Title of Invention

A PROCESS FOR MAKING YTTRIA-ALUMINA-SILICON CARBIDE COMPOSITE USEFUL AS ENGINEERING CERAMICS"

Abstract A process has been developed for marking yttria-alumina-silicon carbide composite using gel derived oxide additive. The process involves the steps of mixing the silicon carbide suspension, yttrium nitrate and aluminium nitrate solutions at a ratio ranging 1:3:4 to 1:5:6, stirring at a particular pH to get a gel, allowing the gel for aging, followed by drying, heat treating, grinding and sieving the gel mass to get the composite.
Full Text The present invention relates to a process for making yttria-alumina-silicon carbide composite useful as engineering ceramics. The process of the present invention particularly relates to the use of gel derived oxide additive for making yttria-alumina-silicon carbide composite.
The main usages of the yttria-alumina-silicon carbide composite are in the field of engineering ceramics for making component parts of automobile engine, pump, and in various other applications where superior thermo mechanical properties are required. The said article may also be used as special refractory material where thermal shock, abrasion, erosion, oxidative corrosion etc are to be countered at room temperature, below room temperature and at elevated temperarure upto 1850°C.
The present day method of making yttria-alumina-silicon carbide composite essentially consists of using powdered ytttii and alumina for which reference may be made to MOmori and HJaker, J.Am. Ceram. Soc. 65 ( 1982 ) C - 92, F.A.Van Dijen and E.Mayer. J. of the Euro. Ceram. Soc. 16 ( 1996 ) 413 - 420, E.Kostic "Powder Metall. Int., 20 (1988 ) 28 - 29, Nitin P. Padture, J.Am.Ceram. Soc. 77 (2) 519-523 ( 1994 ), K.Y.Chia and S.KJLau, Ceram. Eng. Sci. Proc. 12(9-10) 1845-1861 ( 1991 ) leading to a product formed at much higher temperature and considerable inhomogenety and also to W.D.G.Bocker, Euro. Patent 419271 A2, 1990 who have used yttria and aluminium nitride without useful properties. In all the above process the main drawbacks may be listed as bdow.
1. Silicon carbide powder should be very fine, more than 90 percent in the submicron
range.
2. Homogeneous mixing of solid ingredients like silicon carbide, yrtria and alumina require
special processing techniques and costly equipments.
3. Many of the processes require hot pressing which is not only a cost inhibitive process
but also have several limitations.
«.-
4. .All of the processes require 2000-2100°C for firing which not only add on to the cost of
the fuel but also increases cost of the equipment.
5. impurities like silica associated with commercial silicon carbide powder is to be removed
prior to utilising the material for compositing .
'The main object of the present invention is to provide a process for making yttria-alunmni-silicon carbide composite useful as engineering ceramics, which obviates the drawbacks as detailed above.
/Vnother object of the present invention is to use gel derived oxide additive for making yttria-aiumina -silicon carbide composite.
Still another object of the present invention is to eliminate the process of grinding silicon carbide particles to above 10 m2/g to impart sinterability to the material.
Yet another object of the present invention is to eliminate the process of purification of silicon carbide to impart sinterabilit;y to the material.
Still another object of the present invention is to eliminate the process of attrition milling and sieving for homogeneous mixing of solid materials.
Yet another object of the present invention is to eliminate the use of organic solvents for the purpose of mixing of solids.
Still another object of the present invention is to carryout the desired reaction at reduced temperature.
Yet another object of the present invention is to provide a process for making components using the composite prepared by the process of the present invention.
Accordingly, the present invention provides a process for making yttria-alumina-silicon carbide composite useful as engineering ceramics which comprises preparing silicon carbide suspension wherein silicon carbide powder has a solid content in the range of 1 : 2 to 1 : 6 (g/v), preparing yttrium nitrate and aluminium nitrate solutions, mixing the silicon carbide suspension, yttrium nitrate and aluminium nitrate solutions at a ratio ranging 1:3:4 to 1:5:6, under stirring , adding ammonia to the mixture under stirring till the pH is in the range of 9.5 to 11.5 to obtain a gel like mass , allowing the gel to age for a period in the range of
8-48 hours, washing the aged gel like mass, filtering, drying at a temperature of 60° to 80°C for a period of 6 - 48 hours, heat treating the dried gel like mass at a
temperature in the range of 850° - 900°C, followed by grinding and sieving, to
».-. get the desired composite, making green component using the composite by
conventional isostatic pressing and firing at 1700° - 2000°C in inert atmosphere.
Accordingly the present invention provides a process for making components using the composite powder prepared by the above process, which comprises isostatically cold pressing in a mould of desired shaped and firing in an inert atmosphere at a temperature in the range of 1700° - 2000°C for a period of 0.5 - 2 hours.
The details of the process of the present invention are given below:
a) Silicon carbide powder is mixed with dispersing agents and water
(SiC: water = 1 : 2 to 1 : 6 g/v) by constant stirring to prepare a
suspension.
b) 1:5 g/v Yttrium nitrate and 1 : 4 g/v aluminium nitrate solutions are
added in the silicon carbide slip prepared in step 'a'.
c) The entire mixture is stirred for 1 - 5 hours.
d) Ammonium hydroxide solution (1 : 1, 1 : 1.5, 1 : 2, 1 : 2.5, 1 : 3 v/v)
is slowly added or ammonia gas is passed in the mixture produced by
step 'a' - 'c' till the pH is 9.5-11.5.
e) The entire mass converts to a semi solid gel like mass which is allowed to age for 8-48
Hours.
f) Product formed in step 'e' is dispersed in large volume of water and allowed to settle.
g) Settled mass produced in step 'f is filtered and washed by warm water.
h) The washed material produced in step 'g1 is dried at 60- 80 °C for 6-48 hours.
i) The dried material obtained in step :h' is heat treated at 850-900°C for 2-4 hrs. in air environment.
j) The heat treated material obtained in step T is ground and sieved through 100 mesh.
k) Trie sieved composite powder obtained in step 'j" is formed into green shape by cold isc-i:uic pressing in a suitable mould.
1) The green product obtained in step 'k' is fired in inert atmosphere such as argon environment at 1700 - 2000 °C for 0.5-2 hours.
The process of the present invention can be used to produce consolidated yttria-ahunina-silkvn carbide composite of various shapes and sixes required for application as engineering and refractory material. Room temperature fracture toughness of silicon
carbide may be; increased by introducing elongate-shape reinfrocements like whiskers or grains and increasing the thermal expansion mismatch stress.
Yttria-alumina additive may provide the elongate silicon carbide grains as well as high thermal expansion mismatch second phase >ttrium - aluminium - garnet ( YAG ) in situ during processing. A well distributed YAG in SiC - YAG mixture may be obtained by using hydrogel derived oxides as starting material. Hydrogel derived oxides result in the formaiion of YAG at lower temperature due to their higher reactivity. Again, a powder of silicon carbide of surface area Im2g"1 will contain 0.1 weight percent of oxygen.
***
From the equilibrium phase diagram in the system ALO^ - Y2O3 - SiO2 it is seen that the presence of even small amount of silica leads to liquid phase formation at 1700 - 1800°C. Thus, instead cf removing adherent silica layer on SiC. it is used for the advantage of the
process.
The following examples are given by way of illustration of the process of the present invention and should not be construed to limit the scope of the present invention.
EXAMPLE - 1
Silicon carbide of 1200 grit 90 gins is mixed with 133.4 ml of 25 % aluminium nitrate solution and 93.3 ml of 20% yttrium nitrate solution and stirred for 3 hrs. 90.0 ml of ammonium hydroxide solution (1:1 v/v) is slowly added into the mixture with string. The
gel like mass that forms is aged for 48 hrs. followed by filtration and washing with warm water. The entire mass is dried at 80°C for 48 hrs. followed by heat treatment in air environment at 350°C for 2 hrs. The heat treated material is ground to pass 100 mesh sieve. Articles ol" desired shapes are formed from the powder by isostatic pressing at room temperature at 200 Mpa pressure. The compacted articles are fired at 1850°C for half an hour in argon atmosphere.
EXAMPLE -2
Silicon carbide of 1200 grit 85 gms is mixed with 200.1 ml of 25 % aluminium nitrate solution and 140.0 ml of 20% yttrium nitrate solution and stirred for 3 hrs. 135.0 ml of ammonium hydroxide solution (1:1 vv) is slowly added into the mixture with string. The gel like mass that forms is aged for 48 hrs. followed by filtration and washing with warm water. The entire mass is dried at 80°C for 48 hrs. followed by heat treatment in air environment at 850°C for 2 hrs. The heat treated material is ground to pass 100 mesh sieve. Articles of desired shapes are formed from the powder by isostatic pressing at room temperature at 200 Mpa pressure. The compacted ankles are fired at 1850°C for half an hour in argon atmosphere.
EXAMPLE - 3
Silicon carbide of 1200 grit XO gms is mixed with 266.8 ml of 25 % aluminium nitrate solution and 186..6 ml of 20% yttrium nitrate solution and stirred for 3 hrs, 180.0 ml of
ammonium hydroxide solution (1:1 v/'v) is slowly added into the mixture with string. The gel like mass that forms is aged for 48 hrs. followed b}' filtration and washing with warm water. The entire mass is dried at 80°C for 48 hrs. followed by heat treatment in air emironment at 850°C for 2 hrs. The heat treated material is ground to pass 100 mesh sieve. Articles of desired shapes are formed from the powder by isostatic pressing at room temperature at 200 Mpa pressure. The compacted articles are fired at 1850°C for half an hour in argon atmosphere.
EXAMPLE - 4
Silicon carbide of 1200 grit 75 gms is mixed with 333.5 ml of 25 % aluminium nitrate solution and 233.2 ml of 20% yttrium nitrate solution and stirred for 3 hrs. 225.0 ml of ammonium hydroxide solution (1:1 v/v) is slowly added into the mixture with string. The gel Like mass that forms is aged for 48 hrs. followed by filtration and washing with warm water. The eniire mass is dried at 80°C for 48 hrs. followed by heat treatment in air environment al 850°C for 2 hrs. The heat treated material is ground to pass 100 mesh sieve. Articles of desired shapes are formed from the powder by isostatic pressing at room temperature at 200 Mpa pressure. The compacted articles are fired at 1850°C for half an hour in argon almospherc.
EXAMPLE - 5
Silicon carbide of 1200 grit 70 gms is mixed with 400.2 ml of 25 % aluminium nitrate solution and 280.0 ml of 20% yttrium nitrate solution and stirred for 3 hrs. 270.0 ml of ammonium hydroxide solution (1:1 v/v) is slowly added into the mixture with string. The gel like mass that forms is aged for 48 hrs. followed by filtration and washing with warm water. The entire mass is dried at 80°C for 48 hrs. followed by heat treatment in air environment at 850°C for 2 hrs. The heat treated material is ground to pass 100 mesh sieve. Articles of desired shapes are formed from the powder by isostatic pressing at room temperature at 200 Mpa pressure. The compacted articles are fired at 1850UC for half an hour in argon atmosphere.
EXAMPLE - 6
Silicon carbide of 1200 grit 65 gms is mixed with 466.8 ml of 25 % aluminium nitrate soluiion and 326.5 ml of 20% yttrium nitrate solution and stirred for 3 hrs. 315.0 ml of ammonium hydi oxide solution (1:1 v/v) is slowly added into the mixture with string. The gel i'kc mass that forms is aged for 48 hrs. followed by filtration and washing with warm water. The entite mass is dried at 80UC for 48 hrs. followed by heat treatment in air environment at :?50°C for 2 hrs. The heat treated material is ground to pass 100 mesh sieve. Articles ol desired shapes arc formed from the powder by isostatic pressing at room temperature at 230 Mpa pressure. The compacted articles are fired at 1850°C for half an hour in argon atmosphere.
EXAMPLE - 7
Silicon carbide of 1200 grit 60 gms is mixed with 533.5 ml of 25 % aluminium nitrate solution and 373.2 ml of 20% yttrium nitrate solution and stirred for 3 hrs. 360.0 ml of ammonium hydroxide solution (1:1 v/v) is slowly added into the mixture with string. The gel like mass that forms is aged for 48 hrs. followed by filtration and washing with warm water. The entire mass is dried at 80°C for 48 hrs. followed b}' heat treatment in air emironment at 850°C for 2 hrs. The heat treated material is ground to pass 100 mesh sieve. .Articles of desired shapes are formed from the powder by isostatic pressing at room temperature at 200 Mpa pressure. The compacted articles are fired at 1850°C for half an hour in argon atmosphere.
EXAMPLE - 8
Silicon carbide of 1200 grit 80 gms is mixed with 266.8 ml of 25 % aluminium nitrate solution and 186.6 ml of 20% yttrium nitrate solution and stirred for 3 hrs. 180.0 ml of ammonium hydroxide solution (1:1 v/v) is slowly added into the mixture with string. The gci like mass that forms is aged for 48 hrs. followed by filtration and washing with warm water. The entire mass is dried at 80°C for 48 hrs. followed by heat treatment in air environment at 850°C for 2 hrs. The heat treated material is ground to pass 100 mesh sieve. Articles of desired shapes art- formed from the powder by isostatic pressing at room temperature at 200 Mpa pressure. The compacted articles are fired at 1950°C for half an hour in argon atmosphere.
EXAMPLE - 9
Silicon carbide of 1200 grit 75 gms is mixed with 333.5 ml of 25 % aluminium nitrate solution and 233.2 ml of 20% yttrium nitrate solution and stirred for 3 hrs. 225.0 ml of ammonium hydroxide solution (1:1 v/v) is slowly added into the mixture with string. The gel like mass that forms is aged for 48 hrs. followed by filtration and washing with warm water. The entire mass is dried at 80°C for 48 hrs. followed by heat treatment in air environment at 850°C for 2 hrs. The heat treated material is ground to pass 100 mesh sieve. Articles of desired shapes are formed from the powder by isostatic pressing at room temperature at 200 Mpa pressure. The compacted articles are fired at 1950°C for naif an hour in argon atmosphere.
P:XAMPLE -10
Silicon carbide of 1200 grit 70 gms is mixed with 400.2 ml of 25 % aluminium nitrate solution and 280.0 ml of 20% yttrium nitrate solution and stirred for 3 hrs. 270.0 ml of ammonium hydroxide solution (1:1 v/v) is slowly added into the mixture with string. The gel like mass trut forms is aged for 48 hrs, followed by filtration and washing with warm water. The entire mass is dried at 80°C for 48 hrs. followed by heat Ire Iment in air environment at 850°C for 2 hrs. The heat treated material is ground to pass 100 mesh sieve. Articles of desired shapes are formed from the powder by isostatic pressing at room

temperature at 200 Mpa pressure. The compacted articles are fired at 1950°C for half an hour in argon atmosphere.
EXAMPLE-11
Silicon carbide of 1200 grit 65 gms is mixed with 466.8 ml of 25 % aluminium nitrate solution and 326.5 ml of 20% yttrium nitrate solution and stirred for 3 hrs. 315.0 ml of ammonium hydroxide solution (1:1 v/v) is slowly added into the mixture with suing. The gel like mass that forms is aged for 48 hrs. followed by filtration and washing with warm water. The en:ire mass is dried at 80°C for 48 hrs. followed by heat treatment in air emironment a; 850°C for 2 hrs. The heat treated material is ground to pass 100 mesh sieve. .Articles of desired shapes are formed from the powder by isostatic pressing at room temperature at 200 Mpa pressure. The compacted articles are fired at 1950°C for half an hour hi argon f tmosphere.
EXAMPLE - 12
Silicon carbide of 1200 grit 60 gnis is mixed with 533.5 ml of 25 °o aluminium nitrate solution and 373.2 ml of 20% yttrium nitrate solution and stirred for 3 hrs. 360.0 nil of ammonium hydroxide solution (1:1 v/v) i.s slowly added into the mixture with siring. The gel like mass that forms is aged for 48 hrs. followed by filtration and washing with warm water. The entire mass is dried at 80°C for 48 hrs. followed by heat treatment in air

emironment at 850°C for 2 hrs. The heat treated material is ground to pass 100 mesh sieve. Articles of desired shapes are formed from the powder by isostatic pressing at room temperature at 200 Mpa pressure. The compacted articles are fired at 1950°C for half an hour in argon atmosphere.
EXAMPLE - 13
Silicon carbide of 1200 grit 80 gms is mixed with 266.8 ml of 25 % aluminium nitrate solution and 186.6 ml of 20% yttrium nitrate solution and stirred for 3 hrs. 180.0 ml of ammonium hydroxide solution (1:1 v/v) is slowly added into the mixture with string. The gel like mass lhat forms is aged for 48 hrs. followed by filtration and washing with warm water. The entire mass is dried at 80°C for 48 hrs. followed by heat treatment in air en\ironment at 850°C for 2 hrs. The heat treated material is ground to pass 100 mesh sieve. Articles of desired shapes are formed from the powder by isostatic pressing at room temperature ai: 200 Mpa pressure. The compacted articles are fired at 2000°C for half an hour in argon atmosphere.
EXAMPLE - 14
Silicon carbidj of 1200 grit 75 gms is mixed with 333.5 ml of 25 % aluminium nitrate solution and 233.2 ml of 20% yttrium nitrate solution and stirred for 3 hrs. 225.0 ml of ammonium hydroxide solution (1:1 v/v) is slowly added into the mixture with string. The gel like mass lhat forms is aged for 48 hrs. followed by filtration and washing with warm

water. The entire mass is dried at 80°C for 48 hrs. followed by heat treatmc-m in air emironment at 850°C for 2 hrs. The heat treated material is ground to pass 100 mesh sieve. Articles of desired shapes are formed from the powder by isostatic pressing at room temperature at 200 Mpa pressure. The compacted articles are fired at 2000°C for half an hour in argon atmosphere.
EXAMPLE - 15
Silicon carbide of 1200 grit 70 gms is mixed with 400.2 ml of 25 % aluminium nitrate solution and 280.0 ml of 20% yttrium nitrate solution and stirred for 3 hrs. 270.0 ml of ammonium hydroxide solution (1:1 v/v) is slowly added into the mixture with string. The gel like mass that forms is aged for 48 hrs. followed by filtration and washing with warm water. Hie entire mass is dried at 80°C for 48 hrs. followed by heat treatment in air emironment at 850°C for 2 hrs. The heat treated material is ground to pass 100 mesh sieve. .Articles of desired shapes are formed from the powder by isostatic pressing at room temperature a- 200 Mpa pressure. The compacted articles are fired at 2000°C for half an hour in argon atmosphere.
EXAMPLE - 16
Silicon carbide: of 1200 grit 65 grns is mixed with 466.8 ml of 25 % aluminium nitrate solution and 326.5 ml of 20% jttrium nitrate solution and stirred for 3 hrs. 315.0 ml of ammonium hydroxide solution (1:1 v/v) is slowly added into the mixture with string. The

gel like mass that forms is aged for 48 hrs. followed by filtration and washing with warm water. The entire mass is dried at 80°C for 48 hrs. followed by heat treatment in air environment at 850°C for 2 hrs. The heat treated material is ground to pass 100 mesh sieve. Articles of desired shapes are formed from the powder by isostatic pressing at room temperature at 200 Mpa pressure. The compacted articles are fired at 2000°C for half an hour in argon atmosphere.
EXAMPLE - 17
Silicon carbide of 1200 grit 60 gms is mixed with 533.5 ml of 25 % aluminium nitrate solution and 373.2 ml of 20% yttrium nitrate solution and stirred for 3 hrs. 360.0 ml of ammonium hydroxide solution (1:1 v/v) is slowly added into the mixture with string. The gel like mass that forms is aged for 48 hrs. followed by filtration and washing with warm water. The entire mass is dried at 80°C for 48 hrs. followed by heat treatment in air environment at 850°C for 2 hrs. The heat treated material is ground to pass 100 mesh sieve. Articles of desired shapes are formed from the powder by isostatic pressing at room temperature at 200 Mpa pressure. The compacted articles are fired at 2000°C for half an hour in argon atmosphere.
The results obtained by the process of present invention are given below by way of illustration.
(Table Removed)
From the table above it may be inferred that specimens containing silicon carbide upto 75% may be said to be in the useful range and densification is higher with lowering of silicon carbide content upto 60%.
The main advantages of the present invention are :
1. iu usability to produce consolidated yttria-alumina-silicon carbide composite of various
shapes and sizes for application as engineering and refractor}' material,
2. simpler processing technique is sufficient for the production of homogeneous products,
3. firing temperature may be reduced to 1850°C from 21QO°C,
4. impurities like silica associated with commercial SiC powder need not be removed.





WE CLAIM :
1. A process for making yttria-alumina-silicon carbide composite useful as
engineering ceramics which comprises preparing silicon carbide
suspension wherein silicon carbide powder has a solid content in the
range of 1 : 2 to 1 : 6 (g/v) , preparing yttrium nitrate and aluminium
nitrate solutions, mixing the silicon carbide suspension, yttrium nitrate
and aluminium nitrate solutions at a ratio ranging 1:3:4 to 1:5:6, under
stirring , adding ammonia to the mixture under stirring till the pH is in
the range of 9.5 to 11.5 to obtain a gel like mass, allowing the gel to
age for a period in the range of 8 - 48 hours, washing the aged gel like
mass, filtering, drying at a temperature of 60° to 80°C for a period of 6
- 48 hours, heat treating the dried gel like mass at a temperature in the
range of 850° - 900°C, followed by grinding and sieving, to get the
desired composite, making green component using the composite by
conventional isostatic pressing and firing at 1700° - 2000°C in inert
atmosphere.
2. A process as claimed in claim 1 wherein silicon carbide is used in the
range 600 -1200 grit size.
3. A process as claimed in claim 1 & 2 wherein silicon carbide used is of
surface area upto 16m2g"1-
4. A process as claimed in claim 1-3 wherein a suspension is prepared
using water and dispersing agents.
5. A process as claimed in claim 1 - 4 wherein the mixture of silicon
carbide suspension, yttrium and aluminium nitrate solution is stirred for
1 - 5 hrs.
6. A process as claimed in claim' 1-5 wherein the addition of ammonia
is effected using ammonium hydroxide solution of concentration 1:1,
1 : 1.5, 1 : 2, 1:2.5, 1:3 (v/v) , passing ammonia gas through the
mixture containing silicon carbide, yttrium nitrate and aluminium
nitrate.
7. A process as claimed in claim 1-6 wherein the washing of the aged
gel like mass is effected using water at room temperature, warm water.
8. A process as claimed in claim 1 - 7 wherein the dried mass is heat
treated for a period of 2 to 4 hours in air environment.
9. A process as claimed in claim 1 - 8 wherein the heat treated mass is
ground to pass 100 mesh sieve.
10. A process as claimed in claims 1 - 9 wherein the firing is done in an inert
atmosphere such as argon environment.
11. A process for making yttria - alumina-silicon carbide composite useful as engineering ceramics substantially as herein described with references to examples.



Documents:

375-del-1998-abstract.pdf

375-del-1998-claims.pdf

375-del-1998-complete specification (granted).pdf

375-del-1998-correspondence-others.pdf

375-del-1998-correspondence-po.pdf

375-del-1998-description (complete).pdf

375-del-1998-form-1.pdf

375-del-1998-form-19.pdf

375-del-1998-form-2.pdf

375-del-1998-form-3.pdf


Patent Number 242824
Indian Patent Application Number 375/DEL/1998
PG Journal Number 38/2010
Publication Date 17-Sep-2010
Grant Date 14-Sep-2010
Date of Filing 13-Feb-1998
Name of Patentee COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH
Applicant Address RAFI MARG, NEW DELHI-110001,INDIA
Inventors:
# Inventor's Name Inventor's Address
1 SANKAR GHATAK CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, CALCUTTA 700 032, INDIA.
2 ARUP KUMAR SAMANTA CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, CALCUTTA 700 032, INDIA
3 KAJAL KUMAR DHARGUPTA CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, CALCUTTA 700 032, INDIA
4 CHAITANYAMOY GANGULY CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, CALCUTTA 700 032, INDIA
PCT International Classification Number C04B 35/52
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA