Application of Ultrafine Powder and Analysis of Its Surface Modification Mechanism

First, the nature and application of ultrafine powder

1. Ultrafine powder surface characteristics

Ultrafine powder science and technology is a new science and technology developed in recent years and an important part of materials science. For the uniform definition of ultrafine powder, the powder having a particle diameter of more than 1 μm is generally referred to as a micron powder, the powder having a particle diameter of 0.1 to 1 μm is referred to as a submicron powder, and the powder having a particle diameter of less than 100 nm is referred to as a powder. For the nano-powder, a powder having a particle diameter of less than 3 μm is also referred to as an ultrafine powder. Ultrafine powders are usually divided into micron powders, submicron powders and nano powders. The relationship between the particle size of the ultrafine powder and its characteristics is shown in the table below.

2. Ultrafine powder surface structure

According to the spatial structure of the crystal, it can be divided into four types of closely packed structures, skeleton structures, layered structures and chain structures. When the crystal is destroyed by an external force, it will break along the weakest bond in the crystal structure. On the fracture surface, a broken bond that is not compensated is generated, that is, an unsaturated bond. Ultrafine powders of different chemical compositions have very different degrees of unsaturation on fresh surfaces. According to the nature of the cleavage bond energy, the surface unsaturated bond has strong and weak points. The rupture surface is dominated by ionic bonds and covalent bonds, and the surface is polar. The surface of the fracture surface is weak with molecular bonds. Unsaturated bond, the surface is a non-polar surface. Different types of ultrafine powders have different types and amounts of surface functional groups, and the surface functional groups of the same ultrafine powder have a certain distribution.

3. Application of ultrafine powder

(1) Application of ultrafine powder in the field of plastics

Ultrafine powders are widely used in the chemical industry, and are widely used in coatings, plastics, rubber, papermaking, catalysis, cracking, organic synthesis, chemical fiber, ink and other fields. In the plastics industry, the combination of ultra-fine powder and plastic can enhance the toughening effect. For example, after modifying the surface of nano-calcium carbonate, the toughening effect on the notched impact strength and double-notch impact strength of the material is very significant. And the processing performance is still good.

In addition, the addition of ultra-fine powder can improve the aging resistance of the composite material, prevent the plastic radiation aging, and improve the service life of the plastic product. At the same time, ultra-fine powder can also functionalize composite materials, such as antistatic plastics, flame retardant plastics, and self-cleaning plastics.

(2) in the catalyst industry

As a catalyst, the ultrafine powder mainly increases the active position of the surface according to its large specific surface area and incomplete surface atom coordination, and the surface has many active centers. The surface effect of the ultrafine powder determines its good catalytic activity and catalytic reaction selectivity. Catalyst is one of the important fields of ultrafine powder application. It has been researched and developed as a fourth-generation catalyst in the world. The use of nano-scale catalyst can greatly improve the chemical reaction rate, greatly shorten the chemical reaction time, and greatly improve the production efficiency. The heat of combustion per gram of fuel can be doubled.

(3) in the field of coatings

Ultrafine powders can be used to prepare nano-modified coatings and nano-structured coatings. The nano-particles are modified to improve the performance of the coatings by using certain functions of the nanoparticles. The nano-modified coatings are prepared by a special process to prepare ultra-fine nano-materials, so that the nano-coatings have optical, mechanical and environmental functions. Such as: nano ceramic coatings, nano non-stick coatings, self-cleaning coatings, aviation ablative coatings, etc.

(4) Application of ultrafine powder in the field of materials

The application of ultrafine powder in the field of materials is mainly reflected in the application of ceramic materials, building materials and special functional materials. In the field of ceramic applications, due to the high surface energy of the ultrafine powder, the number of surface atoms, and strong activity, it can be used as an activator of the sintering process to accelerate the sintering process, shorten the sintering time, and lower the sintering temperature. At the same time, the ultrafine powder can significantly improve the microstructure of the ceramic material, optimize its performance, and achieve the purpose of densification by sintering at a lower temperature, so it is particularly suitable for the preparation of electronic ceramics.

In the field of special functional materials, the surface properties of ultrafine powders determine that it is very sensitive to the external environment, such as temperature, light, moisture, etc. Changes in the external environment will quickly cause surface or surface ion valence and electron transport. The change, that is, causes a significant change in its electrical resistance. This unique property of ultrafine powder makes it the most promising material for sensors, and can be developed for various purposes such as fast response, high sensitivity, and good selectivity. Sensor.

(5) Application of ultrafine powder in the field of daily chemical industry

Nanotechnology has broad prospects in antibacterial, deodorizing, and purifying air. The photocatalytic performance and biodegradation and bactericidal properties of nano-titanium dioxide and nano-zinc oxide have been verified in air purifiers, nano-washing machines, nano-refrigerators, nano-toothbrushes, nano-towels and other products. In the skin care, cosmetics, clothing and other aspects, the role of ultra-fine powder is also very important.

For example, if nano-titanium dioxide is used in the sunscreen cream, the quality of the paste and the effect of sunscreen skin care can be greatly improved. In toothpaste, shampoo, detergent, and decontamination powder, various powders are also used in large quantities. If these powders are ultra-fine, their performance will be greatly improved.

(6) Application of ultrafine powder in medicine and biology

In the field of medicine and biological applications, the controlled release drug delivery system in pharmacy is to change the structure of the preparation by physical or chemical methods, so that the drug is automatically released at a constant speed from the dosage form at a certain speed within a predetermined time. A type of preparation that is organ or specific target tissue and that maintains the drug concentration for an extended period of time. Microparticles or nanoparticles are used as drug delivery systems, and the preparation materials are basically non-toxic, biocompatible, have certain mechanical strength and stability, and do not chemically react with drugs. When microparticles and nanoparticles are administered parenterally. The material is required to be biodegradable, and the microparticles and nanoparticle system are absorbed by the liver, spleen, lung, etc., which are rich in reticular epithelial cells. As foreign foreign bodies are macrophages, some particles can be attacked by enzymes in the lysing enzyme, resulting in The drug is lysed and released, and the particle size of the particles directly affects its distribution in the body. The ultrafine powder is also targeted to protect the coated material from damage and other superior properties. Processing a drug into an ultrafine powder can increase its residence time in the body and increase bioavailability. It can be seen that the application of ultrafine powder technology in the fields of medicine and biology is very important.

Second, ultra-fine powder filling modification mechanism analysis

In the ultrafine powder-filled modified plastic, it is precisely because of the existence of the interface region that the resin matrix and the filler material are combined into a whole through the interface region, and the external field is transmitted through it. The presence of the interface also divides the composite into many microdomains, thus preventing the expansion of cracks, disruption of material damage, and slowing of stress concentration. At present, interface engineering scientists believe that the interface mechanism mainly has the following theories.

1. Chemical bond theory

The theory holds that some of the filler-filled plastic system filler materials and the resin matrix form a strong bond because the two are joined together by chemical bonds. The chemical bond is connected to several types of resin matrix. The functional group on the molecular chain chemically reacts with the functional group on the surface of the filler. The surface of the filler material is treated with a coupling agent, a hyperdispersant, etc., and a part of the surface treatment agent has a surface functional group with the filler. a reactive group, the other part containing a functional group reactive with the resin matrix macromolecule, forming a surfactant molecule in the chemical bond interface region between the filler material and the resin matrix, one end of which reacts with a functional group on the surface of the filler material to form a chemical bond, The other end chemically reacts with the resin matrix, but forms a strong bond in some form, or vice versa.

The chemical bond theory widely explains the role of surface treatment agents, and plays a decisive role in guiding the selection of surface treatment agents, synthesizing new surface treatment agents, and guiding the preparation of inorganic filler-modified polymer composites.

2. Interface wetting theory

According to this theory, the bonding mode between the filler material and the resin matrix belongs to mechanical adhesion and wet adsorption. The mechanical adhesion mode is a mechanical hinge phenomenon, that is, after the resin is solidified, the macromolecule enters the depression of the surface of the filler material, and the mechanical hinge is formed into a mechanical hinge. The wet adsorption model is a physical adsorption phenomenon, which is a van der Waals force and two effects. In fact, they often exist simultaneously. Good wetting of the resin matrix on the surface of the filler material is extremely important. If the wetting is poor, when it is subjected to external force, the de-drilling occurs at the interface, the interface region becomes a stress concentration, and the stress concentration effect causes the composite material to be low. Destroy under stress. If complete wetting is formed, the adhesion force generated by physical adsorption can exceed the cohesive energy of the resin matrix, and a good composite effect can be produced.

3. Attenuate the theory of local stress on the interface

The theory holds that the treatment agent between the resin matrix and the filler material provides a chemical bond with "self-healing ability". This chemical bond is in a state of dynamic equilibrium that is constantly breaking and forming under the action of external force. When low molecular substances, such as water, etch the composite, the chemical bonds at the interface will be broken, and under the action of stress, the treatment agent can slide along the surface of the filling material to a new position, and the broken bonds can be recombined into The new key maintains a certain salary strength between the resin matrix and the filler material. This change process also relaxes the stress, thereby weakening the first type of microscopic stress concentration in the interface region and also slowing the damage of the composite material.

4, deformation layer theory

According to the theory, the treatment agent for surface treatment of the filler material forms a plastic layer at the interface between the filler material and the resin matrix. When subjected to an external force, it can be deformed, relax the interface stress, and prevent cracks. Expand to protect the composite from damage.

5, inhibition layer theory

According to the theory, the treatment agent for surface treatment of the filler material forms part of the interface region, and the elastic modulus is between the high elastic modulus filler material and the low elastic modulus resin matrix, which can uniformly transmit stress. , thereby weakening the interface stress. Friction Theory This theory holds that the bond between the resin matrix and the filler material is due to friction, and the coefficient of friction between the resin matrix and the filler material determines the strength of the composite. The surface treatment of the filler material serves to increase the coefficient of friction between the resin matrix and the filler material, thereby increasing the strength of the composite material.