SPI Supplies^® Brand Glassy (Vitreous) Carbon Products

Applications for Glassy Carbon:

• Microscopy and Microanalysis
• Metallurgical
• Laboratory Research
• Vacuum Evaporation
• Semiconductor and Electronics
• Nuclear
• Aerospace

What is glassy (sometimes called "vitreous") carbon?

Carbon comes in many forms and there is no other element that can take on so many different appearances, properties and morphologies. We are all familiar with many synthetic polymers, for example "Nylon", which can be found as a yarn in a sweater, tire cord, molded part or an extruded film. We are familiar with carbon as diamond and carbon as graphite, again two forms with dramatically different properties.

Carbon can also be prepared in the glassy state, sometimes called the vitreous state. The glassy carbon products offered by SPI Supplies are completely amorphous with no crystallinity. X-ray diffraction shows only an "amorphous halo". When the glassy carbon is fractured, it exhibits the fracture face that is characteristic of a glassy material. Glassy carbon has a range of properties and applications that makes it a new and exciting material for research and production applications.

The glassy carbon offered by SPI Supplies exhibits properties that are as dramatically different from the properties of graphite as diamond. Our glassy carbon is a unique material with very unusual properties.

How the SPI Supplies^® Brand of vitreous carbon differs from graphite:

From an analytical standpoint, graphite gives strong x-ray diffraction peaks, indicating a high degree of "order" and a high level of x-ray diffraction determined crystallinity. The SPI Supplies Brand of glassy carbon exhibits no diffraction peaks and exhibits only an amorphous halo.

Most graphites (excluding HOPG and pyrolytic graphite) exhibit considerable porosity. The SPI Supplies brand of glassy carbon is quite dense, certainly much more so than graphite. This might sound like a contradiction, but when one looks at the density of glassy carbon in comparison to the theoretical density of the graphite crystal, its density is less, specifically ~ 1.5 vs. 2.25. Because graphite normally has considerable porosity, the ~ 1.5 density is higher than the typical graphite (excluding HOPG and pyrolytic graphite). As a consequence of this high density and the lack of porosity that plagues ordinary graphite, the SPI Supplies glassy carbon can be polished to a mirror finish. It looks like a "black glass".

Another important property of the SPI Supplies Brand of glassy carbon is it a good thermal conductivity, which imparts to it a high level of resistance to thermal shock (making possible its application for crucibles).

Chemical Resistance:

Theoretically, glassy carbon should behave like any other form of carbon, I.E. graphite, but 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. The main reason for the impressive chemical resistance is a consequence of the disordered structure and the inability to form intercalation compounds. This gives rise to high resistance to corrosion by acid and alkaline agents and melts. Because of the high purity, glassy carbon is appropriate for applications in chemical analysis, semiconductor and ultratrace analysis.

Thermal Properties:

Depending on grade, the material can be taken as high as 2500°C without any significant devitrification. Above that temperature some devitrification will occur and there will be a nucleation and growth of a graphite phase. Remember, the higher the density the higher the temperature will be at which these transition occurs.

Note: that the SPI Glas glassy carbon products can be heated in air, depending on grade selected, up to 600°C without undergoing any reaction but above this temperature, any heating should be done strictly either under vacuum or in an inert environment such as argon. If vacuum is not used for higher temperatures, there will be a reaction and the formation of CO and CO₂. A similar kind of reaction will occur above 600°C with water or water vapor, resulting in the evolution of CO and H₂.

Surface State:

Our standard product exhibits an "as produced" surface that is shiney and mirror-like, it is not mechanically polished. We can, upon request, offer highly polished surfaces at an additional cost. The final finishing may also be done by the customer, and at a more cost effective price, based on the particular application.

Available Grades:

SPI Supplies offers its glassy carbon in four grades, each with its own set of properties and which are based on the final heat treatment temperature of the glassy carbon:

SPI-Glas 10 and SPI-Glas 11 are very similar but we make the differentiation because they are produced using somewhat different processes. We find SPI-Glass 22 and SPI-Glas 25 to be similar, but again when the properties of the two are compared, there are significant differences in their properties. The fundamental difference in the properties is the reactivity against oxidizing agents such a nitric acid, perchloric acid and oxygen. For example, the oxidizing rate of SPI-Glas™ 22 vs. SPI-Glas™ 11 is that it is 24 times lower and this is a significant difference.

¹ 4-point bending test; geometry of specimen; circular rod, diameter 3 mm, length 60 mm
² Geometry of specimen: circular rod, diameter 7 mm, length 10 mm