Title of Invention

ALUMINA-ZIRCONIA COMPOSITE POWER

Abstract The present invention for the preparation of alumina - zircona composite powder comprises of heating distilled water to a temperature between 80°c to 90°0 and dissolving 1:100 to 1:110 of aluminium sulphate and zirconium oxychloride in the hot water with continuous stirring. PH of the solution in increased between 4 to 4.5 by the addition of NH3 solution to precipitate the respective hydroxides as fine particles to form a solution. PH is raised between 9 to 10 by further addition of NH3 to convert the solution to gel, which is filtered under vacuum, washed to remove sulphate and chloride ions and dispersed in water and the PH is adjusted between 6 to 6.5 by the addition of nitric acid, resulting fine powders are further dried to remove any free moisture content, calcined and crushed to break soft agglomerates, if any.
Full Text This invention relates to a proceas for the preparation of alumina -zirconia composite powder.
Recant R&D activities in the area of advanced ceramikcs have led to the development of ceramics with improved proprties and performance.
Alumina-zirconia composite is one of the most studied ceranic composites starting from the powder preparation to consolidation and properties.
In this class of ceramics the fracture toughness of alumina is considerably improved by the incorporation of zircoaia in view of its transformation toughening behaviour. These composites are prepared by mechanically mixing the constituent powdns, that is, alumina and zirconia powders and consolidating the mixture. By this process achieving uniform distribution of the zirconia in alumina is difficult So the resulting composite cannot achieve its full potential in properties that is, the purpose of adding zirconia to improve

the fracture toughness is not utilised fully.
Chemical methods of preparation of this powder
mixture will meet the purpose by ensuring a very honogeneous nixture of zirconia in alumina.
The process, according to this invention, for the
preparation of alumina- zirconia composite powder
conprises the heating of disti1 led water to a
tenperature between 80 deg. C to 90 deg. C;
dissolving 1: 100 to 1; 110 of aluminium sulphate and zirconium oxychloride in the hot water and continuously stirring the sane; increasing the pH of the solution between 4 to 4.5 by the addition of ammonla solution, to precipitate the respective hydroxides as fine particles and forn a sol ; converting the solinto gel at a pH between 9 to 10 by the further addition of ammonia solution; fi1tering the get under vacuum; washing the same to remove sulphate and chloride fons; dispersing the washed gel in water and adjusting the pH between 6 to 6.5 by the addition of nitric acid, before spray drying the sane, the resulting fine powders being further dried to remove any free moisture content; calcining the dried powder and

lightly crushing the sane to break soft agglonerates, if any.
EXAMPLE Doubly distil 1ed water contained in a glass beaker is heated to 00 deg. C on a hot plate having a magnetic stirring arrangenent. Required aaount of aluninium sulphate and zirconiua oxychioride are weighed to the accuracy of 0. 1 mg. They are dissolved in the hot water with continuous stirring (salt to water nole ration is 1 to 100). The pH of the solution is 3.
Standardised anount of 25X annonia solution is
then added to increase the pH of the solution to
A. At this pH, the respective hydroxides are
precipitated as fine particles and f orn the sol. This sol is converted into gel at a pH of 9 by the further addition of aanonia solution.
The gel is filtered under vacuun using a Buchner funnel with fit ter paper. The f i 1 tered gel is washed first with dilute ammonia and then with distilled water to remove the sulphate and

chloride ions.
A simple test is perforned to determine the con-pletion of washing. The filtrate is added to silver nitrate solution. A white precipitate is the indication of Incoaplete washing.
Thoroughly washed gel is dispersed in water (having 10 % solid content) and the pH adjusted to 6 by the addition of nitric acid. The gel is then sprayed dry at a rate of 11itre/hour.
The inlet tenperature in the spray drier is 210 deg. C and the out 1et temperature 110 deg. C.
The col 1ected f ine powder is further dried for 24 hours at 110 dag. C in an oven to remove any free moisture present in the powder.
The dried powder is then calcine at 950 deg. C for 5 hours at a heating rate of 5 deg./ mln. After calcination, the powder is lightly crushed to break any soft agglomerates present.

The advantages of the process proposed herein are;
KAverage agglonerate partiale Bize is 3 u mn and surface area 20 square metres/g.
The particles are spherical in shape.
Homogeneous distribution of zirconia particles in aluming
Better mechanical properties of the sintered conposites derived from this powder.
Reliability of the s intered composites is very high.
The terms and express ions in this specification are of description and not of description, there being no intention of excluding any equivalents of the features described and exemplified, but it is understood that various other modes of carrying out the process herein are posslble without departing from the scope and ambit of this invention.




This invention relates to a proceas for the preparation of alumina -zirconia composite powder.
Recant R&D activities in the area of advanced ceramikcs have led to the development of ceramics with improved proprties and performance.
Alumina-zirconia composite is one of the most studied ceranic composites starting from the powder preparation to consolidation and properties.
In this class of ceramics the fracture toughness of alumina is considerably improved by the incorporation of zircoaia in view of its transformation toughening behaviour. These composites are prepared by mechanically mixing the constituent powdns, that is, alumina and zirconia powders and consolidating the mixture. By this process achieving uniform distribution of the zirconia in alumina is difficult So the resulting composite cannot achieve its full potential in properties that is, the purpose of adding zirconia to improve

the fracture toughness is not utilised fully.
Chemical methods of preparation of this powder
mixture will meet the purpose by ensuring a very honogeneous nixture of zirconia in alumina.
The process, according to this invention, for the
preparation of alumina- zirconia composite powder
conprises the heating of disti1 led water to a
tenperature between 80 deg. C to 90 deg. C;
dissolving 1: 100 to 1; 110 of aluminium sulphate and zirconium oxychloride in the hot water and continuously stirring the sane; increasing the pH of the solution between 4 to 4.5 by the addition of ammonla solution, to precipitate the respective hydroxides as fine particles and forn a sol ; converting the solinto gel at a pH between 9 to 10 by the further addition of ammonia solution; fi1tering the get under vacuum; washing the same to remove sulphate and chloride fons; dispersing the washed gel in water and adjusting the pH between 6 to 6.5 by the addition of nitric acid, before spray drying the sane, the resulting fine powders being further dried to remove any free moisture content; calcining the dried powder and

lightly crushing the sane to break soft agglonerates, if any.
EXAMPLE Doubly distil 1ed water contained in a glass beaker is heated to 00 deg. C on a hot plate having a magnetic stirring arrangenent. Required aaount of aluninium sulphate and zirconiua oxychioride are weighed to the accuracy of 0. 1 mg. They are dissolved in the hot water with continuous stirring (salt to water nole ration is 1 to 100). The pH of the solution is 3.
Standardised anount of 25X annonia solution is
then added to increase the pH of the solution to
A. At this pH, the respective hydroxides are
precipitated as fine particles and f orn the sol. This sol is converted into gel at a pH of 9 by the further addition of aanonia solution.
The gel is filtered under vacuun using a Buchner funnel with fit ter paper. The f i 1 tered gel is washed first with dilute ammonia and then with distilled water to remove the sulphate and

chloride ions.
A simple test is perforned to determine the con-pletion of washing. The filtrate is added to silver nitrate solution. A white precipitate is the indication of Incoaplete washing.
Thoroughly washed gel is dispersed in water (having 10 % solid content) and the pH adjusted to 6 by the addition of nitric acid. The gel is then sprayed dry at a rate of 11itre/hour.
The inlet tenperature in the spray drier is 210 deg. C and the out 1et temperature 110 deg. C.
The col 1ected f ine powder is further dried for 24 hours at 110 dag. C in an oven to remove any free moisture present in the powder.
The dried powder is then calcine at 950 deg. C for 5 hours at a heating rate of 5 deg./ mln. After calcination, the powder is lightly crushed to break any soft agglomerates present.

The advantages of the process proposed herein are;
KAverage agglonerate partiale Bize is 3 u mn and surface area 20 square metres/g.
The particles are spherical in shape.
Homogeneous distribution of zirconia particles in aluming
Better mechanical properties of the sintered conposites derived from this powder.
Reliability of the s intered composites is very high.
The terms and express ions in this specification are of description and not of description, there being no intention of excluding any equivalents of the features described and exemplified, but it is understood that various other modes of carrying out the process herein are posslble without departing from the scope and ambit of this invention.

Documents:

549-mas-98 abstract.pdf

549-mas-98 claims duplicate.pdf

549-mas-98 claims.pdf

549-mas-98 correspondence-others.pdf

549-mas-98 correspondence-po.pdf

549-mas-98 description (complete) duplicate.pdf

549-mas-98 description (complete).pdf

549-mas-98 form-1.pdf

549-mas-98 form-19.pdf

549-mas-98 form-26.pdf


Patent Number 199128
Indian Patent Application Number 549/MAS/1998
PG Journal Number 30/2009
Publication Date 24-Jul-2009
Grant Date
Date of Filing 17-Mar-1998
Name of Patentee INDIAN INSTITUTE OF TECHNOLOGY,
Applicant Address IIT P.O, CHENNAI 600036
Inventors:
# Inventor's Name Inventor's Address
1 SANT KUMAR MALHOTRA, DEPARTMENT OF METALLURGICAL ENGINEERING IIT CHENNAI 600036
2 CHIMATA VENKATASUBRAHMANYAM GOKULARATHNAM, PROFESSOR, DEPARTMENT OF METALLURGICAL ENGINEERING, IIT P.O, CHENNAI 600036
3 MUTHIAH BALASUBRAMANIAN, DEPARTMENT OF METALLURIGICAL ENGINEERING, IIT CHENNAI 600036
PCT International Classification Number C04B35/10
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA