Vitreous Carbon

Vitreous Carbon is a ceramic carbon based material. It has the appearance of black glass and it is fragile. It has a closed micro-porosity and is impervious to gas.  Vitreous Carbon has good resistance to thermal shock because of a relatively good thermal conductivity. Vitreous Carbon is sometimes referred to as Glassy Carbon.

Vitreous Carbon is related to graphite crystal but with a very large disorder and submicron voids. It has a low density of 1.51 gm/cc as compared with 2.25 gm/cc for theoretical density of graphite crystal. Vitreous Carbon is unusual in that when it is treated at 2500°C and over it very slightly modifies its crystallographic structure.

Almath Crucibles offers Vitreous Carbon in a Grade A quality only. The operating temperature, when heat treated, of Grade A Vitreous carbon is 2500°C. The normal operating temperature for it is 2000°C and it may be used up to 2800°C in a non-oxygen atmosphere but at this maximum temperature some of the properties of Vitreous Carbon may change.

Grade A is the most useful and the most common grade.

The Grade A of Vitreous Carbon is more stable in dimension during thermal cycles and is preferred when sharp variations of temperature can occur or when maximum operating temperature is above 1000°C.

Grade A Properties
Maximum Service Temperature2000 oC
Electrical Resistivity42 x 10-4 ohm cm
Apparent Porosity1.0 – 3.0%
Coefficient of Thermal Expansion (20 – 200oC)2.0 – 2.2 x 10-6/oC
Thermal Conductivity (30o)5.8 W/mK
Apparent Density1.51 gm/cc
Ash Content< 5 ppm
Permeability Coefficient10-10 ~ 10-12 cm2/sec
Shore Hardness100 – 1101
Young’s Modulus129,500 – 32,400 MPa
Flexural Strength1147 MPa
Charpy Impact Value2.1 – 3.6

1 4-point bending test; geometry of specimen: circular rod, diameter 3 mm, length 60 mm


  • Hydrofluoric Acid at 40%, 25oC, weight loss < 1% in 1 month
  • Sulphuric Acid at 95%, 150oC, weight loss 0.2% in 6 months
  • Nitric Acid at 52%, 75oC, weight loss 2.5% in 6 months
  • Nitric Acid at 93%, 25oC, weight loss < 1% in 1 month
  • Crucible used for melting at 800oC directly on a Meker torch
  • With soda carbonate mixing (Na + K), pyrosulphate – no erosion within the crucible, the weight loss by outside oxidation is about 50 mg in 30 minutes for a crucible 35 mm diameter x 35 mm (weight 10 grams)

Vitreous Carbon is very resistant to attack by the following reagents: bromine, hydrochloric, hydrofluoric, nitric, sulphuric and chromic acids, fused caustic alkalis, fused potassium bisulphate, fused calcium fluoride and nitric acid and hydrogen peroxide, nitric acid and potassium chlorate.


  • Preparation and crystal growth of Group III-V semiconductors.
  • Production of oxygen free single crystal silicon.
  • Spectrographic and polarographic electrodes.
  • Laboratory beakers, basins, boats and containers for handling acids and caustic alkalis.
  • Glass and carbon joints and pieces, mandrels and other equipment for glass work.
  • Steam fuel and rocket nozzles.
  • Surgical and Medical applications.
  • Microphone electrodes and relay contacts.
    and many others…

For a bespoke solution or to enquire about volume discounts, please get in touch.

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