Preparation Of Hausmannite By Manganese Sulphate And The Kinerics Of Its Thermal Decomposition

Ferrite is one kind of soft magnetic material which is widely used incommunication, the audio and video equipment, power switch and magnetichead industry, etc. Hausmannite is the main material to produce ferrite. Nowhausmannite is prepared by electrolyzing manganese metal in our country, thecost of this method is high because of the price of the manganese and the poorof its profitability. In this paper Hausmannite was respectively prepared by amethod of two stage oxidation and thermal decomposition of solid phase usingmanganese sulphate as material. The reaction temperature, the velocity of Mn²⁺,the ratio of the ammonia to Mn²⁺, drying temperature and drying time thataffected the content of the manganese in the samples were discussed throughsingle factor experiments and orthogonal experiment. The optimum condition isthat the ratio of the ammonia to Mn²⁺ is 2:1, the addition rate of Mn²⁺ is 30mL.h^-1, the reaction temperature is 95℃, the drying temperature is 200℃and the drying time is 3 h by experiments. It confirmed that the product wasγ-Mn₃O₄ by using XRD analyzed the sample, the content of the manganese was71.10%, the average size of the powders was 1.23μm in the optimum condition.In preparation of hausmannite by thermal decomposition of manganese sulphate,the calcining temperature, the calcining time, the cooling pattern of the samplewere discussed through single factor experiments and orthogonal experiment.The optimum condition is that the calcining temperature is 1000℃, thecalcining time is 2 h and the cooling pattern of sample is cooling production inthe crucible with cover out of muffle. It confirmed that the product wasγ-Mn₃O₄ by using XRD analyzed, the content of the manganese was 71.80%.The thermal decomposition behavior of manganese sulphate was studied byTG-DSC and XRD, and the dehydration and decomposition kinetics wasdiscussed by non-linear isoconversional method and the universal integralmethod. Mampel Power principle G(α)=α^3/2 can be used to describe thedehydration kinetics of anganese sulphate between 200℃and 400℃. Theaverage activation energy of the dehydration is calculated to be 117.11 KJ·mol^-1.MnSO₄ is decomposed while the temperature is between 750℃Cand 1050℃.The decomposition kinetics can be described as G(α)=1-(1-α)^1/2, and its averageactivation energy is 226.44 kJ·mol^-1. The result of isothermal decompositionkinetics of manganese sulphate is according with its non-isothermal kinetics byTG-DSC analysis.Through researching on the preparation of hausmannite by manganese sulphate and kinetics of thermal decomposition of manganese sulphate, it canprovide theoretical evidences and an experimental foundation on theindustrialization of preparing the hausmannite by manganese sulphate.