capacity improved which reached 613.4 mAh. The discharge capacity was 580.3mAh when the electrolyte content was 38wt.%. When the mass ratio of special flake zinc powder to spherical zinc powder was 3:7, the discharge capacity reached 664.1 mAh, it was 13.5% higher than 584.9 mAh of pure spherical zinc powder and 22.6% higher than 541.5 mAh of pure flake zinc powder. Under 1.8C, compared with alkaline manganese battery prepared using flake zinc powders, the mass specific capacity increased by 57.12% and the volume specific capacity increased by 187.79%.

Surface strengthening aluminum alloy by in-situ TiC-TiB2 composite coating

An integration technology was employed to prepare TiC-TiB2 strengthening coating on aluminum alloys, with the combination of Self-propagating high-temperature synthesis (SHS) and Vacuum-expendable pattern casting (VEPC). During the VEPC process, the Ti-C-B4C-TP SHS reaction was ignited by molten Al alloy, resulting in the simultaneous obtainment of TiC-TiB2 SHS coating with the cast Al alloy. Specifically, Teflon (PTFE) as reaction promoter was introduced into the SHS system to guarantee the reaction to be ignited successfully. With 3.8 wt% PTFE addition, homogeneous and dense TiC-TiB2 coating microstructure was obtained. Compared to the matrix, the hardness of the surface coating increased from 80 HB to 284 HB. And, the weight loss decreased from 533 mg to 52 mg at load of 20 N, indicating the significant improvement of wear resistance. In addition, a comprehensive bonding strength of 160 MPa was achieved. The proposed method for preparing hard coating on Al alloys broadens their industry application, where higher hardness and better wear resistance are required.

Preparation and characterization of mechanically activated aluminum/polytetrafluoroethylene composites and their reaction properties in high temperature water steam

Activated aluminum/polytetrafluoroethylene (Al/PTFE) composites were prepared by ball milling method, and characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). Their reaction properties with the high temperature water steam were systematically studied. The autoignition temperature, delay time to autoignition after igniting of the Al/PTFE composites in the water steam were recorded. Their reaction products with the water steam were observed by SEM, analyzed by XRD, and the residual metal aluminum content in it was obtained through measuring hydrogen production. The experimental results showed that the content of the PTFE was closely related to the size and morphology of the milled particles. Meanwhile, the addition of PTFE significantly promoted the reaction of aluminum with water steam. The samples Al-8%PTFE and Al-10%PTFE exhibited superior combustion properties with the water steam, such as the shorter delay time to autoignition and lower autoignition temperature. Meanwhile, the mechanism of the reaction between Al/PTFE composites and water steam was also discussed. It was suggested that the decomposition products of PTFE in the composites reacted with aluminum and formed AlF3 firstly, then the AlF3 immediately reacted with the water steam and formed the Al2O3.

Investigation on Three body Abrasive Wear Behavior of Polyamide66 / Polytetrafluroethylene(PA66/PTFE) Blends

The three body abrasive wear behaviour of Polyamide66 and Polytetrafluroethylene blends (PA66/PTFE) in 95/5, 90/10, 85/15, 80/20, 75/25 and 70/30 wt.%were investigated as per ASTM G65 by using Rubber wheel abrasion tester (RWAT). The test were conducted for a load of 50N and 75N at a velocity of 2.5m/s using fine abrasive dry sand particles and rubber wheel with a abrading distance of 500 m through 1500 m. The results revealed that the wear volume and the specific wear rate are the functions of abrading distance, load and the composition of blend. The addition of PTFE into the blend PA66/PTFE improved the wear resistance of the blend tested. For a load of 50N with 5wt.% of PTFE, there was a wear volume loss of 27.14 mm3. Higher loading of PTFE (30wt.%), results in 40% reduction in wear volume loss. Wear volume loss was proved to be a function of load and abrading distance. Similar observations were made even at higher load of 75N. The addition of PTFE insteps of 5wt.%decreased the specific wear rate and the wear volume loss. This is due to inherent lubricative and frictional characteristics of PTFE and PA66. The experimental response of the study follows the linear trend for both the loads. Micro cutting, deep abrasion and micro ploughing are the major mechanisms observed during the test.The worn surfaces are demonstrated by using the Scanning Electron Microscope photographs (SEM).

Dry Sliding wear behavior of ABS Composites reinforced with nano Zirconia and PTFE

ABS composites reinforced with nano zirconia and PTFE have been prepared using melt compounding using twin screw extrusion. Dry sliding wear behavior of composites has been studied using pin-on-disc tribometer according to ASTM G99 standards. Experiments have been conducted in accordance with DOE by Response Surface Methodology (RSM). Load, Sliding Velocity,% of nano zirconia and% of PTFE has been considered as the input parameter, whereas response measured are wear and COF. Though the results show that addition of both fillers leads to reduction of wear, addition of PTFE reduces the wear significantly as PTFE acts as lubricant. By increasing load and sliding velocity, wear increases as well. A fuzzy logic based model has been developed to predict the wear of ABS composites and good agreement has been observed between experimental and predicted results. Optimization of process parameters in sliding wear have been obtained by using Desirability approach and the optimized parameters were found to be 2.5% of PTFE, 3% of zirconia, Load of 50N and sliding velocity of 2m/s.

Tribological Properties of Porous PEEK Composites Containing Ionic Liquid under Dry Friction Condition

NaCl particles were added into Polyetheretherketone (PEEK) and its composites to produce porous PEEK-based materials by washing NaCl away after the high-temperature compression molding process. After that, an ionic liquid was added into the porous materials under vacuum condition. Carbon fibers (CF), as reinforcement, and PTFE, as an internal solid lubricant, were employed to prepare PEEK composites. Tribological properties under dry friction condition were studied on a ring-on-disc tribo-meter. The influence of CF and PTFE on tribological properties was carefully investigated. The results indicated that, in comparison with traditional PEEK composites (CF/PTFE/PEEK), the porous PEEK composites containing ionic liquid showed much better tribological properties. It is found that CF can help PEEK form effective pores to suck in the ionic liquid resulting in a better tribological performance. CF reinforced porous PEEK containing ionic liquid (p-CF/PEEK + IL) demonstrated the lowest friction coefficient (27% of CF/PTFE/PEEK) and the lowest wear loss (only 0.9% of CF/PTFE/PEEK). Long time tribological test revealed that the wear mass loss comes from the running-in period, while its wear is negligible after this period. It is also found that the addition of PTFE has a negative influence on the tribological behaviors, especially under high sliding velocity and applied load.