Amorphous binary phases

Historically, oxide catalysts have been used primarily for vapor phase reactions in the petroleum and petrochemical industries. Recent work, however, has shown that these catalysts can also be effective in promoting a number of synthetically useful reactions. While simple oxides show activity for some oxidations they are more commonly used as solid acids or bases. Complex oxides can act as acids or bases as well as oxidation catalysts. Complex oxides can range in composition from the simple, amorphous, binary oxides to the more complex ternary and quaternary systems. The use of zeolites and clays can impart shape selectivity to a number of reactions, a feature that makes these systems particularly appealing for use in synthesis. 

All the mesoporous ceramic oxides obtained by this method are amorphous on the atomic level, but show periodicities on the nanometer length scale and narrow pore size distribution. The outcome of the process is very predictable, as the binary phase diagram of the surfactant can be used as a guideline towards the nanostructure design. The transmission electron microscopy images of siH-cas derived from three different LLC surfactant phases are shown in Fig. 3. 

One of the most commonly used criteria for establishing the phase behavior in amorphous binary polymer blends is the presence of one or more T s. If the blend is one-phase, a single... 

Chemical reactions involving precipitation of elemental (metals) or binary phases (metal oxides, nitrides, chalco-genides, etc.) are relatively straightforward. The process becomes more complicated in the simultaneous precipitation of various components from the reaction mixture this is especially challenging when several stable compositions exist in a multi-component system. The products of room-temperature precipitation reactions are usually amorphous, and calcination or annealing steps are inevitable to obtain a defined material. Since the nature of the amorphous intermediates is difficult to determine by experimental techniques, any inhomogeneity with respect to the elemental distribution shows up, in the form of constituent segregation and secondary products, in the final material. 

Since the first synthesis of silicon monoxide by Potter 1905, the chemical state and atomic structure of this amorphous solid have been discussed controversially. The known binary phase diagrams of silicon and oxygen that... 

The most interesting Ln203-C02 binary phases are the three well characterized structural varieties of lanthanoid dioxymonocarbonate Ln202C03. Amorphous or very poorly crystallized anhidrous phases, Ln2(C03)3, resulting from the dehydration of the corresponding hydrated carbonates are also known. 

Recent studies have shown that incorporation of boron element into sihcon-based ceramics increases their thermal stability and retard crystallization [202-204]. For example, the materials of the binary system Si—N start to crystallize at 7 =1,000 °C forming a-Si3N4, while metastable solid solutions of the ternary and quaternary systems Si—C—N and Si—B—C—N withstand crystallization up to 1,450 and 1,700 °C, respectively [205]. In order to form an amorphous uniform phase in the final multinary ceramics, the ceramic elements are preferably distributed homogeneously in the preceramic polymers. The general consensus in the ceramics community is that the quaternary system Si—B—C—N as well as the ternary systems Si—B—N and Si—B—C would be particularly suitable for producing amorphous ceramics that resist the microstructural changes even at top loads. 

Fig. 1.4.1(a) Binary phase diagram of a binary amorphous polymer/solvent system undergoing phase separation above the lower critical solution temperature (LCST). The temperature of interest, T, intersects with the binodal curve at the composition (wt fraction) of a and p phases at equilibrium, c" and c. On the other hand, T intersects with the spinodal at compositions (wt fraction) c and c . Outside the binodal curve is the single-phase region, while inside it is the two-phase region... 

The present system of composites is a binary phase mixture of two dielectrically different materials, where BNN is ionic and polycrystalline and polystyrene are amorphous atactic and rather non-polar. A great variety of formulae has been suggested for the calculation of permittivity of heterogeneous mixtures. 

Lobmann et al. (2011) prepared co-amorphous binary blends of the two BCS class 2 drugs indomethacin and naproxen with the main aim to further investigate the type of molecular interactions in co-amorphous blends and their influence on recrystallization, dissolution and physicochemical properties. They were able to successfully produce co-amorphous blends at the molar ratios 2 1, 1 1, and 1 2 using quench cooling. Similar to the results obtained by Allespet al. (2009), naproxen showed poor physical stability in its pure amorphous form. However, in combination with indomethacin, stable co-amorphous single-phase systems could be obtained. 

Fig. 18. Composition ranges for the formation of an amorphous phase in melt-spun Al-R (R=Y. La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er or Yb) binary alloys. Their binary phase diagrams were adopted from Massalski (1986). The symbols of Amo. and X represent amorphous and unidentified crystalline phases, respectively.

Reactions were induced by energetic heavy ion bombardments from LN2 temperature to 300°C. A metal-rich mixed binary phase was also formed in the ion beam-induced reactions at 200°C, whereas an amorphous layer with the same composition was formed by the bombardments at RT. The crystalline phase has the same compositions and X-ray diffraction patterns for thermal and ion beam-induced reactions. The reaction progress in the thermal process depends approximately linearly on the duration of the annealing time with an activation energy = 1.3 0.3 eV. A linear dependence of the reacted thickness on the ion fluence was observed between RT and 300°C. An activation energy of = 0.31 0.06 eV was observed in the ion beam-induced process above 100°C. 

Matkar et al. have hypothesized what would happen to crystalline blend phase diagrams if one relaxes the last assumption of the Floty diluent theory of crystalline polymer solutions, namely, the complete rejection of polymeric solvent from the crystalline phase [66, 67]. In addition, Xu et al. have developed a new theory for a binary crystalline polymer blends based on a combination of liquid-liquid phase separation and solid-liquid phase transition by taking into consideration the coupling interaction between the solid crystal and amorphous liquid phase [71]. 

During the preparation of mixed ZnO/Al203 composites a highly X-ray amorphous binary Zn-Al phase is observed as the initial metastable coprecipitation product. Unfortunately, its structure could not be determined up to now as all attempts of thermal recrystallization result in the deeomposition of this phase into ZnO and Zn/Al-hydrotalcite. Nevertheless, the oeeurrence of this binaiy Zn/Al phase turns out to play a major role during the synthesis of the ternary Cu catalyst [2]. 

All the unary and binary phases are presented in Table 2. No stable ternary compound was foimd in the system. During crystallization of amorphous alloy Fe7oCrioB2o, a tetragonal 74 Fe2Cr4Bg ternary boride was identified, which transformed to anoflier Wmcm FeeCr2B4 at further heating [2005San]. 

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