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Nanosized aluminium oxide (nanosized alumina) occurs in the form of spherical or nearly spherical nanoparticles, and in the form of oriented or undirected fibers.
High defectiveness of the material surface and specific structure of the nanoparticles (the volume and size of pores, degree of crystallinity, phase composition, structure, and composition of the surface — modification possibility)
Properties of the nanoscale fibers of aluminium oxide:
The ratio of length-diameter about 20,000,000:1
A high degree of orientation of the fibers
The weak interaction of the fibers among themselves
Methods of obtaining powders of aluminium oxide nanometer scale[edit]
Industrially obtained alumina nano fibers of Nafen brand
1. Grinding powder alumina particles of a nanometer level (for example, 10-50 nm). For example, using a planetary mill using grinding bodies of size less than 0.1 μm.
2. The decomposition of fresh chemically-synthesized AlOOHorAl(OH)3toaluminium oxide in the rapid achievement of the temperature of decomposition 175 °C and use for it the pressure of 5 bars within thirty minutes. The sooner of the temperature of decomposition of the hydroxo-compounds of aluminium is achieved, the smaller the resulting particles nano oxide in size.
The oxidation of the surface of some liquid metal alloys leads to the formation of loose or porous 3D nanostructures. For the first time this effect was observed in the system aluminium-mercury and published more than 100 years ago.[1] The fibers of such kind do not occur in nature and only grown by artificial means. Depending on the method of synthesis can be produced various nanostructures, such as aerogel from oxyhydroxide aluminium (AlOOH or , where , are easily turned into aluminium oxide) or nano-fibers of aluminium oxide (Al2O3).
At this moment, the main ways of production are:
The method for selective oxidation of aluminium on the surface of the molten Ga-AI in a humid atmosphere at a temperature of 20 to 70 °C (Method of IPCE RAS)[2]
The liquid metal technology of synthesis of nanostructural aerogel AlOOH from molten Ga-Bi and Al-Al (Institute of RF IPPE named after A. I. Leipunsky, Obninsk city).
Growing fiber nano oxide of aluminium on the surface of the aluminum melt (a Method of industrial synthesis, developed and patented by the ANF Technology).[3]
Desiccant (for drying of gases (deep dehydrationtodew points of -60 °C and below); the preservation of instruments and equipment, and also for such systems as the respiratory valves, tanks, transformers, etc.; to create protective atmospheres during long-term storage of food and pharmaceutical products)
Sorbent of the ions of metals from solutions of their salts, for example, CsNO3, AgNO3, Ba(NO3)2, Sr(NO3)2, Pb(NO3)2, etc., with the possibility of obtaining of metal oxides on the surface of the fibers during annealing
Ceramics and composites (including composite metals) — high toughness, fire resistance and anti-friction properties, insulating properties. Known use in several products such as burner discharge lamp, the substrate of integrated circuits, shut-off elements ceramic pipeline valves, prostheses, etc.
Refractory (high-temperature component for heat insulation)
In addition to these areas, used as a catalyst and carrier of catalysts. Nanoscale oxide due to the small diameter of the particles/fibers, high specific surface area and activity associated with the defects, and the specific structure of the nanoparticles (the volume and size of pores, degree of crystallinity, phase composition, structure, and composition of the surface) strongly enhances the catalytic properties, and increases the range of massive aluminium oxide as a catalyst.
3. Zhu, Huai Yong, James D. Riches, and John C. Barry. γ-alumina nanofibers prepared from aluminum hydrate with poly (ethylene oxide) surfactant // Chemistry of Materials 14.5 (2002): 2086-2093
4. Azad, Abdul-Majeed. Fabrication of transparent alumina (Al2O3) nanofibers by electrospinning // Materials Science and Engineering: A 435 (2006): 468–473.
5. Teoh, Geik Ling, Kong Yong Liew, and Wan AK Mahmood. Synthesis and characterization of sol–gel alumina nanofibers // Journal of Sol-Gel Science and Technology 44.3 (2007): 177–186.
^H.Wislicenus. Zeitschrift für chemie und industrie der kolloide Kolloid-Z. 2 (1908) XI-XX. Ueber die faserähnliche gewachsene Tonerde (Fasertonerde) und ihre Oberflächenwirkungen (Adsorption).
^Martynov P., Ashadullin R., Judincev P., Hodan A. New industrial technologies, 4 (2008), p.48 – 52.
^US20130192517 A1 / PCT/IB2013/000120 «Method And System For Alumina Nanofibers Synthesis From Molten Aluminum», ANF Technology Limited, 01.08.2013
