Specialised combustion furnace

1 March 2002

AEA Technology has been involved for years in the analysis of hydrogen-3 and carbon-14 isotopes in decommissioning wastes and environmental materials. The company undertakes this analysis by combusting the sample to completion, aided by a suitable catalyst, and selectively trapping the chief combustion products - carbon dioxide and water. The concentration of carbon-14 and tritium in the trapping agents can then be assessed by liquid scintillation counting and thus the tritium and carbon-14 concentrations can be counted.

AEA Technology has joined forces with Carbolite to produce a furnace specifically designed to perform sample combustion. The furnace comprises a silica glass work-tube, which is placed inside a two-zone tube furnace with independent control of each heated zone. The first zone contains the sample in a silica glass combustion boat with a total volume of 20ml. The second zone is occupied by the copper-oxide catalyst.

The second zone is then connected to a series of gas bubblers via a glass exhaust manifold, which is connected to the work-tube by a standard ground glass joint. As well as allowing exhaustion of the combustion gases to the gas bubblers, the arrangement also allows oxygen to be introduced directly to the catalyst through a long stem which passes through the catalyst and introduces the oxygen at right angles to the main carrier gas flow. This ensures optimum operation of the catalyst in an oxygen-rich atmosphere.

The gas bubblers are made entirely of glass and include no plastic or rubber components that can retain contamination. All the components can be removed, cleaned and dried at high temperatures, and as it is not an integral part of the furnace, the sample tube can also be replaced when required.

The furnace has been designed to perform a variety of combustion protocols, which vary according to the flammability of the sample. Up to 16 combustion stages can be controlled by the temperature controller, which can also be linked to a computer, enabling a number of standard combustion protocols to be developed and stored on disk. Several furnaces can be daisy-chained together and linked to a single computer, with each furnace running a different protocol.

While AEA Technology performs the combustion process at 750°C, the furnace will operate above 1000°C.



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