15 Structural Characterization of Graphitic Cokes and the Products Thereof
Downloaded by MONASH UNIV on December 11, 2016 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/bk-1976-0021.ch015
W. BRADSHAW and V. MAMONE Lockheed Missiles & Space Co., Inc., Sunnyvale, Calif.
In the utilization of graphites in an extreme environment where thermal shock may be severe, it is necessary to produce materials of high strain-to-failure and low thermal expansion coefficient with good thermal conductivity. The objective of this initial study was to characterize various bulk graphite precursor cokes and the effect of additions of several types of coke filler fines on the microstructural and mechanical properties of billets fabricated. The ultimate goal was to produce a material model for graphites with higher tensile strength and strain-tofailure, while maintaining a low thermal expansion coefficient and compatible thermal conductivity. Approach Seven types of coke particles were subjected to extensive microstructural characterization with respect to density, morphology, crystalline characteristics, and porosity. From the seven filler precursors (See Table I), four were selected for further analysis in billet fabrication studies. Both isotropic and anisotropic filler precursors were used as particle additions (15%) in a conventional graphite process, i.e., molded and pressed into green graphite shapes, subjected to multiple bakes and reimpregnations and finally graphitized and reheat-treated. The material was tested for tensile strength and strain-to-failure during processing and after post-graphitization heat treatment. The microstructural characterization consisted of optical and scanning electron microscopy, density determinations by displacement in mercury and helium, evaluation of pore size and distribution by mercury porosimetry, and x-ray diffraction analysis. This program was funded by Lockheed Independent Development and Independent Research.
172
Deviney and O'Grady; Petroleum Derived Carbons ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
Deviney and O'Grady; Petroleum Derived Carbons ACS Symposium Series; American Chemical Society: Washington, DC, 1976. -0.46 0.0 -2.56 0.0
2.18 2.21 2.07 2.10
59 42 16.13 33.59
3.48 3.44 3.66 3.44
SPHEROIDAL SEMIACICULAR ANGULAR SPHEROIDAL
GELSO C O K E
INTERMEDIATE P E T R O L E U M C O K E
GLASSY CARBON, 1400 GRADE
SANTA MARIA COKE, 1400 GRADE
3.49
27.5
2.18
-0. 58
-0. 58
-0. 58
SPHEROIDAL
2.18
2.18
FLUID COKE
3.49
30
44
g FACTOR (AS REC'D)
ACICULAR
3.49
(A)
CRYSTALLITE DENSITY fem/cc)
ACICULAR
INTERLAYER SPACING, d (A)
CODE D
CRYSTAL HABIT
CODE C
PRECURSOR
MICROSTRUCTURE O F GRAPHITE PRECURSOR COKES
Table I
Downloaded by MONASH UNIV on December 11, 2016 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/bk-1976-0021.ch015
174
P E T R O L E U M DERIVED CARBONS
Analysis during billet fabrication studies consisted of determination of density and tensile strength and strain-to-failure of in-process material after each fabrication step and after graphitization and final heat treatment. Experimental Methods Apparent crystallite size, L ç , and average crystallite diameter, A » were calculated f r o m the x-ray line width β\/ι of the 0002 and 1120 x-ray reflections occuring at 26.6° and 77.8°, respectively, using the Sherrer formula (1,2) Downloaded by MONASH UNIV on December 11, 2016 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/bk-1976-0021.ch015
L
.—:a— β cos θ
L
ι/2
where Κ i s a constant = 0.90 f o r L Q and 1.77 f o r L A » λ i s the wavelength of the analyzing radiation, β j/2 i s the peak half width c o r rected f o r instrumental broadening and 2 θ i s the respective diffraction angle f o r 0002 and 1120 x-ray diffraction peaks. The data were uncor rected for strain broadening. Consequently, i n the more disordered materials such as glassy carbon, the apparent crystallite size, L Q , i s a measure of the degree of distortion i n interlayer spacing, and the parameter, L ^ , may be described as the average defect-free distance (3,4). The Maire-Méring g-factor, considered a measure of the degree of graphitization (4,5,6), was calculated f r o m the following equation: d
0002
=
3
'
3 5 4
*
+
3.440(1
-g)
where 3.354 and 3.440 are the interlayer spacings f o r graphite and turbostrati c carbon, respectively, and d
