Vitreous Carbon Crucibles | Glassy Carbon Ceramics

Vitreous Carbon

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Vitreous Carbon Crucibles are made from 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.

Nonferrous and ferrous metals such as aluminium, bismuth, germanium, antimony, tin, cadmium, lead, nickel, zinc, copper, magnesium, iron, stainless steel
Glass melting including soda glass and cryolite
Molten salt, fluoride, slag

Material properties

Please note that the information set forth herein is offered for comparison only, and is not to be construed as absolute engineering data or constituting a warranty or representation for which we assume legal responsibility.

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	Value
Maximum Service Temperature	2000 oC
Electrical Resistivity	42 x 10-4 ohm cm
Apparent Porosity	1.0 – 3.0%
Coefficient of Thermal Expansion (20 – 200oC)	2.0 – 2.2 x 10-6/oC
Thermal Conductivity (30o)	5.8 W/mK
Apparent Density	1.51 gm/cc
Ash Content	< 5 ppm
Permeability Coefficient	10-10 ~ 10-12 cm2/sec
Shore Hardness	100 – 1101
Young’s Modulus1	29,500 – 32,400 MPa
Flexural Strength1	147 MPa
Charpy Impact Value	2.1 – 3.6 kgf.cm/cm2

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

Chemical Corrosion Resistance of Vitreous Carbon

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.

Some of the Applications of Vitreous (Glassy) Carbon

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…

View our full range of Vitreous Carbon products.

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Contact us to discuss a custom Vitreous Carbon solution.

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Almath Crucibles Ltd.

Epsom Building,
The Running Horse,
Burrough Green,
Newmarket, Suffolk
CB8 9NE

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(CQS Cert #GB2001792)

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