1 modification principle
The principle and method of surface modification of powder are interrelated, and the modification principle determines the modification method. Due to the hydrophilicity of the surface of the quartz powder, it is difficult to be compatible with the organic polymer material. Therefore, the surface of the quartz powder needs to be modified to change its surface properties from hydrophilic to hydrophobic, thereby improving the surface of the quartz powder particles. The wettability makes the powder particles more easily dispersed in the organic compound.

At present, the technical requirements for the surface modification of quartz powder are getting higher and higher, and the modification effect is improved while reducing the cost. And in different fields of application, there are different requirements for the purity, particle size, whiteness and post-modification effect of quartz powder. In general, the finer the particles of quartz powder, the larger the specific surface area, the more surface active hydroxyl groups, the easier it is to carry out chemical reactions, and the effect after modification is better. There are more and more reports on the surface modification of nano-silica. Chen Yingmin et al. used silane coupling agent KH-570, BYK-163 and titanate coupling agent NDZ-201 to modify the surface of nano-silica. The results showed that KH-570 had the best modification effect, the dosage was 5 %, the reaction for 30 min, the performance of acrylic polyurethane anticorrosive coatings have been greatly improved.

After mechanical pulverization of silicate minerals such as quartz, free radicals or ions are generated on the newly formed surface. Under the external conditions, several groups such as Si-OH, Si-O-Si and Si-OH...H are easily formed on the surface. Bonding with foreign functional groups for modification purposes provides a basis for surface modification. In the modification process, the temperature, the choice of modifier, the amount and treatment method, and the modification process are the main factors affecting the modification effect.

2 modification method and process
2. 1 modification method
There are many methods for modifying the organic surface of quartz powder, but only by physically adsorbing on the surface of quartz powder, not only the modification effect is not good, but it is easy to fall off during the process of stirring and washing, and the product cannot be added too much in the application. performance. High energy modification costs are high and the technology is complicated, making it difficult to achieve industrial production. Mechanical chemical modification is a mechanical pulverization of the powder, which produces temporary active sites on the surface and reduces the surface modification activation energy. For example, Li Jianqiang and the like modified the quartz sand with a silane coupling agent KH-570, and the modifier, ethanol and water were dry-modified in a ball mill , and compared with the wet modification. Chemical coating modification is the most commonly used method for surface modification of quartz powder, such as coupling agent modification and polymer grafting modification. The bonding mechanism forms a covalent bond with the surface of the quartz powder. For example, the modification principle of the coupling agent, the coupling agent hydrolyzes to produce a silanol group, and dehydrates and condenses with the silanol on the surface of the quartz powder to form a covalent bond. The method has lower cost, high modification effect, and the modified product can maintain stability for a long time.

2. 2 modification process
In industrial production, most of them are modified by mechanical force dry method, and the modified modifier is sprayed at the same time of pulverization. The secondary method can shorten the industrial process, and generate temporary active points and high temperature during the pulverization process, which is beneficial to surface modification. The product does not need to be dehydrated and dried. However, the modification effect is larger than the wet method, and the modification is difficult to homogenize. The local high temperature may damage the modifier and the control process is not well controlled. After dry modification, quartz powder is a coarse product in industrial applications and is widely used in plastics, building materials and rubber industries. The wet modification is to soak the quartz powder and the modified reagent together, stir, dehydrate and dry, which is more complicated than the dry process, but the modification effect is good, and is generally applied to high-end industries such as film and coating. Wujianghong used surface modification of nano-SiO ₂ particles with vinyl tris(β-methoxyethoxy)silane, and made modifiers, modifiers and powders into filter cake, and dried at 80 °C. 8 h, a modified product was obtained. In the dry-wet process combined modification process, the reagent addition amount and modification time are required to be high. After the discharge, the temperature is high-temperature drying, the reagent amount is large, the quartz powder is easy to aggregate, and the modifier is not easy to disperse, and the modification effect is small. difference.

3 modifier
The modifier for modifying the quartz powder mainly includes a silane coupling agent, an aluminate coupling agent, a titanate coupling agent, and the like. Some fatty acids commonly used in industry and cationic surfactants (such as cetyl trimethyl ammonium bromide, etc.) on surface modified quartz powder, these modifiers low price, simple process, but the general effect modification, modified Later belongs to the coarse product. The silane coupling agent has the best surface modification effect on quartz powder, but the cost is higher. The cost of aluminate and titanate coupling agent is lower, and the modification is easier, but the modification effect is worse than that of silane coupling agent. The reason is that the silane coupling agent has a higher energy for shrinking the silicon hydroxy group on the surface of the quartz powder, and the Al ³⁺ and Ti ³⁺ radii in the aluminate and titanate coupling agent are large, and it is easy to be combined with silicon. Hydroxyl association, combined with the surface of the quartz powder, is lower than the Si-O-Si bond level, and is not as stable as the silane coupling agent.

When the quartz powder is modified by the aluminate and titanate coupling agent, the hydrolysis of the coupling agent can hardly add water, otherwise the coupling agent can be easily shielded to form a milk, which is most effective in dissolving in an organic solvent. Good, such as toluene, acetone, etc. On the other hand, if the silane coupling agent is not hydrolyzed, it is difficult to bond with the surface of the quartz powder. Gao Zhengnan et al. studied the surface modification of silica with silane coupling agent KH-550. The hydrolysis process of silane coupling agent KH-550 was studied by conductivity measurement and infrared spectroscopy. The results showed that water/ethanol mixed solvent was used. 55%。 KH - 550 hydrolysis volume fraction of 15. 75%.

At present, the surface graft modification of silica powder is widely studied. The polymer is bonded to the surface of the silica powder by a chemical reaction, and the chemical reaction is again carried out with various active groups carried by the polymer. This method can increase the selection of modifiers, contribute to the application effect in different fields, and has a good effect on powder coating, which can reduce the wear on the machine. However, due to the excessive number of reactive groups, it is difficult to control the reaction, and it is difficult to apply to industrial production.
The longer the branch of the modifier, the more unfavorable the modification process due to steric hindrance. Some studies have proved that the effect of compound modification of coupling agent is better than that of single modification. The two coupling agents are entangled and cross-linked to increase the number of modified reactive groups. The gold Hui Lin et al quartz powder by a ball mill to carry out chemical modification of mechanical force, when the silane coupling agent KH-570 and DL-411 aluminum coupling agent mass ratio of 1, a total amount of 0.7% When the modification effect is better than single modification, and the composite modification, the mechanical properties of the filled product are greatly improved.

4 development trends
At present, the grain size requirement of the modified quartz powder tends to be ultra-fine, and the nano-quartz powder has a three-dimensional network structure, which has superior stability, thickening property, thixotropic property, electrical insulation property, absorption property and light-cut property. Performance, unique characteristics in many application fields, has an irreplaceable role and has a good development prospect. However, it is extremely easy to agglomerate, and there are a large number of active sites on the surface, which are easy to adsorb various atoms and molecules. Due to its good light transmittance and infrared reflection ability, it is widely used in the fields of film, paint and the like. However, the preparation of nano-quartz powder is higher than the micron-scale cost, and the market demand is large.

For different application fields, the requirements for modified quartz powder are different. For example, when applied to plastic film, the quartz powder requires high particle size, and if the particle size is too large, the film cannot be blown, and the mechanical properties of the film are greatly reduced. The modifiers will vary depending on the modifier, as the degree of structural compatibility of the different chemical groups will vary widely. If the coupling agent is modified with an alkenyl group or a chlorohydrocarbon group, the quartz powder is largely filled in the PE, and is modified by a coupling agent having a polythiol group to be largely filled in the rubber. With the development of science and technology, the modification technology of quartz powder will become more industrialized, simpler and more efficient. Modifier pluripotency will be enhanced, the scope of application is wider, the cost is lower, and the modification effect is more excellent.

5 conclusions
Due to the characteristics of quartz powder, the application value in various industries is extremely high, and the future will be better developed in the development of science and technology and social life. With the increase in social demand, the development of technology. The quartz powder has a finer particle size and is spheroidized. The preparation technology of ultra-fine quartz powder will be more reasonable and more economical, and will greatly increase the application value of the quartz powder itself. With the continuous improvement of production equipment, high-end modification technology will become more and more industrialized, which will greatly expand its application fields. In short, China's quartz powder modification research has achieved significant results, and will surely shine in some unknown applications in the future.