Polymorphism higher oxides

Wetmur JG, Lehnert G, Desnick RJ (1991) The (5-aminolevulinate dehydrase polymorphism higher blood lead levels in lead workers and environmentally exposed children with the 1-2 and 2-2 isozymes. Environ Res 56 109-119 Woods JS (1988a) Attenuation of porphyrinogen oxidation by glutathione and reversal by porphyrinogenic trace metals. Biochem Biophys Res Commun 152 1428-1434... 

The surface area of synthetic hematite depends upon whether the oxide was produced by calcination or grown in solution. The temperature of (dry) heating influences the surface area. Hematites produced at 800-900 °C have areas < 5 m g due to sintering of the particles. Hematites obtained by dehydroxylation of the various polymorphs of FeOOH or ferrihydrite at temperatures lower than 500-600 °C are mesoporous and have much higher surface areas - up to 200 m g". Commercial hematites are usually produced by calcination and hence have a low surface area. 

They concluded that each oxide exists stably in one form only and that the C forms of Nd2C>3, Sn Os, E112O3 and Gd20s are metastable at lower temperatures. They also believe that all low-temperature forms transform irreversibly to the most stable form at higher temperature. However, Warshaw and Roy [300] have shown that Sn Os, EU2O3, GcfeOs, Tb20s and Dy2<33 can exist in both B- and C-type polymorphs and the trans-... 

Corundum is aluminum oxide, q -A1203, which has a hexagonal crystalline structure that is analogous to hematite. However, water treatment systems most often use activated alumina, which is typically produced by thermally dehydrating aluminum (oxy)(hydr)oxides to form amorphous, cubic (y), and/or other polymorphs of corundum (Clifford and Ghurye, 2002, 220 Hlavay and Poly k, 2005 Mohan and Pittman, 2007). When compared with corundum, amorphous alumina tends to have higher surface areas, greater numbers of sorption sites, and better sorption properties. 

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