HT carbon fibers

Table II. BET Parameters for n-Nonane Adsorption on (HT) Carbon Fibers at 70°C and the Corresponding Specific Surface Areas ...

Bessell and Shorthall [114] studied the nucleation and crystallization of nylon 6 reinforced with carbon fiber. The fibers were shown to nucleate a columnar structure at the interface, which was different between HM and HT carbon fiber types and was primarily due to the physical matching of the graphite crystallites. Surface treatment had a pronounced effect, with treated fibers giving small amounts of fiber pull-out with low fracture energies, whereas untreated fiber exhibited extensive pull-out reflected in high fracture energies. 

Figure 20.8 Tensile strength l/s gage length of Type II (HT) carbon fibers. Source Reprinted with permission from Goggin PR, A method of measuring the quality of carbon fibres, AERE R-7790. Copyright, AEA Technology pic.

Figure 8. Mechanical properties of various carbon-fiber-reinforced composites compared to bone and some biomedical alloys (20). HM and HT refer, respectively, to fibers of high modulus and high tensile strength.

Figure 17. Transmission electron micrographs of PAN-based and mesophase-pitch-based carbon fibers, as delivered and after heat treatment (42,43). HT and HM refer to high strength and high modulus PAN-based fibers P55 and P100 refer to mesophase-pitch-based fibers, with tensile moduli of 55 and 100 Mpsi, respectively.

The sections that follow describe how to make the carbon fiber electrodes used as the working electrodes in FCV, how to set up an FCV amplifier, and how to test and calibrate the carbon fiber electrodes before use. These techniques are suitable for the detection and measurement of dopamine, noradrenaline, and serotonin (5-HT) in the whole bram or in brain slices. 

As a result, the density of PAN based carbon fibers, ranging from 1.76 g/cm for HT fibers to 1.87 g/cm for HM fibers, is lower than that of mesopitch (MP) based carbon fibers, i.e., 2.0-2.20 glonf. As a result, the density of MP based carbon fibers approaches that of the ideal graphite single crystal, i.e., 2.278 g/cm [8]. Finally, a more preferred orientation of the coherent domains is achieved with MP based carbon fibers than with PAN based carbon fibers and it is improved for MP based fibers by raising the heat treatment temperature (HTT) and thereby reaching Z-values as low as 5°. 

Raman spectroscopy and magnetoresistance data provide further structural information. The Raman spectra of carbon fibers are comprised of two main peaks, the E2g Raman allowed graphitic (G) peak at 1580 cm and a disorder induced (D) peak at 1360 cm [34-35]. A dramatic change is observed in the Raman patterns when moving from PAN based HT fibers, which are characterized by broad and overlapping D and G peaks, to mesopitch based carbon fibers treated at high temperatures. The latter exhibit two well separated D and G peaks. The... 

It was believed that this could be achieved commercially by a pumped recirculation of some of the exhaust gases and/or reducing the furnace purge of N2. However, contamination with sodium, which was evolved in the HT furnace when using Courtauld s SAF precursor, could make this impracticable. Work was also undertaken at Harwell to produce carbon fibers from cellulosic and pitch precursors. 

There was an urgent requirement to produce a continuous carbon fiber and at first, a process was developed to produce a continuous high modulus material, which was then currently in demand and a continuous HT fiber followed by early 1969. The first stage of a 25 tpa plant came on stream towards the end of 1969, making Grafil A, made at 1100°C and by the end of 1970, the line was in full production for all types of fiber. 

No consensus has been reached on the roles of physical absorption and chemical bonding when investigating the surface chemistry of carbon fibers and made more difficult by the buried interface. Jones [47] claims that the electrolytic surface treatment process produces a surface on which the known concentration of chemical functionalities cannot be accommodated on the surface of a smooth cylinder. Absorption studies [48] support the fact that erosion could occur and active species can be deposited in the vicinity of intercrystallite voids. Types A and HT fibers have more basal planes that emerge directly to the surface than is the case with HM fiber and hence are more readily surface treated. Hence, it was suggested [49,50] that HM fiber would require an active epoxy group of smaller dimensions that could be accommodated within the micropore. 

Harvey [100] studied the surface area by gas adsorption (BET) and the adsorption of aqueous solutions of the dyes, methylene blue and metanil yellow, on Courtaulds types A, HT and HM carbon fibers. 

Chiu HT, Lin JS, Electrochemical deposition of polypyrrole on carbon fibers for improved adhesion to the epoxy resin matrix, J Mater Sci, 27, 319, 1992. 

An HT fiber composite was found to be dimensionally and structurally unstable well below the maximum fiber processing temperature of 1400 C. The fiber shrank (the frozen in process stress relaxes) at temperatures as low as 850°C. The shrinkage of the fiber bundle embedded in phenolic resin during the carbonization process was influenced by matrix shrinkage stresses and pyrolysis products. Above 1000°C, the HTA carbon fiber in carbon-carbon bundles continuously changed its structure. After heat treatment at a temperature of 2800°C, the structure (lattice distance, orientation of the crystallites, crystallite size) was very similar to that of HM fibers. 

Prandy JM, Hahn HT, Compressive strength of carbon fibers, SAMPE Quarterly, Society for the Advancement of Materials and Process Engineering, 22(2), 47-52, 1991. 

Theoretical value for graphite single crystal Type HT PAN based carbon fiber Type IM PAN based carbon fiber Type HM PAN based carbon fiber Type UHM Pitch based carbon fiber... 

CARBON FIBERS TYPE IM (INTERMEDIATE MODULUS) are related to CARBON FIBERS TYPE HT because of the comparable values of tensile strength, but are characterized by greater stiffness. 

Fig. 9. Tensile strength and Young s modulus of amorphous Pe7sB sSi o fibers compared to other reinforcement fibers. HT and HM are high tensile strength and high modulus carbon fibers.

Exocytosis that results in the secretion of 5-hydroxytryptophan and insulin has been monitored from single pancreatic -cells (human, porcine, canine, mouse, and cultured tumor cells), using 9-gm-diameter carbon fiber electrodes [110]. Unmodified electrodes allowed 5-HT quantitation, while modification with a ruthenium ox-ide/cyanoruthenate film allowed selective quantitation of insulin at electrodes positioned 1 pm away from cell surfaces. 

Properties Natural fibers (flax) E-glass Carbon (HT) Carbon (HM)... 

Although mechanical performance of composites can depend on the processing conditions, the batch-mixed and the twin-screw extraded nanocomposites developed in this study did not show any significant ddfeience. Also, we note that while the nanocomposites were generally less flexible as compared to the pure LLDPE, they still retained a fairly high elon tion-at-break of about 140%, compared to about only 30% displayed by short P-55 carbon fiber composites. Coupled with an EM SE of about 22-24 dB, PR-19 HT and MWNT HT nanocomposites indicate a potential in applications that require significant mechanical flexibility. 

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