Presence Of Impurity Ions Research Articles

Measurement of the Metastable Zone Width of Phosphoric Acid Hemihydrate in the Presence of Impurity Ions

The effect of five different impurities, the cations Al3+, Fe2+, and Mg2+ and the anions SO42- and Cl-, on the metastable zone width of phosphoric acid hemihydrate has been investigated using a laser method with a linear cooling rate. The metastable zone width was measured as a function of impurity concentration and cooling rate in the seeded system. The influences of impurity ions on the metastable zone width of phosphoric acid hemihydrate take place by different mechanisms. Mg2+ has enlargement effects on the metastable zone width, whereas Al3+ and Fe2+ have both enlargement or suppression effects under different impurity concentrations. Cl- and SO42- have relative weak effects on the metastable zone width.

Time dependent changes in zeta potential of freshly precipitated calcium carbonate

Abstract We were interested in monitoring zeta potential of CaCO3 freshly precipitated from Na2CO3 and CaCl2 solutions at 30 °C and in pH changes of the slurry. This seemed interesting to us in aspect of hard scale formation. The influence of impurity ions and magnetic field (MF) on the parameters were also investigated. Before calcium carbonate precipitation the solutions were exposed to a permanent N–S (B=0.4 T) MF applied orthogonally to silicone tubes in which the solutions circulated for 30 min. Then, after CaCO3 precipitation time dependent changes of zeta potential and pH were measured. The same parameters were also determined for the reference systems in which the solutions were not MF-treated. Besides the zeta potentials of CaCO3 precipitated from equimolar (8×10−3 M) Ca2+/CO32−, also these precipitated from excess 1.2×10−2 M of Ca2+ and 8×10−3 M CO32−, or reverse, were measured up to 60 min (in some systems up to 240 min). Simultaneously pH of the suspensions was recorded. It was found that MF effect on the zeta potential depended on the Ca2+/CO32− ratio and the “memory effect” lasted for a longer time if calcium carbonate was precipitated at the excess of Ca2+ or CO32− ions. The experiments of CaCO3 precipitation in the presence of impurity ions: Mg2+, Fe2+, or SO42−, which are very common in natural deposit of the scale showed that both the ions and MF affect all the investigated parameters. In these systems precipitation and sedimentation rates were determined by measuring the light absorbance at λ=543.3 nm. The effects depended on the kind of the impurity ion present.

Highly Ordered Nanoporous Alumina Films: Effect of Pore Size and Uniformity on Sensing Performance

The effect of pore size and uniformity on the humidity response of nanoporous alumina, formed on aluminum thick films through an anodization process, is reported. Pore sizes examined range from approximately 13 to 45 nm, with a pore size standard deviations ranging from 2.6 to 7.8 nm. The response of the material to humidity is a strong function of pore size and operating frequency. At 5 kHz an alumina sensor with an average pore size of 13.6 nm (standard deviation 2.6 nm) exhibits a well-behaved change in impedance magnitude of 103 over 20% to 90% relative humidity. Increasing pore size decreases the humidity range over which the sensors have high sensitivity and shifts the operating range to higher humidity values. Cole–Cole plots of 5 to 13 MHz measured impedance spectra, modeled using equivalent circuits, are used to resolve the effects of water adsorption and ion migration within the adsorbed water layer. The presence of impurity ions within the highly ordered nano-dimensional pores, accumulated during the anodization process, appear highly beneficial for obtaining a substantial variation in measured impedance over a wide range of humidity values.

Molecular Dynamics Simulations of the Growth Inhibiting Effect of Fe2+, Mg2+, Cd2+, and Sr2+ on Calcite Crystal Growth

Molecular dynamics simulations were employed to investigate the initial stages of growth of calcium, magnesium, iron, cadmium, and strontium carbonates at two experimentally observed calcite steps. The calculated energies suggest that in a solution containing all five cations MgCO3, FeCO3, and SrCO3 grow onto the steps in preference to CdCO3 and especially CaCO3. Initial incorporation of all impurity ions is more exothermic at the more open, obtuse step than at the acute step edge (by 44−86 kJ mol-1), although growth next to an existing CaCO3 unit occurs preferentially at the acute step. Growth of full rows of impurity carbonates is highly exothermic for the first row at −25 to −155 kJ mol-1 per MCO3 depending on M (M = Mg, Fe, Cd, Sr), but is much less so for a subsequent row (−5 to −80 kJ mol-1 per MCO3), due to increasing mismatch between the rows of MCO3 at the surface and the underlying calcite lattice, especially for the large strontium ion. Calcite growth, which is a slightly endothermic process in its pure form (on average +1.8 to +35 kJ mol-1 per CaCO3), is severely hindered by the presence of impurity ions at the step edges, when the average enthalpies of the CaCO3 growth process increase to +15 to +75 kJ mol-1 per CaCO3, depending on the type of cation decorating the step. The results of these molecular dynamics simulations therefore suggest that growth of impurity carbonates at the calcite steps is initially an energetically very favorable process, hence competing effectively with growth of pure calcite. Subsequent incorporation of impurities, however, becomes more and more endothermic, until finally the presence of steps decorated with rows of impurities inhibits further crystal growth, in agreement with experimental evidence, which shows for example that the presence of magnesium and iron ions inhibits calcite growth.

Electron irradiation of single crystal thorium dioxide and electron transfer reactions

This first study of electron irradiation (3 MeV) of single crystals of thoria has revealed that the crystals turn blue, as seen with neutron irradiation, but the absorption profiles in the 12 000–17 260 cm−1 (1.49–2.14 eV) region were similar but not identical. Calculations showed that the electrons transferred energy sufficient to displace lattice oxygen atoms, but not thorium atoms. The crystals were the purest currently available and supported the proposal that the fundamental absorption edge occurs close to 47 600 cm−1 (5.9 eV). Theoretically, thoria is colourless and cannot exhibit intervalence bands, but aggregates of impurity ions having more than one oxidation state can produce such bands, and some crystals showed pale amber or grey zones. The most likely impurity involved was lead. The effect of electron irradiation on defect generation after various oxidising and reducing anneals, up to 1000°C, was studied, together with the loss of the blue radiation-induced absorption on isochronal anneals at temperatures up to 400°C. The generated profile could be resolved equally well into three or four Gaussian bands and hence band assignments are not possible. It is concluded that electrons transfer energy to thoria to create defects of shallow energy, and electron transfer involving intervalence bands can occur in the presence of impurity ions.

The Effect of Impurity Cations on the Transport Characteristics of Perfluorosulfonated Ionomer Membranes

Ion and water transport characteristics of perfluorosulfonated ionomer membranes are investigated in the mixed cation form of H/Fe, H/Ni, and H/Cu systems. Nafion membranes, which were equilibrated with HCl/FeCl3, HCl/NiCl2, or HCl/CuCl2 mixed aqueous solutions of various mixing ratios, were prepared as test samples, and equilibrium and transport properties were measured systematically. Membrane cationic composition showed that trivalent cations had more affinity than divalent cations. Also larger valence cations caused less water content in the membrane. The membrane ionic conductivity was markedly influenced by counterions, and H+ mobility uH+ was altered according to the nature of coexisting cations. In the presence of Cu2+, uH+ increased from its inherent value, while in the presence of Fe3+, uH+ decreased to a large extent, Ni2+ bringing about nearly no change in uH+. The ionic transference number of H+ was also influenced by coexisting cations in several ways. Despite the unique influence of impurity cations on the mobility of H+, the mobility of impurity cations was not affected by the presence of H+. The interaction between adjacent cationic species in the membrane ion exchange sites, although plausible in general for multivalence cations, appeared to be not specific due probably to the shielding of the cationic charge by water molecules or by sulfonic acid groups. The water transference coefficient tH2O as measured by streaming potential measurements showed unique changes with membrane ionic composition, and tH2O increased from 2.5 to over 13 by the presence of impurity ions. These impurity ions were found to result in more water molecules dragged than in the case of individual ions, when coexisting with the H+ ion. Overall, it was noted that the water molecules within the influence of impurity cations appeared to play a large role in the H+ movement in the membrane.

Low-temperature spectroscopy of nonequivalent Pr3+ optical centers in a Y2SiO5 crystal

An analysis of the absorption and luminescence spectra of a Y2SiO5:Pr3+ crystal has revealed the existence of two Pr3+ optical centers associated with the presence of impurity ions at nonequivalent cation sites. It is found that energy is transported nonradiatively between the nonequivalent Pr3+ optical centers. and a preliminary analysis of the transport mechanism is carried out.

Ion acoustic double layers in a magnetized plasma in the presence of impurity ions

We present here an analytic solution for small amplitude ion acoustic double layers in a magnetized plasma consisting of mobile impurity ions, hot background electrons and ions. Considering the fluid equations to describe the impurity ions and Boltzmann equation of state for both electrons and ions we derive a linear dispersion relation and investigate the existence of small amplitude double layer solution. We show that double layer solutions can be obtained for both positively and negatively charged impurity ions.

Isotope scaling and ηi mode with impurities in tokamak plasmas

The ion temperature gradient- (ITG) driven instability, or ηi mode, is studied for discharges with hydrogen, deuterium, or tritium in a toroidal magnetic configuration. Impurity effects on the mode and the instability (impurity mode) driven by the presence of impurity ions with negative density gradient are studied. It is found that the maximum growth rate of the ηi mode scales as M−1/2i for pure hydrogenic plasmas, where Mi is the mass number of the working gas ion. With the inclusion of impurity ions, the growth rate of the ηi mode decreases in all three kinds of plasmas, with a hydrogen plasma still having the highest maximum growth rate, tritium the lowest, and deuterium in between. However, the isotope effects are weaker and scale as M−1/2eff with the presence of impurity ions, where the effective mass number, Meff=(1−fz)Mi+fzMz, with Mz and fz= Zn0z/n0e being the mass number and charge concentration of impurity ions, respectively. For the impurity mode, the scaling is similar to that of the ηi mode without impurity ions. The experimental database shows that the plasma energy confinement time scales as τE∝M1/2i for a wide range of clean plasmas. The correlation of the theoretical results with the experimental confinement scaling is discussed.

Octacalcium phosphate as a precursor in biomineral formation.

What are biominerals and how are they formed? It is usually assumed: (i) that the prototype for most apatitic biominerals is hydroxyapatite (OHAp), Ca5(PO4) 3OH; and (ii) that the OHAp structure has been modified by the presence of impurity ions and vacancy defects in specific OHAp lattice sites. The usual answer, at least implicitly, to the second question is that the apatitic mineral is formed directly by the precipitation of ions from the surrounding solution. Our answers are: (i) that apatitic biominerals are formed through a precursor mechanism in which octacalcium phosphate (OCP), Ca8H 2(PO4)6·5H2O, precipitates first and then hydrolyzes ireversibly in situ to a transition product intermediate to OCP and OHAp; and (ii) that this product, "octacalcium phosphate hydrolyzate" (OCPH), may contain (a) OHAp-like and OCP-like domains in varying amounts, (b) vacancy defects and impurity ions in lattice sites in these domains, and (c) various kinds of one-, two-, and three-dimensional defects which are not present in either the OHAp or the OCP lattice, these defects being formed during the in situ hydrolysis step. A calcification model of this type was first proposed in 1957, but full acceptance was delayed because most of the evidence was circumstantial and in vitro in nature. The situation has changed radically because of three unrelated studies that are in vivo in nature but lead to the same conclusion: I. 32P-pyrolysis studies of rat enamel: The results clearly demonstrated that an acidic calcium phosphate precursor was involved. II. Precipitation of calcium phosphates in serum. Ultrafiltered serum was equilibrated with brushite. Subsequent changes in the ionic concentrations revealed that OCP was formed at first and then hydrolyzed to a more basic form, OCPH, but never reached the solubility of OHAp. III. Physicochemical properties of cardiovascular biominerals: We recently characterized biominerals in cardiovascular deposits in an encompassing variety of ways. As an overall conclusion, OCPH was the prototype most compatible with the data [including indices of refraction, solubility, P2O74- formation on pyrolysis, thermogravimetric analysis (TGA) measurements, presence of water, and incorporation of CO32-, Na+, and Mg2+]. This calcification model has important consequences relative to all kinds of calcification and decalcification processes, including those of enamel.

Eliminierung und Rückgewinnung von Metallionen aus Abwässern — eine Übersicht

AbstractThe present state and the trends of the recovery of heavy metals from wastewaters are presented. The classical precipitation techniques are insatisfactory due to increases of solubility in the presence of impurity ions and/or complexing agents. At present, ion‐exchange processes constitute the most frequently used method of metal recycling with an effective enrichment of metal ions. For the effective separation of metals from solutions of a low concentration the electrolytic reduction demands large electrode surface areas. In cells with fixed‐bed or fluidized cathodes one can obtain specific electrode surface areas of some 103 m2/mm3. For the future, processes of extraction and especially membrane separation will gain in importance. In the past few years, a large number of highly selective metal extracting agents as well as the liquid membrane permeation with suitable carriers were developed. Combinations of membrane separation processes with chemical reactions may attain the same importance, as e.g. ultrafiltration in connection with the fixation of metal ions to watersoluble polymers. In the long run, especially techniques will prevail which will not only result in metal enrichment but also in the recovery of the raw material water.

Thermal current transients in polyethylene

A thermal current transient technique, using a step input of radiations, has been employed in this work to study the nature of induced polarization in untreated and hexanetreated (commercial) low-density polyethylene film as a function of charging fields. The results show that for charging fields smaller than 4.0 × 10 7 V m −1 the current transients may arise from a presence of impurity ions, and at fields greater than 4.0 × 10 7 V m −1 injected space charge becomes the dominant contributor.

A phase transition in doped I. Heat capacity measurement

Abstract Heat capacities of U 4 O 9−y doped with Th4+and Nb5+ions as impurities were measured in the temperature range from 200 to 505 K by means of adiabatic calorimetry and the effect of doping on the phase transition of U 4 O 9−y was investigated. The transition temperature, enthalpy change and entropy change for samples U0.99Th.0.1O2.252 U0.99Th0.01O2.232, U0.99Nb0.01O2.250 and U0.99Nb0.01O2.231 were 343, 347, 344 and 348 K; 628, 748, 673 and 767 Jmol−1; and 1.92, 2.32, 204 and 2.35 Jmol−1K−1, respectively. The λ-typepeak in the heat capacity curve becomes broadened on doping, resulting from U4+ and U5+sites being disordered by the presence of impurity ions. The enthalpy change during the transition is proportional to the transition temperature for both doped and undoped samples, but at the same enthalpy change the transition temperature of doped samples is higher than that of undoped samples. The entropy changes during the transition are interpreted in terms of the average valence of the uranium.

Calculation of the diffusion of light impurities in tokamaks

Using numerical methods, the authors investigate plasma diffusion in tokamaks when impurity ions of light elements are present. The model considered makes use of neoclassical expressions for diffusion fluxes and takes ionization and recombination processes into account. The question of the boundary conditions for the initial system of equations is discussed. The new boundary conditions for the proton and impurity ion densities are zero partial ion-ion fluxes at the boundary of the plasma column. The computational results show that the presence of impurity ions in the plasma column of a tokamak – even in relatively small amounts – strongly influences the spatial distribution of the protons. The entire diffusion process can be broken down into a number of stages which differ one from the other with regard to the amount of impurities in the system. If the proportion of impurities ξim does not exceed 0.01 of the electron density, the highly ionized ions collect at the centre of the plasma. If ξim > 0.01, the proton profile becomes flat within a short time and the impurities become more evenly distributed over the plasma cross-section.

Effects of Ultraviolet Irradiation on KBr: Gd

AbstractThe results of UV irradiation on Gd3+ doped KBr single crystals were investigated. Thermoluminescence (TL) glow curves, excitation spectra, and optical absorption were measured in comparison with pure and Sr2+ doped KBr crystals. The concentration of anion vacancies was found to be markedly enhanced by the presence of impurity ions. TL excitation spectra of Gd3+ doped samples had maxima at the α band and at the 212 nm band, which is attributed to a localized exciton state perturbed by a Gd3+ ion. Results suggest that defects responsible for the TL are created by an excitonic process.

Effect of impurities on trapped particle modes

The nature of the trapped particle modes in a toroidal geometry has been investigated in the presence of impurity ions using a model magnetic field configuration. The various trapped ion and electron modes have been studied and the condition for their stabilization derived. Existence of some new modes with impurities in the ’’banana’’ regime has been shown.

Effect of impurities on dissipative trapped ion modes

The stability of dissipative trapped ion modes in the presence of impurity ions is investigated and compared with previous theories of these modes in pure plasma. The impurities are assumed to be either in the plateau or Pfirsch–Schluter regime as is typical of either present day or the next generation of toroidal plasmas. The important effects of the impurities are found to be different depending on whether the parallel wave phase velocity is above or below the impurity thermal velocity. However, it can, in general, be stated that when the impurity density gradients are in the same direction as the electron and hydrogen ion density gradients, the impurity ions exert stabilizing effects on the modes. The critical density for stabilization of the modes is found to be significantly reduced, even at rather small impurity concentrations. On the other hand, cases of inverse impurity gradients are likely to be unstable. Numerical applications of the theory to nominal parameters of the PLT tokamak are given.

Dielectric and electrooptic properties of ADP crystals doped with chromate ions

The presence of impurity ions in ADP crystals grown in aquous solutions containing 5–10% (NH 4) 2 Cr 2O 7 causes a decrease of the dielectric constant ϵ 11 and ϵ 33 and an asymmetry of the electrooptical coefficient r 63. This assymmetry is equivalent to an effective small rotation of the axis.

Self-Diffusion of Sodium in Sodium Chloride and Sodium Bromide

The self-diffusion coefficient of sodium in sodium chloride and sodium bromide has been measured as a function of temperature. A comparison of the self-diffusion coefficient with the electrolytic conductivity reveals that the Einstein relation is satisfied at high but not at low temperatures. The temperature dependence of the diffusion coefficient may be explained by the Schottky-Wagner vacancy theory if the presence of impurity ions is taken into account. A possible explanation for the failure of the Einstein relation in terms of association between multivalent foreign ions and vacancies is suggested.