碳酸盐共沉法制取锰锌铁氧体超细粉末的热力学分析

Thermodynamic Analysis on Preparation of Fine Powders of Mn-Zn Ferrites With Carbonate Coprecipitation Process

锰锌铁氧体具有优良的热敏性能,作为热敏传感器能广泛用于许多领域。锰锌铁氧体的制备包括三个步骤:粉末制备、成型和烧结。每个工序特别是粉末制备工序直接影响材料的性能.制备 Mn-Zn 铁氧体有两种方法,即固相法和液相法。固相法很难制得很细,组分均匀的粉体,往往要花费很长时问进行碾磨,同时粉末被杂质沾污。采用湿法治金方法可以制得超细、分散良好、组成均匀一致及纯净的陶瓷粉体,对多组分的粉体特别有利.本研究采用碳酸盐共沉法制备 Mn-Zn 铁氧体,以 FeSO_4,ZnSO_4和 MnSO_4为原料,NH_4HCO_3作沉淀剂。为寻求最宜工艺条件,以指导制备工艺,对共沉法制取 Mn-Zn 铁氧体粉末的 FeSO_4-ZnSO_4-MnSO_4-NH_4HCO_3-H_2O 体系进行热力学分析,结果表明,Mn-Zn 铁氧体粉末沉淀的最佳值为7.2～8.5,实验结果表明,pH 在7～9范围内锰、锌和铁沉淀率在99%以上。说明热力学计算与实际结果一致,热力学分析指导了共沉工艺,减少实验,节约时间和费用.用碳酸盐共沉淀粉末制的锰锌铁氧体起始磁导率达6153左右,温度敏感度≤±1℃,并在舌簧开关中应用,取得良好的结果。

Mn-Zn ferrites possess excellent thermal sensitivity,and can be widely used as thermal sensor in many fields.The preparation process of Mn-Zn ferrites includes three stapes:powder preparing,shaping and sintering.All of them especially the powder preparing,affect directly properties of materials.There are two ways to prepare Mn-Zn ferrite powdes,i.e.the solid phase method and liquid phase method.The solid phase method is difficuet to make powder size fine enough and to make te conponents of powders homogenized,and it would cost much time to mill raw materials.Especially it makes powders contamina- teel by impurities.It is possible to prepare ultrafine,well dispersed,homoge- neous,and pure ceramic powder with hydrometallurgical method,especially muti-component powder.The carbonate coprecipitation process was used to prepare Mn-Zn ferrite powders in the preseut study,FeSO4、ZnSO4、MnSO4 were used as raw materials,and NH4 HCO3 as precipitant.In ordr to fine optimum processing cohditions,and direct the preparation process,the thermo- dynamic analysis on preparation of fine Mn-Zn ferrite powders in FeSO4- ZnSO4-MnSO4-NH4HCO3-H2O system with coprecipitation process has been carried out.It has been obtained from the thermadynamic analysis that the optimum precipitation pH range of Mn-Zn ferrite powders is 7.2～8.5.The experimental results showed that precipitation rates of Mn、Zn and Fe can be obtained over 99% in the pH ranpe of 7～9.It has been shown that the thermo- dynamic analysis agrees with experimental results,the themodynamic analysis has ditrected the coprecipitation process.The Mn-Zn ferrite and the switch made of powders which were prepared by the carbonate coptecipiration process had good properties,its maqnetoconductivity is about 6100,and temperature sensitivity is±1℃.