DE3833525A1 - Pressure reducer for withdrawing test gases with reactive components - Google Patents

Abstract

In the use of commercially available pressure reducers for withdrawing test-gas mixtures with reactive components, sufficient stability of the mixture composition is not guaranteed, particularly in the case of exacting requirements, since interactions take place between the flowing gas and the gas-conducting parts of the pressure reducer. In order to avoid these interactions, the gas-conducting parts are provided with a coat of nickel. This coat preferably consists of a chemically applied base layer and an electrochemically deposited covering layer thereon.

Description

The invention relates to a pressure reducer for removal of test gases with reactive components such as HCl, Cl₂, HF, F₂, BCl₃ and SF₄.

Such test gases are often used as calibration standards for analysis equipment use, e.g. B. in environmental analysis. This requires a high mixture consistency, i. H., The user must have the test gas mixture in the same composition can remove from the pressure vessels, with which it was certified by the manufacturer. In the gas analytical laboratories of trace analysis it is preferable to use needle valves to remove the Test gas mixtures. These show due to their low dead volume only low absorption properties and are easy to clean. Therefore, they influence  the constancy of the mixture when the test gas mixture is withdrawn not or only insignificantly.

However, the regulatory authorities are demanding for reasons of Operational safety and easy handling as well better constant gas throughput of pressure reducers instead of the less safe needle valves. For extreme stability requirements of the test gas mixtures in the concentration ranges between ppb and 0.5 vol .-% are found in the trade available pressure reducer as completely unsatisfactory, because of the interaction between the flowing Test gas mixture and the inner wall and other inner Share the pressure reducer the composition of the extracted mixture is changed and no longer the composition certified by the manufacturer having. This includes pressure reducers from the Materials copper, steel, austenitic steel, Brass and nickel-copper alloys, for example the one known under the protected name Monel Alloy. These materials form with the aggressive ones Components of the test gas machine already in presence poorly soluble salts from slight traces of moisture, such as chlorides, fluorides and oxides. These salts influence the composition of the test gas mixture extraordinarily strong. The removal of this Salt residues are mechanical or possible with acids, but does not lead to a solution the actual problem, the mixture constancy also with extreme requirements under all operating conditions to guarantee. Have different examinations demonstrated that extreme demands on the consistency of the mixture and reproducibility in use commercially available pressure reducers are not met can.

The invention is therefore based on the object  a pressure reducer for taking test gas mixtures with reactive components in the trace area, which is the highest level of mixture stability and reproducibility guaranteed the gas composition.

Starting from that considered in the preamble of claim 1 This object is the state of the art according to the invention solved with those in the characterizing part of claim 1 specified features. Beneficial Further developments of the invention are in the subclaims specified.

The invention enables inexpensive, commercially available Pressure reducer z. B. made of brass also for removal of test gas mixtures with reactive additives extreme demands on the stability of the mixture to use by the inner surface, the mechanical Internal parts and possibly a purge gas device the pressure reducer protected with a nickel layer becomes. One delivers particularly good results Nickel plating made from a chemically applied Base layer and an electrochemically deposited thereon Cover layer exists. This gives you a pore-tight nickel coating without phosphor inclusions, which have no protection against chemical attacks would offer. Chemically applied nickel phosphorus Alloys to protect against wear and corrosion are also known for fittings.

The pressure reducer according to the invention enables Test gas mixtures with reactive components with extreme Take accuracy and the composition of the Ensure mixtures over the entire withdrawal. The advantages of the invention and that achieved by it Progress is made from the examples below  can be seen, which are explained using tables.

In these examples, the influence was different Tapping valves on the analysis accuracy of a Test gas mixture with a reactive admixture in the Comparison compared to the pressure reducer according to the invention. A PTFE tube from 10 cm length used for the connection to the analyzer. Test gas mixtures of nitrogen and a reactive admixture, namely 11 ppm HCl, 16.6 ppm HF, 0.124 ppm SO₂ and 98 ppm BCl₃. The one for the Measurements used analyzer worked on the basis the electrical conductivity measurement of the reaction solution. It usually needed due to long reaction routes a response time of 10 to 25 min.

Table 1

Test gas mixture of 11 ppm HCl in nitrogen

Table 2

Test gas mixture of 16.6 ppm HF in nitrogen

Table 3

Test gas mixtures from 0.124 ppm SO₂ in synthetic air

Table 4

Gas mixture of 98 ppm BCl₃ in nitrogen

From Tables 1-4 it can be seen that the invention pressure regulator with a nickel coating no interaction with the reactive additives shows. So now it is with the help of the invention Pressure reducer possible, test gas mixtures with reactive components with extreme accuracy reproducible over a short sampling time. Because of the short removal time, the removal is not only very precisely, but also very economically.

Claims (4)

1. Pressure reducer for the removal of test gases with reactive components, characterized in that the gas-carrying inner parts and the inner surface of the pressure reducer are provided with a nickel coating. 2. Pressure reducer according to claim 1, characterized, that the nickel plating from a chemically applied Base layer and an electrochemical layer on top of it deposited top layer. 3. Pressure reducer according to claim 1 or 2, characterized, that it is made of brass, copper, steel, austenitic steel and / or Monel® is. 4. Use of a pressure reducer according to one of the Claims 1 to 3 for the removal of test gas mixtures, which are added as chlorine, hydrogen chloride, fluorine, Hydrogen fluoride, boron trichloride, sulfur tetrafluoride, Ammonia, phosgene, boron trifluoride, cyanogen chloride or contain dicyan.