Physical Properties
• Good electrical conductivity: the temperature coefficient of electrical resistance of graphite is negative in a certain range of temperature, unlike that of metals. Near absolute zero, graphite has only a few free electrons and acts as an insulator. As temperature rises, electrical conductivity increases.
• Good thermal conductivity: outstanding heat transfer properties.
• Unique mechanical strength: the tensile, compressive and flexural strength of graphite increases as temperature increases to 2700 K. At 2700 K graphite has about double the strength it has when at room temperature. Above this temperature, its strength falls (see graph).
• Low coefficient of thermal expansion.
• High thermal shock resistance: rapid heating or cooling is not a problem.
• Graphite is not wetted by the molten glass or by most molten metals.
• Low coefficient for friction.
• High chemical resistance .
• Corrosion resistance: oxidation resistance in air up to 500 C.
• Low capture cross-section for neutrons.
• Problem-free machining with standard machine tools: graphite can be machined easily. Complicated parts with close tolerances can be machined with precision.
• Reasonable cheap material in comparison to other material with similar corrosion resistance.
• Graphite does not melt but sublimes at about 3900 K. In air, graphite is resistant to oxidation up to temperatures of about 750 K.
• Graphite displays extremely low creep at room temperature, its flow characteristics being comparable to those of concrete. Creep in graphite is strongly dependent on the grain orientation (creep is defined as plastic flow under constant stress).
High-temperature properties
• Electrical resistivity GRAPH
• CTE delta
• CTE
• Thermal conductivity
• Specific heat
• Strenght
• Young’s modulus From room temperature up to >2000 C All graphs are showing typical property trends. Absolute values will vary according to raw materials and processing.
1. Lattice
Both natural and electro-graphite have a hexagonal layer lattice. It's more or less perfect formation in the electro graphite depends largely on the degree of crystalline order of the solid particles and the primary products obtained upon carbonizing the carbonaceous binder materials used for its manufacture. The particle size of the solids used plays an important role as it strongly influences the final properties.
Graphite Lattice Formation GRAPH
2. Classification of grain size
Fine-grained Graphite
Fine-grained particles are produced by milling from coarse-grained raw material. Within the wide field of carbon ceramics, the technology of fine-grained carbon and graphite was developed. This proved to be in many respects an independent manufacturing technique. The materials thus obtained are called fine-grained graphite. Their grain size distribution ranges from 1 mm to 0.001 mm. Quite a number of combined properties, especially in small-sized shapes, can only be obtained by using fine-grained solids, being the lower end of coarse-grain material down to dust particles in teh sub-micron range.
Coarse-grained Graphite
Coarse-grained graphite has a maximum grain size less than 25 mm. Nearly all of these grades are manufactured by extrusion. The processing of a lump or coarse-grain solid, as it is received as shipment, is economically more advantageous.
Classification of grain size
Classification of fine grain size (based on size measuring techniques of the initial raw materials. The measuring techniques involved are not applicable to the finished product).
