Evaluation On Mechanism And Heating Effect During Microwave Induced Typical Metal Discharge

Developing efficient recycling technology of waste printed circuit boards with precious metal components has become a hot point today.Microwave-induced metal discharge technology has been applied in many fields such as sintering,pyrolysis,gasification,gas reforming,and development of new materials.The discharge mechanism and thermal effect of typical metal components(Al,Cu,Ni80Cr20,Ni,Fe,W)of waste circuit board was evaluated by indirect calorimetry and photoelectric conversion circuit.By using air as the discharge medium and quartz sand as the thermal storage medium,the effects of microwave power(119-700 W),irradiation time(1-3 min),diameter(0.2-3.0 mm),length(20-50 mm),placement,number(1-5)of copper wire and metal type(Al,Cu,Ni80Cr20,Ni,Fe,W)on photoconversion voltage and thermal effect were examined.Metal tip faced with the magnetron was the most conducive radiation angle for discharge,which occurred on one single or two tips.The average photoconversion voltage of copper wire increased significantly with the increasing of microwave power and irradiation time.2.5 mm and 30 mm were the most suitable diameter and length of copper wire to get the maximum average photoconversion voltage,respectively.With the number of copper wire increased from 1 to 5,the average photoconversion voltage dropped by about 67%.Except for tungsten wire,the average photoconversion voltage decreased as the melting point increasing(Al-Cu-Ni80Cr20-Ni-Fe).With the microwave power increasing from 119 W to 700 W,the average thermal storage of the copper wire increased by about 8 times.The thermal storage of copper wire increased by about 3 times with the irradiation time lifting from 1 to 3 min.The average thermal storage was the largest with the copper diameter of 3.0 mm and length of 30 mm.As growing the number of copper wires from 1 to 5,the thermal storage increased by about 33%.Tungsten wire had the largest average thermal storage capacity within one minute,while nickel had the smallest.If the light of discharge is pay attention,aluminum should be selected to get short-term light or tungsten to get continuous light.If the high thermal effect is required,tungsten should be used as the discharge metal.Microwave power,diameter,length and number of metal had significant effect on the average photoconversion voltage and thermal effect.Irradiation time had little effect on the average photoconversion voltage but significant effect on the thermal effect.Through numerical simulation analysis,one of the copper tip faced with the magnetron,the maximum electric field intensity of the tip was 40709 V/m,which was the most conducive to discharge,which was consistent well with the experimental result.The electric field intensity at the tip increased by about three times with the increasing of microwave power from 119 W to 1000 W.Copper wire with length of 20 mm had the maximum electric field intensity,which was 2 times for 50 mm length.This work could provide basic data and empirical support for further processing of waste printed circuit boards and in-depth investigation of microwave-metal interaction mechanisms.