Synthesis Of Ferrites Via Solid-State Reaction At Low Heat And Study On Their Properties

Ferrites are a broad class of complex magnetic oxides of considerable technological importance,which occur in several different crystal structure forms.Within this group,spinel is a kind of the most important structure that occurs in two forms:spinel and inverse spinel structure.Ferrites are widely applied in many fields such as ferrofluids,magnetic drug delivery,magnetic high-density information storage.Nickel ferrite and zinc nickel ferrite are two kinds of ferrites which properties depend on their preparation methods.Therefor,they have been received considerable amount of attention.In this paper,pure phase nanocrystalline NiFe₂O₄ and Zn_0.5Ni_0.5Fe₂O₄ were synthesized via solid-state reaction at low heat.Besides, thermal decomposition kinetics of Zn_0.5Ni_0.5Fe₂O₄ precursor and crystallization kinetics of Zn_0.5Ni_0.5Fe₂O₄ were also investigated.The paper consists of four chapters:Chapter one:IntroductionPrinciple,preparation progress,and its advantage of preparing inorganic material via solid-state reaction were summarized.Characteristic,purpose,and preparation progress of ferrite were also introduced.Crystallization kinetics of was summarized.Chapter two:Preparation of NiFe₂O₄ via solid-state reaction at low heat and CharacterizationThe nanocrystalline NiFe₂O₄,with inverse spinel structure,was obtained via solid-state reaction at low heat in the presence of surfactant PEG-400 when NiSO₄·7H₂O,Fe₂(SO₄)₃ and NH₄HCO₃ were used as raw materials.The precursor and its calcined products were characterized by TG/DTA,IR,XRD,TEM,and VSM.The uniform design method was used for obtaining the optimal experimental conditions.The optimal experimental conditions as follow:molar ratio of NH₄HCO₃ to NiSO₄·7H₂O was 10:1,PEG-400 dosage was 499.8μL, grinding time was 38 min,calcining temperature and time were 550℃and 170 min respectively.The cubic NiFe₂O₄ crystalline with inverse spinel structure was obtained under the optimum conditions.Its appearance close to roundness,and average diameter about 55 nm. The saturation magnetization of NiFe₂O₄ was 50.7 emu·g-1,coercive force Hc was 40 Oe, remanence Mr was 1.5 emu·g-1,and crystallinity was 88.5%.Chapter three:Preparation of zinc nickel ferrite via solid-state reaction at low heat and CharacterizationThe Zn_xNi_1-xFe₂O₄ was prepared via solid-state reaction at low heat when ZnSO₄·7H₂O, NiSO₄·7H₂O,Fe₂(SO₄)₃,and NH₄HCO₃ were used as raw materials.The precursor and its calcined products were characterized by TG/DTA,IR,XRD,SEM,and VSM.The uniform design method was used for obtaining the optimal experimental conditions.The optimal experimental conditions as follow:x=0.5,NH₄HCO₃ dosage is as 1.2 times as theoretic value, grinding time was 38 min,calcining temperature was 800℃.The cubic Zn_0.5Ni_0.5Fe₂O₄ crystalline was obtained under the optimum conditions.Its appearance closes to roundness, and average diameter was about 59.1 nm.The saturation magnetization of Zn_0.5Ni_0.5Fe₂O₄ was 75.4 emu·g-1,coercive force Hc was 40 Oe,remanence Mr was 3 emu·g-1,and crystallinity was 91.5%.Chapter four:Study on crystallization kinetics of Zn_0.5Ni_0.5Fe₂O₄A study on crystallization process of Zn_0.5Ni_0.5Fe₂O₄ was carried out on the basis of theory of isothermal and non-isothermal crystallization kinetics.The kinetics parameters and mechanism functions of Zn_0.5Ni_0.5Fe₂O₄ crystallization process were obtained from different analysis theories respectively,that is:E = 110.6～113.3 kJ/mol,crystallization exponent Avrami constant(n)= 0.2～0.6,3D for growth mechanism for isothermal crystallization kinetics theory based on Jander model,and E = 155.6～242.4 kJ/mol,crystallization exponent Avrami constant(n)= 0.4579,lnv= 17.81～36.16 for non-isothermal crystallization kinetics theory,and crystallization kinetics mechanism function g(x)was[1-(1-x)^1/3]^1/2,which is one of the Jandle model.