Powder plasma surface modification is a specific method of surface treatment of powder materials in a specialized plasma treatment device, which changes the surface characteristics of the powder and endows it with new functions to meet the application requirements of various properties of the powder. The purpose of surface modification of powders can be summarized as: improving or altering the dispersibility of powder particles in the medium of use; Compensate for the inherent defects of the powder and improve its durability, such as light resistance, heat resistance, corrosion resistance, weather resistance, etc; Endow particle surfaces with new functionalities such as electrical, optical, magnetic, mechanical, and chemical properties. Thus, it can expand product applications, develop new products, and enhance the added value of powder materials. Therefore, surface modification of powders is an important means of material preparation process engineering, as well as an important content of new materials, new processes, and new product development.

Principle of low-temperature plasma treatment for modified powders

Low temperature plasma is a non thermal equilibrium plasma, with particle energy parameters ranging from electrons (0-20eV), metastable particles (0-20eV), ions (0-2eV), and photons (3-40eV). The surface modification of materials requires the breaking or activation of chemical bonds on the material surface and the formation of new chemical bonds, which first requires various particles in low-temperature plasma to have sufficient energy to break the chemical bonds on the material surface. 

Due to the energy characteristics of plasma, the surface morphology and structure of the powder after plasma treatment have undergone significant changes. The influence on the surface morphology and structure of the powder is related to the characteristics of the gases used for plasma treatment (polymeric gases, non polymeric gases). When using non polymeric gas plasma to treat the surface of powders, the main method is to use high-energy particle bombardment in the plasma to generate a large number of free radicals on the material surface. These free radicals interact with oxygen and nitrogen components in the air, thereby changing the chemical structure of the material surface; When using plasma of polymeric gas to treat the surface of the powder, a polymer film is formed on its surface and a strong chemical bond is formed with the powder.

Powder low-temperature plasma treatment method

There are two main aspects of low-temperature plasma for surface treatment of powders: non polymeric gases (Ar, He, H2O, etc.) can be used for plasma treatment of powder surfaces to remove impurities adsorbed on the powder surface and introduce various active groups; The surface treatment of the powder can also be carried out using plasma of polymeric gases, that is, plasma polymerization, to form a polymer film on the surface of the powder. In recent years, low-temperature plasma has mainly been used for surface modification of powders through plasma polymerization technology. This technology is achieved by stimulating and activating organic compound monomers to form gas-phase free radicals. When gas-phase free radicals adsorb on the solid surface, surface free radicals are formed. Surface free radicals polymerize with gas-phase original monomers or derived monomers generated in plasma on the solid surface, producing high molecular weight polymer films. In plasma organic polymerization, energy is mainly concentrated on the surface of the material and hardly changes the properties of the matrix, while traditional surface modification methods have a significant impact on the matrix. Plasma polymerization has a wide range of applications. In addition to ethylene based elemental gases and cyclic compounds, saturated hydrocarbon compounds, aromatic compounds, and organic metal compounds that are difficult to polymerize by conventional methods are highly prone to plasma polymerization. The chemical structure and physical properties of plasma polymers are also different from traditional polymers.

Application of Plasma Modified Powder

Change the dispersibility of the powder

When preparing composite materials, inorganic powder is often added as a filler to organic polymers. Due to the small particle size and high surface energy of the powder, it is easy to form aggregates, resulting in uneven dispersion within the polymer and the formation of defects at the interface between the two materials, leading to a decrease in the mechanical properties of the composite material. For this purpose, low-temperature plasma can be used to modify the surface of inorganic powders, forming a polymer layer on their surface through reaction, which can reduce the surface energy of the powder and thus reduce the tendency for agglomeration. At the same time, the polymer layer can also increase the compatibility between the powder and organic polymers, thereby improving the dispersion performance of the powder in it.

Improve the hydrophilicity of the powder

Plasma instruments can generate a large number of active molecules that undergo inelastic collisions with material surfaces. This surface based physicochemical effect can break the main chain of the matrix and form free radicals. On the other hand, high-energy electron beams can transfer energy to the surface of the substrate material and increase surface energy. When materials with high surface energy and free radicals come into contact with air, the free radicals undergo related chemical reactions, generating oxygen-containing functional groups such as hydroxyl and carboxyl groups, which reduce the water contact angle of the powder surface and improve its hydrophilicity.

Change the catalytic performance of the powder

Plasma systems contain a large number of active substances such as free electrons, which can achieve some physical and chemical reactions that cannot be completed under conventional conditions. Therefore, plasma technology has received increasing attention in the fields of materials and chemistry In recent years, plasma technology has been widely applied in the preparation and modification of catalysts. In the preparation and modification of nanocatalysts, plasma technology can achieve the transformation of material phases, doping of elements, and control of microstructure. Through the direct or indirect action of high-energy particles in low-temperature plasma, catalysts can be oxidized or reduced to obtain more suitable chemical forms of catalysts, or more surface active sites can be generated through high-energy particle bombardment.

Low temperature plasma surface modification of powder can cause a series of physical and chemical changes on the surface of the powder, thereby improving the surface properties of the powder, while the matrix properties of the powder are almost unaffected. Compared to other methods, low-temperature plasma technology has the advantages of simple process, convenient operation, fast processing speed, good treatment effect, low environmental pollution, and energy saving, and can achieve treatment effects that traditional chemical methods cannot achieve.