The effect of H2O on the sulfation of Havelock limestone under oxy-fuel conditions in a thermogravimetric analyser

A gas mixture representing oxy-fuel combustion conditions was employed in a thermogravimetric analyser to determine the effect of water vapor and SO₂ concentration on limestone sulfation kinetics over the temperature range of 800 to 920 °C. Here, experiments used small samples of particles (4 mg), with small particle sizes (d_p < 38 µm) and large gas flow rates (120 mL/min@NTP) in order to minimize mass transfer interferences. The gas mixture contained 5000 ppm_v SO₂, 2% O₂, and the H₂O content was changed from 0% to 25% with the balance CO₂. When water vapor was added to the gas mixture at lower temperatures (800–870 °C), the limestone SO₂ capture efficiency increased. However, as the temperature became higher, the enhancement in total conversion values decreased. As expected, Havelock limestone at higher temperatures (890 °C, 920 °C, and 950 °C) experienced indirect sulfation and reacted at a faster rate than for lower temperatures (800–870 °C) for direct sulfation over the first five minutes of reaction time. However, the total conversion of Havelock limestone for direct sulfation was generally greater than for indirect sulfation.     

Interaction of thorium(IV) with nitrate in aqueous solution: medium effect or weak complexation?

Microcalorimetric titrations were performed to study the Th(IV)/nitrate interaction in aqueous solution. The results show the formation of a weak mononuclear complex of Th(IV) with nitrate and allow the determination of the complexation thermodynamic parameters at 298 K and ionic strength 1.0 mol dm(-3). The reaction is endothermic and entropy driven. Data and comparison with similar actinide(IV) complexes allow to confirm the inner-sphere nature of the Th(NO(3))(3+) complex.     

Sr(II)-UPRM-5 titanium silicate framework thermally induced contraction: in situ high temperature XRD and 29Si MAS NMR

The thermally induced contraction process of a titanosilicate prepared with tetraethylammonium hydroxide and ion exchanged with Sr(II) (Sr-UPRM-5) after detemplation has been characterized via in situ high temperature X-ray diffraction (XRD) and (29)Si magic angle spinning nuclear magnetic resonance (MAS NMR). The as-synthesized material was prepared via conventional and microwave-assisted hydrothermal methods, the latter resulting in a reaction time an order of magnitude shorter than the former case. In situ high temperature XRD tests performed on Sr-UPRM-5 indicate that at 120 °C, water coordinated to the structure is released initiating the collapse of the framework. At much higher temperatures, the material eventually becomes an amorphous phase. Indexing of the XRD patterns indicates that lattice constant a was more affected by the heat treatment, probably related to the material's pore system, while the unit cell volume experienced a 44% reduction. (29)Si MAS NMR analyses for as-synthesized UPRM-5 confirmed two different silicon environments: Si(2Si, 2Ti(octa)) and Si(3Si, 1Ti(semi-octa)), which are similar to those exhibited by titanosilicate ETS-4. On the other hand, in situ high temperature (29)Si MAS NMR analyses for Sr-UPRM-5 demonstrated that changes in the silicon environment due to the presence of titanium centers possessing additional multiple coordination states, which arise from elimination of framework coordinated water molecules, are responsible for the structure collapsing. In general, these results underline the importance of avoiding complete removal of tenacious water molecules in order to preserve the Sr-UPRM-5 properties suitable for adsorption and catalysis applications.     

Synchronization regions of two pulse-coupled electronic piecewise linear oscillators

Stable synchronous states of different order were analytically, numerically and experimentally characterized in pulse-coupled light-controlled oscillators (LCOs). The Master-Slave (MS) configuration was studied in conditions where different time-scale parameters were tuned under varying coupling strength. Arnold tongues calculated analytically – based on the piecewise two-time-scale model for LCOs – and obtained numerically were consistent with experimental results. The analysis of the stability pattern and tongue shape for (1 : n) synchronization was based on the construction of return maps representing the Slave LCO evolution induced by the action of the Master LCO. The analysis of these maps showed that both tongue shape and stability pattern remained invariant. Considering the wide variation range of LCO parameters, the obtained results could have further applications on ethological models.     

Computational studies on azaphosphiridines, or how to effect ring-opening processes through selective bond activation

The relative energies of azaphosphiridine and its isomers, the ring stability towards valence isomerization, and the ring strain, as well as the kinetics and thermodynamics of possible ring‐opening reactions of P^III derivatives ( 1 – 5 ) and P^V chalcogenides ( 6 – 9 ; O to Te), were studied at high levels of theory (up to CCSD(T)). The barrier to inversion at the nitrogen atom in the trimethyl‐substituted P^III derivative 5 increases from 12.11 to 15.25 kcal mol^?1 in the P‐oxide derivative 6 (P^V); the relatively high barrier to inversion at the phosphorus in 5 (75.38 kcal mol^?1) points to a configurationally stable center (MP2/def2‐TZVPP//BP86/def2‐TZVP). The ring strain for azaphosphiridine 5 (av. 22.6 kcal mol^?1) was found to increase upon P‐oxidation ( 6 ) (30.8 kcal mol^?1; same level of theory). Various ring‐bond‐activation processes were studied: N‐protonation of P^III ( 5 ) and P^V ( 6 , 7 ) derivatives leads to highly activated species that readily undergo P? N bond cleavage. In contrast, metal chlorides such as LiCl, CuCl, CuCl₂, BeCl₂, BCl₃, AlCl₃, TiCl₃, and TiCl₄ show little P? N bond activation in 5 and 7 . Remarkably, TiCl₃ selectively activates the C? N bond, and induces stronger bond activation for P^V ( 6, 7 ) than for P^III azaphosphiridines ( 5 ). The ring‐expanding rearrangement of P^V azaphosphiridines 6 – 9 to yield P^III 1,3,2‐chalcogena‐azaphosphetidines 32 a – d is predicted to be preferred for the heavier chalcogenides 7 – 9 , but not for the P‐oxide 6 . The first comparative analysis of three bond strength parameters is presented: 1) the electron density at bond critical points, 2) Wiberg’s bond index, and 3) the relaxed force constant. This reveals the usefulness of these parameters in assessing the degree of ring bond activation.     

Synthesis, structural charaterization, and electrochemical and optical properties of ferrocene-triazole-pyridine triads

The synthesis and electrochemical, optical, and cation-sensing properties of the ferrocene-triazole-pyridine triads 3 and 5 are presented. Azidoferrocene 1 and 1,1'-diazidoferrocene 4 underwent the "click" reaction with 2-ethynylpyridine to give the triads 3 and 5 in 81% and 68% yield, respectively. Electrochemical studies carried out in CH(3)CN in the presence of increasing amounts of Zn(2+), Ni(2+), Cd(2+), Hg(2+), and Pb(2+) metal cations, showed that the wave corresponding to the ferrocene/ferrocenium redox couple is anodically shifted by 70-130 mV for triad 3 and 167-214 mV for triad 5. The maximum shift of the ferrocene oxidation wave was found for 5 in the presence of Zn(2+). In addition, the low-energy band of the absorption spectra of 3 and 5 are red-shifted (Δλ = 5-10 nm) upon complexation with these metal cations. The crystal structures of compounds 3 and 5 and the complex [3(2)·Zn](2+) have been determined by single-crystal X-ray methods. (1)H NMR studies as well as density functional theory calculations have been carried out to get information about the binding sites that are involved in the complexation process.     

Design of progressively censored group sampling plans for Weibull distributions: An optimization problem

Optimization algorithms provides efficient solutions to many statistical problems. Essentially, the design of sampling plans for lot acceptance purposes is an optimization problem with several constraints, usually related to the quality levels required by the producer and the consumer. An optimal acceptance sampling plan is developed in this paper for the Weibull distribution with unknown scale parameter. The proposed plan combines grouping of items, sudden death testing in each group and progressive group removals, and its decision criterion is based on the uniformly most powerful life test. A mixed integer programming problem is first solved for determining the minimum number of failures required and the corresponding acceptance constant. The optimal number of groups is then obtained by minimizing a balanced estimation of the expected test cost. Excellent approximately optimal solutions are also provided in closed-forms. The sampling plan is considerably flexible and allows to save experimental time and cost. In general, our methodology achieves solutions that are quite robust to small variations in the Weibull shape parameter. A numerical example about a manufacturing process of gyroscopes is included for illustration.     

A modifier that enables the easy dispersion of alkyl-coated nanoparticles in an epoxy network

Nanoparticles (NPs) coated with alkyl chains cannot be dissolved in diglycidylether of bisphenol A (DGEBA), which is a typical monomer used in the synthesis of epoxy networks. We show that adding small amounts of the linear amphiphilic polymer obtained by reaction of DGEBA with dodecylamine, produced a stable dispersion of dodecanethiol-coated gold NPs in DGEBA. The anionic homopolymerization of this blend initiated by a tertiary amine led to a nanocomposite with a uniform dispersion of gold NPs. The selected crosslinking chemistry allowed covalent bonding of the modifier to the matrix, avoiding phase separation and enabling easy tuning of the thermal properties of the matrix.     

α-Axis oriented ZnS thin film synthesised by dip coating method

The structural, morphological, optical and electrical properties of α-axis oriented nanostructured ZnS thin film prepared by dip coating have been studied in this article. The X-ray diffraction studies of the film shows that the ZnS was crystallized with cubic structure of particle size 27 nm with a strong orientation along (200) plane which is advantageous for optoelectronic devices. The scanning electron microscopy and TEM micrograph reveals that the film consists of nano crystalline columnar particles. From the investigation of the absorption spectra of this ZnS film, the band-gap is found to be higher (4 eV) than bulk (3.7 eV) indicating a blue shift. It is found that the film is having a transparency of >90 % in the visible-near IR region from 400 to 800 nm. From the photoconductivity measurements, it is evident that the film is photosensitive in nature. From the electrical resistivity measurements the conductivity of the film was found to be 3.4 × 10^?2 Ω^?1 cm^?1. Hot probe method indicates that the synthesized ZnS film is n-type.