Study On Preparation And Doping Modification Of Mn-Ni Based Thermal Sensitive Ceramic Materials

Negative temperature coefficient?NTC?thermistors have significant capabilities of measuring temperature,compensating temperature and suppressing the inrush current,so applied in automotive electronics,household appliances,aerospace and medical field,etc.However,the rapid development of industry needs exploring the NTC thermistors with higher sensitivity and stability,which can be obtained via changing the preparation methods,thermal sensitive material systems and so on.Thus,the effects of co-precipitation and solid state methods and elements doping on the phases,microstructure and electrical properties of Mn-Ni based ceramics were investigated in this study.The main results and conclusions are as follows:Firstly,Mn_2.25Ni_0.75O₄ thermal sensitive ceramics were prepared successfully by co-precipitation and solid state methods.It can be concluded that the size of pre-sintered particles synthesized by co-precipitation method is more uniform,and the sintered samples present the smaller grain sizes,fewer pores in the cross-section and higher bulk density compared to the solid state method.Moreover,the values of resistivity and material constant?B?of co-precipitation sample are 3365??cm and 4448 K,while those of solid state sample are 4905??cm and 4502 K,respectively.Secondly,Mn_2.25Ni_0.75-x.75-x Cu_x O₄?0?x?0.5?ceramics were prepared by co-precipitation method.The influences of Cu content and sintering temperature on the phases,microstructure and electrical properties were studied.At 1150°C,the grain sizes reveal an increasing trend with the copper content increasing.The number of pores in the cross-section,the room-temperature resistivity and B value gradually decrease with the copper molar ratio increasing from 0 to 0.4,and there are the formation of CuO and Cu₂O impurity phases when x is equal to 0.4.The stomata of cross-section is more obvious when x is equal to 0.5,and the grains at the surface grow abnormally,as well as the resistivity and the B value are higher.In addition,during the process of Mn_2.25Ni_0.45Cu_0.3O₄ceramics sintered from 1050°C to 1200°C,the grain sizes gradually increase and the bulk density reaches to the maximum at 1150°C.Mn₂O₃ and NiO impurity phases appear at 1250°C.The curves of room-temperature resistivity and B value show a positive V shape in the whole heating process.Subsequently,the effects of Co content on the phases,morphology and electrical properties ofMn_2.25-xNi_0.45Cu_0.3Co_xO₄?0?x?0.8?ceramics were researched.With the increase of Co content,the grain sizes and the number of pores of samples gradually decrease,while the values of resistivity and B increase.And when the molar ratio of cobalt is 0.8,Co₃O₄ and CoO impurity phases generate.One of the Mn_1.75Ni_0.45Cu_0.3Co_0.5O₄ sample has optimal electrical performance.Finally,the influences of Zn-doping on properties of Mn_1.75-x.75-x Ni_0.45Cu_0.3Co_0.5Zn_xO₄?0?x?0.5?ceramics were investigated.The content of Co₃O₄,CoO and CuO impurity phases,the grain sizes,the bulk density,the resistivity and B value increase with the increase of zinc,while the number of pores in the cross-section decrease.Meanwhile,the Zn-doping can effectively enhance the stability of Mn1.75-xNi0.45Cu0.3Co0.5ZnxO4 ceramics,and the Mn1.35 Ni0.45Cu0.3Co0.5Zn0.4O4 ceramic has the first-rank stability,with resistance drift rate of 0.65%.