Method for producing nanocrystals from piezoelectric aluminium nitride for sorption filters

Abstract

A method for producing nanowires from piezoelectric aluminum nitride is provided. Nanowires formed from cubic AIN having a diameter of 10-20 A and a length of 1000-1500 A are obtained from a batch of AI+2-10% by volume AIH3 at a temperature of 1500-2300 K in a gaseous environment of N2+(3-5% by volume NH3) at a pressure of 200-2000 MPa.

Claims

1. A method for producing nanowires from piezoelectric aluminum nitride, comprising the acts of: generating cubic AlN from by subjecting Al+2-10% by volume AlH.sub.3 in a gaseous atmosphere of N.sub.2+(3-5% by volume NH.sub.3) to a temperature of 1500-2300 K under a pressure of 200-2000 MPa; and growing nanowires having a diameter of 10-20 and a length of 1000-1500 from the generated cubic AlN.

2. The method in accordance with claim 1, further comprising the act of: generating the Al+2-10% by volume AlH.sub.3 from a SAP powder aluminum by addition of AlH.sub.3 solution in tetrahydrofurane (5 g/100 g) between 2-10% by volume in a graphite container having a cross-section of 5010 mm.

3. The method in accordance with claim 2, wherein the act of generating the cubic AlN includes the acts of placing the graphite container containing the SAP powder aluminum into a pressure chamber, conducting a plurality of rinses with a mixture of helium and oxygen, increasing a pressure in the pressure chamber with a mixture of N.sub.2+(3-5% by volume NH.sub.3) to 200-2000 MPa, increasing a temperature in the pressure chamber to 2000 K at a rate of no more than 10 C./minute, and maintaining the increased temperature for 3-5 hours.

4. The method in accordance with claim 3, wherein the act of generating the cubic AlN includes after the 2000 K exposure, cooling and reducing pressure, applying a vacuum of 10.sup.6 Torr, filling the pressure chamber with a mixture of helium+30% by volume oxygen to a pressure of 200-2000 MPa for 30 minutes, reducing the pressure chamber pressure to atmospheric pressure, opening the chamber, and removing the AlN crystals.

Description

DETAILED DESCRIPTION

(1) The following is an example embodiment of the method of the present invention. 1. The batch for growing the nanowires was produced in a vibration mill from SAP aluminum powder with an addition of AlH.sub.3 solution in tetrahydrofurane (5 g/100 g) on the order of magnitude of 2-10% by volume within 30-45 minutes. 2. The finished batch was added to graphite containers made of fine-grained dense graphite (MPG) having a cross-section of 505 mm and a thickness of 1.5 mm in a max. 2 mm-thick layer. 3. The containers with the batch were placed on a frame on the specimen stage of the pressure chamber oven, subjected to a vacuum of 10.sup.2 Torr, helium having a 30% by volume admixture of oxygen was admitted up to a pressure of 100 atm, then the vacuum pressure was re-applied and the entire process was repeated three times, then the pressure of the nitrogen (with a 3-5% by volume addition of ammonia) was increased to 200-2000 MPa and the heater was turned on, the temperature was increased to 2000 C. at a speed of max. 10 C./min and held for 3-5 hours. 4. After this exposure concluded, pressure and temperature were reduced to normal values, the pressure chamber was subjected to a vacuum with a non-lubricant electrophysical pump at 10.sup.6 Torr, and then filled with a mixture of He+30% by volume O.sub.2 up to a pressure of 200-2000 MPA and left in this condition for 30 minutes; after this, the pressure was reduced to atmospheric pressure and the containers with the nanowires were removed from the pressure chamber. 5. The nanowires that were removed have the appearance of cotton wadding and are packed between layers of Petryanov filter cloth and placed into an electrical field of 100-1000 V. 6. The nanowires are placed on the filter from the top containers that are applied to the inside of the filter facing the respiratory organs. 7. Analysis of the nanowires from the top and lower containers evidenced a strong difference in the increase in weight of the absorption components (He+30% by volume O2), by an average of 10-15%. 8. Measurement of the specific surface of the nanowires demonstrated that they fluctuate between 15000-35000 m/g as a function of the elevation of the containers. 9. The cross-section of the nanowires that were grown is also a function of the elevation of the container and according to data from the electron microscope is 10-20 for 99% of the batch volume. 10. The determination of the capacitive charge on the inside of the filter evidenced distribution of the measured values between 0.8-0.95 Q, which is apparently caused by the different specific surface of the nanowires and consequently of the absorbed quantity of He+O2. 11. The crystal density, calculated with the Lauegram of a highly focused electron bundle of the microscope with a voltage of 1 million volts was 3.2-3.25 g/cm3, which means a cubic lattice type.

(2) The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.