Zircon formation

Hoskin P. W. O. and Black L. P. (2000) Metamorphic zircon formation by solid-state recrystallization of protolith igneous zircon. J. Metamorph. Geol. 18(4), 423 -439. 

With allowances for the actual metal content of zirconium (a small correction is also necessary for the hafnium content of about 2 /2%) and postulation of barium zirconate formation (see Table 27), reasonable accord between calculated and measured caloric output is established. However, the situation is more complex with boron mixtures where one encounters increase of heat output with increase of the percentage of boron in the mixtures much beyond the amounts of Equation (la). Thus, even with the reasonable assumption of secondary barium borate formation, the stoichiometry and heat output of the mixtures with more than about 10% of technical boron theoretical 8%) is obscure. Chromium boride formation may be a fector. 

Another important class of titanates that can be produced by hydrothermal synthesis processes are those in the lead zirconate—lead titanate (PZT) family. These piezoelectric materials are widely used in manufacture of ultrasonic transducers, sensors, and minia ture actuators. The electrical properties of these materials are derived from the formation of a homogeneous soHd solution of the oxide end members. The process consists of preparing a coprecipitated titanium—zirconium hydroxide gel. The gel reacts with lead oxide in water to form crystalline PZT particles having an average size of about 1 ]lni (Eig. 3b). A process has been developed at BatteUe (Columbus, Ohio) to the pilot-scale level (5-kg/h). 

The chlorination is mostly carried out in fluidized-bed reactors. Whereas the reaction is slightly exothermic, the heat generated during the reaction is not sufficient to maintain it. Thus, a small amount of oxygen is added to the mixture to react with the coke and to create the necessary amount of heat. To prevent any formation of HCl, all reactants entering the reactor must be completely dry. At the bottom of the chlorination furnace, chlorides of metal impurities present in the titanium source, such as magnesium, calcium, and zircon, accumulate. 

Multicomponent sol—gel fibers have been successfuUy developed (1,52). The early stages of sol formation and gelation are cmcial for controlling the fiber microstmcture. Aluminosilicates, zirconates, and aluminates (1,18,52) can be prepared by sol—gel methods. MuUite [55964-99-3] 3AI2 O3 -2Si02, fibers... 

The elements for which the results can be underestimated because of an incomplete digestion of refractory accessory minerals such as zircon and garnet, and/or formation of insoluble fluoride complexes have been distinguished. Recommendations on the choice of the decomposition procedure for such samples are given. 

The above intramolecular diene cyclizations are likely to proceed through a similar set of reactions as shown in Scheme 6.2 for the intermolecular variants. Thus, as depicted in Scheme 6.6, formation of the zirconacyclopropane at the less hindered terminal alkene (—> ii), generation of the tricyclic intermediate iii, Zr—Mg exchange through the intermediacy of zirconate iy and 3-H abstraction and Mg alkoxide elimination in v may lead to the formation of the observed product. Additional kinetic and mechanistic studies are required before a more detailed hypothesis can be put forward. 

In the JRS the Dalhousie Group is divided into five formations (Walker and McCutcheon 1995). Only the upper three Archibald Settlement, Sunnyside and Big Hole Brook formations (described below), are exposed in the vicinity of Nash Creek. The Archibald Settlement Formation is the lowermost of these and consists of massive flows and domes of orange to red, aphyric, commonly flow-layered rhyolite. Up section massive flows are interlayered with fine- to coarse-grained volcaniclastic rocks including heterolithic lapilli-tuff and agglomerate, as-well-as volumetrically minor feldspar-phyric rhyodacite. A U/Pb zircon age of 415.6 +/-0.4 Ma has been returned from rhyolite of... 

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