Glassy carbon

Glassy carbon, also called vitreous carbon, a high-tech material of pure carbon, the vitreous ceramic properties is united with that of the graphite.

Properties

Glassy carbon has a high thermal stability under inert gas or vacuum up to 3000 ° C, extreme corrosion resistance, liquid and gas tightness (He- permeability 10-9 to 10-11 cm ² / s), no wetting by melting, high hardness (HV 250-350 ) and strength ( bending strength of 250 MPa, stiffness by 35 GPa ), low density ( 4.1 to 5.1 g / cc), high surface quality, low thermal expansion ( about 2.5 x 10-6 1 / K between 20-2000 ° C ), extreme resistance to thermal shock, thermal moderate (4-6 W / ( K x m ) at 20 ° C) and electrical conductivity (2 x 104 1 / ( Ω × m ) ), the isotropy of the physical and chemical characteristics and good biocompatibility.

Glassy carbon is a form of carbon with a highly disordered graphite structure. The carbon atoms with sp2 bond are arranged in layers with hexagonal symmetry. The TEM image shows graphite crystallites, which include small pore size of 1 nm. The electron microscope is from only the basal planes, which are oriented in the direction of Elektronenststrahls.

The model illustrates the microstructure of glassy carbon. The webs are made of graphite crystallites with a thickness of 4-10 basal levels. Unlike activated carbon, the pores are not interconnected. The scatter of the size of the closed pores is low. It is, depending on the production, by 1-5 nm macroscopically appear glassy carbon isotropic. The model explains the low density compared to graphite, the high hardness and strength, and the isotropy of the material parameters.

A mechanical machining is possible due to the high hardness with diamond tools. A machining is not possible. Alternative processing methods are electrical discharge machining ( EDM), water jet cutting (water-jet cutting machine ) or laser cutting.

Use

• Electrode material