Application of powder preparation based on thermal plasma technology in thermal management materials
The miniaturization and integration of electronic devices put forward higher heat dissipation requirements for polymer-based thermal management materials. The development of new high thermal conductivity fillers to construct effective thermal conduction paths is the key to achieving high-performance thermal management materials.
Thermal plasma technology has great advantages in the preparation of nano- and micron-shaped spherical powders, such as spherical silicon powder and alumina powder, due to its high temperature, controllable reaction atmosphere, high energy density and low pollution.
Thermal plasma technology
Plasma is the fourth state of matter in addition to solid, liquid and gas. It is an overall electrically neutral aggregate composed of electrons, cations and neutral particles. According to the temperature of heavy particles in plasma, plasma can be divided into two categories: hot plasma and cold plasma.
The temperature of heavy ions in hot plasma can reach 3×103 to 3×104K, which basically reaches the local thermodynamic equilibrium state. In this state, the thermal plasma has the following relationship: electron temperature Te = plasma temperature Th = excitation temperature Tex = ionization reaction temperature Treac, so the thermal plasma has a uniform thermodynamic temperature.
Plasma preparation of spherical powders
Based on the characteristics of high temperature and fast cooling rate of high-frequency thermal plasma, physical vapor deposition technology is used to prepare nanopowders.
There are two main ways to prepare spherical powders with plasma.
One is to pass irregularly shaped and large-size raw material powders into the high-temperature arc of thermal plasma, and use the high-temperature environment generated by thermal plasma to quickly heat and melt the raw material particles (or melt the surface). Due to the surface tension, the melted powder forms a sphere and solidifies at a suitable cooling rate to obtain a spherical powder. The second is to use irregular powders or precursors as raw materials and thermal plasma as a high-temperature heat source. The raw materials react with the active particles therein and are rapidly cooled and deposited to generate ideal powder materials.
Taking advantage of the characteristics of high temperature, high energy, controllable atmosphere and no pollution of thermal plasma, high-purity, high-sphericity, and different-size spherical powders can be prepared by controlling the parameters in the preparation process such as feeding, cooling rate, and plasma power. Therefore, the use of plasma technology to prepare spherical powders has been increasingly widely used in energy, aerospace, chemical industry and other fields.