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Diagram of a Castner lengthwise graphitization furnace. a - Mixture of Coke and Sand, b - Bricks, c - Carbon Electrodes, d - Refractory Material, e - Rods to Graphitize, f - Granulated Coke File usage
To finish the items, the process is run for approximately 20 hours at 200 V with a starting current of 300 A (60 kW) for a furnace approximately 9 meters long by 35 cm in width and 45 cm in depth, and the resistance drops as the carbon heats due to a negative temperature coefficient, causing the current to increase. [2] Cool down takes weeks.
Graphitization generally occurs at high temperatures (up to 3,000 °C (5,430 °F)), and can be accelerated by catalysts such as iron or nickel. [ 2 ] When carbonaceous material is exposed to high temperatures for an extended period of time, the carbon atoms begin to rearrange and form layered crystal planes.
This is because carbon must diffuse out of the graphite until it has reached the equilibrium concentration dictated by the temperature and the phase diagram. This step may be done in many types of furnaces, in a high-temperature salt bath, or via direct flame or induction heating. Numerous patents describe specific methods and variations.
Graphite's high thermal stability and electrical and thermal conductivity facilitate its widespread use as electrodes and refractories in high temperature material processing applications. However, in oxygen-containing atmospheres graphite readily oxidizes to form carbon dioxide at temperatures of 700 °C and above.
The iron-carbon phase diagram. While cementite is thermodynamically unstable, eventually being converted to austenite (low carbon level) and graphite (high carbon level) at higher temperatures, it does not decompose on heating at temperatures below the eutectoid temperature (723 °C) on the metastable iron-carbon phase diagram.
Operating a vacuum heat treating furnace, c. 1959–1962. A vacuum furnace is a type of furnace in which the product in the furnace is surrounded by a vacuum during processing. The absence of air or other gases prevents oxidation, heat loss from the product through convection, and removes a source of contamination
STM can be performed in a constant current or a constant height mode. The low temperature STM measurements provide thermal stability, which is a requirement for high resolution imaging and spectroscopic analysis. The first atomically resolved images of graphene grown on a platinum substrate were obtained using STM in the 1990s. [126] [128]