Recycle And Utilization Of Silver From Conductive Silver Paste In Electronic Waste

The era of information technology has made electronic products change with every day.However,it is not only the gospel of the times,but also the worry of the times.As more and more electronic products are put into use,it inevitably brings overwhelmed discarded electronic products,one of the major types of substrates containing precious metal silver used in which is conductive silver paste.The conductive silver paste is in high demand in the electronics industry,and the silver content in it is high.Discarding electronic products at will can cause great waste of silver resources.What's more,unreasonable treatment will cause the accumulation of metal-containing waste liquid into the soil,rivers,etc.,which is a serious threat to human health.China is a country with scarce silver resources.Coupled with a large population,high demand of products and large consumption of various resources,effectively recycling silver resources will help realize sustainable development of resources and the environment,and protect people's health and make meaningful social value.In this thesis,the waste dried conductive silver paste is taken as the research object,and the high purity silver nitrate is finally crystallized through Al sheet reduction method.Based on this,a series of properties and application research on silver nanofluids are carried out.The main research contents and results are listed as follows:(1)Silver nanoparticles with different morphologies and sizes were prepared by using the extracted silver as raw material and polyvinylpyrrolidone as protective agent.The formation mechanism of silver nanoparticles was described and the morphology of silver nanofluids was investigated in detail.The thermal conductivity of the linear and spherical particles with a volume fraction of 0.46 vol% is 13.72% and 4.76% higher than that of the base liquid ethylene glycol,respectively.What's more,the linear particles are more effective than spherical shaped ones.At the same time,the measured values of thermal conductivity and H-C thermal conductivity model are compared.It is found that the two are well matched,indicating that the thermal conductivity of uniform granular nanofluids such as linear and spherical can be predicted by H-C model.(2)Two kinds of silver nanowires with high different aspect ratio,and same diameter were prepared.The thermal conductivity model was established after testing the thermal conductivity of the two nanofluids,and the effect of length of the nanowires on the viscosity of nanofluids was verified.The UV-Vis spectra of the two nanowires were tested as well,which verified the structure of the two nanowires.The photothermal conversion efficiency was calculated by temperature rise.The temperature rise results of the two nanowires were related to the thermal conductivity,and then the relation between thermal conductivity and photothermal conversion was demonstrated.Under certain conditions,the larger the aspect of the nanowire,the better the thermal conductivity,and the better the photothermal conversion.(3)Combining nano-silver particles with strong absorption in the visible region and barium tungstate particles with strong absorption in the near-infrared region to enhance spectral broad-band absorption.According to the transmittance spectrum,extinction spectrum,and more intuitive solar energy weighted absorption coefficient of silver and barium tungstate single component nanofluids and two-component mixed nanofluids,it is found that the combination of the two particles can enhance the broadband absorption.Furthermore,the temperature rise and photothermal conversion efficiency of the four nanofluids are obtained.When the mass ratio of barium tungstate/silver is 7:3 at a total concentration of 1000 ppm,the maximum photothermal conversion efficiency in this experiment was 67%,which was 32% higher than that of the base solution.