Title of Invention	A METHOD OF MANUFACTURING A SUBSTRATE OF ALUMINIUM OR ITS ALLOY WITH AN ANODISED ELECTRICALLY CONDUCTING SURFACE
Abstract	The invention provides a method of manufacturing a substrate of asluminium or its alloy with an anodized electrially conducting surface. The method comprises anodizing the substrate in a sulphuric acid bath in a conventional manner; sensitizing the anodised substrate by immersing in a sensitization bath, activating the sensitized anodized substrate in an activation bath containing a noble metal salt and removing bloom formed on the surface of the substrate in a known manner.

Title of Invention

A METHOD OF MANUFACTURING A SUBSTRATE OF ALUMINIUM OR ITS ALLOY WITH AN ANODISED ELECTRICALLY CONDUCTING SURFACE

Abstract

The invention provides a method of manufacturing a substrate of asluminium or its alloy with an anodized electrially conducting surface. The method comprises anodizing the substrate in a sulphuric acid bath in a conventional manner; sensitizing the anodised substrate by immersing in a sensitization bath, activating the sensitized anodized substrate in an activation bath containing a noble metal salt and removing bloom formed on the surface of the substrate in a known manner.

Full Text	The invention relates to a method of manufacturing a substrate of aluminium or its alloy with an anodized, conducting surface. Components made out of aluminum and its alloys are anodized in order to get a protective oxide coating as well as to get higher emissive. The infrared emissive of aluminum is only about 0.03, but this can be greatly increased by anodizing. The anodic film with sufficient thickness obtained by conventional sulphuric acid electrolyte can provide infrared emissive of the order of 0.8, whereas its solar absorptance is only around 0.3. The anodic film, therefore acts as a good solar reflector with good infrared emissive, Indication of substrate of aluminum or its alloy is known and it is possible to prepare substrate with good optical properties by known methods of ionization. The anodic coating is a dielectric material. The dielectric external surface of such a substrate when used in space craft is prone to get electrically charged to several thousand volts when encountered with geomagnetic sub storm environment and plasma with particle energies tromp 1 to 50 KeV. Such charging can produce potential difference between spacecraft surface and spacecraft ground. When a breakdown threshold is exceeded, an electrostatic discharge can occur due to the transfer of electrostatic charge between objects at different potentials due to direct contact or induced by electrostatic fields. The transient generated by this discharge can couple into spacecraft electronics causing upsets ranging from logic switching to complete system failure. Discharge can also cause long-term degradation of exterior sources coating and enhance contamination of surface. The ultimate result is disruption in spacecraft operation. Therefore it is desirable to create a conducting source on an anodized surface in such applications. Conventional sulphuric acid anodizing is employed to provide a surface coating with good corrosion resistance, high thermal emittance and electrical insulation. The coating also serves as an undercoat to the application of organic paints, lacquers, dyes etc. However, the anodic coating is ceramic in nature and therefore it stores electrostatic charge. In order to drain the charge it is desirable to make the anodic coating electrically conductive. However increasing electrical conductivity in dielectric anodic film by conventional electrodeposition is difficult and the metal deposition leads to sharp drop in thermal emissive of the surfeited. The object of the invention is to provide a substrate of aluminium or its alloy with an anodized film having electrically conducting surface. The process consists generally the following sequential steps. 1. Solvent degreasing in a conventional manner. 2. Alkaline cleaning in a conventional manner. 3. Neutralizing and demitting in a conventional manner. 4. Anodizing in a conventional manner. 5. Sensitizing of the anodic coating by an electrochemical process. 6. Activation of the sensitized anodic coating by an electrochemical process. 7. Removal of bloom in a conventional manner. Accordingly the present invention provides a métier of manufacturing a substrate of aluminium or its alloy with an anodized, conducting source said method comprising the steps of: (i) anodizing the substrate in a sulphuric acid bath in a conventional manner to obtain an anodized film of at least 5 microns thick; (ii) sensitizing the anodized substrate by immersing in a sensitization bath containing 1 to 100 gms of stannous chloride per litre of dilute hydrochloric acid with 0.2 to 5 percent concentration at a temperature not exceeding 45°C for at least 20 minutes followed by rinsing with water, (iii) activating the sensitized anodized substrate by immersing in a solution containing 0.2 to 50 gms of a noble metal salt per litre of dilute hydrochloric acid with 0.2 to 5 percent concentration for at least 5 minutes followed by rinsing with water, and (iv) removing bloom formed on the surface of the substrate in a known manner to obtain the substrate with an anodized, conducting source. A clean substrate of aluminium or its alloy is anodized in a conventional manner in a dilute sulphuric acid bath. Generally canonization is carried out in a sulphuric acid bath of 7 to 14 percent concentration by volume at a current density of 100 to 250 amperes per decimeter squared. The substrate is anodized to obtain an anodized surface film of at least 5 micron thickness. The anodised substrate is cleaned with water and immersed in a sensitization bath of dilute hydrochloric acid of 0.2 to 5 percent concentration containing 1 to 100 gms of stannous chloride. Preferably the sensitization bath temperature is kept below 45 and the sensitization is carried out for at least 30 minutes. The anodised, sensitized substrate is activated by immersing in a solution containing 0.2 to 50 gms of a noble metal salt per here of dilute hydrochloric acid with 0.2 to 5 percent concentration. Preferred noble metal salts are selected from chlorocuric acid, palladium chloride and chloroplatinic acid. The activation may be carried out for at least 5 minutes at a temperature not exceeding 45 Preferably addition of 50 to 200 gms of sodium chloride and 0.2 to 20 gms of palladium chloride per litre of the sensitization bath solution was found to be desirable. Alter activation the substrate is cleaned with water and gently rubbed with a soft cloth to remove bloom. The substrate of aluminium or its alloy after the abovementioned process steps showed an acceptable surface resistively of less 100 kilo ohms per square area, to avoid surface charge accumulation on the substrate. The infrared emittance and solar absorption of the surface of the substrate after activation was found to be above 0.70. No change was observed during environmental tests on substrates after activation. During electrostatic discharge test, 400 volts build up was observed on the anodic film for a test potential of 1000 volts on the electrostatic discharge simulator. After sensitizing and activation, this voltage build up was brought down to The coated articles withstood humidity test (RH 95%, 50°C, 48 Hrs.). Thermal cycling (-45°C to +65°C) and thermo vacuum (vacuum 10' torr, at -45°C to +65°C) tests without degradation. The coatings passed corrosion test and adhesion test. Example: A sample substrate was degreased in trichloroethelene followed by alkaline cleaning and water rinsing. The substrate was neutralized with dilute acid and rinsed with water. The substrate is then anodised in a sulphuric acid bath in a conventional manner to obtain anodised layer of about 16 microns. The anodised substrate is cleaned with water and sensitized in a bath of dilute hydrochloric acid with 2 percent concentration containing 2 gms of stannous chloride per litre of dilute hydrochloric acid. The pH of the bath was maintained at 0.7 and the sensitization was carried out for 60 minutes at room temperature. WE CLAIM : 1. A method of manufacturing a substrate of aluminium or its alloy with an anodized, conducting surface said method conspiring the steps of: (i) anodizing the substrate in a sulphuric acid bath in a conventional manner to obtain an anodized film of at least 5 microns thick; (ii) sensitizing the anodised substrate by immersing in a sensitization bath containing 1 to 100 gms of stannous chloride per litre of dilute hydrochloric acid with 0.2 to 5 percent concentration at a temperature not exceeding 45for at least 20 minutes followed by rinsing with water, (iii) activating the sensitized anodized substrate by immersing in a solution containing 0.2 to 50 gms of a noble metal salt per litre of dilute hydrochloric acid with 0.2 to 5 -percent concentration for at least 5 minutes followed by rinsing with water, and (iv) removing bloom formed on the source of the substrate in a known manner to obtain the substrate with an anodized, conducting source. The method as claimed in claim 1, wherein sensitization bath optionally contains 50 to 200^ gms of sodium chloride per litre of the solution. The method as claimed in claim 1, wherein the sensitization bath optionally contains 0.2 to 20 gm of palladium chloride and 1 to 10 gms of a known secant per litre of the solution. The method as claimed in claim 1, wherein said noble metal salt is selected from chloroauric acid, palladium chloride and chloroplatinic acid. The method as claimed in claim 4, wherein said noble metal salt is chloroauric acid. A method of manufacturing a substrate of aluminium or its alloy with an anodized. conducting surface, substantially as hereinabove described and exemplified.

Full Text

The invention relates to a method of manufacturing a substrate of aluminium or its alloy with an anodized, conducting surface.
Components made out of aluminum and its alloys are anodized in order to get a protective oxide coating as well as to get higher emissive. The infrared emissive of aluminum is only about 0.03, but this can be greatly increased by anodizing. The anodic film with sufficient thickness obtained by conventional sulphuric acid electrolyte can provide infrared emissive of the order of 0.8, whereas its solar absorptance is only around 0.3. The anodic film, therefore acts as a good solar reflector with good infrared emissive, Indication of substrate of aluminum or its alloy is known and it is possible to prepare substrate with good optical properties by known methods of ionization.
The anodic coating is a dielectric material. The dielectric external surface of such a substrate when used in space craft is prone to get electrically charged to several thousand volts when encountered with geomagnetic sub storm environment and plasma with particle energies tromp 1 to 50 KeV. Such charging can produce potential difference between spacecraft surface and spacecraft ground. When a breakdown threshold is exceeded, an electrostatic discharge can occur due to the transfer of electrostatic charge between objects at different potentials due to direct contact or induced by electrostatic fields. The transient generated by this discharge can couple into spacecraft electronics causing upsets ranging from logic switching to complete system failure. Discharge can also cause long-term degradation of exterior sources coating and enhance contamination of surface. The ultimate result is

disruption in spacecraft operation. Therefore it is desirable to create a conducting source on an anodized surface in such applications.
Conventional sulphuric acid anodizing is employed to provide a surface coating with good corrosion resistance, high thermal emittance and electrical insulation. The coating also serves as an undercoat to the application of organic paints, lacquers, dyes etc. However, the anodic coating is ceramic in nature and therefore it stores electrostatic charge. In order to drain the charge it is desirable to make the anodic coating electrically conductive. However increasing electrical conductivity in dielectric anodic film by conventional electrodeposition is difficult and the metal deposition leads to sharp drop in thermal emissive of the surfeited. The object of the invention is to provide a substrate of aluminium or its alloy with an anodized film having electrically conducting surface.
The process consists generally the following sequential steps.
1. Solvent degreasing in a conventional manner.
2. Alkaline cleaning in a conventional manner.
3. Neutralizing and demitting in a conventional manner.

4. Anodizing in a conventional manner.
5. Sensitizing of the anodic coating by an electrochemical process.
6. Activation of the sensitized anodic coating by an electrochemical process.
7. Removal of bloom in a conventional manner.

Accordingly the present invention provides a métier of manufacturing a substrate of aluminium or its alloy with an anodized, conducting source said method comprising the steps of:
(i) anodizing the substrate in a sulphuric acid bath in a conventional manner to obtain an anodized film of at least 5 microns thick;
(ii) sensitizing the anodized substrate by immersing in a sensitization bath containing 1 to 100 gms of stannous chloride per litre of dilute hydrochloric acid with 0.2 to 5 percent concentration at a temperature not exceeding 45°C for at least 20 minutes followed by rinsing with water,
(iii) activating the sensitized anodized substrate by immersing in a solution containing 0.2 to 50 gms of a noble metal salt per litre of dilute hydrochloric acid with 0.2 to 5 percent concentration for at least 5 minutes followed by rinsing with water, and
(iv) removing bloom formed on the surface of the substrate in a known manner to obtain the substrate with an anodized, conducting source.
A clean substrate of aluminium or its alloy is anodized in a conventional manner in a dilute sulphuric acid bath. Generally canonization is carried out in a sulphuric acid bath of 7 to 14 percent concentration by volume at a current density of 100 to 250 amperes per decimeter squared.

The substrate is anodized to obtain an anodized surface film of at least 5 micron thickness. The anodised substrate is cleaned with water and immersed in a sensitization bath of dilute hydrochloric acid of 0.2 to 5 percent concentration containing 1 to 100 gms of stannous chloride. Preferably the sensitization bath temperature is kept below 45 and the sensitization is carried out for at least 30 minutes.
The anodised, sensitized substrate is activated by immersing in a solution containing 0.2 to 50 gms of a noble metal salt per here of dilute hydrochloric acid with 0.2 to 5 percent concentration. Preferred noble metal salts are selected from chlorocuric acid, palladium chloride and chloroplatinic acid. The activation may be carried out for at least 5 minutes at a temperature not exceeding 45
Preferably addition of 50 to 200 gms of sodium chloride and 0.2 to 20 gms of palladium chloride per litre of the sensitization bath solution was found to be desirable.
Alter activation the substrate is cleaned with water and gently rubbed with a soft cloth to remove bloom.
The substrate of aluminium or its alloy after the abovementioned process steps showed an acceptable surface resistively of less 100 kilo ohms per square area, to avoid surface charge accumulation on the substrate.

The infrared emittance and solar absorption of the surface of the substrate after activation was found to be above 0.70. No change was observed during environmental tests on substrates after activation.
During electrostatic discharge test, 400 volts build up was observed on the anodic film for a test potential of 1000 volts on the electrostatic discharge simulator. After sensitizing and activation, this voltage build up was brought down to The coated articles withstood humidity test (RH 95%, 50°C, 48 Hrs.). Thermal cycling (-45°C to +65°C) and thermo vacuum (vacuum 10' torr, at -45°C to +65°C) tests without degradation. The coatings passed corrosion test and adhesion test.
Example:
A sample substrate was degreased in trichloroethelene followed by alkaline cleaning and water rinsing. The substrate was neutralized with dilute acid and rinsed with water. The substrate is then anodised in a sulphuric acid bath in a conventional manner to obtain anodised layer of about 16 microns. The anodised substrate is cleaned with water and sensitized in a bath of dilute hydrochloric acid with 2 percent concentration containing 2 gms of stannous chloride per litre of dilute hydrochloric acid. The pH of the bath was maintained at 0.7 and the sensitization was carried out for 60 minutes at room temperature.

WE CLAIM :
1. A method of manufacturing a substrate of aluminium or its alloy with an anodized, conducting surface said method conspiring the steps of:
(i) anodizing the substrate in a sulphuric acid bath in a conventional manner to obtain an anodized film of at least 5 microns thick;
(ii) sensitizing the anodised substrate by immersing in a sensitization bath containing 1 to 100 gms of stannous chloride per litre of dilute hydrochloric acid with 0.2 to 5 percent concentration at a temperature not exceeding 45for at least 20 minutes followed by rinsing with water,
(iii) activating the sensitized anodized substrate by immersing in a solution containing 0.2 to 50 gms of a noble metal salt per litre of dilute hydrochloric acid with 0.2 to 5 -percent concentration for at least 5 minutes followed by rinsing with water, and
(iv) removing bloom formed on the source of the substrate in a known manner to obtain the substrate with an anodized, conducting source.
The method as claimed in claim 1, wherein sensitization bath optionally contains 50 to 200^ gms of sodium chloride per litre of the solution.

The method as claimed in claim 1, wherein the sensitization bath optionally contains 0.2 to 20 gm of palladium chloride and 1 to 10 gms of a known secant per litre of the solution.
The method as claimed in claim 1, wherein said noble metal salt is selected from chloroauric acid, palladium chloride and chloroplatinic acid.
The method as claimed in claim 4, wherein said noble metal salt is chloroauric acid.
A method of manufacturing a substrate of aluminium or its alloy with an anodized. conducting surface, substantially as hereinabove described and exemplified.

Documents:

573-mas-2002-abstract.pdf

573-mas-2002-claims filed.pdf

573-mas-2002-claims granted.pdf

573-mas-2002-correspondnece-others.pdf

573-mas-2002-correspondnece-po.pdf

573-mas-2002-description(complete)filed.pdf

573-mas-2002-description(complete)granted.pdf

573-mas-2002-form 1.pdf

573-mas-2002-form 19.pdf

573-mas-2002-form 26.pdf

573-mas-2002-form 3.pdf

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Patent Number

210250

Indian Patent Application Number

573/MAS/2002

PG Journal Number

50/2007

Publication Date

14-Dec-2007

Grant Date

25-Sep-2007

Date of Filing

30-Jul-2002

Name of Patentee

M/S. INDIAN SPACE RESEARCH ORGANISATION

Applicant Address

ISRO HEADQUARTERS, DEPARTMENT OF SPACE, ANTARIKSH BHAVAN, NEW BEL ROAD, BANGALORE - 560 094,

Inventors:

#	Inventor's Name	Inventor's Address
1	DR. ANAND KUMAR SHARMA	TPS, TSG, ISRO Satellite centre, Bangalore,
2	DR. RAMACHANDRAN UMA RANI	TPS, TSG, ISRO Satellite Centre, Bangalore,

PCT International Classification Number

C23C002/12

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA