Stability and SPECTRA-SEAL

The SPECTRA-SEAL treatment process enhances the cylinder's interior aluminium surface, rendering it chemically inert.

The mixture must remain stable over time, during the changing pressure range of the cylinder as it is used and throughout the temperature range to which the cylinder will be exposed in normal operation.

Normally gas mixtures remain homogenous and stable once mixed.  In certain cases, where easily liquefiable components are included in the mixture, exposure of the cylinder to temperatures of less than 10°C may affect the composition of the mixture in use.

Customers who have a concern about this or any other stability queries should speak to BOC Technical Services by calling 1800 355 255.

All BOC quotations will include the guaranteed stability or 'shelf life' of the product.

Many of the products in our range will have a 5 year 'shelf life'. 

Any Alpha Volumetric, Alpha Gravimetric, or SPECTRA-SEAL products will automatically have a 5 year stability period unless otherwise stated.

When reactive gases such as oxides of nitrogen, sulphur dioxide, carbon monoxide, volatile organic compounds (VOCs) and sulphides are blended at low concentration in an inert balance gas, instability within the cylinder can become a problem.

Cylinder treatment techniques which allow reactive gases to be made stable in mixtures were pioneered by BOC in the US over 20 years ago.  Since then we have remained at the forefront of developing this technology.

Parts per billion mixtures of sulphur dioxide in air are now routine and parts per trillion mixtures of some components have been developed.

Gas mixtures supplied with a SPECTRA-SEAL stability assurance have undergone a rigorous cylinder treatment process followed by a controlled filling and mixing operation and an extensive analytical procedure.  They have also been evaluated and accepted by BOC and independent laboratories to confirm long term stability.

The cylinder's interior aluminium surface is enhanced by a special treatment which renders it chemically inert.

A second proprietary process converts this passivation layer into a smooth, non-reactive, tightly adherent surface, with negligible adsorptive properties.

This processing removes all contamination, which ranges from moisture to traces of the oils used during the cylinder manufacturing process and removes sites which could catalyse the reaction of components with each other or the cylinder.

As a result, BOC-certified cylinder gas mixtures meet their original certification, both in storage and during use.

Special treatment renders the internal cylinder surface chemically inert.  Passivated surface limits the cylinder's potential for adsorption/desorption and is non-catalytic.

Stability of low ppm reactive gas mixtures contained in BOC SPECTRA-SEAL aluminium cylinders.

The flexibility and effectiveness of this process can be judged from the variety of mixture cylinders that are treated in this way and the uses to which those mixtures are put.

There are cylinders in-use, treated with SPECTRA-SEAL, providing calibration for the major motor manufacturer's exhaust emission tests.  BOC are also very proud to publicise that a SPECTRA-SEAL treated cylinder was even used on the moon, taken by NASA during one of its missions, for calibrating one of the lunar instruments.