Research On NASICON Material CO₂Sensor And Mobile Phone Measure System

CO2sensor is playing an indispensable role in today’s agricultural and industrial production, household security, and environment monitoring, energy, hygiene and medicine fields. With the development of science and technology, traditional gas sensors have undergone a continuous revolution in terms of usage of new materials; meanwhile, the originally uniquely functioning gas sensors are evolving into intelligent and networked gas sensing systems on account of electronic technology innovation.The research work by the thesis proceeds from the theory of mixed electric potential, with the use of the NASICON material as the conductive layer material by the sol-gel method, has not only succeeded in making the CO2sensor operating at room-temperature but also made a CO2sensor operating at room-temperature with the use of different metal oxides as sensitive electrode materials thus made a further development and breakthrough in solid-electrolyte NASICON sensors.The thesis firstly explained the preparing methods of solid-electrolyte NASICON: Sol-gel Method I with ZrOCl2·8H2O (A.R), NH4OH(A.R),HNO3(A.R),NaNO3(A.R),Si(OC2H5)4)(C.P),C2H5OH)(A.R),(NH4)2HPO4)(A.R) and Sol-gel Method2withZrO(N03)2·2H2O),Si(OC2H5)4),Na3PO4·I2H2O)(A.R),C6H8O7·H2O)(A.R). NASICON materials were prepared respectively by the2methods and underwent XRD, IR, Raman, XPS, SEM and AFM characterization. With the analysis of the material structure, component, granularity and element proportion, we draw the following conclusions:1. NASICON materials prepared by Sol-gel Method I and Sol-gel Method2both have the best sintering conditions at900℃, when the structure is monocline with no other mixed phases and the material surface is dense2. The particle formula calculated by XPS spectrum is Na3.3Zr2.4Si1.5PO12which is remarkably close to our expectation3. Result from the SEM testing of the NASICON material sintered at900℃shows that the NASICON material has a compact structure and materials are closely connected and lumps have no significant inanition. By comparing the results of AFM and SEM, we can find clear boundary among grains, in trigeminal structure and the grains are either round or elliptic. The grains fully grow and remain in a stable status and closely connected with a relatively high cleanliness and phase purity. The experiment has amended the planar structure for the CO2sensor operating at room temperature and made a module with the NASICON material as the base material. The components are the NASICON solid electrolyte as the base, Li2CO3and BaCO3at12mol ratio as sensitive electrode. The sensitive electrode is smeared with silver mesh, and modified by the sputtering of metal oxides and introduced by electrode. Then we observed the surface morphology ofall layers of CO2gas sensor, including the Ag mesh surface, mi sensitive electrode LiiCO3-BaCO3surface, solid-electrolyte NASICON surface and surfaces of different metal oxides sputtered by DC magnetron. By comparing the metal oxide sensitive electrodes and conditions for preparation, we can draw the following conclusions:1. We consider it more reasonable to insert the Ag electrode of the first4lines inside the Li2CO3-BaCO3sensitive electrode than outside2. CO2sensor has the largest output electromotive force when the Ag electrode is decorated inside the metal oxide, sputtering the metal oxide with5%W and95%In and NASICON prepared from ZrOCh by Sol-gel method is used as the solid electrolyte base3. The temperature of sputtering metal oxide at250℃is better than25℃(room temperature) given all the other conditions are identical4. The larger the square of the solid-electrolyte NASICON is, the higher the CO2sensor’s output electromotive force becomes, given the raw materials of the solid-electrolyte NASICON and the sputtering metal oxide conditions are identical5. Given the other sputtering conditions are identical, the longer the sputtering takes, the thicker the metal oxide membrane becomes, the larger the particle size gets and the higher output electromotive force CO2sensor hasIn order to make conventional CO2sensor, the thesis adopts the structure of hollow tube ceramic bottom to make thick-membrane CO2sensor and improves the heater efficiency by inserting micro heater inside the hollow tube. Furthermore, the thesis has succeeded in making the CO2sensor temperature controlling system that is able to set and control up to3CO2sensors simultaneously and independently. The temperature controlling accuracy can satisfy the CO2requirements and has the advantage of low cost and high temperature controlling accuracy.The thesis has designed a’mobile-based gas sensing system’on the MTK.6225mobile developing platform and has combined gas sensors and other environment monitoring sensors to monitor the environment parameters in real time. This terminal can receive orders (short message); send data at definite time (short message) and alarm by sending data. This equipment can not only facilitate the environment monitoring for the mobile user, but also can act as a portable environment sampling equipment and can be easily introduced into Internet of Things to monitor the environment in a large scale.