Oxidizing melting

Treatment of the melt in an oxygen-containing furnace atmosphere.

In this process, an oxidizing flame, i.e. combustion with excess oxygen, is set in fuelled furnaces. The oxygen in the exhaust gases inevitably reacts with the respective melt. This results in oxide formation (see Oxidation) and slagging or gasification (see Slag).

The hydrogen has to be generally removed from the melt of copper and copper alloys as it is contained in the melt in dissolved form and would be diffused as blisters during solidification (Gas porosity, Gas blister). Thus, the dissolved hydrogen is oxidized during oxidizing melting.

With respect to the degree of oxygen affinity of the respective alloy, the oxygen added to the liquid metal of copper alloys forms first a metal oxide (see Affinity) and also reduces afterwards metal oxides. For this reason, oxidizing melting can be used for degassing of copper alloys. The oxygen charge causes formation of copper(I) oxide which is reduced by the dissolved hydrogen and forms vapor (Eq. 1).

Eq. 1:

The reaction is reversible, i.e. increasing oxygen content leads to higher oxidation and respectively to the removal of more hydrogen.

The most common processes for oxidation of the melt include oxidizing flames (excessive air) and addition of oxygen-emitting cleaners that are added onto the molten bath and simultaneously form a slag cover.

Additional references:
Non-oxidizing melting
Degree of oxidation