Chemistry of the incomplete decomposition of ammonium perchlorate (AP)

Results are presented to show that as the thermal decomposition of orthorhombic ammonium perchlorate proceeds there is an accumulation, in the solid, of hydrochloric and nitric acids, the concentrations of which increase up to 15% decomposition after which they decrease until they reach the original values.

Solid-state chemistry of high-temperature oxide superconductors:The experimental situation

High-temperature superconductivity in oxides of the type(La, Ln)2?xBax(Sr)xCuO4, Y(Ln)Ba2Cu3O7??, La3?xBa3+xCu6O14, and related systems is discussed with emphasis on aspects related to experimental solid-state chemistry. All of these oxides possess perovskite-related structures. Oxygen-excess and La-deficient La2CuO4 also exhibit superconductivity in the 20�40 K just as La2?xBax(Srx)CuO4; these oxides are orthorhombic in the superconductivity phase. The crucial role of oxygen stoichiometry in the superconductivity ofYBa2Cu3O7?? (Tc = 95 ± 5K) is examined; this oxide remains orthorhombic up to ? ? 0.6 and becomes tetragonal and nonsuperconducting beyond this value of ?. Oxygen stoichiometry in this and related oxides has to be understood in terms of structure and disorder. The structure of La3?xBa3+xCu6O14 is related to that of YBa2Cu3O7, the orthorhombic structure manifesting itself when the population of O1 oxygens (along the Cusingle bondOsingle bondCu chains) is preponderant compared to that of O5 oxygens (along thea-axis); nearly equal populations of O1 and O5 sites give rise to the tetragonal structure. A transition from a high-Tc (95 K) superconductivity regime to a low-Tc (not, vert, similar60 K) regime occurs in YBa2Cu3O7?? accompanying a change in ?. There is no evidence for Cu3+ in these nominally mixed valent copper oxides. Instead, holes are present on oxygens giving rise to O? or O2?2 species, the concentration of these species increasing with the lowering of temperature. Certain interesting aspects of the superconducting oxides such as domain or twin boundaries, Raman spectra, microwave absorption, and anomalous high-temperature resistivity drops are presented along with the important material parameters. Preparative aspects of the superconducting oxides are briefly discussed. Phase transitions seem to occur atTc as well as at not, vert, similar240 K in YBa2Cu3O7.

Kinetics of TiO2-catalyzed ultrasonic degradation of rhodamine dyes

The ultrasonic degradation of two dyes, Rhodamine B (C28H31ClN2O3) and Rhodamine Blue (C28H32N2O3), were studied in the absence of catalyst and in the presence of two catalysts (combustion-synthesized anatase TiO2 and commercial Degussa P-25 TiO2. The rate of degradation of catalyzed reaction was higher than that obtained with in the absence of the catalysts. Among the catalysts, combustion-synthesized anatase TiO2 degraded the dyes faster when compared to the degradation with commercial Degussa P-25 catalyst. A Langmuir-Hinshelwood kinetic model was developed and the kinetic rate parameters were determined. The effect of other operating parameters, such as initial concentration, pH, temperature, and power intensity, was also investigated. The degradation rate increased with decreasing pH, increasing temperature, and higher intensity.

Recent Advances and Industrial Applications of Multilevel Converters

Multilevel converters have been under research and development for more than three decades and have found successful industrial application. However, this is still a technology under development, and many new contributions and new commercial topologies have been reported in the last few years. The aim of this paper is to group and review these recent contributions, in order to establish the current state of the art and trends of the technology, to provide readers with a comprehensive and insightful review of where multilevel converter technology stands and is heading. This paper first presents a brief overview of well-established multilevel converters strongly oriented to their current state in industrial applications to then center the discussion on the new converters that have made their way into the industry. In addition, new promising topologies are discussed. Recent advances made in modulation and control of multilevel converters are also addressed. A great part of this paper is devoted to show nontraditional applications powered by multilevel converters and how multilevel converters are becoming an enabling technology in many industrial sectors. Finally, some future trends and challenges in the further development of this technology are discussed to motivate future contributions that address open problems and explore new possibilities.

Chemistry in Confined Spaces: High-Energy Conformer of a Piperidine Derivative is Favored Within a Water-Soluble Capsuleplex

Propyloxy-substituted piperidine in solution adopts a conformation in which its alkoxy group is equatorially positioned Surprisingly, two conformers of it that do not interconvert in the NMR time scale at room temperature have been found within an octa-acid capsule The serendipitous finding of the axial conformer of propyloxy-substituted piperidine within a supramolecular capsule highlights the value of confined spaces in physical organic chemistry.

Microwave Assisted Synthesis of Nanostructured Titanium Dioxide with High Photocatalytic Activity

TiO2 (anatase) was synthesized using a microwave-irradiation-assisted chemical method. The reaction conditions were varied to obtain unique nanostructures of TiO2 comprising nanometric spheres giving the materials a very porous morphology. The oxide was characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA). The specific surface area and porosity were quantified by the BET method, and the degradation of dyes was carried out using these materials. The photocatalytic activity of the nanometric TiO2 was significantly higher than that of commercially available TiO2 (Degussa P25) for the degradation of the dyes.

Crystal Chemistry of the Noncentrosymmetric Eulytites: A(3)Bi(XO4)(3) (X = V, A = Pb; X = P, A = Ca, Cd, Sr, Pb)

Eulytite compounds, A(3)Bi(XO4)(3) (X = P, A = Ca, Cd, Sr, Pb), belong to the noncentrosymmetric space group l (4) over bar 3d (No. 220) as determined by single-crystal X-ray diffraction studies. The crystals were grown from the melt-cool technique with considerable difficulty as the compounds melt incongruently at their melting temperature, except for the compound Pb3Bi(PO4)(3). The unit cell parameter a is 9.984(5), 9.8611(3), 10.2035(3), and 10.3722(2) angstrom for Ca3Bi(PO4)(3), Cd3Bi(PO4)(3), Sr3Bi(PO4)(3), and Pb3Bi(PO4)(3) respectively, and there are four formula units in the unit cell. The structure of Pb3Bi(VO4)(3), a unique eulytite with vanadium substitution, is compared with all these phosphorus substituted eulytites. The A(2+) and Bi3+ cations occupy the special position (16c) while the O anions occupy the general Wyckoff position (48e) in the crystal structure. Only one O position has been identified for Pb3Bi(PO4)(3) and Pb3Bi(VO4)(3), whereas two O atom sites were identified for Ca3Bi(PO4)(3), Cd3Bi(PO4)(3), and Sr3Bi(PO4)(3). The UV-vis diffuse reflectance spectra indicate large band gaps for all the phosphate eulytites while a lower band gap is observed for the vanadate eulytite. The feasibility of the use of these compounds in optoelectronic devices has been tested by measuring the second-harmonic generation (SHG) values which have been found to be of a magnitude equivalent to the commercially used KDP (KH2PO4).

The chemistry of vetivalene-type vetivalene-type naturally-occurring sesquiterpenoids

Vetivalene, 1,4-dimetiiyl-6-isopropylnaphl1tlmlenc(1 ) represents a new sesquiterpene skelcton which 15 presumed to originate from eudesmane by a shift of the angular nicthyl group. Novel sesquiterpenm related to vetivalene have been isolated from plant sources ill ~s c e o ig ears. A suriey dealing xith the chemistry (structure, synthesis and configuration) of members of this interesting new class OF yesquiterpenes, coniprising occidol, risbitinol and the various ernmotinn is presented

The chemistry of vetivalene-type naturally occurring sesqufterpenoids

Vetivalene, 1,4-dimetiiyl-6-isopropylnaphl1tlmlenc(1 ) represents a new sesquiterpene skelcton which 15 presumed to originate from eudesmane by a shift of the angular nicthyl group. Novel sesquiterpenm related to vetivalene have been isolated from plant sources ill ~s c e o ig ears. A suriey dealing xith the chemistry (structure, synthesis and configuration) of members of this interesting new class OF yesquiterpenes, coniprising occidol, risbitinol and the various ernmotinn is presented.