Method of coating a substrate with a particle stabilized foam
A method of coating a substrate with a foam is described. The method comprises: (a) introducing a foam into a substrate comprising a plurality of channels through open ends of the channels at a first end of the substrate; and (b) applying at least one of (i) a vacuum to open ends of the channels at a second end of the substrate and (ii) a pressure to the open ends of the channels at the first end of the substrate; wherein the foam comprises a particulate material, and wherein the foam is particle stabilized.
1. A method of coating a substrate with a foam, wherein the method comprises:
(a) introducing a particle-stabilized, alumina-based foam into a substrate comprising a plurality of channels through open ends of the channels at a first end of the substrate; and
(b) applying at least one member selected from the group consisting of (i) a vacuum to open ends of the channels at a second end of the substrate, wherein the vacuum draws the foam into the substrate through the open ends of the channels at the first end, and (ii) a pressure to the open ends of the channels at the first end of the substrate wherein the pressure pushes or blows the foam into the substrate through the open ends of the channels at the first end,
wherein the substrate is constructed of a material containing at least one of silicon carbide, aluminium nitride, silicon nitride, aluminium titanate, cordierite, mullite, pollucite, a thermet, an Fe—Cr—Al alloy, a Ni—Cr—Al alloy, and a stainless-steel alloy;
wherein the substrate is a honeycomb monolith substrate having a plurality of channels that extend longitudinally along the length of the substrate; and
wherein the foam comprises a particulate material.
2. A method according to claim 1 further comprising the step of (c) drying and/or calcining the substrate containing the particle stabilized foam to obtain a solid foam layer disposed or supported on the substrate.
3. A method according to claim 2 , wherein the solid foam layer comprises an open cell structure.
4. A method according to claim 2 , wherein the solid foam layer has a cell volume, wherein more than 20% of the cell volume is interconnected.
5. A method according to claim 1 , wherein step (a) comprises the steps of (i) holding the substrate substantially vertically and (ii) pushing or injecting the foam into the substrate through the open ends of the channels at the first end.
6. A method according to claim 5 , wherein step (ii) pushing or injecting the foam into the substrate, then this may be (ii) pushing or injecting the foam using a piston.
7. A method according to claim 1 , wherein the foam is obtained by a method comprising the steps of: (i) preparing a suspension of the particulate material in an aqueous medium; and (ii) foaming the suspension by introducing a gas into the suspension to generate a particle-stabilised foam.
8. A method according to claim 7 , wherein step (i) is a step of preparing a suspension of a particulate material in an aqueous medium containing an amphiphile.
9. A method according to claim 1 , wherein step (a) comprises the steps of: (i) locating a containment means on top of the first end of the substrate, (ii) dosing the foam into the containment means.
10. A method according to claim 1 , wherein the particulate material has a median particle size of 1 nm to 50 μm.
11. A method according to claim 1 , wherein the foam contains bubbles having a diameter from 1 μm to 1 mm.
12. A method according to claim 1 wherein step (b) comprises applying a vacuum to open ends of the channels at a second end of the substrate, wherein the vacuum draws the foam into the substrate through the open ends of the channels at the first end.
13. A method according to claim 1 wherein the particulate material is a catalytic material comprising a catalytically active metal supported on a support material.
14. A method according to claim 1 wherein the foam contains bubbles having a diameter from 10 to 300 μm.