Hi Aala Aziz,

Various techniques include Sol Gel, Combustion Synthesis , MIcrowave assisted combustion, Mechano Milling Process or Bayer Process Method has been employed to synthetize ultrafine Al2o3 powders, in general the choise of the method depending of the properties that you like to find, in you alumina powder like to: size, chemical composition, crystalography phase, and temperature of calcination between other parameters.

Please review a next reference:

http://www.academicjournals.org/article/article1380712960_Ramesh%20et%20al.pdf

http://www.sciencedirect.com/science/article/pii/S0272884208002101

http://jcpr.kbs-lab.co.kr/file/JCPR_vol.11_2010/JCPR11-6/03.652-655_2009-180.pdf

http://www.imp.kiev.ua/?lang=eng&a=org_structura

by easy ppt method from AL2O3 or AlCL3 salts with NaOH  solution (1-5M)