| Micro- and nano- magnetic ferrites are very important functional materials. Thesynthesis of size, morphology, and properties controllable magnetic materials has become ahot topic in magnetism research areas because of their widely applications. With thedevelopment of modern science and technology, single magnetic material can not meet thedemands of applications. To assign ferrite materials with other functions is the aim ofresearchers, such as magnetic-electric multiple functions, magnetic-optical multiple functions,and magnetic-heat multiple functions. However, the applications of composites are stilllimited because of their aggregations, irregular size, difficult shapes control, poor loadingeffect, and properties uncontrollable.In this dissertation, many efforts have been made to solve these problems. First,controlled disperse, size, morphology magnetic ferrite have been prepared, such as magnetite,hematite. Then, we usedα-Fe2O3micro-flowers as core to load Ag or Cu to prepareelectromagnetic composites. The formation mechanism of magnetic Fe3O4with spheres,micropores, and hollow-spheres shapes and composites have been systematicallyinverstigated. Direct subsidence loading method with new, simple, and effective propertieshas been proposed and systematically discussed in the electromagnetic compositespreparation process. It provides a new way for preparing other types of composites. The maincontents and major results are listed as follows:⑴Uniform sized, monodispersed and morphology controlled magnetite have beensuccessfully synthesized using solvothermal route. We systematically investigated theinfluence of reaction time, temperature, urea (CON2H4) factors on the morphology, size andmagnetic properties. Such as spheres, micropores, hollowspheres shape control, saturationmagnetization changes from 83.3 to 71.03 emu/g, size of products can changes from 247 to404 nm. Finally, we proposed the formation mechanism for the magnetite hollow spheres. ⑵Hematite with micro-flowers has been successfully prepared by ethylene glycol assistroute base on the reaction betewwn ethylene glycol and ferric chloride. First, we preparedhematite precursor, and then calcined at 450℃for three hours to prepar flower-like hematite.Magnetic properties are controlled by changing reaction conditions, such as reaction agents,temperature, and time. The formation mechanism of micro-flowers has been studied. It isfound that the micro-flowers have been assembled by nanoplates which were formed withnanoparticles.The highest saturation magnetization and coercive force is 0.67 emu/g and 127Oe, respectively⑶Direct subsidence loading method was first presented for preparing electromagneticcomposites (α-Fe2O3/Ag) by usingα-Fe2O3as magnetic core. The effects of reactiontemperature, time, formaldehyde concentration, and silver nitrate content on the morphologies,magnetic, and electroconductivity properties have been studied. The results show that thecomposites own regular shape when the temperature is 60℃, 60 min, and 0.2 mol/Lformaldehyde conditions. When the dosage of silver nitrate is 0.5 g, the composites provideda minimum electrical resistivity 0.00016·cm. At that time, the saturation magnetization ofcomposites is 0.11 emu/g. Further, we studied the loading mechanism of subsidence loadingmethod deeply. These results showed that the silver nanoparticles are loaded and grown onthe surface of nanoparticles which assembled intoα-Fe2O3nanoplates.⑷Improvement and optimization direct subsidence loading method was present forpreparingα-Fe2O3/Cu composites. To obtain better effect electromagnetic composites, wefirstly explore a process to control the morphology, size, and electroconductivity properties ofmetallic copper. Investigation on the influence of reaction temperature, time, and hematitecontent on the morphology of composites has been performed systematically. The possibleformation processe of composites was proposed, and the magnetic and electroconductivityproperties have also been investigated.
|
PDF Full Text Request