Abstract
A method making ultrafine nano-silver particle by chemical reduction were studied in this work. On the basis of the former method by formaldehyde, one recently adopts dextrose as the reducing agent because of its advantage of free-toxic, cheaper price and capable of producing finer particle size ( below 10 nm ). Looking after both sides of fine particle size and high conversion is a key point in this thesis. Not only discussing the effects of temperature, procedure of adding reagent and others, but also making investigation on mechanism, rate equations, activation energy and kinetics. It is helpful for us to improve the production after understanding the overall reaction. Besides precursor ( silver nitrate ) and reductant ( dextrose ), it is essential to add some alkaline agent and surfactant here. Surfactant such as PVP is capable of adsorbing on the particle surface and provides stereo-barrier to reduce the aggregation between nano-silver particles. A great deal of research claim that the reduction needs to be carried out under the condition of high pH values by adding moderate alkaline agent, which is used to promote the reaction rate. However, there are few research considering the effects of alkaline ion in the redox reaction. This work not only focuses on the influence upon alkaline ion in the system, but also the behavior on the reaction mechanism and kinetics. In this work, one can get the information that the conversion of silver is proportional to the adding quantity of alkaline agent. Regardless of that the reaction conversion will be promoted quickly after adding NaOH of high concentration, the aggregation owing to physical un-uniform will likely occur. Nowadays, one can take both NaOH and urea as reaction promoter to avoid the aggregation. Except being a chelating agent, the urea with amino group will release OH- ions under high temperature condition. For this reason, it can be served as a stable supporter of alkaline ion. Combining dextrose as new reductor with the mixed alkaline agent ( NaOH & urea ) can produce high stable nano-silver colloids in high conversion (above 95%) and fine-sized particles ( below 10nm ). Besides, one can concentrate the previous colloids by solvent with specific contents to get the dry-powders containing 85% silver finally.