| Aluminum alloys have been widely used in aerospace,military,transportation and other fields for their outstanding advantages such as corrosion resistance,low density,high specific strength,excellent mechanical properties and casting performance.Especially in the case of energy shortage,energy conservation has become a technological development trend,and the lightweight manufacturing with aluminum instead of steel has become an important way to save energy.China is the world's largest aluminum producer,but there is still a big gap in high-quality aluminum production with the developed countries.One of the most critical reasons is the control techonology of hydrogen content in alloy melt during the preparation of aluminum alloy materials.The porosities relulted from hydrogen dissolved in molten aluminum will seriously weaken the strength,corrosion resistance and other properties of the material.For the materials with high performance,the measurement of hydrogen content is always inevitable.At present,the widely used hydrogen determination technologies of aluminum melt often have shortcomings such as long testing time,complicated operation,discontinuous detection and low automation level.Therefore,developing a technology with the characteristics of high efficiency,convenience,continious testing and independent intellectual property rights to measure hydrogen contents in aluminum melt is of great significance.In this paper,the method of concentration cell was employed to measure the hydrogen content in aluminium melt,and the high temperature proton conductor material was synthesized,with which many solid state electrolyte tubes were prepared.The on-line continuous hydrogen content measurement sensor with zirconium hydride as the reference electrode was developed subsequently,as well as corresbonding hydrogen probe and analyzer.Finally,on-line continuous determinations of hydrogen contents in various grades of aluminum alloy melt were carried out by the calibrated sensors.The following research results have been achieved in the above research process:The solid phase reaction synthesis of CaZr0.9In0.1O3-? high temperature proton conductor was studied and the effect of calcination temperature on In doping effect of CaZrO3 matrix was systematically analyzed.The results show that the CaZrO3 matrix can be synthesized directly or by means of a CaZr4O9 mesophase step-by-step in the temperature range of 1000 °C –1200 °C.The higher the temperature is,the more obvious the doping effect of In can be achieved in the temperature range of 1200 °C –1400 °C.At 1550 °C.However,the doping effect decreases sharply because of the volatilization of In elements.CaZr0.9In0.1O3-? synthesized at the calcination temperature of 1400 °C for 10 h exhibits the best doping effect and the highest doping phase purity of 98.75 wt.%.The doped CaZrO3 phase is a orthorhombic crystal structure with Pcmn(62)space lattice group.The "U-type" CaZr0.9In0.1O3-? solid state electrolyte tube,which is the core components of the hydrogen sensor,was prepared by the low pressure injection molding method.The rheological properties of the slurry were studied,as well as the influence on mouding process.The results show that,the slurry for mouding is a pseudoplastic fluid characterised with shear thinning properties.critical solid volume fraction of the slurry is about 66.5 vol.% at 70 °C –90 °C and increases slightly by increasing temperature.With the lowest flow activation energy,slurry with a solid volume fraction of 56.4 vol.% is the best candidate for molding.The optimum mouding parameters of the electrolyte tube are: mold temperature of about 35 ° C,packing time of 15 s,injection pressure of 0.55 MPa and The slurry temperature of 80 ° C.After mouding,debinding and sintering,the uniform electrolyte tubes were prepared with an average weight of 1.345 g.Hydrogen sensing performance of the solid electrolyte tube was tested and the influence of reference hydrogen partial pressure on measurement accuracy of the sensor was analyzed.The results show that,in the temperatures range of 500 °C –800 °C,the higher the temperature is,the higher the proton transport number of CaZr0.9In0.1O3-? can be achieved.The material is close to the pure proton conductor at 700 °C –800 °C.Proton transport number of CaZrO3 is significantly lower than that of CaZr0.9In0.1O3-?.The calculation error ? of hydrogen partial pressure at meausrement part,the hydrogen pressure ratio k and the test error ? of electromotive force meet the model of = 1-6).The closer the hydrogen partial pressure of reference part is to that of the measured side,the smaller the calculated error is.The fabrication of the sensor and the preparation of ZrHx reference electrode were investigated,and a Ca-Al-Ba-B-Ox composite oxide glass used for electrolyte tubes encapsulation was developed.The results show that only when the glass sealing temperature matches the hydrogen partial pressure of the encapsulated atmosphere,the synthesized ZrHx can be in the ? and ? phase coexistence zone,in which zone the reference hydrogen partial pressure is only a function of temperature at 700 °C–800 °C.Two kinds of aluminum liquid hydrogen probe are designed and manufactured,which are modular probe and integrated probe.Corresponding aluminum liquid continuous hydrogen analyzer was developed.The modular probe can realize a quick replacement of sensor.With advantages of simple structure,short production cycle and lower cost,the integrated probe is especially suitable for hydrogen measurement with a small amount of aluminum liquid.With various functions such as real-time dynamic displaying of hydrogen content and melt temperature curve,real-time saving of data,and outputing measuremeng report,the hydrogen analyzer is easy to operate and contains an operated software with a good man-machine interface based on PC and a hardware system based on data module.The modified mathematic model of measuring hydrogen content in aluminum liquid was established.The calibration method of sensor was studied,and a testing device for high temperature hydrogen sensor was developed.For a specific sensor,four calibration coefficients in the hydrogen measurement model are calculated from the calibration results.The calibrated internal hydrogen partial pressure of different sensors are in good agreement,and he reference hydrogen partial pressure of snesor is in the ?+? coexistence zone at the testing temperature.The thermodynamic process of phase transition between ?-ZrHx and ?-ZrHx solid solutions has been studied with calibration results.The formation enthalpy is-208.5 kJ·mol-1,and the formation entropy is-0.274 kJ·K-1·mol-1.The response speed of hydrogen sensor is mainly controlled by electrode reaction speed and temperature.The hydrogen contents of pure aluminum,ZL104 and A356.2 melts were continious measured.The results show that the calibrated sensor can accurately measure the hydrogen content in aluminum melt,the sensor is well sealed and the measurement performance is stable.Test error will be increased at a high content of hydrogen in aluminum.When the melt temperature is relatively constant,the continuous measuring results of hydrogen content will not fluctuate greatly.The continuous hydrogen measurement results of the sensor coincide with the results of the first bubble sampling method... |
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