The Research Of Sensing Technology On Two-electrode Clark-type Micro Dissolved Oxygen

Dissolved oxygen concentration is one of the most important measurement indexes of water quality detection.The detection of dissolved oxygen is not only widely used in the fields of domestic water,industrial water,wastewater and sewage,but also in environmental science field,biomedical field,aquaculture industry,food service industry,and even in thermal power plants and nuclear power plants which use large boilers as the main equipment,the detection of dissolved oxygen has very important social significance and economic benefits.The concentration of dissolved oxygen in water decreases with the increasing temperature and pressure.Therefore,the dissolved oxygen concentration in water at high temperature and high pressure is minute quantity,and the detection of trace dissolved oxygen a difficult problem at present.In order to improve the stability and detection accuracy of self-made two-electrode Clark-type micro dissolved oxygen sensor on the premise of guaranteeing its original response rate and sensitivity,in this paper,the research objects are the oxygen permeable membrane,the auxiliary electrode and the polarization potential.Using the method of combining theory with experiment,the stability of the sensor is improved,and the sensor can detect the dissolved oxygen concentration with PPB-level.Aiming at the study of oxygen permeable membrane for sensors,in this paper,we design two experiments to test and assess respectively of oxygen permeable membranes with different materials and thickness,consisting of oxygen permeability,thermal contractibility,tensile property and the effects of immersion in liquid chemicals.According to the results of the permeable membranes tests,we analyze the combination properties of these membranes.Compared with polyethylene membrane(PE),poly tetra fluoroethylene membrane(PTFE),fluorinated ethylene propylene membrane(FEP),which are in thickness of 0.03mm,as well as FEP membranes in thickness of 0.045mm,and 0.05mm.We can get the result that FEP membrane in thickness of 0.03mm has the best quality,and use it as an oxygen permeable membrane of self-made sensor.The response rate of the sensor is increased,and the sensor detects PPB-level dissolved oxygen concentration.For the auxiliary electrode of the sensors,firstly,the experimental analysis of the purity of the auxiliary electrode shows that high purity silver material should be used as the auxiliary electrode of the dissolved oxygen sensors.And then,a mathematical relationship between the reaction rates of the working electrode and the auxiliary electrode is derived,and a computational formula for calculating the effective superficial area of electrode contacted with electrolyte is derived.The optimal effective superficial area of the auxiliary electrode contacted with electrolyte is obtained by experiments.When the superficial area of the auxiliary electrode is above area,the detection accuracy of the sensor can be improved.For the polarization potential which is applied between the working electrode and the auxiliary electrode,a function relationship is derived,which is between polarization potential E and two time parameters,one of the parameters is working time t of the sensor,and the other is the time t' that the dissolved oxygen concentration on both sides of the oxygen permeable membrane is balanced.And then a stable polarization period of two-electrode dissolved oxygen sensor is proposed.Though experiments we obtain the stable polarization period is 0-3h.When the sensor works in above period,the detection stability and accuracy of self-made two-electrode sensor can be improved.