Lead Impurities Research Articles

An XPS investigation of the surface of natural sphalerites under flotation-related conditions

The surface composition of two natural sphalerites of different iron and lead content has been determined under flotation-related conditions by X-ray photoelectron spectroscopy (XPS). Oxidation of the mineral samples in air-saturated alkaline solutions has been found to be very slow. In the presence of copper (II) species in solution, copper exchanges with zinc, and metal-deficient environments are formed in the sulfide lattice at the surface. Cyanide removes the copper and some sulfur from the surface, but a metal-deficient sulfide layer remains. Treatment of sphalerite with cyanide can also result in lead impurity in the mineral migrating to the surface to form lead cyanide and hydrated lead oxide. Zinc-oxygen species were detected at the surface of sphalerite that had been immersed in alkaline zinc solutions and washed with dilute sodium hydroxide before examination. Copper was found to diffuse to the surface when sulfur was deposited on sphalerite by air oxidation of hydrosulfide ions. The resulting surface was a metal-deficient sulfide rather than an overlayer of elemental sulfur.

The effect of lead impurity on amorphous Si thin film transistors

The effect of lead impurity on amorphous Si thin film transistors

Lead corrosion behaviour in simulated media of an underground repository

A study on the corrosion resistance of lead in simulated natural media of an underground repository of high-level radioactive wastes was made. Potentiostatic polarization tests and weight-loss measurements were carried out between 293 K and 353 K. The media studied were: groundwater, bentonite suspensions (10 wt%) as well as sodium chloride, acetate and nitrate solutions, extending over a broad range of concentrations. The increase in temperature led to an increase in corrosion, being particularly noticeable in media yielding soluble lead salts. The lowest corrosion rate was found in natural groundwater (NG) at 348 K, even under the most aggressive conditions (348 K and saturation with oxygen). The increase of lead impurities content also increases the corrosion rate by a factor of six, compared with that a pure lead (99.999%). In the case of bentonite suspensions the corrosion rates at 348 K were very low.

合成無機吸着剤によるめっき浴中の微量不純物の除去 Ｉ シリカ‐チタニア吸着剤によるめっき浴中の鉛（ＩＩ）と亜鉛（ＩＩ）の相互分離

Lead (II) impurity in zinc or zinc-alloy plating baths has an adverse effect on the finish. To remove this lead (II) we attempted the separation of lead (II) and zinc (II) coexisting in aqueous solutions using silica-titania gel, which is known to be porous and stable at high temperatures.It was first found that in a solution containing 10mg dm-3 of both lead (II) and zinc (II) equimolar silica-titania gel solely adsorbed lead (II) at pH 2.4 and it was therefore realized that the separation of both metals dissolved in solutions was possible at this pH range by means of gel adsorption. At the zinc concentrations up to 104mg dm-3, lead removal efficiency was high. The relationship between the equilibrium concentration in solution and the amount of metal adsorbed obeyed the Freundrich adsorption isotherm. The optimum composition of silica-titania gel here was 3:1. The silica-titania gel may be reused repeatedly with elution of the adsorbed lead (II) using 1M nitric acid, followed by surface treatment with 1M sodium nitrate solution.

Kinetic Segregation of Lead Impurities in Garnet LPE Films

The incorporation of solvent lead ions in LPE grown garnet layers is investigated by means of film misfit measurements and EPMA in dependence on growth conditions. It is shown that the lead incorporation is essentially due to kinetical effects rather than the consequence of thermodynamic equilibrium. In particular, the lead content increases rapidly with the growth rate according to a linear function. The temperature dependence of the ascent of this function can be described by an Arrhenius law. It is shown that trapping models being in common use fail in explaining the results whereas a reasonable description can be achieved within the frame of an alternative trapping theory based on the SOS-lattice model. Der Einbau von Bleiionen des Losungsmittels in LPE-Granatschichten wird in Abhangigkeit von den Wachstumsbedingungen mit Hilfe von Misfitmessungen und EPMA untersucht. Es wird gezeigt, das der Bleieinbau im wesentlichen durch kinetische Effekte verursacht wird. Insbesondere steigt der Bleigehalt linear mit der Wachstumsrate an. Die Temperaturabhangigkeit dieses Anstieges kann mit einem Arrheniusgesetz beschrieben werden. Es wird gefunden, das die ublich verwendeten Trappingmodelle die Ergebnisse nicht erklaren konnen. Eine vernunftige Beschreibung der Resultate ist dagegen mit einer alternativen Trappingtheorie moglich, welche auf dem SOS-Gittermodell basiert.

Effect of lead impurities on the hot tensile properties of 3004 aluminium castings

Effet d'une addition de plomb (0 a 0,38%) sur la ductilite a chaud et par consequent sur la fissuration durant le laminage de l'alliage Al-1% Mn-1% Mg. On montre qu'une teneur de 2% en plomb decroit de facon significative la ductilite

Fast metal impurity diffusion in metals and the Miedema model

The Miedema-Niessen model for the volume effects which occur when two transition metals are alloyed is applied to the fast diffusion of metallic impurities in metals. The use of the model is also extended to other metallic systems. A correlation is found between fast diffusivities and the volumes corrected using this model. A similar correlation is found for the activation volumes for the diffusion of impurities in lead. The difference in the diffusion behaviour of gold and silver, which have equal uncorrected volumes, can be explained. It can be understood why gold is a fast diffuser in lead, praseodymium, thallium, indium and zinc, but not in γ-U although other impurities are fast diffusers in this metal. Predictions are made for other fast-diffusing systems.

Effect of thermocyclic treatment on the properties of precipitation-hardening austenitic steel containing lead

1. The mechanical properties of precipitation-hardening austenitic steel 37Kh12N8G8MFB after thermal cycling depend on the amount of the lead impurity. 2. The sharp reduction in the mechanical properties of the steel with a high lead content (0.003%) after TCT is due to the formation and development (due to the Rebinder effect) of intergranular microcracks of the thermal fatigue type. 3. The relationship between the TCT temperature and the susceptibility of the steel with a high lead content and carbide hardening is ambiguous; the susceptibility depends on the thermal stresses that occur during thermal cycling and the decomposition of the super-saturated solid solution.

Atomic-absorption determination of lead impurities in nonferrous metals and their alloys using a furnace-flame atomizer

Atomic-absorption determination of lead impurities in nonferrous metals and their alloys using a furnace-flame atomizer

Photoconductive response of lead-doped silver bromide to sub-bandgap light

To increase understanding of the effects of doping silver bromide with divalent lead ions, both the photoconductive response and the photoelectron kinetics of doped binderless powder precipitates were studied as a function of exciting wavelength. Excitation wavelengths both above and below the pure silver bromide bandgap energy were included. Lead doping enhanced the microwave photoconductivity signal and extended the photoresponse to photon energies well below the AgBr bandgap energy. Analysis of the photoelectron kinetics suggests that a sequential two-photon absorption process involving a lead(II) impurity level deep in the AgBr gap provides the mechanism for the extended wavelength response.

Raman spectra of NaCl:Pb crystals

Single crystals of NaCl doped with divalent lead impurities were studied by Raman spectroscopy. Evidence was found to suggest that the lead impurities precipitate as a separate phase of the type described by Suzuki (1961) for NaCl crystals containing cadmium.

Toxic effects of lead impurities found in aluminum factories.

A study of workers exposed to low levels of lead as impurities in aluminum (as low as 0.07%) shows a statistically significant difference in blood and urine lead levels as compared with a control group. In addition, alterations in precursors of heme were demonstrated as reflected in elevated levels of urinary delta-aminolevulinic acid and erythrocyte protoporphyrin IX. This study has implications for workers who are exposed to metals with low concentrations of lead (less than 1%) since this exposure tends to go unnoticed both by the workers, even when symptoms are present, and by physicians who ignore or discard signs of lead intoxication because they relate the occupational exposure of the workers to other metals, not directly to lead.

Novel Measurement of Hyperfine Interactions in Solids:Pb+3207in YPO4and LuPO4

Stable trivalent lead impurities have been observed at room temperature in "flux-grown" single crystals of YP${\mathrm{O}}_{4}$ and LuP${\mathrm{O}}_{4}$ by electron paramagnetic resonance. Because of a fortuitous set of circumstances, a unique measurement of the hyperfine constant of $^{207}\mathrm{Pb}^{3+}$ in these materials was possible. The resulting values are the largest ever observed for the trivalent lead ion in a solid. A super hyperfine interaction with $^{31}\mathrm{P}$ neighbors has also been measured and, surprisingly, this interaction is larger for the second $^{31}\mathrm{P}$ neighbors than for the first $^{31}\mathrm{P}$ neighbors.

Activation volume for self-diffusion and for the diffusion of impurities in lead

A recently derived representation of the Gibbs free energy of a defect process in terms of the thermoelastic properties of the host crystal is shown to be applicable to the calculation of the activation volume for the diffusion of impurities in solids. The experimental data for the diffusion of several metals (Ag, Au, Cu, Hg, Zn, Sn, Tl, Ni, Pd) in lead and the self-diffusion are discussed showing a fair agreement with the theoretically determined activation volumina.

Cathode ray polarography and differential pulse polarography of the catalytic molybdenum(VI) wave

The optimum conditions of electrolyte composition and pH were studied for the cathode ray polarography (c.r.p.) of the catalytic molybdenum(VI) wave; 1–2 M potassium nitrate at pH 1.6–2.2 is optimum, the detection limit is 3 × 10 -9 M (0.3 ppb) molybdenum(VI). Equal molar concentrations of foreign electroactive substances do not interfere at the potential of the molybdenum wave and 500-fold amounts of these can be tolerated if their c.r.p. peaks are separated from the molybdenum wave by 0.1 or 0.2 V. Similar conditions were used for the differential pulse polarography of the catalytic wave. The detection limit is 2 × 10 -8 M (2 ppb). being limited in part by lead impurities which contribute to the background.

Impurity distribution in AgBr

The spatial distribution of lead impurity ions in AgBr single crystals has been determined with ion scattering spectroscopy. AgBr crystals containing three different concentrations of lead and with two surface orientations have been examined. The experimental results are found to be consistent with the impurity distribution curves predicted by the ionic space charge model but alternative models should also be considered.

Optical studies of colour centres formed in KCl by electron-hole recombination

Experiments have been carried out to determine whether the recombination of electrons with highly oriented Vk centres creates oriented H centres, in the same way as orientation is maintained during the photolysis of U2 centres. The work has confirmed optically that H-like centres are formed by electron-Vk recombination in KCl, but no polarization in the H band can be detected even when the starting Vk centres are highly oriented. This implies that if H centres do separate from F centres via correlated (110) collision sequences the direction of the sequence is not maintained to its end. It has also been found that the lead impurities significantly enhance the production of H-like centres.

Monitoring of impurities in molten lead by e.m.f. measurements. Application to the Harris process of lead refining

E.m.f. measurements on the cell Pt, Fe, M(Pb)¦NaOH¦Cu2O, Cu, Pt (M=As, Sn, Sb) at 450°C have shown the feasibility of using this system for direct monitoring of the impurity content of molten lead during the Harris process of lead refining. The reference electrode/electrolyte system described can be used to achieve the selective separation of antimony from the other impurities, arsenic and tin. Besides laboratory experiments, some tests of the system on an industrial scale are described.

Rotation Effects on the Isothermal Growth of (Eu,Y)8(Fe,Ga)5O12Magnetic Bubble Films by Liquid Phase Epitaxy

An isothermal liquid phase epitaxy dipping technique for the growth of garnet films from PbO-B2O2-Fe2O3 fluxed melts was studied. Films were grown on Gd3Ga5O12 substrates which were rotated axially while being held in a horizontal plane. To a first approximation, the film growth rate varies with the square root of rotation rate (r), as predicted by diffusion boundary-layer theory. This rotation effect is modified by the interfacial reaction which involves the integration of garnet constituent units into the growth surface of the film. By holding all growth parameters constant except for changing r from 36 to 169 rpm, the film composition and magnetic properties can be changed. Lead impurity content, lattice mismatch, magnetic anisotropy, and saturation magnetization increase with increasing rotation up to a limiting r >121 rpm. Thereafter, these properties decrease with increasing r, presumably as a result of a growth interface instability.

ESR Analysis ofPb3+Ions inY3Ga5O12

Trivalent lead impurity ions $5{d}^{10}6{s}^{1}$ have been detected by electron-spin resonance (ESR) to occur in diamagnetic garnet crystals of ${\mathrm{Y}}_{3}$${\mathrm{Ga}}_{5}$${\mathrm{O}}_{12}$ which were grown from a PbO-Pb${\mathrm{F}}_{2}$ based flux. From the observed weak anisotropy of the ${\mathrm{Pb}}^{207}$ hyperfine interaction, it could be positively established that the ${\mathrm{Pb}}^{3+}$ ions occupy the dodecahedral sites in the garnet lattice. Trivalent lead impurity ions were also found to occur in the other diamagnetic garnet hosts, ${\mathrm{Y}}_{3}$${\mathrm{Al}}_{5}$${\mathrm{O}}_{12}$, ${\mathrm{Lu}}_{3}$${\mathrm{Ga}}_{5}$${\mathrm{O}}_{12}$, and ${\mathrm{Lu}}_{3}$${\mathrm{Al}}_{5}$${\mathrm{O}}_{12}$.