Several methods of obtaining spherical submicron particles of aluminium oxide from a molten pool of aluminium oxide are known. These particles can be used as fillers and catalyst materials for functional ceramics, as well as abrasives and polishing agents.
To produce spherical aluminium oxide particles, a molten aluminium oxide pool is heated to a temperature of at least 2050 degrees Celsius. An anode and a cathode are positioned to attract the aluminium ions. The anode is a carbon electrode that is positively charged, while the cathode is a graphite electrode that is negatively charged.
The molten aluminium oxide is then electrolysed to form a solution. The aluminium ions that are negatively charged lose electrons at the anode. The aluminium ions that are positive gain electrons at the cathode. The resulting mixture of aluminium sub-oxides is combusted to form oxygen and carbon monoxide. The reaction products have been studied by electron microprobe analysis and scanning electron microscopy.
In a current method of extracting aluminium, large amounts of electrical energy are required to perform the process. Because of the high temperatures involved, this process is not economical. The rate of oxide growth is much higher than reported lattice self-diffusion coefficients of oxygen.
An electrolytic cell is used to perform the reaction. In the cell, a negatively charged anode attracts the anions, while a positively charged cathode attracts the positive ions. The ions then pass an electric current through the cell. The resultant reaction produces an oxygen gas at the anode and a carbon dioxide gas at the cathode.