Aluminum Oxide Sapphire

The availability of sizable single crystals has led to a significant literature on the deformation of sapphire of various orientations, and at various temperatures. As already noted, the first such study was by Wachtman and Maxwell in 1954 [6], who activated (0001) 1/3 (1120) basal slip at 900 °C via creep deformation. Since that time, it has become clear that basal slip is the preferred slip system at high temperatures, but that prism plane slip, 1120 (1100), can also be activated and becomes the preferred slip system at temperatures below 600°C. Additional slip systems, say on the pyramidal plane 1012 1/3 (1011), have very high CRSSs and are thus difficult to activate. Both, basal and rhombohedral deformation twinning systems, are also important in AI2O3 (these are discussed later in the chapter). 

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The most important gemstones are varieties of diamond, corundum (aluminum oxide sapphires and rubies), beryl (beryllium aluminum silicate ... 

Corundum, aluminum oxide (sapphire), a-Al203, has a crystal structure in which oxygen ions are close-packed and the aluminurn ions occupy two-thirds of the octahedral interstices. The mineral is trigonal (R3c) and the close-packed oxygen plane is basal, i.e. (0001). 

The system Ni-Al203 was chosen for study primarily because it is of interest as a practical composite system ( ), but also because single-crystal aluminum oxide, sapphire, is transparent in the visible region. The latter feature allows direct observation of internal interface morphologies without any disturbance to the system. 

The compounds of greatest importance are aluminum oxide, the sulfate, and the soluble sulfate with potassium (alum). The oxide, alumina, occurs naturally as ruby, sapphire, corundum, and emery, and is used in glassmaking and refractories. Synthetic ruby and sapphire are used in lasers for producing coherent light. 

Aluminum oxide. Al3+ ions are present in corundum Heft), ruby (top right), and sapphire (bottom right). The anion in each case is 02-. 

A colorless mineral known as corundum (composed of aluminum oxide) is colorless. A red variety of corundum known as ruby, a precious stone, owes its color to impurities of chromium within the crystal structure of corundum. Blue and violet varieties of corundum are classified as sapphires, the blue being the result of iron and titanium impurities, and the violet of vanadium impurities within the corundum crystal structure. Another colorless mineral is beryl (composed of beryllium aluminum silicate) but blue aquamarine, green emerald, and pink morganite, are precious varieties of beryl including different impurities aquamarine includes iron, emerald chromium and vanadium, and morganite manganese. 

Ruby and Sapphire. Ruby and sapphire are "sister stones" both are gemstone forms of the mineral corundum (composed of aluminum oxide). Pure corundum is colorless, but a variety of trace elements cause corundum to exhibit different colors. Ruby is red corundum, while sapphire is corundum in all colors except red. The red in rubies is caused by trace amounts of chromium the more intense the red color of a ruby, the more chromium it contains. The blue in sapphires is caused by titanium and/or iron impurities (Garland 2002 Hughes 1997). 

Aluminum oxide is used to make synthetic rubies and sapphires for lasers beams. It has many pharmaceutical uses, including ointments, toothpaste, deodorants, and shaving creams. 

An aluminum ion carries a 3+ charge, and an oxide ion carries a 2— charge. Together, these ions make the ionic compound aluminum oxide, AI203, the main component of such gemstones as rubies and sapphires. Figure 6.10 illus-... 

Rubies and sapphires are color varieties of the mineral corundum, which is simple aluminum oxide. This mineral is second only to diamond in hardness, but is much tougher and harder to break. Rubies are, by definition, red or purplish red. The term sapphire is used for every other color. 

Aluminum, gallium, and thallium form mixed oxides with other metals. First, there are aluminum oxides containing only traces of other metal ions. These include ruby (Cr3+) and blue sapphire (Fe2+, Fe3+, and Ti4+). Synthetic ruby, blue sapphire, and gem-quality corundum are now produced synthetically in large quantities. Second, there are mixed oxides containing macroscopic proportions of other elements, such as spinel (MgAl204) and crysoberyl (BeAl204). 

Corundum. Corundum [1302-75-5] (see Aluminum COMPOUNDS) is a naturally occurring massive crystalline mineral composed of aluminum oxide. It is an impure form of the gems ruby and sapphire. Prior to 1900 corundum was an important abrasive for the production of grinding wheels. Today it is mainly employed as a loose abrasive for grinding and polishing optical lenses. Almost all the world s supply of corundum now comes horn Africa, primarily from Zimbabwe. 

Bauxite aluminum oxide (alumina, corundum, emery, ruby, sapphire) aluminum sulfate alum ammonium alum. Aluminum chloride aluminum acetate. Uses of aluminum compounds. 

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