X-ray diffraction and Mössbauer spectroscopy of high energy ball-milled α-Fe2O3/TiO2 composite powders

α–Fe₂O₃/TiO₂ Composite powders have been prepared by high energy ball-milling for different times. The composites were studied using Mössbauer Spectroscopy (MS) and X-ray diffraction (XRD). The patterns of XRD show broadening in the diffraction peaks, indicating a decrease in the particle size of the composites with milling time. Also, the XRD patterns show an evolving new structural phase correlated with an evolving Titanium ferrite species with milling time. Mössbauer Spectroscopy shows the evolving titanium ferrite species characterized by a quadrupole doublet at the expense of the α–Fe₂O₃ represented by the magnetic sextet. The doublet corresponding to the Ti-ferrite phase dominates the Mössbauer spectra at long milling time (greater than 100 h of milling).     

Polaronic and charge ordering effects in Pr 0.5 Sr 0.5 Mn 1− x Fe x O 3

In this work we report the results of X-ray diffraction and Mössbauer spectroscopy for the systems Pr_0.5Sr_0.5Mn_1???x Fe _x O₃ (with x?=?0.05, 0.10, 0.15, 0.20, 0.25, 0.30). XRD patterns indicated that all samples were single phase with slightly distorted orthorhombic symmetry. Room temperature Mössbauer spectra are all quadrupole split, indicating paramagnetic relaxation of the Fe moment for all values of Fe concentrations. The spectra are fitted with two doublet components associated with Fe^3?+? ions in octahedral sites with different distortions. Mössbauer spectra recorded at liquid nitrogen temperature for this system also indicate paramagnetic relaxation of the Fe moments down to liquid nitrogen temperature (LNT). In these spectra a third quadrupole component with quadrupole splitting close to zero develops. This component is associated with the delocalization of the charge carriers and the consequent disappearance of lattice distortions produced by the polaronic effect at room temperature. The component with the high quadrupole splitting (0.81 to 1.07 mm/s) results from Jahn–Teller distortion as a consequence of charge ordering transition at low temperature.     

Ion Exchangers as catalysts I. Catalytic decomposition of hydrogen peroxide in presence of Dowex 50 W resin in the form of ethylamine-copper(II) complex ion in aqueous medium

Summary Dowex 50 W resin in the form of an ethylamine-Cu¹¹ complex ion was used as potentially active catalyst for the decomposition of H₂O₂ in aqueous medium. The stoichiometry of the amine-Cu¹¹ complex on the resin, determined experimentally, was found to have the total [Cu²⁺]: [ethylamine]=14 concentration ratio. The kinetics of the decomposition was studied and the calculated rate constant (per g of dry resin) was found to decrease with increase the degree of resin crosslinking. The active species, formed as an intermediate at the beginning of the reaction, had an inhibiting effect on the reaction rate. The brown peroxo-copper complex formed as a result of H₂O₂ decomposition, was found to contain the catalytic active species. The order of the reaction increased with decreasing initial H₂O₂ concentration, a sign of a step-wise mechanism. A quantitative treatment of the decomposition of H₂O₂ was provided in terms of activation parameters.     

Structure, magnetic properties and M?ssbauer spectra of La0.67Sr0.33FexMn1???xO3 manganites oxide prepared by mechanical ball milling method

La_0.67Sr_0.33Fe_xMn_1-xO₃, with x = 0.0, 0.1, 0.2 and 1 have been elaborated by mechanical system. X-ray diffraction, Scanning electron microscopy, Magnetic measurements and M?ssbauer spectroscopy for the systems have been investigated. Rietveld analysis of the X-ray powder diffraction show that the samples crystallise in the orthorhombic perovskite system with Pnma space group. The average particle size of about 60 nanometre was obtained from scanning electron microscopy and X-ray diffraction. The investigated samples exhibit a ferromagnetic to paramagnetic transition with increasing temperature. The presence of manganese in the structure leads to an increase of the Curie temperature as well as to spontaneous magnetization. The magnetization versus applied magnetic field shows a small coercive field and an unsaturated magnetization which indicates that the nanoparticles of all samples are superparamagnetic at around room temperature. Room temperature M?ssbauer spectra show that the samples with x = 0.1 and x = 1.0 contain minority α-Fe₂O₃ and other spinel ferrite species. Also, they indicate that Fe^3?+? ions are present in slightly distorted octahedral sites in the samples with x = 0.1 and 0.2, while mixed Fe valency was observed for the sample with x = 1.0.     

Effect of variation of the structure of amino acids on inhibition of the corrosion of low-alloy steel in ammoniated citric acid solutions

Potentiodynamic polarization, electrochemical impedance spectroscopy, and the new technique electrochemical frequency modulation were used to study the effect of the different structures of three amino acids (tryptophan, tyrosine, and serine) on inhibition of the corrosion of ASTM A213 grade T22 low-alloy steel in ammoniated citric acid solutions. The effects on corrosion inhibition of inhibitor concentration, temperature, and stirring velocity were studied. Thermodynamic data for corrosion and adsorption were calculated and are discussed. The results obtained from the different techniques reveal that the efficiency of inhibition follows the sequence: tryptophan > tyrosine > serine. Inhibition occurs as a result of adsorption of inhibitor molecules by the alloy surface. Adsorption of the inhibitors is a good fit with the Temkin isotherm model.     

Mössbauer Spectroscopy Study of Fe–Si Solid Solution Prepared by Mechanical Milling

A specimen of Fe–Si solid solution is prepared by ball milling of proper amounts of the pure elements (3Fe:Si) for different milling times. X-ray diffraction and Mössbauer spectroscopy have been used to characterize the solid solution. The Mössbauer spectra show four different sites corresponding to Fe atoms in a bcc structure having 0, 1, 2 and 3 Si atoms in the 1st nearest-neighbor (nn) shell. The hyperfine magnetic field decreases by 31 kOe for each Si atom in the 1st nn shell. A magnetic component with hyperfine field around (180 kOe) characterized by a broadened sextet was observed which could be due to iron sites having more than 3 Si atoms in the 1st nn. A theoretical model based on the binomial distribution was adopted to analyze the data. Good agreement between the experimental and the theoretical hyperfine field distribution in the high hyperfine field region was found, and the silicon content in the disordered A2 phase is deduced from the parameters which give the best agreement.     

Mössbauer Spectroscopy Study of Iron Nickel Alloys

Three samples of Fe_100–x Ni _x (with x=30, 35 and 40) were prepared by arc melting technique. The Mössbauer spectra of the three samples were collected and analyzed. The spectrum of the sample with x=30 consists of a singlet and a sextet. The singlet component which has isomer shift (IS=–0.08 mm/s) is attributed to a superparamagnetic phase. The value of the magnetic hyperfine field associated with the sextet component, 34.0 T, is consistent with that of -Fe–Ni alloy. In the spectra of the other samples the central line disappears. The magnetic component, used in fitting the spectrum of the sample with x=40 has a hyperfine magnetic field B _hf=30.0 T. This component is assigned to the high-spin -FCC Fe–Ni phase. Two magnetic components of 16.3 T and 27.3 T are used to fit the spectrum of the sample with x=35. The 27.3 T component is associated with the typical high-spin -FCC Fe–Ni phase while the 16.3 T component is associated with a -FCC Fe–Ni phase with magnetic relaxation.     

Synthesis of some new hetarylpyranopyridazines,cinnolines, and hetarylpyridazine derivatives

4-Acetyl-5,6-diphenylpyridazin-3(2H)-one was condensed with 6-chloro-3-formylchromone under different reaction conditions to yield the enone or pyranopyridazine. Both compounds were used in the synthesis of some new hetarylpyranopyridazines. Pyranodipyridazine was obtained via a sequence of reactions of 4-acetyl-5,6-diphenylpyridazin-3(2H)-one with diethyl carbonate, acetic anhydride, and 4-bromobenzenediazonium chloride. The reactions of pyridazinylbutane-1,3-dione with conc. H2SO4, POCl3, hydrazines, hydroxylamine hydrochloride, cyanoacetamide, thiourea, and thiosemicarbazone were also studied.