Developing A Spark-discharge-based-equipment And Its Use In Preparation Of Metal Oxide Nanoparticles

With the rapid development of nanotechnology,nanoparticles show more and more potential applications in sensing,catalysis and other fields.Since the properties of nanoparticles are related to their size,morphology,surface,composition and other factors,researchers usually need to control the preparation of nanoparticles for application requirements in order to optimize the best performance.Among all the fabrication strategies,spark discharge process has been favored in recent years because of its advantages such as simple equipment,flexible process,good compatibility,environmental friendliness.It also has the capability of fabricating nanostructure with clean surfaces and high purity.However,the spark discharge technology still has some problems such as low yielding efficiency and bad particle size uniformity to be solved.In addition,when the spark discharge approach is used to prepare oxide nanostructures,the oxidation of electrodes and the re-deposition on the electrode surfaces may crucially affect the fabrication stability.Focusing on the above issues,this thesis designs a new spark discharge equipment based on a commercial one to improve the fabrication efficiency and stability.New internal configurations are considered and designed.Simulations of the electric field distribution and the airflow are performed with COMSOL software.Finally,the optimized components are manufactured and a new set of spark discharge equipment is achieved and tested.Moreover,oxide nanoparticles are fabricated with this new equipment using Zn,Ti and Sn as electrodes,respectively.The main work and results of this thesis are listed as follows.(1)Design and simulation of the rod-to-tube electrode structure.Simulations show that the rod-to-tube structure can effectively improve the gas flow rate in the electrode gap,improving the breakdown field strength and reduce the spark discharge frequency.These improvements can reduce the time of plasma aerosol staying in the electrode gap per unit time and reduce the re-deposition process,which are beneficial to the continuous preparation of oxide nanoparticles.Moreover,the rod-to-tube structure can also effectively improve the particle collection efficiency.(2)Design and simulation of a buffer tube and its effect on particle growth modulation.Simulation results show that when the internal diameters of the buffer tube are 10 mm,20 mm and 30 mm respectively,the internal carrier gas flow rate decreases by 28.8 %,40.4 % and46.1 % off related to the flow rate in the electrode tube region under the same preparation condition.However,the vortex phenomenon has occurred in the 30 mm diameter buffer tube,which is negative to particle growth and uniformity.Therefore,the 20 mm diameter is selected as the final solution for equipment manufacturing.(3)Based on the simulation results,a set of spark discharge equipment is manufactured and tested.Based on the new equipment,oxide nanoparticles are fabricated using Zn,Ti,and Sn as electrodes.By analyzing the size distribution of the obtained nanoparticles,the geometric standard deviations of the corresponding size distribution are 1.15,1.04 and 1.06,respectively,which are about 20 % lower than those of the rod-to-rod electrode structure by the commercial equipment.This indicates that the particle size uniformity can be effectively improved.Furthermore,it is found that this design can effectively prevent the re-deposition process of oxide nanoparticles on electrode surface.