Preparation & application of nano-silica
Nano-silica is an inorganic chemical material, commonly known as “ultra-fine white carbon black”. It is a non-toxic, odorless, and pollution-free inorganic non-metallic material and high-tech ultra-fine inorganic new material. The size is between 1~100nm, and it has a three-dimensional network structure, which is easy to agglomerate and has poor storage stability.
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The main technical indicators of nano silica |
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| Particle size /nm | Density /g.cm-3 | Specific surface area /m2.g-1 | Thermal conductivity W.(m.K-1) | Sound speed /m.s-1 | Tap density /g.m-3 | Impurity content /% |
| 15~20 | 0.128~0.141 | 559~685 | 0.01 | <100 | <0.15 | Cl<0.028
Common metals<0.01 |
Preparation of nano-silica
At present, the research on nano-silica mainly uses sodium silicate and ethyl orthosilicate as raw materials, while the raw materials for industrial production are mainly low-cost sodium silicate.
- Physical method
It is mainly mechanical pulverization. The large-particle silica is ultra-finely pulverized through the combined action of impact, shear, friction and other forces generated by the ultra-fine pulverizing machine. Then, a high-efficiency grouping device is used to separate the particles of different particle sizes, so as to realize the uniformity and specificity of the particle size distribution of the nano-silica powder.
The physical production process is simple, the production volume is large, and the production process is easy to control. However, the requirements for raw materials are higher, and as the particle size decreases, the particles agglomerate due to the increase of surface energy, and it is difficult to further reduce the particle size of the powder particles.
- Chemical method
1.Chemical gas phase reaction
This method uses organosilicon compounds (such as organohalosilanes, silanes, etc.), hydrogen and oxygen or air to mix and burn. After the organosilicon compounds are burned at high temperatures, they undergo high-temperature hydrolysis in the water produced by the reaction to prepare nano-silica.
The chemical gas phase reaction method has uniform particle size, small particle size and spherical shape, high product purity and few surface hydroxyl groups. In order for this method to cause chemical reactions, heating, radiation or plasma must be used to activate the reactants into molecules. Therefore, the equipment used in this method requires high requirements, the raw materials used are expensive, and the product prices are relatively high.
2. Precipitation
The precipitation method is to mix the reactant solution with other auxiliary agents, then add an acidifier to the mixed solution to precipitate, and the resulting precipitate is dried and calcined to obtain nano-silica.
The precipitation method has a simple process and a wide range of raw materials and has been widely studied and applied, but the problem of difficult control of its product properties has not been solved.
3. Sol-gel method
This method generally uses silicate or silicate as the precursor to dissolve in a solvent to form a uniform solution, and then adjust the pH value to hydrolyze and polymerize the precursor to form a sol.
The sol-gel process is easy to control and has been extensively studied, and the resulting product has a larger specific surface area. However, difficulty in washing, high requirements for raw materials and too long drying time limit its use.
4. Microemulsion method
By adding acidulant or catalyst dropwise to the microemulsion prepared from the precursor, the preparation reaction takes place in the microemulsion bubble, and the microemulsion is used to confine the nucleation, growth, coagulation, and agglomeration of the solid phase to a tiny spherical shape. In the droplet microbubbles, nano-spherical particles are formed, and further agglomeration between the particles is avoided, and it is easy to realize the controllable production of the body size.
Because of its nano-scale self-assembly ability, it is easy to realize the controllable preparation of particle size and morphology, which has attracted the interest of many researchers and has become a research hotspot in recent years. Because of its high cost, difficult to remove organic ingredients and easy environmental pollution, it has not been widely used in industry.
Surface modification of nano-SiO2
There are a large number of active silicon light bases on the surface of nano-silica, with small size and large specific surface area, which makes it easy to agglomerate. Filled directly into organic materials, because it is difficult to infiltrate and disperse, and has poor compatibility, it is difficult to play a role, which limits its industrial application.
- Physical method
The surface coating method is a modification method in which the surface is modified and there is no chemical reaction with nano-SiO2 , and the coating and the particles are connected by intermolecular force.
The heat treatment modification is a comprehensive process in which nano SiO2 is placed on the back of a certain medium for heating, heat preservation and cooling, and the performance is controlled by changing the surface or internal structure of the nano SiO2 .
- Chemical method
Fatty alcohol reacts with the hydroxyl groups on the surface of SiO2 to remove water molecules. The hydroxyl groups on the surface of SiO2 are replaced by alkyl groups, and alcohols are used as modifiers.
Application of Nano SiO2
- coating
Nano-silica has a three-dimensional network structure, has a huge specific surface area, shows great activity, can form a network structure when the coating is dried, and improves the suspension of the pigment, which can keep the color of the coating without fading for a long time. In building interior and exterior wall coatings, it has excellent self-cleaning ability and adhesion.
- Adhesive/sealant field
In the field of adhesives and sealants, nano-silica is an important product with a large amount and a wide range of applications. At present, domestic high-end sealants and adhesives mainly rely on imports.
- rubber
It can improve the strength, toughness, and life of rubber products. In addition, it can also be used to make transparent rubber soles, and this type of products used to rely on imports.
- plastic
Improve the toughness, strength, abrasion resistance, aging resistance of plastics and improve the aging resistance of plastics.
- Textile field
The composite powder of the appropriate ratio of nano-silica and nano-titanium dioxide is an important additive for anti-ultraviolet radiation fibers, and can also increase the warmth retention effect and reduce the weight of clothes.
- Antimicrobial agent field/catalysis field
Nano-silica is physiologically inert and highly absorbent. It can absorb antibacterial ions to achieve antibacterial purposes. It can be used in the manufacture of refrigerator shells and computer keyboards.
- Agriculture and food
Can make the vegetables ripen earlier.