Parameters influencing the electrodeposition of a Ni-Cu coating on Fe powders. II. Effect of particle size fraction,suspension density and rotation speed

The composition of a two-component Ni-Cu coating and the efficiency of its electrochemical deposition on Fe powder was studied by constant current electrolysis. A fluidized bed arrangement was applied. The variable parameters were: the particle size fraction, the density of the suspension of the Fe powder in the plating bath, and the intensity of the stirring of the fluidized bed. Both the Cu and Ni contents in the deposit decrease with increase in the particle size, and with decrease in the suspension density. Thus, the surface area available for the electrochemical process proved to be of high importance. Another important factor is the quality of the contacts of the powder particles with the current carrying compact electrode during which the deposition of Ni is preferred. This influence is manifested in a decrease of the Ni-Cu ratio in the deposit with an increase in the particle size and rotation speed and, consequently, with a decrease in the suspension density. The current efficiency values on the powder for optimum conditions reached 80%.     

Retention indices as identification tool in pyrolysis-capillary gas chromatography

Pyrolysis-capillary gas chromatography (Py-cGC) represents important method to identify the analytes in the mixture after thermal degradation. This combines high effective analyte separation on-line coupled with thermal degradation process that depends on analyte structure. System of retention indices has been used for identification of the analytes after on-line pyrolysis and chromatographic separation. The pyrolysate composition has been studied during thermal degradation of polymethylmethacrylate (PMMA) at different pyrolysis temperatures and chromatographic column conditions. Homologues series of n-alkanes have been used for calculation of pyrolysate Kováts retention indices (I) and compared with mass spectrometric (MS) data of pyrolysate model mixture. To identify PMMA thermal degradation products the high density polyethylene (HDPE) as additive standard producing triplets of the olefin homologous series during co-pyrolysis has been used. These homologous series enable to calculate programmed temperature retention indices (ITPGC) to identify the analytes present in the pyrolysate. Calculated I values were compared with published I values databases to identify analytes yielded at different pyrolysis temperatures.     

Thermal properties and crystallization of BaO–MoO3–P2O5 glasses

Journal of Thermal Analysis and Calorimetry - The thermal behavior and crystallization of barium molybdate-phosphate glasses were studied in two compositional series, namely A:...     

Preparation,spectral, thermal,and biological properties of zinc(II) 4-chloro- and 5-chlorosalicylate complexes with methyl 3-pyridylcarbamate and phenazone

New zinc(II) 4-chloro- and 5-chlorosalicylate complex compounds of the general formula ((4- or 5-Cl)C₆H₃(2-OH)COO)₂Zn · L _n (where L = methyl 3-pyridylcarbamate, phenazone; n = 2, 4) were prepared and characterized by elemental analysis, thermal analysis (TG/DTG, DTA), and IR spectroscopy. During thermal decomposition, mpc, phen, chlorosalicylic acid, chlorophenol, carbon dioxide, and carbon monoxide were released. Volatile products of the thermal decomposition were confirmed by mass spectrometry. The final solid product of the thermal decomposition up to 700°C was zinc oxide or metallic zinc. Antimicrobial activity of the compounds prepared was tested against various strains of bacteria, yeasts and filamentous fungi. The highest antimicrobial effect was determined against the G⁺ bacteria S. aureus.     

Magnetotransport properties of epitaxial Pr0.5Ca0.5MnO3 films grown by a solution technique

Epitaxial Pr_0.5Ca_0.5MnO₃ films have been synthesized on (0 0 1) SrTiO₃ substrate using a chemical solution deposition technique and two-step post-annealing process. The zero field resistivity of the films shows semiconducting behavior and a characteristic of charge ordering is observed at 230 K. The resistivity of the 10 nm film did not show any effect with the magnetic field. However, melting of charge ordering was observed for the 120 nm film at an applied magnetic field of 4 T. Large decrease in the resistivity of the 120 nm film (<100 K) resulted in magnetoresistance of nearly −100% at 75 K.     

On Hurst exponent estimation under heavy-tailed distributions

In this paper, we show how the sampling properties of the Hurst exponent methods of estimation change with the presence of heavy tails. We run extensive Monte Carlo simulations to find out how rescaled range analysis (R/S), multifractal detrended fluctuation analysis (MF-DFA), detrending moving average (DMA) and generalized Hurst exponent approach (GHE) estimate Hurst exponent on independent series with different heavy tails. For this purpose, we generate independent random series from stable distribution with stability exponent α changing from 1.1 (heaviest tails) to 2 (Gaussian normal distribution) and we estimate the Hurst exponent using the different methods. R/S and GHE prove to be robust to heavy tails in the underlying process. GHE provides the lowest variance and bias in comparison to the other methods regardless the presence of heavy tails in data and sample size. Utilizing this result, we apply a novel approach of the intraday time-dependent Hurst exponent and we estimate the Hurst exponent on high frequency data for each trading day separately. We obtain Hurst exponents for S&P500 index for the period beginning with year 1983 and ending by November 2009 and we discuss the surprising result which uncovers how the market’s behavior changed over this long period.     

Synthesis,biological and physicochemical properties of Zinc(II) salicylate and 5-chlorosalicylate complexes with theophylline and urea

New zinc(II) salicylate complex compounds of general formula (X-C₆H₃-2-(OH)COO)₂Zn · L_n · xH₂O (where X = H, 5-Cl; L = theophylline, urea; n = 2, 4; x = 1, 2, 4) were prepared and their thermal, spectral and biological properties were studied. It was found that the thermal decomposition of hydrated compounds starts with the release of water. During the thermal decomposition of anhydrous compounds, the release of salicylic acid, theophylline, urea, CO₂, H₂O and C₆H₅Cl takes place. Zinc oxide was found as the final product of the thermal decomposition heated up to 900 °C. The complexes were tested against bacteria, yeasts and filamentous fungi. The highest biological activity show 5-chlorosalicylate compounds.