Silane coupling agent is the most commonly used modifier for surface modification of silicon micro powder. Its application effect is related to the selected type, dosage, hydrolysis, substrate characteristics, application occasions of organic polymer materials, modification methods and equipment.

1. How to select silane coupling agent?
There are dozens of silane coupling agents, such as amino group, chloro group, alkenyl group, epoxy group, methacryloyloxy group, mercaptoalkyl group, cationic group, bifunctional group, etc., which are highly targeted from the perspective of application. It is crucial to select appropriate silane coupling agents.
The selection method is mainly based on the test preselection, and should be based on the structure and property of silane coupling agent and the mechanism of its interaction with silicon micro powder. At the same time, the composition of the base material of downstream products and the reaction effect on silane coupling agent should also be comprehensively considered.
In addition, if more than two coupling agents are selected, the question of which coupling agent is added first or later should also be carefully considered.

2. How to determine the dosage of silane coupling agent?
The dosage of silane coupling agent is determined by the number of reactive points (such as Si-OH) occupied by the specific surface area of the powder and the thickness of the single molecular layer and multi molecular layer covered by silane coupling agent.
Generally, the content of Si-OH in silica micro powder is 4-12 μ M2, 1mol silane coupling agent can cover about 7500m2 powder surface area. After hydrolysis, silane coupling agent will also produce condensation reaction, which will affect the accuracy of calculation dosage, so a certain amount of silane coupling agent shall be added.
Calculation formula for dosage of silane coupling agent:
Silane coupling agent dosage (g)=powder mass (g) × Powder surface area (m2/g)/coverage area of silane coupling agent (m2/g)

3. How to select surface modification process?
The surface modification process shall be determined according to the reaction mechanism of the selected silane coupling agent and silicon powder:
First, the silicon micro powder shall be dynamically heated to 100-110 ℃, and then the hydrolyzed silane coupling agent or composite coupling agent shall be added by atomization method.
A certain reaction time should be kept in the reaction process of silane coupling agent, because the modification effect is different with different reaction time. This heating reaction process is dehydration, condensation and solidification to form stable and firm covalent bond between silane coupling agent and silicon powder.
The powder modified by coupling agent will produce false particles and hard particles after condensation, which have a great impact on the product quality. Therefore, effective grading must be carried out to ensure the product quality.

4. How to select surface modification equipment?
The selection of surface modification equipment is a crucial link in the surface modification of silicon micro powder. The following requirements should be considered when selecting surface modification equipment:
The surface modification equipment can heat and keep the silicon powder warm under dynamic conditions, and the holding time can be automatically controlled.
Exhaust device shall be provided to discharge the water removed before and after surface modification in the form of steam, so that silane coupling agent can produce condensation reaction with the powder to form covalent bond.
To ensure that the silicon powder is in a high-speed dynamic state in the surface modification machine.
The surface modification equipment shall meet the requirements for dispensing of surface modifier.
In order to solve the problem of false agglomeration and hard aggregate produced in surface modification, effective grading must be carried out, and special grading equipment should be provided.
At present, domestic activated silicon micro powder products are only used for simple mixing treatment with silicon coupling agent, so the effect is not ideal, and the powder and resin are easy to agglomerate when mixed. Many foreign patents have proposed active treatment of silicon micro powder, for example, German patents proposed mixing polysilane and silicon micro powder, and stirring under ultraviolet radiation to obtain activated silicon micro powder; Japanese experts proposed that silane glycol derivatives should be used to treat silica fume, and a catalyst should be added in the mixing process to make the coupling agent evenly wrap the powder, so that the epoxy resin can achieve an ideal binding effect with silica fume.
Therefore, domestic silicon powder manufacturers have a long way to go in the road of surface modification, which requires not only the close cooperation of upstream coupling agent manufacturers, but also the full cooperation of downstream application manufacturers. As long as the technical problems of modification are solved, the market of activated silicon micropowder will be very promising.