Carbon-filled PTFE

Carbon reduces creep, increases hardness and elevates thermal conductivity of polytetrafluoroethylene. Wear resistance of carbon filled compounds improves, particularly when combined with graphite. Carbon-graphite compounds perform well in non-lubricated applications such as piston rings in compressor cylinders. Carbon-filled PTFE has some electrical conductivity. Close tolerances can be achieved... 

PTFE is by far the material of choice, however, ETFE is also sometimes used. Carbon-filled PTFE is often used where static discharge is desired. Although hoses are available in sizes up to 8" (20 cm), the most common size is 1" (2.5 cm) with 2" (5 cm) occasionally encountered. Smooth bore hoses are used where residual liquid is a safety or environmental concern. However, smooth bore lacks the flexibility that a convoluted bore provides. Although metal overbraiding is commonly used, elastomeric ones are also encountered. 

Figure 7. Wear rate as a function of initial counterface roughness for a series of carbon filled PTFE composites running in air against a steel counterface. The fillers are present at 10% by weight and the carbons differ in particle size, aspect ratio and surface chemistry. Little change in counterface topography is noted during the course of this experiment these carbons are not particularly abrasive towards steel. The evidence of a minimum in wear is not strong but it is consistent with other work. In this experiment there is a detectable inverse trend in the friction the lower the wear the higher is the friction. The symbols refer to carbons of different particle size and aspect ratio.

Figure 10. The influence of environment on the wear of three carbon filled PTFE composites, (a) the effect of relative humidity in air, (b) the effect of oxygen (as air) compared with nitrogen at a nominal zero humidity. The three carbons are ...

The wear behaviour of polytetrafluoroethylene (PTFE), carbon-filled PTFE, high density polyethylene (HDPE), ultrahigh molecular weight polyethylene (UHMPE), low density polyethylene (LDPE) and polymethyl methacrylate (PMMA) was studied. To ensure consistent and controlled properties of the samples, many of the materials were processed in the authors laboratory. The details of sample preparation and processing techniques are reported elsewhere ( ). ... 

Shelestova and co-workers [68], studied the effects of modification of carbon fibres on the thermo-physical properties of carbon filled PTFE. 

Confirmation of chain scission and, at least, liberation of a radical species arises from degradation studies achieved using filled PTFE. By electron spin resonance spectroscopy, Fock [31] found that the carbon black used in carbon-filled PTFE contained large numbers of unpaired electrons and that pyrolysis of carbon-filled PTFE showed vastly different decomposition rates to neat and bronze-filled PTFE. He concluded that the difference in degradation behavior is due to radical intermediates being stabilized by the unpaired carbon black electrons. 

Campbell et al. [84] developed DEs made out of glass fiber webs filled wifh carbon and PTFE particles. The same research group later designed special DEs made with different carbons claiming to improve the overall fluid diffusion toward the catalyst layer [85]. 

Other experiments were carried out with filled PTFE material, using steam as fluidizing gas. Fillers were carbon black, glass fibres, and bronze. Important parameters are listed in Table 24.10. In the first three experiments, the inflnence of the temperatnre was investigated, in the following were other fillers nsed. 

The highest yields of monomers such as TFE, HFP and C-C4F8 of aronnd 90 wt% were obtained at pyrolysis temperatures of between 645 and 600° C. Formation of oligomeric PTFE waxes can be explained by repolymerization of TFE in the cooling steps where the steam is condensed. The same phenomena occnr dnring indnstrial production of TFE. Carbon black and glass fibres have nearly no inflnence on the prodnct composition (compare Table 24.9). For the bronze-filled PTFE the yields of TFE, HFP and C-C4F8 were... 

Figure 12.5. Schematic of the cell (viewed from the top, the side, and an expanded view of a single electrode) which was used for electrochemical screening of the 64-element array (A) vitreous carbon electrode, (C) spring-loaded electrical contact, and glass filled PTFE array base plate, (D) polypropylene contact holder, and (E) a printed circuit hoard [14]. (Reprinted with permission from J Comh Chem 2004 6 149-58. Copyright 2004 American Chemical Society.)...

Polymers used for seat and plug seals and internal static seals include PTFE (polytetrafluoroeth ene) and other fluorocarbons, polyethylene, nylon, polyether-ether-ketone, and acetal. Fluorocarbons are often carbon or glass-filled to improve mechanical properties and heat resistance. Temperature and chemical compatibility with the process fluid are the key selec tion criteria. Polymer-lined bearings and guides are used to decrease fric tion, which lessens dead band and reduces actuator force requirements. See Sec. 28, Materials of Construction, for properties. 

Figure 12-8A. Piston rings. The piston rod is manufactured from heat-treated stainless steel and is coated with wear-resistant overlays, such as ceramic, chromium oxide, and tungsten carbide applied by plasma techniques. Piston rod cross-head attachment has mechanical preloading system for the threads. Rider rings and seal rings are manufactured from PTFE filled resins fillers are matched to the gas, piston speed, and liner specifications. Typical fillers are glass, carbon, coke, or ceramic. (Used by permission Bui. BCNA-3P100. Howden Process Compressors Incorporated. All rights reserved.)...

Special grades can be filled with graphite and possibly carbon or aramid fibres, PTFE, or molybdenum sulfide. 

To improve the properties of the raw polymer (wear resistance, creep resistance, thermal and electrical conductivity), various fillers, such as glass fibers, powdered metals, and graphite, are combined with all three types of PTFE polymers, mostly by intimate mixing. Filled fine powders are produced mostly by adding fillers into a dispersion and then coagulating the mixture. Aqueous dispersions can also be modified by the addition of certain fillers, pigments, heat resistant dyes, carbon blacks, and powdered metals, especially when processed into films (see Chapter 6). 

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