Study On The Preparation And Characteristics Of Mn-Cu-O NTC Thermistors For Low Temperature Application

In recent years,the rapid development of space science and low temperature superconducting technology promote the development of low temperature sensor technology, at the same time,put forward higher request on it. The low temperature NTC (negative temperature coefficient) manufactured on the basis of spinel structure transition metal composite oxide ceramic materials has the advantages of high sensitivity, good stability, small thermal inertia,small influence of magnetic field, large resistance of low temperature and remote sensing,and it can be widely used in low temperature physics and cryogenic engineering. However, the development of domestic research and production of high precision low temperature thermistor is relatively slow, Products manufactured by stable production process is still less, NTC thermistor temperature sensor in temperature range of 20-100K supplied to current market mainly foreign products, the production process is complex, the price is expensive, the domestic did not master the core technology of it,so it is difficult to meet the domestic space science and the needs of development of low temperature superconducting technology. So this paper puts forward the manganese copper (Mn-Cu-O) as the substrate material, to carry out the low temperature usage of NTC thermistor sensor, to conduct research according to its preparation method and performance characterization, focuses on the theoretical and experimental research on the following aspects:1. Introduces the characteristics and advantages of NTC thermometer for low temperature measurement,specifically introduces the process methods and structure characteristics of NTC thermistor for low temperature measurement, emphatically describes different process methods of NTC thermistor, analyzes its structure characteristics,conductive mechanism and effect of adding contents of different elements on the properties, For its aging mechanism is analyzed;2. In profits from the design of domestic and foreign high accuracy cryogenic thermometer calibration device,we developed a set of high accuracy cryogenic thermometer testing device. To control the heat leak loss by the structure characteristics, the analysis of thermodynamics and fluid mechanics were conducted. In the process of temperature control, put forward the piecewise fuzzy-proportional integral differential (Fuzzy-PID) control method to achieve rapid heating and temperature stability; the test results show that in the 20K to 200K temperature range, the temperature fluctuation is less than+ 8mK within 30 minutes,it has good stability and can satisfy the characterization thermistor thermometer resistance requirements;3. Using Pechini preparation of La3+doped Mn-Ni-Cu-Fe-0 NTC oxide NTC thermistor thermometer, and characterize liquid hydrogen temperature-liquid nitrogen temperature-temperature characteristics. Results show that the lower temperature,the higher sensitivity, has the advantages of deep and low temperature measurement, sensitivity is very small over liquid nitrogen temperature range,not suitable for usage. The resistance characteristic changes to the rate of magnetic field strength is low, more suitable for working in high magnetic field. In addition, the thermometer with good aging resistance and stability; study the effects of La content on resistance characteristic, the results show that La element content increase can reduce the resistance value; analyzes the influence of the 4 calibration equations to curve fitting. Using fitting method for nonlinear least square method to solve the parameters of the equation to inspectthe effects of different values of the residuals of the fitting equation, the Hoge-3 equation can be best fit,its residual value can meet the requirements;4. Using solid phase reaction to prepare Mn-Ni-Cu-Fe-0 NTC oxide thermistor and test and analyze the resistance of the liquid nitrogen temperature under room temperature. The results show that the higher resistance value can not only be obtained below liquid nitrogen temperature,but also has very high sensitivity, but under the room temperature, resistance and sensitivity are all decreased; the thermometer at the liquid nitrogen temperature changes rate to the magnetic field strength is less,magnetic field strength changes from OT to 10T, the resistance change rate is less than 0.45%, relatively suitable for working in high magnetic field; thermometer has good aging resistance and stability and bad interchangeability, the maximum can cause measurement deviation of plus or minus 1.5K, must be calibrated before use; after thermometer was calibrated, using Hoge-3 calibration equation fitting,the uncertainty can be less than 10mK.