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SPI-Glas™ Brand glassy carbon, also known as "vitreous" carbon, can be manufactured into various shapes. These products can used for chemical analyses and preparation of fluorophosphate and other glassy materials. Crucibles fabricated in SPI-Glas™ Brand glassy carbon material are also used in the growing of single crystals and other ultra-high purity materials. The SPI-Glas™ Brand glassy carbon exhibits excellent biological compatibility with live tissues meaning it has high potential for applications in life science research and medicine in general.
The SPI-Glas glassy carbon crucibles exhibit the very highest purity. 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. 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 cost relative to platinum makes them especially attractive 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. The high density prevents any of the molten species from leaching into the glassy carbon surface.
One of the biggest applications for SPI-Glas™ Brand glassy carbon crucibles is for the melting of precious group metals
Glassy carbon should be thought of in relation to graphite, ordinary carbon and diamond. Its hardness is close to that of diamond but its appearance (e.g. black) is reminescent of graphite. The properties of the SPI-Glas™ Brand glassy carbon is considerably different from those of either diamond or graphite.
The SPI-Glas™ Brand Glassy Carbon Crucibles, compared to ceramic crucibles. Also, 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, the cycle time for a casting is greatly reduced and the useful life of the crucibles is greatly extended.
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 virtually zero oxidation rate prevents the formation of a molten metal surface and oxide layer. The melting aids usually associated with ceramic crucibles are not needed since the molten metal freely flows out without ever wetting the crucible wall. 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.
The SPI-Glas™ Brand Glassy Carbon Crucibles will not fracture when they are still red hot, and then placed on a cold surface.
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 (not the case for ceramic crucibles), they read the desired operating temperature far more quickly. This means the metal will melt more quickly, resulting in much shorter cycle times per run.
The SPI-Glas™ Brand Glassy Carbon Crucibles are commonly used in dental laboratories with induction-heated casting centrifuges. They can also be used for the melting of high-Pd containing alloys which will not have defects and no flaking after ceramic veneering.
Theoretically, glassy carbon should behave like any other form of carbon, such as graphite, but in fact it is far less reactive because of its high density relative to more porous graphite. Its resistance is more like to HOPG and high density pyrolytic graphite, then regular graphite.
The material can be taken to 2500°C depending on grade, without any significant devitrification. 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. Above this temperature any heating should be done strictly either under vacuum or in an environment of argon.
The SPI-Glas™ Brand Glassy Carbon Crucibles should never be used for the melting of chromium-cobalt-molybdenum alloys. Similarly, they should not be usedfor melting anything that easily carbides, such as silicon or tungsten.
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.
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