Heat Treatment and the Change of Material Properties
MRF furnaces have been part of many R&D breakthroughs and discoveries over the years. Mass production of these new applications has helped us continue serving multiple markets even after the initial process has been defined or commercialized. One of these processes that have gained more interest within the various markets over the last few decades is graphitization.
Graphitization is the enhancement of graphite properties through the use of a high-temperature furnace. With these improvements, graphite is used in many applications such as ceramics, brakes, seals, batteries, electrodes, artificial diamonds, and carbon fiber, just to name a few.
Due to its allotropic nature, carbon exists in different forms including a) Diamond, b) Graphite, c) Lonsdaleite, d) C60 (Buckminsterfullerene or buckyball), e) C540, f) C70, g) Amorphous carbon, and h) single-walled carbon nanotube, or buckytube as shown in Figure 1.
Figure 1. (Boundless, n.d.)
Graphene is the separate supramolecule layers that make up graphite as shown in Figure 2. The process of graphitization causes these structural layers to change from chaotic or flawed carbon atom structures and perfects them into a precise 3D crystal of pure graphite.
Figure 2. (Zavašnik,2019)
In order to arrange graphite molecules into a semblance of order, a heat treatment process is performed. Basic structural units (BSU) are graphene molecules that are contained within the carbon material. During the heat treatment the BSU will begin to grow while all differences in orientation within the layers are removed. The graphite is heated up to 3000°C in an inert atmosphere and as the temperature ramps up, the graphite eventually forms large straight layers, as Figures 3 and 4 show.
Figure 3. Graphitization process and the semblance of order within the basic structural units (BSU) as the temperature increases. (Poco Graphite, 2015)
Figure 4. Comparison of graphite layers before and after heat treatment. (Mondal, Kunal & Pawar, Gorakh & Mcmurtrey, M. & IITK, Ashutosh 2020)
Graphitization causes composites with surface-treated fibers to increase in flexural strength. (Chung, 2017) This allows materials to be augmented through impregnation, infiltration with resin or metal, or simply used to help:
• Increase strength
• Increase electrical conductivity
• Increase thermal conductivity
• Reduce porosity
• Render a body impervious thus being capable of forming a seal, and/or enhance functionality
• Improve application performance
(St. Marys Carbon, 2020)
As you can see, these are all desirable material properties for many applications and the reason why graphitization is increasing in importance within the high-temperature material processing industry.
Graphitization Furnaces
MRF offers several furnaces for graphitization, from lab scale units to large production furnaces. Our graphitization furnaces come in top, bottom, or front loading configurations and offer a maximum temperature of 3000°C. All furnace models are customizable to suit your application needs. Here is a sample of the furnaces we offer for graphitization.
Our top loading high temperature furnace features include:
• Maximum operating temperature: 3000ºC in inert gas
• Hot zone size 20 in. diameter X 20 in. high (508 mm dia. x 508 mm high), other sizes available
• Graphite heating element with fibrous graphite insulation
• Optional Retort for process isolation and improved thermal uniformity
• Pressure range: Vacuum to 2 PSIG
• Vacuum chamber is double-walled, water-cooled; 304L stainless steel
• Pneumatically operated chamber lid swings clear of hot zone
• Graphite hearth plate with graphite pins for load support
• Customizable vacuum and gas system
• Three phase power supply, SCR controlled, voltage rated for country of destination
• Controlled with PLC and touch screen HMI or classic instrumentation
Other options are available for this furnace. Learn more here
Our front loading high temperature furnace features include:
• Maximum operating temperature: 3000ºC in Inert Gas.
• Hot zone size 12 in. H X 12 in. D X 12 in. W (305 mm H x 305 mm D X 305 mm W), other sizes available.
• Graphite Heating Element with fibrous graphite insulation
• Optional Retort for process isolation and improved thermal uniformity
• Pressure range: vacuum to 2 psig
• Vacuum chamber is double-walled, water-cooled; 304L stainless steel
• Front and rear door gives full and easy access to hot zone area
• Graphite Hearth plate with graphite pins for load support
• Customizable vacuum and gas system
• Three phase power supply, SCR controlled, voltage rated for country of destination
• Controlled with PLC and touch screen HMI or classic instrumentation
Other options are available for this furnace. Learn more here
Who We Are…
MRF is a global leader in precision thermal systems essential for the research, development, and production of advanced materials. These advanced materials include ceramic matrix composites (CMC’s), advanced ceramics, and SiC crystals. For decades, we have pioneered some of the world’s most innovative, customized furnace systems, with a focus on enabling the processing of materials at high temperatures in controlled atmospheres or vacuum. For additional information about MRF’s capabilities, please visit our products page by clicking on this link: mrf-furnaces.com.
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Reference
Boundless. (n.d.). Boundless Chemistry. Retrieved August 19, 2020, from https://courses.lumenlearning.com/boundless-chemistry/chapter/carbon/
Chung, D. D. (2017). Carbon Composites (Second Edition) Composites with Carbon Fibers, Nanofibers and Nanotubes. Retrieved August 19, 2020, from https://doi.org/10.1016/B978-0-12-804459-9.00012-9
Mondal, Kunal & Pawar, Gorakh & Mcmurtrey, M. & IITK, Ashutosh. (2020). Finetuning hierarchical energy material microstructure via high temperature material synthesis route. 16. 10.1016/j.mtchem.2020.100269.
Poco Graphite. (2015). Properties and Characteristics of Graphite. Entegris.com. Retrieved 2 September 2020, from https://www.entegris.com/content/dam/web/resources/manuals-and-guides/manual-properties-and-characteristics-of-graphite-109441.pdf.
St. Marys Carbon. (2020, March 04). What Is Carbon Graphite: St. Marys Carbon. Retrieved August 19, 2020, from https://www.stmaryscarbon.com/what-is-carbon-graphite/
Zavašnik, Janez. (2019). Re: Graphitic layers distance?. Retrieved August 19, 2020, from https://www.researchgate.net/post/graphitic_layers_distance/5ddd20993d48b7fdc6545c72/citation/download.
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