Mn_2.125Ni_0.625Fe_0.25O₄Thermistor Ceramic Material’s Sol-gel Preparation

Negative Temperature Coefficient (NTC) ceramic composition material is a kind of d3transition metal composite oxide with spinel structure comprised of Mn-Ni-O, Mn-Ni-Cu-O, Mn-Ni-Co-O and Mn-Ni-Fe-O etc. The B value and electrical resistivity in electrical parameters of such material are relatively determined by its the crystal structure, crystal boundary and grain size. The Mn2.125Ni0.625Fe0.25O4thermistor ceramic material are wildly applied in cars and household appliance such as heaters, air conditioners, office supplies, automotive electronic control and etc due to its excellent electrical properties. Therefore, the study of its preparation has a practical significance. So far, the research on sol-gel preparation of Mn2.125Ni0.625Fe0.25O4thermistor ceramic is not perfect, nor the optimal parameters. In this thesis, impact factors about sol-gel preparation of Mn2.125Ni0.625Fe0.25O4thermistor ceramic have been experimentally analysed and optimal parameters are eventually obtained.In this thesis, Mn2.125Ni0.625Fe0.25O4thermistor ceramic with lower resistivity and higher B value has been prepared starting from Mn(NO)2, Ni(NO3)2·6H2O, Fe(NO3)3·9H2O as raw materials by sol-gel in a molar ratio of17:5:2. XRD and SEM have been applied as characterization method. The influence of the pH value, calcining temperature and sintering temperature upon thermistor ceramic has been discussed. Processing parameters have been optimized. The main works and results of this thesis are listed as follows.(1)The better pH value is3.5;(2)The better calcining temperature is800℃;(3) The better sintering temperature is1000℃. In this condition, the resistivity of Mn2.125Ni0.625Fe0.25O4thermistor ceramic is4650Ωcm, B value is4030.