Preparation And Characterization Of Silver Coated Nanocomposites

Electromagnetic shielding materials have been widely used in military engineering and civil project. It has become a research hotspot in military equipment shielding technology and civil control of electromagnetic radiation technology. The present silver as a filler in these materials has many shortages such as high density and high cost. In this work, , the silver-coated core-shell shielding particles were prepared by using submicron silicon dioxide and glass microspheres as based core through Self-assembly Liquid Phase Reduction and Liquid Phase Chemical Deposition. The influences of the preparation conditions on the structure of the synthesized core-shell particles and their forming mechanism were also systemically studied. The conclusions are as follows:(1) Activated submicron silicon dioxide spheres in the size range of 230～600 nm are synthesized by Sol-Gel method using the ammonia as the catalyst and mercaptopropyltrimethoxysilane as the coupling agent.(2) Ag/SiO₂ core-shell composite particles with strawberry-shaped, thickness controllable silver shells and activated submicron silicon dioxide as core, are prepared by Self-assembly Liquid Phase Reduction, take advantage of the silver nitrate as silver precursor and the formaldehyde as reductant. In the reaction solution, firstly, Ag-S covalent bond was formed between Ag⁺ and the sulfhydryl group of the surface of the activated silica; then, silver heterogeneously nucleated on the surface of silica under the effect of the reductant. The dense, uniform silver-coated layer can be formed on the surface of silica by controlling the reaction conditions.(3) Silver-coated core-shell particles can be prepared through Liquid Phase Chemical Deposition, which would enhance the external surface activity of the glass microspheres modified by sulfhydryl. The hollow silver particles can also be obtained via desolating the glass microsperes. In the reaction solution, silver precursors linkaged with the sulfhydryl group on the surface of the glass microsperes in priority and nucleate on the surface of the glass microspheres directionally and heterogeneously. At first, the silver nanoparticals with the size about 5 nm were deoxidized on the surface of the glass microspheres. Consequently, the silver nanoparticals gradually spreaded on the surface of the glass microspheres, relaxedly grew up, and finally formed a complete silver-covered membrane controlled the competitive reaction between heterogeneous nucleation and homologous nucleation.(4)The electrical conductivity and the electromagnetic shielding effectiveness of the electromagnetic shielding coatings consisting of silver-coated core-shell particles can be measured by four-probe surface resistivity tester and vector network analyzer. It suggests that the surface resistivity of these coatings is up to 0.13 mΩ/â–¡and their electromagnetic shielding effectiveness is between 60dB and 100dB.