Polycrystalline graphite

The aggregates of crystallites also have widely different sizes and properties. Some, such as soot, are extremely small and contain only afew small crystallites. In such cases, the properties are mostly related to the surface area (see Ch. 10). 

Other aggregates may be relatively large and free of defects and essentially parallel to each other, in which case the structure and its properties closely match those of the ideal graphite crystal. Such large aggregates are often found in pyrolytic graphite (see Ch. 7). 

In other aggregates, the crystallites have an essentially random orientation. This occurs in turbostratic (i.e., showing no evidence of three-dimensional order) or amorphous carbon shown in Fig. 3.4. In such cases, the bulk properties are essentially isotropic. 

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Brocklehurst, J.E. and Kelly, B.T., Analysis of the dimensional changes and structural changes in polycrystalline graphite under fast neutron irradiation. Carbon, 1993, 31, 155 178. 

I. loka, S. Yoda and T. Konishi. Behavior of acoustic emission caused by microfracture in polycrystalline graphites. Carbon 1990,28(6), 879 885. 

I. loka and S. Yoda. Acoustic emission caused by reversed plastic deformation in polycrystalline graphites. J. Nucl. Mater. 1987, 148, 344 350. 

N. McLachlan. The Modelling of Polycrystalline Graphite Fracture and Deformation Properties, Ph.D. Thesis, University of Exeter, UK, 1992. 

J. E. Brocklehurst, Fracture in Polycrystalline Graphite, In Chemistry and Physics of Carbon, Vol. 13, ed. Philip L. Walker, Jr. and Peter A Thrower, Marcel Decker, New York, 1977, pp. 145 279. 

M. Sakai, K. Urashima, and M. 1 nagaki, Energy Principle of Elastic-Plastic Fracture and Its Application to the Fracture Mechanics of a Polycrystalline Graphite, Journal of the American Ceramic Society, 1983, 66(12), 868 874. 

The measured mass susceptibility values for bucky-bundle (both xb aid xu). Qo. the gray-shell material, the polycrystalline graphite anode, and the... 

From Table 1, we see that the measured susceptibility of the polycrystalline graphite anode (used to produce the fullerenes measured here) is 6.50 x 10 ... 

Fig. 5. Temperature dependence of the magnetic suseepli-bilities measured in a magnetic field of 2 T (a) Qo powder, (b) polycrystalline graphite anode, (c) gray-shell material, (d) buckybundle axis perpendicular to H, and (e) buckybundle axis parallel to H.

Figure 16. Model In PC based electrolytes, solvent co-intercalation, gas formation and crevice formation in polycrystalline graphite materials are inter-related reactions. In fact, there is a subsequence of reactions (1) PC co-intercalation, (2) gas formation, (3) crevice formation ultimately resulting in exfoliation and macroscopic destruction of graphite [40],...

Brocklehurst [37] has written an exhaustive review of the early work (prior to 1977) on fracture in polycrystalline graphite. Much of this work focused on the fracture behavior of nuclear graphites. In most investigations considered, conventional fracture mechanics tests and analysis were performed for macroscopic cracks. LEFM provided an adequate criterion for failure. Additionally, results on work of fracture, strain energy release rate, and fatigue crack propagation were reported. 

These examples notwithstanding, the unusual electronic properties of HOPG, the adsorption common to EPG, and the relative difficulty of handling anisotropic materials have prevented widespread practical applications. Polycrystalline graphite and glassy carbon exploit some of the same principles as HOPG and PG, but are more broadly applicable. 

Most polycrystalline graphite is made by heat treating high-molecular-weight petroleum fractions ( pitch ) at high temperatures to bring about graphitization. 

A key property of polycrystalline graphite is porosity. The density of HOPG is 2.26 g/cm3, while that of a typical spectroscopic graphite rod (Ultracarbon... 

Also known as vitreous carbon, glassy carbon has been the subject of intense electroanalytical research in the past 10 years. It is impermeable to liquids and gases, and thus porosity is not an issue, as it is with polycrystalline graphite. It is easily mounted, polishable, and compatible with all common solvents. These properties have led to widespread use in mechanistic electrochemistry, LC detection, and voltammetric analysis. 

Cokes with binder pitches Polycrystalline graphite blocks Various densities, various degrees of orientation... 

Liquid-phase carbonization occurs for some precursors, such as pitches, which become viscous fluids before carbonization. This process has been used to produce various polycrystalline graphite blocks for steel refining and electrical discharge machining, jigs for the growth of semiconductor crystals, structural components of nuclear reactor, etc. 

Inagaki, M. and Kang, F. Polycrystalline graphite blocks. In Carbon Materials Science and Engineering, Beijing, China Tsinghua University Press, 2006 269. 

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