Preparation Of Porous Silver Material By Alloying Method

Silver is an important precious metal,which has unique economic and application value in currency,decoration and industry.Nanoporous silver,with its unique three-dimensional nano-continuous ligament/channel structure,has a very high specific surface area,which shows unique properties different from traditional dense materials and foaming materials.It has broad application prospects in catalysis,sterilization,sensing,mechanics,optics and other fields.In this paper,silver and gallium is raw materials,and the preparation and corrosion of gallium-silver alloy?'-phase were studied.The reaction diffusion method was used to prepare?'-phase of gallium-silver alloy from two preparation stages of alloying and De-alloying by means of optical microscopy?OM?,energy dispersive spectrometer?EDS?,field emission scanning electron microscopy?FESEM?,electrochemical workstation and X-ray diffraction?XRD?.The target product porous silver was prepared by etching the?'-phase.On this basis,the?'-phase and the corresponding parameters-diffusion temperature and time of reaction diffusion preparation of gallium-silver alloy at low temperature were systematically studied,the phase composition of?'-phase was measured,the reaction diffusion mechanism was analyzed,the reaction diffusion rate and reaction activation energy were calculated,and the?'-phase was used as the precursor of de-alloying by chemical corrosion and electrolytic corrosion respectively.Porous structure silver was prepared.The effects of different kinds of corrosive solution,temperature of corrosive solution,electrolytic voltage and surfactant addition on the morphology and structure of porous silver were systematically studied.The formation mechanism of dealloying to porous structure was discussed.The results were as follows:1.It is found that the?'-phase of gallium-silver alloy can be prepared by reaction diffusion method by infiltrating gallium into silver matrix,the diffusion temperature can be as low as100?.The growth rate of?'-phase can up to 0.95 um/min at 100?.For the sample of 1 mm thick silver sheet,the optimum preparation parameters are diffusion temperature 100?and diffusion time 10 hours.2.Observing the cross-section of reaction-diffusion sample,it is found that the interface between?'-phase and silver matrix is parallel to the straight line of the sample surface.As diffusion proceeds,the content of gallium in?'-phase is stable at about 33 at.%?the upper limit of gallium solid solubility in?'-phase?.The cross-section's energy spectrum results show that gallium contains from the sample surface to the interface between?'-phase and silver matrix is the same,the amount remained stable and changed only in the 300 nm width region of the interface,which indicated that the reaction diffusion rate of gallium in silver was controlled by the reaction rate at the?'phase-silver matrix interface rather than the diffusion rate of gallium atoms in?'-phase layer.By measuring the thickness of?'-phase layer at different diffusion time,it is found that?'-phase grows at a steady rate,which verifies the above findings.The growth rate of?'-phase and the reaction activation energy Ea for producing?'-phase at different temperatures are calculated.3.Through chemical corrosion the?'-phase,it is found that the?'-phase has a degree of resistance to corrosion?except for these strong acid which can corrode silver?,the corrosion effect of various common acid and alkali corrosive liquids on?'-phase is not good.Only hydrochloric acid which has heated can corrode for a considerable period of time?72 hours?so that the surface of the sample can be detected to produce silver completely by XRD.The electrochemical test of?'-phase shows that its self-corrosion current in hydrochloric acid is only10^-3A/cm².The corrosion rate is observed by weight loss method.It shows that?'-phase has a degree of resistance to corrosion and the chemical corrosion rate is slow,so it is not suitable to use chemical corrosion for De-alloying of?'-phase.4.Porous silver with three-dimensional continuous structure was successfully prepared by electrolytic etching.The effects of various parameters on the corrosion morphology were systematically studied.It was found that if the surface morphology of porous silver needs to be refined,the following aspects can be started:1)hydrochloric acid is used for the electrolyte,2)the concentration of electrolyte should be increased,3)the electrolytic voltage should be increased appropriately,and 4)Put some surfactant such as sodium dodecyl sulfonate?SDS?into the electrolyte.The mechanism of preparation of porous silver by de-alloying?'-phase was verified.It was found that De-alloying can be divided into two steps:intergranular corrosion and intragranular corrosion.The formation of island-like regions and single grains with porous structure were found on the surface of single grains,which had not been completely de-alloyed.