Evolution Research And Quantitatively Characterization Characterization On The Nanoporous Structure Of Gold Foam

Nanoporous metal foams have many novel physical,chemical and mechanical properties, which makes them ideal candidates for many technological applications.The pore and ligament structure are closely related to its preparation conditions,and are the key parameters to decide the properties.The study on controllable preparation and evolution of nanoporous gold foam based on quantitative characterization of their sponge-like structure is of great significance.Base on scanning electron microscopic image analysis,a new method was developed to analyze the sponge-like structure quantitatively.The image magnification,image gray level threshold,background correction and image filtering methods are investigated.Ligaments were separated into a string of nanometer particles by an image split technique.The size distribution of these nanometer particles is equivalent to ligament width distribution.To characterize the size and shape of the sponge-like structure,many parameters are defined, such as pore diameter,pore area,porosity,pore density,pore roundness,pore aspect and ligament width,ligament area,the ligament area ratio per unit area and so on.A macro program of image processing and measurement was designed.By running it,many images can be processed semi-automatically.The relative standard deviation of measurement and calculation of the size parameters is not more than 4%,and which of the shape parameters is not more than 5%.Nanoporous metal foams were prepared by a selective dissolution of silver in Ag-Au alloys under electrochemically driven corrosion in nitric acid.From the results of the quantitative characterization of the sponge-like structure,it can be seen that with increasing electrochemical etching time from beginning to 235s,the pore size and ligament width increased,pore density decreased gradually.But the pore size and ligament width decreased, pore density increased gradually after 235s.It may be resulted of the self-assembly of the gold atoms under the surface tension.Same area of nanoporous metal foams with about 10 nm pore,before and after annealing, was observed using scanning electron microscopy.With increasing annealing temperature, the mean widths of both ligament and pore increased,and their porosity,pore density decreased.It was first found that Nanoporous metal foams with about 10 nm pore coarsen in ethanol.