Wet Chemical Synthesis And Thermal Stability Of Silica-coated Silver Nanoparticles

When the size of particles decreases to the range of nanometer, the corresponding material properties change considerably compared with bulks. Nanomaterial usually has a lower melting degree than normal size material. As for metal nanoparticles, the decrease in melting point result from the size decrease has improtant effects on metal material’s choice, design and application.The experiment mainly works on the preparation of metal-oxygen composition material as well as the research on its stability. The research mainly focus on Ag@SiO₂system. Firstly using liquid phase reduction method to prepare silver nanoparticles. During the experiment, we take sodium citrate as the stabilizer in the reaction, synthesis different size of the quasi-spherical silver nanoparticles by changing the reducing agent, use the developed St?ber method and deposition method to prepare core-shell structure of Ag@SiO₂ and finally mainly research on the effect of concentration of tetraethoxysilane（TEOS） and reaction time on the thickness of oxide silicon shell.The analysis of the results shows that choosing the strong reducing agent sodium borohydride we could get silver nanoparticles less than 20 nm. The ammonia concentration, the way of stirring, the tetraethoxysilane（TEOS） concentration and reaction time all affect the result of coating and the shell thickness of Ag@Si O₂. When increase the quantity of TEOS, the shell thickness will incrase.In the same way, increasing reaction time will make the hydrolysis more complete,and then incrase the shell thickness of silicon oxide. Besides, the coating rate of core-shell structure will affect the content of silver nanoparticles and then affect the final test results in DSC. From the DSC results of 35 nm silver nanoparticles coated with silicon oxide we find out that its melting point decreases about 19 degrees compared with its bulk phase. Also after the high temperature burning,crystallization phenomenon appears among amorphous silica in core-shell structured Ag@SiO₂. By analyzing the changes in size in XRD we could find that silver nanoparticles increase their size at a certain extent after the high temperature burning.