Tantalum reaction layer from

The CVD reactor consists of a vitreous silica tube of about 20 cm in diameter (8") and a height of 30.5 cm (1 ft). The filament was made from tantalum wire with 0.5 mm diameter and attached to water-cooled copper electrodes. Heat treatment in a methane atmosphere produces a thin layer of tantalum carbide that protects the sample from contamination with metallic tantalum. A gas-leaking unit allows the introduction of various gases and their mixtures into the reaction chamber under controlled pressure. Before introducing or changing the gas the unit s internal pressure was reduced by a mechanical pump to about 0.1 Pa. 

Hydrogen peroxide is produced in various enzymatic reactions, and its determination is the basis for a number of assay methods. A direct ECL method is based on the use of tantalum or zirconium electrodes covered with a terbium(III)-doped oxide layer. Light with the typical emission spectrum of terbium(III) is emitted from the surface of the electrode in the presence of hydrogen peroxide. 

At the oxide/solution interface, one may visualize the reaction as occurring by tantalum ions popping out and capturing O" from species in the solution, or suppose that O" ions enter the oxide and the reaction occurs in some sort of transition layer in the oxide surface. 

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