ac Conductivity of mixed spinel NiAl0.7Cr0.7Fe0.6O4

ac Conductivity measurements are carried out across the metal to insulator transition in NiAl_0.7Cr_0.7Fe_0.6O₄. The low frequency data is analyzed using Summerfield scaling theory for hopping conductivity. The exponent of the scaling behavior has significantly different values in the conducting and insulating regimes. The hopping frequency and the zero frequency conductivity are found to increase with temperature, slowly in the metallic regime and rapidly in the insulating regime.     

Local canted spin behaviour in Co1.4−x Zn x Ge0.4Fe1.2O4 spinels: A macroscopic, mesoscopic and microscopic study

DC magnetization, neutron depolarization and neutron diffraction (with both polarized and unpolarized neutrons) measurements have been reported for the Co_1.1−x Zn _x Ge_0.1Fe_1.2O₁ spinels with x=0.5, 0.6 and 0.7. Neutron depolarization and neutron diffraction measurements confirm the presence of a long range ferrimagnetic ordering of the local canted spins in these ferrite samples. The observed features of low field magnetization have been explained under the framework of thermally activated domain wall movement of ferrimagnetic arrangement of local canted spins. An important role of magnetic anisotropy (due to the presence of Co²⁺ ions) in establishing the magnetic ordering and domain kinetics in these ferrites has been observed.     

Sorption and thermodynamic behavior of zinc(II)-thiocyanate complexes onto polyurethane foam from acidic solutions

The uptake of Zn(II)-SCN complex onto polyurethane foam (PUF) has been investigated in detail with respect to different composition and variable concentration of electrolyte, zinc, thiocyanate ions and PUF, and equilibration time. The sorption data followed both Langmuir and Dubinin-Radushkevich (D-R) sorption isotherms over the entire concentration range of zinc investigated whereas Freundlich sorption isotherm is obeyed upto 13.6^.10^-3M concentration. The Langmuir constants Q = 202±7 mmole^.g^-1 and of b = (1.78±0.31.10⁴ dm^3.mole^-1 and of D-R paraneter X _m = 493±1 mmole^.g^-1, b = activity coefficient = -0.028±0.0002 and of sorption energy E = 13.2±0.5 kJ^.mole^-1 and Freundlich constants 1/n = 0.42±0.03 and c _m = 6.47±1.7 mmole^.g^-1 were evaluated. The influence of temperature variation on sorption have yielded DH = -77.5±2.9 kJ^.mole^-1, DS = -5±0.09 J^.mole^-1.K^-1 and DG = -6.67±0.05 kJ^.mole^-1. The effect of common anions and cations on the sorption has been examined. Sulphate, ascorbate and bromide ions enhances the sorption to some extent whereas nitrite, Pb(II), Fe(III), Al(III), Cu(II) and Co(II) decrease to sorption significantly. A possible mechanism has been envisaged for Zn(II)-SCN sorption onto PUF.     

Elemental analysis of special materials by X-ray fluorescence spectrometry

The special materials like phosphor bronze for P, Fe, Ni, Cu, Zn, Sn and Pb; mild steel for P, S, V, Cr, Mn, Co, Ni, Cu, As, Nb, Sb and W; special alloys for Ti and Mo, zircaloy and zirconium oxide for Hf; and zircon ore for Zr have been analyzed by X-ray fluorescence spectrometry (XRFS). The measured values along with certified values, precision and accuracy have been given for all the elements analyzed. Some of these materials have also been analyzed by atomic absorption spectrometry (AAS), neutron activation analysis (NAA) and inductively coupled plasma emission spectrometry (ICP-ES). The analytical data of XRFS are in agreement with the results obtained by AAS-ICP-ES and NAA. In most cases the precision is within ±2% and accuracy is ±4%. The precision and accuracy for S, P, Ni and Hf are poor at low concentrations. Practical low detection limit of about 40 g/g of Hf in zirconium matrix has been achieved. It is established that precise and accurate determination of Ti and Mo in special alloys is possible using XRFS.     

Spectrophotometric determination of microamounts of thorium with disodium salt of 2-(2-hydroxy-3,6-disulfo-1-naphthylazo)-benzenearsonic acid (Thorin) as a chromogenic reagent

A sensitive spectrophotometric method has been developed for the determination of microamounts of thorium using 0.05% thorin in a 3M perchloric acid solution as a chromogenic reagent and measuring the absorbance at 544 nm. The complex of thorium thus formed, is stable for more than two months with a constant absorbance of ±0.55%. Beer's law is obeyed from 0 to 25 g g^–1 of thorium in a solution with a molar absorptivity (544 nm) = 1.69×10⁴ M^–1 cm^–1 at 26±1 °C. Among the anions tested, only phosphate, acetate and cyanide at >200-fold excess of thorium interfere in the determination, whereas cations like Zn(II), Al(III), Na(I), Mg(II), and Ca(II) do not effect the absorbance. Thorium can be determined in the presence of oxalate, nitrate, tartrate, sulfate, thiosulfate, citrate, and ascorbate. The accuracy of the method has been checked by measuring the known concentration of thorium in the range of 100 g-5 mg g^–1 and found to be in the range of 7.7–0.9%. The method has been applied successfully to determine thorium at g g^–1 level in local ore samples with a precision of ±0.3%. The sensitivity of the method on Sandell's scale is 0.082±0.002 g g^–1 cm^–1.     

Optical and gamma irradiation studies of morin in ethanol

Spectral studies of morin in aqueous ethanol and other alcohols have been carried out as a function of its concentration and that of ethanol, and the pH of aqueous buffer. The effect of gamma radiations on morin solution in ethanol was also studied as a function of dose in the range of 0.15–2.28 kGy and of morin concentration (10^–5–10^–4 mole·dm^–3). Morin concentration in ethanol solution showed a linear response for G values to a dose of 1.83 kGy. Molar absorption coefficients () for morin in ethanol have been estimated to be _260nm=2.28·10⁴ dm³·mol^–1·cm^–1 and _291nm=8.22·10³ dm³·mol^–1·cm^–1 for unirradiated and _{291 nm}=1.75·10⁴ dm³·mol^–1·cm^–1 for irradiated solutions to a dose of 1.83 kGy.     

Adsorption studies of cerium on lead dioxide from aqueous solutions

The adsorption of cerium from aqueous solutions on lead dioxide has been investigated and optimized as a function of pH, equilibration time, sorbate and sorbent concentrations. The effect of other anions and cations on its adsorption has also been studied. Citrate, EDTA, tartrate, oxalate, U(VI), Th(IV), Pb(II), Cr(III) and Al(III) drastically reduce the adsorption. Adsorption of other metal ions on the same oxide has been measured under identical conditions. The distribution coefficient indicates that cerium can be separated from Fe(III), Tc(VII), In(III), Ag(I), Hg(II) and Ta(V). The data fitted very well to Freundlich as well as Dubinin-Raduskevich (D-R) isotherms. A mean free energy of sorption 11.62±0.2 kJ·mol^–1 was calculated, using the D-R equation and corresponds to an ion exchange reaction.     

A simple model for a two-stage chemical reaction with diffusion

We analyse the evolution of a two-stage chemical reaction betweentwo neighbouring plumes of reactants. Under the assumption thatthe plumes are approximately Gaussian we derive a system ofordinary differential equations for the total amount, the centroidand the variance of each reactant. We compare the solution ofthese equations with full numerical simulation of the reaction.Excellent agreement is obtained, with solution of the near-Gaussianmodel requiring considerably less computational effort thanthe full simulations. Of key importance is the yield of thereaction, and we discuss this feature in particular.     

Adsorption of cadmium from aqueous solutions on manganese dioxide

Journal of Radioanalytical and Nuclear Chemistry - The adsorption of cadmium on manganese dioxide has been investigated from different media in relation to shaking time, pH, composition and...     

Gas-phase deprotonation of arylalkylamines. A collision-induced dissociation study

The collision-induced dissociation (CID) of deprotonated arylalkylamines of general formula R(1)C(6)H(4)CHR(2)CH(2)NR(3)(2) (where R(1) = H, OH, F or NO(2); R(2) = H or OH; R(3) = H or CH(3)) generated by negative chemical ionization with H(2)O and D(2)O as ionizing reagents, is discussed. The negative chemical ionization mass spectra show that, in the absence of a hydroxy group in the aromatic ring, deprotonation takes place at the benzylic position whereas the proton is lost from the OH group when present. The nitro compound forms only M(-.) ions. The CID spectra of the deprotonated molecules show that fragmentations are strongly dependent on the structural features of the molecules, namely the presence or absence of substituents in the aromatic ring or aliphatic chain. Copyright 1999 John Wiley & Sons, Ltd.