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With the development of science and technology, users put forward more and more requirements for the performance of ultrafine powder, such as the requirement that ultrafine powder must have good dispersibility, and other materials are required to have good compatibility when mixed with other materials, for this reason, ultrafine powder workers have invested a lot of energy to carry out surface modification research of ultrafine powder, and gradually form another branch of ultrafine powder technology - surface science and technology
.
The research of ultrafine powder surface technology includes the study of surface modifiers and the study of surface modification technology and modification equipment
.
Due to its own properties and processing methods, the physical and chemical properties of the powder are coatingol.
com
on the line.
The process of using physical or chemical methods to surface treat a powder to purposefully change its surface physicochemical properties to meet specific use requirements is called powder surface modification
.
Many classification methods vary depending on the angle of analysis of the problem
.
▲The purpose of powder modification
Koishi Makoto proposed that the classification method based on the properties of the modification process has its own unique features, and he divides the powder surface modification method into 6 categories, namely: (1) surface cover modification
.
The use of surfactants to cover the surface of the powder with polymers, inorganic substances, organic compounds, etc.
to achieve surface modification; (2) Surface chemical modification
.
The use of surface modifiers to chemically react with the surface of the powder or chemical adsorption to complete the production of new functions on the surface; (3) Mechanical and chemical law modification
.
Enhance the surface activity of particles by crushing, grinding, friction and other methods, the surface of the powder with strong activity reacts with other substances and adheres to achieve the purpose of surface modification; (4) Capsule modification
.
A film coated with one or more layers of homogeneous other substances on the surface of the powder changes the surface characteristics of the powder; (5) High-energy treatment modification
.
Use corona discharge, ultraviolet light, plasma beam, etc.
to modify the surface of the powder; (6) Precipitation reaction modification
.
A method of using chemical reactions and depositing the product on the surface of a powder to form one or more modified layers
.
▲Powder modification method
Among them, mechanical chemical modification refers to enhancing the surface activity of particles through crushing, grinding, friction and other methods, so that the surface of the powder with strong activity reacts with other substances and attaches to achieve the purpose of
surface modification.
High-energy mechanical forces will not only change the physical structure and crystallization state of minerals, but also lead to chemical bond breakage, unsaturated groups, free ions and electrons, resulting in new lattice defects, and ultimately induce chemical reactions
.
The application research results of mechanical chemistry provide a new method for the surface modification of the powder to achieve the purpose of surface modification while making the powder ultra-refined, with the characteristics
of simple process, good product modification effect and high production efficiency.
1.
Wet mechanical force chemical surface modification
Wet mechanical chemical surface modification refers to the modified powder and modifier in the solid-liquid two-phase environment, subject to the grinding medium high-speed impact, shearing, extrusion and other effects, the powder surface is activated while pulverizing, and then with the modifier physical and chemical reaction, to achieve the purpose of
surface modification.
After the modification is completed, the modified powder is obtained by solid-liquid separation, drying and other processes
.
Wet mechanical chemical surface modification is usually done by ball mills, stirring mills, vibration mills, etc.
, of which stirring mills are more commonly
used.
The wet process has the characteristics of good dispersion of surface modifier and uniform surface coating, which is suitable for the use of the final product in the form of slurry, or the front section is the wet powder process and the rear section needs to be dried
.
However, if the product needs to be made into dry powder, it is also necessary to carry out solid-liquid separation, drying and other treatments, and the production process is more complicated
.
In the wet process, in addition to imparting special functions to the powder, the surface modifier can also play the role of a grinding aid, so that the fluidity of the powder is improved, thereby improving the crushing efficiency
.
2.
Dry mechanical force chemical surface modification
Dry mechanical force chemical surface modification is carried out
in a single solid phase environment.
Compared with wet modification, dry modification has the characteristics
of high efficiency, large yield and no pollution.
The dispersion of surface modifiers in the dry process and the uniformity of surface coating depend to a large extent on the surface modification equipment, but there are few special modification equipment, usually transformed by mixing equipment or crushing equipment, such as high-energy ball mills, vibration mills, etc
.
The dry surface modification process is simple and suitable for various organic surface modifiers, especially non-water-soluble surface modifiers
.
In the dry modification process, the main process parameters are the modification temperature, the action time of the powder and the surface modifier, etc
.
In recent years, people have begun to pay attention to the use of airflow pulverizers to carry out mechanical and chemical surface modification of powder
.
Compared with other crushing equipment, the airflow pulverizer has the outstanding advantages of high crushing efficiency, low energy consumption, small wear, and narrow particle size distribution of non-polluting products, which can be used to crush materials with high hardness, so the airflow pulverizer as the main equipment has developed rapidly
in the integration process of surface modification.
3.
Airflow pulverization and surface modification integration process
The integrated process of surface modification of airflow pulverization (referred to as the integrated process) uses the high turbulence effect of airflow milling to complete the surface activation modification of the powder while ultra-fine pulverizing the powder, which can effectively overcome the shortcomings
of the modifier and the surface of the powder when the airflow pulverization and surface modification are completed separately, and the adhesion is weak and uneven 。 In the process of integrated process, on the one hand, the powder produces a fresh surface with high activity under the action of mechanical force, so that the modifier can cover the surface of the powder more effectively and achieve the purpose of surface modification; On the other hand, under the action of the modifier, the free energy of the powder surface is greatly reduced, and the grinding efficiency is improved
.
The integrated process combines ultra-fine pulverization and surface modification, which promote each other to reduce energy consumption and improve production efficiency
.
▲High temperature air flow pulverization + modification process: high temperature air flow grinding / high temperature air flow crushing and modification
4.
Characterization of mechanical force chemistry
In order to know exactly how the substances of a certain system change under the action of mechanical forces, there must be corresponding detection methods
.
There are many methods for detecting the chemical effects of mechanical forces, which can be summarized in the following table
.
Detection method | Detect content | |
Archimedes' principle | Determination of the bulk density of the powder | |
X-ray diffraction (XRD) | Changes in crystallization degree can also be used for semi-quantitative analysis of grain size and lattice distortion of powder | |
Electron Microscopy (SEM) | Observe the particle size distribution, agglomeration status and structural changes of the powder material before and after the force | |
Laser particle size analysis | It is used to determine the particle size distribution, specific surface area of the powder, etc | |
Thermal Analysis Technology (TG-DTA) | It is used to determine whether there is a change before and after the force of the substance, especially for the analysis of the dehydration process and the degree of dehydration of the aqueous substance | |
Infrared spectroscopy (IR) | Detect the bond energy and properties of the bonds of a substance before and after subjected to mechanical force chemistry to infer the effects that occur | |
Photoelectron spectroscopy (XPR) | Determine the binding energy of different elements and oxygen to determine the changes that occur in the system, its measurement accuracy is high, the resolution is also high, and it can be analyzed layer by layer from the longitudinal stripping layer of the surface of the object to determine the depth and degree of change | |
Solid State Nuclear Magnetic Resonance Spectroscopy (NMR) | Determines the state in which an element in a substance is located |
Reference source:
1.
Development and application of mechanical chemical powder surface modification technology; Department of Mechanical Engineering, Jiangsu Institute of Petrochemical Technology; Liu Xuedong, Zhuo Zhen waited
.
2.
Research progress in the preparation of functional mineral materials by mechanical force chemical method; School of Mining Engineering, Liaoning University of Science and Technology; Ma Tian, Liu Chunqi, Li Zhao, Dai Shujuan, Guo Xiaofei, Wang Qianqian, Zhao Tonglin and so
on.
3.
Mechanical force chemistry and its development trend; School of Materials and Chemical Engineering, Jiangxi University of Science and Technology; Yin Yanhong, Zhu Yinglu and so on
.
4.
Research progress in the preparation of modified ultrafine powder by mechanical force chemistry; Henan University; Su Xiaoli, Cao Zhi Zhang Zhijun and so
on.