High Field Stabilization Research Articles

Mixed Zn–Ni spinel ferrites: Structure, magnetic hyperthermia and photocatalytic properties

Synthesis of high quality, narrow size distributed superparamagnetic nanoparticles with high saturation magnetization is imperative for biomedical and environmental remediation applications. This study reports the synthesis of narrow size distributed, small diameter, high-quality Zn1-xNixFe2O4 (x = 0.1, 0.3 and 0.5) nanoparticles with increased saturation mass magnetization for localized superparamagnetic hyperthermia and photocatalysis applications. Narrow size distributed samples with around 10 nm average diameter were synthesized, in the presence of surfactant, by solvothermal reflux method. All the samples show good colloidal stability through electrostatic stabilization with zeta potentials around - 60 mV. The heating capacity or specific heat generation rate (SHR) of synthesized superparamagnetic nanoparticles was determined through the calorimetric method. The x = 0.1, 0.3 and 0.5 samples show SHR = 372, 399 and 410 W g−1 of nanoparticles, respectively, under 35.28 kA/m and 316 kHz field parameters. These SHR values are higher than that of samples synthesized by other methods. Similarly, saturation mass magnetization value increases with Ni2+ concentration in the sample. The enhancement was attributed to preferential octahedral ligand sites occupation by Ni2+ ions in spinel lattice due to high crystal field stabilization energy. Photocatalytic activity of all nanoparticles was studied by methylene blue (MB) dye degradation under visible light. The data shows that degradation efficiency increases with Ni2+ concentration in the sample. All samples were characterized through X-ray powder diffraction (XRPD) profile, transmission electron microscopy (TEM), Fourier transformed infrared spectra (FT-IR), zeta potential distribution curve, thermogravimetric analysis (TGA) curve, vibrating sample magnetometer (VSM), transient temperature curves, and UV–visible–NIR photo-absorption spectra.

On the deposition of Cr 3−δO 4 spinel particles upon laser-heated pedestal growth of Cr:YAG fiber

The microstructures of Cr 4+:YAG crystal fibers grown along [1 1 1] direction by laser-heated pedestal growth method were studied by optical and analytical electron microscopy. Curved growth ledges were found on the round side surface of the fiber grown at a relatively high speed. In contrast, nonepitaxial Cr 3− δ O 4 crystallites with spinel-type structure were formed on the {1 1 2} side surfaces, via an intermediate surface melt, when the fibers were grown at a lower speed. The deposition of Cr 3− δ O 4, rather than segregation of Cr and Ca codopants, as of concern to the Cr 4+ fluorescence, can be rationalized by a high crystal field stabilization of octahedrally coordinated Cr 3+ attained in rather refractory and close packed oxide.

Effect of pressure on liquid‐liquid miscibility gaps: A case study of the systems CaO‐SiO2, MgO‐SiO2, and CaMgSi2O6‐SiO2

In order to investigate the effects of liquid‐liquid phase separation on the igneous evolution of planetary bodies, we investigated immiscibility in the systems CaO‐SiO2, MgO‐SiO2, and CaMgSi2O6‐SiO2 at pressures to 1.5 GPa. Few changes are observed in the size of the miscibility gaps in these systems at 1.0 GPa. The decrease of the stable area of the gaps is mainly due to the increase of the monotectic temperature because the latter closely follows the melting temperature of SiO2 at high pressure. The pressure at which the whole CaO‐MgO‐SiO2 miscibility gap becomes metastable is estimated to be 1.81 GPa. The thermal and compositional extents of miscibility gaps associated with network‐modifier cations (such as Ca2+) do not change significantly with increasing pressure, but the extents are increased for amphoteric cations (such as Mg2+), and the change is more pronounced if the latter have small ionic radii and high ionic potentials. Cations possessing high crystal field stabilization energies produce the largest immiscibility fields at atmospheric pressure, and the passage from the high‐spin to the low‐spin state with increasing pressure is expected to yield even larger miscibility gaps. Magmas containing substantial amounts of amphoteric cations and cations with high crystal field stabilization energies are therefore potential candidates to develop immiscibility at high pressures.

Control and data acquisition systems for high field superconducting wigglers

This paper describes the control and DAQ system of superconducting wigglers with magnetic field range up to 10.3 T. The first version of the system controls a 7 T superconducting wiggler prepared for installation at Bessy-II (Germany). The second one controls a 10 T wiggler which is under testing now at the SPring-8 site (Japan). Both systems are based on VME apparatus. The set of specialized VME modules is elaborated to arrange wiggler power supply control, full time wiggler monitoring, and magnetic field high accuracy measurement and field stabilization. The software for the control of the wigglers is written in C language for VxWorks operation system for a Motorola-162 VME controller. The task initialization, stops and acquisition of the data can be done from the nearest personal computer (FTP host for VME), or from the remote system as well.

"Scarring" and suppression of ionization in very intense radiation fields.

The interaction of a model atom with very intense radiation fields is well approximated by a map that describes a free particle being kicked periodically by a double-well potential. Both the classical and quantum versions of the map are studied and are shown to provide a compact description of high-field stabilization in this strongly perturbed quantum system. In particular, we find that the ``stabilized'' wave function results from the excitation of a superposition of eigenstates of the periodic, time-evolution operator that are localized near classically unstable and weakly stable orbits. These ``scarred'' wave functions correspond to localized wave packets that oscillate back and forth in the strong external field while in the neighborhood of the attractive Coulomb field. The periodic bremsstrahlung, emitted as this wave packet passes the nucleus, provides a distinct experimental signature of the stabilized state.

Concentration and form of dissolved sulfide in the oxic water column of the ocean

During May through July 1987, we analyzed for hydrogen sulfide in the oxic water column of the eastern Mediterranean Sea (May–June) and the northwest Atlantic Ocean (July). Cathodic stripping square wave voltammetry was used to detect and quantify sulfide species. This is a direct method requiring no sample preparation. Our measurements show a consistent profile of 2 nM in the Mediterranean Sea, except for increases that occur at the oxygen maximum in the photic zone and above the hypersaline anoxic brine of the Bannock Basin (2.9 mM sulfide maximum). The measurements in the Atlantic Ocean are lower and more variable as a result of different source waters. Sulfide increases are noted near the surface and in cold pool waters along the East Coast of the United States. Experimental manipulation of seawater samples suggests that the sulfide is bound covalently to a metal. The metal (s) is likely to have an electron configuration consistent with inert complexes, which do not dissociate readily to form free sulfide. Free sulfide reacts with iodate and oxygen in seawater. Sulfide in an inert metal complex should not dissociate and react with iodate and oxygen readily. We propose that the kinetic stability of sulfide-metal complexes is the primary control on the distribution and reactivity of sulfide in the oxic water column of the ocean, rather than thermodynamic considerations alone. This kinetic effect results from high ligand field stabilization energies associated with the electron configuration of the metal (e.g. d 3 and d 6 low spin octahedral metal complexes).

Experimental Study of Trace Metal Chemistry in Soft-Water Lakes at Different pH Levels

The biogeochemistry of Hg, Zn, Co, Fe, Mn, Cr, V, Th, Ba, Cs, As, and Se in two soft-water lakes of the Canadian Shield was investigated by means of carrier-free γ-emitting isotopes introduced into limnocorrals in which the pH of the water was varied from 6.8 to 5.1. The residence times of the radionuclides in the water were determined, and the partitioning of the nuclides among different metal-binding agents in the water and sediments was studied with the aid of membrane filtration, dialysis, solvent extractions, and fractionation on Sephadex columns.Metal behaviour varied systematically with metal properties. Metals of high crystal field stabilization energy, high electronegativity, or small ionic radius were most readily scavenged by> 0.45 μm suspended particles and dispersed colloids in the water, disappeared most rapidly from the water column, and were preferentially accumulated by sedimentary binding agents, including organic substances. Which property of a metal had the dominant effect on metal behavior depended on environmental factors, such as the ambient pH and the nature of the binding agents. Thus, Hg was removed fairly rapidly from the water at pH 6.7–6.8 owing to its high electronegativity but was removed more slowly than any other metal at pH 5.1 owing to its large ionic radius.Most metals were strongly chemisorbed or complexed by mud and organic ooze, and only Ba could be redissolved by cation exchange. Therefore, 0.1 N NaOH and 0.1 N or 1 N HCl were more efficient extractants than H2O, 1 N CaCl2, or benzene/methanol, and the metals were largely nonextractable by any of these solvents. The major NaOH-extractable metal-binding agents were the higher molecular weight fractions of a group of organic (probably humic) substances characterized by a UV absorption band at [Formula: see text]. The affinity of metals for the highest molecular weight "humic" (NaOH-extractable) substances increased with electronegativity, being greatest for Hg. Hg and Se were nonextractable by HCl but were the elements most readily extracted by NaOH, implying exceptionally strong covalent bonding by humic matter. The more electropositive metals were more readily extracted by HCl than by NaOH, suggesting weaker, less highly covalent bonding or preferential sorption by acid-soluble hydrated oxides.Acidification of lake water to pH 5.1 interfered with accumulation of Hg and other metals by organic ooze, probably owing in part to interference with the deposition or formation of the complexing agents with the 265 nm absorption band. Acidification also lowered the concentration of NaOH-extractable colloidal phosphate in the ooze but had no effect on NaOH-extractable orthophosphate content.Key words: metals, lakes, chemistry, pH, humic matter, organic matter, phosphorus, radioactive tracers, acidification

Trivalent and divalent chromium ions in spinels

Phase relations in the ternary system MgO-Al 2O 3-Cr 2O 3 were determined at 1700 ± 15°C to delineate the stability field of spinel crystalline solutions. It was found that there is no solubility of Cr 2O 3 in MgCr 2O 4 spinel, and this is attributed to the high octahedral field stabilization energy for Cr 3+ ion. By heating mixtures consisting of MgO and 50–66 mole % Cr 2O 3 in a reducing atmosphere at 1800–2000°C a new spinel-type crystalline solution was obtained having the general formula, (Mg 8− x Cr x 2+) IV Cr 16 3+ VIO 32. Data are presented concerning the synthesis, structure, electronic spectra and magnetic susceptibility of these crystalline solutions.

High frequency field stabilization of a low pressure plasma

This paper discusses the possibility of using a high frequency field to stabilize the boundary of a low temperature plasma located in a corrugated static magnetic field. It is shown that for stabilization to occur the pressure of the high frequency field must be less than the pressure of the plasma.

Transmission of Electronic Effects in Transition Metal Complexes

AN interesting aspect of transition metal chemistry relates to the influence which one ligand partner, in a mixed complex, may exert on another. The importance of electronic effects transmitted through a central metal ion is demonstrated, for example, by the directing influence of certain ligands in substitution reactions1. We report here some preliminary results on the influence of certain anionic ligands on the nature of the metal–pyridine bond in mixed complexes of cobalt (II). Our evidence for transmitted electronic effects in these complexes rests on certain striking differences in the influence of X on the position of equilibrium in the following configurational transformation : in chloroform solution. Py = pyridine and X = Cl−, Br−, I−, OCN−, SCN− or SeCN−. Co(II) complexes are well suited to configurational equilibria investigations of this kind because of the relatively high crystal field stabilization energy expected for the d7 configuration in a tetrahedral field2, and experimentally, because of the separate well-defined visible spectral characteristics of the two stereo -chemical arrangements. Equilibrium constants derived from spectrophotometric measurements were coupled with enthalpies determined calorimetrically and the associated entropy changes calculated. Since chloroform is relatively non-co-ordinating, the derived thermo-dynamic quantities refer, fairly closely, to the actual association reaction as represented in equatior (1).