ROLE OF COLLOIDAL CHEMISTRY IN SYNTHESIS AND PROCESSING OF ALPHA-ALUMINA

Open Access
Author:
Kumar, Rajneesh
Graduate Program:
Materials Science and Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
June 13, 2005
Committee Members:
  • James Hansell Adair, Committee Chair
  • Gary Lynn Messing, Committee Member
  • Kwadwo Osseo Asare, Committee Member
  • Serguei Lvov, Committee Member
Keywords:
  • Alpha
  • Alumina
  • Aluminium oxide
  • glycothermal
  • morphology
  • seeding
  • milling
  • attrition
  • chemically aided
  • CAM
  • CAChe
  • MOPAC
  • nanoalumina
  • nanparticle
  • surface energy
Abstract:
The role of colloidal chemistry in solution synthesis and processing of alpha-alumina (alpha-Al2O3, corundum) was investigated. Experiments were designed to investigate the role of water, produced by degradation of 1,4-butanediol, on equilibrium morphology of alpha-Al2O3 particles synthesized under glycothermal conditions. Development of platelet like morphology was promoted by low water concentrations in the solvent, and development of polyhedron morphology was promoted by high water concentrations in the solvent. A theoretical model predicting morphology for particles produced under solution conditions is proposed, with the possibility of extension of the model to any particle produced under solution conditions. A comparison was made between theoretically predicted and experimentally observed morphologies of alpha-Al2O3. Glycothermal synthesis process for preparing sub 100 nm phase pure alpha-Al2O3 nanoparticles with platelet morphology has been developed. The role of treatment temperature, seed concentration, stirring speed and solvent water content was investigated in controlling particle size and shape. Phase pure alpha-Al2O3 nanoparticles were synthesized with specific surface area (SSA) as high as 40 m2/gm and temperatures as low as 235 ¢XC. An attempt has been made towards understanding the aggregation mechanism in alumina nanoparticles. The modeling of hydration and aggregation of alumina clusters was done using PM5 semi-empirical parameters as implemented in CAChe Worksystem. Prolonged aging of hydrated nanoparticles, even under ambient conditions, can cause bridging among the particles that can lead to neck formation resulting in aggregation of nanoparticles. Nanophase alumina powder was de-aggregated and successfully dispersed from 11 ƒÝm agglomerate/aggregate sizes down to 20 nm in 1 hr by using a chemically aided attrition milling (CAM) technique. Design of Experiments (DOE) was used to determine the important experimental factors to efficiently mill alumina by the CAM process. The size of grinding media had the most significant effect in achieving average agglomeration number (AAN) less than 10, indicating well dispersed suspensions. Shaft rpm emerged as the most significant factor in controlling impurity through media wear.