Plasma preparation of graphene breaks through the technical bottleneck of thermal plasma high energy consumption

Plasma preparation of graphene breaks through the technical bottleneck of thermal plasma high energy consumption

[ Instrument Network Instrument R & D ] Xia Weidong, a professor in the Department of Thermal Science and Energy Engineering, School of Engineering Science, University of Science and Technology of China, cooperated with Hefei Carbon Arts Technology Co., Ltd. The new method breaks through the technical bottleneck of thermal plasma technology or high energy consumption, or low product uniformity and insufficient production stability, and is expected to achieve large-scale continuous production.
Plasma is the fourth state of matter that is different from solids, liquids, and gases. Matter is composed of molecules, molecules are composed of atoms, and atoms are composed of a positively charged nucleus and negatively charged electrons surrounding it. When heated to a sufficiently high temperature or for other reasons, the outer electrons get rid of the bondage of the atomic nucleus and become free electrons, just like the students after class run to the playground and play at will. When electrons leave the nucleus, this process is called "ionization." At this time, the substance becomes a uniform "paste" composed of positively-charged atomic nuclei and negatively-charged electrons. Therefore, people jokingly call it an ion plasma. The total amount of positive and negative charges in these ion plasmas is equal. Therefore, it is approximately electrically neutral, so it is called plasma.
Graphene has excellent optical, electrical, and mechanical properties, and is considered to be a future revolutionary functional / structural material. It has important applications in energy and environment, biomedicine, electronic devices, chemicals and aerospace. . The use of radio frequency induction heating and microwave heating plasma to prepare graphene has high energy consumption and is difficult to industrialize.
Plasma (plasma), also called plasma, is an ionized gas-like substance composed of positively and negatively ions generated by the deprivation of some electrons and atomic groups. The scale is larger than the length of Debye. Movement is mainly dominated by electromagnetic forces and exhibits significant collective behavior. It exists widely in the universe and is often regarded as the fourth state of matter except solid, liquid, and gas. Plasma is a very good electrical conductor, and it uses a cleverly designed magnetic field to capture, move, and accelerate the plasma. The development of plasma physics has provided new technologies and processes for the further development of materials, energy, information, environmental space, space physics, and geophysics.
Thermal plasma pyrolyzes hydrocarbons to synthesize graphene. Due to the rapid increase in plasma conductivity as the temperature increases, the arc automatically shrinks to a small range. For the millisecond response time required for the synthesis of graphene, it is difficult to achieve uniform heating. Poor product uniformity and high energy consumption. The technology of large-area uniform plasma generated by magnetically dispersed arc developed by the research group is adopted to solve the problem of rapid and uniform heating of materials by plasma. The prepared graphene has a plane size of 50-300 nm and a number of layers of 2-5 layers, showing good crystal structure and large specific surface area, and good product uniformity; the preparation method and equipment are simple, one-step synthesis, no reduction, and no substrate , Catalyst, solution or acid, with a high yield (~ 14%), low energy consumption of ~ 0.4kW · h / g, low cost, and has the prospect of low-cost large-scale continuous production.
Graphene has special significance for basic research in physics, which enables some quantum effects that could only be demonstrated theoretically through theoretical verification. In two-dimensional graphene, the mass of the electron seems to be non-existent. This property makes graphene a rare condensed matter that can be used to study the theory of relativity quantum mechanics-because massless particles must move at the speed of light Therefore, it must be described by relativistic quantum mechanics, which provides a new direction for theoretical physicists: some experiments that originally needed to be performed in giant particle accelerators can be performed in small laboratories using graphene.
The research work explored the relationship between plasma parameters, raw material gas composition, nanographene morphology, number of layers, and defects, and revealed the process conditions required to produce high-purity graphene. Combining the numerical simulation of the flow field temperature field of the plasma reactor and the calculation of chemical reaction kinetics, a possible formation mechanism of graphene is proposed: a nucleation precursor with a low collision frequency is favorable for forming a sheet-like core, and Planar growth is maintained in a hydrogen and high-temperature plasma environment. The elucidation of graphene formation mechanism provides theoretical guidance for product production control.
Source: University of Science and Technology of China, Encyclopedia

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