Synthesis Of The Proton Conductor By Liquid Phase Reaction And The Research Of Its Application For Hydrogen Sensor

Steel reactors exposed to hydrogen gas at high temperature and high pressure in petroretlning plants and ammonia production plants often suffer from a marked reduction in their mechanical properties, which is well know as hydrogen embrittlement. To develop a kind of realtime and online hydrogen sensor for measuring the hydrogen content in steels at high temperature is a very useful method. One of the promising candidates for the solid electrolyte in such hydrogen sensor used at elevated temperature is MCeO3 (M~Sr, Ba) based ceramics which was found to exhibit appreciable proton conduction under the condition of hydrogen atmosphere. The properties of solid electrolytes have direct relationship with those of the hydrogen sensor. Before our work, the solid electrolytes were often prepared by solid state reaction, which not only coated much time and effort, but also the properties of products were not satisfactory. In this paper, the SrCeO3 and BaCeO3 based ceramics precursors of having exact component were synthesized by coprecipitation method using oxalic acid--aqua ammonia solution (Whose pH value is 6.4) reacting with nitric acid solution of SrCO3, Ce(N03)3 6H20 and Yb203 if the quantity of every ion was excessively modified (Sr: 1.8%, Ba: 1.7%, Ce:3.70/o, Yb:8. 1%). The SrCeO3 dried coprecipitation powder was calcined at 920C for 5h and then the pressed pellets were sintered in air at 1450 0C for 5h. The sintered pellets were pure phase and their relative densities were greater than 95%. However, we didn抰 get BaCeO3 pure sintered pellets because of the volatilization of BaO. The conductivities of doped SrCeO3 sintered pellets have been measured in the temperature range 200桞OO 0C using conductormeter. The effect of the varying concentration of Yb dopant in the range 1-10% was studied. It was found that there is II 2001.2 a proximate linear relationship between dopant concentration and electron conductivity within 2%~~4 00/a. However, to protonic conductivity, there is no such relationship. The results of experiment showed that 5% doped SrCeO3 as solid electrolyte was fit for hydrogen sensor. In this study, using a 5%-Yb-doped SrCeO3 protonic conductor as solid electrolyte, a high temperature hydrogen sensor was constructed and was used to measure the diffusivity and the content of hydrogen permeated through 45# steel at high temperature of 300-500 憕C . Based upon the results of electrochemical measurement and mathematical analysis, a new method--the Inflexion Tangent Approach was proposed to analyse the permeation curves of hydrogen. By means of the Inflexion Tangent Approach, hydrogen diffusivity and content in steel were obtained. By mathematical treatment, the Arrhenius relationship of diffi.tsivity, solubility and permeability with temperature were calculated respectively.