Concentrations Of Ionic Species Research Articles

Determinants of laser-induced breakdown spectra in N2–O2 mixtures

Potential determinants of the laser-induced breakdown spectra in N2–O2 mixtures are investigated with varying species concentration, laser energy, and exposure time (equal to the detector’s intensifier gate time). A focused laser beam with pulse energy 29 mJ, 38 mJ, or 46 mJ generates the breakdown plasma in a N2 mixture containing O2 from 0% to 21% in mole fraction. Time-resolved measurements of the breakdown emission spectra with 2 or 10 ns exposure are carried out beginning from the arrival of the laser beam at the focal point up to several μs later. These measurements show the temporal evolution of the instantaneous spectrum in the range 550–825 nm that contains multiple N and O atomic/ionic emission lines. Analyses of the baseline-subtracted spectra, normalized by the peak intensity of the N atomic emission line at 747 nm, indicate that the temporal evolution of each emission line is independent of species concentration and laser energy, though the instantaneous emission line intensity is strongly dependent on the species concentration and exposure time. The plasma temperature, estimated using two atomic oxygen lines and assuming local thermal equilibrium, and its temporal evolution are shown to be independent of the species concentration and a weak function of the laser energy at a given gas density, e.g. atmospheric pressure and room temperature. In addition, thermal equilibrium calculations, for predicting atomic and ionic species concentrations in the plasma, are carried out, and the combined results dictate that the emission-line intensity is linear with the atomic/ionic species concentration because of the consistent plasma temperature and its temporal evolution, independent of species concentration.

Optical waveguide modeling of refractive index mediated pH responses in silica nanocomposite thin film based fiber optic sensors

Recent experiments have demonstrated a pH-dependent optical transmission of silica based nanocomposite thin film enabled evanescent wave absorption spectroscopy based fiber optic sensors in aqueous solutions. Although the response was observed to linearly correlate with the pH-dependent surface charge density of the silica matrix, the responsible mechanism was not fully clarified. In this manuscript, an optical waveguide model is applied to describe observed responses through a modified effective refractive index of the silica matrix layer as a function of the solution phase pH. The refractive index dependence results from a surface charge dependent ionic adsorption, resulting in concentration of ionic species at charged surfaces. The resultant effective index modification to porous silica is estimated through effective medium theories and applied to an optical waveguide model of a multi-mode fiber optic based sensor response capable of reproducing all experimental observations reported to date.

Nature and Sources of Ionic Species in Precipitation across the Indo-Gangetic Plains, India

ABSTRACTThe spatial distribution of rainwater chemistry over the densely-populated and highly polluted Indo-Gangetic Plains (IGP) was investigated using samples (total = 687) collected during three consecutive summer monsoon seasons from 2009 to 2011. The concentrations of secondary ionic species (SO42– and NO3–) were measured along with the other major ions (F–, Cl–, Na+, K+, Ca2+, Mg2+ and NH4+) and pH and specific conductivity. The weighted mean pH (± std) and conductivity of rainwater were 5.73 (± 0.17) and 31.6 (± 31.0) µS cm–1, respectively. Approximately 16% of rainwater samples were acidic (pH 5.61) (mean pH = 6.34 for the more basic samples). Specific conductivity was ~39% lower (20.6 µS cm–1) for the acidic rain compared to the more basic (33.6 µS cm–1) samples. The mean sum of all of the measured ions is 351.6 ± 130.1 µeq L–1 with the highest contributions being Ca2+ (30%) and SO42– (15%). Mean [SO42–] (52 µeq L–1) and [NO3–] (29 µeq L–1) were approximately five and ten times higher, respectively, compared to background hemispheric values. Secondary ions had the highest deposition fluxes (SO42–, 25.2 kg ha–1 y–1 and NO3–: 18.3 kg ha–1 y–1). The mean ratio of H+/(NO3– + SO42–) was 0.02 indicating ~98% of the acidity was neutralized. Ca2+, (57%), Mg2 (25%), NH4+ (15%) and K+ (4%) were important neutralizing species. Positive Matrix Factorization (PMF) was applied to the deposition fluxes. Five factors were identified and identified as ammonia neutralized, sea salt, soil, biomass burning, and calcium neutralized.

Physico-chemical interaction between mineral admixtures and OPC–calcium sulfoaluminate (CSA) cements and its influence on early-age expansion

The present study aims at examining the physico-chemical factors influencing the expansion characteristics of OPC–CSA blend in the presence of mineral admixtures. Three different admixtures: Class ‘F’ fly ash (‘F’FA), Class ‘C’ fly ash (‘C’FA) and silica fume (SF) were used as 15%, 15% and 5% replacement of total cementitious binder. Longitudinal expansion of cement pastes prepared at w/cm – 0.44 showed that the Class ‘F’FA increased the expansion whereas the Class ‘C’FA and SF reduced the expansion. The pore solution of the OPC–CSA cement pastes was extracted at different ages to monitor the concentration of various ionic species. The saturation level of ettringite was determined using a geochemical modeling program (GEMS). Furthermore, an upper bound of crystallization stress was estimated. The expansion behavior in the presence of Class ‘F’FA and SF was found to be influenced by the changes in the stiffness, whereas the expansion of the Class ‘C’FA-based mixture was governed by faster hydration of ye'elimite.

Study of Enzyme Kinetics using Capacitive Biosensor-An Alternate to Colorimeter

A novel sensor approach based on measurement of changes in capacitance of an electrochemical cell produced during enzyme catalyzed formation of products is described. The electrochemical property such as capacitance of an electrolyte between electrochemical cell depends on its ionic compositions, in turn depends on the resulting ionic constituents caused by catalytic action of the enzyme. Generation of micromolar (μM) concentration of ionic species causes large changes in capacitance that is measurable in picofarad (pF) range in capacitive electrodes. Broad clinical analytical application of this technique is demonstrated in this report by application to diagnostically valued enzymes measurements like pyrophosphatases and phosphatases. Specific measurements of enzyme activities were achieved over the concentration range of 0.125 – 5.0 mM of respective substrates. The performance of the electrochemical sensor based enzyme biochemical assays were compared directly with identical assays employing spectrophotometric detection and found to match well.

A new approach for monitoring and controlling the extraction of gold by tri-butyl phosphate from chloride media

The objective of this work was to control and monitor the solvent extraction process of gold chloride by tri-butyl phosphate (TBP) through measuring Oxidation Reduction Potential (ORP). The results effectively indicate the application of ORP measurement approach in on-line monitoring/controlling the process of gold chloride solvent extraction. This approach showed that any decrease in gold extraction leads to an increase in ORP value. Based on this finding and by applying the slope analysis method, it was proved that Au tetrachloride is the predominant anion in aqueous phase and each mole of Au is absorbed by three moles of TBP. Considering the fact that a variety of ions are extracted from aqueous media in solvent extraction process a new equilibrium would be created. On the basis of Nernst equation, the electrochemical potential of system is changed. This research aims at anticipating the kind and concentration of ionic species based on the potential value of solution.

Chemical speciation of aerosols and air quality degradation during the festival of lights (Diwali)

Ambient PM2.5 (particulate matter less than 2.5 μm) samples, collected in a 8-week wintertime sampling program in two residential sites of Bhilai, India during the Indian Diwali festival in November 2012, were chemically characterized for 38 chemical species including eight speciated carbonaceous fractions (SCFs) of elemental (EC) and organic carbon (OC), twenty one metallic elements, and nine water soluble ionic species. Our objectives were to investigate: 1) relative abundances of SCFs contained in PM2.5during the Diwali festival period compared to normal days, and 2) enrichment pattern of potential inorganic markers of firework emission in ambient PM2.5during the festival days. Eight-fold increase inPM2.5mass concentrations were measured during the Diwali festival days compared to concentrations occurring in normal days. Bursting of firecrackers in the residential streets have shown significant contribution to the emission markers (K, Mg, Zn, S, EC and OC) along with crustal markers (Ca, Fe, Al) in ambient PM2.5aerosol samples. Concentrations of water soluble ionic species were found to be 10 times greater than those found in normal days. Further, the anion/cation ratios were found to reach a factor of 2; indicating the acidic character of emissions resulting from fireworks. The relative abundance of SCFs and higher ratios of OC to EC during the Diwali episode suggested the significant formation of secondary organic carbon (SOC) aerosols. We estimate that aerosols emitted from firework bursting contribute up to 32% of total ambient PM2.5 during the Diwali festival.

Computational study of the afterglow in single and sequential pulsing of an atmospheric-pressure plasma jet

The spatial distribution of charged species in the afterglow of a helium plasma jet impinging atmospheric air has been computed using a 2D axisymmetric fluid model. The model is solved for two consecutive pulse periods of a rectangular voltage waveform (duration of 60 ns) and for two different frequencies (25 and 50 kHz). The most abundant ionic species in the afterglow are found to be and with their concentrations increasing by about an order of magnitude (up to about 1018 m−3 and 1017 m−3 respectively) in the initial 1 μs. In the first pulse, these species form a halo around the diffusing He+ and electron rich central channel, the shape of the former being strongly correlated with the shape of He–air mixing layer computed using a hydrodynamic model. In the next pulse, this general configuration is also observed; however is more concentrated on the axis of the jet, this being due to influence of residual electrons in the central channel. For there is little difference in their spatial distribution compared to the initial pulse. For higher frequency pulsing, the higher concentration of residual electrons lowers the necessary ignition electric field reducing the concentrations (by 25%) of charged species in a period of the applied waveform. This work provides new information on the concentration and distribution of ionic species generated by atmospheric-pressure capillary discharges of interest to those developing such sources for range of applications, particularly in the field of plasma medicine.

A Computational Model for Sodium Sulfur Battery Analysis

Energy storage from the renewable energy sources is one of the challenging issue of clean energy technologies. Recently, sodium sulfur (Na-S) battery has gained considerable attention as a viable candidate of energy storage application. However, Na-S battery technology comes with the disadvantages of relatively high temperature operating conditions, brittle insulator and safety concern with regarded to temperature management. In this study, a two-dimensional heat transfer model is integrated with a zero-dimensional, transient electrochemical model for Na-S batteries to predict the temperature distribution inside the Na-S battery under cell operating conditions. Properties required for solving the heat transfer governing equation and electrochemical model, such as electronic and ionic conductivity, species concentrations and heat conductivity are calculated and updated as a function of time. Additionally, the instant outputs of these combined computational tools for single sodium sulfur battery, temperature, open circuit voltage, polarization and ohmic losses are used as input values for a designed Simulink model to analyze a stack of Na-S batteries. These computational tools aim to enable the thermal management and to a complete design procedure of storage systems made of Na-S batteries. The present model is tested against experimental results found in literature. Good agreement is achieved between current model and the available experiments. Validated model is used to perform a parametric study.

The PM10 compositions, sources and health risks assessment in mechanically ventilated office buildings in an urban environment

Office buildings can be considered a “second home” for working people and so the contribution of pollutants in this indoor environment to a person’s overall exposure is significant. The aims of this study were to examine the composition of PM10 and the sources influencing the indoor and outdoor office environments. The PM10 sampling was performed using a mini-vol portable sampler at two sampling sites from May to August 2014 for daily 24 h sampling. The concentrations of ionic species (F−, Cl−, NO3−, SO42−) were analysed using ion chromatography while the concentration of major elements (Mg, Ca, K, Na) and trace elements (Mn, Ni, Fe, Cu, Zn, Pb, Cr, Cd, Al) were determined by inductively couple plasma-mass spectrometry (ICP-MS). The concentration of NH4+ was determined using the indophenol blue method. The results showed that the average concentrations of PM10 were 61.3 ± 27.0 μg/m3 (indoor) and 101 ± 42.8 μg/m3 (outdoor) with an indoor/outdoor ratio value of <1. The dominant components in PM10 for both the indoor and outdoor environments were NO3−, SO42−, Na, Fe, Al and Zn. Source apportionment analysis of the PM10 composition identified three sources of PM10 in the indoor and outdoor environments. The major source for indoor PM10 was Earth’s crust elements (95 %) followed by oil burning and human activities (4 %) and motor vehicles (1 %). The major source for outdoor PM10 was the Earth’s crust and motor exhaust emissions (80 %) with contributions of other sources such as oil burning and human activities (18 %) and motor vehicles (2 %). The potential health risks for trace elements in PM10, via inhalation exposure to the indoor occupants, show that the total hazard quotient (HQ) value was slightly higher than acceptable limits (1.0). The total excess life time carcinogenic risk (ELCR) value for both sampling stations was higher than the acceptable limit (1.0 × E−6), suggesting a high exposure to carcinogenic risk. This study suggests there is a high contribution of outdoor sources to the indoor office environment where PM10 can significantly affect the indoor air quality and occupant health.

A Comparison Between a Semi-Continuous Analyzer and Filter-Based Method for Measuring Anion and Cation Concentrations in PM10at an Urban Background Site in London

A comparison between the filter-based, laboratory ion chromatography technique and a semi-continuous analyzer (URG 9000B Ambient Ion Monitor [AIM]) was conducted to evaluate the performance of the AIM in measuring the concentrations of the main airborne ionic species in PM10. The study was carried out in an urban background area of London (UK) in 2013. The two methods showed an overall good correlation (R2 > 0.83) for nitrate, sulfate, chloride, ammonium, and magnesium and poor correlation was found for sodium, potassium, and calcium (R2 < 0.50). The AIM gave consistently higher concentrations for sodium and potassium, possibly due to a positive bias within the sampling unit. During high concentration episodes, both the efficiency of the particle extraction and removal of gases by the denuder may be reduced. A HEPA filter test demonstrated that the denuder was removing gaseous components effectively but that there was some potential for contamination. Overall, the AIM was found to be a good instrument for...

24. Diffusion limited ice crystallisation + a comment on liquidus tracking

Diffusion limited ice crystallisation. During conventional cryopreservation many of the changes which occur in a CPA solution following ice nucleation are not linear with temperature. Parameters such as the ice fraction, concentration of ionic species, osmolality, pH, viscosity and gas solubility, all vary in a non-linear manner with temperature. In addition, the biophysical characteristics of cells which determine the response to freezing, for example the cellular permeability to water, also change in a nonlinear manner with temperature. We have measured the viscosity of the residual unfrozen solution that cells are exposed to during conventional freezing, and the effect of high viscosities encountered on the diffusion of water at a constant temperature during freezing and during cooling at different linear rates has been estimated. At rates of cooling faster than 100 °C min−1 the diffusion distance during freezing was calculated to be less than 15 μ m. Validation of the diffusion calculations were confirmed by examination of the ultrastructure of the freeze concentrated matrix in samples prepared at a range of cooling rates. At a critical rate of cooling, water diffusion becomes limited by the high viscosity and the composition of the freeze concentrated matrix deviates from that of the equilibrium phase diagram, the effects on cell viability of this non equilibrium state are demonstrated. Liquidus tracking. In 1965 Farrant proposed the “liquidus tracking” method of preservation in which cryoprotectant is added progressively during cooling so that samples remain on or above the liquidus line of the equilibrium phase diagram. Low temperatures protect against cryoprotectant toxicity at high concentrations. This method has also been termed the equilibrium approach to vitrification. However due to practical issues associated with high viscosities and mixing at low temperatures the method was largely abandoned. Recently there has been revived interest in the technique as applied to the preservation of cartilage and encapsulated hepatocytes and also in ultrastructural studies where the method is known as progressive lowering of temperature (PLT). Planer products have modified their controlled rate freezer to deliver the process for cartilage. Asymptote are developing equipment for this process which will allow preservation of clinical biopsies with native immunology which can be immunolabelled and from which viable cells may be isolated for adoptive cell therapies and personalised medicine.

A Multiphysics Finite-Element Performance Model of a Vanadium Redox Flow Battery

The growing penetration of renewable energy power in the electric grid has boosted the development of new technologies for stationary energy storage. All-vanadium redox flow batteries (VRFBs) exhibit a very high potential for both medium and large-scale applications. This is due to power/energy independent sizing, high efficiency, room temperature operation, and long charge/discharge cycle life. A number of challenges need to be tackled before commercialization, i.e. cell and stack design, highly efficient materials, and optimal power management and control operations [1]. Numerical models are very important for designing control and monitoring systems, which are needed for the electric grid interfacing. Both 1D and 2D finite element models have been developed in order to reduce computing cost and allow for a real-time simulation of VRFB operations [2]-[4]. In this work novel 1D steady-state and dynamic finite-element model of an all-vanadium redox flow battery are proposed. The reference cell model includes current collectors, positive and negative porous electrodes, where chemical reactions occur, and the polymer membrane for proton conduction. The FEM model incorporates the following multiphysics phenomena: momentum, charge and species conservation, mass transport (Nernst-Plank equation), electric conduction, charge generation (Butler-Volmer equation) inside the porous electrodes, and the proton conduction inside the membrane. In particular, for charge generation the effect of mass transport is taken into account by considering surface concentration of the electrolytes, which differs from bulk concentration. The VRFBs charge and discharge dynamics is taken into account by including reservoir mass balance equations. In such a way the energy storage cell performance can be properly simulated. The independent variables of the model are the electrode and electrolyte potentials and the ionic species concentrations in the porous electrodes. From potentials the overall cell voltage is derived as a function of the State of Charge (SoC) during charge and discharge cycles. The cell runtime and the storage efficiency can be deduced from the voltage time profile of the dynamic model. Numerical results of both the static and the dynamic 1D model are compared with those of 2D models, with the same parameters, showing good agreement. The proposed model is expected to be a useful tool in driving and optimizing the stack design.

A Computational Model for Sodium Sulfur Battery Analysis

Energy storage from the renewable energy sources is one of the challenging issue of clean energy technologies. Recently, sodium sulfur (Na-S) battery has gained considerable attention as a viable candidate of energy storage application. However, Na-S battery technology comes with the disadvantages of relatively high temperature operating conditions, brittle insulator and safety concern with regarded to temperature management. In this study, a two-dimensional heat transfer model is integrated with a zero-dimensional, transient electrochemical model for Na-S batteries to predict the temperature distribution inside the Na-S battery under cell operating conditions. Properties required for solving the heat transfer governing equation and electrochemical model, such as electronic and ionic conductivity, species concentrations and heat conductivity are calculated and updated as a function of time. Additionally, the instant outputs of these combined computational tool for single sodium sulfur battery, temperature, open circuit voltage, polarization and ohmic losses are used as input values for a designed Simulink model to analyze a stack of Na-S batteries. These computational tools aim to enable the thermal management and to complete design procedure of storage systems made of Na-S batteries. The present model is tested against experimental results found in literature. Good agreement is achieved between current model and the available experiment in the literature. Validated model is used to perform a parametric study.

How to determine the relative ion concentrations of multiple-ion-species plasmas generated in the multi-dipole filament source

This paper introduces how to determine concentrations of ion species in a mixed gas plasma that are not linearly proportional to their neutral partial pressures. A particle balance model was developed to predict the relative ion concentrations in multiple-ion-species plasmas, considering their ionization rates and loss fluxes to the wall. Analysis is carried out especially with Ar/Xe and Ar/He multi-dipole plasmas in which the neutral gases are directly ionized by the mono-energetic primary electrons. The experimental data of ion concentrations were obtained using the ion acoustic wave measurement method of the concentration of two ion species. The comparison reveals that the ion concentration ratio is linearly proportional to the ratio of the ionization cross sections and the ion loss velocity between two gas species. Especially, the model prediction is improved with using the two-ion-species sheath model (recently reported by Baalrud and Hegna) for obtaining the ion loss velocity at the sheath boundary.

Vertical characteristics of PM2.5 during the heating season in Tianjin, China

In this study, PM2.5 samples were collected at four heights (10m, 40m, 120m and 220m) at a meteorological tower in the daytime and nighttime during the heating season in Tianjin, China. The vertical variation and diurnal variability of the concentrations of PM2.5 and main chemical compositions were analyzed in clear days and heavy pollution days. Generally, mass concentrations of PM2.5 and the chemical compositions showed a decreasing trend with increasing height, while mass percentages of SO42−, NO3− and OC showed an increasing trend with increasing height. Concentrations of ion species and carbon compound in PM2.5 samples in the daytime were higher than those collected at night, which was due to intense human activities and suitable meteorological condition in the daytime. The ratios of NO3−/SO42− and OC/EC were also considered, and we have observed that their levels on heavy pollution days were higher than those on clear days. In addition, source apportionments were identified quantitatively using the CMB-iteration model. The results indicated that contributions of secondary ion species increased with increasing height, while contributions of other pollutant sources decreased, and contributions of vehicle exhaust were relatively high on clear days.

On the crystallization kinetics of highly soluble salts

Abstract For the spontaneous crystallization of highly soluble salts, a sufficiently high concentration of certain ionic species (complexes) or clusters has to be created in the solution, so that their grouping could yield a suitable crystal nucleus in a reasonably short time. The lowest critical supersaturation needed for nucleation and the highest rate of crystallization are displayed by those salts whose complexes in the solution have analogues in the crystal structure of the crystallizing salt, i.e., when the structure and the composition of the complexes enable their incorporation into the crystal lattice of the crystallizing salt with minimum changes. From this point of view a crystallochemical nucleation mechanism for explaining the Ostwald step rule is advanced. Concerning the rate of crystallization this concept was confirmed by studies on the system Na+, Mg2+/Cl–, SO4 2–//H2O and by parallel Raman spectroscopic studies of the microstructure of these solutions. It was established that upon increasing the concentration of Mg2+ ions and respective lowering of the water activity in the solution, the variety of the SO4 2– complexes increases. A direct correlation was found between the presence of various SO4 2– associations and the rate of crystallization of the corresponding salts in these systems.

Preventing hydrolysis of BaTiO3 powders during aqueous processing and of bulk ceramics after sintering

This present article addresses the reactive behaviour of barium titanate (BaTiO3, hereafter referred to as BT) with water either in powder form or as bulk ceramics. Chemisorbing a suitable phosphate-based protective agent at the surface of BT particles prevented hydrolysis reactions and made aqueous processing of BT a safe and viable route. Highly concentrated (50vol.%) fluid and long term stable suspensions could be easily prepared from surface treated BT particles, contrasting with the poor stability and high viscosity of slurries derived from the as received powders. For aqueous suspensions, the course of hydrolysis reactions was monitored through changes in pH and concentrations of leached ionic species along ageing time. For bulk ceramics, the extent of hydrolysis reactions was assessed through the microstructural changes occurred at polished surfaces without and with surface treatment, which have been kept in contact with water for a certain time period.

Integrated experimental investigation and mathematical modeling of brackish water desalination and wastewater treatment in microbial desalination cells

Desalination of brackish water can provide freshwater for potable use or non potable applications such as agricultural irrigation. Brackish water desalination is especially attractive to microbial desalination cells (MDCs) because of its low salinity, but this has not been well studied before. Herein, three brackish waters prepared according to the compositions of actual brackish water in three locations in Israel were examined with domestic wastewater as an electron source in a bench-scale MDC. All three brackish waters could be effectively desalinated with simultaneous wastewater treatment. The MDC achieved the highest salt removal rate of 1.2 g L−1 d−1 with an initial salinity of 5.9 g L−1 and a hydraulic retention time (HRT) of 0.8 d. The desalinated brackish water could meet the irrigation standard of both salinity (450 mg L−1 TDS) and the concentrations of major ionic species, given a sufficient HRT. The MDC also accomplished nearly 70% removal of organic compounds in wastewater with Coulombic efficiency varied between 5 and 10%. A previously developed MDC model was improved for brackish water desalination, and could well predict salinity variation and the concentrations of individual ions. The model also simulated a staged operation mode with improved desalination performance. This integrated experiment and mathematical modeling approach provides an effective method to understand the key factors in brackish water desalination by MDCs towards further system development.

The dominance of small ions in the electric double layer of size- and charge-asymmetric electrolytes: a mean-field study on the charge reversal and surface charge amplification

The dominance of counterions in the electric double layer of size-asymmetric semi-punctual ions was proposed more than 30 years ago by Valleau and Torrie. According to their theoretical prescription, at large colloidal surface charges, the double layer properties of a fully asymmetric binary electrolyte become similar to those of a completely symmetric electrolyte if the properties of counterions are the same in both instances. In the same theoretical framework, we propose here that, for a fixed concentration of the smallest ionic species and weakly/moderate colloidal surface charges, the valence of small ions rules or mainly determines the structural and thermodynamic properties of the electric double layer regardless of the colloidal polarity. In other words, we show that the characteristics of the small ions dominate the double layer structure of non-highly charged colloids, independently if the small ions are coions or counterions. This is illustrated by a comprehensive analysis of the ionic and integrated charge profiles around a spherical macroion immersed in a fully size- and charge-asymmetric semi-punctual electrolyte. Charge reversal and surface charge amplification are observed in the regime of low/medium colloidal surface charge densities. The origin of these counterintuitive phenomena, and their corresponding localisation properties in the Helmholtz zone, are explained in terms of the electric double layer structure.