Baddeleyite

Luminescence of Eu has not been detected in natural samples yet, but is well studied in artificially activated Zr02 (Gutzov et al. 1998 Gedanken et al. 2000 Reisfeld et al. 2000). The main emission occurs between the Dq level to the Fj multiplet with a decay time of approximately 0.5 ms (Eig. 5.13). The luminescence intensity is relatively weak, but may b e substantially increased by co-doping with nanoparticles of semiconductors, such as CdS. The origin of the 

Eigures 5.14a,b represent luminescence spectra of scheelite enriched by Eu. Luminescence of Eu is well known in steady-state spectra of scheelite (Tarash-chan 1978 Gorobets and Kudrina 1980). In time-resolved spectroscopy its relative intensity is stronger after a long delay time, which is explained by the longest decay time of Eu in scheelite compared to other REE. 

The possible luminescence of Eu in scheelite is a very interesting problem. It was not detected by steady-state luminescence spectroscopy. The possible reason is that the very strong intrinsic luminescence of scheehte is situated in the same spectral range, which covers the weaker emission of Eu . We tried to solve this problem by the time-resolved method using different decay times for intrinsic and Eu bands. Time-resolved spectroscopy 

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Zirconium occurs naturally as a siUcate in zircon [1490-68-2] the oxide baddeleyite [12036-23-6] and in other oxide compounds. Zircon is an almost ubiquitous mineral, occurring ia granular limestone, gneiss, syenite, granite, sandstone, and many other minerals, albeit in small proportion, so that zircon is widely distributed in the earth s cmst. The average concentration of zirconium ia the earth s cmst is estimated at 220 ppm, about the same abundance as barium (250 ppm) and chromium (200 ppm) (2). 

Zirconium is found in at least 37 different mineral forms (6) but the predorninant commercial source is the mineral zircon, zirconium orthosiUcate. Other current mineral sources are baddeleyite and eudialyte [12173-26-1]. 

Baddeleyite, a naturally occurring zirconium oxide, has been found in the Poco de Caldas region of the states of Sao Paulo and Minas Geraes in Brazil, the Kola Peninsula of the former USSR, and the northeastern Transvaal of the Repubflc of South Africa. BraziUan baddeleyite occurs frequently with zircon, and ore shipments are reported to contain 65—85% zirconium oxide, 12—18% siUca, and 0.5% uranium oxide. Veryhttle of this ore is exported now because all radioactive minerals are under close control of the BraziUan government. 

The Phalaborwa complex ia the northeastern Transvaal is a complex volcanic orebody. Different sections are mined to recover magnetite, apatite, a copper concentrate, vermicuhte, and baddeleyite, Hsted in order of aimual quantities mined. The baddeleyite is contained in the foskorite ore zone at a zirconium oxide concentration of 0.2%, and at a lesser concentration in the carbonatite orebody. Although baddeleyite is recovered from the process tailings to meet market demand, the maximum output could be limited by the requirements for the magnetite and apatite. The baddeleyite concentrate contains ca 96% zirconium oxide with a hafnium content of 2% Hf/Zr + Hf. A comminuted, chemically beneficiated concentrate containing ca 99% zirconium oxide is produced also. 

Mixed zircon, coke, iron oxide, and lime reduced together produce zirconium ferrosiUcon [71503-20-3] 15 wt % Zr, which is an alloy agent. Fused zirconia [1314-23-4] has been made from zircon but baddeleyite is now the preferred feed for the production of fused zirconia and fused alumina—zirconia by electric-arc-fumace processing. 

Normally, zircon sand is readily available as a by-product of mtile and ilmenite mining at ca 150 per metric ton. However, zircon and baddeleyite are obtained as by-products of their operations, and therefore, the supply is limited by the demand for other minerals. In 1974, when a use for zircon in tundish nozzles developed in the Japanese steel industry, a resulting surge in demand and stockpiling raised zircon prices to 500/t. Worldwide production by country is given in Reference 80. 

Zirconium oxide is fused with alurnina in electric-arc furnaces to make alumina—zirconia abrasive grains for use in grinding wheels, coated-abrasive disks, and belts (104) (see Abrasives). The addition of zirconia improves the shock resistance of brittle alurnina and toughens the abrasive. Most of the baddeleyite imported is used for this appHcation, as is zirconia produced by burning zirconium carbide nitride. 

Figure 21.2 (a) The tetragonal unit cell of rutile, Ti02- (b) The coordination of Zr in baddeleyite Zr02 the 3 O atoms in the upper plane are each coordinated by 3 Zr atoms in a plane, whereas the 4 lower O atoms are each tetrahedrally coordinated by 4 Zr atoms. 

Pressure-induced phase transitions in the titanium dioxide system provide an understanding of crystal structure and mineral stability in planets interior and thus are of major geophysical interest. Moderate pressures transform either of the three stable polymorphs into the a-Pb02 (columbite)-type structure, while further pressure increase creates the monoclinic baddeleyite-type structure. Recent high-pressure studies indicate that columbite can be formed only within a limited range of pressures/temperatures, although it is a metastable phase that can be preserved unchanged for years after pressure release Combined Raman spectroscopy and X-ray diffraction studies 6-8,10 ave established that rutile transforms to columbite structure at 10 GPa, while anatase and brookite transform to columbite at approximately 4-5 GPa. 

The room temperature transformation of the columbite phase to baddeleyite commences at 13-17 GPa 6, with transition pressure increasing linearly with temperature Direct transition from rutile to baddeleyite phase at room temperature and 12 GPa has also been reported 7. The baddeleyite phase undergoes further transition to an as yet undefined high-symmetry structure at 70-80 GPa. The most likely candidate for the high-pressure phase is fluorite, which is consistent with the general pattern of increasing Ti coordination number from 6 in rutile, to 7 in baddeleyite (a distorted fluorite structure), and to 8 in fluorite. 

Preliminary results for baddeleyite phase indicate that it is very close in energy to columbite but at P=0 its volume is 8% smaller than that of the columbite structure. The predicted structure for this monoclinic phase at 0 GPa is a=4.7901 A, b=4.9151 A,... 

High pressure polymorphs are naturally characterized by wider bands with a smaller gap between the upper and lower VBs. The upper VB width in columbite, baddeleyite and fluorite structures is 5.37 eV, 6.22 eV and 7.44 eV, respectively, while the lower VB width is 2.32 eV, 3.30 eV and A.60 eV, respectively. This trend is due to the increasing overlap between the 2s-states of oxygen under compression. 

H. Sato, S. Endo, M. Sugiyama, T. Kikegawa, O. Shimomura, and K. Kusaba, Baddeleyite-type high-... 

J. Tang and S. Endo, P-T boundary of a-Pb02 type and baddeleyite type high-pressure phases of titanium... 

Palabora, Namibia Apatite, copper, baddeleyite, vermiculite, uranothorite, magnetite... 

Kovdor (Russia) Apatite, magnetite, baddeleyite, vermiculite... 

Oxides and hydroxides Cuprite, uraninite, baddeleyite, corundum, haematite, rutile, cassiterite, brucite, diaspore, goethite, limonite... 

Symmetrically equivalent positions -x,-y,z -y,x,z y,-x,z 2.9 Calculate the Zr-O bond lengths in baddeleyite (Zr02), considering only interatomic distances shorter than 300 pm. What is the coordination number of Zr ... 

Baddeleyite, see Zirconium(IV) oxide Baking soda, see Sodium hydrogen carbonate Barite (barytes), see Barium sulfate... 

Bacteriological sulfur, 23 577-578 Bacteriophages, 3 135 12 474 in fermentation, 11 46 Bacteriorhodopsin, 20 826, 840 photochromic material, 6 603 Bacteriosins, 12 76. See also Bacteriocins Bacteriostatic water, 18 714 Bacterium lactis, 11 7 Baculovirus expression system, 5 346 Baddeleyite, 21 489 26 623-624 colorants for ceramics, 7 346t Badische Anilin und Soda Fabrik (BASF) terpenoid manufacture process, 24 481 Baeyer-Villiger oxidation reactions, 14 592 chiral recognition by enzymes, 3 675 microbial, 16 401 Baffled shellside flow, 13 262 Baffles, in stirred tank geometries,... 

Zirconium vanadium yellow baddeleyite formula and DCMA number,... 

Occurrence. The more important minerals are zircon (ZrSi04) and baddeleyite (a form of Zr02). 

Preparation. It is made by the Kroll method that involves the reaction of chlorine and carbon upon baddeleyite (Zr02). The resultant zirconium tetrachloride, ZrCl4,... 

It is found in the ores baddeleyite (also known as zirconia) and in the oxides of zircons, elpidite, and eudialyte. 

Zirconium oxide (ZrO ) is the most common compound of zirconium found in nature. It has many uses, including the production of heat-resistant fabrics and high-temperature electrodes and tools, as well as in the treatment of skin diseases. The mineral baddeleyite (known as zirconia or ZrO ) is the natural form of zirconium oxide and is used to produce metallic zirconium by the use of the Kroll process. The KroU process is used to produce titanium metal as well as zirconium. The metals, in the form of metaUic tetrachlorides, are reduced with magnesium metal and then heated to red-hot under normal pressure in the presence of a blanket of inert gas such as helium or argon. 

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