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The specialty gas production technology enables to add ingredients both in gaseous and liquid phase at normal conditions.
High purity gases or liquids are used for the calibration gas preparation.
On customer’s requests, calibration gases may contain one or more components in concentrations that start from units of ppb up to the level of percents.
Experience of the Linde company reaches to more than 400 types of pure gases or liquids that are used as ingredients.
In practice, the gas mixture preparation is subject to various limitations which follow from physical and chemical properties, safety rules, etc. For example, filling pressure reduction may be unavoidable by filling of mixtures which contain ingredients in the form of vaporised liquids,
Our customer may rely on the long-term experience of the Linde Gas company in cases when it is neccesary to decide about the feasibility of requested mixture.
Package and valve selection
Preferentially, pressure vessels (pressure cylinders) from steel or alumina alloys are used in the Linde Gas company; in exceptional cases, high-grade steel vessels are used.
The internal cylinder surface is treated by various methods, e.g. passivation, when needed.
Cylinders for calibration gases are thoroughly cleaned before the filling; they are rinsed by gas and evacuated, in some cases evacuated with heating. Traces of gas, vapours, and, mainly, traces of humidity are removed by this procedure to a level that lies under the determination limit. Cylinder valves are produced from brass or stainless steel, according to the material suitability for the specified gas mixture. From the constructional point of view, mainly membrane valves are used. The reduction valve connections meet the valid standards.
Mainly a gravimetric filling method is used for the gaseous mixture preparation,. Owing to the modern scale utilisation followed by checking of the composition at the up-to-date analytical devices, this method ensures a very narrow production allowance range of the prepared mixtures.
After the filling, the gas mixture is homogenized. It has been proven both by theoretical analyses and frequent tests that the homogenized mixtures do not separate any more. Nevertheless, this principle is valid only if the recommended storage conditions are not broken.
The mixture stability interval is a period in which the mixture composition (related to the individual components concentration) changes in the range of analytical uncertainty specified on the certificate only. The reason of the time-dependent stability loss are chemical reactions of components with the cylinder material, adsorption on the internal cylinder surface, changes caused by the non-adherence to the recommended storage temperature, etc.