Mercury Discharge Research Articles

Highly reliable silicon carbide photodiodes for visible-blind ultraviolet detector applications

Highly efficient polytype 4H silicon carbide (4H-SiC) p–n diodes for ultraviolet (UV) light detection have been fabricated, characterized, and exposed to high-intensity mercury lamp irradiation (up to 17 mW/cm2). The behavior of the photocurrent response under UV light irradiation using a low-pressure mercury UV-C lamp (4 mW/cm²) and a medium-pressure mercury discharge lamp (17 mW/cm²) has been studied. We report on long-term UV photoaging tests performed for up to 22 mo. Results demonstrate the robustness of SiC photodiodes against UV radiation. The devices under test showed an initial burn-in effect, i.e., the photocurrent response dropped by less than 5% within the first 40 h of artificial UV aging. Such burn-in effect under UV stress was also observed for previously available polytype 6H silicon carbide (6H–SiC) p–n photodetectors. After burn-in, no measurable degradation has been detected, which makes the devices excellent candidates for high irradiance UV detector applications.

The Prohibition of Mercury Discharges from Coal-Fired Power Stations under European Law

Coal-fired power plants emit mercury trough the air and the water pathway into surface water. Often the occurring depositions from the air and air-soil pathway are higher then the direct depositions through the water pathway. The following article explores the question whether these depositions are in line with the Industry Emission Directive and the Water Framework directive. Whilst the IED does not contain emission limits, there are limitations via the phase-out requirement of the WFD and via the environmental quality standards for mercury contamination of biota in the daughter directive on priority hazardous substances. The phase-out requirement demands the cessation of mercury depositions by 23.12.2006. And based on the biota requirements any new deposition of mercury by coal power plants is inadmissible. These requirements do not only apply to the permission of new power plants, but also to existing plants.

Assessment of environmental mercury discharge at a four-year-old artisanal gold mining area on Lombok Island, Indonesia

Indonesian artisanal and small-scale gold mining activities (ASGM) have been described for the islands of Borneo (Kalimantan) and Sulawesi. But the increased gold price over recent years has seen operations extend to the islands of Lombok and Sumbawa. For the current research, an environmental assessment was conducted across three new ASGM locations. Gold is recovered by miners through a two-stage process of whole-ore amalgamation and cyanidation. Waste (tailings) is discharged to land or sea with no concern for contaminants in the tailings. The gold grade of ore is up to 5000 mg kg(-1). The mean gold grade of the amalgamation tailings is 7 mg kg(-1), dropping to 1.2 mg kg(-1) for the cyanidation tailings. The mean mercury concentration of the amalgamation tailings is about 3000 mg kg(-1) and greater than 1600 mg kg(-1) for the cyanidation tailings. Samples of paddy rice grain collected adjacent to cyanidation tailings ponds showed methyl mercury concentrations greater than 100 ng g(-1). This is five times above the Chinese permissible level for total mercury in food crops. The mean total mercury concentration in hair of Lombok ASGM workers was greater than that in a non-exposed population; however there was no difference in methyl mercury concentration. This indicates the primary pathway of mercury exposure is inhalation of volatile mercury in the atmosphere. Future exposure may come from ingestion of methyl mercury contaminated rice where discharge of cyanide tailings to paddies continues. To protect the environment and to enhance the sustainability of ASGM, appropriate tailings management must be implemented. The gold grade of the tailings indicates that the residual value might be recoverable with appropriate technology. Ongoing research is investigating systems such as phytoextraction that might assist ASGM operators in Lombok and Sumbawa to improve their environmental performance.

The Environmentally Responsible Dentist - Dental Amalgam Recycling: Principles, Pathways and Practice

Abstract Dental amalgam waste is a significant contributor of mercury discharges to municipal wastewater treatment facilities, often referred to as publicly-owned treatment works (POTWs). While POT...

Metallothioneins failed to reflect mercury external levels of exposure and bioaccumulation in marine fish – Considerations on tissue and species specific responses

The suitability of metallothioneins (MT) in fish as biomarker of exposure to mercury has been questioned. Therefore, this study aimed at investigating the relationship between external levels of exposure, mercury accumulation and MT content, assessing species and tissue specificities. Two ecologically different fish species –Dicentrarchus labrax and Liza aurata – were surveyed in an estuary historically affected by mercury discharges. Total mercury (T-Hg) and MT content were determined in gills, blood, liver, kidney, muscle and brain. All tissues reflected differences in T-Hg accumulation in both species, although D. labrax accumulated higher levels. Regarding MT, D. labrax revealed a depletion in brain MT content and an incapacity to induce MT synthesis in all the other tissues, whereas L. aurata showed the ability to increase MT in liver and muscle. Tissue-specificities were exhibited in the MT inducing potential and in the susceptibility to MT decrease. L. aurata results presented muscle as the most responsive tissue. None of the investigated tissues displayed significant correlations between T-Hg and MT levels. Overall, the applicability of MT content in fish tissues as biomarker of exposure to mercury was uncertain, reporting limitations in reflecting the metal exposure levels and the subsequent accumulation extent.

Contrast between the vertical and horizontal mercury discharge lamps

This paper discusses the thermal behavior of a high pressure mercury lamp in a horizontal position, compared with that of a vertical lamp. The model adopted is three-dimensional, steady, and powered DC. After the model validation, we analyzed temperature fields and velocities for the case of the lamp in a horizontal position by comparing it with those of a lamp in vertical position. This setting initially fixed the wall temperature equal to 1000 K. However, the morphology of the temperature profile in the case of the horizontal lamp indicates that the temperature of the wall cannot be uniform. Thus, we have, in a second time, performed an energy balance at the wall to calculate its temperature. This aims to understand the influence of convection on the thermal properties of the source.

Photoluminescence spectra of thenardite Na 2SO 4 activated with rare-earth ions, Ce 3+, Sm 3+, Tb 3+, Dy 3+ and Tm 3+

Five Na 2SO 4:RE 3+ phosphors activated with rare-earth (RE) ions (RE 3+=Ce 3+, Sm 3+, Tb 3+, Dy 3+ and Tm 3+) were synthesized by heating natural thenardite Na 2SO 4 from Ai-Ding Salt Lake, Xinjiang, China with small amounts of rare-earth fluorides, CeF 3, SmF 3, TbF 3, DyF 3 and TmF 3, at 920 °C in air. The photoluminescence (PL) and optical excitation spectra of the obtained phosphors were measured at 300 and 10 K. In the PL spectrum of Na 2SO 4:Ce 3+ at 300 K, two overlapping bands with peaks at 335 and 356 nm due to Ce 3+ were first observed. Narrow bands observed in PL and excitation spectra of Na 2SO 4:RE 3+ (RE 3+=Sm 3+, Tb 3+, Dy 3+ and Tm 3+) phosphors were well identified with the electronic transitions within the 4f n ( n=5, 8, 9 and 12) configurations of RE 3+. The existence of excitation bands with high luminescence efficiency at wavelengths shorter than 230 nm is characteristic of Na 2SO 4:RE 3+ (RE 3+=Sm 3+, Tb 3+, Dy 3+ and Tm 3+) phosphors. The obtained results suggest that these phosphors are unfavorable as the phosphor for usual fluorescence tubes, i.e., mercury discharge tubes, but may be favorable as the phosphor for UV-LED fluorescent tubes and as cathodoluminescence, X-ray luminescence and thermoluminescence phosphors.

Experimental and theoretical investigations on the warm-up of a high-pressure mercury discharge lamp

Modern high-pressure discharge lamps are forced to provide instant light and hot relight capabilities—if possible at lower power units. A detailed understanding of the warm-up of high-pressure discharge lamps is therefore required. Complex fluid model codes were developed for the past years including more and more processes like two-dimensional treatment of convection trying to provide a more comprehensive and consistent description of high-pressure discharge lamps. However, there is a lack of experimental data to examine the performance of these models. This work provides a very complete set of geometrical, electrical, spectroscopic, and thermographic data according to the warm-up of a high-pressure mercury discharge lamp that is compared to the results of a state of the art fluid code. Quantitative agreement is achieved for single parameters like wall temperatures. But the paper also reveals the need for further investigations and improvements of the code.

Study of photometric properties of high-pressure mercury discharge with thallium iodide additives (HgTℓI) using the ray-tracing method

The photometric properties of HgTℓI high intensity discharge (HID) lamps have been calculated by solving the radiation transport equations in the discharge, using the ray-tracing method. The partial pressures of the various chemical species in the plasma are computed assuming the plasma is in local thermodynamic equilibrium (LTE), using a curve fit to an experimentally measured temperature profile. The plasma is also assumed to be fully mixed, implying a constant mercury/thallium ratio throughout the discharge tube. The spectral line broadening includes neutral Van der Waals and charged particle Stark broadening. The potential influence of ‘de-mixing’ on the spectra is also considered.

Simultaneous removal of arsenic and mercury from natural-gas-co-produced water from the Gulf of Thailand using synergistic extractant via HFSLM

The simultaneous separation of arsenic and mercury ions from natural-gas-co-produced water was well achieved by a synergistic extractant through a hollow fiber supported liquid membrane (HFSLM). Aliquat 336, Bromo-PADAP, Cyanex 923 and Cyanex 471 dissolved in toluene were used as the organic extractants or carriers. The transport system was studied on several variables: types of the extractants, concentration of the synergistic extractant, concentration of H 2SO 4 (a co-extractant) in feed solution, types of stripping solutions (NaOH, DI water, HNO 3, H 2SO 4 and thiourea), and the number of separation cycles. The results indicated the superior performance of mercury removal to arsenic by every single extractant in this study. The synergistic effect on arsenic removal was observed by adding Cyanex 471 in Aliquat 336 resulting in the synergistic coefficient of 2.8. The regulate mercury discharge to the environment not higher than 5 ppb was attained within 1-cycle separation by using the mixture of 0.22 M Aliquat 336 and 0.06 M Cyanex 471 as the synergistic extractant and 0.1 M thiourea as the stripping solution with 0.2 M H 2SO 4 in feed solution. By 3-cycle separation, 94% arsenic extraction, which was below the legislation limit of 250 ppb, was obtained.

Are native naiads more tolerant to pollution than exotic freshwater bivalve species? An hypothesis tested using physiological responses of three species transplanted to mercury contaminated sites in the Ebro River (NE, Spain)

In the lower Ebro River exist the paradoxical convergence of relatively well preserved river dynamics with the historical presence of a chloralkali plant with a long history of mercury discharges and the recent invasion of foreign bivalves species. Here we performed a comparative study on two alien bivalves, the Zebra mussel and the Asian clam ( Dreissena polymorpha and Corbicula fluminea), and one protected species of naiads ( Psilunio littoralis), which is the most common species of the freshwater mussel assemblages in this river. Individuals of the three species were transplanted to three sites that included a clean unpolluted upstream site, a contaminated location next to the mercury source and a downstream one. The study focused on digestive gland antioxidant and oxidative stress responses such as antioxidant enzymes, glutathione S transferase, glutathione levels, metallothionein proteins, DNA strand breaks and lipid peroxidation levels. Results evidenced interspecies differences on accumulation levels of mercury, antioxidant defensive systems and oxidative tissue damage. The naiad species, despite of accumulating more mercury showed the greatest antioxidant defensive potential, which was characterized by having high constitutive activities of glutathione S transferase and inducible activities and levels of key antioxidant enzymes and glutathione. Exposed individuals of C. fluminea had moderate levels of metal accumulation, the highest activities of antioxidant enzymes but also high levels of lipid peroxidation. D. polymorpha mussels showed the lowest levels of mercury but the lowest antioxidant responses and consequently the highest levels of oxidative injuries in the DNA and of mortality. Our results support the hypothesis that naiad species might be more tolerant to pollution than exotic species.

On the Aging Effects of 4H-SiC Schottky Photodiodes Under High Intensity Mercury Lamp Irradiation

Ultraviolet (UV) germicidal irradiation uses high-power 254-nm radiation from low-pressure mercury discharge lamps to kill or inactivate viral, bacterial, and fungal species. Since UV germicidal irradiation effectiveness depends primarily on the UV dose delivered to the microorganisms, it is essential to monitor the power emitted from the source by using appropriate UV-light detectors. We report on preliminary aging tests performed on high signal-to-noise ratio 4H-SiC Schottky photodiodes under high intensity mercury lamp irradiation (10 mW/cm2).

A two-dimensional modeling of the warm-up phase of a high-pressure mercury discharge lamp

The main objective of this work is to provide a better understanding of the warm-up phase of high-intensity discharge lamps. As an example of application, we chose the high-pressure mercury lamp. Based on two-dimensional fluid model parameters, such as the electric current, the length and the diameter of the burner are modified and the effect of the convective transport is studied. This allows us to obtain a thorough understanding of the physics of these lamps in their transitory phase. The simulation of the warm-up phase is a must for the proper predictions of the lamp behavior and can be conducted by solving the energy balance, momentum, and Laplace’s equations for the plasma, using the frame of the local thermodynamic equilibrium coupled with the energy balance of the wall.

Versatile Thin-Film Reactor for Photochemical Vapor Generation

A novel thin-film reactor is described and evaluated for its analytical performance with photochemical vapor generation (TF-PVG). The device, comprising both the generator and a gas-liquid separator, utilizes a vertical central quartz rod onto which the sample is pumped to yield a thin liquid film conducive to the rapid escape of generated hydrophobic species. The rod is housed within a concentric quartz tube through which a flow of argon carrier/stripping gas is passed to remove and transport the generated species to a detector, which in this study is an inductively coupled argon plasma optical emission spectrometer (ICP-OES). The concentric quartz tube is itself surrounded by a 78-turn 0.5 m long quartz coil low-pressure mercury discharge lamp operating at 20 W. The performance of this thin-film photoreactor was evaluated through comparison of analytical figures of merit for detection of a number of elements undergoing PVG in the presence of formic or acetic acid with those arising from conventional solution nebulization under optimized conditions. The TF-PVG reactor provided sensitivity enhancements, of 110-, 120-, 130-, 250-, 120-, 230-, 78-, 1.3-, 16-, and 32-fold for As, Sb, Bi, Se, Te, Hg, Ni, Co, Fe, and I, respectively, and detection limit enhancements of 110-, 140-, 170-, 270-, 200-, 300-, 160-, 2.7-, 50-, and 44-fold for these same elements. Vapor generation efficiencies ranged from 20-100% for this suite of analytes. The utility of this technique was demonstrated by the determination of Fe and Ni in Certified Reference Materials DORM-3 (fish protein) and DOLT-4 (dogfish liver tissue).

Effects of Mercury on Growth, Emergence, and Behavior of Chironomus riparius Meigen (Diptera: Chironomidae)

Mercury is a pervasive toxicant that can be found in the environment due to anthropogenic activity as well as natural sources. The majority of studies in freshwater environments focus mainly on bioaccumulation, population dynamics, and biomagnification. Here, we study the effects of mercuric chloride on Chironomus riparius Meigen, simulating a mercury discharge on a freshwater ecosystem. Growth, emergence, development time, and behavior were the end points assessed. Growth was measured after 8 days of exposure and behavior was recorded on days 4 and 10 of the experimental period. The behavioral responses of C. riparius to different mercury treatments were recorded with an online biomonitor, which allows a more objective and precise behavioral understanding than visual observation. Mercury exposure resulted in reductions in growth and emergence, a delayed development time, and a decrease in locomotor activity of the larvae. Our results demonstrate that mercury exposure can impair life-history responses of chironomids.

Metal-halide lamp design: atomic and molecular data needed

Metal-halide lamps are a subset of high intensity discharge (HID) lamps so named because of their high radiance. These lamps are low temperature (∼0.5 eV), weakly ionized plasmas sustained in refractory but light transmissive envelopes by the passage of electric current through atomic and molecular vapors. For commercial applications, the conversion of electric power to light must occur with good efficiency and with sufficient spectral content throughout the visible (380–780 nm) to permit the light so generated to render colors comparable to natural sunlight. This is achieved by adding multiple metals to a basic mercury discharge. Because the vapor pressure of most metals is very much lower than mercury itself, metal-halide salts of the desired metals, having higher vapor pressures, are used to introduce the material into the basic discharge. The metal compounds are usually polyatomic iodides, which vaporize and subsequently dissociate as they diffuse into the bulk plasma. Metals with multiple visible transitions are necessary to achieve high photometric efficiency (efficacy) and good color. Compounds of Sc, Dy, Ho, Tm, Ce, Pr, Yb and Nd are commonly used. The electrons, atoms and radicals are in local thermodynamic equilibrium (LTE), but not with the radiation field. Strong thermal (106 K m−1) and density gradients are sustained in the discharge. Atomic radiation produced in the high-temperature core transits through colder gas regions where it interacts with cold atoms and un-dissociated molecules before exiting the lamp. Power balance and spectral output of the lamp are directly affected by the strength of atomic transitions. Attempts to simulate the radiative output of functional metal-halide lamps have been successful only in very simple cases. More data (e.g. the atomic transition probabilities of Ce i) are necessary to improve lamp performance, to select appropriate radiators and in scaling the lamp geometry to various wattages for specific applications.

Synthesis of L-tryptophan labeled with hydrogen isotopes in the indole ring

The isotopomers of L-tryptophan (L-Trp) labeled with hydrogen isotopes in the indole ring were obtained by isotope exchange method. Heavy and tritiated water were used as the sources of stable and radioactive label. Three isotopomers, i.e., [4′-2H]-L-Trp, [4′-3H]-L-Trp, and doubly labeled [4′-2H/3H]-L-Trp were synthesized by isotope exchange enhanced by irradiation with a mercury discharge lamp. The indole whole ring labeled isotopomers, i.e., [2′,4′,5′,6′,7′-2H5]-L-, [2′,4′,5′,6′,7′-3H5]-L-, and doubly labeled [2′,4′,5′,6′,7′-2H/3H]-L-Trp were synthesized by isotope exchange between L-Trp and D2O or DTO in the presence of deuteriated trifluoroacetic acid.

New Generation of Low Pressure Mercury Lamps for Producing Ozone

Producing ozone by means of a low pressure mercury discharge is still limited by such economical and technical factors as efficiency and lifetime of Low Pressure Mercury Lamps (LPMLs). With the introduction of a new “long life coating” technology for LPMLs at Heraeus, these lamps show up as an effective and reliable VUV-light source that can be used in ozone generation. Different coating technologies are compared in terms of radiation losses in the coating and depreciation of the mercury resonance line at λ=185 nm. The parameters of new ozone generating lamps are presented. A simple model with consideration of both the resonance lines at λ=185 nm and λ=254 nm for a practical calculation of ozone concentration in an air flow is proposed.

Absorption and emission lines of a mercury molecule in a mercury discharge lamp

Absorption lines are revealed in spectra of a mercury discharge lamp (Planck’s radiator). Some of the lines were identified by Lord Rayleigh as the absorption lines of a Hg2 molecule. New absorption lines at 253.29, 253.53, 253.76, and 254.20 nm, as well as emission lines at 264.80, 254.96, 265.11, 279.89, 288.82, 301.50, 301.74, and 301.95 nm are discovered, which enabled the construction of a diagram of the lower excited electronic states of a mercury molecule. It is demonstrated that the dips in the intensity profiles of the atomic mercury lines at 253.65, 435.83, 404.65, and 546.07 nm arise from the radiation absorption in vibronic transitions of diatomic Hg2 molecules. The concentration of mercury molecules in the plasma of mercury discharge lamps is determined to be of the order of 108 cm−3. However, their contribution to the formation of the emission line profiles is essential due to the multiple radiation passage through the emitting plasma.

Application of an antenna excited high pressure microwave discharge to compact discharge lamps

A novel type of high pressure microwave discharge has been investigated to feed the microwave power at the centre of the compact high pressure discharge lamps using the antenna effect. This method of microwave discharge is named as the antenna excited microwave discharge (AEMD). The 2.45 GHz microwave of around 50 W from the solid state microwave generator can sustain a stable plasma column in the small gap between a couple of antennas fitted on the compact lamp filled with discharge gases at a pressure higher than atmosphere. The AEMD has been applied to a compact metal halide lamp and an extremely high pressure mercury discharge lamp. As a result, the metal halide lamp showed high luminous efficacy of around 130 lm W−1. The excellent lamp properties obtained here can be explained by the low heating loss at the antennas and the lamp wall. The profiles of the microwave electric field in the lamp and the microwave launcher have been numerically calculated to consider the microwave power supply into the lamp.