Research On Micromorphologies And Properties Of Ultrafine Cu Powder Prepared By Micro-Abrasive Milling

Ultrafine Cu powder has a wide application prospect in the fields of chemistry,environmental treatment and electronics.At present,ultrafine Cu powder is mainly prepared by wet chemical method,but the complex process leads to high cost,which seriously limits its application.Mechanical milling（MM）technology is an important method to prepare ultrafine powder.However,for high ductility materials such as pure copper,it is prone to plastic deformation and cold welding during the milling process,which can not be effectively refined.On the basis of conventional MM technology,a certain number of stainless steel microspheres with the size of 0.5 mm were added as micro-abrasive to prepare pure Cu powder.The effects of milling parameters on the micro morphologies,compositions and performances of the powders were characterized by scanning electron microscope（SEM）,transmission electron microscope（TEM）,XRD,nanoparticle size detection,specific surface area detection（BET method）,inductively coupled plasma spectrometer（ICP）and XPS.And the powder refining mechanism is discussed.This study has important guiding significance for refining pure copper powder and improving the preparation quality of ultrafine powder.Cu₂O powder and Cu powder were processed by conventional MM.The results showed that because Cu₂O powder is brittle,particle refinement can both be achieved by wet and dry milling.Cu₂O powder reached the milling limits after dry milling for 30 h and wet milling for 80 h,and the average particle sizes were 0.42 μm and 0.73 μm,respectively.Due to the strong plastic deformation ability of Cu powder,its particles were still coarse and flat after vacuum dry milling for 20 h,with an average particle size of 5.7 μm;milling in air atmosphere could promote the refinement of Cu powder,and the particles changed from flat to aggregates composed of a large number of fine particles.However,it took 50 h to reach the milling limit,and its average particle size was 1.4 μm.By adding stainless steel microspheres as micro-abrasives for milling,under vacuum condition,controlling the ratio of micro-abrasive 1:1 and milling speed 300 rpm,the flattened Cu powder with the particle size of 3 μm can be obtained.With the participation of oxygen,the particle size of the powder after micro-abrasvie milling（MAM）for 30 h was about 375.4 nm,which was composed of fine particles in the range of 100～200 nm;XRD results showed that all Cu powders were transformed into Cu₂₊₁O after MAM for 20 h.The three-ball-model shows that this is because the oblique collision of MAM improved the energy utilization efficiency in the process of milling without changing the total milling energy;oxygen reacted with the fresh metal surface to form a stable Cu₂₊₁O oxide film,which hindered the cold welding between powder particles;with the extension of milling time,Cu₂₊₁O was stripped layer by layer and finally transformed into Cu₂₊₁O nanoparticles.Cu₂₊₁O soft aggregates were dispersed and sorted by wet milling,ultrasonic treatment and centrifugal separation,sequentially.The results showed that the powder solution with a uniform particle size distribution could be obtained by 10 h ethanol wet milling,adding 10 vol.%ethylene glycol and centrifuging at 1500 rpm for 5 min,and its average particle size was 179.5 nm.However,the powder was oxidized to some extent during the treatment,and finally was composed of Cu₂₊₁O and CuO.The reduction behaviors of dry and wet milled Cu₂O powders,and MAMed Cu powder were studied.When the reduction temperature was 250℃,all three powders could be completely reduced;when the temperature droped to 200℃,the reduction rates of dry and wet milled Cu₂O decreased rapidly,which were 41.6%and 31.6%,respectively;when the reduction temperature droped to 150℃,dry and wet milled Cu₂O powder basically did not reduce.However,when the reduction temperature droped to 200 and 150℃,the reduction rates of MAMed Cu powder were still as high as 87.5%and 51.1%,respectively.It showed that the reduction activity of MAMed Cu powder was higher than that of dry and wet milled Cu₂O powders.This may be related to the existence of more oxygen vacancies and deformation defects in MAMed Cu powder.