Graphite’s most notable, and most unique property, has to be its incredible thermal properties. Not only does it conduct heat very well, but it also has impressive CTE values (coefficients of thermal expansion), and the material is very difficult to melt ~ yielding an intensely high melting point. In fact, technically speaking, graphite has no melting point until you get to approximately 100 atmospheres [8]. And at the point, the melting point is between 3,600-4,200°K, which is approximately 6,000-7,000°F [9]. This is roughly two thirds the temperature of our sun’s photosphere [10]. And much like carbon dioxide, the material goes directly from a solid state to a gaseous state [8]. Therefore, carbon is certainly one of the go to materials when it comes to applications involving heat and heat transfers.
1. Melting Point
Due to the material’s surprising melting point, graphite is frequently used to make crucibles, products that are molded, and specialty plates (or wall liners) for high temperature furnaces and fireproofing systems; rooms, lockers, safes, etc. Many consumer products that are molded can, and often do use graphite molds to manufacture them. However, before a product can be molded, a molten material is first required. This is where a crucible comes in to play. When metallurgists first melt down a material, graphite crucibles are typically used to melt it down and hold them, before they can be poured. Then when these molten materials are poured into a cavity (ingot molds, injection molds, blow molds, casting dies, etc.), graphite materials are often used for the actual molds as well. This is obviously due to graphite’s natural resistance and immunity to extremely high temperatures. Carbon fibers are also used in flame retardant materials; including wearables, furniture, and other domestic products as well. While these products can and still do catch on fire, the carbon fibers that are interjected, blended, and woven into these materials often reduce the overall flammability, and they sometimes offer self-extinguishing characteristics too. Not only is carbon used in fire retardant materials, it is also used in fireproofing systems as well ~ in the form of graphite plates. These plates are often placed with the walls of rooms, lockers, and safes to protect them (and ultimately their contents) from fire.
2. High Thermal Conductivity
Graphite also possesses remarkable heat transfer properties. This is inevitably due to their impressive thermal conductivities. Many graphite materials have conductivities as high as 120-240 W/m°K (70-140 btu•ft/hr•ft²•°F). The conductivity of some graphite composites are being measured as high as 1,000-2,000 W/m°K [11]. Materials with a high thermal conductivity (materials such as these) are often used in applications where heat energy needs to be dissipated. Heat sinks, heat shields, and heat exchangers are prime examples here. Many are made of graphite and carbon composites. Sometimes carbon fibers are used in motherboards and circuit boards to dissipate heat away from the critical, heat sensitive components. These same materials are also being used in LED thermal management systems, and in the thermal cores of advanced avionics [12].
3. Low Coefficient of Thermal Expansion
Graphite is also unique due to its thermal expansion properties (CTE). Typically, when a material or substance is heated, it expands. However, graphite has a remarkably low coefficient of thermal expansion; which means that it can be heated and be exposed to extremely high temperatures without expanding all that much. This is very useful and very important when it comes to furnace components, molds that are used in the mold making industry, glass making tools, and even some epoxies and thermal pastes.
