Two properties of a standard gas
The uniformity of standard gases is a very important feature. Although all kinds of gases have great fluidity and diffusivity, due to the preparation of standard gases, several components of gases have been successively filled into the high-pressure cylinder, and the molecular weight of each component of the gas is different, as a result, the distribution of gas components in the cylinder is not uniform, and some of them may be stratified. In addition, there exists an equilibrium process of adsorption and desorption between the gas components and the cylinder inner wall, which adversely affects the uniformity of the standard gas components. Because of the above reasons, the preparation of standard gas still needs to adopt a certain blending treatment method to solve the problem of gas uniformity of various components filled into the cylinder. Cylinder rotating rolling method is a fast, simple and effective method to solve standard gas blending. The natural diffusion method can also make the standard correction gas mix evenly, but it takes a long time to reach the uniform state.
Calibration gas stability is also a very important basic feature. The stability of standard gas consists of two aspects: the variation of the standard corrected gas component content with time and the variation of the standard corrected gas component content with pressure. Generally speaking, it takes more than one year to investigate the stability of primary gas standard substances, and more than half a year to investigate the stability of secondary gas standard substances. The validity period of the standard gas, that is, the validity period of the standard calibration gas, can be determined based on the investigation and experiment results. The validity period of the standard calibration gas cannot be arbitrarily given and must be based on the experimental results of stability investigation. It is very important to maintain long-term stability of component content in standard gas. The material and inner wall treatment of standard calibration gas packaging container are the key factors affecting the stability of standard calibration gas