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Abstract

A method and apparatus for applying a dry powder to a porous substrate (10) comprising:

a) locating the porous substrate (10) in a holder (2) such that an inlet face (11) is in communication with an inlet chamber (15) and an outlet face (12) is in communication with a vacuum generator;b) establishing a primary gas flow through the porous substrate (10) using the vacuum generator to apply a pressure reduction to the outlet face (12);c) spraying the dry powder into or within the inlet chamber (15) such that dry powder is entrained in the primary gas flow and passes through the inlet face (11) of the porous substrate (10) to contact a porous structure (13) of the porous substrate (10); 1d) during the spraying of the dry powder directing a secondary gas flow onto and/or across the inlet face of the porous substrate (10); ande) using a pressure and/or a flow rate of the secondary gas flow to control an axial distribution of the dry powder that is deposited in the porous structure (13) of the porous substrate (10).

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