In the pyrolysis process, the asphalt molecules undergo polymerization as the number of condensation rings gradually increases in the liquid state. Due to the free movement of molecules in the liquid environment, large aromatic planar molecules tend to take a certain direction by van der Waals force And the layers start to overlap, and there are small spheres similar to liquid crystals. This is the state of the liquid crystal called mesophase. Due to the different choices of the reaction process, it is also possible to generate non-equilibrium bonds, the molecules of which do not exhibit orientation, in this case it becomes glassy carbon. For example, by adding some cross-linking agent to the asphalt, the cross-linking reaction can occur before the asphalt molecules are converted to the mesophase state, so that the matrix obtained has a chaotic layer structure state. Whether or not to pass through the mesophase state, and the state of the mesophase, usually determines the basis of the C / C composite matrix structure formed later. Generally speaking, after the liquid asphalt passes through the mesophase liquid crystal state, the resulting C / C material matrix can be treated with high temperature to obtain a graphitized structure.
Due to the simple equipment, the atmospheric pressure impregnation-carbonization process is a commonly used compact method for making asphalt-based C / C carbon composites. In this process, liquid green is immersed in the voids inside the preform under vacuum, and the subsequent carbonization process is carried out under normal pressure and in an inert atmosphere.
The impregnation-carbonization process needs to be repeated many times (usually 5-6 times), resulting in a long preparation cycle, and because the carbonization yield of asphalt under normal pressure is low (about 50%), the density of parts obtained by this process is generally only 1.60g / cm3 or so, which is the deficiency of atmospheric pressure impregnation-carbonization process.
Reflecting Liquid Crystal Display
Reflecting Liquid Crystal Display,Electronic Instrument Displays,Electronic Watch Display,Clock Lcd Display
Dongguan Yijia Optoelectronics Co., Ltd. , https://www.everbestlcdlcms.com