Research On NASICON Material, Micro Gas Sensor And Measure System

The gas sensor is an important branch in the sensor domain. It is widely used in domains of industry, agriculture production, family security, environmental monitoring, energy, health and so on. Along with development of the science and technology, the tradition tubular and the piece type gas sensor have showed the tendency which develops to the micro direction; at the same time, the former sole function gas sensing instrument is also changed along with the innovation of electronic technology. The gas sensor measure system is developing to intellectualized, and the network directions.This article combines the high and new technology development planning subject of Jilin Science and Technology Office"Research on new type CO₂ sensor and testing instrument"and the subject of Natural Science Foundation of China"Research on characteristic and design and fabrication of the integrated multifunctional poisonous gas sensors". The preparation and characterization of NASICON powder and thin film materials and the fabrication were studied deeply. The micro gas sensor was designed and the gas detecting system was build at same time. The obvious progress was obtained.1. The NASICON nano-powder materials were prepared through sol-gel method using C6H8O7 and ZrO(NO3)2:Na3PO4:Si(OC2H5)4 = 2:1:2. XRD, FTIR, Raman, TEM, XPS and resistance analysis were used to characterize the obtained NASICON materials. And the conclusions are as follows:(1)The best sintered temperature for preparing NASICON powder materials through sol-gel method is 900℃. The obtained materials have single diagonal structure and the components are pure. The average size of the particles is 10-20nm.(2) Through the XPS analysis on the obtained NASICON powder materials, we can calculate the molecular formula is Na_3.05Zr₂Si₂P_0.95O₁₂ that is very close to the ideal chemistry computation ratio.(3) Compared with the obtained materials sintered under 800℃and 1000℃, the obtained NASICON powder materials sintered under 900℃have the higher conductivity.2. We have explored a new method for preparing NASICON thin films through sol-gel method using C₆H₈O₇ and ZrO(NO₃)₂:Si(OC₂H₅)4:NaNO₃:(NH₄)H₂PO₄ = 2:2:3:1. The obtained NASICON thin films materials were characterized by XRD, SEM and resistance analysis. The conclusions are as follows:(1) The best sintered temperature for preparing NASICON thin films materials through sol-gel method assisted with citric acid is 900℃. The average size of the particles in NASICON thin films is about 15nm which was estimated through XRD analysis.(2) Through the SEM images analysis on the NASICON thin films materials obtained at different sintering temperature, we can find that the size of the particles increased as the sintered temperature changing. But the quality of the thin film is not very good and need to be improved later. (3) Through the resistance analysis on the NASICON thin films materials obtained under different sintering temperature, we can find that comparing with the obtained materials sintered under 800℃and 1000℃, the obtained NASICON thin films materials sintered under 900℃have the higher conductivity.3. We design and produce the micro heat plank with analysis method with the thermal field analysis software—ANSYS, besides calculate out the distributing state of the temperature simulate. On the basic of this, we made the underlay of the micro heat plank and through the analysis to the table of the temperature distributing, we got the conclusions:(1) The temperature distributing of the model of the micro heat plank is uniformity that the width of the Pt calefaction bar is 1.2mm ,the domain difference of the temperature occur in the two corners of the down-lead connect point that far from the Pt electrode. Also the grad changes of temperature compared with the former design(width of the Pt calefaction bar is 0.3mm ) has advanced greatly. So the model of the latter more fix to the design.(2) The shape of the Pt calefaction bar should take the thick and the less bend. The simulate analysis of ANSYS indicated that if the Pt calefaction bar takes the thick and the less bend ones the using rate of the heat will advanced greatly, and this plan will be more suitable for designing the micro heat plank of the micro gas sensor practically.4. We have fabricated micro NH₃ gas sensor and micro CO₂ gas sensor based on the obtained NASICON powder materials, and studied its fabrication process, sensor characteristic and sensitivity mechanism. The conclusions are as follows:(1) The best working temperature for the fabricated micro NH₃ gas sensor is 300℃then the sensitive is 26.92mV/decade. The response to the interfering from H2,CO and CH4 are very less in the same conditions, that indicates it has better gas selectivity. In the 200ppm NH₃ gas concentration, the response time is 20s and the recover time is 30s. The water resistance is not very good from the experiment. So the sensitivity and humidity of the sensor need be improved later.(2) The sensitivity of the micro CO₂ gas sensor which uses molecules ratio 1:1.5 Li2CO3-BaCO3 as the sensitive electrode materials is higher than the molecules ratio 1:1. The sensitivity of the sensor is 56.3mV/decade when the working temperature is 370℃.In the same test circumstance, the sensor shows good property of selectivity among CO, CH4 and SO2. When the temperature is 370℃, in the 500ppm CO₂ gas concentration, the response time is 26s and the recover time is 35s. The sensor shows good water-resistance but need be improved also.For the experiment, the"solid electrolyte gas sensor properties instrument system"is designed by ourselves .Then the"portable solid electrolyte CO₂ gas sensor apparatus"is designed. Taking ARM controller LPC2148 as the cores, uses embeddedμC/OS-â…¡operating system, joined the free TCP/IP stack LwIP to make the terminal measurement, the"network embedded gas sensing measure system"is build at the end of the thesis.