Recrystallization primary

The development of a sharp COE texture in the finished strip requires complex control of numerous variables. The conventional commercial process (18) involves hot-rolling a cast ingot at ca 1370°C to a thickness of about 2 mm, annealing at 800—1000°C, and then cold-rolling to a final thickness of 0.27—0.35 mm in two steps of 70 and 50%, respectively, with a recrystallization (800—1000°C) aimeal in between. The cold-roUed strip is decarburized (800°C) to ca 0.003% C in mixtures of wet results in a primary recrystallized stmcture containing grains of the COE... 

Electrolytic etching reagents are especially suited for the detection of the distribution of dislocations in a heterogeneous strained metal. It is also possible to distinguish au even slightly work-hardened metal from a perfectly recrystallized one. Electroetching is so sensitive that it is possible to distinguish a crystal of secondary recrystallization from a crystal of primary recrystallization by differences in etch- pit den si ties (10). 

Aside Classical primary recrystallization is the nuclea-tion and growth of new strain-free grains in a matrix of heavily deformed material. The driving force arises from the decrease in strain energy. There is an induction period as the system forms stable nuclei. 

The introduction of large numbers of defects (strain) into the crystal by the explosive shock treatment may correspond to cold working in metals. If it is assumed that such cold worked ceramics behave similarly to cold worked metals on subsequent heat treatment... such materials should display the phenomenon of primary recrystallization when heated to some minimum temperature, similar to observations made by Klein et al. (5). ... 

Adapted from P. Parrini and G. Corrieri, The Influence of Molecular Weight Distribution on the Primary Recrystallization Kinetics of Isotactic Polypropylene, Die Makromolekulare Chemie, 1963, Vol. 62, p. 89. Copyright Wiley-VCH Verlag GmbH Co. KGaA. Reproduced with permission.)... 

The oxidation reactor effluent and methanol ate sent to the esterification reactor, which operates at up to 250°C and a pressure sufficient to maintain the Hquid phase. This latter is about 2500 kPa (25 atm). The oxidation products are converted to methyl -toluate and dimethyl terephthalate without a catalyst. Excess methanol is suppHed, and steam and vaporized methanol ate removed and enter a methanol recovery column. The esterification products flow to a cmde ester column, which separates the toluate from the terephthalate. The overhead stream of methyl -toluate is returned to the oxidation reactor, and the bottoms stream of dimethyl terephthalate goes to a primary distillation. The distillate is dissolved in methanol, crystallized, and sohd dimethyl terephthalate is recovered. The dimethyl terephthalate can then be either recrystallized or distilled to yield the highly pure material needed for the polyesterification reaction. 

Titanium Dioxide. The recrystallization of titanium dioxide in a cover-coat glass is very important to the development of thin, highly opaque finish coats. Titania, Ti02, is the primary opacifying agent for white finish coats. Two polymorphic forms of titania, anatase and mtile, may be present in... 

The method based on the precipitation of peroxometalate precursors enables to achieve additional purification during the process. Thus, the addition of complexonates, such as OEDP or EDTA, which form stable complexes with some polyvalent metals, prevents co-precipitation of the main impurities such as Fe, Co, Ni, Mn, Mg, etc., which in turn significantly increases the purity of the final product. Enhanced purification can also be achieved by recrystallization of the precursor. Particularly, the precipitation of ammonium peroxofluorometalates, such as ammonium peroxofluoroniobate ((NH4)3Nb04F4), as a primary precursor, leads to significant reduction of the titanium contamination. Ammonium peroxofluoroniobate, (NH4)3Nb04F4, is... 

The synthesis of key intermediate 12, in optically active form, commences with the resolution of racemic trans-2,3-epoxybutyric acid (27), a substance readily obtained by epoxidation of crotonic acid (26) (see Scheme 5). Treatment of racemic 27 with enantio-merically pure (S)-(-)-1 -a-napthylethylamine affords a 1 1 mixture of diastereomeric ammonium salts which can be resolved by recrystallization from absolute ethanol. Acidification of the resolved diastereomeric ammonium salts with methanesulfonic acid and extraction furnishes both epoxy acid enantiomers in eantiomerically pure form. Because the optical rotation and absolute configuration of one of the antipodes was known, the identity of enantiomerically pure epoxy acid, (+)-27, with the absolute configuration required for a synthesis of erythronolide B, could be confirmed. Sequential treatment of (+)-27 with ethyl chloroformate, excess sodium boro-hydride, and 2-methoxypropene with a trace of phosphorous oxychloride affords protected intermediate 28 in an overall yield of 76%. The action of ethyl chloroformate on carboxylic acid (+)-27 affords a mixed carbonic anhydride which is subsequently reduced by sodium borohydride to a primary alcohol. Protection of the primary hydroxyl group in the form of a mixed ketal is achieved easily with 2-methoxypropene and a catalytic amount of phosphorous oxychloride. 

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