Abstract
The continuous precipitation of silver nanoparticles was performed at room temperature using sodium borohydride (NaBH4) as the reducing agent. The effects of the silver precursor concentration (i.e. silver nitrate), the quantity of dispersing polymer (polyvinyl pyrrolidone, PVP) and the flow rates of the reacting solutions on the resulting particle size and its distribution were investigated and reported here. Particles with average sizes ranging from 13 to 130 nm were obtained. Our results show that there is an optimal flow rate for each precursor concentration to obtain uniform size distribution of the silver nanoparticles. This phenomenon was explained via the sequence of mixing, reaction, generation of supersaturation and subsequent nucleation, growth and agglomeration steps. Size control was mainly achieved via the use of a relative quantity of PVP/AgNO3 weight ratios from 0.05 to 1.5. Other properties such as residual PVP quantity, boron and sodium contamination were also reported here for several representative samples. Finally, we can produce nano silver particles which has average size at 38nm by 0.1M AgNO3、PVP/AgNO3(wt/wt)=0.25、NaBH4/AgNO3(molar ratio)=1. The conversion is 98%. And the residual quantity of PVP after washing was only 3.01%. After washing step, we use organic solvent to prepare silver ink whose solid content is 25wt%. This ink can be drawn into pattern on AutoCAD software by a XY-plotter. We can set the different velocity to draw the lines. A faster velocity results in thinner lines. After heat treatment at 250℃for 3minutes, the silver lines were measured for its thickness by alpha-step. The mountain-like profile was mainly caused by evaporation of solvent which moved the silver nanoparticles.This phenomena can be improved to some extend by changing the heat procedure. By vacuum heating the silver lines at 80℃ first, then to 250℃ for 3 minutes, the profile of thichness become short and broad. Finally, we can use 1cm/s to draw interdigitated electrode (28mm×15mm). The average width of Ag line is 814 μm. After new heat treatment, the resistivity of electrode is 2.5 × 10-5 Ω．cm .