Title

Research And Development On Advanced Graphite Materials. Volume XXXIX - Diamagnetic Susceptibility Of Graphite By The Faraday Method

Date

1963

Index Abstract

Contrails and DTIC truncated

Photo Quality

Incomplete

Report Number

WADD TR 61-72 Volume 39

Creator

Soule, D. E.

Nezbeda, C. W.

Corporate Author

Research Laboratory of National Carbon Company Division of Union Carbide Corporation

Laboratory

AF Materials Laboratory

Extent

60

Identifier

AD0426781

AD0426781

Access Rights

OTS

Distribution Classification

1

Contract

AF 33(616)-6915

DoD Project

7350

DoD Task

735002

DTIC Record Exists

No

Distribution Change Authority Correspondence

None

Report Availability

Full text available

Is Referenced By

Latham, C.D., Heggie, M.I., Gamez, J.A., Suarez-Matinez, I., Ewels, C.P. & Briddon, P.R., "The di-insterstitial in graphite", Journal of Physics: Condensed Matter, 20:1-8, 2008

Date Issued

1963-11

Abstract

The diamagnetic susceptibility of several types of graphite, both single and polycrystalline, was investigated at room temperature by the Faraday method. This method measures the entire sample; it can be used to obtain the three components for a trace; and it can account for ferromagnetic impurities. For single crystals, the conduction electron component (∥ c-axis) is χ∥= -21.8x10-6 emu/gm; whereas the isotropic ionic core component is χ⊥= -0.32x10-6 emu/gm, resulting in a maximum anisotropy ratio of 68. Anisotropies found for polycrystals range from 25 for annealed pyrolytic down to 1.01 for lampblack-base grade CEP graphite. The susceptibility trace, representing the contribution of the truly graphitic portion of a sample, ranges from -22.8x10-6 emu/gm for single crystals down to -19.1x10-6 emu/gm for grade ZTA graphite. Direct orientation measurements showed that both single crystals and polycrystals display a true cosine-squared dependence, modified in amplitude by the degree of preferred crystallite orientation. These results are justified theoretically.
A study of the effect of annealing temperature up to 3360°C on the anisotropy and trace pyrolytic samples showed a competition of processes depending upon the properties of the "as received" material, where trace values vary from -18.2x10-6 emu/gm to -24.0x10-6 emu/gm according to the amount of non-graphic carbon and the degree of turbostraticity. Above ~ 3200°C, all sample traces tend toward the single crystal value.
A study of the effect of acceptor boron doping from 1 to 5000 ppm showed a decrease in the magnitude of χ∥ with increasing boron concentration, following the lowering of the Fermi level, becoming asymptotic to the ionic core component at ~ 3x10-3 B/C. This effect correlates with the Hall coefficient, which shows a peak due to the transition at the bottom of the conduction band from mixed conduction to single hole cinduction. Both effects give an ionization efficiency for boron of 75 ±15%. Magnetoresistance and conductivity results show that there is predominantly impurity scattering in the measured range of 77°K to 299°K.

Publisher

Wright-Patterson Air Force Base, OH : AF Materials Laboratory, Aeronautical Systems Division, Air Force Systems Command

Distribution Conflict

No

Provenance

IIT

Lockheed Martin Missiles & Fire Control

Type

report

Subject

Measurement

Graphite

Graphite

Transport

Boron

Ferromagnetism

Symmetry (Crystallography)

Pyrolytic Permeability (Magnetic)

Hall Effect

Format

1 online resource