Thermodynamics of Refractory Powder Passivation Surface Oxide Reduction
Controlling oxygen partial pressure and furnace dew point during thermal reduction strips surface oxides without triggering particle necking or tap density loss.
Gas Phase Deoxidation
Meaning
Measured against the residual oxygen content of a metal powder, this thermal treatment process removes impurities by exposing the material to a reactive gas at high temperatures. During gas phase deoxidation, the reducing agent reacts with surface or internal oxides to form a volatile byproduct that is carried away by the gas stream. This method is essential for producing high performance titanium or niobium powders where residual oxygen embrittles the final product.
Surface Interaction
The effectiveness of gas phase deoxidation depends on the ability of the gas to reach the oxide sites and the rate at which the byproduct leaves the surface. Higher temperatures increase the diffusion rate of oxygen from the bulk of the material to the surface where the reaction occurs.
Atmosphere Control
Pure hydrogen or calcium vapor is frequently employed in gas phase deoxidation to ensure a high chemical driving force for the removal of oxygen. Maintaining a low dew point in the furnace prevents the re-oxidation of the cleaned metal surfaces.
Material Purity
Removing oxygen through gas phase deoxidation improves the ductility and electrical conductivity of the metal. Producers measure the success of the process by analyzing the parts per million of oxygen remaining in the substrate after treatment.