Quick guide: Specialty Practice (1)

Special applications – for example the calibra- Using Mixtures: tion and adjustment of measuring equipment or scientific experiments – require precisely deter- Handling, Connection, mined gases. The test and reference gases re- quired may be available for many applications in what are known as standard mixtures. However, Special Cases. for very special applications, individual gas com- positions are also often developed. A gas mixture is defined by its basic gas, the admixture(s) and data on concentration or substance amounts. To ensure user safety, various aspects need to be considered in the handling of gas mixtures:

Transport and storage. Individual gas compositions tend to segregate at low temperatures. Accordingly Westfalen cer- tificates state the minimum storage temperature to be observed as from the point of delivery. Adherence to this specification ensures the qual- ity of the gas mixture both during storage and during further internal handling.

Please observe the minimum storage temperatures: +5 °C when filling in summer, -10 °C when filling in winter.

5°C 0 -10 °C From gas store to point of use. • For reactive gas mixtures, interactions occur Many gas stores are in the open; the contain- between the moisture and reactive compo- ers stored here assume the applicable ambient nents of the mixture. That produces a reduc- temperature. However, if the point of use is con- tion of the desired and certified concentration. siderably warmer than the storage area, conden- sation from moisture in the air may form on the Example reactions: cylinder surface and the cylinder valve. Critical SO2 + H2O ⇐⇒ H2SO3 here is the possible build-up of moisture inside 2 NO + 2 H2O ⇐⇒ 2 HNO2 + H2 the valve: COS + H2O ⇐⇒ H2S + CO2

• For inert, non-reactive gases, this moisture is To prevent such interactions, Westfalen as a pushed into the pressure regulator and so into matter of principle supplies reactive mixtures the pipe system of the gas supply device – with cap nuts on the cylinder valves. To avoid resulting in contamination. condensation inside the valve we recommend removing the cap nut only after the cylinder Example: temperature has equalised to the ambient  6.0 (purity 99.9999 % by volume) has a conditions at the location where it is to be maximum moisture content of 0.5 ppm by used. Immediately afterward, the pressure volume. Reckoned against the content of a 50 regulator should be connected. litre cylinder, that results in a permitted mois- After disconnecting the pressure regulator, the ture content of maximum four milligrams. cap nut must be re-fitted. Highly concentrated That corresponds to about one tenth of a drop reactive mixtures may otherwise corrode the of water. Were only one drop of condensation inside of the valve. water to get into the gas supply device, gas quality would be drastically reduced with regard to moisture content. In order to remedy such contamination, extensive rinsing of the entire supply system is required – in the quoted example using purity 6.0 argon.

Correct handling of gas mixtures protects against moisture (left) and corrosion (right) within the cylinder valve.

1.0/09 The pressure regulators employed must be suitable for the gas mixture in use. We would be pleased to advise you.

Tapping of gas mixtures. Know-how for practitioners. To tap gas mixtures, suitable systems – For further questions on handling gas pressure regulator and suitable hoses or pipes – mixtures or on our product range, Westfalen's are required: Specialty Gases experts are at your disposal at any time. Use our personal consultation! • Pressure regulators are mostly made of brass or stainless steel. For mixtures in the ppm- We would also be happy to send you previous range and reactive gas compositions we publications in the “Specialty Gases Practice” recommend stainless steel designs. Generally, range: different pressure regulators should be used for acidic and alkaline mixtures. • Specialty Gases Practice (2) – Gases in the • Pressure regulators should be rinsed with inert Laboratory: Risk Factor Tube Material. gas before use and should be dry. • Specialty Gases Practice (3) – Accredited Test • In the universal use of pressure regulators and Calibration Laboratory: The Westfalen intensive rinsing between uses is required as Specialty Gases Centre. applicable. This is particularly the case if acidic • Specialty Gases Practice (4) – Nuclear Species: and base mixtures are used alternately. Isotopes. • Specialty Gases Practice (5) – Precious Droplets: Cyclic pressure rinsing. . After connecting the atmospheric air or other unwanted gases will still remain in the pressure regulator, which can be reliably removed using so-called cyclic pressure rinsing. To do this, the cylinder valve is turned with the pressure regulator open, until the gauge displays the current cylinder pressure. By immediately closing the cylinder valve, the impurities now escape. Shortly before the gauge again shows ambient pressure, reopening the cylinder valve again increases the pressure in the equipment and so on ... To eliminate contamination by impurities we recommend repeating cyclic pressure rinsing up to ten times.

1.0/09 Phone Leobersdorf 2544 323 21/TOP Aumühlweg GmbH Austria Westfalen Fax info@westfalen-.fr www.westfalen-france.fr Fax Phone France Rosselange 57780 Fontaine Belle d‘Activités Parc S.à.r.l. France Westfalen [email protected] www.westfalen.at [email protected] www.westfalen-ag.de Fax Phone Münster 48155 43 Industrieweg AG Westfalen

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