Title of Invention	NANO POWDERS BY ELECTROLYTIC OXIDATION OF ALUMINUM TO GAMMA-ALUMINA (NEO-ALUMINA)
Abstract	1. A process for the preparation of nanopowders by electrolytic oxidation of aluminum to alumina (neo-alumina) comprising the steps of setting up a commercially pure aluminum sheet of size 107 x 70 x 2 mm3 as an anode and a s"tainless steel sheet of size 107 x 70 x 2 mm as a cathode; the electrolysis being carried out in an electrolyte consisting of a solution of NaCl in distilled water; ensuring a continuous supply of air during the process by an aerator connected to an air pump located between cathode and anode; and regulating the voltage and current density by a dc power supply, the voltage range being 10-40V and current densities range being 1x10" to 3.3x10" A cm" .

Title of Invention

NANO POWDERS BY ELECTROLYTIC OXIDATION OF ALUMINUM TO GAMMA-ALUMINA (NEO-ALUMINA)

Abstract

1. A process for the preparation of nanopowders by electrolytic oxidation of aluminum to alumina (neo-alumina) comprising the steps of setting up a commercially pure aluminum sheet of size 107 x 70 x 2 mm3 as an anode and a s"tainless steel sheet of size 107 x 70 x 2 mm as a cathode; the electrolysis being carried out in an electrolyte consisting of a solution of NaCl in distilled water; ensuring a continuous supply of air during the process by an aerator connected to an air pump located between cathode and anode; and regulating the voltage and current density by a dc power supply, the voltage range being 10-40V and current densities range being 1x10" to 3.3x10" A cm" .

Full Text	This invention relates to a process and device for preparation of nanopowders by electrolytic oxidation of aluminum to alumina (neo-alumina). In particular, this invention relates to simple and inexpensive means of synthesizing high quality nanocrystalline Alumina (AI2O3) particles, A pure aluminum sheet as initial raw material, an inert electrode, an electrolytic bath using an aqueous solution as electrolyte with a DC power supply and an aerator constitutes the complete set-up. The Aluminum Hydroxide produced by this invention can be transformed to the nanocrystalline Alumina powder, which is essentially strain-free and below 20 nm in size. It is possible to control the crystallite size by varying the parameters involved. This invention finds wide and varied industrial applications as catalysts in automobile and petroleum industries, soft abrasives, sensors, coatings, substrates for electronics and opto¬electronics application, composites, among others The process proposed herein is inexpensive in ternis of initial investment and running cost. In the as-synthesized condition it is hydrated alumina that transforms on heating to y-alumina at a temperature of 450°C. By changing the process parameters such as voltage, current density, electrolyte concentration and position of aerator,' it is possible to regulate the particle size. Corundum that is a-Al203 is the thermodynamically stable phase of alumina under normal temperature and pressure. In the nano-size regime Y-AI2O3 is more stable because of its lower surface energy. Y-AI2O3 is a functionally important oxide ceramic material. Owing to its high temperature stability and lesser tendency for grain growth as compared to a-Al203, it is used in several industries including automobile industries, as soft abrasives, substrates in electronic industries among others. y-Al203 is mainly produced by thermal decomposition 'of boehmite (a major constituent of bauxite) and by sol-gel methods . The process proposed herein relates to a synthesis of nano particles of y-Al203 ' by an electrochemical process that offers greater control of particle size by varying the process parameters. As stated above, on an industrial scale Y-AI2O3 is produced by thermal decomposition of boehmite and to some extent by sol-gel routes. In both these methods it is not possible to precisely control the particle size of the synthesized compound, which is a major drawback in the era of tailored materials. In the process proposed herein an oxidative electrodeposition technique for the synthesis of nanoparticles of y-Al203 is proposed. The process proposed herein will now be described with reference.to the accompanying drawings which illustrate by way of example, and not by way of limitation, in Fig.l one of possible embodiments of the procedural apparatus consisting of of an electrolytic bath, an aerator, a metallic anode plate, a stainless steel cathode plate and a DC power supply Fig. 2 illustrates the X-ray diffractogram (XRD) of sample prepared at 40 Volts (a) as-synthesised (b) calcined at 450 degree C.alumina powder as well as the powders dried at different temperatures Fig.3 illustrates variation of the crystallite size with the applied vohage (at an electrolyte concentration of 3 g/1 of NaCl) Fig. 4 illustrates variation of the crystallite size with the current density (at an electrolyte concentration of 3 g/1 of NaCl) Fig. 5 illustrates variation of the crystallite size with he salt (NaCl) concentration in electrolyte. The following conditions/parameters are maintained: • A commercially pure aluminium sheet of size 107 x 70 X 2 mm^ is used as anode and a stainless steel sheet of size 107 x 70 x 2 mm^ is used as cathode. • The electrolyte used is essentially a solution of NaCl in distilled water. • The aerator, which is connected to a small air pump, is used between cathode and anode to ensure the continuous supply of air during the synthesis process. • The voltage and current density are regulated using the DC power supply. The voltage range used is 10-40V and current densities range from 1x10'"^ to 3.3x10'^ A cm"l The deposited powder is fdtered using a Whatman filter paper, washed thoroughly with distilled water and dried at a fixed temperature. The X-ray diffractogram (XRD) of as-synthesised alumina powder as well as the powders dried at different temperatures are presented as Figure 2. Absence of distinct peaks in the XRD of as synthesized sample indicates its amorphous nature. XRD of sample calcined at 450^C shows distinct peaks that indicate improved crystallinity. Presence of peaks at 45.8° and 66.9° confirms the presence of Y-AI2O3 (on comparison with standard JCPDS tables). The broad peaks in the diffractogram clearly indicate nanocrystalline nature of the deposited powders. Crystallite sizes are calculated from the peak broadening using the Scherrer formula . Table 1 gives the variation of the crystallite sizes (obtained after calcining at 450°C) with the process parameters (current and voltage). The following aspects may be noted:: • The finest crystallite size (3 nm) was obtained at operating conditions of lOV and 3 g/1 NaCl concentration and also at 40 V and 1 g/1 • The maximum' production rates of 20 g/day were obtained at 40V and 3 g/1 NaCl concentration resulting in a crystallite size of 3 nm. • In general the aerator is positioned midway between the anode and cathode, but it is found that the position of the aerator in the proximity of the anode or cathode also influences the crystallite size. The following salient features of this invention may be emphasized A novel process and experimental set-up for the synthesis of nanopowders of D-Alumina is established. The experimental set-iip is simple and inexpensive, with the process parameters easy to control. As-synthesised powders of alumina are amorphous and transform to essentially strain-free, nanocrystalline □-Alumina on heating to a temperature of 450°C. Crystallite sizes in the range well below 20 nm are obtained after drying at 450°C Changing the process parameters such as voltage, current density, electrolyte concentration and position of aerator can regulate the crystallite size. The powder production rate is reasonable and can be upscaled. The energy consumption per unit weight for this process is very small and is around 25 - 250 kJ/g. It will be appreciated that various other modes of carrying out the process proposed herein and various other embodiments of the apparatus proposed herein are possible without departing from the scope and ambit of this invention. We Claim: 1. A process for the preparation of nanopowders by electrolytic oxidation of aluminum to alumina (neo-alumina) comprising the steps of setting up a commercially pure aluminum sheet of size 107 x 70 x 2 mm3 as an anode and a s'tainless steel sheet of size 107 x 70 x 2 mm as a cathode; the electrolysis being carried out in an electrolyte consisting of a solution of NaCl in distilled water; ensuring a continuous supply of air during the process by an aerator connected to an air pump located between cathode and anode; and regulating the voltage and current density by a dc power supply, the voltage range being 10-40V and current densities range being 1x10" to 3.3x10' A cm" . 2. A process for the preparation of nanopowders by electrolytic oxidation of aluminum to alumina (neo-alumina) substantially as herein described with reference to, and'as illustrated in, the accompanying drawings. 3. A device for preparation of nanopowders by electrolytic oxidation of aluminum to alumina (neo- alumina) comprising a commercially pure aluminium sheet of size 107 x 70 x 2 mm3 as an anode and a stainless steel sheet of size 107 x 70 x 2 mm3 as a cathode; an electrolyte consisting of a solution of NaCl in distilled water; an aerator connected to an air pump located between cathode and anode to ensure the continuous supply of air during the synthesis process; the voltage and current density being regulated by a dc power supply, the voltage range being 10-40V and current densities range being lxlO"3 to 3.3xl0"2 A cm"2, 4.A device for preparation of nanopowders by electrolytic oxidation of aluminum to alumina (neo-alumina) substantially as herein described and

Full Text

This invention relates to a process and device for preparation of nanopowders by electrolytic oxidation of aluminum to alumina (neo-alumina). In particular, this invention relates to simple and inexpensive means of synthesizing high quality nanocrystalline Alumina (AI2O3) particles, A pure aluminum sheet as initial raw material, an inert electrode, an electrolytic bath using an aqueous solution as electrolyte with a DC power supply and an aerator constitutes the complete set-up.
The Aluminum Hydroxide produced by this invention can be transformed to the nanocrystalline Alumina powder, which is essentially strain-free and below 20 nm in size. It is possible to control the crystallite size by varying the parameters involved.
This invention finds wide and varied industrial applications as catalysts in automobile and petroleum industries, soft abrasives, sensors, coatings, substrates for electronics and opto¬electronics application, composites, among others

The process proposed herein is inexpensive in ternis of initial investment and running cost.
In the as-synthesized condition it is hydrated alumina that transforms on heating to y-alumina at a temperature of 450°C.
By changing the process parameters such as voltage, current density, electrolyte concentration and position of aerator,' it is possible to regulate the particle size.
Corundum that is a-Al203 is the thermodynamically stable phase of alumina under normal temperature and pressure. In the nano-size regime Y-AI2O3 is more stable because of its lower surface energy. Y-AI2O3 is a functionally important oxide ceramic material. Owing to its high temperature stability and lesser tendency for grain growth as compared to a-Al203, it is used in several industries including automobile industries, as soft abrasives, substrates in electronic industries among others. y-Al203 is mainly produced by thermal decomposition 'of boehmite (a major constituent of bauxite) and by sol-gel methods .
The process proposed herein relates to a synthesis of nano particles of y-Al203 ' by an electrochemical process that offers greater control of particle size by varying the process parameters.

As stated above, on an industrial scale Y-AI2O3 is produced by thermal decomposition of boehmite and to some extent by sol-gel routes. In both these methods it is not possible to precisely control the particle size of the synthesized compound, which is a major drawback in the era of tailored materials. In the process proposed herein an oxidative electrodeposition technique for the synthesis of nanoparticles of y-Al203 is proposed.
The process proposed herein will now be described with reference.to the accompanying drawings which illustrate by way of example, and not by way of limitation, in
Fig.l one of possible embodiments of the procedural apparatus consisting of of an electrolytic bath, an aerator, a metallic anode plate, a stainless steel cathode plate and a DC power supply
Fig. 2 illustrates the X-ray diffractogram (XRD) of sample prepared at 40 Volts (a) as-synthesised (b) calcined at 450 degree C.alumina powder as well as the powders dried at different temperatures
Fig.3 illustrates variation of the crystallite size with the applied vohage (at an electrolyte concentration of 3 g/1 of NaCl)
Fig. 4 illustrates variation of the crystallite size with the current density (at an electrolyte concentration of 3 g/1 of NaCl)

Fig. 5 illustrates variation of the crystallite size with he salt (NaCl) concentration in electrolyte.
The following conditions/parameters are maintained:
• A commercially pure aluminium sheet of size 107 x 70 X 2 mm^ is used as anode and a stainless steel sheet of size 107 x 70 x 2 mm^ is used as cathode.
• The electrolyte used is essentially a solution of NaCl in distilled water.
• The aerator, which is connected to a small air pump, is used between cathode and anode to ensure the continuous supply of air during the synthesis process.
• The voltage and current density are regulated using the DC power supply. The voltage range used is 10-40V and current densities range from 1x10'"^ to 3.3x10'^ A cm"l
The deposited powder is fdtered using a Whatman filter paper, washed thoroughly with distilled water and dried at a fixed temperature.

The X-ray diffractogram (XRD) of as-synthesised alumina powder as well as the powders dried at different temperatures are presented as Figure 2.
Absence of distinct peaks in the XRD of as synthesized sample indicates its amorphous nature. XRD of sample calcined at 450^C shows distinct peaks that indicate improved crystallinity. Presence of peaks at 45.8° and 66.9° confirms the presence of Y-AI2O3 (on comparison with standard JCPDS tables). The broad peaks in the diffractogram clearly indicate nanocrystalline nature of the deposited powders. Crystallite sizes are calculated from the peak broadening using the Scherrer formula . Table 1 gives the variation of the crystallite sizes (obtained after calcining at 450°C) with the process parameters (current and voltage).

The following aspects may be noted::
• The finest crystallite size (3 nm) was obtained at operating conditions of lOV and 3 g/1 NaCl concentration and also at 40 V and 1 g/1
• The maximum' production rates of 20 g/day were obtained at 40V and 3 g/1 NaCl concentration resulting in a crystallite size of 3 nm.

• In general the aerator is positioned midway between the anode and cathode, but it is found that the position of the aerator in the proximity of the anode or cathode also influences the crystallite size.
The following salient features of this invention may be emphasized
A novel process and experimental set-up for the synthesis of nanopowders of D-Alumina is established.
The experimental set-iip is simple and inexpensive, with the process parameters easy to control.
As-synthesised powders of alumina are amorphous and transform to essentially strain-free, nanocrystalline □-Alumina on heating to a temperature of 450°C.
Crystallite sizes in the range well below 20 nm are obtained after drying at 450°C
Changing the process parameters such as voltage, current density, electrolyte concentration and position of aerator can regulate the crystallite size.
The powder production rate is reasonable and can be upscaled.
The energy consumption per unit weight for this process is very small and is around 25 - 250 kJ/g.

It will be appreciated that various other modes of carrying out the process proposed herein and various other embodiments of the apparatus proposed herein are possible without departing from the scope and ambit of this invention.

We Claim:
1. A process for the preparation of nanopowders by electrolytic oxidation of aluminum to alumina (neo-alumina) comprising the steps of setting up a commercially pure aluminum sheet of size 107 x 70 x 2 mm3 as an anode and a s'tainless steel sheet of size 107 x 70 x 2 mm as a cathode; the electrolysis being carried out in an electrolyte consisting of a solution of NaCl in distilled water; ensuring a continuous supply of air during the process by an aerator connected to an air pump located between cathode and anode; and regulating the voltage and current density by a dc power supply, the voltage range being 10-40V and current densities range being 1x10" to 3.3x10' A cm" .
2. A process for the preparation of nanopowders by electrolytic oxidation of aluminum to alumina (neo-alumina) substantially as herein described with reference to, and'as illustrated in, the accompanying drawings.
3. A device for preparation of nanopowders by
electrolytic oxidation of aluminum to alumina (neo-
alumina) comprising a commercially pure aluminium
sheet of size 107 x 70 x 2 mm3 as an anode and a
stainless steel sheet of size 107 x 70 x 2 mm3 as a

cathode; an electrolyte consisting of a solution of NaCl in distilled water; an aerator connected to an air pump located between cathode and anode to ensure the continuous supply of air during the synthesis process; the voltage and current density being regulated by a dc power supply, the voltage range being 10-40V and current densities range being lxlO"3 to 3.3xl0"2 A cm"2,
4.A device for preparation of nanopowders by electrolytic oxidation of aluminum to alumina (neo-alumina) substantially as herein described and

Documents:

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Patent Number

279040

Indian Patent Application Number

4/CHE/2009

PG Journal Number

02/2017

Publication Date

13-Jan-2017

Grant Date

09-Jan-2017

Date of Filing

01-Jan-2009

Name of Patentee

INDIAN INSTITUTE OF TECHNOLOGY MADRAS

Applicant Address

IIT P.O. CHENNAI 600 036

Inventors:

#	Inventor's Name	Inventor's Address
1	GAURAV JETLY	DEPARTMENT OF METALLURGICAL & MATERIALS ENGINEERING, IIT, CHENNAI 36
2	MD. IMTEYAZ AHMAD	DEPARTMENT OF METALLURGICAL & MATERIALS ENGINEERING, IIT, CHENNAI 36
3	DR. S.S. BHATTACHARYA	ASSOCIATE PROFESSOR DEPARTMENT OF METALLURGICAL & MATERIALS ENGINEERING, IIT, CHENNAI 36

PCT International Classification Number

B01J21

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA