Title of Invention

"AN APPARATUS FOR MAKING ULTRAFINE/NANOMETRIC MATERIALS"

Abstract An apparatus for making ultrafine/nanometric materials such as carbides, nitrides and oxides, which comprises a circular water cooled double walled reactor chamber (1), characterized in that the said reactor chamber being provided with a movable vertical co-axially placed graphite I metal cathode (2) having a central axial hole for passing plasmagen gas to the said reactor chamber (1), the said cathode (2) being provided at the bottom end inside the chamber (1) with a detachably fixed graphite /metal bit (4) having matching central hole, the said chamber (1) being provided with a vertical bottom graphite I metal anode (3) concentrically placed and co-axially aligned with the said vertical cathode (2), the said anode (3) being provided at the top end inside the chamber (1) with a detachably fixed graphite crucible (6) capable of holding the charge material, the said crucible (6) being provided with a concentric and co-axialy placed removably fixed conducting pin (7), the said chamber (1) being provided with concentrically placed horizontal top and bottom radiation shields (8 & 9), the said chamber being also provided on the side with a horizontal water cooled lead pipe (10) capable of passing gas onto the reaction zone (5).
Full Text The present invention relates to an apparatus for making ultrafine/ nanometric materials such as carbides, nitrides and oxides.
The ultrafine / nanometric materials prepared using the novel apparatus of the present invention have exceptional new properties which find use such as catalyst, catalyst support, pigment. These powders due to its very small particle size having large surface area can be sintered at much lower temperature with superior properties.
High enthalpy thermal arc plasma is harnessed in many ways for synthesis of ultrafine/ nanometric particles of different materials. In most cases torch is used wherein high amount of plasmagen gas is required and there are chances of metal contamination in the final product. In some cases costly charge materials are also used along with costly instrumentation.
Reference may be made to P. Kong, T.T. Huang and £. Fender, Transaction of plasma science vol.- P.S-14, No.4, Aug. 1946, 357-369, wherein an equipment for synthesis of carbides is used by arc discharge using carbon cathode and Si or SiC anode operating in vacuum with carbonaceous gas as reactant and with inert gas feeding. Anode is consumable and its preparation is cumbersome and expensive.
Reference may be made to C.W. Zhu, G.Y. ZHAO, V. Revankar and V. Hlavacek, journal of material science, 28 (1993) 659-668 wherein a d.c. plasma torch is used in vacuum. The process is expensive due to use of torch wherein use of large quantity of gas and high power requirement makes the process costlier. Further due to use of large quantity of costly plasmagen gas in torch substantial amount of heat is lost in the flue gas thereby adding to the cost of production.
Reference may be made to F. Allaire, L. Parent and S. Dallaire, jour. Of Mat. Sc. 26(1991)4160-4165; S. Bousrich, E. Ershov-Pavlov. S. Megy and J.M. Baronnet Plasma Chemistry and Plasma processing, Vol.l5.No.2, 1995, 333-350; and B. Kumar and M.M. Godkhindi, Journal of material science letters, 15(1996) 403-405, wherein though the reaction chamber is operated around atmospheric pressure the cathode is made up of water cooled thoriated tungsten. Often erosion of water-cooled metal cathode causes contamination of the product as well as its maintenance & replacement adds to the cost of production.
The main object of the present invention is to provide an apparatus for making ultrafine / nanometric materials of carbides, nitrides and oxides wherein extended arc plasma is produced without using costly prebaked electrodes and with low consumption of plasma gas.
Another object of the present invention is to use high energy density thermal plasma to cause flash evaporation/ sublimation followed by condensation of nanoparticles so formed.
Still another object of the present invention is to use thermal plasma for increasing the production rate with improved thermal efficiency.
Yet another object of the present invention is to provide an efficient water cooling system for the reactor assembly for enabling effective condensation.
A further object of the present invention is to provide a graphite pin in the anode for enabling use of non-conducting powders as charge material.
In the apparatus of the present invention there is provided an extended arc
thermal plasma having plasma having graphite / metallic electrode and operating in
both transferred and nontransferred mode where relatively small amounts of
plasmagen gas is passed through the narrow hole of the cathode and a very stable arc
plasma is formed for heating the charge and synthesing ultrafine materials. For
synthesis of carbides graphite electrode and graphite crucibles are used and for
synthesis of oxides and nitrides of metals respective metal electrodes are used. In
this process there is no contamination as it happens in case of copper anode. The
production rate is high, thermal efficiency is also high due to use of less quantity of
plasmagen gases as compared to torches. The reactor with extended arc plasma
heating is simple, is easy to operate and produce ultrafine materials at lower cost as
compared to the torch type reactors.
The novel apparatus of the present invention for making ultrafine/ nanometric materials has resulted due to the following non-obvious inventive steps: 1. Capable of using of both conducting & non-conducting charge material due to the provision of a removably fixed conducting pin in charge holding crucible.
2.Low consumption of plasmagen gas due to the provision of a narrow central axial hole in the
cathode.
3ft on use of costly pre-backed electrodes.
4.Eliminating the necessity of vacuum.
5.Efficient water cooling system
In the drawing accompanying this specification Fig-1 depicts an embodiment of the novel apparatus of the present invention for making ultrafine/nanometric materials, wherein the various parts are :
1. Reactor chamber
2. Graphite cathode
3. Graphite anode
4. Graphite bit

5. Arc plasma
6. Graphite crucible
7. Conducting / Graphite pin
8.&9 Radiation shield
10. Water cooled lead / exhaust pipe
11. Exhaust collection chamber
12. Safety valve
Accordingly the present invention provides an apparatus for making ultrafine/nanometric materials such as carbides, nitrides and oxides, which comprises a circular water cooled double walled reactor chamber (1), characterized in that the said reactor chamber being provided with a movable vertical co-axially placed graphite / metal cathode (2) having a central axial hole for passing plasmagen gas to the said reactor chamber (1), the said cathode (2) being provided at the bottom end inside the chamber (1) with a detachably fixed graphite / metal bit (4) having matching central hole, the said chamber (1) being provided with a vertical bottom graphite / metal anode (3) concentrically placed and co-axially aligned with the said vertical cathode (2), the said anode (3) being provided at the top end inside the chamber (1) with a detachably fixed graphite crucible (6) capable of holding the charge material, the said crucible (6) being provided with a concentric and co-axialy placed removably fixed conducting pin (7), the said chamber (1)
being provided with concentrically placed horizontal top and bottom radiation shields (8 & 9), the said chamber being also provided on the side with a horizontal water cooled lead pipe (10) capable or passing gas onto the reaction zone (5).
In an embodiment of the present invention the apparatus consists of an extended arc plasma reactor with provision for forming arc plasma (5) across the electrodes (2 & 3) and the conducting charge in transferred mode with provision for introduction of plasmagen gases through the central hole of the cathode (2).
In another embodiment of the present invention the lead pipe (10) capable of passing gas to the reaction zone is provided optionally with a water-cooled exhaust pipe (10) connected to an exhaust collection chamber (11) having a safety valve (12).
In yet another embodiment of the present invention a conducting pin (7) such as a graphite pin is introduced through a non-conducting charge to enable establish a nontransferred arc plasma which subsequently changes to transferred mode when the charge acquires ionic conductivity at elevated temperature.
In still another embodiment of the present invention graphite electrode and graphite crucible are used for carbides and respective metal electrodes are used for oxides and nitrides of metals. The apparatus of the present invention is described below along with function of various parts.
Referring to the Fig.-l of the drawing the reactor comprises a water-cooled reaction chamber (1) with upper electrode (2) and lower electrode (3). The upper electrode (2) has a central hole for introducing plasmagen gases. An electrode bit (4) is attached to the lower end of the upper electrode (2) which also has a matching central hole for passing the plasmagen gas forming the plasma in the arcing zone. A crucible (6) is attached to the upper end of the lower electrode (3) for holding the charge. A conducting pin (7) is introduced through the said crucible (6) and is connected to the lower electrode (3). Both the electrodes (2 & 3) are adequately water-cooled. The radiation shields (8 & 9) are placed at top and bottom of the reaction chamber (1) concentric with upper electrode (2) and lower electrode (3) to protect the components from high temperature radiation damage. A water cooled exhaust pipe (10) is fixed to the water cooled reactor (1) with provision for moving the pipe axially to adjust the location from the center of the plasma for introducing reactant gases as and when necessary. The particle condenses on the water-cooled surfaces within the water-
cooled chamber (1). The out let pipe (12) of the collection chamber (11) may be used to lead the gaseous exhaust into the atmosphere or may be connected to a vacuum system for getting ultrafine/nanometric particles at low pressure.
In the present invention oi an apparatus for making ultrafine/ nanometric materials which comprises an arc plasma reactor (1) with provision for forming an arc plasma (5) in transferred mode for the conducting charge materials , the arc initiated across electrodes (2 & 3) in non-transferred mode by extending the electrode through the charge material and the arc then subsequently changes to transferred mode when the charge becomes an ionic conductor at elevated temperature, where the said reactor comprises a water cooled reaction chamber(l), a crucible support on the bottom (6) to the electrode (3) for holding the charge to cause flash evaporation by heat of the arc plasma, and subsequent condensation of the vapour or reactive condensation of the gaseous product with introduction of gaseous reactants forming ultrafine and nanometric materials.
In this invention the intense heat produced by D.C. extended arc plasma is used to directly vaporise the compound to condense the same in the ultrafine from or vaporise the solid precursor or reactive vaporization of precursor for gas phase synthesis of desired compound by reacting with other gaseous precursor fed separately into the reactor. The reactor can operate in transferred mode with higher thermal efficiency if the charge is conducting or semiconducting.
The present apparatus makes use of an extended arc thermal plasma using graphite/ metallic electrode and operating in both transferred and non transferred mode wherein very small amount of plasmagen gas is required to be passed through cathode for a stable arc plasma to be formed. For synthesis of carbides graphite electrodes and crucibles can be used where as for oxides and nitrides suitable metal electrodes can be used. The other advantages of this apparatus are that production rate is high with high thermal efficiency, easy to operate and leads to low cost of production as a whole.
The novel apparatus of the present invention for making ultrafine/nanometric materials has eliminated the use of costly prebaked electrode and use of vacuum as used by P. Kong, T.T. Huang and E. Fender, Transaction of plasma science vol.- P.S-14, No.4, Aug. 1946, 357-369.
The novel apparatus of the present invention also uses very small amount of plasmagen gas for a stable plasma operation unlike large amount of gas required in the plasma torch system used by C.W. Zhu, G.Y. ZHAO, V. Revankar and V. Hlavacek, journal of material science, 28 (1993) 659-668, F. Allaire, L. Parent and S. Dallaire, jour. Of Mat. Sc. 26(1991)4160-4165, S. Bousrich, E. Ershov-Pavlov. S. Megy and J.M. Baronnet Plasma Chemistry and Plasma processing, Vol,15.No.2, 1995, 333-350 wherein the production cost increases due to increased cost of gas, use of vacuum, and loss of heat through flue gases.
This novel apparatus of the present invention also eliminates in many cases use of metal electrodes thereby avoiding contamination and separate water cooling facility.
The novel apparatus is easy to fabricate and reduces the cost of production by increasing the thermal efficiency of the plasma and reducing the quantity of plasmagen gas significantly.
The novel apparatus can work both in transferred mode and nontransferred mode and capable of handling large spectrum of materials which includes carbides, nitrides and oxides by suitably choosing the reactants and plasmagen gas combination.
The following examples are given by way of illustration and should not be construed to limit the scope of the invention.
Example 1 Production of Silicon Carbide
The charge material for the production of silicon carbide chosen here were a mixture of 10 gm of silica of particle size ~ 100µ and 6 gm of carbon of particle size ~ 100µ. The components were intimately mixed and put in the crucible (6) in the apparatus. Plasmagen gas Argon 0.5 ltr/m was passed through the upper electrode (2) for some time prior to starting arc by touching the conducting pin (7) and raising the electrode slowly to a stable arc with plasma specification.
Voltage = 25-30 V Current = 70 -80 amp
The arc was maintained for 10 minutes. The ultrafine powders was collected from the reaction chamber. The amount of silicon carbide produced was 1.025 gm. In this example the plasma started as non transferred arc but later due to temperature of the charge become a transferred arc.
Example - 2 Production of silicon carbide
The procedure of using the apparatus was same except that in this the charge material was taken as normal silicon carbide powder wherein due to its good electrical conductivity the plasma works in transferred mode which gives higher thermal efficiency.
Charge material silicon carbide -12 gm of size ~ 200µ
Plasmagen gas = 0.5 ltr/m
Voltage = 28 to 30 V
Current = 70 80 amp
Time = 10 min
The amount of ultrafine silicon carbide produced = 1.127 gm
Example-3 Production of silicon nitride
In this case the charge material taken was 10 gm of fine silica power of size ~ 70µ. The plasmagen gases used are argon and ammonia. The experiment was carried out in a similar fashion as explained in example 1.
Charge material used = 10 gm of silica powder
Plasmagen gas : = Argon (0.1 ltr/m) + Ammonia (0.1 ltr/m)
Voltage = 28-30 V
Current = 90-100 amp
The amount of nanocrystalline silicon nitride produced is 1.762 gm.
The main advantages of the present invention are :
1. Use of an extended arc thermal plasma using graphite electrode and operating both in transferred arc and non- transferred arc mode.
2. The production rate is high, the thermal efficiency is also high due to use of less quantity of plasmagen gas as compared to torches.
3. Carbides and oxides can be prepared easily with the reactor.
4. The reactor with extended arc plasma heating is easy to fabricate and produce ultra fine material at lower cost as compared to the torch type reactors.
5. It eliminates the use of costly prebaked electrodes and vacuum.
6. It also eliminates in many cases the use of metal electrodes thereby avoiding contamination.






We claim:
1. An apparatus for making ultrafine/nanometric materials such as carbides, nitrides and oxides, which comprises a circular water cooled double walled reactor chamber (1), characterized in that the said reactor chamber being provided with a movable vertical co-axially placed graphite / metal cathode (2) having a central axial hole for passing plasmagen gas to the said reactor chamber (1), the said cathode (2) being provided at the bottom end inside the chamber (1) with a detachably fixed graphite / metal bit (4) having matching central hole, the said chamber (1) being provided with a vertical bottom graphite / metal anode (3) concentrically placed and co-axially aligned with the said vertical cathode (2), the said anode (3) being provided at the top end inside the chamber (1) with a detachably fixed graphite crucible (6) capable of holding the charge material, the said crucible (6) being provided with a concentric and co-axialy placed removably fixed conducting pin (7), the said chamber (1) being provided with concentrically placed horizontal top and bottom radiation shields (8 & 9), the said chamber being also provided on the side with a horizontal water cooled lead pipe (10) capable of passing gas onto the reaction zone (5).
2. An apparatus as claimed in claim 1 wherein the lead pipe (10) provided for passing gas to the reaction zone is provided optionally with a water-cooled exhaust pipe (10) connected to an exhaust collection chamber (11) having a safety valve (12).
3. An apparatus as claimed in claim 1-2, wherein the conducting pin (7) such as a graphite pin is introduced through a non-conducting charge to enable establish a non-transferred arc plasma which subsequently changes to transferred mode when the charge acquires ionic conductivity.
4. An apparatus as claimed in claim 1-4, wherein graphite electrode and graphite crucible is used for carbides and respective metal electrodes are used for oxides and nitrides of metals.
5. An apparatus for making ultrafine/nanometric materials such as carbides, nitrides and oxides substantially as herein described with reference to the examples and drawings accompanying this specification.


Documents:

1177-del-2001-abstract.pdf

1177-del-2001-claims.pdf

1177-del-2001-correspondence-others.pdf

1177-del-2001-correspondence-po.pdf

1177-del-2001-description (complete).pdf

1177-del-2001-drawings.pdf

1177-del-2001-form-1.pdf

1177-del-2001-form-18.pdf

1177-del-2001-form-2.pdf

1177-del-2001-form-3.pdf


Patent Number 243466
Indian Patent Application Number 1177/DEL/2001
PG Journal Number 43/2010
Publication Date 22-Oct-2010
Grant Date 19-Oct-2010
Date of Filing 26-Nov-2001
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 KEDAR NATH JENA REGIONAL RESEARCH LABORATORY, BHUBANESHWAR-751013, ORISSA (INDIA)
2 KALI CHARAN BESHRA REGIONAL RESEARCH LABORATORY, BHUBANESHWAR-751013, ORISSA (INDIA)
3 PARTHA SARATHI MUKHERJEE REGIONAL RESEARCH LABORATORY, BHUBANESHWAR-751013, ORISSA (INDIA)
4 BISHNU CHARNARBINDA MOHANTY REGIONAL RESEARCH LABORATORY, BHUBANESHWAR-751013, ORISSA (INDIA)
PCT International Classification Number C01G 21/06
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA