Matter & Energy


Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.

Alumina

.
Alumina or Aluminum Oxide, an oxide found in nature as the minerals corundum, diaspore, gibbsite, and most commonly, bauxite, an impure form of gibbsite. It is the only oxide formed by the metal aluminum. The precious stones ruby and sapphire are composed of corundum colored by small amounts of impurities.

Fused alumina, alumina that has been melted and recrystallized, is identical in chemical and physical properties with natural corundum. It is exceeded in hardness only by diamond and by a few synthetic substances, notably carborundum, or silicon carbide. Both impure natural corundum (emery) and pure synthetic corundum (Alundum) are used as abrasives. At room temperature alumina is insoluble in all ordinary chemical reagents. Its melting point is high, slightly above 2000°C (3632°F), and so alumina is useful as a refractory, for example, for the linings of special furnaces.

Alumina can be purified by fusing it with sodium carbonate. The resulting sodium aluminate is dissolved in water, leaving impurities, such as iron, as an insoluble residue. Hydrated alumina is reprecipitated from the solution by carbon dioxide. Because the alumina contained in bauxite is soluble in sodium hydroxide solution, a less expensive method may be used. By alternately concentrating and diluting the solution, hydrated alumina is precipitated, and the sodium hydroxide may be reused without neutralization. Hydrated alumina, also called aluminum hydroxide or aluminum hydrate, is readily soluble in acids or alkalies and is used as a raw material in the manufacturing process of all aluminum compounds.