Sinter Bonded Porous Metallic Coatings
A composite structure includes a substrate with pores of a first mean pore size and a coating on at least one surface of that substrate. This coating has pores of a second mean pore size where the first mean pore size is equal to or greater than said second mean pore size. When the pore size of the coating is effective to capture particulate greater than 0.2 micron, the composite may be formed into a filter effective to remove microbes from a fluid medium. One method to form the porous coating on the substrate includes the steps of: (a) forming a suspension of sinterable particles in a carrier fluid and containing the suspension in a reservoir; (b) maintaining the suspension by agitation in the reservoir; (c) immersing the substrate in the reservoir; (c) applying a first coating of the suspension to the substrate; (d) removing the substrate with the applied first coating from the reservoir; and (e) sintering the sinterable particles to the substrate thereby forming a coated substrate.
1 . A composite structure, comprising:
a substrate having pores with a first mean pore size; and
a coating on at least one surface of said substrate, said coating having pores with a second mean pore size wherein said first mean pore size is equal to or greater than said second mean pore size.
2 . The composite structure of claim 1 wherein said substrate is selected from materials having a Media Grade of between 0.2 and 5.
3 . The composite structure of claim 2 wherein said second mean pore size is less than 0.2 micron.
4 . The composite structure of claim 3 wherein said coating pores are effective to capture particulate greater than 0.2 micron.
5 . The composite structure of claim 4 wherein said coating has a thickness of from 20 microns to 250 microns.
6 . The composite structure of claim 5 wherein said coating has a thickness of from 30 microns to 75 microns.
7 . The composite structure of claim 4 wherein said coating if a mass of particles having an average particle size of 50 nanometers to 350 nanometers.
8 . The composite structure of claim 7 wherein said coating if a mass of particles having an average particle size of 60 nanometers to 200 nanometers.
9 . The composite structure of claim 7 wherein said substrate and said mass of particles are both predominantly stainless steel.
10 . The composite structure of claim 7 wherein said substrate and said mass of particles are both predominantly titanium.
11 . The composite structure of claim 7 wherein said substrate and said mass of particles are sintered.
12 . The composite structure of claim 11 formed into a filter effective to remove microbes from a fluid medium.
13 . The composite structure of claim 12 formed into a flat disk.
14 . The composite structure of claim 13 formed into a tube.
15 . The composite structure of claim 14 wherein said coating is on an outward facing surface of said tube.
16 . A method for forming a porous coating on a substrate, comprising the steps of:
(a) forming a suspension of sinterable particles in a carrier fluid and containing said suspension in a reservoir;
(b) maintaining said suspension by agitation in said reservoir;
(c) immersing said substrate in said reservoir;
(c) applying a first coating of said suspension to said substrate;
(d) removing said substrate with applied first coating from said reservoir; and
(e) sintering said sinterable particles to said substrate thereby forming a coated substrate.
17 . The method of claim 16 including forming said substrate as a tube having an interior bore and applying a vacuum to said interior bore during said applying step.
18 . The method of claim 17 including applying ultrasonic energy to said suspension.
19 . The method of claim 18 wherein a ratio of said sinterable particles to said carrier fluid in said suspension is less than or equal to 15 grams of sinterable particles to 1 liter of carrier fluid.
20 . The method of claim 18 wherein said first coating has a thickness of about 10 to 25 microns, whereby shrinkage cracks during step (e) are avoided.