Alumina/Ethanol Colloidal Suspensions for Seeding Hot Flows

The alumina for making a suspension according to this concept must be in the form of a highly pure (preferably >99.99 percent) powder with a suitable particle-size distribution — preferably monodisperse with a mean particle size of a fraction of a micron, as illustrated in the figure. The alumina powder is mixed with an ethanol solution, the pH of which has been lowered to a predetermined value (typically between 1 and 5) as explained below. The amounts of alumina powder and ethanol solution are chosen to obtain the desired concentration of solid material in the suspension. Optionally, the suspension can be made initially in a high concentration (e.g., 20 weight percent alumina), then diluted. During mixing or dilution, the liquid and solid contents are agitated with an ultrasound to break up agglomerations of particles.