Non-graphitizable carbon

Figure 2.3 Schematic contrasting (a) non-graphitizable carbons versus (b) graphitizable carbons.

CARBON-CARBON COMPOSITE is a carbon fiber reinforced carbon matrix material. The carbon matrix phase is typically formed by solid, liquid or gaseous pyrolysis of an organic precursor material. The matrix is either a GRAPHITIZABLE CARBON or NON-GRAPHITIZABLE CARBON, and the carbonaceous reinforcement is fibrous. The composite may also contain other components in particulate or fibrous forms. 

GLASS-LIKE CARBON is an AGRANULAR, NON-GRAPHITIZABLE CARBON, with isotropy of its structural and physical properties and with a very low permeability for liquids and gases. 

Note NON-GRAPHITIZABLE CARBONS do not transform into GRAPHITIC CARBON on heat treatment at temperatures above 2500K and therefore, are not GRAPHITIZED CARBONS. 

NON-GRAPHITIZABLE CARBON is a NON-GRAPHITIC CARBON which cannot be transformed into GRAPHITIC CARBON solely by high temperature treatment up to 3300K under atmospheric or lower pressure. 

These terms of graphitizable and non-graphitizable carbons were introduced by Rosalind Elsie Franklin (1950, 1951), a pioneer researcher into structures of coals and carbons, as... 

Figure 2.6. High-resolution fringe-image electron micrographs of structure in different carbons, (a) Single-crystal graphite showing parallelism of layers, (b) A partially graphitized carbon from PVC (1573 K). (c) A non-graphitizable carbon from PVDC (2973 K).

The model of Franklin (1950) for non-graphitizable carbon is remarkably accurate. If this model is re-designed into three dimensions, then the models of Figures 3.9, 3.16 and 3.17... 

Figure 2.7. Drawings to illustrate the essential differences between (a) graphitizable and (b) non-graphitizable carbons (Franklin, 1950, 1951).

The above discussions have stressed that porosity in this family of carbons essentially is that space where carbon material (atoms and heteroatoms) is absent. If the structure or relative arrangements of carbon atoms is changed in some way then automatically a new set of porous properties will be created. It therefore follows that a knowledge of structure assists with knowledge of the nature of porosity in that carbon. This aspect was mentioned earlier when graphitizable and non-graphitizable carbons were introduced. 

A further possibility can be considered in analyses of line-broadeiung phenomena. Considering again the model of non-graphitizable carbon of Franklin (1950) of Figure 2.7(b), its microporosity (extent of) could relate to the thickness of the carbon material (pore wall) which separates (individualizes) the microporosity. This material contributes to linebroadening, the thinner the pore wall, the broader the peak. Thus, there is a possibility (to be explored further) that line-broadening in porous carbons may relate more to porosity than pore wall carbon. 

Sadly, this graphitic microcrystallite concept appears to have been passed down over the years (perhaps uncritically) from publication to publication. Now, it requires a careful reassessment to enable the subject of structure in non-graphitizable carbons to move on. 

Figures 2.<>0 and 2.61. The artist who designed this advertisement for the Barracas of La Fiesta de Fogueres of Alicante, Spain, used as a background a multi-ring system as may be found in the graphene layers of an isotropic, non-graphitizable carbon (right). Antoni Gaudi I Comet (1852-1926) may have been an influence with his ceramic mosaics.

Generally, non-graphitizable carbons are formed (with few exceptions) from non-melting parent substances (macromolecular), for example coconut shell and thermo-setting resins. The macro-structure within such carbons generally follows closely the original structures... 

Figure 5.26. Scanning electron micrograph of surface of non-graphitizable carbon from PFA, HTT 1123 K, non-oxidized (Adair eta/., 1971).

---