Hg Vapor Research Articles

Determination of Hg activity in Hg0.8Cd0.2Te liquid and solid solutions by a quasi-closed-space method

A quasi-closed-space method is proposed for accurately measuring the vapor pressure of a volatile component over solid compounds (solutions) and melts containing this component. The method is used to determine the equilibrium Hg vapor pressure pHg over the Hg0.8Cd0.2Te solid solution between 623 and 1268 K within the homogeneity range of HgCdTe and at its boundaries. The results indicate a jump in pHg and a break in its temperature dependence at about 920 K, corresponding to the onset of melting. Above 623 K, the total equilibrium excess of Te in solid homogeneous Hg0.8Cd0.2Te is close to the concentration of charged Hg vacancies, as determined by Hall effect measurements.

X-ray absorption imaging of high-pressure lighting plasmas

X-ray absorption has been used to image the distribution of mercury (Hg) in high-pressure arc lamps used for lighting. Here, several images are presented showing the analytic transformation of raw X-ray data into an image of the Hg vapor density in a cylindrically symmetric arc.

Evaluation of slurry preparation procedures for the determination of mercury by axial view inductively coupled plasma optical emission spectrometry using on-line cold vapor generation

Five different slurry preparation procedures were tested, after grinding the solid samples to a particle size ≤53 μm: (1) using aqua regia plus HF, 30 min of sonication, standing time of 24 h followed by another 30 min of sonication; (2) same as the previous one, except that the standing time and the second ultrasound treatment were omitted; (3) same as the previous one, except that HF was not used; (4) same as the previous one, except that the aqua regia was replaced by nitric acid; (5) same as the previous one, except that the acid nitric was replaced by tetramethylammonium hydroxide (TMAH). The Hg vapor was generated on-line, and the emission signal intensity measured at 253.652 nm by axial view inductively coupled plasma optical emission spectrometry. Initially, four experimental conditions were optimized using a multivariate factorial analysis: the concentrations of HCl and of the reducing agent, NaBH 4, used in the cold vapor generation, and two instrumental parameters, the plasma radiofrequency power and the carrier gas flow rate. The radiofrequency power was statistically significant, but limited to 1.2 kW for practical reasons. The procedures were applied to 11 biological and environmental materials. Both, the slurries and the filtrates were analyzed, using calibration solutions in the same medium as in the slurries. The first three procedures produced results in agreement with the certified values. The two last procedures, using nitric acid or TMHA could not be used for quantitative analysis. For practical reasons, Procedure 3, with a detection limit (3s, n=10) of 0.06 μg g −1 for a sample mass of 20 mg in a final volume of 15 mL is recommended. The relative standard deviations for mercury in the investigated materials, using the recommended procedure, were lower than 12.5%, indicating a good precision for slurry sampling. The recommended procedure is simple, rapid and robust.

Ultra-trace determination of mercury in water by cold-vapor generation isotope dilution mass spectrometry

Determination of total Hg at the ppt level in water using cold vapor generation and inductively coupled plasma mass spectrometry for calibration by isotope dilution (ID) with both sector field (SF-ICP-MS) and time-of-flight MS (ICP-TOF-MS) detection is described. Samples were reduced on-line in a flow injection manifold with SnCl2 to generate Hg vapor for both steady-state and transient sample introduction following gold trapping. No significant difference in final Hg concentrations was detected using either approach. Certified reference material ORMS-3 river water (NRCC, Ottawa, Canada) was used for method validation. Mercury concentrations of 12.75 ± 0.24 and 12.34 ± 0.11 pg g−1 (mean and one standard deviation, n = 4) were obtained using steady-state generation with SF-ICP-MS and ICP-TOF-MS, respectively, in agreement with the certified value of 12.6 ± 1.1 pg g−1 (combined uncertainty, k = 2). Concentrations of 12.55 ± 0.41 and 12.65 ± 0.30 pg g−1 (one standard deviation, n = 4) were obtained following gold trapping and SF-ICP-MS and ICP-TOF-MS detection, respectively. Compared with SF-ICP-MS, a 2-fold enhancement in the precision of the measured 200Hg/201Hg and 202Hg/201Hg ratios in a 100 ppt Hg standard solution was obtained using ICP-TOF-MS. Consequently, improved precisions of 0.87–2.33% RSD in Hg concentrations obtained by steady-state and transient signal acquisition, respectively, in ORMS-3 were obtained using ICP-TOF-MS, compared with 1.88–3.25% RSD obtained with SF-ICP-MS. Method detection limits (LODs, three times standard deviation) of 0.024 and 0.15 pg g−1 for Hg using direct CV and following gold trapping, respectively, were obtained using SF-ICP-MS. These were superior to corresponding LODs of 0.30 and 0.87 pg g−1 obtained using ICP-TOF-MS as a result of its 15-fold lower sensitivity.

Fabrication of Au nanostructures in the process of amalgam formation followed by Au–Hg alloy thermal decomposition

Au films deposited under ultra-high vacuum conditions on air-cleaved mica substrates were exposed in situ to Hg vapor (residual gas pressure ∼1×10−7 Pa, with Hg vapor pressure of 0.24 Pa). This led to transformation of continuous gold film into isolated amalgam islands of nanometer scale. The changes of Au thin film surface topography caused by amalgamation carried out within ∼40 h were studied by the atomic force microscopy method, while the phase transition in the bulk of Hg-dosed Au films was monitored by means of X-ray diffraction. The island's morphology varies from irregular, ramified structures on terraces to compact shapes along the steps on the mica substrate. After thermal decomposition of the amalgam, thin gold films consisting of isolated Au nanostructures on mica can be obtained.

The use of free energy relationships to rationalise structural and solvent effects on the photoreduction of cobalt(III) complexes in aqueous organic solvent medium

Quantum yields for the photoreduction of a series of CoIII complex ions, [CoClen2 (RC6H4NH2)]2+ where R=p-OMe, p-OEt, p-Me, m-Me, H and p-F using a low pressure Hg vapour lamp (254 nm) in aqueous ethanol mixtures (15–40% v/v organic cosolvent), increase with increase in mole fraction of the cosolvent in the binary solvent mixture under investigation. The Hammett correlation is linear, affording negative reaction constants, which indicate that the excited state is electron deficient. Correlation of the quantum yield data with Kamlet–Taft's solvatochromic parameters indicates that the specific solvent–solute interactions play a dominant role in governing the reactivity.

Solid sampling–electrothermal vaporization–inductively coupled plasma mass spectrometry for the direct determination of Hg in different materials using isotope dilution with a gaseous phase for calibration

This paper evaluates the potential of electrothermal vaporization–inductively coupled plasma mass spectrometry (ETV–ICPMS) for the direct determination of Hg in solid samples, using a 200Hg-enriched gaseous phase for calibration based on isotope dilution. Three different samples were studied, BCR CRM 320 River sediment, IAEA-086 Hair and a real (wet) freshwater fish sample (M1). The samples selected show important differences in their matrix composition, and especially the fish sample constitutes a challenge as a result of its high water content (≈80%). The main conclusion of the work is that the calibration approach investigated succesfully corrects for all the matrix effects (suppression) observed during Hg vaporization, allowing accurate values to be obtained in all cases. Moreover, practically the same operating conditions could be used for all sample types. The method finally proposed presents interesting features for the direct determination of this challenging element in solid samples, such as: a low sample consumption (a few milligrams), a high sample throughput (10 min/sample), a low limit of detection (6 ng g −1) and a reduced risk of analyte losses or contamination. Precision values depend on the homogeneity of the sample studied, and are typically in the vicinity of 10% RSD, except for the more inhomogenous river sediment (18% RSD).

Diagnostics of capillary mercury–argon high-frequency electrodeless discharge using line shapes

The profiles of the 253.7 nm spectral line, emitted from the capillary argon–mercury isotope high-frequency electrodeless discharge, are measured by means of a pressure-scanned Fabry–Perot spectrometer. Spectral line profiles are collected from two lamps at the argon pressure of 2 and 10 Torr, in dependence on the discharge current and Hg vapor densities corresponding to the cold spot temperatures of 25–80 °C. By means of a multi-parameter non-linear line profile fitting procedure of multiple overlapping self-reversed Voigt profiles, the temperature of the radiating atoms and the optical density were estimated. The capillary and spherical discharge conditions were compared. The optimal working conditions avoiding self-absorption were obtained. The measurements were completed by means of the Zeeman scanning spectrometer, allowing the getting of additional information about the instrument functions. The necessity to take into account the instrument function also by comparable small values of its width was shown.

Power balance in highly loaded fluorescent lamps

Discrepancies reported in the literature between numerical predictions and experimental measurements in low-pressure Hg discharges at high current densities are considered. Elements of a one-dimensional fluid model and recent spectroscopic and Langmuir probe measurements are combined in a semi-empirical way to individually examine components of the positive column power balance and the discharge conductivity. At a Hg vapour pressure of 0.81 Pa (6.1 mTorr) and a current density of 300 mA cm−2, previous discrepancies in the power balance and discharge conductivity are simultaneously resolved by assuming a higher electron density than that obtained from the Langmuir probe measurements. This conclusion is supported by independent measurements of ion density reported in a companion paper. The importance of radial cataphoresis under these conditions, particularly with regard to radiation transport, is highlighted. This work is of particular interest for the design of fluorescent lamps operating at high current densities.

Regulatory Off-Gas Analysis from the Evaporation of Hanford Simulated Waste Spiked with Organic Compounds

After strontium/transuranics removal by precipitation followed by cesium/technetium removal by ion exchange, the remaining low-activity waste in the Hanford River Protection Project Waste Treatment Plant is to be concentrated by evaporation before being mixed with glass formers and vitrified. To provide a technical basis to permit the waste treatment facility, a relatively organic-rich Hanford Tank 241-AN-107 waste simulant was spiked with 14 target volatile, semi-volatile, and pesticide compounds and evaporated under vacuum in a bench-scale natural circulation evaporator fitted with an industrial stack off-gas sampler at the Savannah River National Laboratory. An evaporator material balance for the target organics was calculated by combining liquid stream mass and analytical data with off-gas emissions estimates obtained using U.S. Environmental Protection Agency (EPA) SW-846 Methods. Volatile and light semi-volatile organic compounds (<220 °C BP, >1 mm Hg vapor pressure) in the waste simulant were found to largely exit through the condenser vent, while heavier semi-volatiles and pesticides generally remain in the evaporator concentrate. An OLI Environmental Simulation Program (licensed by OLI Systems, Inc.) evaporator model successfully predicted operating conditions and the experimental distribution of the fed target organics exiting in the concentrate, condensate, and off-gas streams, with the exception of a few semi-volatile and pesticide compounds. Comparison with Henry's Law predictions suggests the OLI Environmental Simulation Program model is constrained by available literature data.

The characteristics of Hg Vaporization from Zn-Hg Pellet for Fluorescent Lamps

The characteristics of Hg Vaporization from Zn-Hg Pellet for Fluorescent Lamps

Evaluation of sensory evoked potentials in Long Evans rats gestationally exposed to mercury (Hg0) vapor.

Mercury is known to alter neuronal function and has been shown to cross the placental barrier. These experiments were undertaken to examine if gestational exposure to mercury vapor (Hg(0)) would result in alterations in sensory neuronal function in adult offspring. Dams were exposed to 0 or 4 mg/m(3) Hg(0) for 2 h/day from gestational days 6-15. This exposure paradigm has been shown to approximate a maximal tolerated dose of Hg(0) for the dams. Between postnatal days 140-168, male and female offspring (one of each gender/dam) were examined using a battery of sensory evoked potentials. Peripheral nerve action potentials, nerve conduction velocity, somatosensory evoked responses (cortical and cerebellar), brainstem auditory evoked responses, pattern evoked potentials, and flash evoked potentials were quantified. Gestational exposure to 4 mg/m(3) Hg(0) did not significantly alter any of the evoked responses, although there was a suggestion of a decrease in compound nerve action potential (CNAP) amplitudes in male animals for the 3 mA stimulus condition. However, this possible change in CNAP amplitudes was not replicated in a second experiment. All evoked potentials exhibited predictable changes as the stimulus was modified. This shows conclusively that the evoked responses were under stimulus control, and that the study had sufficient statistical power to detect changes of these magnitudes. These results indicate that gestational exposure to 4 mg/m(3) Hg(0) did not result in changes in responses evoked from peripheral nerves, or the somatosensory, auditory, or visual modalities.

Some trends in the development of microplasmas for spectrochemical analysis.

The development of microplasmas for spectrochemical analysis by optical methods is discussed. Recent achievements in miniaturization are highlighted, especially for three types of plasmas, namely high-frequency plasmas, dc-discharges and microwave plasmas. The potentials of each of these groups of plasmas as sources for atomic emission spectrometry are discussed. Literature citations and experiments indicate that the plasmas are also very useful as atom reservoirs for atomic absorption spectrometry. Methods of sampling, including feeding with gas chromatography effluents, the use of electrothermal vaporization, and the evolution of gaseous species (as shown for the case of Hg vapor), are discussed as prominent interfaces to make use of these sources for elemental analysis.

X-ray absorption imaging of Hg vapour in a ceramic metal-halide lamp using synchrotron radiation

The diagnostic technique of x-ray absorption imaging of Hg vapour in high-intensity discharge lamps has been extended. X-ray absorption imaging has been used previously to determine the time-averaged absolute Hg density (Curry J J, Sakai M and Lawler J E 1998 J. Appl. Phys. 84 3066). Now, using an intensified charge-coupled device detector and synchrotron radiation, time-resolved measurements have been made. Although no significant time-dependence was seen as a function of the electrical phase for an electronically ballasted lamp, real-time observations were made of the decaying Hg density during the cool-down period. The cold-spot temperature in a 150 W ceramic lamp containing Hg and rare-earth iodides decreased with a time constant of 48.4 s following arc extinction. The primary limitation to the sensitivity of these measurements has been identified, and methods for overcoming this limitation in future work are proposed. Other aspects of the technique are also discussed.

Superconductivity in high‐quality (Hg 0.9 Re 0.1 )Ba 2 CaCu 2 O 6+ δ HTSC thin films

High-quality epitaxial (Hg0.9Re0.1)Ba2CaCu2O6+δ (HgRe-1212) HTS thin films were successfully prepared using pulsed laser deposition (PLD) of the Re0.1Ba2CaCu2O6+δ precursor and subsequent Hg vapor annealing. The thin films exhibit a sharp superconducting transition at Tc ≈ 120 K. The resistive transitions have been investigated in magnetic fields up to 6 T parallel and perpendicular to the c-axis. We have determined the activation energy of thermally activated flux-motion for both magnetic field orientations. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Solvent and substituent effects on the photoreduction of cobalt(III)-aryl amine complexes in an aquo-organic solvent medium

The photoreduction of a series of CoIII complex ions, [Coen2Cl(RC6H4NH2)]2+ where R = p-OMe, p-OEt, p-Me, m-Me, H, and p-F, has been studied using a low pressure Hg vapour lamp as the light source (254 nm) in an aquo-organic solvent [15–40% (v/v) 2-methylpropan-2-ol] medium. Quantum yields for CoII production by redox decomposition have been determined in all cases. The quantum yield increases considerably with the increase in concentration of the organic co-solvent in the binary solvent mixture under investigation. The Hammett correlation is linear, affording negative reaction constants, which indicate that the excited state is electron deficient. Correlation of the experimental results with Kamlet–Taft's solvatochromic parameters indicates that the solvent hydrogen bond donor acidity plays a dominant role in governing the reactivity.

Foliar exchange of mercury as a function of soil and air mercury concentrations

Previous research has indicated that foliar mercury (Hg) flux is bi-directional, with influence from both atmospheric and soil Hg. This work investigated the role of soil and air Hg concentrations on foliar Hg exchange using a single-plant gas-exchange system. The exchange of Hg vapor with aspen seedlings grown in soil Hg concentrations of 0.03±0.01, 5.8±0.5, and 12.3±1.3 μg g −1 and exposed to atmospheric Hg concentrations of 2.4±0.5, 11.0±0.9, and 30.4±2.2 ng m −3 was measured. At background atmospheric Hg concentrations of 2.4 ng m −3, foliage released Hg at all three soil Hg concentrations and fluxes ranged from 1.6 to 5.5 ng/m 2/h. At higher atmospheric Hg concentrations (>11 ng m −3), net deposition to foliage ranged from −9 to −47 ng/m 2/h, exhibiting increase uptake with higher air Hg concentrations. Fluxes associated with aspen showed an immediate response to changes in atmospheric Hg concentrations. Compensation points, the air concentration where no net flux of Hg vapor occurred, were 3–4 ng m −3 in the light and 2–3 ng m −3 in the dark for trees grown in soils of 0.03 and 6 μg g −1 Hg content, and 5–6 ng m −3 in the light and 2.5–3.5 ng m −3 in the dark for trees grown in 12 μg g −1 Hg soils.

MOCVD of p-CdxHg1 – xTe/GaAs Heteroepitaxial Structures

Metalorganic chemical vapor deposition from Cd and Te alkyl compounds and Hg vapor is used to grow p-type Cd x Hg1 – x Te epitaxial layers on semi-insulating GaAs(111)Bsubstrates by the interdiffused multilayer process (alternating CdTe and HgTe layers) at a substrate temperature of 350°C, followed by postgrowth annealing. Layers are obtained with x = 0.2–0.4, 77-K carrier concentrations in the range (1–5) × 1016 cm–3, and 77-K carrier mobilities from 200 to 400 cm2 /(V s). The rocking curves of the epilayers have a full width at half maximum in the range 2–4 min of arc.

Matrix studies of the thermal and photolytic reactions of Zn, Cd and Hg (M) atoms with H2O: formation and characterisation of the adduct M⋯OH2and photoproduct HMOH

IR spectra have been used to chart the thermal and photolytic reactions occurring during or after the codeposition of Zn, Cd or Hg (M) vapour with an excess of H2O-doped Ar. Following the formation of the contact pair M⋯OH2, detected after deposition of a matrix including thermally evaporated metal atoms, UV irradiation (200 ≤ λ/nm ≤ 400) causes M⋯OH2 to rearrange with insertion of the metal atom into an O–H bond in forming the M(II) hydride HMOH. Characterisation of the molecules has been underpinned by reference (i) to the effects of isotopic change (1,2H) and (ii) to the results of density functional theory (DFT) calculations. The properties of the molecules are compared with those of related species, and the mechanism of the photochemical change is discussed.

High temperature arsenic doping of CdHgTe epitaxial layers

AbstractExperimental results on solid‐state arsenic doping of the n‐type bulk and ISOVPE epitaxial CdXHg1‐XTe (X = 0.19 ÷ 0.3) alloys are presented. The arsenic doped thin epitaxial CdxHg1‐xTe films (nAs ≈ 5 · 1016 ÷ 1 · 1020 cm‐3; d = 2 ÷ 5 μm) obtained by RF sputtering in a mercury glow discharge were used as As diffusion sources. The arsenic diffusion and activation were carried out at temperatures T = 500 ÷ 600 °C under Hg vapour pressure. Immediately after the high temperature treatment all samples were annealed to annihilate point defects. The SIMS analysis was used for determination of the quantitative admixture distribution of As in the diffusion area. The arsenic electrical activity has been evaluated by means of differential Hall, resistivity and thermoemf measurements. The analysis of experimental data obtained as well as their comparison with previously obtained results has been performed. (© 2004 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)