Ex-Pitch

Fig. 2. Schematic representation of basal plane orientation in several types of carbon fibers. (A) Single crystal graphite. (B) ex-pitch carbon fiber. (C) ex-PAN carbon fiber, (D) VGCF.

Carbon fibers like parent graphite are good electrical conductors (e.g., 1000-10,000 pQ.cm) and exhibit thermal conductivities ranging from 50 W.m K for ex-PAN fibers to 1100 W.m K for ex-Pitch fibers. 

A few observations have also been carried out on fiber architectures (without matrices) [64], but the weave patterns have not been examined in a systematic way [14]. The irradiation behavior of the cloth was dominated by fiber axial shrinkage, and the internal voids of the structure were eliminated, causing it to swell [65]. It was not possible with these data to decide on the best fibers, because the irradiation temperatures were too low and the thermal properties had not been determined. At an irradiation temperature of 620°C, the smallest volume change was obtained for ex-pitch fibers, whereas the ex-Pan fibers swelled instead of shrinking. 

Irradiation studies on C/C have been performed mainly in the US (fusion and fission 1991—2011), Japan (fusion and fission 1993—now), and Europe (fusion 1994—2000). Studies were, in each coimtry, generally focused on a few preferred materials 3D pitch-based C fiber/ex-pitch C matrix (FMI-222) in the US, 2D PAN-based C fiber/mix (ex-phenolic - - ex-pitch) C matrix (CX-270G) in Japan, 2.5D PAN-based C fiber/mix (pyrolytic - - ex-pitch) C matrix (N 112) in Europe (cf. Table 13.6). This variety of matrices and fibers is in agreement with the difficulty to choose between the different constituents of the C/C materials and probably also to the will of industrial companies to promote their specific materials. 

In Japan, the studies were facilitated by the access to the fusion (JT-60) and fission neutron reactor (JMTR, HTTR), for quite large samples, and by the know-how of Japanese industry in the field of carbon fibers and composites. PAN-based C fibers, instead of pitch-based ones (for 2D composites, with an ex-pitch C matrix), were chosen for irradiation tests (for fission application), since a larger fracture load and deformation could be obtained [34]. By the end of the 1990s, the main material studied in Japan was a 2D PAN-based C fiber/mix (ex-phenolic - - ex-pitch) C matrix material... 

In Europe, irradiation studies on C/C have been realized only for fusion applications. New studies for fission were planned, about 10 years ago, but have been given up. The material that has been the most studied, a 2.5D PAN-based C fiber/mix (pyrolytic + ex-pitch) C matrix ( N 112 ), provided the lowest dimensional changes, compared to the others (Fig. 13.4), but with lower mechanical properties (Table 13.6). Another quite similar industrial material, with the same fiber architecture, but with a matrix comprising only pyrolytic C (deposited with CVI) ( AOS ), possesses dimensional changes about twice as significant. It appears that a matrix mix can notably improve the dimensional behavior under irradiation. 

The power-time-pitch representations px (t, z) and py(t, z) are convolved with the frequency-smearing function A, as can be derived from Eq. (1.1), leading to excitation-time-pitch (dB exc, seconds, Bark) representations Ex (t, z) and Ey (t, z) (see Appendices B, C, D of [Beerends and Stemerdink, 1992]). The form of the frequency-smearing function depends on intensity and frequency, and the convolution is carried out in a non-linear way using Eq. (1.2) (see Appendix C of [Beerends and Stemerdink, 1992]) with parameter afreq ... 

Figure 1.7 Overview of the basic transformations which are used in the development of the PAQM (Perceptual Audio Quality Measure). The signals x(t) and y t) are windowed with a window w(t) and then transformed to the frequency domain. The power spectra as function of time and frequency, Px (t, f) and Py(t, /) are transformed to power spectra as function of time and pitch, px(t, z) and py(t, z) which are convolved with the smearing function resulting in the excitations as a function of pitch Ex (/, z) ar 6Ey(t, z). After transformation with the compression function we get the internal representations x(f, z)and ,(, z) from which the average noise disturbance Cn over the audio fragment can be calculated.

According to Keating s theory, the pitch decreases with increasing temperature. However, the pitch in the cholesteric liquid crystals of polypeptides increases below T. Furthermore the cholesteric sense inverts at T. These results can not been ex-... 

Crystic Kollerdur. [Scott Bader] One-pack polyurethane resins for primers, sealers, coatings, or formulatimis such as aggregate-filled floors, pitch-ex-tend roofing systems. 

Two types of commercial C/C composites were used in this study a two directional randomly chopped pitch fiber reinforced composite with charred resin/CVI matrix (CC-A21) and a three directional composite with needled felt ex-PAN fibers and CVl matrix (CC-D21). The C/C composites were kindly provided by Honeywell Aircraft Landing Systems. The as-received densified C/C composite samples were heat-treated at 2100°C in a graphitization furnace (Model TP-4X10-G-G-D64A-A-27, Centorr Associates Inc) with protective argon atmosphere. 

Reactor Facility Lattice Pitch (in.) Coolant Fuel Assembly Type DJO Purity Ex )crimental HAMMER Calculations ... 

MAJOR DIAM. Do PITCH DIAM. Eo CHAMFER 4T xMlN. DIAM. GG PITCH DIAM. Eb LENGTH U(4) MAJOR DIAM. APPROX. Dio OVERAU LENGTH APPROX. Lio BORE MAX K> PITCN DIAM. Ex LENGTH Li U LENGTH OFFUU ROOT MIN. U(5)... 

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