Large-Deviation Local Theorem for Additive Functionals of a Markov Gaussian Field. II

This paper is a continuation of [1].     

Electrochemical and structural characterization of sputter-deposited Mg–Nb and Mg–Nb–Al–Zn alloy films

Nanocrystalline Mg–Nb and Mg–Nb–Al–Zn alloy films were deposited by dc magnetron sputtering on glass and quartz substrates in a wide range of niobium concentrations from 6 to 80 at.%. Structural, electrochemical and corrosion properties of the films were studied by X-ray diffraction, dc voltammetry, electrochemical impedance spectroscopy and electrochemical quartz crystal microbalance. Development of body-centred cubic Nb structure in the Mg–Nb alloy matrix yielded the effects of lattice contraction, grain refining and electrochemical passivity. The measurements showed high corrosion resistance of the films in alkaline solutions when niobium content was one third or more. An increased corrosion resistance was achieved by introducing minor amounts of Al (ca. 2 at.%). In particular, such Al effect was pronounced at lower Nb concentrations (20 to 30 at.%). Semiconductor properties of spontaneously formed oxide on Mg–Nb alloy were studied by Mott–Schottky plots, which indicated highly doped n-type oxide structures on Mg–Nb surface. The paper fills some gap in understanding of niobium–magnesium systems, which show potential for applications in hydrogen storage, switchable mirrors and corrosion protection.     

Antioxidant potential and phytochemical composition of extracts obtained from Phyllanthus phillyreifolius by different extraction methods

Abstract

Phyllanthus phillyreifolius (Euphorbiaceae), poorly studied plant species, was fractionated using conventional and high pressure extraction techniques such as supercritical fluid and pressurized liquid extractions. Lipophilic substances were extracted with n-hexane and supercritical CO₂ with or without co-solvent ethanol, meanwhile higher polarity fractions were recovered with acetone and 70% ethanol. Antioxidant potential was assessed by various chemical assays, which revealed that 70% ethanol was the most effective solvent for recovery of antioxidants. UPLC-MS phytochemical analysis of hydrophilic extracts confirmed geraniin as the main constituent of P. phillyreifolius. Other quantitatively important compounds were phyllanthusiin D and elaeocarpusin. Three isomers of tocopherol (α, β and γ) were quantified by HPLC in lipofhilic extracts. Generally, the results from this study revealed high antioxidant potential of P. phillyreifolius; consequently the plant may be considered as a promising source of antioxidants for functional foods, nutraceuticals and pharmaceutical formulations.     

Hydration of cement with superabsorbent polymers

Hydration of cement is a complex thermodynamic system where a number of heterogeneous compounds interact with each other to form cement hydrates. Superabsorbent polymers (SAP) can be added to cement systems with many different reasons, so it is relevant that the basic knowledge of this new compound on the development of hydration is well understood. This paper reports basic research on thermal analysis of cement pastes with SAP—a suspension-polymerized poly acrylic acid–acrylamide copolymer. Several parameters were analysed: the concentration of SAP, the effect of particle size distribution and their influence on the hydration process with focus on ordinary Portland cement. The methodology included thermogravimetric analysis and differential scanning calorimetry. Combined water method was employed at different thermodynamic conditions, so the energy of activation in the different systems can be accessed. The introduction of SAP in cement-based materials significantly affects the chemical balance of ordinary Portland cement. The effect is not only in terms of the amount of hydrates, but also the type of hydrates being generated, thermodynamically favourable to precipitation of calcium hydroxide. This paper provides information relevant to hydration modelling and comprehension of cementitious materials when internal curing is active.