سال انتشار: ۱۳۸۷

محل انتشار: دومین کنگره بین المللی علوم و فناوری نانو

تعداد صفحات: ۲

نویسنده(ها):

L Torkian – Department of Chemistry, Engineering, Islamic Azad University, South Branch, Tehran, Iran
M. M. Amini – Department of Chemistry, Shahid Beheshti University, G.C., Tehran
Z Bahrami – Department of Chemistry,Tarbiat Moallem University, Tehran, Iran

چکیده:

Spinel is a ternary oxide whose chemical formula is AB2O4, where A represent a divalent metal cation that normally occupies a tetrahedral site and B represents trivalent metal cations that normally occupy the octahedral sites of a cubic packed crystal. The low temperature synthesis of the MgAl2O4 spinel is featured in this report.Magnesium aluminate spinel is a ceramic material with good mechanical strength, thermal, chemical and opticalproperties which find applications in metallurgical, chemical, electro technical, catalysis and electronic industries [1–۲]. The conventional method of preparation of MgAl2O4 spinel is calcination of the mixture of MgO and Al2O3 or other raw materials at high temperature, which has disadvantages of large aggregates and inhomogeneous compositions. In recent years, several types of wet-chemical techniques have been successfully used for the preparation of pure spinel powders at relatively low temperatures, such as co-precipitation, sol–gel of metal alkoxides, spray-drying, freeze-drying, modified Pechini process, hydrothermal technique, plasma spray decomposition of oxides, combustion of metal nitrate and urea, controlled hydrolysis of metal alkoxides, decomposition of organometallic compounds in supercritical fluids, magnesium aluminum double alkoxide, and an aerosol method [3-6].In the present paper we have used two different chemical routes for the preparation of nanocrystalline (average particle size around ~ 30 nm), single-phase MgAl2O4 powder from comparatively cheaper raw materials. In the first procedure combination of precipitation and gelation process is used to prepare spinel from aluminum and magnesium sulphates. In this process, concentration of starting solutions is increased to such an extent that during the gelation process, when the gel becomes fully viscous, a substantial amount of starting solute is still remained in the solution in which the liquid phase permeating through the gel network. On drying this solute precipitates out in the pores between hydroxide particles of the gel network and upon calcinations, it is decomposed to form oxide. The other involved rapid evaporation of polyvinyl alcohol (PVA) that added to a mixed metal nitrate solution, followed by pyrolysis of the dried mass.