EPR between 4·2°K and 300°K of a carbon black family: P33

355

ABSTRACTS 184. Galvanomagnetic

effects in multi-phase

carbon system

Y. Hishiyama (Musashi Institute of Technology, Setagaya-ku, Tokyo, Japan) and M. Inagaki and K. Kamiya (Nagoya University, Faculty of Engineering, Nagoya, Japan). Galvanomagnetic effects in multi-phase.carbon

black system, are investigated at liquid nitrogen temperature. For all the specimens investigated, abnormal magnetic field dependence is observed in Hall coefficient and magnetoresistance; Hall coefficient varies with inverse of magnetic field and, magnetoresistance is positive, increases with H’ at first and tends to saturate at higher fields. 185. Electronic

properties

of very thin graphite crystals

Y. Fujibayashi

and S. Mizishima (School ofEngineering, Keio C’niverGty, Tokyo, Japan). Graphite crystals with thickness ranging from about 100 to 1500 ,A and were prepared b) cleavage. From measurement of the magnetoresistance and the Hall coefficient the electronic properties were determined by the McClui-e’s method. The total carrier density does not change much with thickness. with n,. exceeding IL,,,while pLr,ph and p,,/~~ decreases with decreasing thickness. 186. EPR between 4~2°K and 300°K of a carbon black family:

P33

P. Delhaes and F. Carmona (Centre de Kecherches Paul Pascal Domain Uniuersitaire, 33-Talence, France). EPR measurements relative to paramagnetic susceptibility, g factor and line width are reported. The thermal variations of these physical properties are interpreted from a phenomenological model which involves two interacting paramagnetic systems in connection with the lattice. This model explains the additivity law previously used by several authors and allows us to give several relationships between g factor, line width and diamagnetic susceptibility. 187. Diamagnetism

of carbon fibers

C. 1’. Scott and D. B. Fischbach (Department of Mining, sity of Washington, Seattle, Washington). The total (tensor

have been measured for several types of commercial creased with increasing tensile modulus (or increasing behavior varied with fiber type. Structure-dependence that of other non-graphitizing carbons. 188. Insertion

kinetics and diamagnetism

of pyrocarbon

Metallurgical

and Ceramic Engineering,

Uniuer-

trace) susceptibility and the anisotropy ratio carbon fibers. In general, both parameters inthermo-mechanical treatment), but the detailed of the fiber diamagnetism appeared similar to

bromine

residue compounds

A. Marchand, J. C. Rouillon l.‘,Gversitaire, 33-Pessac, France).

and F. Courtois d’Arcollieres (Centre de Recherches Paul Pascal, Domaine Simultaneous in situ measurements of the changes of weight and diamagnetic anisotropy of pyrocarbon samples were performed during bromine insertion. Insertion kinetics was studied separately as a function of sample temperature and bromine pressure. The variation of the diamagnetic anisotropy of residue compounds with ambient temperature was also investigated and found to exhibit a \‘ery interesting behavior. 189. Thermal

annealing

of neutron-irradiated

carbons; changes in electronic

properties

A. Pacault, A. Marchand, J. Amiell, E. Dupart (Centre de Rechmches, Paul Pascal Domaine Cniuersitaire, 33-Talence, France). J. Rappeneau, C. Micaud and R. Wlodarsky (Commissariatia 1’Energie Atomique, Centre d’Etudes Nucleaires de Saclay, France). A study has already been made of the changes in the electronic properties of carbons irradiated with neutrons (paper presented at the 9th Carbon Conference, Boston 1969). This work was continued: the thermal annealing of the same carbons was studied and the variations in their electronic properties (electrical resistivity, Hall effect, magnetoresistivity, magnetic susceptibility) were followed. The similarity in behaviour between PGCCL and graphite was confirmed. Pyrocdrbon is more quickly damaged and recovers its initial properties less easily, although the preliminary damage does not affect its later graphitization kinetics. The results obtained by electronic paramagnetic resonance during the earlier study were supplemented. X. GENERAL 190. Carbon-an

old but new material (George

P. L. Walker, Jr. (Pennsylvania

SUBJECTS

Skakel Award

Lecture)

State Universzty, University Park, Pennsylvania)