Title of Invention	"AN IMPROVED PROCESS FOR PREPARATION OF ULTRAFINE AND NANOCRYSTALLINE COMPOUNDS."
Abstract	The present invention relates to an improved process for preparation of ultra fine and nanocrystalline compounds. The present invention particularly relates to a process of preparation of ultra fine particles of B-SiC, WC, TiC2, SiC2, SisN4 of size in the range of 1 -100 nm. In the reported processes ultra fine SiC is synthesized using various gaseous reactants derived from silane or organo-silane, with CHU using radio frequency and arc plasma torches and also by sublimation of a mixture of SiC and Si wherein the present invention ultra fine SiC is synthesized by sublimation of primary SiC grains using extended arc plasma in transferred mode and subsequent condensation of the vapour phase on the chilled water cooled surfaces of the reactor.

Title of Invention

"AN IMPROVED PROCESS FOR PREPARATION OF ULTRAFINE AND NANOCRYSTALLINE COMPOUNDS."

Abstract

Full Text	The present invention relates to an improved process for preparation of ultrafine and nanocrystalline compounds. The present invention particularly relates to a process of preparation of ultrafine particles of B-SiC, WC, TiO2, SiO2, Si3N4 of size in the range of 1 - 100 nm. Nanomaterials exhibit properties that are not only much better than the conventional coarse grain but also often entirely different e.g. ZrO2 is a brittle material but when produced in the size range 2- 20 nm behaves like chewingum at high temp. Thus there is an up surge in the area of preparation of these nano-sized materials. In course of the present elaboration we take SiC a very useful hard ceramic material for illustration. However the process developed here can also be used for preparation of other ultrafine nanometric carbides, nitrides and oxides which are given as examples. The ultrafine and nanometric p-SiC powder manufactured using the process of said invention finds application in the preparation of self bonded SiC product, kiln furniture and substrate material for x-ray mirrors. The said product is also useful as a phoiocatalyst and support material for catalyst. Due to the abrasive property, the said particles can be used for preparation of grinding and lapping compounds. Again the particles are used in paints to have a wear resistance coating. The said powder can be used in the preparation of high temperature composite materials such as gas turbine blades. Further the product can be used as polishing material and can develop high wear resistance properties when used as a coating with other adhesive binders. A Ultrafme SiC is synthesized by vapour phase reaction of silanes, organo-silanes and silicon with CH4, C2H4 using radio frequency and arc plasma torches (1-8). [ J.Y.Guo, F.Gitzlofer, M.L. Boulas ( Plasma Tech. Research Centre), Univ. of Sherbrooke, PQ Can. J1K 2R1), J. Mater Sc. 1995, 30 (22), 5569-99, SuO Duluo; Li Shimini; Xu, Zhene; Wen, Jie; Li, Daohuo; Liu, Zongea; National Engineering & Research Centre for Laser processing centre, China, Univ. of Sci. & Tech. Wuhan, people Republic of China, 430074, Wuji Cailino, Xuebao, 1995, 10(3) 301-6, G.J. Vogt. C.M. Hollabaugh, D.E. Hull, L.R. Wewkirk and J.J. Petrovic (1984), United States,_Department of Energy Report, DE 84-00 377*1 LOS Alamos; Department of Energy. Taylor, Patrick R; Poirzada, Shhid, A. (Daho \research foundation) U.S. US 5, 486, 675 (1. 217-121.59; 1323JCIO) 23 Jan. 1996. T. Hmeyma, K.Saknaka, A Mote, T.Tsunoda, T. Nakanaga, N.I. 'Wahayama, H. Takeo, K.Fukuda, Journal of mater Sci. 25 (1990) 1058-1065. Y. Anodo and m. Ohkohchi, J.Cryst. Growth, vol. 60, P. 147, 1982, J.D.F. Ramsay and R.G. Avery (1977), United Kingdom patent 1, 479, 727. P.C. Kong, E. Pfender (1987),^Larigmuir, E, p. 259-65}. Draw back of the processes is that they make use of expensive precursors and the yield of SiC is low. It is also difficult to maintain stoichiometry in gaseous phase. p-SiC is also synthesized using carbon cathode and silicon anode. [ T. Inukai, J. Japan Soc. Powder and Powder Metall., Vol.27, No.8, p.249 (1980)]. The process is associated with high rate of erosion of carbon electrode since the source of carbon is from electrode. In this process the product is contaminated with free silicon. Ultrafine P-SiC is also prepared by arcing across electrodes made form a mixture of silica and carbon. [ W.U. Kuhn, J-Electrochem. Soc. Vol. 110, No.4 , p. 298, 1963]. Ultrafme p-SiC is also synthesized by sublimation of SiC with SiC in are plasma. [Yusufumi Nariki, Yasunoby Inoue, Kohichi Tanaka, Jour. Of Mater Sic. 25 (1990) 3101 - 3104]. Use of silicon in the charge results free silicon and silica on the surface of P-SiC. The main object of the present invention is to provide, an improved process for preparation of ultrafme/nanocrystalline compounds. Another object of the present invention is to utilize the high temperature and high energy density available in thermal plasma for sublimation of SiC resulting in a high yield. Still another object of the present invention is to make the transferred plasma operative with silicon carbide bulk without addition of costly silicon metal. Yet another object of the present invention is to obtain particles in the size range of 1 - 100 nm. Yet another object of the present invention is to obtain in spite SiC/SiN composite in a single run. Accordingly the present invention provides an improved process for preparation of ultra fine and nano-crystalline compounds which comprises; characterized in that subjecting primary grains of compounds selected from SiC, WC, TiC, TiO2 SisN4 for sublimation and condensation of the vapour on water cooled chilled surfaces of the reactor wherein the primary grain is taken in a graphite crucible having a graphite pin attached to its centre forms the anode and the other graphite electrode having a central hole forms the cathode, generating the plasma across the electrodes by connecting the cathode with anode and then separating the same under the constant flow of argon as plasmagen gas fed through the central hole of the cathode, collecting the deposited ultrafine nano crystalline compounds from the wall, removing the impurities such as carbon and silicon/silica by conventional methods such as herein described to get nano-crystalline compound. In another embodiment of the present invention the transferred are plasma is established thorough the said graphite pin placed centrally within the primary SiC charge (grains) materials which provides the electrical continuity for the are plasma as SiC does not possess electrical conductivity at ambient temperature. In another embodiment of the present invention the carbon present in ultra fine/ nanometric product prepared in the said process is removed by heating the product in the rnage of 500 -900°C in air. In yet another embodiment of the present invention the surface silica impurity is removed by HF treatment. The process of preparing ultrafme/nanometric 0-SiC comprises sublimation of primary SiC grains in an extended transferred are plasma reactor using graphite electrodes and argon as plasmagen gas. The primary SiC in the said process is taken in the graphite crucible and is then fixed on the anode. which provides structural support as well as electrical connection to the crucible. At the centre of the crucible a graphite pin is fixed which acts as anode tip. Argon passes through the central hole in the cathode and generate a stable extended arc thermal plasma in transferred mode with the arc routes linking the cathode and primary SiC grains. Initially the arc is struck between the said graphite cathode and the graphite anode tip forming the plasma. The SiC grains being placed close to the said plasma attains high temperature and becomes a conductor and then the said non-transferred arc plasma transforms to transferred mode which spreads over the entire surface of the charge. The vapour formed by sublimation under intense heat of plasma is allowed to condense on the water-cooled walls of the chamber. Additional large area chilled surfaces can be introduced to cope with high rate of sublimation. The ultrafine SiC deposited on the walls is collected intermittently. The product is treated for removal of carbon and silicon/silica. In the reported processes ultrafine SiC is synthesized using various gaseous reactants derived from silane or organo-silane, with CH4 using radio frequency and arc plasma torches and also by sublimation of a mixture of SiC and Si wherein the present invention ultrafine SiC is synthesized by sublimation of primary SiC grains using extended are plasma in transferred mode and subsequent condensation of the vapour phase on the chilled water cooled surfaces of the reactor. The following example is given by way of illustration of the present invention and should not be construed to limit the scope of the present invention. A general procedure is given with full details of the process with specific parameters: Charge material say SiC in the size range of+210 um was taken in a graphite crucible having inserted a graphite pin at the centre. The crucible was then mounted on the bottom electrode. Argon gas was introduced into the reactor through the top hollow electrode at the rate of 0.5 I.p.m. The top hollow electrode was lowered to make contact with the graphite pin in the bottom electrode and separated away to generate the arc plasma in the flowing gas. SiC was sublimed due to the intense heat of the plasma. The sublime vapour was made to condense at the water-cooled cold wall of the reactor. The deposits thus made were collected from wall and were found to be ultrafine nanocrystalline compounds (SiC) in the range of 20-60nm. The process was repeated with different charge materials to obtain ultrafine nanocrystalline compounds. The ultrafine powders obtained in the above way were subjected to purification in the following manner. At first, the powder was heated in presence of oxygen at 700-1 SO^C for 1/2 an hour to remove unreacted carbon. Then the resulting substance was subjected to repeated Hydrofluoric acid treatment in a platinum crucible till constant weight is obtained which indicates that silica has been removed. The following are some of the examples of the processes. 1. Ultrafine SiC powder in the size range of 20-60 nm has been prepared by transferred arc plasma using current of 75 amperes with argon gas flow rate of 0.5 slpm. The charge used was primary SiC of 10 \|im size. The duration of the experiments was 10 minutes. 2. Ultrafine WC or TiC powders were also prepared in the size range 50-80 nm by transferred arc plasma using current of 150 amp with argon gas flow rate of 1 s.l.p.m. and H2 flow rate of .1 s.l.p.m. The charges used were primary bulk WC or TiC respectively. The duration of the experiments was 15 minutes. 3. Ultrafine nanocrystalline SiC of 30-80 nm was prepared using calculated amount of silica and graphite in the above ways by argon gas flow rate of 0.25 s.l.p.m. A current of 50 amperes for 10 minutes was enough for the better yield. 4. In some other sets of experiments silica in the size range of 210,000 nm was taken as charge material with a current of 100 ampere. The plasmagen gas argon with flow rate of 0.1 s.l.p.m. and NH3 with flow rate of 0.1 s.l.p.m. for ten minutes produced Si3N4 in the size range of 60-120 nm. Introduction of hydrogen improves the thermal conductivity of plasma thereby increasing the quench rate and leading to smaller particle size. Addition of H2 gas 0.1 litre/min. increases the production rate from 0.05 gm/min. to 0.17 gm/min. (about 3 times) and particle size decreases form 90 nm to 38 nm. Increase in wattage from IKW to 3KW increases the rate of production from 0.02 gm/min. to 0.05 gm/min and particle size increases from 45 nm to 80 nm. Increase in flow rate of argon from 0.1 Itr/min to 1 Itr/min reduces the production rate from .05 gm/min to .03 gm/min but decreases the particle size from 80 nm to 50nm. Unlike the vapour phase synthesis of ultrafine SiC from different precursors, the ultrafine SiC produced by sublimation of SiC as described herein has low impurities. The yield of ultrafine SiC is as high as 5 jugm/J which is about 50 times higher than the vapour phases synthesis (12 H. Oya; T. Ichihashi and N. Wada Japn. J. Appl. Phys. 21 (1982) 554). The main advantages of the present invention are (i) Since it is a sublimation and condensation process it is not required to have elaborate arrangement to maintain required stoichiometry as in the case of vapour phase synthesis. (ii) The yield is as high as 5 um/J which is about 50 times higher than the vapour phase synthesis. (iii) The process is simple and the cost of production is low and therefore the new process described in this invention will meet the requirement of the industry at the reasonable price. (iv) The product prepared has uniform size range and results are highly reproducible. (v) The particle size of SiC made by the said process can be varied easily by control of plasma parameters. (vi) The process can be easily scaled up for commercial production. The investment as well as the cost of production is low. (vii) The said process is amenable and can be used for synthesis of a variety of nanocrystalline compounds such as TiC, WC, TiO2, SiO2, Si3N4 and SiC/SiN nano-composite powders. We Claim: 1. An improved process for preparation of ultra fine and nano-crystalline compounds which comprises; characterized in that subjecting primary grains of compounds selected from SiC, WC,TiC, TiC2 SisN4 for sublimation and condensation of the vapour on water cooled chilled surfaces of the reactor wherein the primary grain is taken in a graphite crucible having a graphite pin attached to its centre forms the anode and the other graphite electrode having a central hole forms the cathode, generating the plasma across the electrodes by connecting the cathode with anode and then separating the same under the constant flow of argon as plasmagen gas fed through the central hole of the cathode, collecting the deposited ultrafine nano crystalline compounds from the wall, removing the impurities such as carbon and silicon/silica by conventional methods such as herein described to get nano-crystalline compound. 2. The process as claimed in claim 1 wherein removal of carbon impurities present in ultra fine and nanometric product prepared in the said process by heating the same in a furnace at temperature of 500-900°C in air. 3. The process as claimed in claims 1,2 wherein SiO2 / SiO is removed by treating with HF acid. 4. An improved process for preparation of ultra fine and nano-crystalline compounds, substantially as herein described with reference to the examples.

Full Text

The present invention relates to an improved process for preparation of ultrafine and nanocrystalline compounds. The present invention particularly relates to a process of preparation of ultrafine particles of B-SiC, WC, TiO2, SiO2, Si3N4 of size in the range of 1 - 100 nm.
Nanomaterials exhibit properties that are not only much better than the conventional coarse grain but also often entirely different e.g. ZrO2 is a brittle material but when produced in the size range 2- 20 nm behaves like chewingum at high temp. Thus there is an up surge in the area of preparation of these nano-sized materials. In course of the present elaboration we take SiC a very useful hard ceramic material for illustration. However the process developed here can also be used for preparation of other ultrafine nanometric carbides, nitrides and oxides which are given as examples.
The ultrafine and nanometric p-SiC powder manufactured using the process of said invention finds application in the preparation of self bonded SiC product, kiln furniture and substrate material for x-ray mirrors. The said product is also useful as a phoiocatalyst and support material for catalyst. Due to the abrasive property, the said particles can be used for preparation of grinding and lapping compounds. Again the particles are used in paints to have a wear resistance coating. The said powder can be used in the preparation of high temperature composite materials such as gas turbine blades. Further the product can be used as polishing material and can develop high wear resistance properties when used as a coating with other adhesive binders.
A

Ultrafme SiC is synthesized by vapour phase reaction of silanes, organo-silanes and silicon with CH4, C2H4 using radio frequency and arc plasma torches (1-8). [ J.Y.Guo, F.Gitzlofer, M.L. Boulas ( Plasma Tech. Research Centre), Univ. of Sherbrooke, PQ Can. J1K 2R1), J. Mater Sc. 1995, 30 (22), 5569-99, SuO Duluo; Li Shimini; Xu, Zhene; Wen, Jie; Li, Daohuo; Liu, Zongea; National Engineering & Research Centre for Laser processing centre, China, Univ. of Sci. & Tech. Wuhan, people Republic of China, 430074, Wuji Cailino, Xuebao, 1995, 10(3) 301-6, G.J. Vogt. C.M. Hollabaugh, D.E. Hull, L.R. Wewkirk and J.J. Petrovic (1984), United States,_Department of Energy Report, DE 84-00 377*1 LOS Alamos; Department of Energy. Taylor, Patrick R; Poirzada, Shhid, A. (Daho \research foundation) U.S. US 5, 486, 675 (1. 217-121.59; 1323JCIO) 23 Jan. 1996. T. Hmeyma, K.Saknaka, A Mote, T.Tsunoda, T. Nakanaga, N.I.
'Wahayama, H. Takeo, K.Fukuda, Journal of mater Sci. 25 (1990) 1058-1065. Y. Anodo and m. Ohkohchi, J.Cryst. Growth, vol. 60, P. 147, 1982, J.D.F. Ramsay and R.G. Avery (1977), United Kingdom patent 1, 479, 727.

P.C. Kong, E. Pfender (1987),^Larigmuir, E, p. 259-65}. Draw back of the processes is that they make use of expensive precursors and the yield of SiC is low. It is also difficult to maintain stoichiometry in gaseous phase. p-SiC is also synthesized using carbon cathode and silicon anode. [ T. Inukai, J. Japan Soc. Powder and Powder Metall., Vol.27, No.8, p.249 (1980)]. The process is associated with high rate of erosion of carbon electrode since the source of carbon is from electrode. In this process the product is contaminated with free silicon. Ultrafine P-SiC is also prepared by arcing across electrodes made form a mixture of silica and carbon. [ W.U. Kuhn,

J-Electrochem. Soc. Vol. 110, No.4 , p. 298, 1963]. Ultrafme p-SiC is also synthesized by sublimation of SiC with SiC in are plasma. [Yusufumi Nariki, Yasunoby Inoue, Kohichi Tanaka, Jour. Of Mater Sic. 25 (1990) 3101 - 3104]. Use of silicon in the charge results free silicon and silica on the surface of P-SiC.
The main object of the present invention is to provide, an improved process for preparation of ultrafme/nanocrystalline compounds.
Another object of the present invention is to utilize the high temperature and high energy density available in thermal plasma for sublimation of SiC resulting in a high yield.
Still another object of the present invention is to make the transferred plasma operative with silicon carbide bulk without addition of costly silicon metal.
Yet another object of the present invention is to obtain particles in the size range of 1 - 100 nm. Yet another object of the present invention is to obtain in spite SiC/SiN composite in a single run.
Accordingly the present invention provides an improved process for preparation of ultra fine and nano-crystalline compounds which comprises; characterized in that subjecting primary grains of compounds selected from SiC, WC, TiC, TiO2 SisN4 for sublimation and condensation of the vapour on water cooled chilled surfaces of the reactor wherein the primary grain is taken in a graphite crucible having a graphite pin attached to its centre forms the anode and the other graphite electrode having a central hole forms the cathode, generating the plasma across the electrodes by connecting the cathode with anode and then separating the same under the constant flow of argon as plasmagen gas fed through the

central hole of the cathode, collecting the deposited ultrafine nano crystalline compounds from the wall, removing the impurities such as carbon and silicon/silica by conventional methods such as herein described to get nano-crystalline compound.
In another embodiment of the present invention the transferred are plasma is established thorough the said graphite pin placed centrally within the primary SiC charge (grains) materials which provides the electrical continuity for the are plasma as SiC does not possess electrical conductivity at ambient temperature.
In another embodiment of the present invention the carbon present in ultra fine/ nanometric product prepared in the said process is removed by heating the product in the rnage of 500 -900°C in air.
In yet another embodiment of the present invention the surface silica impurity is removed by HF treatment.
The process of preparing ultrafme/nanometric 0-SiC comprises sublimation of primary SiC grains in an extended transferred are plasma reactor using graphite electrodes and argon as plasmagen gas. The primary SiC in the said process is taken in the graphite crucible and is then fixed on the anode.

which provides structural support as well as electrical connection to the crucible. At the centre of the crucible a graphite pin is fixed which acts as anode tip. Argon passes through the central hole in the cathode and generate a stable extended arc thermal plasma in transferred mode with the arc routes linking the cathode and primary SiC grains. Initially the arc is struck between the said graphite cathode and the graphite anode tip forming the plasma. The SiC grains being placed close to the said plasma attains high temperature and becomes a conductor and then the said non-transferred arc plasma transforms to transferred mode which spreads over the entire surface of the charge. The vapour formed by sublimation under intense heat of plasma is allowed to condense on the water-cooled walls of the chamber. Additional large area chilled surfaces can be introduced to cope with high rate of sublimation. The ultrafine SiC deposited on the walls is collected intermittently. The product is treated for removal of carbon and silicon/silica.
In the reported processes ultrafine SiC is synthesized using various gaseous reactants derived from silane or organo-silane, with CH4 using radio frequency and arc plasma torches and also by sublimation of a mixture of SiC and Si wherein the present invention ultrafine SiC is synthesized by sublimation of primary SiC grains using extended are plasma in transferred mode and subsequent condensation of the vapour phase on the chilled water cooled surfaces of the reactor.
The following example is given by way of illustration of the present invention and should not be construed to limit the scope of the present

invention. A general procedure is given with full details of the process with specific parameters: Charge material say SiC in the size range of+210 um was taken in a graphite crucible having inserted a graphite pin at the centre. The crucible was then mounted on the bottom electrode. Argon gas was introduced into the reactor through the top hollow electrode at the rate of 0.5 I.p.m. The top hollow electrode was lowered to make contact with the graphite pin in the bottom electrode and separated away to generate the arc plasma in the flowing gas. SiC was sublimed due to the intense heat of the plasma. The sublime vapour was made to condense at the water-cooled cold wall of the reactor. The deposits thus made were collected from wall and were found to be ultrafine nanocrystalline compounds (SiC) in the range of 20-60nm. The process was repeated with different charge materials to obtain ultrafine nanocrystalline compounds. The ultrafine powders obtained in the above way were subjected to purification in the following manner. At first, the powder was heated in presence of oxygen at 700-1 SO^C for 1/2 an hour to remove unreacted carbon. Then the resulting substance was subjected to repeated Hydrofluoric acid treatment in a platinum crucible till constant weight is obtained which indicates that silica has been removed.
The following are some of the examples of the processes.
1. Ultrafine SiC powder in the size range of 20-60 nm has been prepared by transferred arc plasma using current of 75 amperes with argon gas flow rate of 0.5 slpm. The charge used was primary SiC of 10 |im size. The duration of the experiments was 10 minutes.

2. Ultrafine WC or TiC powders were also prepared in the size range 50-80 nm by transferred arc plasma using current of 150 amp with argon gas flow rate of 1 s.l.p.m. and H2 flow rate of .1 s.l.p.m. The charges used were primary bulk WC or TiC respectively. The duration of the experiments was 15 minutes.
3. Ultrafine nanocrystalline SiC of 30-80 nm was prepared using
calculated amount of silica and graphite in the above ways by argon
gas flow rate of 0.25 s.l.p.m. A current of 50 amperes for 10 minutes
was enough for the better yield.
4. In some other sets of experiments silica in the size range of 210,000
nm was taken as charge material with a current of 100 ampere. The
plasmagen gas argon with flow rate of 0.1 s.l.p.m. and NH3 with flow
rate of 0.1 s.l.p.m. for ten minutes produced Si3N4 in the size range
of 60-120 nm.
Introduction of hydrogen improves the thermal conductivity of plasma thereby increasing the quench rate and leading to smaller particle size. Addition of H2 gas 0.1 litre/min. increases the production rate from 0.05 gm/min. to 0.17 gm/min. (about 3 times) and particle size decreases form 90 nm to 38 nm. Increase in wattage from IKW to 3KW increases the rate of production from 0.02 gm/min. to 0.05 gm/min and particle size increases from 45 nm to 80 nm. Increase in flow rate of argon from 0.1

Itr/min to 1 Itr/min reduces the production rate from .05 gm/min to .03 gm/min but decreases the particle size from 80 nm to 50nm. Unlike the vapour phase synthesis of ultrafine SiC from different precursors, the ultrafine SiC produced by sublimation of SiC as described herein has low impurities. The yield of ultrafine SiC is as high as 5 jugm/J which is about 50 times higher than the vapour phases synthesis (12 H. Oya; T. Ichihashi and N. Wada Japn. J. Appl. Phys. 21 (1982) 554).
The main advantages of the present invention are
(i) Since it is a sublimation and condensation process it is not required to have elaborate arrangement to maintain required stoichiometry as in the case of vapour phase synthesis.
(ii) The yield is as high as 5 um/J which is about 50 times higher than the vapour phase synthesis.
(iii) The process is simple and the cost of production is low and therefore the new process described in this invention will meet the requirement of the industry at the reasonable price.
(iv) The product prepared has uniform size range and results are highly reproducible.

(v) The particle size of SiC made by the said process can be varied easily by control of plasma parameters.
(vi) The process can be easily scaled up for commercial production. The investment as well as the cost of production is low.
(vii) The said process is amenable and can be used for synthesis of a variety of nanocrystalline compounds such as TiC, WC, TiO2, SiO2, Si3N4 and SiC/SiN nano-composite powders.

We Claim:
1. An improved process for preparation of ultra fine and nano-crystalline compounds
which comprises; characterized in that subjecting primary grains of compounds selected
from SiC, WC,TiC, TiC2 SisN4 for sublimation and condensation of the vapour on water
cooled chilled surfaces of the reactor wherein the primary grain is taken in a graphite
crucible having a graphite pin attached to its centre forms the anode and the other
graphite electrode having a central hole forms the cathode, generating the plasma across
the electrodes by connecting the cathode with anode and then separating the same under
the constant flow of argon as plasmagen gas fed through the central hole of the cathode,
collecting the deposited ultrafine nano crystalline compounds from the wall, removing
the impurities such as carbon and silicon/silica by conventional methods such as herein
described to get nano-crystalline compound.
2. The process as claimed in claim 1 wherein removal of carbon impurities present in ultra
fine and nanometric product prepared in the said process by heating the same in a
furnace at temperature of 500-900°C in air.
3. The process as claimed in claims 1,2 wherein SiO2 / SiO is removed by treating with HF
acid.
4. An improved process for preparation of ultra fine and nano-crystalline compounds,
substantially as herein described with reference to the examples.

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Patent Number

218001

Indian Patent Application Number

311/DEL/2001

PG Journal Number

19/2008

Publication Date

09-May-2008

Grant Date

31-Mar-2008

Date of Filing

19-Mar-2001

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI - 110 001, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	PRATHA SARATHI MUKHERJEE	REGIONAL RESEARCH LABORATORY, BHUBNESWAR-751013, ORISSA, INDIA.
2	KEDAR NATH JENA	REGIONAL RESEARCH LABORATORY, BHUBNESWAR-751013, ORISSA, INDIA.
3	BISHNU CHARANDRBINDA MOHANTY	REGIONAL RESEARCH LABORATORY, BHUBNESWAR-751013, ORISSA, INDIA.

PCT International Classification Number

C04B 040/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA