Title of Invention

"A PROCESS FOR THE MANUFACTURE OF ALUMINIUM NITRIDE"

Abstract

Aluminum nitride prepared by direct nitridation of aluminum metal has limitation of high synthesis temperatures. Further it requires that aluminum metal to be in finely divided state. The present invention describes a process that overcomes these limitations. The novelty of the process is that: 1. The reaction temperatures are below 1000°C. 2. Aluminum metal need not be in a finely divided state. 3. The process achieves essentially 100% nitridation.

Full Text

The present invention relates to a process for the manufacture of aluminum nitride. This invention relates particularly to a process for the manufacture of aluminum nitride from metallic aluminum. More particularly this invention provides a process for the preparation of aluminum nitride from aluminum alloy. Aluminum Nitride has very good electrical insulation, similar to other ceramics. It also has very high thermal conductivity like metals. It is also very hard. It has a low coefficient of thermal expansion. It is non-corrosive to most molten metals. Because of these properties Aluminum Nitride finds wide usage in industry. In the general engineering industry, it can be used as a wear resistant coating, and a hard coating, either on its own or in combination with other materials. It can be used to make cutting tool tips. In the electronic industry as a substrate, wherein both its high electrical resistivity and high thermal conductivity are simultaneously required. In the metallurgical industry as a crucible material because of its low thermal expansion and high corrosion resistance. It is used as a reinforcement in metal matrix composites. It is used in polymer matrix composites as a filler to modify the thermal expansion coefficient and improve the heat transfer properties. There are several methods for synthesizing Aluminum Nitride which are describeda by L.M.Shepperd in Am.Ceram.Soc.Bull., 69 ,(11) 1801 (1990) and T.J.Mroz, in J.Am.Ceram.Soc.,72 , (6) 78 (1993). One such method is the reduction of alumina (AlaO}) by carbon in the presence of nitrogen or ammonia gas or a suitable mixture of both at temperatures of 1650 degrees Kelvin or above, and the other is the direct nitridation of Aluminum metal by Nitrogen gas at similar temperatures. These are the currently used methods for industrial scale production of Aluminum Nitride. There are other, less common and expensive methods for producing Aluminum Nitride based on the reduction of Aluminum tri-chloride with Ammonia gas and Plasma Nitridation, and the calcination of a poly-aluminolane compound produced by heating i diird i'el made In ihe anodic dissolution of metallic Aluminum in an electrolyte containing a prim,IP jiiiinc and the pyrolysis of the resulting organometallic precursor, specifically, diiniili\ I ammo alummoiane. 1 'in1 "i i In- diaul wok:-, of i he existing processes for direct nitridation of aluminum is that very hi"h u mp.-iatuies are required for the synthesis. Another drawback is that very high pressures in uqniu'd durum ilie reaction. Yet another drawback is that the metal has to be in a finely i IK \> huh has a naturally formed layer. Yet another drawback is that there is a black minded Mirlace which is difficult to remove in the case of finely divided .iiinnni i Ml ihese disadvantages have necessitated a new and simple method as described ii mam "hirei ;•(' '!R- present invention is to provide a process for the manufacture of \liiiiiiiiiiin Niirule lioni aluminum alloy which obviates the drawbacks as detailed above. .'•.Mom, i objeet dl ilu- present invention is to provide a method, which is simpler and cost iin nl)|cc!i\e of the present invention is to produce Aluminum Nitride at relatively ln'.\ irmpi-iaimes and low pressures. Shii ,ii,,iihri elm-it of the present invention is to provide a method which is reproducible. \n..iii.-i ..I'M•' i IN io piuvule a process wherein the metal need not be in a finely divided state .UK! il trii and ilnouiili mtiklalion of the bulk metal is achieved. Miiiiuiiiiiii niiinle prepared hy direct nitridation of aluminum metal has limitation of high .-.nUie r u-nipeiaiiires. further it requires that aluminum metal to be in finely divided state. i he pi. ,i.,! mu-niior describes a process that overcomes these limitations. The novelty of ilu enM (.",-. i', ihal: a) The reaction temperatures are below 1000°C. b) Aluminum metal need not be in a finely divided state. c) The process achieves essentially 100% nitridation. In the present invention conventionally produced aluminum alloy with the composition Cu -0.019 , Fe -0.22 , Mn- 0.28, Si- 0.03-0.3 , Ni- 0.02, Mg- 0.5-5, Zn- 0.06 ,Ti- 0.02 weight % and remainder Al is placed in a reaction vessel and the lid secured, the vessel is evacuated and back filled with pure Nitrogen sufficient number of times to remove any residual Oxygen present in the vessel at the time of closing. Finally, the vessel is pressurized with Nitrogen pressure of atleast 0.5 Mpa. The vessel is then heated to a temperature of atleast 750 degree Celsius. This temperature is held constant and the Nitrogen gas pressure inside is also maintained constant for the required length of time, which can be several hours. At the end of the reaction the furnace is switched off and the Aluminum Nitride recovered after the vessel has cooled. Accordingly, the present invention provides a process for the manufacture of aluminum nitride which comprises nitriding conventionally produced aluminum alloy having composition Cu 0.019 , Fe 0.22, Mn 0.28, Si 0.03 to 0.3 , Ni 0.02, Mg 0.5 to 5, Zn 0.06 , Ti 0.02 weight % and remainder Al in oxygen free atmosphere, in the presence of nitrogen at a pressure of atleast 0.5Mpa and a temperature in the range 750 to 1000 degree Celsius for a period in the range of 15 to 50 hours, cooling to ambient temperature at the holding pressure, followed by gradual reduction to ambient pressure. In an embodiment of the present invention, the Aluminum used in the conventionally produced aluminum alloy with the composition Cu 0.019 , Fe 0.22, Mn 0.28, Si 0.03 to 0.3 , Ni 0.02, Mg 0.5 to 5, Zn 0.06 , Ti 0.02 weight % and remainder Al, may be commercially pure aluminum metal. In another embodiment of the present invention, Aluminum alloy used may be in bulk form. In still another embodiment of the present invrention, the nitrogen gas used may be of grade 1. The process steps of the present invention are described below: Conventionally produced aluminum alloy with the composition Cu -0.019 , Fe -0.22, Mn-0.28, Si- 0.03-0.3 , Ni- 0.02, Mg- 0.5-5, Zn- 0.06 ,Ti- 0.02 weight % and remainder Al is kept in a pressure vessel which is kept in a temperature controlled furnace. Before beginning heating, the vessel is sealed leak-tight for vacuum and pressure. All traces of Oxygen are removed by repeated vacuuming and back flushing with pure nitrogen gas. The vessel is brought up to the operating pressure with pure nitrogen gas and the temperature raised to the required nitriding temperature. The system is held at these temperature and pressure conditions for the necessary time. Both temperature and pressure are automatically held constant throughout the period. After the set time the system is allowed to cool to room temperature holding the pressure at the original value. The pressure is released gradually and the sample recovered for further processing after the pressure reaches ambient pressure. Nitrided aluminum alloy usually has a thin black covering which can be scraped off. The material can be ground to required fineness depending on the use such as electronic substrate making. The noveltv of the present invention is that Aluminum nitride is prepared at a low temperature of the order of 750 to 1000 degree Celsius as against commercial processes working at greater than 1400 degree Celsius. Moreover the pressure under which nitriding is effected is as low as 0.5 Mpa. Further instead of aluminum powder and chips, in the process of the present invention , the starting material is conventionally produced bulk aluminum alloy with the composition Cu -0.019 , Fe -0.22, Mn- 0.28, Si- 0.03-0.3 , Ni- 0.02, Mg- 0.5-5, Zn- 0.06 ,Ti- 0.02 weight % and remainder commercially pure Al . The process achieves 100% nitridation and provides pure ALN. The inventive step of the process of the present invention which results in the novelty resides in the conventionally produced bulk aluminum alloy with the composition Cu -0.019 , Fe - 0.22, Mn- 0.28, Si- 0.03-0.3 , Ni- 0.02, Mg- 0.5-5, Zn- 0.06 ,Ti- 0.02 weight % and remainder Al. The following examples are given by way of illustrating the present invention and therefore should not be construed as limiting the scope of the present invention. Example 1. Conventionally produced bulk aluminum alloy with the composition Cu -0.019, Fe -0.22, Mn- 0.28, Si- 0.03, Ni- 0.02, Mg 0.5, Zn- 0.06,Ti- 0.02 weight % and remainder Al comprising of lathe turnings, are kept in a graphite crucible, which is placed in the pressure vessel. The vessel is sealed leak-tight. All traces of Oxygen are removed by repeated vacuuming and back flushing with pure Nitrogen gas. The Nitrogen gas pressure is brought up to the operating pressure of 0.8 MPa. The temperature is brought up to the operating temperature of 800 degrees Celsius. The pressure vessel is maintained at these conditions for a period of 48 hours. At the end of this time the heating is switched off and the pressure vessel cooled to room temperature, while maintaining the Nitrogen gas pressure. After the vessel has cooled, the Nitrogen pressure is reduced to ambient pressure, the vessel opened and the product removed. X-Ray-Diffraction studies show that the material is pure A1N without any contamination. Example 2. Conventionally produced bulk aluminum alloy with the composition Cu -0.019 , Fe -0.22, Mn- 0.28, Si-0.06, Ni- 0.02, Mg- 0.5, Zn- 0.06 ,Ti- 0.02 weight % and remainder Al comprising of pieces of approximately 5mm size, are kept in an alumina crucible, which is placed in the pressure vessel .The vessel is sealed leak-tight. All traces of Oxygen are removed by repeated vacuuming and back flushing with pure Nitrogen gas. The Nitrogen gas pressure is brought up to the operating pressure of 0.9 MPa. The temperature is brought up to the operating temperature of 850 degrees Celsius. The pressure vessel is maintained at these conditions for a period of 24 hours. At the end of this time the heating is switched off and the pressure vessel cooled to room temperature, while maintaining the Nitrogen gas pressure. After the vessel has cooled, the Nitrogen pressure is reduced to ambient pressure, the vessel opened and the product removed. X-Ray-Diffraction studies show that the material is pure A1N without any contamination Example 3. Conventionally produced bulk aluminum alloy with the composition Cu -0.019, Fe -0.22, Mn- 0.28, Si- 0.1, Mg -1.0, Ni- 0.02, Zn- 0.06 ,Ti- 0.02 weight % and remainder Al comprising of approximately 10mm size, are kept in a silica crucible, which is placed in the pressure vessel. The vessel is sealed leak-tight. All traces of Oxygen are removed by repeated vacuuming and back flushing with pure Nitrogen gas. The Nitrogen gas pressure is brought up to the operating pressure of 1 MPa. The temperature is brought up to the operating temperature of 1000 degrees Celsius. The pressure vessel is maintained at these conditions for a period of 18 hours. At the end of this time the heating is switched off and the pressure vessel cooled to room temperature, while maintaining the Nitrogen gas pressure. After the vessel has cooled, the Nitrogen pressure is reduced to ambient pressure, the vessel opened and the product removed. X-Ray-Diffraction studies show that the material is pure A1N without any contamination. The main advantages of the present invention are : 1) Economical process as reaction temperature is below 1000° C. 2) Bulk form of metal can be used instead of finely divided state. 3) 100% nitridation is achieved. 4) Pure A1N is obtained. We claim: 1. A process for the manufacture of aluminum nitride which comprises nitriding conventionally produced Aluminum alloy having composition Cu 0.019, Fe 0.22, Mn 0.28 , Si 0.03 to 0.3, Ni 0.02, Mg 0.5 to 5, Zn 0.06, Ti 0.02 weight % and remainder Al in oxygen free atmosphere , in the presence of nitrogen at a pressure of 0.5 Mpa and a temperature in the range 750 to 1000 degree Celsius for a period in the range of 15 to 50 hours , cooling to a temperature ranging 25-35°C in the holding pressure, followed by gradual reduction to ambient pressure . 2. A process as claimed in claim 1 , where in the Aluminium used in the conventionally produced aluminium alloy with the composition Cu 0.019, Fe 0.22, Mn 0.28, Si 0.03 to 0.3, Ni 0.02, Mg 0.5 to 5, Zn 0.06, Ti 0.02 weight % and remainder Al, is commercially pure aluminium metal. 3. A process as claimed in claim 1-2 , where in the Aluminium alloy used is in the bulk form . 4. A process as claimed in claim 1 -3, where in the nitrogen gas used is of grade 1 5. A process for the preparation of aluminum nitride from metallic aluminum substantially as herein described and explained with reference to the examples and drawings accompanying this specification.

Documents:

283-del-2002-abstract.pdf

283-del-2002-claims.pdf

283-del-2002-correspondence-others.pdf

283-del-2002-correspondence-po.pdf

283-del-2002-description (complete).pdf

283-del-2002-form-1.pdf

283-del-2002-form-19.pdf

283-del-2002-form-2.pdf

283-del-2002-form-3.pdf