Additional Materials

Binding agents are used to agglomerate the solid particles to each other. Their high wetting ability thus transforms the mix into a plastic state for subsequent molding or extrusion. In addition, binders must produce a high coking residue in order to produce the necessary strength, density and sliding properties of the artefacts. The structure of the binder coke formed plays a marked role for many technical applications, as its graphitizability depends largely on the binder coke structure. In addition to the solid phase, the binder also influences substances, especially some resin systems, yield only a relatively low coking residue, and they are not suited for the manufacture of all products which require a carbonising or graphitising step. Consequently the binders tend to dominate the properties of the final product as it is consisting up to 70% by weight of the binding agent. Organic binding agents are: pitch, phenolic resins, cellulose compounds. Click here to view their chemical structure. The yield of the coking residue may be increased by condensation processes, either by thermal condensation up to 300 C or above or by chemically adding sulphur, chlorine or nitrogen compounds, also at elevated temperatures. This increased coke yield is coupled with a higher isotropy of the binder coke structure depending on the nature and amount of the condensating agents. For a number of special carbon grades, synthetic resins with a high coke yield may be used as binders. These are almost exclusively thermally setting, duroplastic resins on the base of phenol formaldehyde, furan and furfuryl alcohol.

Chemical structure GRAPH

Pitch

Pitch is an organic compound and has a distinct aromatic structure. Due to its high proportion of substituted and condensed benzene rings, it already has the distinctly preformed hexagonal lattice structure of graphite, thus facilitating the formation of well-ordered graphitic domains during graphitisation. Pitch proves to be the most advantageous binder. It is the distillation residue of coal tar; and according to the desired application purpose, it is produced from selected or thermally processed raw tars. Since it is a solid at room temperature, it is usually characterised by its softening point and coking residue and selected according to its application.

Phenolic resins

Upon thermal curing, phenolic resins form an amorphous three-dimensional network structure, which is interconnected by oxygen and/or aliphatic methylene bridges. Therefore the formation of a graphitic layer lattice is considerably impeded so that the graphitizability of a phenol based resin coke is markedly less in comparison to a pitch coke although the pure phenol itself has an aromatic configuration.

Cellulose compounds

Cellulose compounds are systems without aromatic structures at all and yield a binder coke residue, which is practically impossible to graphitise.

Furan or furfuryl alcohol resins

Furan or furfuryl alcohol resins do not have an aromatic structure nor a six-member ring configuration. They are thus practically impossible to graphitise.