1. What are the types and working principles of oxygen analyzers?
The oxygen analyzers currently on the market mainly use two technologies, namely electrochemical fuel cell and zirconia sensor technology. The working principles of these two technologies are quite different.
1) Electrochemical fuel cell technology:
The working principle of an electrochemical fuel cell is based on oxygen as the positive electrode and metallic lead as the negative electrode, and the electrolyte is potassium hydroxide. The electrolyte and metallic lead are contained in a small solvent-resistant cylindrical container, and the opening is sealed with a polytetrafluoroethylene film. The use of a completely sealed fuel pool oxygen sensor is one of the most advanced oxygen measurement methods in the world. Oxygen diffuses into the battery through the PTFE membrane. When the oxygen gets electrons on the positive electrode and the metal lead loses electrons on the negative electrode, a current is generated. The size of the current is proportional to the oxygen concentration.
The negative electrode reaction formula is: 2Pb -4e-== 2Pb2+ The positive electrode is: O2 + 2H2O + 4e-== 4OH-
Total reaction: O2 + 2H2O+2Pb==2Pb2+4OH
2. Analysis of the advantages and disadvantages of two oxygen analyzers.
1. Electrochemical fuel cell
Advantages: 1) The zero point is accurate, not easy to drift, and only a single point calibration is required; from the chemical reaction formula, it can be seen that when there is no oxygen, there is no current, so the zero point of the electrochemical fuel cell is accurate, and only a single point is required for calibration. Correction.
2) Strong resistance to the influence of organic solvents. Electrochemical fuel cell detection of oxygen is a redox chemical process at room temperature, so it is less affected by a small amount of common organic solvents.
3) The replacement cost is low, only the fuel cell needs to be replaced. When the fuel cell fails and the oxygen analyzer fails, the user only needs to replace the chemical fuel cell in the oxygen analyzer, and the replacement cost is less than one-third of the entire analyzer price.
Disadvantages: 1) Prolonged contact of oxygen analyzer with high concentration oxygen will affect its life. The battery needs to be stored in high-purity inert gas. When the glove box continues to operate normally and there is no misoperation, the analyzer life will be relatively Long, up to more than 1 year. If there is a mistake in the glove box operation and more oxygen enters, the loss of the analyzer will be faster. Moreover, when the analyzer fuel cell is damaged, the oxygen value is generally zero, which is not easy to find.
2) Cannot be used to detect high temperature gas
2. Zirconia sensor
Advantages: 1) The reaction time is fast, and the oxygen concentration can be measured at high temperature, high pressure, and low pressure, such as boiler exhaust, etc.;
2) It can be in contact with air when it is not detected, and can be stored in the air for a long time because the physical properties of the zirconia sensor are stable.
3) The zero point is not easy to deviate. When measuring PPM gas, it is usually calibrated with standard gas; the analyzer measurement value is very accurate, the offset is small, and the detection repeatability is high. It is not what a glove box company said. Air is the reference gas. When detecting 1PPM gas, its concentration difference is more than 200,000 times. It is difficult to accurately detect and needs to be calibrated frequently. It is best to calibrate with a standard gas before each detection.
Disadvantages: 1) Zirconia sensors need to work at high temperatures. When the detection gas contains an organic solvent, the organic solvent will chemically react on the electrode, and the oxygen will react with organic matter and be consumed, making the measured oxygen value higher than the actual value.
2) The zirconia analyzer has a long service life. Generally, it can be used normally for 3 to 5 years in an environment containing organic solvents. The service life of a solvent-free environment can generally reach more than 5 years. The sensor can be replaced if the analyzer is damaged. But the cost is higher.
3. Which oxygen analyzer is more suitable for glove box?
Based on the above analysis, both the zirconia analyzer and the electrochemical fuel cell analyzer are suitable for testing the trace oxygen in the glove box, and each has advantages and disadvantages
What are the concept, purpose, type and characteristics of the glove box?
Glove box usually refers to a kind of equipment used in industrial scientific research and production to provide an anhydrous and oxygen-free environment. This equipment usually has a fully enclosed cavity, which is generally filled with nitrogen, argon, and helium. For inert gas, one or more sides of the cavity are equipped with windows and special gloves, usually with transition chambers, which completely isolate the environment inside and outside the cavity, which can isolate air from entering the cavity and avoid atmospheric pollution in the cavity. The operator can manipulate the materials in the cavity through gloves. Due to the H2O and oxygen permeability of gloves and sealing materials and the H2O and oxygen contained in the operating materials will enter the glove box in a small amount, to maintain a very low H2O and oxygen content in the environment, we usually need materials that strongly absorb H2O and oxygen. The gas purification equipment continuously adsorbs H2O and oxygen molecules in the box. In order to know the H2O and oxygen content of the atmosphere in the glove box, usually an accurate trace H2O and oxygen analyzer is needed to detect the atmosphere in the glove box.
The glove box has many uses:
1) When operating toxic and hazardous materials, the glove box can protect the operator and the environment;
2) When materials in the atmosphere, such as bacteria and dust, can contaminate materials, the glove box can be used to isolate the materials outside the box and protect the materials in the box from pollution;
3) When the moisture, oxygen, nitrogen and other gases in the air can chemically react with a certain material and affect the performance of the material, the glove box can be filled with an inert gas (nitrogen, helium, argon, etc.), and the glove box is It can isolate the air outside the box and protect the materials in the box from being contaminated and destroyed by moisture, oxygen, and even nitrogen in the air.
Classification of inert gas protective glove box:
Usually divided into three types:
1) Vacuum glove box: Before operation, vacuum the entire box body to remove the air in the box completely, and then fill it with high-purity gas for use. Advantages: cheap equipment. Disadvantages: The content of H2O and oxygen impurities is high, usually above 100PPM.
2) Inert gas purging type glove box: Continuously ventilate nitrogen to the glove box, and uninterruptedly purge gas impurities leaking into the glove box out of the glove box. Advantages: cheap equipment. Disadvantages: high operating costs, a large amount of inert gas needs to be consumed. The content of H2O and oxygen impurities is usually above 10PPM.
3) Inert gas circulating purification type glove box: The glove box is equipped with a gas purifier, and the higher purity inert gas in the glove box circulates through the gas purifier uninterruptedly to adsorb the trace H2O oxygen molecules and organic solvents in the inert gas. In the purification material, the atmosphere in the box is ultimately maintained in a high-purity inert gas atmosphere to protect the materials in the glove box. Advantages: low operating cost, low H2O and oxygen content, usually less than 1PPM; including PLC and touch screen, multiple functions. Disadvantages: higher equipment prices.
The third type of inert gas circulating glove box is the most used in scientific research and production, the most widely used, and the best use effect
