Study of local environment of Ag in Ag/CeO2 catalyst by EXAFS

The combustion synthesized Ag/CeO2 catalysts have been characterized by Extended Xray Absorption Fine Structure (EXAFS) spectroscopy at the Ag K-edge. It has been found that Ag+ like species is present in 1% Ag/CeO2 catalyst, whereas mostly Ag metal clusters are found in 3% Ag/CeO2. The analysis of EXAFS spectra indicates that about one oxygen atom is coordinated to Ag central atom at a distance of 2.19 Angstrom in 1% Ag/CeO2 catalyst along with eight coordinated Ag-Ag bond at 2.86 Angstrom. The Ag-O bond is absent in 3% Ag/CeO2. (C) 2002 Elsevier Science Ltd. All rights reserved.

Evolution of metastable phases during crystallization of pulsed laser deposited amorphous Al–Fe films

Amorphous thin films of different Al–Fe compositions were produced by plasma/vapor quenching during pulsed laser deposition. The chosen compositions Al72Fe28, Al40Fe60, and Al18Fe82 correspond to Al5Fe2 and B2-ordered AlFe intermetallic compounds and α–Fe solid solution, respectively. The films contained fine clusters that increased with iron content. The sequences of phase evolution observed in the heating stage transmission electron microscopy studies of the pulsed laser ablation deposited films of Al72Fe28, Al40Fe60, and Al18Fe82 compositions showed evidence of composition partitioning during crystallization for films of all three compositions. This composition partitioning, in turn, resulted in the evolution of phases of compositions richer in Fe, as well as richer in Al, compared to the overall film composition in each case. The evidence of Fe-rich phases was the B2 phase in Al72Fe28 film, the L12- and DO3-ordered phases in Al40Fe60 film, and the hexagonal ε–Fe in the case of the Al18Fe82 film. On the other hand, the Al-rich phases were Al13Fe4 for both Al72Fe28 and Al40Fe60 films and DO3 and Al5Fe2 phases in the case of Al18Fe82 film. We believe that this tendency of composition partitioning during crystallization from amorphous phase is a consequence of the tendency of clustering of the Fe atoms in the amorphous phase during nucleation. The body-centered cubic phase has a nucleation advantage over other metastable phases for all three compositions. The amorphization of Al18Fe82 composition and the evolution of L12 and ε–Fe phases in the Al–Fe system were new observations of this work.

Photoluminescence of Sr(2-x)Ln(x)CeO(4+x/2) (Ln = Eu, Sm or Yb) prepared by a wet chemical method

A wet chemical route is developed for the preparation of Sr2CeO4 denoted the carbonate-gel composite technique. This involves the coprecipitation of strontium as fine particles of carbonates within hydrated gels of ceria (CeO2.xH(2)O, 40

Properties of concrete containing ultra-fine fly ash

Fly ash and silica fume are two pozzolans that have been widely used for improved concrete strength and durability. Silica fume displays a greater pozzolanic reactivity than fly ash primarily due to its finer particle size. The reactivity of fly ash can be improved by reducing its particle size distribution. This paper discusses the fresh and hardened properties of concrete made with an ultra-fine fly ash (UFFA) produced by air classification. Durability testing for chloride diffusivity, rapid chloride permeability, alkali-silica reaction (ASR), and sulfate attack was also conducted It was found that at a given workability and water content, concrete containing UFFA could be produced with only 50% of the high-range water-reducer dosage required for comparable silica fume concrete. Similar early strengths and durability measures as silica fume concrete were observed when a slightly higher dosage of UFFA was used with a small reduction (10%) in water content.

The utility of Bacillus subtilis as a bioflocculant for fine coal

The application of Bacillus subtilis as a flocculant for fine coal has been reported here. Zeta-potential measurements showed that both the coal and bacteria had similar surface charge as a function of pH. Surface free energy calculations showed that the coal was hydrophobic while the bacterium was hydrophilic. The adhesion of the bacteria to coal and subsequent settling was studied in detail. Adhesion of bacteria to coal surface and subsequent settling of coal was found to be quick. Both adhesion and settling were found to be independent of pH, which makes the process very attractive for field applications. The presence of an electrolyte along with the bacterium was found to not only enhance adhesion of bacteria, but also produce a clear supernatant. Further, the settled fraction was more compact than with bacteria alone. Interaction energy calculations using the extended DLVO theory showed that the electrical forces along with the acid-base interaction energy play a dominant role in the lower pH range. Above pH 7, the acid-base interaction energy is the predominant attractive force and is sufficient enough to overcome the repulsive forces due to electrical charges to brine about adhesion and thus settling of fine coal. With increase in electrolyte concentration, the change in total interaction energy with pH is minimal which probably leads to better adhesion and hence settling. (C) 2003 Elsevier Science B.V. All rights reserved.

Pyrene appended bile acid conjugates: Synthesis and a structure-gelation property study

A wide variety of novel compounds obtained by combining two types of known organogelators, viz., bile acid alkyl amides and pyrene alkanoic acids, were synthesized and screened for their gelation ability. The 3 alpha esters of 1-pyrene butyric acid (PBA) of alkylamides of deoxycholic acid (DCA) turned out to be effective in the gel formation with many organic solvents although the gelation has to be triggered by the addition of a charge transfer (CT) agent 2,4,7-trinitrofluorenone (TNF). The special feature of these molecules is that the organogelation is achieved only after derivatizing the acid moiety of the 1-pyrenealkanoic acids. Additionally, the gelation properties can be fine-tuned by inserting different functional groups at the bile acid side chain. The gels obtained are deep red in colour and optically transparent up to 2% w/v. The SEM studies of the obtained xerogels revealed bundled rod-like morphology without specialized branching.

A Single-Crystal Study Of The Defect Chemistry And Transport-Properties Of Silver Selenide, Ag2+Delta-Se

Electronic and ionic conductivities of silver selenide crystal (Ag$_2+\delta$ Se) have been measured over a range of stoichiometry through the $\alpha - \beta$ transition by using solid state electrochemical techniques. In the high temperature $\beta$-phase Ag$_2$Se shows metallic behaviour of electronic conductivity for high values of $\delta$; with decrease in $\delta$, the conductivity of the material exhibits a transition. The magnitude of change in electronic conductivity at the $\alpha - \beta$ transition is also determined by stoichiometry. Ionic conductivity of the $\beta$-phase does not vary significantly with stochiometry. Ionic conductivity of the $\beta$-does not vary significantly with stoichiometry. A model to explain the observed transport properties has been suggested.

Novel Algorithm for estimation of Swell Pressure of Fine Grained Soils Based on Diffuse Double Layer (DDL) Theory

Use of engineered landfills for the disposal of industrial wastes is currently a common practice. Bentonite is attracting a greater attention not only as capping and lining materials in landfills but also as buffer and backfill materials for repositories of high-level nuclear waste around the world. In the design of buffer and backfill materials, it is important to know the swelling pressures of compacted bentonite with different electrolyte solutions. The theoretical studies on swell pressure behaviour are all based on Diffuse Double Layer (DDL) theory. To establish a relation between the swell pressure and void ratio of the soil, it is necessary to calculate the mid-plane potential in the diffuse part of the interacting ionic double layers. The difficulty in these calculations is the elliptic integral involved in the relation between half space distance and mid plane potential. Several investigators circumvented this problem using indirect methods or by using cumbersome numerical techniques. In this work, a novel approach is proposed for theoretical estimations of swell pressures of fine-grained soil from the DDL theory. The proposed approach circumvents the complex computations in establishing the relationship between mid-plane potential and diffused plates’ distances in other words, between swell pressure and void ratio.

Ultra fine scale phase separated microstructure for Ag-Fe nanoparticle

We report the formation of Ag-Fe nanoparticles with an ultrafine scale phase separated microstructure consisting of Ag and Fe(3)O(4) phases. Ag-Fe particles were synthesised by the co-reduction of Ag and Fe salts in water medium. The co-existing Ag and Fe(3)O(4) phase volumes were around similar to 1 nm in one of the dimensions. (C) 2011 Elsevier B. V. All rights reserved.

10 Years of Click Chemistry: Synthesis and Applications of Ferrocene-Derived Triazoles

Click chemistry has played a significant role as a rapid and versatile strategy for conjugating two molecular fragments under very mild reaction conditions. Introduction of ferrocene-derived triazole systems using click chemistry has attracted enormous interest in various fields due to its potential applications in electrochemical techniques for detection and sensing. The present discussion focuses on the synthesis of ferrocene-triazole and the importance of using a CuAAC reaction for such conjugation. Applications of ferrocene-based click reactions in conjugate chemistry, asymmetric catalysis, medicinal chemistry, host-guest interactions, and materials chemistry have been highlighted.