Mechanism of interaction of pyrite with hematite as simulation of slagging and fireside tube wastage in coal combustion

Iron-bearing minerals have been recognised as a mayor source of fire-side wall slagging in pulverised fuel boilers, which not only reduces the thermal efficiency of heat transfer of the exchangers surface, but also affects its integrity as a result of corrosion and erosion. Nevertheless, the root cause of adhesion and growing of deposits has not been clearly addressed. Our approach suggests that differential scanning calorimetry (DSC) combined with simultaneous thermogravimetry can follow the chemical reaction between pyrite and the outer layer of iron oxide on tubewalls. The changes in composition are followed by X-ray diffraction (XRD). The results indicated that the mechanism of wetting and adherence of molten pyrite over iron oxides is chemically induced: both di and mono iron sulphides interact with the oxide layer, changing the oxidation state of iron in oxide scale, from hematite to magnetite. This would imply a change in the protective ability of the scale as well as a great increment in corrosion tendency.     

Rapid purification of the main allergen of Lolium perenne by high-performance liquid chromatography

The main allergen from rye grass (Lolium perenne) pollen was purified by size-exclusion high-performance liquid chromatography. The purified allergen had a molecular weight of 32,000 daltons and was significantly more active in solid phase radioimmunoassay than the whole extract. The highly purified antigen can be obtained very rapidly and with a recovery of 30%.     

Weak solutions of the forward problem in EEG for different conductivity values

The potential distribution on the scalp produced by current sources in the brain can be measured by an EEG recorder. The relationship between these sources and the scalp potential distribution may be described by a well-known mathematical model where some simplifications are usually introduced. The head is modeled as a multicompartment nested set and the conductivity of the different tissues is approximated by a positive piecewise constant function. This simplified model is used to solve the forward problem (FP), i.e., to calculate the scalp potential for a current source configuration. In this work, we prove that the weak solutions of the FP are continuous with respect to the conductivity values, that is, the difference between the scalp potentials is small if the conductivity values are closed enough. We present numerical examples that illustrates this property.     

Application of a Microwave Helium Plasma Torch Operating at Atmospheric Pressure to Destroy Trichloroethylene

We examined the influence of the gas flow-rate, microwave power and trichloroethylene concentration on the destruction of trichloroethylene with a system based on a microwave helium plasma operating at atmospheric pressure. Based on the experimental results obtained, the proposed system allows input concentrations of C₂HCl₃ in the ppmv range to be reduced to output concentrations in the ppbv range (i.e. virtually quantitative destruction) by using a microwave plasma power below 1000 W. High helium flow-rates and C₂HCl₃ concentrations allow energy efficiency values above 600 g/kW h to be obtained. Analyses of the output gases by gas chromatography and species present in the plasma by optical emission spectroscopy confirmed the negligible presence of halogen compounds resulting from the destruction of C₂HCl₃, and that of CCl₄ and C₂Cl₄ as the sole chlorine species exceeding levels of 30 ppbv. Gaseous by-products consisted mainly of CO₂, NO and N₂O in addition to Cl₂ traces.     

Arsenic speciation using HPLC-HG-ICP-AES with gas-liquid separator

Summary The determination of different chemical species of arsenic in aquatic media has been carried out using several separation and detection techniques. As separation techniques GC, HPLC, HG and cold trap-selective thermal desorption are the most frequently used. As detection techniques FAAS, ETAAS or, to a lesser extent, ICP-AES are applied. In this work the optimization conditions are presented for As(III), As(V), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) determination using (IC)HPLC coupled to HG with gas-liquid separator, and using ICP-AES as detector is presented. The gas-liquid separator impedes the entrance of mobile phase into the nebulizer and consequently into the plasma torch. The experimental conditions for HG (kind of acids and concentration, borohydride concentration, reagent flows) as well as plasma conditions have been optimized.The quality parameters: LOD, precision and accuracy are reported for all the species studied.     

Thermal behaviour of carbon clusters and small fullerenes

The structural and thermal properties of small carbon clusters (C _N , N = 13, 20, and 32) are investigated by constant energy Molecular Dynamics simulations over a wide range of temperatures, i.e., from T = 0K to above the melting point of graphitic carbon. The Tersoff interatomic potential [6] is used to mimic the covalent bond between the carbon atoms in the cluster. We find that small carbon clusters start to fragment or to evaporate atoms or C₂ or C₃ units before fully developing a liquidlike phase. As a consequence, some relevant isomers (such as rings, bowls, hollow cages) are thermally isolated from each other i.e., there are no thermally activated isomerization transitions between them. Possible implications of our results on the growth mechanism of fullerenes are discussed.     

Synthesis,characterization, and metal complexes of polyacetylenes with pendant 2,2′‐bipyridyl groups

5‐Ethynyl‐2,2′‐bipyridine ( 1 ; bpyC≡CH) polymerized in the presence of catalytic amounts of [RhF(COD)(PPh₃)] or [Rh(μ‐OH)(COD)]₂ (COD = 1,5‐cyclooctadiene) in 74–91% yields. In contrast, [Rh(μ‐X)(NBD)]₂ (X = Cl or OMe; NBD = norbornadiene) did not catalyze the polymerization of 1 or gave low yields of the polymer. The obtained polymer, poly(5‐ethynyl‐2,2′‐bipyridine) [ 2 ; (bpyC?CH)_n], was highly stereoregular with a predominant cis–transoidal geometry. Random copolyacetylenes containing the 2,2′‐bipyridyl group with improved solubility in organic solvents were obtained by the treatment of a mixture of 1 and phenylacetylene ( 3 ) or 1‐ethynyl‐4‐n‐pentyl‐benzene with catalytic amounts of [RhF(COD)(PPh₃)]. A block copolymer of 1 and 3 was prepared by the addition of 1 to a poly(phenylacetylene) containing a living end. The reaction of 2 with [Mo(CO)₆] produced an insoluble polymer containing [Mo(CO)₄(bpy)] groups, whereas with [RuCl₂(bpy)₂] or [Ru(bpy)₂(CH₃COCH₃)₂](CF₃SO₃)₂, it gave soluble metal–polymer complexes containing [Ru(bpy)₃]²⁺ groups. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43:3167–3177, 2005     

Cubic lines relative to a triangle

An extension of the traditional geometry of the triangle is derived through the construction of two 30-points particular cubics. Two generation procedures founded on triangular quadratic transformations and dual associate properties of the two cubics are presented.     

Optimal control of quantum rings by terahertz laser pulses

Complete control of single-electron states in a two-dimensional semiconductor quantum-ring model is established, opening a path into coherent laser-driven single-gate qubits. The control scheme is developed in the framework of optimal-control theory for laser pulses of two-component polarization. In terms of pulse lengths and target-state occupations, the scheme is shown to be superior to conventional control methods that exploit Rabi oscillations generated by uniform circularly polarized pulses. Current-carrying states in a quantum ring can be used to manipulate a two-level subsystem at the ring center. Combining our results, we propose a realistic approach to construct a laser-driven single-gate qubit that has switching times in the terahertz regime.     

Vibrational properties of hexagonal boron nitride: inelastic X-ray scattering and ab initio calculations

The phonon dispersion relations of bulk hexagonal boron nitride have been determined from inelastic x-ray scattering measurements and analyzed by ab initio calculations. Experimental data and calculations show an outstanding agreement and reconcile the controversies raised by recent experimental data obtained by electron-energy loss spectroscopy and second-order Raman scattering.