Pressure Mercury Vapor Research Articles

Comparability of calibration strategies for measuring mercury concentrations in gas emission sources and the atmosphere

Abstract. A primary mercury gas standard was developed at Van Swinden Laboratory (VSL) to establish an International System of Units (SI)-traceable reference point for mercury concentrations at emission and background levels in the atmosphere. The majority of mercury concentration measurements are currently made traceable to the empirically determined vapour pressure of mercury. The primary mercury gas standard can be used for the accurate and precise calibration of analytical systems used for measuring mercury concentrations in air. It has been especially developed to support measurements related to ambient air monitoring (1–2 ng m−3), indoor and workplace-related mercury concentration levels according to health standards (from 50 ng m−3 upwards) as well as stationary source emissions (from 1 µg m−3 upwards). The primary mercury gas standard is based on diffusion according to ISO 6154-8. Calibration gas mixtures are obtained by combining calibrated mass flows of nitrogen and air through a generator holding diffusion cells containing elemental mercury. In this paper, we present the results of comparisons between the primary gas standard and mercury calibration methods maintained by NPL (National Physical Laboratory in the United Kingdom), a National Metrology Institute (NMI), and the Jozef Stefan Institute (JSI), a Designated Institute (DI). The calibration methods currently used at NPL and JSI are based on the bell-jar calibration apparatus in combination with the Dumarey equation or a NIST (National Institute of Standards and Technology in the United States) reference material. For the comparisons, mercury was sampled on sorbent traps to obtain transfer standards with levels between 2 and 1000 ng with an expanded uncertainty not exceeding 3 % (k=2). The comparisons performed show that the results for the primary gas standard and the NIST reference material are comparable, whereas a difference of −8 % exists between results traceable to the primary gas standard and the Dumarey equation.

Primary mercury gas standard for the calibration of mercury measurements

Mercury poses one of the greatest current direct threats to human, animal and environmental health across the globe. Robust, defensible and traceable measurements of mercury concentrations are essential to underpin global efforts to reduce the concentration of mercury in the environment, meet the obligations of legislation and to protect human health. Currently, instruments for gaseous mercury concentration measurements are calibrated based on mercury vapour pressure equations (e.g., the Dumarey or the Huber equation). Currently these equations differ from each other by more than 7% at 20 °C. In this paper, the performed characterisation and implementation of mercury diffusion cells and the development of the first primary mercury gas standard show that metrological traceability to the International System of Units (SI) is possible for mercury concentrations. The primary mercury gas standard will provide a lower measurement uncertainty (between 1.8% and 3%) than can be obtained using the most commonly adopted mercury vapour pressure equations (5% up to 21%). Measurement methods have been developed for the SI traceable calibration of mercury analysers and mercury gas generators which have been used for the comparison between the primary mercury gas standard and the Dumarey equation. The developed primary mercury gas standard will contribute to more reliable mercury measurement results at emission and ambient air levels.

Mathematical Model of the Evaporation of Amalgam Components in Discharge Radiation Sources

The urgency of creating a mathematical model of the evaporation of amalgam components in discharge radiation sources (lamps) is due to the dependence of the parameters of the infrared (IR) radiation of special discharge sources on the vapor pressure of an emitting additive. The pressure in turn depends on the sizes and temperature of the discharge, cathode, and anode volumes. In connection with the diverse range of designs of gas-discharge lamps, a set of equations is proposed, which makes it possible to determine the vapor pressure of amalgam components taking into account the specific design of the discharge tube (the burner) and its temperature profile. The design of a discharge source of IR radiation for safety systems of aircraft, for which the calculation of cesium and mercury vapors is presented, is described. As a result of calculations, the dependences of the vapor pressure of cesium and mercury on the temperature of the discharge-tube cold point at various amalgam weights are obtained. The features of the increase in the cesium pressure on the transition from saturated vapors into unsaturated are revealed.

Mercury solubility measurements in natural gas components at high pressure

Saturated vapor pressure of elemental mercury (Hg) and Hg solubility in compressed gaseous methane, ethane, and carbon dioxide were investigated. The apparatus designed for this study was based on a flow method and equipped with a cold vapor atomic absorption survey meter to measure Hg concentration in gas phase. The saturated Hg vapor pressure ranged from 4.579 × 10−2 to 2.757 × 10−1 Pa at 278–298 K. The Hg solubility was measured up to 6.042 MPa for methane, 3.533 MPa for ethane, and 2.070 MPa for carbon dioxide at 268–303 K. The Hg mole fraction ranged from 4.842 × 10−9 to 8.683 × 10−7 in the vapor phase. The Hg solubility decreases with increasing pressure, and the pressure dependencies are similar in the three gases. The activation energy of Hg solubility was determined from the Arrhenius plot at the 1.55 and 3.55 MPa isobars. The activation energy at 1.55 MPa is about 60 kJ/mol·K for the three gases, similar to that at the saturated Hg vapor pressure. At 3.55 MPa the activation energy has the same value for methane but decreases to around 60 kJ/mol·K for ethane. The Peng–Robinson equation of state (PR-EOS) was used to correlate the saturated Hg vapor pressure and the Hg solubility in the vapor phase. The attractive parameter in the PR-EOS was fitted with the saturated Hg vapor pressure, and its temperature dependence was investigated using the van der Waals one-fluid mixing rule. The average absolute deviations were 0.322, 0.265 and 0.197 % for Hg solubility in gaseous methane, ethane and carbon dioxide, respectively. This investigation contributes to predicting mercury partitioning in natural gas processing facilities.

A Study on the Knowledge and Awareness among Dental Students of Mercury Toxicity and Amalgam Disposal

Dental amalgam consists of 50% mercury. An average amalgam filling consists of 1 gram of mercury which continously leaks mercury vapour due to the low vapour pressure of mercury. Mercury vapour can spread rapidly throughout the human body. It crosses cell membranes easily. Mercury can penetrate the blood brain barrier and result in mercury accumulation in the brain. Mercury is among the top three most toxic substances that affects people in large numbers. Amalgam is the largest source of mercury. As amalgam is the number one source of mercury production, dentists and dental students are at a very high risk of mercury poisoning due to repeated exposure to dental amalgam. This study intends to assess the knowledge and awareness levels among dental students of mercury toxicity and its potential risks, and the various disposal methods for amalgam. Though most of the students were aware of mercury toxicity and amalgam disposal methods as a whole, only a handful were aware about the absorption efficiency rate and the critical threshold of mercury, which was as low as 20.83% and 21.66% respectively. Almost 50% of the students interviewed had answered less than 8 out of 15 questions correctly. It is recommended that more effective methods for delivering information regarding mercury, its complications and management are deviced.

Electrophysical properties of Cd x Hg1–x Te (x = 0.3) films grown by molecular beam epitaxy on Si(013) substrates

The electrophysical properties of CdxHg1–xTe (x ≈ 0.3) films undoped and doped with indium during their growth were investigated. The as-grown films were subjected to heat treatment in mercury vapor. The magnetic field dependences of the Hall effect in the magnetic field range of 0.05–1.0 T at 77 K were explained by the fact that, in the films, there are two types of electrons with high and low mobilities. The analysis of the temperature dependences of the minority carrier lifetime in the range of 77–300 K revealed that the as-grown films contain two types of traps with different energies. It was found that annealing at a saturated mercury vapor pressure increases the minority carrier lifetime due to the suppression of recombination centers, which can be associated with growth defects in CdxHg1–xTe/CdTe/Si heterostructures.

Antenna induced hot restrike of a ceramic metal halide lamp recorded by high-speed photography

The hot restrike is one of the biggest challenges in operating ceramic metal halide lamps with mercury as buffer gas. Compared to a cold lamp, the pressure within a ceramic burner is two orders of magnitude higher during steady state operation due to the high temperature of the ceramic tube and the resulting high mercury vapour pressure. Room temperature conditions are achieved after 300 s of cooling down in a commercial burner, enclosed in an evacuated outer bulb. At the beginning of the cooling down, ignition voltage rises up to more than 14 kV. A significant reduction of the hot-restrike voltage can be achieved by using a so called active antenna. It is realized by a conductive sleeve surrounding the burner at the capillary of the upper electrode. The antenna is connected to the lower electrode of the lamp, so that its potential is extended to the vicinity of the upper electrode. An increased electric field in front of the upper electrode is induced, when an ignition pulse is applied to the lamp electrodes. A symmetrically shaped ignition pulse is applied with an amplitude, which is just sufficient to re-ignite the hot lamp. The re-ignition, 60 s after switching off the lamp, when the mercury pressure starts to be saturated, is recorded for both polarities of the ignition pulse with a high-speed camera, which records four pictures within the symmetrically shaped ignition pulse with exposure times of 100 ns and throws of 100 ns. The pictures show that the high electric field and its temporal variation establish a local dielectric barrier discharge in front of the upper electrode inside the burner, which covers the inner wall of the burner with a surface charge. It forms a starting point of streamers, which may induce the lamp ignition predominantly within the second half cycle of the ignition pulse. It is found out that an active antenna is more effective when the starting point of the surface streamer in front of the sleeve is a negative surface charge on the inner tube wall. The high-speed photos show that the ignition process is very similar in lamps with Hg or Xe as buffer gas.

The transition mechanisms of the E to H mode and the H to E mode in an inductively coupled argon-mercury mixture discharge

In our experiment, the transition points between the two operational modes of capacitive coupling (E mode) and inductive coupling (H mode) were investigated at a wide range of mercury vapor pressures in an inductively coupled plasma, varying with the input radio-frequency powers and the total filling pressures (10 Pa–30 Pa). The electron temperatures were calculated versus with the mercury vapor pressures for different values of the total filling pressures. The transition power points and electron density also were measured in this study. It is shown that the transition powers, whether the E to H mode transition or the H to E mode transition, are lower than that of the argon discharge, and these powers almost increase with the mercury vapor pressure rising. However, the transition electron density follows an inverse relationship with the mercury vapor pressures compared with the transition powers. In addition, at the lower pressures and higher mercury vapor pressures, an inverse hysteresis was observed clearly, which did not appear in the argon gas plasma. We suggest that all these results are attributed to the electron-neutral collision frequency changed with the additional mercury vapor pressures.

Atomic mercury vapor inside a hollow-core photonic crystal fiber.

We demonstrate high atomic mercury vapor pressure in a kagomé-style hollow-core photonic crystal fiber at room temperature. After a few days of exposure to mercury vapor the fiber is homogeneously filled and the optical depth achieved remains constant. With incoherent optical pumping from the ground state we achieve an optical depth of 114 at the 6(3)P(2) - 6(3)D(3) transition, corresponding to an atomic mercury number density of 6 × 10(10) cm(-3). The use of mercury vapor in quasi one-dimensional confinement may be advantageous compared to chemically more active alkali vapor, while offering strong optical nonlinearities in the ultraviolet region of the optical spectrum.

International System of Units Traceable Results of Hg Mass Concentration at Saturation in Air from a Newly Developed Measurement Procedure

Data most commonly used at present to calibrate measurements of mercury vapor concentrations in air come from a relationship known as the "Dumarey equation". It uses a fitting relationship to experimental results obtained nearly 30 years ago. The way these results relate to the international system of units (SI) is not known. This has caused difficulties for the specification and enforcement of limit values for mercury concentrations in air and in emissions to air as part of national or international legislation. Furthermore, there is a significant discrepancy (around 7% at room temperature) between the Dumarey data and data calculated from results of mercury vapor pressure measurements in the presence of only liquid mercury. As an attempt to solve some of these problems, a new measurement procedure is described for SI traceable results of gaseous Hg concentrations at saturation in milliliter samples of air. The aim was to propose a scheme as immune as possible to analytical biases. It was based on isotope dilution (ID) in the liquid phase with the (202)Hg enriched certified reference material ERM-AE640 and measurements of the mercury isotope ratios in ID blends, subsequent to a cold vapor generation step, by inductively coupled plasma mass spectrometry. The process developed involved a combination of interconnected valves and syringes operated by computer controlled pumps and ensured continuity under closed circuit conditions from the air sampling stage onward. Quantitative trapping of the gaseous mercury in the liquid phase was achieved with 11.5 μM KMnO4 in 2% HNO3. Mass concentrations at saturation found from five measurements under room temperature conditions were significantly higher (5.8% on average) than data calculated from the Dumarey equation, but in agreement (-1.2% lower on average) with data based on mercury vapor pressure measurement results. Relative expanded combined uncertainties were estimated following a model based approach. They ranged from 2.2% to 2.8% (k = 2). The volume of air samples was traceable to the kilogram via weighing of water for the calibration of the sampling syringe. Procedural blanks represented on average less than 0.1% of the mass of Hg present in 7.4 cm(3) of air, and correcting for these blanks was not an important source of uncertainty.

254 nm Radiant Efficiency of High Output Low Pressure Mercury Discharge Lamps with Neon-Argon Buffer Gas

High output low pressure mercury (LPM) discharge UV lamps have been briefly introduced. In order to measure the 254 nm radiant efficiency simply and preciously, Keitz formula was used and its advantage was illustrated. The LPM lamps had outer diameter of 19 mm (T6). The buffer gases are neon (65%) and argon (35%) with total pressure 1-10 Torr (133-1333 Pa). The lamps were operated with cold spot temperatures from 20°C to 80°C and discharge current from 0.8 A to 2.0 A. The electric field, input power, 254 nm UV irradiance and irradiance of other Hg lines from 265 to 579 nm in positive column were measured. The radiant power of each wavelength can be calibrated according to the 254 nm output and the Keitz formula. It was shown that the radiant efficiency of 254 nm can reach a maximum of above 40% at cold spot temperature 45-47 °C and current 1.6 A for filling pressure less than 3 Torr. The optimal mercury vapor pressure was 1.2 to 1.4 Pa. The output percentage of other Hg lines was below 5%. With the decrease of buffer gas pressure, the 254 nm radiant efficiency increased obviously.

Long-lived Ar-Hg plasma in the afterglow of a high-current pulsed discharge

High-density (n > 1012 cm−3) argon-mercury plasma produced by a short (t ∼ 20 μs) high-power pulsed discharge in argon with an admixture of mercury vapor at a discharge current of ∼50 A, an argon pressure of ∼4 mm Hg, and a mercury vapor pressure of ∼10−3 mm Hg was studied using optical spectroscopy and radio physics methods. It is found that the lifetime of this plasma after the end of the discharge pulse is up to 10−2 s. It is shown that such an abnormally long lifetime of such an afterglow plasma, as compared to the plasma of an argon discharge without an admixture of mercury vapor, is related to the long residence time of atoms and ions of both argon and mercury in highly excited states due to chemi-ionization processes involving long-lived metastable argon ions. It is suggested that dissociative recombination of highly excited molecular ions of argon play an important role in the transfer of excitation to argon atoms and ions that are close to autoionization states.

Mercury emissions in equilibrium: a novel approach for the quantification of mercury emissions from contaminated soils

Mercury emissions from soil samples with different mercury contents have been estimated using a closed circuit array. The samples were collected from the Almaden mercury mining district. The emissions confirmed that temperature and light radiation favour mercury desorption due to the increase in the mercury vapour pressure. An additional positive factor could be the photocatalytic reduction of soluble Hg2+ to volatile Hg0 at the soil surface. A physicochemical model based on mass transfer and equilibrium was developed and was used to reproduce the mercury emissions at the laboratory scale. The use of this model allowed us to obtain the unknown mass transfer coefficient (KL) and adsorption parameters required to quantify the possible gaseous mercury fluxes from these contaminated soils. Experimental results indicate that an equilibrium between the solid and gas phases was established. The proposed kinetic model reproduced perfectly the experimental data, with KL found to be proportional to the inverse of temperature and independent of the radiation. The concentration of mercury in the gas phase was mainly dependent on the soluble mercury content (HgS). Equilibrium data were fitted by Langmuir and Freundlich models and the best fit was obtained using the multi-layer model attending to the convex shape of the curves, which is characteristic of non-porous or possibly macroporous materials having a low adsorption energy. The Freundlich constant (KF) was also fitted as a polynomial function with temperature and this gave a straight line for the light radiation and a second grade equation for dark conditions. Once the parameters had been obtained, the Hg emission fluxes from contaminated soils were estimated and the values were between two and three orders of magnitude higher than those published in the literature for non-contaminated soils.

Mercury Vapor Pressure of Flue Gas Desulfurization Scrubber Suspensions: Effects of pH Level, Gypsum, and Iron

Calcium-based scrubbers designed to absorb HCl and SO(2) from flue gases can also remove oxidized mercury. Dissolved mercury halides may have an appreciable partial vapor pressure. Chemical reduction of the dissolved mercury may increase the Hg emission, thereby limiting the coremoval of mercury in the wet scrubbing process. In this paper we evaluate the effects of the pH level, different gypsum qualities, and iron in flue gas desulfurization (FGD) scrubber suspensions. The impact of these parameters on mercury vapor pressure was studied under controlled laboratory conditions in model scrubber suspensions. A major influence is exerted by pH values above 7, considerably amplifying the mercury concentration in the vapor phase above the FGD scrubber suspension. Gypsum also increases the mercury re-emission. Fe(III) decreases and Fe(II) increases the vapor pressure significantly. The consequences of the findings for a reliable coremoval of mercury in FGD scrubbers are discussed. It is shown that there is an increased risk of poor mercury capture in lime-based FGD scrubbers in comparison to limestone FGD scrubbers.

The effect of the operation modes of a gas discharge low-pressure amalgam lamp on the intensity of generation of 185 nm UV vacuum radiation

The effect of the discharge current, mercury vapor pressure, and the inert gas pressure on the intensity and efficiency of the 185 nm line generation are considered. The spectra of the UV radiation (vacuum ultraviolet) transmission by protective coatings from the oxides of rare earth metals and aluminum are investigated.

Vapour phase concentrations of volatile nuclear reaction products in the MEGAPIE cover gas

The licensing of the prototype liquid lead bismuth spallation target MEGAPIE required the assessment of the amount of radioactivity that can be released from the liquid metal to the gas phase under various scenarios. To estimate the radiological consequences of evaporation processes under normal operation conditions, the concentrations of hazardous volatile radionuclides in the gas phase of the MEGAPIE expansion volume were estimated using a simplified model based on an equilibrium state. In this report, we focus on those volatile impurities that do not show a strong retention in the liquid metal caused by chemical interactions, comprising mercury, cadmium and thallium. For mercury, temperature functions for the effective vapour pressure of mercury over liquid eutectic lead bismuth alloy were deduced from experimental data and compared to literature data available for the binary systems Hg–Pb and Hg–Bi. Conservative functions were selected from the data on hand for the evaluation of the maximum possible amounts of mercury, cadmium and thallium radioactivity in the gas phase of the MEGAPIE target. Substantial amounts of radioactive mercury are predicted to be released to the cover gas phase of MEGAPIE and liquid lead-alloy based spallation targets in general. The radioactivity resulting from evaporation of cadmium and thallium nuclides is expected to be low. Consequences for liquid metal spallation target systems are discussed.

Comparison of Mercury Vapor Pressure of Silver Amalgam-Based Electrode Materials Using AAS

Nowadays, several amalgam-based electrodes are commonly used in electrochemistry as a less toxic alternative to mercury electrodes. Therefore, a comparison of the mercury vapor pressure of several silver amalgam-based electrode materials with the mercury vapor pressure of liquid mercury and of dental amalgam using AAS was done in this study. Method was optimized to get the highest mercury signal. Results showed that the mercury vapor pressure of amalgam-based electrode materials not containing liquid mercury is far lower than the mercury vapor pressure of liquid mercury (about two orders of signal magnitude) and comparable with mercury vapor pressure of dental amalgam.

Elemental mercury vapour in air: the origins and validation of the ‘Dumarey equation’ describing the mass concentration at saturation

The Dumarey equation has been the dominant relationship used to calculate the mass concentration of saturated elemental mercury vapour in air for the calibration of mercury vapour measurement equipment for over 25 years. However, the origin of the equation, and the validation data supporting its accuracy have never been published. This paper addresses that deficiency, compares the Dumarey equation with other data sets to which it has been wrongly attributed in the past, and describes why it remains superior to the use of mercury vapour pressure data in combination with the ideal gas law, for the purposes of calibrating mercury vapour measurement equipment.

Estimation of the Enhancement Factor for Mercury in Air

A combination of classical thermodynamics and molecular theory was used to calculate the enhancement factor (ratio of vapor-phase partial pressure to saturated vapor pressure) for liquid mercury in equilibrium with air at standard atmospheric pressure at temperatures from 0 °C to 40 °C. The enhancement factors range from 1.0025 at 0 °C to 1.0016 at 40 °C. This enhancement is too small in magnitude, and in the wrong direction, to explain a difference that has been noted between equilibrium vapor concentrations implied by the vapor pressure of pure mercury and those assumed in some calibration procedures.

The mercury vapour pressure vs. temperature relation between (500 and 665) K

A gas-controlled heat-pipe is used at the Italian National Research Institute of Metrology (INRIM) to realise the mercury (liquid + vapour) equilibrium from (450 to 700) K. The pressure in the heat pipe is controlled between (5 and 200) kPa by means of an innovative computer-driven system having a pressure sensitivity of a few parts per million. The vapour pressure of 0.9999999 pure mercury has been measured between (500 and 665) K. A standard pressure balance and a standard platinum resistance thermometer (SPRT) calibrated at the ITS-90 fixed points, were used. The experimental data obtained are fitted to a semi-empirical relationship between vapour pressure and temperature. The basic features of gas-controlled heat pipes and the metrological quality of the temperature and pressure measurements available in the laboratory, allowed the determination of the mercury vapour pressure at the level of a few parts in 10 −5. The paper reports the acquired data and the evaluated relationship, together with the uncertainty budget of the associated measurements. A complete description of the mercury heat-pipe, the gas controlled system, the measuring instruments involved and the temperature and pressure data acquisition and processing is also presented. The relationship between temperature and pressure of the mercury liquid–vapour transition has then been derived and it is here reported together with the mathematical and experimental uncertainty budgets. An accurate comparison with the existing data is also reported.