The chemical reduction method is the most commonly used method for preparing ultrafine spherical silver powder. Various parameters must be precisely controlled during the reaction process, because small changes in each parameter will cause differences in the particle size and morphology of the ultrafine silver powder. Its preparation flow chart . The principle of chemical reduction method is to add appropriate reducing agents such as triethanolamine, ascorbic acid, hydrazine hydrate, formaldehyde, glucose, etc. during the reaction to reduce silver from its silver salt solution to silver and grow into elemental silver particles. Generally, the spherical silver powder prepared by chemical reduction method is prone to agglomeration, so dispersants, such as polyethylene glycol, gelatin, organic acid, oleic acid, etc. are often added to reduce the agglomeration of silver particles; at the same time, the pH value and reaction temperature of the chemical reduction reaction solution It will also affect the reaction rate. Too fast a reaction rate will lead to secondary agglomeration, and too slow a rate will cause serious agglomeration, reduced dispersibility, irregular shape, and uneven shape. Spherical silver powder with different particle diameters can be prepared.
Different scholars use the same chemical reduction method to prepare spherical silver powder, the research field and related application focus are different, mainly as follows:
1. The study on the preparation of ultrafine silver powder with glycerin as the reducing agent was carried out. The average particle size and powder cluster size of the obtained silver powder were 60~250 nm and 6-30 μm, respectively, the surface area was 1.1~2.9 m21g, and the apparent density was. 0.6~1.2 g/cm’.
2. The chemical reduction method using amines as reducing agents and organic acids as dispersing agents was studied to prepare ultrafine silver powder, and the experiment showed that the concentration of silver nitrate is different, and the particle size of the prepared silver powder is also different. The flow performance of the slurry product has a greater impact.
3. Water and hydrazine are selected as reducing agents. While adding the dispersant, the BMT method is also introduced in the process, and the average particle size is 0.3~0.5 μm, the tap density is 1.5 g/mL, and the appearance Silver powder with a spherical or approximately spherical shape and a purity greater than 99.95%.
4. Using chemical reduction precipitation process to prepare spherical silver powder, adjusting reaction conditions, such as reaction concentration, pH value, reaction temperature, dosing speed, etc., will affect the particle size of the prepared silver powder.
5. Using trisodium citrate as a dispersant, reduce AgNO with ascorbic acid to prepare ultrafine spherical silver powder. The research shows that at a temperature of 40C, the initial solution pH is 7, and the mass ratio of dispersant to AgNO; is 0.08, The prepared ultrafine silver powder has a small particle size, about 0.8 μm, with excellent dispersibility.
6. The reaction of ascorbic acid to reduce AgNO3 was studied, and the influence of dispersant dosage, temperature, pH, AgNO, solution concentration and other process parameters on the morphology and particle size of silver powder was explored.