Crystallization product composition

The crystallization of glassy Pd-Ni-P and Pd-Cu-P alloys is complicated by the formation of metastable crystalline phaf s [26]. The final (stable) crystallization product consists of a mixture of a (Pd,Ni) or (Pd,Cu) fee solid solution and more than one kind of metal phosphide of low crystallographic symmetry. Donovan et al. [27] used transmission electron microscopy (TEM) and X-ray microanalysis to study the microstructure of slowly cooled crystalline Pd4oNi4oP2o- They identified the compositions of the metal phosphides to be Pd34Ni45P2j and Pdg8Ni[4Pjg. 

Hemozoin, also known as malaria pigment, is, in teims of its chemical composition, identical to (3-hematin. Hemozoin is formed as a crystallization product of heme under the acidic conditions present in the food vacuole of malarial parasites. In the crystal, the heme molecules are linked into dimers through reciprocal iron-carboxylate bonds to one of the propionate side chains of each porphyrin. The dimers form chains linked by hydrogen bonds. 

The ballistic properties of ADN, HNF, and HNIW as monopropellants and as oxidizers in composite propellants have been extensively studied.P2-351 Since ADN, HNF, and HNIW particles produce excess oxygen among their combustion products, these particles are used as oxidizer crystals in composite propellants. The pressure exponents of crystalline ADN and HNIW particles are both approximately about the same value as those for HMX and RDX when they are burned as pressed pellets. However, the pressure exponent of HNF is 0.85-0.95,135] higher than those of the other energetic crystalline oxidizers. 

The trihydrate, MgC03 3H20 or other hydrates on heating form basic magnesium carbonates, the product compositions depending on degree of water of crystallization and temperature. 

To a chemist concerned Tyith the synthesis of new high-explosive compounds the ability to compute detonation properties (detonation pressure, energy, and velocity as well as product composition) from a given molecular structure and the known or estimated crystal density is a problem of the utmost importance. The calculated properties could be meaningful in the decision as to whether it is worth the effort to attempt a new and complex synthesis. One reason behind the recent development of detonation-properties programs for use on high-speed computers has been to supply this desired information. One such program, the ruby code,1 has recently been made available to a number of laboratories, the authors included. 

The carbonyl platinum anions, [Pt3(CO)6]2, (n = 1-6,10) were first synthesized and characterized by Chini and coworkers1 3. They obtained these compounds by reaction of Pt(IV) or Pt(II) salts at room temperature with bases such as sodium hydroxide or sodium acetate under a carbon monoxide atmosphere. The product composition is quite sensitive to the Pt-base ratio, reaction time, and reaction conditions. As a consequence of this sensitivity, product mixtures with An = 1 are usually obtained, which are separable only with difficulty by fractional crystallization. Interest in this series of compounds for (a) their unique redox solution chemistry, (b) their use as precursors for higher nuclearity carbonyl platinum anions,4 and (c) their use as precursors for novel supported Pt catalysts5 8 prompted efforts to develop... 

The conversion rates of n-hexane are shown as a function of the crystallinity parameter Qai for different temperatures. We found that the catalytical activity increases simultaneously with the increased crystallinity of the composites, the crystallization products. According this linear correlation it can be concluded that the catalytical active sites, the acidic centers in the zeolitic framework, are always, independent of the crystal content of the composite material, accessible for educt of the test reaction, the n-hexane molecules. This leads to the assumption that the crystallization must start on the interface (at the phase border) between the solution (contains the alkalinity and the template) and the solid (porous glass) surface and has to carry on to the volume phase of the glass resulting finally in complete transformed granules. 

We have used our Single Turnover (STO) reaction sequence to characterize dispersed metal catalysts with respect to the numbers of alkene saturation sites, double bond isomerization sites, and hydrogenation inactive sites they have present on their surfaces (ref. 13). Comparison of the product composition observed when a series of STO characterized Pt catalysts were used for cyclohexane dehydrogenation with those observed using a number of instrumentally characterized Pt single crystal catalysts has shown that the STO saturation sites are comer atoms of one type or another on the metal surface (ref. 10). 

The chemical analysis of the synthesized samples expresses in the framework composition, that is, (MeIAlyPz)02 provides the as-synthesized sample framework composition, which is shown in Table 3.7, indicating the presence of about 1% of Me in the synthesized aluminophosphate [29], From the x-ray powder diffractograms (Figure 3.14), it is noted that the crystallized products exhibit all the characteristic reflections of the MeAPO-5 molecular sieves [140] and a high crystallinity and degree of purity [29],... 

Typically, the ammonium or hydronium form of the zeolite is slurried in water and reacted with the requisite amount of the ammonium fluoride salt of either iron or titanium. Given the sparingly soluble nature of ammonium fluotitanate, the (NH )2TiF6 can be added to the zeolite slurry in slurry form, or directly as salt. Alternatively, the iron may be added to the zeolite slurry as a slurry of the ammonium fluoride salt crystals in water, or the FeF3 crystals can be mixed with a water solution of ammonium fluoride or ammonium bifluoride, such that the composition of the treatment solution contains the stoichiometry of the ammonium iron fluoride salt, (NH4)3FeF6. The (NH )3FeF6 crystals can also be added directly to the zeolite slurry. The amount of either metal ammonium fluoride salt added during the reaction is determined by the desired product composition and the anticipated completeness of the reaction. 

The intermediate stages of the gel aging may be viewed as nuclei incubation periods, and the presence of even small amounts of residual methanol may influence the final products. We have examined both the influences on the crystallization products of potassium cations(an undisclosed impurity in some commercial TEA products), and the variability in products derived from optimized ZSM-20 gel compositions seeded in a variety of ways. Although the original ZSM-20 patent describes successful syntheses based on TMOS as a silica source (1), we have been unsuccessful in duplicating the patent examples using presently... 

Composition 9.7(TEA)20 1.14Na20 AI2O3 24.2Si02 370H20. Seeding mode Crystallization Products... 

Main factors which affect a hydrothermal reaction are the initial eomposition, reaction temperature and time. In mild hydrothermal synthesis, reaction temperatures lower than 240 °C are respected for both safety of high pressure in normal autoclaves and protection of softness of Teflon line. In our specific synthesis system, high temperature favorites the reaction and the most important factor was the base concentration in the initial reaction mixtures. The reaction time associated with reaction temperature affected the reaction. Crystallization kinetic experiment for a typical reaction showed that a reaction time more than lOh gave well-crystallized product and the further crystal growth needed additional time. Table 1 lists the starting reaction compositions and phase identification of products obtained at 240 °C for lOh. 

The molecule under study was Pd[(dmpz)2(Hdmpz)2]2, where Hdmpz = 3,5-dimethylpyrazole, 3-XXIII. The material is trimorphic. The reaction mixture yields mostly (90 per cent) the monoclinic (C2/c, racemic) a phase, the remainder being the triclinic (PI, racemic) y phase. The latter can be removed by recrystallization from 1,2-dichloroethane, which suggests that it is the more soluble and hence, the less stable polymorph in that solvent. Masciocchi et al. (1997) found that mixtures of various amounts of a and y polymorphs could be obtained by varying the solvent and precipitation temperature (-70 °C to -1-50 °C), with a preferred at higher temperatures, consistent with the earlier observation of relative stability. Pure polymorph y may be obtained by a different synthetic route which, when employing an excess of 3,5-dimethylpyrazole, leads to an approximately 50 50 mixture of polymorphs a and y. This system thus also represents a case in which the polymorph obtained, or the polymorphic mixture obtained, depends on the synthetic route to the desired material. It is probably more correct to state that as usual, the polymorph or polymorphic mixture depends on the crystallization conditions, and these will clearly differ in the solvent/reagent/product compositions resulting from different synthetic conditions and routes. 

The passage of allene into a benzene solution of dicobalt octacarbonyl at room temperature produces air-sensitive yellow crystals of composition [(C3H4)Co(CO)3]2 (428). The spectral data indicate a 77-allyl complex in which a CO grouping has been transferred to the 2-position of each allylic moiety. Although Co2(CO)g does not form a 77 complex with tetraphenylallene, cyclopentadienyldicarbonylcobalt does react under reflux in isooctane to yield the product [C3(C(,H5)4]Co(CO)(C5H6) in which the olefin appears to be a monodentate ligand (434). 

TJew references to uranium borates appear in the literature. Larson (12) reported that yellow crystals, whose composition was assumed to be 3UO3 B2O3 (uranyl orthoborate), were obtained among other products from a melt of uranium niobate in boric oxide. Bruhat and Dubois (2) stated that perborate solutions react with uranium oxide to give an anhydrous stable yellow salt of the composition UBO4. No further information has appeared on either of these compounds. 

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