|Place of Conferral||北京|
|Keyword||Pechini 法 氧化物法 Mn0.43ni0.9cufe0.67o4 微波烧结 热敏材料|
采用Pechini 法和氧化物法制备了均匀性好的Mn0.43Ni0.9CuFe0.67O4 NTC 热敏电阻材料，并对材料进行微波烧结研究，以期获得低B 值、高精度、宽温区NTC 热敏电阻，并采用多种检测手段对样品进行了分析和表征，同时探讨了微波烧结的机理，为高互换精度热敏电阻器的研制奠定基础。得到以下结论：(1) 采用Pechini 法制备了Mn0.43Ni0.9CuFe0.67O4 材料，经微波煅烧、压制成型后进行微波烧结，并测试元件的电学性能。由实验结果可知：微波降低了煅烧温度，最佳温度为650℃；粉体比常规煅烧的颗粒粒径细小且分布均匀；1000℃下微波烧结能够获得微观结构均匀的致密陶瓷体 (相对密度为96.61%)，元件的B 值和电阻率ρ 的均匀性较好，B 值的平均偏差为0.31%，ρ 的平均偏差为4.55%，而常规烧结后元件的B 值的平均偏差为1.47%，ρ 的平均偏差为25.34%；微波烧结后样品的晶粒电阻率ρb 和晶界电阻率ρgb 较大，分别为307.8Ω·cm 和368.1Ω·cm，而常规烧结样品的ρb 和ρgb 分别为241.4Ω·cm 和277.6Ω·cm。(2) 采用氧化物法制备了Mn0.43Ni0.9CuFe0.67O4 材料，通过比较微波烧结和常规烧结后样品的微观结构和元件的B 值，电阻率和复阻抗分布，得到结论：相同烧结温度下，微波烧结提高了陶瓷体的烧结特性和元件的电学性能，从而提高了元件的均匀性和一致性。(3) 通过微波烧结机理分析可知：相同温度下，微波烧结能增加样品的致密度，降低样品的孔隙率，减小晶粒尺寸，晶粒生长速率由常规烧结的1.107μm·min-1/2 降为0.620μm·min-1/2，降低烧结活化能，由常规烧结的180.4 kJ/mol 降为119.7kJ/mol。(4) 通过能量散射谱 (EDS) 分析可知，Mn0.43Ni0.9CuFe0.67O4 陶瓷体均由缺铜相(NiFe2O4 和少量CuMn2O4) 和富铜相 (CuO) 组成。
In order to obtain the NTC thermistors with small B constant, high accuracy, applied to wide temperature range, uniform Mn0.43Ni0.9CuFe0.67O4 NTC thermistor materials were prepared by Pechini method and Oxides method. The crystal structure, phase compositions, morphology, particle size distribution and the electrical properties of the samples were analyzed with TG-DTA, FT-IR, XRD, SEM, Laser Particle Size Analyzer, EDS, four-probe digital multimeter and impedance analyzer. Meanwhile, the mechanisms for the microwave sintering were discussed so as to make a foundation for more NTC thermistors with higher accuracy and uniformity. Some results have been obtained and can be attributed to four parts: (1) Mn0.43Ni0.9CuFe0.67O4 materials prepared by Pechini method were microwave-calcined at different temperatures. The compacted samples were microwave-sintered and then analyzed. The experimental results show that the application of microwave leads to a lower calcining temperature (650℃), small particles with narrow size distribution and ceramics with densified uniform microstructures. Microwave sintering can obtain the components with well uniformity of B constant and resistivity, the deviations of which are 0.31% and 4.55%, respectively. However, the deviations are respectively 1.47% and 25.34% for the conventionally sintered components. From complex impedance analysis, the grain resistivity (ρb) and grain boundary resistivity (ρgb) are respectively 307.8Ω•cm and 368.1Ω•cm for the microwave-sintered samples. The ρb and ρgb are respectively 241.4Ω•cm and 277.6Ω•cm for conventionally sintered samples. (2) Mn0.43Ni0.9CuFe0.67O4 materials prepared by Oxides method were sintered by microwave and conventional method, respectively. The grain size and pore size distributions of the bulk were determined to characterize the sinterability of the ceramics. The B constant, resistivity, impedance distributions of the components were also determined to characterize the uniformity of the materials. The experimental results confirm that the sinterability and electrical properties of ceramics are homogenously improved by microwave sintering at the same temperature. Therefore, the uniformity and the consistency of the components are improved. (3) From the analysis of the mechanism for the microwave sintering, it can be concluded that microwave sintering leads to densified microstructures with low porosity and small grains. The grain growth rate constant decreases to 0.620μm•min-1/2 from 1.107μm•min-1/2 for the conventional sintering process. Moreover, the sintering activation energy decreases to 119.7kJ/mol from 180.4 kJ/mol for the conventional sintering process. (4) From EDS analysis, it can be concluded that the Mn0.43Ni0.9CuFe0.67O4 ceramics mainly consist of poor-Cu phase (NiFe2O4 and a little CuMn2O4) and rich-Cu phase (CuO mainly).
|靳先静. Mn0.43Ni0.9CuFe0.67O4 热敏材料的制备及微波烧结研究[D]. 北京. 中国科学院研究生院,2009.|
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