Study On SmCo Super Fine Powders Synthesized By Wet Chemical Method

The SmCo rare earth permanent magnets have a good magnetic properties.It is a key functional material in the fields of aviation,spaceflight,information communication,electronics,automobile,petroleum,national defense,and so on.In order to expand its applications,the performances of SmCo magnets need to be improved further.There is a big gap between the coercivity of commercial SmCo magnet and the theoretical value.So there is still a lot of room for improvement.The coercive force is the structure sensitivity.The magnetic performances mainly depend on the microstructure of the magnet,such as grainsize,morphology and grain boundary structure.At present,commercial SmCo magnets are mainly prepared by powder metallurgy process.Firstly,the SmCo alloy powders are prepared by using strip casting and jet milling,and then the powders are formed into row block with presser in the magnetic field and CIP.Finally,the row blocks are sintered and aged into the SmCo magnets with high magnetic properties.Although we have introduced advanced technology of strip casting,hydrogen explosion and air mill into preparation of SmCo powder.Those technologies are still not good enough to obtain SmCo powders with good quality,such as the narrow particle size distribution and uniform morphology,which lead to the difference of the grain uniformity of the subsequent sintered magnets.Because SmCo is very easy to aggregate in the preparation process,it is very difficult to acquire high quality monodisperse SmCo magnetic powders.The development of new technology to obtain high quality magnetic powders has been a hot spot in the field of SmCo magnets.Based in the background,we proposed a chemical method to synthesize SmCo super fine powders with controllable size and morphology.In this study,we applied the Sm(acac)3 and Co(acac)2 as the reaction precursor.The precursor was reduced from solution by reducing agent.Meanwhile oleylamine and oleic acid were added as stabilizers so that the reaction is more controllable.On the basis of a large number of experiments,we have obtained the SmCo super fine powders with submicron or nano size and good quality.The main results are as follows:(1)SmCo powder with good dispersion and similar structure can be obtained by wet chemical method.The composition of the SmCo powder can be controlled by changing the ratio of the precursors.Finally,we will acquire SmCo super fine powders;(2)Reaction processes(including temperature,time and reaction environment)have a great influence on the SmCo super finepowders.With the increase of the reaction temperature,the particle size increases.We have studiedthe growth mechanism of SmCo particles with reaction time.First the precursor is reduced to atoms and then to form nucleus.The nuclei grow up to nanoparticles.These nanoparticles connected each other and formed flower-like aggregations.Finally,the aggregations grow together particle with lager size.The argon atmosphere can reduce the oxidation of synthesized particles and improve the magnetic properties of the powders;(3)Reaction reagents(including reducing agent,solvent,and surfactant)also have important influence on the SmCo super finepowders.With the increasing amount of reducing agent,the number of particles increases.The particle size of SmCo particles increases at first and then decreases.The amount of solvent has a certain effect on the size of SmCo super finepowders,the size of the particles increases with the increase of the amount of solvent.Controlling the types of surfactants can change the morphology and size of SmCo particles.