Ultrafine powders usually include micron grade (1 ~ 30 jm), sub-micron (0.1 ~ 1 um) and nanoscale particles (1 ~ 100 nm), as is different from the original solid material surface effect and volume effect, and showed the unique optical, electrical, magnetic, catalysis, thermal and mechanical properties, etc., it is not only itself is a kind of functional materials, and for the composite with the development of new functional materials shows broad should be In future, in the national economy in various fields has been widely used.
Nanoscale powders have very small particle size and high surface energy, which can easily agglomerate and form secondary particles, and cannot show their favored surface area effect, volume effect and quantum size effect, etc. The most effective way to solve the agglomeration problem of ultrafine powder and improve its dispersibility and rheology is to modify the surface of the powder.
1 Why powder surface modification for ultrafine powders?
Because of superfine powder particle size is small, high surface energy, it is easy to occur together, forming secondary particles, unable to show its popular green stubbornly surface effect, volume effect, etc.
Powder together to make it in use process is often lost many superiority of ultrafine powder, make its performance cannot give full play to.
To solve the problem of superfine powder of reunion, to improve the dispersion and mobility, the most effective way is to surface modification of powder.
Can increase the repulsive force between powder particles through powder surface modification, reduce the gravity between powder particles, the easy to disperse, improve the application performance of powder.
The purpose of the surface modification include:
- To improve or change powder particle dispersion;Improve the durability, such as drug resistance, light resistance, heat resistance, weather resistance, etc;
- The activity of particle surface,Make the particle surface produces a new physical, chemical and mechanical properties and new features, so as to improve the added value of powder.
2 superfine powder surface modification method：
The surface modification of the method are many, generally can be divided into:
- the surface coating modification,
- surface chemical modification,
- mechanochemical method,
- capsule type modification,
- high energy modification,
- precipitation reaction modification.
(1) the surface coating modification,
the surface coated modificationIs coated on the surface modification of the surface modification agent and particle surface chemical reaction, coating material depend on physical methods or van der Waals force between particles and connection, this method is suitable for almost all kinds of surface modification of inorganic particles. This method is the main use of inorganic compounds and organic compounds was carried out on the particle surface coating, together, to reduce the particle and the result of the cladding material space steric repulsion, it is very difficult to make the particles reunited again.
Used in coating modification of the modifier such as surface active agent and super dispersing agent and inorganic substances.
(2) the surface chemical modification
Surface chemical modification is the use of functional groups of the organic molecules on the surface of the inorganic powders, adsorption or chemical reaction of particle surface modification. In addition to the use of surface functional groups of modified, the method also includes the use of free radical reaction, integration, sol adsorption and surface modification.
(3) Mechanochemical modification
Mechanical force chemical modification is through crushing, grinding, friction, such as mechanical method, the mineral crystal lattice structure, the type change, system of internal energy increases, temperature, dissolved, thermal decomposition, prompting particles to produce free radicals or ion, strengthen the mineral surface activity, prompt reaction of minerals and other substances or attached to each other, reach the purpose of the surface modification of modified method.
(4) capsule type modification
Capsule type modification is homogeneous in powder particles on the surface coverage and a certain thickness of film is a kind of surface modification method.
(5) the high-energy modification method
High-energy modification method is to use from the cease or radiation treatment such as polymerization reaction and the realizing methods of modification.
(6) precipitation reaction modification
Precipitation reaction method is to add a solution containing the powder particles precipitating agent, or join can trigger of precipitant generated in the reaction system, the modified ion precipitation reaction, precipitation in the surface of particles, thus to coated particles. Precipitation mainly can be divided into direct precipitation, homogeneous precipitation method, heterogeneous nucleation method, coprecipitation method, hydrolysis method, etc.
3 Factors affecting the effect of surface modification
The main factors affecting the effect of surface modification of powders are the nature of the powder raw materials, surface modifier formulations, surface modification processes, surface modification equipment, etc.
(1) The nature of raw materials
The specific surface area of powder raw materials, particle size and size distribution, specific surface energy, surface physicochemical properties, agglomeration, etc. have an impact on the surface modification effect, is the choice of surface modifier formulations, process methods and equipment is one of the important factors to examine.
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(2) Surface modifier formulation
Powder surface modification is largely through the role of surface modifiers on the surface of the powder to achieve, therefore, the formulation of surface modifiers (species, dosage and usage) on the surface of the powder modification effect and the modified product application performance has an important impact. The formulation of surface modifier includes the selection of species, determine the dosage and usage, etc.
(3) Surface modification process
After the surface modifier formula is determined, the surface modification process is one of the most important influencing factors to determine the surface modification effect. Surface modification process to meet the application requirements of surface modifiers or application conditions, good dispersion of surface modifiers, surface modifiers can be achieved in the powder surface uniform and solid coating; at the same time requires a simple process, good control of parameters, stable product quality, and low energy consumption, low pollution.
(4) surface modification equipment
In the case of surface modifier formulation and modification process is determined, the surface modification equipment becomes a key factor affecting the surface modification or surface treatment effect of the powder. High-performance surface modification machine should be able to make the powder and surface modifier dispersion, powder and surface modifier contact or equal opportunity; at the same time, can easily adjust the modified temperature and reaction time, low energy consumption per unit of product and grinding, no dust pollution, easy operation of equipment, smooth operation.
lee. Ultrafine powder surface modification research progress
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