Electrochemical Sensor For Determining The Manganese Content In Molten Iron

Manganese could enhance the strength and wear resistance,change the state of sulfur in steel and thus the hot-shortness could be diminished.In the steelmaking process,Mn is a volatile element in liquid iron and its content varies dramatically.Mn concentration should be determined precisely in the end of the converter smelting or among the fining process,such that proper amount of Fe-Mn alloy could be added to tune the composition,which could also be achieved by smelting reduction of manganese ore.Manganese content in high-quality steel needs to be controlled strictly,currently,as a routine process,manganese in molten iron is sampled by a sublance accompanied with the quantification of oxygen content,and consequently spectrochemical analysis is performed.The exact manganese amount could be accquired,however,the procedure is complex and time-consuming,and expensive device is needed.Accordingly,the development of a technique which could provide the accurate information on the quantity of Mn in molten iron rapidly assumes great importance.The subject of this dissertation is an electrochemical method for determining the manganese level in molten iron.The conventional solid-state reaction method was employed to prepare Zr1-xMgxO2-x(0.06≤x≤0.20)and 8mol%Y2O3-ZrO2(8YSZ)solid electrolytes,while the co-precipitation approach was utilized to synthesize 8mol%MgO-ZrO2(8mol%Mg-PSZ)oxygen ion conductor,a powder slurry imprenation technique and a co-firing method were exploited to deposit MnO auxiliary electrode coating on the 8mol%Mg-PSZ substrate,plug-type and tube-type electrochemical Mn sensors were designed and applied to detect Mn content in steel melts with complicated composition at different temperatres.This work will provide the theoretical and practical basis for the new way of rapid determination of the manganese content in steel melt.Some conclusions are drawn:(1)Zr1-xMxO2-x(0.06≤x≤0.20)solid electrolytes were synthesized by solid state reaction method under diverse sintering conditions.XRD analysis and SEM results show that close-packed coral-like grains exists in all the obtained compact samples.The proportion of cubic solid solution phase rises with increasing sintering temperature,conversely,the amount of monoclinic phase falls with an increase in temperature.When held at sintering temperature for a longer time,the volume of tetragonal phase could be raised and the quantity of monoclinic phase can be reduced.(2)The ionic coductivities measured using the AC impedance spectroscopy,increase with increasing temperature,and because of the decomposition of cubic solid solution,Arrhenius curves of Zr1-xMxO2-x(0.06≤x≤0.09)bend uniformly at 1400℃.8mol%Mg-PSZ sintered at 1600℃ for 5h shows the best electrical property relative to others,the ionic conductivity alters from 1.18×10-2S/cm to 8.03×10-2S/cm in the temperature interval of 1000～1600℃.The relationship between ionic conductivity and temperature over the temperature ranges of 1000～1400℃ and 1400～1600℃ are ln(σT)=11.89-11743.00/T and ln(σT)=6.65-3062.10/T,respectively.(3)The 8YSZ samples prepared under different sintering conditions comprise only cubic solid solution phases,presenting dense microstructures and the elements are distributed homogeneously.The grains grew bigger with an increase in sintering temperature or a longer dwelling time.The ionic conductivities of 8YSZ specimens increase with rising temperatures and the corresponding Arrhenius cures are approximately a straight line,the activation energies change between 0.55 to 0.60eV.The 8YSZ sample sintered at 1600℃ for 5h exhibits the highest ionic conductivity over the measuring temperatures,varying from 1.97×10-2 to 7.26×10-2S/cm,the Arrhenius equation is ln(σT)=8.54-6610.60/T.(4)Co-precipitation was used to prepare 8mol%Mg-PSZ precipitates,the sample sintered at 1600℃ for 5h,composed of monoclinic phase of small size,tetragonal phase and a coral-like cubic phase of relatively large dimension,possesses a dense microstructure.The ionic conductivity increases with temperature,differs from 6.08×10-3 S/cm at 950℃ to 5.36×10-2 S/cm at 1600℃.The activation energy within the temperature range of 950～1350℃ is 1.01eV,while that at the high-temperature interval of 1400～1600℃ is 0.52eV,the corresponding Arrhenius equations are ln(σT)=11.20-11696.69/T and ln(σT)=7.83-59935.70/T,respectively.(5)The powder slurry impregnation process and a co-firing procedure were adopted to fabricate MnO coating,after sintering at 1600℃ for different soaking time,both coarse MnO powder with a particle size of 76μm and fine powder with a granule size of 1.25μm,could be used to achieve compact microstructure and strong adhesion between the coating and the substrate.Additionally,MnO deposited on the substrate retained its initial phase and no oxidation happened after co-firing in an Ar atmosphere.(6)Mn sensors with the MnO auxiliary electrodes were applied to detect the Mn contents in liquid steel,the mean response time was about 3s,the stable electromotive force which could suggest the Mn content lasted about 7s.The electromotive force of the galvanic cell is inversely proportional to the Mn content,and a linear relationship could be found between the measured voltages and the Mn content determind by spectrochemical analysis,under the current experimental condition and within the Mn concentration range of 0.50%-2.15%,a derived equation between the two is E=172.27-40.16 w[Mn].(7)The Henry activity coefficient derived from the relationship between the Mn activities calculated from the measured voltages of the Mn sensors,and the Mn contents obtained from spectrochemical analysis,is 1.56,suggesting the formation of other metal oxides at the interface between the MnO electrode and the steel melts with complicated composition,and thus the MnO activity is less than unity.