Effect Of Low-temperature Preparation On Magnetic Properties Of NiCuZn Ferrites

The dissertation study on effect of low-temperature preparation on magnetic properties of NiCuZn ferrites;The impact between microstructure and magnetic properties of ferrite was investigated systematically by adjusting the main prescription,production process and additives.As a result,high-properties NiCuZn ferrites were synthesized successfully at low sintering temperature.At first,the conventional ceramic process has been applied to prepare high-properties NiCuZn ferrites with special attenion paid to lower the sintering temperature.The content of NiCuZn ferrites was determined according to the project's intention,the effect of CuO content on the magnetic properties was mainly investigated in the main prescription.It is found that CuO reduces the forming temperature of the spinel phase and induces liquid phase during sintering,which favors the densification,graln growth and magnetic properties.The NiCuZn ferrites have synthesized at a low temperture 975℃through adding 10mol%CuO with stoichiometric:initial permeability of 1078,power loss of 269kw/m³,saturated flux density of 336.5mT.But with further increasing CuO,the magnetic properties could be deteriorated by more porosity and abnormal grain growth.It was confirmed with the optimal composition of 49mol%Fe₂O₃,31mol%ZnO,10mol%NiO,10mol%CuO.Second,the effect of calcining temperature,sintering temperature and heating rate on the microstructure and magnetic properties of ferrite were investigated.The result showed that raising the calcining temperature properly is favorable to the grain growth and few porosity so as to the improvement of magnetic properties of the NiCuZn ferrites.However,with further improving calcinations temperature,the reatibe ability of calcined powders can be decreased,the second-milling time can be prolonged,the sintering temperature can be rised,leading to the decrease in magnetic properties.The sintering temperature acts as a crucial effect in the microstructure and magnetic properties of ferrite.To evealuate the singtering temperature appropriately will be of benefit to the grain growth and densification of the ferrites so as to the improvement of magnetic properties of the NiCuZn ferrites.But the magnetic properties could be deteriored by more porosity and abnormal grain growth.When heating rate is too fast,the microstructure and magnetic properties of ferrite become worse.However,slow heating insults in wasting the resource and hardly improveing magnetic properties.Consequently,we can optimize technical parameters:calcining temperature at 800℃,sintering at low temperature of 975℃,heating rate being 2～2.5℃/min.Finally,the effect of doped V₂O₅,MoO₃ and combined addition on magnetic properties of low-temperature sintering NiCuZn ferrites was investigated.The addition of V₂O₅ also induces liquid phase during sintering,leading to the decrease in sintering temperatures,having little effect to magnetic properties.The multivalent ions Mo⁶⁺could improve the ferrite's microstructure,for example:grain refinement,decreasing porosity.Therefore,the densification of ferrite materials was improved,which increase magnetic properities.The paper also adopt the method of orthogonal test to design multiple additionBy adopting the method we can not only reduce plenty of experiments' time and human and mateial resources,but also provide a high efficient mathematical method for late analysis of experimental data processing.It is found that the initial permeability with 1269,relative saturated flux density with 331.8mT and power loss with 254 kw/m³ were obtained with 0.3wt%V₂O₅+0.12wt%MoO₃ at 950℃.