Title of Invention	STABILIZED ZIRCONIA PLASMA SPRAYABLE POWDER AND INDUSTRIAL PROCESS FOR ITS MANUFACTURE
Abstract	A method for preparing stabilized zirconia based plasma sprayable powder comprising: stabilizing mono clinic Zr02 adding suitable additives and subjecting the mixture to the step of arc melting; crushing the stabilized mixture to form fine particles; preparing a slurry of the stabilized Zr02 particles, subjecting the slurry to the step of spray drying; and sieving the spray dried powder to obtain free flowing plasma sprayable powders.

Title of Invention

STABILIZED ZIRCONIA PLASMA SPRAYABLE POWDER AND INDUSTRIAL PROCESS FOR ITS MANUFACTURE

Abstract

A method for preparing stabilized zirconia based plasma sprayable powder comprising: stabilizing mono clinic Zr02 adding suitable additives and subjecting the mixture to the step of arc melting; crushing the stabilized mixture to form fine particles; preparing a slurry of the stabilized Zr02 particles, subjecting the slurry to the step of spray drying; and sieving the spray dried powder to obtain free flowing plasma sprayable powders.

Full Text	This invention relates to a method for preparing stabilized zirconia based plasma sprayable powder. BACKGROUND OF THE INVENTION: Thermal barrier coatings (TBC) are ~ 250pm thick ceramic coatings applied on bond coated metallic substrates. They provide thermal insulation and protect metals from high temperature degradation. They have a vide variety of Industrial applications which include Automobile, Power, Space etc. The coating processes are being carried out by plasma spray technique. Usually Ceramic powders are coated on metallic parts in order to protect them from severe environments like high temperature. For process of plasma spraying the powders should have very controlled particle size, suitable composition and above all good flowing nature. Presently ceramic powder compositions having good flowabiUty are being imported. Large-scale manufacture of flowing powders with controlled composition and particle size is a very difficult task. Among the several ceramic compositions zirconia (Zr02) based powders are very popular for TBC applications because of their good adhesion, low thermal conductivity and high thermal shock resistance characteristics. A novel process for preparing Zr02 based ceramic coating material capable of being plasma coated has been established at the Central Power Research Institute, Bangalore, to suit the requirement of industry so that it can be manufactured in tons. OBJECT OF THE INVENTION: An object of this invention is to propose a method for preparing stabilized zirconia based plasma sprayable powder. Another object of this invention is to propose a method for preparing stabilized zircoma based plasma sprayable powder which provide thermal insulation and protect metals from high temperature degradation. Further object of this invention is to propose a method for preparing stabilized zirconia based plasma sprayable powder which has good adhesion and high thermal shock resistance characteristics. Still further object of this invention is to propose a method for preparing stabilized zirconia based plasma sprayable powder which is highly free flowing plasma sprayable powders. STATEMENT OF INVENTION. According to this invention a method for preparing stabilized zirconia based plasma sprayable powder comprising: Stabilizing mo no clinic Zr02 Adding suitable additives and Subjecting the mixture to the step of arc melting; Crushing the stabilized mixture to form fine particles; Preparing a slurry of the stabilized Zr02 particles, Subjecting the slurry to the step of spray drying; and Sieving the spray dried powder to obtain free flowing plasma sprayable powders. DETAILED DESCRIPTION OF THE INVENTION: Normally starting raw material is in the form of mo no clinic Zr02. This has to be stabilized to cubic / tetragonal Zri>2 to attain the TBC Characteristics. Mo no clinic ZrO? can be stabilized to cubicAetragonai ZrOa either with Calcia (CaO) or Yttrium Oxide (Y203) or Magnesium Oxide (MgO) or Ceriun Oxide (Ce02) as stabilizers. Dense and hard stabilized Zr02 has been made by subjecting the bait milled composition (5% CaO +95% monocKnic Zr02) to arc melting (to stabilize the desired high temperature phase) and crushing using high energy water jet milling to form fine particles of 25 urn average size. This stabilized Zr02 with up to 99% purity can be processed in batches of 1 ton or above without loss in purity in composition. The stabilized Zr02 powder is made into slurry using distilled water media and mixed with 10% PVA solution and with 10% addition of this prepared PVA solution to slurry. The slurry. The slurry is spray dried using a commercially available industrial spray drier. The spray-dried powder is sieved through commercially available sieve shakers and ASTM meshes to produce free flowing plasma sprayable powders with average size of 50 microns. The powder thus prepared when plasma sprayed is ideally suited as thermal barrier coatings. The powder preparation involves following processes. 1. Ball milling of raw material composition to handle tons of material in single batch 2. Formation of the desired cubic/tetragonal phase by using arc fusion technology. 3. Water jet mHllng to crush the hardened composition very much essential to make fine powders. This also is a process suitable for industrial usage In tons. 4. Industrial scale spray drying used for preparing highly free flowing plasma sprayable powders in tons. The sprayable powder prepared by the process of the present invention has microstructure indicting presence of distinct round shaped particles having good flow. Wfc ULAIM: 1. A method for preparing stabilized zirconla based plasma sprayable powder comprising: stabilizing mono clinic Zr02 adding suitable additives and subjecting the mixture to the step of arc melting; crushing the stabilized mixture to form fine particles; preparing a slurry of the stabilized Zr02 particles, subjecting the slurry to the step of spray drying; and sieving the spray dried powder to obtain free flowing plasma sprayable powders. 2. The method as claimed in claim 1, wherein said additives are selected from calcia (CaO), Yttrium Oxide (Y2O3), Magnesium Oxide (MgO) and Ceriun Oxide (Ce02). 3. The method as claimed in claim 2, wherein the additive used is preferably caicia (CaO). 4. The method as claimed in claim 1, wherein step of crushing is preferred by high energy water jet milling to form particles of 25 urn average size. 5. The method as claimed in claim 1, wherein said stabilized Zr02 powder is made into slurry using distilled water mixed with 10% PVA solution. 6. The method as claimed in claim 1, wherein the step of spray drying is preferred using industrial spray drier. . The method as claimed in claim 1, wherein the step of sieved is preferred using sieve shakers and ASTM meshes to produce free flowing plasma sprayable powders with average sizes of 50 microns.

Full Text

This invention relates to a method for preparing stabilized zirconia based plasma sprayable powder.
BACKGROUND OF THE INVENTION:
Thermal barrier coatings (TBC) are ~ 250pm thick ceramic coatings applied on bond coated metallic substrates. They provide thermal insulation and protect metals from high temperature degradation. They have a vide variety of Industrial applications which include Automobile, Power, Space etc. The coating processes are being carried out by plasma spray technique. Usually Ceramic powders are coated on metallic parts in order to protect them from severe environments like high temperature. For process of plasma spraying the powders should have very controlled particle size, suitable composition and above all good flowing nature. Presently ceramic powder compositions having good flowabiUty are being imported. Large-scale manufacture of flowing powders with controlled composition and particle size is a very difficult task. Among the several ceramic compositions zirconia (Zr02) based powders are very popular for TBC applications because of their good adhesion, low thermal conductivity and high thermal shock resistance characteristics.
A novel process for preparing Zr02 based ceramic coating material capable of being plasma coated has been established at the Central Power Research Institute, Bangalore, to suit the requirement of industry so that it can be manufactured in tons.
OBJECT OF THE INVENTION:
An object of this invention is to propose a method for preparing stabilized zirconia based plasma sprayable powder.

Another object of this invention is to propose a method for preparing stabilized zircoma based plasma sprayable powder which provide thermal insulation and protect metals from high temperature degradation.
Further object of this invention is to propose a method for preparing stabilized zirconia based plasma sprayable powder which has good adhesion and high thermal shock resistance characteristics.
Still further object of this invention is to propose a method for preparing stabilized zirconia based plasma sprayable powder which is highly free flowing plasma sprayable powders.
STATEMENT OF INVENTION.
According to this invention a method for preparing stabilized zirconia based plasma sprayable powder comprising:
Stabilizing mo no clinic Zr02
Adding suitable additives and
Subjecting the mixture to the step of arc melting;
Crushing the stabilized mixture to form fine particles;
Preparing a slurry of the stabilized Zr02 particles,
Subjecting the slurry to the step of spray drying; and
Sieving the spray dried powder to obtain free flowing plasma sprayable powders.
DETAILED DESCRIPTION OF THE INVENTION:
Normally starting raw material is in the form of mo no clinic Zr02. This has to be stabilized to cubic / tetragonal Zri>2 to attain the TBC Characteristics. Mo no clinic ZrO? can be stabilized to cubicAetragonai ZrOa either with Calcia (CaO) or

Yttrium Oxide (Y203) or Magnesium Oxide (MgO) or Ceriun Oxide (Ce02) as stabilizers. Dense and hard stabilized Zr02 has been made by subjecting the bait milled composition (5% CaO +95% monocKnic Zr02) to arc melting (to stabilize the desired high temperature phase) and crushing using high energy water jet milling to form fine particles of 25 urn average size. This stabilized Zr02 with up to 99% purity can be processed in batches of 1 ton or above without loss in purity in composition. The stabilized Zr02 powder is made into slurry using distilled water media and mixed with 10% PVA solution and with 10% addition of this prepared PVA solution to slurry. The slurry. The slurry is spray dried using a commercially available industrial spray drier. The spray-dried powder is sieved through commercially available sieve shakers and ASTM meshes to produce free flowing plasma sprayable powders with average size of 50 microns.
The powder thus prepared when plasma sprayed is ideally suited as thermal barrier coatings. The powder preparation involves following processes.
1. Ball milling of raw material composition to handle tons of material in single batch
2. Formation of the desired cubic/tetragonal phase by using arc fusion technology.
3. Water jet mHllng to crush the hardened composition very much essential to make fine powders. This also is a process suitable for industrial usage In tons.
4. Industrial scale spray drying used for preparing highly free flowing plasma sprayable powders in tons.
The sprayable powder prepared by the process of the present invention has microstructure indicting presence of distinct round shaped particles having good flow.

Wfc ULAIM:
1. A method for preparing stabilized zirconla based plasma sprayable powder
comprising:
stabilizing mono clinic Zr02
adding suitable additives and
subjecting the mixture to the step of arc melting;
crushing the stabilized mixture to form fine particles;
preparing a slurry of the stabilized Zr02 particles,
subjecting the slurry to the step of spray drying; and
sieving the spray dried powder to obtain free flowing plasma sprayable
powders.
2. The method as claimed in claim 1, wherein said additives are selected from calcia (CaO), Yttrium Oxide (Y2O3), Magnesium Oxide (MgO) and Ceriun Oxide (Ce02).
3. The method as claimed in claim 2, wherein the additive used is preferably caicia (CaO).
4. The method as claimed in claim 1, wherein step of crushing is preferred by high energy water jet milling to form particles of 25 urn average size.
5. The method as claimed in claim 1, wherein said stabilized Zr02 powder is made into slurry using distilled water mixed with 10% PVA solution.
6. The method as claimed in claim 1, wherein the step of spray drying is preferred using industrial spray drier.

. The method as claimed in claim 1, wherein the step of sieved is preferred using sieve shakers and ASTM meshes to produce free flowing plasma sprayable powders with average sizes of 50 microns.

Documents:

1284-che-2005-abstract.pdf

1284-che-2005-claims.pdf

1284-che-2005-correspondnece-others.pdf

1284-che-2005-correspondnece-po.pdf

1284-che-2005-description(complete).pdf

1284-che-2005-form 1.pdf

1284-che-2005-form 26.pdf

1284-che-2005-form 3.pdf

1284-che-2005-form 9.pdf

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Patent Number

229939

Indian Patent Application Number

1284/CHE/2005

PG Journal Number

13/2009

Publication Date

27-Mar-2009

Grant Date

24-Feb-2009

Date of Filing

14-Sep-2005

Name of Patentee

CENTRAL POWER RESEARCH INSTITUTE

Applicant Address

PROF SIR.C.V. RAMAN ROAD, SADASHIVANAGAR SUB PO, P.B. NO.8066, BANGALORE 560 080,

Inventors:

#	Inventor's Name	Inventor's Address
1	DR. PARVATI RAMASWAMY	C/O. CENTRAL POWER RESEARCH INSTITUTE, PROF SIR. C.V.RAMAN ROAD, SADASHIVANAGAR SUB PO, P.B. NO.8066, BANGALORE 560 080,
2	DR. S. SEETHARAMU	C/O. CENTRAL POWER RESEARCH INSTITUTE, PROF SIR. C.V.RAMAN ROAD, SADASHIVANAGAR SUB PO, P.B. NO.8066, BANGALORE 560 080,
3	MR. S. VYNATHEYA	C/O. CENTRAL POWER RESEARCH INSTITUTE, PROF SIR. C.V.RAMAN ROAD, SADASHIVANAGAR SUB PO, P.B. NO.8066, BANGALORE 560 080,

PCT International Classification Number

C23C4/10

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA