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Factors affecting the stability of calibration gas

(1) The balance of the original standard gas is mainly composed of nitrogen and air. The lower the water content of the gas balance, the higher the stability of the standard concentration of the gas composition.

(2) Pipeline materials (mainly involving valves, pressure reducing valves and pipelines) usually contain highly active and corrosive components. When copper valves and copper vacuum valves are used, they will adsorb standard gas and react to it. Therefore, in order to ensure the stability of concentration, stainless steel valves and pressure reducing valves must be used.

Calibrating gas

(3) Cylinder material: standard cylinders are usually made of aluminum alloy, but there are many aluminum alloy materials with different alloy content and reaction degree of materials in the cylinder. After testing various aluminum alloys in liquid air, 6061 materials are determined to ensure the stability of standard gas most effectively. At present, it is used to fill steel cylinders with liquid gas Cylinder manufacturing process: wire drawing cylinder is used for liquid air This kind of gas cylinder is made of metal at high temperature and is completely formed by stamping die, so the pattern on the inner wall of the gas cylinder is relatively small. Why use this method? This is because if there is a small crack in the inner wall of the cylinder, the water will be absorbed when cleaning the inner wall of the cylinder. The service life of standard gas is generally six months to one year. The dynamic balance between dry gas and water cracks in the cylinder leads to the reaction between water cracks and gas analysis. This also explains why some standard gas concentrations are accurate at the beginning of application, but later become inaccurate. Cleanliness of cylinder inner wall: you may have heard of coated cylinder, which can effectively isolate the gas from the cylinder wall, so as to ensure the stability of standard gas. Liquid air has passed the tests of various technologies At present, the main choice is to passivate the inner wall of the cylinder to ensure the stability of the standard gas. Passivation refers to filling the cylinder with high concentration standard gas (such as high concentration SO2), and then static installation, so that the cylinder wall can absorb saturated SO2, and then filling the cylinder after cleaning, vacuum and drying according to the customer's requirements. At this time, the bottle wall has reached adsorption saturation, so there is no reaction to the gas.

(4) The residual pressure of standard gas cylinder will also affect the stability of standard gas concentration. Each standard gas contains at least two components According to Dalton's law of pressure separation, different pressures are applied to different parts of the cylinder. In the process of natural gas utilization, the fractionation pressure changes with the gradual decrease of pressure Some substances react to pressure When the pressure of different components is different, the chemical equilibrium reaction will move, resulting in the change of component concentration. Therefore, it is recommended to keep the residual pressure of each bottle of standard gas at the level of 3-5 bar.

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