Crystal growth process for preparing inorganic dynamic membranes

DETAILED DESCRIPTION I claim: 1.
The process for forming a composite membrane comprising a porous inorganic substrate and an integral particle porous film directly bound only to one surface of said substrate, said particle porous film being bonded together by crystal growth to form an integral film which comprises depositing a film of said inorganic particles said one surface of said inorganic porous substrate and passing a solution supersaturated with a composition comprising the composition of said inorganic particles through said film thereby to effect crystal growth on said particles until a bonded porous of said particles is formed.
2.
The process of claim 1 wherein the crystal growth is conducted at a temperature of between about 40.
degree.
C.
and 70.
degree.
C.




Description:
BACKGROUND OF THE INVENTION This invention relates to inorganic microporous or ultrafiltration membranes and to a process for preparing such membranes.
Prior to the present invention, two basic processes have been available for the preparation of inorganic membranes.
In both processes, insoluble inorganic particles are first deposited from a slurry onto a porous inorganic substrate.
A layer or film of particles is formed on the substrate surface.
The film is a porous structure resulting from the spaces between the film particles.
Bilayers of different sized inorganic particles can also be used to form the film on a coarse substrate.
The first bilayer comprises relatively large particles while the second layer comprises smaller particles that are too small to be deposited directly on the coarse substrate.
In one process, after the particles have been deposited on the substrate, the particles are first dried and then bonded to each other and to the substrate by sintering.
During sintering, the film of particles are fused together, and may also become fused to the substrate, by partial melting that occurs at the high sintering temperatures that are generally between about 400.
degree.
C.
and 2,000.
degree