Basic Element and Different Coating
Ceramisis can supply basic elements in a variety of materials, including graphite, carbon composite, and refractory metals. Elements can be flat meander type, or tubular picket fence type, or wire wound from refractory metals such as Tungsten.Elements can be produced from customer's own drawings, or Ceramisis can offer a design service to produce the required element profile.The enquiry sheet at the back of this document makes it easy to specify the exact element design required. Please use the overview table to select the correct material.To stop the problems of out gassing, particle contamination and oxidation that occurs with high density graphite and carbon carbon composite elements, there are various coatings that can be applied as follows: Silicon Carbide, Pyrolytic Graphite, Vitreous Carbon and PBN Coatings, Plus Vitreous Carbon Impregnation.
Pyrolytic Boron Nitride Coating
This white Pyrolytic Boron Nitride coating can be applied to very specific grades of high density graphite (see picture left) to seal the porosity and improve the oxidation and chemical resistance of the element. It will oxidise at 900°C if oxygen is present, but can withstand 2000°C in an inert atmosphere or vacuum (with N2 present).
Vitreous Carbon Coating
Vitreous carbon surface treatment is a cheap alternative to pyrolytic graphite coating, and is produced by vitrifying a resin applied to the surface of the high density graphite component. It seals in the particles but does not totally seal the porosity, although it can be drastically reduced. Vitreous carbon coating is better at sealing the porosity than the impregnation and gives a nice black glassy appearance to the component. It is chemically the same as high density graphite and so will still react chemically in the same way and with oxygen at 500°C.
Silicon Carbon Coating
Is a dark grey coating applied by a CVD method to specific grades of high density graphite. This silicon carbide ( SiC ) coating is an electrical insulator and therefore can not be applied to the electrical contact points on the element (see picture middle left). We can supply a SiC paint that can be applied to connection points after connection has been made. This paint is then thermally cured. The silicon carbide coating can operate in oxygen environments up to 1400°C and can resist some chemically corrosive environments better than graphite.