سنتز اندازه کنترل شده نانو ذرات α-آلومینا با روش سل-ژل

ABSTRACT Size-controlled synthesis of nano α-alumina particles through the sol–gel method

Ceramics have many applications in high technology from structural to electrical and electronic because of their excellent properties, but sometimes their low mechanical properties limit their wide applications. However, nanocrystalline ceramics can enhance their mechanical properties. So nanometer size powder processing is of great importance in the range of nanotechnology since it affords to fabricate various kinds of nanocrystalline materials and the nanocomposite ceramics have such advantages over monolithic ceramics as high strength and high toughness [1,2].

To obtain nanostructure ceramics, nanoscale powders with high performance are necessary. However nanoscale a-alumina (a-Al2O3) powder is difficult to obtain, because of two reasons: First, a-Al2O3 is in a stable phase after calcining at high temperature, which easily prompt the grain growth of powder, and make it difficult to get nanoscale particles; secondly, aAl2O3 particles tend to aggregate during dehydration process in wet chemistry method. Therefore, it is necessary to develop new methods to overcome this problem [3,4].

Conventional synthesis processes of a-Al2O3 involve mechanical milling, vapor phase reaction, precipitation, sol– gel, hydrothermal and combustion methods. Mechanical synthesis of a-Al2O3 requires extensive mechanical ball milling which easily introduces impurities. Vapor phase reaction for preparation fine a-Al2O3 powder from a gas phase precursor demands high temperature above 1200 8C. The precipitation method suffers from its complexity and time consuming (long washing times and aging time) [5,6]. The direct formation of a-Al2O3 via the hydrothermal method needs high temperature and pressure. The combustion method has been used to yield a-Al2O3 powders, whereas the powder obtained from the process is usually hard aggregated but contains nano-sized primary particles [7]. Sol–gel, a commonly used technique, involves the formation of an amorphous gel from a precursor solution. This method based on molecular precursors usually makes use of metal alkoxides as raw material. Some advantages of the sol–gel method are better homogeneity and purity from raw material, lower preparation temperature which save energy cost and the ability to form unique composition [8]. The purpose of this work is to synthesize nano-sized a-Al2O3 by controlling the particle size distribution and shape.