preface

    A reference substance is "a substance or material that is uniform enough and has been well defined for the purpose of calibrating an instrument, evaluating a measurement method, or determining the quantity of a substance." Standard gas is a gas standard substance, and its stability is a key problem in the process of preparation and use because it has a certain period of validity.

       It is well known that an important condition of standard gases in high-pressure containers (cylinders) is that their magnitude should not change during storage and use. In fact, when the component gas or impure substance in the standard gas contacts with the inner wall of the container, it often causes the phenomenon of adsorption, desorption, chemical reaction and so on, and causes its quantity value to change with the time, when the content is lower, the composition is more complex, this kind of change is bigger.

○ The stability of standard gas is studied as follows:

●  Factors influencing stability

      The stability of standard gas is closely related to the material properties of the container, the pretreatment of the inner wall of the container, the chemical properties of the gas itself and the conditions of use.

●  Container selection

      Containers containing standard gases should be made of materials with corrosion resistance, pressure resistance, less adsorption, no rust, stable chemical characteristics, high mechanical strength, usually used for high pressure containers is aluminum alloy bottles, and carbon steel bottles because of its inner wall is not smooth, large adsorption and has been phased out.

●  pretreatment

      Cylinders containing standard gas should be cleaned and painted before use, and then heated to about 100 ℃ and vacuumed for about 4 h. After the cylinder is processed, the content of H2O, O2 and other impurities must be analyzed and qualified before use.

Calibration gas is widely used in industry for its stability

Properties of standard gases —— Stability（Ⅱ）