Heat Treatment Temperature HTT

The effect of the maximum HTT as an important variable has been discussed in some detail in Section II.E. Here we only need to point out that most often 

Apparent BET surface area, MPV, and yields of activated carbons prepared with NaOH at increasing NaOH/carbon ratios (weight), keeping the remaining experimental variables constant (physical mixing method, heating rate 5 C/min to 750°C, holding time 1 h, Nj flow 500 mL/min) 

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Fig. 13. Increase in stack width parameter, L with heat treatment temperature, HTT, for some graphitising cokes, [Adapted from 1 12],...

Table I. Effect of Heat Treatment Temperature (HTT) on Chemisorption of Oxygen... 

Figure 10.5 compares the spin-lattice relaxation time (7)) obtained after inversion-recovery sequences of the APP/PER and the APP/PER-4A systems versus heat treatment temperature (HTT). At every HTT, only one 7) value was obtained and it can be therefore expected that the slow relaxation domains size will be smaller than 10 nm. 

In this paper we report on the synthesis of new types of intrinsically conducting polymers using high-temperature reaction of condensation polymers and polyfunctional monomers. We shall show that the new polymers can be regarded as low-dimensional graphites both macroscopically and microscopically and discuss the change in their structural and electronic properties with heat-treatment temperature (HTT). 

Pyrolysis of polyoxadiazole (POD) yielded a highly conductive pyropolymer at heat treatment temperatures (HTT) near 1000 C and... 

The properties of PAN fibers ( 10 pm diameter) are very dependent on the final heat treatment temperature (HTT). Tensile strength reaches a maximum (3.5 GPa) at a HTT of around 1500°C, and then decreases, while Young s modulus continues to... 

Carbon fibers scatter both x-rays and electrons, and the corresponding diffraction patterns can be used to assess structural parameters [4] [31]. The diffraction patterns of carbon fibers contain a limited number of reflections, i.e., usually a strong 002 reflection and (when present) weaker 004,10 and 11 reflections, due to the turbostractic character of the carbon. The OOl and hk reflections become less dif se as the heat treatment temperature (HTT) is increased. Finally, the separation of the 10 reflection into its 100 and 101 components and the appearance of the 112 reflection are observed only for true graphite fibers, prepared from mesopitch fibers and formed at 3000 C. 

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°. 

Temperature is one of the processing parameters which has a pronounced effect on the failure strength of carbon fibers. This effect is quite different for MP based and PAN based fibers. As the heat treatment temperature (HTT) is raised, the strength of a mesopitch based fiber, tested at room temperature, progressively increases [3] [38] [54-55]. Conversely, that of most PAN based fibers undergo a maximum at about 1300-1500 C (Figure 12). 

Experiments performed on PAN based fibers at a heat treatment temperature (HTT) of 1300°C) have shown that the creep is primary and that the creep rate decreases regularly with time. Furthermore, creep appears to be logarithmic and the inverse of the creep rate increases linearly as a function of time [59]. 

In this equation, pe is expressed in jjQ.m and l in A [35]. The electrical conductivity of mesopitch based fibers remains similar to that of PAN based fibers for a low heat treatment temperature (HTT). It becomes much higher when the heat treatment temperature is raised from 2500 to 3000°C, i.e., where graphitization actually takes place. Finally, and as illustrated in Table V, the electrical conductivity along the fiber axis of the best mesopitch based fibers (P 120 and P 140) is still lower than those of highly oriented pyrolytic graphite and copper [61]. 

The rate of oxidation increases with temperature but decreases with time (Figure 14.20). An increased composite heat treatment temperature (HTT) will reduce the oxidation rate, probably due to a reduced level of impurities, less edge sites and an overall reduction in carbonization stress [102],... 

Effect of maximum heat treatment temperature (HTT) on porous texture (KOH/anthracite 3/1... 

Charcoals were prepared from three plants, balsa from Ecuador, giant ipil-ipil from the Philippines, and bamboo from Japan, with various conditions of heating rate—8,10, and 50°C/min—and final heat treatment temperature (HTT) ranging from 300 to 700°C. 

Organic matter exposed to a heat treatment temperature (HTT) of 1000°C was assumed to be pure carbon polluted by other forms of carbon often referred to as amorphous [14,16] and sometimes as interstitial carbons [69-70]. 

FIGURE 1.35 Vickers microhardness data (a) Variation with carbon content [67]. (b) Variation with heat treatment temperature (HTT) (°C) for different carbonaceous materials [91]. 

Group A Nitrogen is adsorbed to a lesser extent than carbon dioxide. This group of porous carbons adsorbs smaller amounts of N2 at 77 K than CO2 at 273 K and contains carbonized materials, such as those (a) of heat treatment temperature (HTT) <600 °C and >800 °C, (b) the molecular sieve carbons with their limited PSDs and (c) activated carbons with <5 wt% bum-off. The restrictive activated diffusion of the nitrogen at 77 K into narrow micropores (or pore entrances) is responsible for this phenomenon. 

Currently, because of the frequency of their occurrence in wastewaters, the adsorption of phenolic compounds on carbons and the influence of surface oxygen complexes on their uptake are the most frequently studied, Radovic et al. (1997). It is well established that an increase in surface acidity of AC, after an oxidation, causes a decrease in phenol adsorption from dilute aqueous solution. For example. Figure 8.8 shows the adsorption isotherms of phenol on oxidized carbons, Mahajan et al. (1980). There was a large decrease in phenol uptake after oxidation, the effect of oxidation not being trivial. This phenol uptake progressively increased as the surface acidity decreased, and the oxidized sample (heat treatment temperature (HTT) 950 °C) had the same adsorption capacity as the original carbon (about 1.5 xmolg" ). 

Oxidative stabilization of the PAN precursor is an important step in the fabrication of carbon fibres, because improper stabilization may result in a blow out of the core portion of the fibre during carbonization due to its incomplete oxidation. Therefore, the proper conditions of rate of heating and the time and temperature of the final heat-treatment temperature (HTT) for optimum stabilization have to be investigated for each precursor fibre. Several methods of stabilization, such as heating the precursor fibre in air at 220-250 °C in a batch process or passing the precursor tow continuously through a furnace with several temperature zones, have been used. 

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