Oxygen in coal ash: a simplified approach to the analysis of ash and mineral matter in coal

Oxygen was determined accurately in eight U.S. Bureau of Mines coal ash samples A, B, D, F, G, I, and J, NBS coal fly ash 1633 reference material, and two low-temperature ashes (LTA) from lllinois State Geological Survey. The method uses fast-neutron activation (FNA) analysis employing a dual counting and irradiation system which is essentially free from interferences. The stoichiometric balance based on analyses of the ashes performed by the USBM is calculated and summations given in oxide and element percent. Excellent agreement is found with the chemical data obtained by classical silicate analysis methods. Accurate oxygen determination for coal ash and LT-ash (or mineral matter) is important for calculation of data in the ultimate analysis of coal as such. Knowledge is required for recalculation of the data on a dry and dry-ash-free basis. The routinely used ‘oxygen by difference’ values are inadequate for accurate work. In order to determine the organic oxygen in coal one also has to correct for oxygen in mineral matter and oxygen in the water removed as moisture. The Parr formula and other methods of empirical estimation are inadequate and may be replaced in some cases by the oxygen determination. The complete data provide a quantitative basis for stoichiometric interpretation of coal analyses. It was found that the eight coal-ash samples analysed contained 45.5 ± 3% oxygen. Since these ashes represent a large variety of U.S. coals, this figure can be used as an estimate for recalculation and evaluation of the proximate and ultimate coal analyses. It is better, however, to use values actually determined in ash by the rapid fast-neutron activation method. This permits a better estimation of the sum of cations plus sulphates in the ash.     

Synthesis and oxidation behavior of nanocrystalline MCrAlY bond coatings

Thermal barrier coating systems protect turbine blades against high-temperature corrosion and oxidation. They consist of a metal bond coat (MCrAlY, M = Ni, Co) and a ceramic top layer (ZrO₂/Y₂O₃). In this work, the oxidation behavior of conventional and nanostructured high-velocity oxyfuel (HVOF) NiCrAlY coatings has been compared. Commercially available NiCrAlY powder was mechanically cryomilled and HVOF sprayed on a nickel alloy foil to form a nanocrystalline coating. Freestanding bodies of conventional and nanostructured HVOF NiCrAlY coatings were oxidized at 1000 °C for different time periods to form the thermally grown oxide layer. The experiments show an improvement in oxidation resistance in the nanostructured coating when compared with that of the conventional one. The observed behavior is a result of the formation of a continuous Al₂O₃ layer on the surface of the nanostructured HVOF NiCrAlY coating. This layer protects the coating from further oxidation and avoids the formation of mixed oxide protrusions present in the conventional coating. The original version of this article was published as part of the ASM Proceedings, Thermal Spray 2003: Advancing the Science and Applying the Technology, International Thermal Spray Conference (Orlando, FL), May 5–8 2003, Basil R. Marple and Christian Moreau, Ed., ASM International, 2003.     

Modeling and biological investigations of an unusual behavior of novel synthesized acridine-based polyamine ligands in the binding of double helix and G-quadruplex DNA

Three novel 2,7-substituted acridine derivatives were designed and synthesized to investigate the effect of this functionalization on their interaction with double-stranded and G-quadruplex DNA. Detailed investigations of their ability to bind both forms of DNA were carried out by using spectrophotometric, electrophoretic, and computational approaches. The ligands in this study are characterized by an open-chain (L1) or a macrocyclic (L2, L3) framework. The aliphatic amine groups in the macrocycles are joined by ethylene (L2) or propylene chains (L3). L1 behaved similarly to the lead compound m-AMSA, efficiently intercalating into dsDNA, but stabilizing G-quadruplex structures poorly, probably due to the modest stabilization effect exerted by its protonated polyamine chains. L2 and L3, containing small polyamine macrocyclic frameworks, are known to adopt a rather bent and rigid conformation; thus they are generally expected to be sterically impeded from recognizing dsDNA according to an intercalative binding mode. This was confirmed to be true for L3. Nevertheless, we show that L2 can give rise to efficient π-π and H-bonding interactions with dsDNA. Additionally, stacking interactions allowed L2 to stabilize the G-quadruplex structure: using the human telomeric sequence, we observed the preferential induction of tetrameric G-quadruplex forms. Thus, the presence of short ethylene spacers seems to be essential for obtaining a correct match between the binding sites of L2 and the nucleobases on both DNA forms investigated. Furthermore, current modeling methodologies, including docking and MD simulations and free energy calculations, provide structural evidence of an interaction mode for L2 that is different from that of L3; this could explain the unusual stabilizing ability of the ligands (L2>L3>L1) toward G-quadruplex that was observed in this study.     

Dewetting and Adsorption in Homopolymer Films Containing Triblock Copolymers: Role of Chain Architecture and Anchoring Block Molar Fraction

Triblock copolymer additives are found to stabilize thin-film dewetting of B-type homopolymers with degree of polymerization (DOP) P deposited on silicon oxide. The triblock copolymers’ architectures are ABA and BAB, where A and B represent anchoring and nonadsorbing blocks with DOP's N _A and N _B, respectively. Upon adding 1 vol.% of the ABA additive, dewetting is only observed for anchoring block molar fractions, f _A, below 4%. Dewetting is arrested in films containing 1 vol.% ABA, BAB, or AB that have similar values of f _A ～ 8%, showing that chain architecture is not the only indicator of a successful additive. Compared with films containing diblock copolymers, the interfacial excess, z*, of triblock copolymers at the melt/substrate interface is relatively small as measured by low-energy forward-recoil spectrometry. Because adsorbed copolymers can reduce the capillary driving force for dewetting and participate in entanglements with matrix chains, the higher coverage and grafting density observed for diblock copolymers suggests that diblocks are more effective than triblocks in improving thin-film stability.     

Effect of the surface modification of the synthetic meshes used in the surgical treatment of pelvic organ prolapse on the tissue adhesion and clinical functionality

Stress urinary incontinence and pelvic organ prolapse represent important conditions affecting adult women’s health. Lately, the properties and performance of the polymer materials used in the treatment of pelvic organ prolapse have been improved by modulating from their formula. Materials investigated in our study are polypropylene meshes used by clinicians in surgical treatment of urinary incontinence and utero-vaginal prolapse. In order to make a comparative analysis, we confronted the structure and surface morphology of native synthetic polypropylene meshes with explanted fragments from the same mesh type after clinical use. FTIR investigations revealed little change in structure after implantation, somehow insignificant. Scanning electron microscopy (SEM) demonstrates modification in surface morphology even just by passing through the transobturator passage, whereas after implantation the surface deteriorates. SEM on explanted meshes proves the encapsulation process of the mesh to be more similar to a foreign body reaction rather than to the adhesion and integration of the synthetic mesh into the organism. Histological analysis of the surrounding tissues near explanted mesh was made in some relevant clinical cases, because the tissue response is an important factor in order to evaluate the tissue adhesion at the polypropylene mesh surface. Based on our experiments and clinical experience we’ve designed an adhesion score. It applies to meshes used in pelvic organ prolapse surgery measuring the following important factors: tenacity, extent of adhesion, macroscopic and microscopic aspects and ease of dissection from surrounding tissues.     

Microstructure models for cellular materials

Laguerre tessellations generated by random sphere packings are promising models for the microstructure of cellular or polycrystalline materials. In this paper, the case of hard sphere packings with lognormal or gamma distributed volumes is investigated. The dependence of the geometric characteristics of the Laguerre cells on the volume fraction of the sphere packing and the coefficient of variation of the volume distribution is studied in detail. The moments of certain cell characteristics are described by polynomials, which allows to fit tessellation models to real materials without further simulations. The procedure is demonstrated by the examples of open polymer and aluminium foams.     

A non-conventional approach for crack problems in piezoelectric media under electromechanical loading

In this paper the elastostatic solution of an inclined crack problem has been analyzed. The approach is analogous to the one proposed over the past years for orthotropic materials by Piva andViola (1988) (Eng Fract Mech, 29: 535–548), and it may be considered an alternative to the mathematical formalisms currently used. A general expression of the stress field is determined in terms of complex potentials. The stress distribution and the displacement field in the proximity of the crack tip are finally obtained. An expression of the energy release rate is provided in terms of the field intensity factors. Numerical results are presented and discussed under different remote electro-mechanical loading conditions and varying the crack inclination. Particular attention has been focused on the effect of the lateral load on the fracture quantities and on the direction of the incipient branching angle.     

Thermal stability against reduction of LaMn1−yCoyO3 perovskites

Thermal and reduction-oxidation stability of substituted LaMn_1−yCo_yO₃ perovskite-type oxides (0.0 ≤ y_Co ≤ 1.0) prepared by the citrate route have been studied by means of surface area, X-ray diffraction, FTIR spectroscopy and magnetic properties. The perovskite orthorhombic structure is found for y_Co ≤ 0.5, with the exception of y_Co = 0.1, which corresponds better to rhombohedral LaMnO_3.15. For y_Co > 0.5 the diffraction profiles are quite similar to the cobaltite’s rhombohedral structure. Magnetic iso-field studies (ZFC-FC) reveal that, for y_Co ≤ 0.50, the system presents an antiferromagnetic canted-like ordering of the Mn/Co sublattice, in which the presence of divalent Co ion creates Mn³⁺-Mn⁴⁺ pairs that interact ferromagnetically through the oxygen orbital. This interpretation is confirmed by the magnetization loops, in which the magnetic moment increases when substituting Mn for Co. Therefore, the general trend is: for y_Co ≤ 0.5, the Co ions are inserted in the manganite structure and for y_Co > 0.5, the Mn ions are inserted in cobaltite structure. The enhancement of the ferromagnetic properties and the thermal stability against reduction for y_Co = 0.5 is attributed to optimized Co²⁺-Mn⁴⁺ interactions.     

Development and Validation of Europium-Sensitized Luminescence (ESL) Method for the Determination of Tetracycline Residues in Milk

The development of a fast and reliable screening method for the determination of tetracycline residues in milk is described and compared to high-performance liquid chromatography. The method is based on europium-sensitized luminescence: The emissive properties of the lanthanide cation are used as a fingerprint of europium (III) complexation with tetracycline. The optimization of the extraction and purification procedures provided a simple and convenient route to prepare stable tetracycline samples that can safely resist freezing cycles. The method is validated for the first time in milk matrix: The results show that accuracy and precision of the method meet complaints with the criteria of the Commission Decision 2002/657/EC. The proposed method has a false compliant rate (β error) lower than 5%.