Amorphous mixed phase

The nature of the solidification process in these cements has received little attention. Rather, attention has focussed on the crystalline components that form in cements which have been allowed to equilibrate for some considerable time the nature of such phases is now quite well understood. Gelation is reasonably rapid for these cements and occurs within a significantly shorter time than does development of crystalline phases. The conclusion may be drawn that initial cementition is not the same as crystallization, but must occur with the development of an essentially amorphous phase. Reactions can continue in the amorphous gelled phase, but are presumably limited in speed by the low diffusion rates possible through such a structure. However, reactions are able to proceed substantially to completion, since in many cases X-ray diffraction has demonstrated almost quantitative conversion of the parent compounds to complex crystalline mixed salts, though several days or weeks of equilibration are required to bring this about. 

B,c,Oj. Mixed phases of the B-C—O system have been prepared from amorphous B, B2O3, and C in various ratios at 1700°C and up to 7.5 GPa. A wide range of compositions from Be.sC and B6C0.45O0.77 was observed with intermediate stmcmres between B4C and BoO [548]. 

Carbon in the carbonaceous chondrites does not exist as polymer or organic molecules alone. Carbonates are also present in relatively small amounts 20,23) and the same is true for elemental carbon. Elemental carbon seems to exist as carbynes (triple-bonded allotropes of carbon). At least three types of carbynes have been described in Murchison 341 but these results were questioned in 1982 by Smith and Buseck63). According to these authors, sheet silicates mixed with elemental carbon could be misidentified as carbynes in X-ray diffraction patterns. These particular carbonaceous phases (carbynes or otherwise) and other carbonaceous phases (polymer and amorphous carbon phases called C-oe and C- 3) are carriers of noble gases trapped in the chondritic material. Some of these carbynes seem to be condensates from the protosolar nebula while others are probably of presolar origin34 >. 

Our support precursor having a Mg Al molar ratio of about 3 1 shows an x-ray diffraction pattern typical of hydrotalcite (see Figure la) (10). After calcination at 873 K the resulting diffraction pattern exhibits diffuse peaks corresponding to MgO (Figure lb). No evidence for separate crystalline aluminum phases was found so A1 cations probably remain closely associated with or dissolved in the MgO structure. However, it is possible that amorphous alumina phases, not detectable by x-ray diffraction, may be present in our mixed oxide. 

PEO homopolymer) to the 1.2-1.4 range of values shown in Table IV for the copolymers " In other words, what carbon to oxygen stoichiometries in a mixed phase of amorphous PEO and amorphous PS will result in measured intensity ratios of 1.2-1.4 ... 

The above procedure was used to calculate the composition of the mixed phase in each of the triblock copolymers. The results of the calculations are tabulated in Table IV, and they show that the molar ratio of ethylene oxide to styrene in the mixed phase varies from 0.6 1 to 1.5 1 in going from sample A to C. Mixing of PS with amorphous PEO is most prevalent in sample A, which has the smallest concentration of PS and the shortest PS block length (M = 5.IK). Almost 50% of the PS in the surface region of sample S films is mixed with PEO, whereas only 6% of the surface PS is mixed in sample C. It seems clear that PS and PEO are partially miscible in the surface regions of these triblock copolymers. Our finding that PS... 

Pt-based electrocatalysts have proven to be ideally suited to the Ap analysis primarily because of the extensive morphological characterizations (X-ray diffraction, single crystal electrochemical evaluations, UHV spectroscopies, etc.) performed over the past decades. In contrast, chalcogenide electrocatalysts are comprised of nanoscale amorphous clusters making a detailed analysis of the strac-ture/property relationships inherently difficult. In light of these considerations, we have recently applied the Ap technique to a novel mixed-phase chalcogenide electrocatalyst (RhxSy, commercially available from A-TEX, Inc). Rh Sy shows remarkable per-... 

The photoactivities of ultrafme Ti02 nanoparticles in anatase, rutile, or mixed phases were tested in the photocatalytic degradation of phenol [322]. For Ti02 nanoparticles, mainly in the anatase phase and mixed-phases, the photocatalytic activities increased significantly with the content of the amorphous part decreasing. The completely crystallized rutile nanoparticles exhibited size effects in this photocatalytic reaction and the photocatalytic activity of rutile-type Ti02 nanoparticles with a size of 7.2 nm was much higher than that with 18.5 nm or 40.8 nm and was comparable to that of anatase nanoparticles. 

By far the most successful method of preparation was via an amorphous organic precursor to the required mixed molybdates, following the method of Delmon et al.(jrT). The method has proved successful for the pure iron, chromium and aluminum molybdates, and also for the mixed phases. A detailed outline of the method taking the example of FeCr(Mo0i )3 is as follows ... 

In heterogeneously catalyzed gas-phase reactions, one of the problems encountered in the first publication was the fact that only relatively large thermal signals could be detected. This problem was solved by the work of Holzwarth et al. [18], who used a background subtraction technique to reduce the detection limit to differences of about 0.1 K. With this set-up it was possible to analyze the activity of several metal-doped, amorphous, mixed metal oxides in total oxidation reactions of hydrocarbons. 

The bulk structures of most minerals important to soil chemists are well known from x-ray and neutron diffraction studies. Exceptions to this generality would be the various amorphous oxides and mixed oxide precipitates. Methods pioneered by Catlow s group should find increasing applicability to the structural study of these amorphous soil minerals and mixed phases. Their approach has been to develop ionic-type force fields for performing static energy minimizations of general oxide and halide minerals. Since ionic force fields rei uire far fewer parameters than va-... 

By analogy with photosensitive anodic films appearing over the surface of silicon during its treatment in fluorine-containing electrolytes, it can be suggested that the built-in film represents a mixed phase of electrochemical reaction products or results from the anodized surface amorphization [27,28]. In its turn, this indicates that under potentiostatic conditions the chemical processes at the SiC/HF junction are predominant. The results obtained emphasize that not every porous-like phase formed as a result of SiC anodization can be considered as PSC. 

Physical blends of bisphenol-A polycarbonate (PC) and a poly-arylate (PAr) exhibit by thermal analysis two amorphous phases a pure PC phase and a PAr-rIch miscible mixed phase. On controlled thermal treatment, transreaction between PC and PAr takes place mainly in the mixed phase, producing a new copolymer. Reaction progression from block to random copolymers has been traced by DSC, 13c NMR and CPC. The final product of transreaction is an amorphous copolymer showing a single T depending on the original binary composition. ... 

In this study, it has been demonstrated that elementally pure amorphous metal oxide thin films of Zr, Ti, and Mn may be prepared photochemically from thin film precursors at room temperature by our method. By using these and other compounds which are compatible were able to prepare amorphous mixed metal oxides. In the case of thin films of Pb(ZrxTii.x)03 thermal annealing studies indicated that the polycrystalline tetragonal phase of Pb(Zro.48Tio.52)03 could be produced from the amorphous films. 

In the practical systems, the mixing free energy change is estimated with the reference to the amorphous bulk phase of the polymer, so... 

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