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SPI-Glas™ Brand Glassy (Vitreous) Carbon Crucibles

These crucibles can be used as a direct replacement for platinum in many applications





Introduction:
SPI-Glas™ Brand glassy carbon, some times referred to as "vitreous" carbon, can be fashioned into crucibles and bowls which are universally used in laboratories worldwide for carrying out chemical analyses and also for the preparation of fluorophosphate and other glassy materials. Crucibles fabricated in SPI-Glas™ Brand glassy carbon are also used in the growing of single crystals and other ultra-high purity materials. The SPI-Glas™ Brand glassy carbon also exhibits excellent biological compatibility with live tissues and therefore has high potential for applications in life science research and medicine generally.

The SPI-Glas glassy carbon crucibles exhibit the very highest purity and absolutely nothing will ever leach out of a crucible made from SPI-Glas™ glassy carbon so long as they are not heated above their recommended maximum use temperature. Glassy carbon is a unique material and exhibits properties entirely different from other forms of carbon with which one everyone already has some high amount of familiarity. The glassy carbon crucibles offered by SPI Supplies are available in several different grades, and are plug-in compatible in many applications where presently only platinum crucibles are being used. Their low economical cost, relative to platinum makes them especially in demand in days of shrinking research budgets. The very high density of the product literally prevents many molten materials from spreading on the glassy carbon surface. And the high density prevents any of the molten species from leaching into the glassy carbon surface. And of course one does not experience "mysterious disappearances" of a glassy carbon crucible as is often times the case for platinum crucibles.

One of the biggest applications for SPI-Glas™ Brand glassy carbon crucibles is for the melting of precious group metals

How is SPI-Glas™ Brand glassy carbon different from graphite and "ordinary" carbon?
Glassy carbon should be thought of in perspective with regard to graphite, ordinary carbon, and diamond. Its hardness is close to that of diamond but its appearance (e.g. black) is reminescent of graphite. Quite predictably, the properties of the SPI-Glas™ Brand glassy carbon is considerably different from those of either diamond or graphite.

SPI-Glas™ Brand Glassy Carbon Crucibles exhibit some very unusual properties:

For example, the SPI-Glas™ Brand Glassy Carbon Crucibles, relative to ceramic crucibles, exhibit far higher thermal conductivity and show virtually no adhesion of precious group metals. Thermal cycling times are reduced, sometimes substantially. This also means that the heater coils can be operated at lower temperatures than would otherwise be mandated if ceramic crucibles were being used.

As a result of the above, the cycle time for a casting is greatly reduced and the useful life of the crucibles is greatly extended.

Useful lifetimes of SPI-Glas™ Brand Glassy Carbon Crucibles:
The useful lifetime of SPI-Glas™ Brand Glassy Carbon Crucibles is much longer than for graphite crucibles because of the much slower oxidation rate of glassy carbon at high temperatures in air. When a reducing atmosphere over the crucible is employed, the resulting virtually zero oxidation rate prevents the formation on the molten metal surface an oxide layer. The melting aids usually associated with the use of ceramic crucibles are normally not needed since the molten metal freely flows out without ever wetting the crucible walls and the casting that is obtained has a uniform and featureless surface. The metal-repelling characteristics of the SPI-Glas™ Brand Glassy Carbon Crucibles remain unchanged throughout the crucible's lifetime.

Resistance to thermal shock:
The SPI-Glas™ Brand Glassy Carbon Crucibles will not fracture when still red hot, are placed on a cold surface.

Application to induction-heating casting centrifuges:
The SPI-Glas™ Brand Glassy Carbon Crucibles are used widely in applications involving induction-heating casting centrifuges. Since glassy carbon crucibles couple in the inductive field (which is not true for ceramic crucibles), they read the desired operating temperature far more quickly, and the metal will melt more quickly, resulting in much shorter cycle times per run.

Applications in dental laboratories:
The SPI-Glas™ Brand Glassy Carbon Crucibles are used extensively in dental laboratories for use with the induction-heated casting centrifuges. They can also be used for the melting of high-Pd containing alloys which will not have defects and will not flake after ceramic veneering.

Chemical resistance:
Theoretically, glassy carbon should behave like any other form of carbon, such as graphite, but in fact it is far less reactive because of the higher density relative to the normally more porous graphite. Its resistance is more akin to HOPG and high density pyrolytic graphite.

Thermal properties:
The material can be taken to 2500°C depending on grade, without any significant devitrification. However above that temperature, some devitrification will occur, and there will be a nucleation and growth of a graphite phase.

Note: that the SPI Glas glassy carbon products can be heated in air up to 500°C without undergoing any reaction but above this temperature, any heating should be done strictly either under vacuum or in an environment of argon.

Precaution:
The SPI-Glas™ Brand Glassy Carbon Crucibles should never be used for the melting of chromium-cobalt-molybdenum alloys. Similarly, they should not be used for melting anything that easily carbides, for example silicon or tungsten.

Available grades:
The SPI-Glas™ Brand Glassy Carbon Crucibles are available in only one grade, SPI-Glas™ 20, which has the same identical properties as premium grade SPI-Glas™ 25, except that its maximum service temperature is 2000° C instead of 2500° C.

Available products:
Cylindrical crucibles with nozzle
Electron beam evaporating crucibles
Tapered crucibles (Type "K")
Tapered crucibles (Type "T")
Crystal growth crucibles
Cylindrical crucibles


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Sunday July 20, 2008
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