Phase Equilibria in the System HfO2–Y2O3–CaO

Phase equilibria in the system HfO₂–Y₂O₃–CaO were studied in the temperature range 1250° to 2850°C by both experimental methods (X-ray phase analysis at 20° to 2000°C, petrography, annealing and quenching, differential thermal analysis in He at temperatures to 2500°C, thermal analysis in air using a solar furnace at temperatures to 3000°C, and electron microprobe X-ray analysis) and theoretical means (development of a mathematical model for the liquidus surface by means of the reduced polynomial method). Phase equilibria were determined by the structure of the restricting binary systems. No ternary compounds were found. The liquidus was characterized by the presence of six four-phase, invariant equilibria. Solid solutions were based on monoclinic (M), tetragonal (T), and cubic (F) modifications of HfO₂; C and H forms of Y₂O₃; CaO; and CaHfO₃ that crystallized in two polymorphous modifications, namely, the cubic and rhombic perovskite-type structure.     

Dispersing Behavior of Hydroxyapatite Powders Produced by Wet-Chemical Synthesis

Three hydroxyapatite powders with different surface properties were produced by wet-chemical synthesis and characterized. The electrokinetic properties of powders dispersed in water were investigated by electroacoustic spectroscopy measurements. The different surface reactivity (pH_iep and ζ potential versus pH curves) was related to the interplay of dissolution and adsorption of Ca²⁺ ions. With a view toward the preparation of porous bodies by sponge impregnation, the behavior of powder suspensions was studied. Four deflocculants were tested, and the optimum dispersing conditions for each powder were found. Anionic polyelectrolytes resulted in the best effective dispersing agent, with different optimum amounts added to the suspensions.     

Stability of a chitosan layer deposited onto a polyethylene surface

A two‐step procedure was applied to obtain antimicrobial films; this procedure involved a corona treatment of the polyethylene (PE) surface and its chemical activation with 1‐ethyl‐3‐[3‐dimethylaminopropyl] carbodiimide hydrochloride and N‐hydroxysuccinimide, and this led to the covalent bonding of chitosan on the PE surface. Electrochemical methods were used to investigate the stability of the deposited chitosan layer. The potentiometric and polyelectrolyte titrations showed that some amount of chitosan desorbed faster from the surface until equilibrium was reached and also that the grafted chitosan layer was more stable than the physically adsorbed one. The chitosan immobilized on the PE surface exhibited the expected antibacterial activity when tested against three bacteria, which included two Gram‐negative bacteria, Salmonella enteritidis and Escherichia coli, and one Gram‐positive bacterium, Listeria monocytogenes. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2444–2457, 2013     

A Sequential and Iterative Testing Procedure to Identify the Nature of a Time Series Generating Process

Abstract

An inferential approach is proposed to identify the nature of the generating process corresponding to a real time series. This new sequential and iterative testing procedure goes beyond the Box and Jenkins methodology for the identification, estimation, and validation of linear data generating processes by investigating the probabilistic structure of non-Gaussian estimated residuals {? _t } for the possible presence of nonlinear serial dependence. The testing procedure aims at indicating the right type of dependence present in a series by means of specific inferential tests on the moments of the generating structure probability distribution. The test statistics adopted are very popular and powerful and encompass a wide range of stochastic nonlinearity alternatives. The U.S. Industrial Production Index series is used to illustrate the iterative testing procedure proposed.     

Tuning morphology of mesoporous titanium oxides through fluorinated surfactants-based systems

Four different fluorinated surfactant-based systems were used as template for the synthesis of highly ordered TiO₂ mesoporous materials with large-pore wormhole structures. The calcined materials exhibit large pore diameters (up to 5.9 nm), high surface areas (900–1,180 m² g^?1), pore volumes (0.90–1.25 cm³ g^?1) and thick pore walls (4.6–7.7 nm) depending of the synthesis route. It is established that the self-aggregation behavior of fluorinated amphiphile systems can be manipulate and provides a rich phase behavior to obtain well-organized titania sieves with adjustable pore size and surface topography. By comparison to titania and silica sieves obtained by the same procedure, it can be established that there is a deep interaction between head groups of fluorinated surfactants and Ti(IV)(iPrO)₄ showing that the inorganic precursor has a great influence on the properties of the final materials.     

Mechanical and Electrical Properties of SomeSilicon-Containing Poly(Amide-Imide)s

Aromatic silicon-containing poly(amide-imide)s have been prepared by low temperature solution polycondensation reaction of various aromatic diamines having ether bridges between phenylene rings with a diacid chloride, namely bis[N-(4-chlorocarbonylphenyl) phthalimidyl]dimethylsilane. These polymers were easily soluble in polar amidic solvents such as N-methylpyrrolidone,N,N-dimethylacetamide, and N,N-dimethylformamide and can be cast from solutions into thin, flexible films. They showed good thermal stability, with initial decomposition temperature being above 410°C and glass transition temperature in the range of 263–285°C. The polymer films exhibited good mechanical properties with tensile strengths in the range of 78–109 MPa, tensile modulus in the range of 1.44–1.76 GPa, and elongation at break values ranging from 11% to 24%. Electrical insulating properties of two polymer films were evaluated on the basis of dielectric constant and dielectric loss and their variation with frequency and temperature.     

Gas Phase Catalytic Oxidation of β-Picoline to Nicotinic Acid: Catalysts,Mechanism and Reaction Kinetics

An overview of the fundamental studies on a new method of nicotinic acid synthesis by the gas phase catalytic oxidation of β-picoline by oxygen is presented. The nature of active component in vanadia catalysts and reactivity of vanadium species are considered. Common features and differences in the mechanistic steps of nicotinic acid formation on various catalysts investigated by in situ FTIR spectroscopy are discussed. Effects of the reaction mixture components on the yield of nicotinic acid are considered in detail. Attention is paid to the kinetic equations of β-picoline oxidation on vanadia-titania catalysts.     

Non-Covalent Synthesis of Metal Oxide Nanoparticle–Heparin Hybrid Systems: A New Approach to Bioactive Nanoparticles

Heparin has been conjugated to Fe₃O₄, Co₃O₄, and NiO nanoparticles (NPs) through electrostatic interactions, producing colloidal suspensions of hybrid metal oxide heparin NPs that are stable in water. Negative zeta potentials and retention of heparin’s ability to capture toluidine blue indicate that heparin’s negative charges are exposed on the surface of the coated NPs. IR results confirmed the formation of nanohybrids as did NMR experiments, which were also interpreted on the basis of toluidine blue tests. Transmission electron microscopy results revealed that the heparin coating does not modify the shape or dimension of the NPs. Dynamic light scattering and negative zeta potential measurements confirmed that heparin surface functionalisation is an effective strategy to prevent NP aggregation.     

Microwave assisted combustion synthesis in the system Ti–Si–C for the joining of SiC: Experimental and numerical simulation results

Microwaves at 2.45 GHz have been applied to ignite the combustion synthesis of compacted Ti–Si–C powders mixtures, having 1:1:1 atomic ratio, in order to join SiC-based components. A mixture of different refractory phases such as TiC and TiSi₂ were obtained. Depending on the synthesis conditions, no residual silicon in the joint was detected, suggesting the suitability of the here proposed experimental joining approach for nuclear plants and high temperature applications. A simplified model was developed with the aim of obtaining a deeper understanding of the here proposed rapid, almost pressure-less and localized heating joining method. Experimental and numerical simulation results demonstrate that joining of SiC can be rapidly obtained with minimization of heat affected zones in the SiC substrates. Maximum apparent shear strength values of the joints ranged from 9.9 to 45.1 MPa, depending on the process conditions.     

Rhodium‐Catalyzed Enantioselective Hydrogenation of (E)‐Enol Acetate Acids

The novel rhodium complex [Rh(S)‐Phanephos(cod)]‐catalyzed hydrogenation of disubstituted (E)‐enol acetate carboxylic acids is reported. The catalytic cycle works under 30 bar of hydrogen under conventional heating giving different 3‐acetoxy‐2,3‐disubstituted carboxylic acids with ee ≥90%. Hydrogenation occurred also under microwave dielectric heating without eroding the enantioselectivity but improving the overall efficiency of the process. With microwaves, hydrogen pressure and reaction time required for complete hydrogenation dropped to 5 bar and 30 min, respectively. The best performance of this catalyst under microwave irradiation was TON 100, TOF 196 h⁻¹ with ee 99% on a 6‐g scale.