Synthesis Of NASICON Solid Material And Fabrication Of CO₂ Sensor

In this paper, solid material of NASICON (sodium super ionicconductor) was synthesized by two sol-gel methods. One choosesnitric acid as dissolution reagent, while the others chooses oxalic acidas chelate reagent. The synthesized procedure and the resulted materialwere characterized by employing FT-IR, TG-DTA, XRD, FE-SEM andAFM. Infrared (IR) spectra of the NASICON xerogel, which wassynthesized by choosing nitric acid as dissolution reagent, and silicaxerogel were analyzed. The result indicates that the other componentsof NASICON were finely dispersed in the silica network with theformation of silica alcogel, and as a result, the tranquilized NASICONsol was formed. While for the other method, which chosen oxalic acidas chelate reagent, Zr4+ ion was complexed with oxalic acid, whichavoided the precipitation of Zr3(PO4)4, and as a result, a moretransparent and steady solution was obtained. It realized short-distanceand uniform component distribution, which decreased sinteringtemperature of the resulted material effectively. The TG-DTA resultsshow that the crystalline phase of NASICON synthesized by choosingnitric acid as dissolution reagent was gradually formed above 750℃,while by choosing oxalic acid as chelate reagent, it would formedabove 600 ℃ . XRD, FE-SEM and AFM results indicate thatNASICON solid material synthesized by choosing nitric acid asdissolution reagent was made of mass solid body which combinedeach other tightly except for little cracks, and there were not largeholes existing in it, suggesting that the resulted material exhibited highdensity. The grain boundaries could be observed clearly which lies intrifurcate structure, and the ellipse and round grains with goodcrystalline and high phase purity are their stability state and combinedtightly with each other. By choosing oxalic acid as chelate reagent, thesintering temperature of NASICON solid material could be decreased100℃, while the resulted material with porous structure has lowerdensity compared with the material synthesized by choosing nitric acidas dissolution reagent. Moreover, FE-SEM results indicate that therewere noodle-like crystals appearing as an impurity of NASICON, andEDAX analyses suggest that the impurity could be identified to beNa3PO4 and its ramification. Further more, the grain boundary was notclear, and the grain size was different. An aggregation of grains 60occurred, and some grains melted to each other resulting in a liquidphase occurred, which decreased the phase purity and crystallinity ofthe resulted material. Impedance spectrum (IS) shows that the conductivity of the materialsynthesized by choosing nitric acid as dissolution reagent increasedwith increasing sintering temperature. A linear Arrhenius plot for thematerial was achieved and the activation energy for total conductivityestimated from it was a little higher, which would decrease withincreasing sintering temperature of the material. Because the contact ofgrain boundaries was weakened with elevating sintering temperature,the conductivity of the material was varied little with the limitchanging range of the resistance of the grain boundaries. So thedescend rate of the resistance of the grain boundaries was decreasewith the environmental working temperature. And hence the activationenergy of the solid material decreased with increasing sinteringtemperature. For the material synthesized by choosing oxalic acid aschelate reagent, the activation of the material sintered at 1000℃ islower than that of the material sintered at 900℃, which resulted fromthe ZrO2 impurity phase and the hydronium NASICON existing in thematerial. Furthermore, the material sintered at lower temperature haslower ionic conductivity. The reason is that the material sintered atlower temperature has low crystallinity, and low crystallinity wouldbring about some structure defects, which hindered the channel pathfor sodium ion and degrad...