March 14, 2022
CeraGrapheTM applies graphene to deal with extreme heat.
Mag7 has begun to seek collaborators for its patent pending process to make graphene ceramics. Trademarked CeraGrapheTM, this patent pending process uses mechanical and chemical methods in a single process to separate graphene sheets from graphite in situ to render a graphene ceramic matrix composite (CMC), or G-CMC.
The resulting G-CMCs — CeraGrapheTM — will not decompose or burn up in applications like super-hot rocket engine exhausts or high-speed ceramic brakes. They also exhibit the high hardness and compressive strength characteristics of ceramics. One obvious benefit is increased fracture toughness. For example, ceramic coffee cups are strong but brittle. They can withstand high temperatures without burning or melting, yet they can crack or shatter if dropped on a hard floor. But CeraGrapheTM has high fracture toughness. If a crack starts to form at the surface of the ceramic part, like from a hammer blow, that crack can only proceed through the ceramic until it encounters a graphene “sheet of paper” that stops it from continuing through rest of the ceramic structure, thereby protecting the ceramic part from catastrophically failure. This occurs on a microscopic scale, so no cracks are detected and the part behaves as if it had never suffered that hammer blow at all.
Other benefits include the ability to fabricate intricately shaped CMCs and micro-scale ceramic parts, and the ability to use a wide variety of plastics forming techniques to manufacture these CMCs. Such techniques include pour-molding, injection molding, extrusion, and even the manufacture of continuous ceramic fiber.
While graphene is rare and expensive, graphite is plentiful and relatively cheap. The problem is that the individual graphene sheets that form graphite are “glued” together by electrostatic force. However, this electrostatic force can be disrupted in several ways. Some methods are chemical, and some are mechanical.
How it works. To visualize this, one might think of graphite as a ream of individual sheets of paper. In graphite these “sheets of paper” are called graphene. To exhibit the attributes unique to graphene, the graphene sheets that make up the structure of graphite must be separated into individual sheets that can freely incorporate into other materials (such as plastics) to reinforce them or to impart unique electrical or thermal properties to them.
For example, the recently patented Rutgers University process is mechanical. It’s like taking a ream of paper and running your hand across the top of it with a little pressure. If you do this, smaller clumps of paper sheets separate out, some containing perhaps 30 sheets, others maybe 20. If you continue doing this the smaller clumps of sheets separate into ever thinner ones, some now containing maybe 10 sheets. Continuing further, these thinner clumps of sheets separate into ever thinner clumps, some containing maybe 5 sheets, while others might have only 3. With more processing you will eventually get single sheets. In the case of graphite, these individual “sheets of paper” are called “graphene.”
The Rutgers process primarily uses such a mechanical method to separate clumps of graphene “paper sheets” from the graphite “ream.” A thick, molten plastic material works like the “hand” that pushes against the surface of the “ream” of graphite to separate the graphene “sheets.” An injection molder applies the shearing force to that molten plastic “hand” to push against the surface of the graphite sheets and separate them.
One can enhance this process through chemical means. Certain chemicals can worm their way in between the graphene sheets in the graphite “ream.” They pry the sheets apart on a molecular level as they wedge their way between them and increase the distance between sheets. As this distance increases the electrostatic “glue” that holds them together becomes weaker, so it becomes easier to separate them mechanically, i.e. running a “mechanical hand” across the surface of the graphene “ream” to release thinner and thinner stacks of graphene (the “paper”). Currently, the graphene “stacks of paper” generated using the process are about 40 nanometers thick.
Other benefits include the ability to fabricate intricately shaped CMCs, micro-scale ceramic parts, and the ability to use a wide variety of plastics forming techniques to manufacture these CMCs. Such techniques include pour-molding, injection molding, extrusion, and even the manufacture of continuous ceramic fiber.
In addition to graphite, other platey materials, such as boron nitride, mica, and molybdenum disulfide can also be used to make CMCs for different applications. Those materials could offer properties of interest to engineers who need lighter weight materials that are stable at high temperatures.
Mag7’s process is in early testing and has not been optimized for every conceivable application, so there is ample opportunity for collaboration. Each production run must be tested by an independent testing lab that certifies its results, which takes time. It is now being performed using only lab-scale equipment, analogous to large equipment that can accommodate volumes as high as 2,000 gallons per unit. The commercial product will be a liquid graphene slurry that can be shaped, solidified, and then converted to a CMC in the desired geometry. By mid-2020 Mag7 expects to begin licensing the technique to companies that already have equipment to produce graphene CMC in scale.