System and method of anodized aluminum oxide nano-porous membrane preparation

Abstract

A system and method for preparation of nano-porous membrane using anodized aluminium oxide and the membrane/film/thin lamina produced thereof. The system comprises a template forming device that comprises of two rolls provided with one or plurality of projections wherein the Al sheet is passed through the said rolls that are rotatable in opposite direction with respect to each other wherein in operation as the Al sheet is passed through the said rolls, the said projections of the rolls punch depressions to the predetermined depth in the said sheet wherein the depth of the depression is governed by the height of the projections. A method for preparation of anodized aluminum oxide nano-porous membrane comprising electro polishing of Al substrate; first step anodization; chemical etching of alumina; second stage anodization; etching Al for separation of alumina and barrier layer removal or voltage pulse detachment for barrier layer removal and detachment of membrane from Al substrate.

Description

FIELD OF INVENTION[0001]The present invention relates to a system and a method for preparation of nano-porous membrane using anodized aluminium oxide and the membrane / film / thin lamina produced thereof.BACKGROUND OF THE INVENTION[0002]Anodized Aluminum Oxide (AAO) membranes are gaining popularity in the field of sensors, hemodialysis, protein separation, photovoltaics, high density memories, control molecular release, drug release, nano dots, nano rods, nano tubes, and making masks for semiconductors industry. The vital aspects to characterize AAO membrane include pore size, pore depth, inter-pore distance, thickness of membrane and pore geometry.[0003]The method of fabrication of the AAO membrane is reported in the prior art.[0004]U.S. Pat. No. 3,850,762 discloses fabrication of AAO free standing membrane wherein steps include anodizing one side of Al sheet, etching Al substrate for exposing back side of alumina, and then etching of barrier layer (BL) for making AAO membrane. The O-...

AI Technical Summary

Benefits of technology

[0041]Yet another object of the invention is to provide a simple method, preferably single stage method obviating number of complex steps;

[0042]Yet another object of the invention is to provide a method to substantially reduce Al substrate wastage.

Problems solved by technology

However, these methods suffer from the drawback that the area of AAO free standing membrane actually produced is substantially lower than that of Al sheet used for fabrication leading to wastage of material.

If 99.999% pure Al is used in the fabrication of AAO membrane then wastage of material cause vital problem.

The 99.999% pure Al is much expensive leading to increasing the cost of the membrane.

However, the limitation is that two extra steps of depositing insulting layer and then again removing this layer are required.

The limitation of the above mentioned methods result in fabrication of AAO plane membrane in one piece at a time.

It is necessary to have plurality of setups for fabrication of number of membrane pieces leading to substantially increasing production and process cost.

This process can only be used for the manufacture of centimeter and / or millimeter size tubular membrane.

However, this process is not appropriate for the manufacture of tubular membranes in micrometer and below size.

It is a challenge to make Al tube in small size, covering and uncovering the outer surface for different steps, blocking the two ends to protect AAO from inside during etching process and again opening the two ends to give final shape.

However this imposes serious limitation in case of nanostructure membranes.

One of the challenges in the development of aluminum oxide membrane is the issue of cracks that occur during the conversion of alumina from aluminum by virtue of ion exchange process.

Cracks inside AAO normally occur due to rapid growth of AAO as in hard anodization.

Another type of cracks occurs at the edges wherein aluminum (Al) surfaces are substantially perpendicular to each other.

These cracks are due to volume expansion when Al is converted into AAO.

This type of cracks made obstacles in preparation of AAO 3D membranes.

However, this method suffers disadvantage due to the lack of development of the shaping aspect of Al and relevant production mass production process.

The methods provided in prior art suffer from following limitations:Substantially reduced area of AAO free standing membrane produced from available Al sheet used for fabrication leading to wastage of material and reduced productivity;Need to insulate Al from any side in the electrolyte solution or cutting any surface mechanically;Necessity of two extra steps of depositing insulting layer and then again removing this layer;It is necessary to have plurality of setups for fabrication of number of membrane pieces leading to substantially increasing production and process cost.There is need to develop a method to fabricated plurality of membranes at the same time out of a single Al sheet or blockOnly single surface anodization of the substrate (rectangular or square) and removal of entire substrate leading to material waste, increase in specific energy consumption, substantially reduced productivity, posing limitation on scaling of the process / productionLack of utilization of all the surfaces of the substrate to form the membrane;Need of Al solid cylinder to manufacture tubular membrane,Lack of flexibility and possibility to manufacture tubular member from rectangular / square, circular geometry substrate;Lack of flexibility and possibility to manufacture tubular as well as laminar membrane from the same rectangular / square substrate.

Images