Dominant Chemical Species Research Articles

Raman spectroscopy and multivariate curve resolution of concentrated Al2O3–Na2O–H2O solutions

AbstractMultivariate curve resolution was applied to a series of Raman spectra for samples representing highly concentrated alkaline aluminate slurries. Factors are extracted that represent the behavior of the dominant chemical species present, including aluminate monomer, aluminate oligomers, water and hydroxide. The analysis is particularly useful in unraveling the numerous overlapping contributions in the ν(OH) region of the spectrum. These extracted factors were further examined by comparing their scores with measured physiochemical properties such as density, relative humidity and molar concentrations of components, weight fractions and water activity. Published in 2003 by John Wiley & Sons, Ltd..

Actinide Speciation in Environmental Remediation

Environmental actinide remediation is often performed in the absence of a clear understanding of the contaminant chemical forms. Remediation efforts are more concerned with the initial and final concentration of the contaminant actinides. Allowable final concentrations of actinides in remediation sites are mainly based on expected dose or prenegotiated levels. However, understanding the chemical forms of actinides in the environment is key to assessing their long-term behavior and developing enhanced analytical methods for their environmental detection. The dominant environmental chemical form will dictate the actinide transport behavior through solubility, colloid formation, or the interaction with natural ligands/ This information can be used to evaluate the fate and potential transport of actinides. If the dominant environmental chemical species are understood, analytical methods, for enhanced counting statistics and a reduction of counting error can be developed. A reduction in counting error will increase the fraction of verifiable waste below a given threshold, thereby increasing the rate of site clean up while reducing the cost. The impact of actinide speciation is presented in 2 sites contaminated with Am and Pu undergoing remediation. Actinide speciation has affected remediation strategies, regulatory response, and costs.

A 3‐year record of simultaneously measured aerosol chemical and optical properties at Barrow, Alaska

Results are presented from 3 years of simultaneous measurements of aerosol chemical composition and light scattering and absorption at Barrow, Alaska. All results are reported at the measurement relative humidity of ≤ 40%. Reported are the annual cycles of the concentration of aerosol mass, sea salt, non‐sea‐salt (nss) sulfate, methanesulfonate or MSA−, NH4+, and nss K+, Mg+2, and Ca+2 for the submicron and supermicron size ranges. Submicron nss SO4=, NH4+, and nss K+, Mg+2, and Ca+2 peak in winter and early spring corresponding to the arrival and persistence of Arctic Haze. Submicron sea salt displays a similar annual cycle presumably due to long‐range transport from the northern Pacific Ocean. Supermicron sea salt peaks in summer corresponding to a decrease in sea ice extent. Submicron and supermicron MSA− peak in the summer due to a seasonal increase in the flux of dimethylsulfide from the ocean to the atmosphere. A correlation of MSA− and particle number concentrations suggests that summertime particle production is associated with this biogenic sulfur. Mass fractions of the dominant chemical species were calculated from the concentrations of aerosol mass and chemical species. For the submicron size range the ionic mass and associated water make up 80 to 90% of the aerosol mass from November to May. Of this ionic mass, sea salt and nss SO4= are the dominant species. The residual mass fraction, or fraction of mass that is chemically unanalyzed, is equivalent to the ionic mass fraction in June through October. For the supermicron size range the ionic mass and associated water make up 60 to 80% of the aerosol mass throughout the year with sea salt being the dominant species. Also reported for the submicron size range are the annual cycles of aerosol light scattering and absorption at 550 nm, Ångström exponent for the 450 and 700 nm wavelength pair, and single scattering albedo at 550 nm. On the basis of linear regressions between the concentrations of sea salt and nss SO4= and the light scattering coefficient, sea salt has a dominant role in controlling light scattering during the winter, nss SO4= is dominant in the spring, and both components contribute to scattering in the summer. Submicron mass scattering efficiencies of the dominant aerosol chemical components (nss SO4=, sea salt, and residual mass) were calculated from a multiple linear regression of the measured light scattering versus the component concentrations. Submicron nss SO4= mass scattering efficiencies were relatively constant throughout the year with seasonal averages ranging from 4.1 ± 2.9 to 5.8 ± 1.0 m2 g−1. Seasonal averages for submicron sea salt ranged from 1.8 ± 0.37 to 5.1 ± 0.97 m2 g−1 and for the residual mass ranged from 0.21 ± 0.31 to 1.5 ± 1.0 m2 g−1. Finally, concentrations of nss SO4= measured at Barrow were compared to those measured at Poker Flat Rocket Range, Denali National Park, and Homer for the 1997/1998 and 1998/1999 Arctic Haze seasons. Concentrations were highest at Barrow and decreased with latitude from Poker Flat to Denali to Homer revealing a north to south gradient in the extent of the haze.

INVESTIGATION ON OPTICAL EMISSION SPECTRA DURING ECR PLASMA ENHANCED MAGNETRON SPUTTERING CARBON NITRIDE FILM DEPOSITION

Emission spectra from the ECR plasma enhanced magnetron sputtering discharge used for CNx film deposition were investigated in the wavelength range 350 – 550 nm. The optical emission spectra from both the negative glow discharge zone near the target surface and the plasma zone formed by ECR discharge and magnetron discharge were studied separately. The dominant chemical species in both zone were found to be N2+, N2* , and CN radicals. But the intensity of CN radical in the plasma zone was greater than that in the negative zone, where an emission band of C2 was detected. The dependence of the intensities of CN band on the working gas pressure was investigated, and the formation of CN radicals, which could be vital in the CNx film deposition process, was discussed. It was shown that a possible mechanism could be the reaction of N2+ and N 2 with C 2 in the gas phase.

Measurement of aerosol chemical, physical and radiative properties in the Yangtze delta region of China

In order to understand the possible influence of aerosols on the environment in the agricultural Yangtze delta region of China, a one-month field sampling campaign was carried out during November 1999 in Linan, China. Measurements included the aerosol light scattering coefficient at 530 nm, σ sp, measured at both dry relative humidity (RH<40%) and under ambient conditions (sample RH=63±19%), and the absorption coefficient at 565 nm, σ ap, for aerosol particles having diameters <2.5 μm (PM 2.5). At the same time, daily filter samples of PM 2.5 as well as aerosol particles having diameters <10 μm (PM 10) were collected and analyzed for mass, major ion, organic compound (OC), and elemental carbon (EC) concentrations in order to determine which anthropogenic chemical species were primarily responsible for aerosol light extinction. The aerosol loading in the rural Yangtze delta region was comparable to highly polluted urban areas, with mean and standard deviation (S.D.) values for σ sp, σ ap and PM 2.5 of 353 Mm −1 (202 Mm −1), 23 Mm −1 (14 Mm −1) and 90 μg m −3 (47 μg m −3), respectively. A clear diurnal pattern was observed in σ sp and σ ap with minimum values occurring in the middle of the day, most likely associated with the maximum midday mixing height. The ratio of the change in light scattering coefficient at ambient RH to that at controlled RH (RH<40%), F σ sp (RH), indicates that condensed water typically contributed ∼40% to the light scattering budget in this region. The mass scattering efficiency of the dry aerosol, E scat_2.5, and mass absorption efficiency of EC, E abs_2.5, have mean and S.D. values of 4.0 m 2 g −1 (0.4 m 2 g −1) and 8.6 m 2 g −1 (7.0 m 2 g −1), respectively. PM 2.5 concentrations in Linan and two other locations in the Yangtze delta, Sheshan and Changshu (which have monthly mean values ranging from ∼80 to 110 μg m −3), are all significantly higher than the proposed 24-h average US PM 2.5 NAAQS of 65 μg m −3. Organic compounds are the dominant chemical species accounting for ∼50% of the PM 2.5 mass at all three sites. The results indicate that aerosol loadings in the agricultural Yangtze delta region of China are relatively high, and suggest that aerosols have a significant impact on visibility, climate, crop production, and human health in this region.

Fresh snow chemistry from high mountain regions in central himalayas

During 1997 summer, fresh snow samples were collected from the high elevation region (5400–7000 m) of Dasuopu Galcier on the northern slope of Mt. Xixabangma (28°33′ N, 85°44′ E). Compared with other remote regions in the world, major ion concentrations in fresh snow are very low during summer in Mt. Xixabangma, suggesting that the atmosphere is very clean and may represent background value for the middle/upper troposphere in the middle/low latitude area. During summer at Mt. Xixabangma the fresh snow chemistry is minimally influenced by anthropogenic pollutants as revealed by the snow pH (mean value of 6.0). Conductivity of fresh snow are low and constant. A multi-regression curve of pH vs conductivity shows a strong correlation; snow pH is negatively correlated with conductivity when pH 6.0. This suggests that the dominant chemical species of snow are interchanging between acid anions (e.g. SO42−, NO3−) and crustal cations.

Dominant Overall Chemical Reaction in a Chlorine Trifluoride–Silicon–Nitrogen System at Atmospheric Pressure

This study evaluates the overall chemical reaction in a chlorine trifluoride–silicon–nitrogen system at atmospheric pressure, based on the observation of the dominant chemical species in the gas phase using a quadrupole mass spectra analyzer coupled with a horizontal cold-wall single-wafer epitaxial reactor. Chlorine trifluoride gas etches the silicon surface, producing two major products, silicon tetrafluoride gas and chlorine gas, at room temperature and 530 K. The production of chlorosilanes was not observed in this study. The results obtained in this study indicate that the dominant overall chemical reaction in a chlorine trifluoride–silicon–nitrogen system is 3Si + 4ClF3 →3SiF4 ↑+ 2Cl2 ↑.

Plasma-Wall Interactions in Dual Frequency Narrow-Gap Reactive Ion Etching System

The effects of plasma-wall interactions on the plasma chemistry in a dual frequency narrow-gap reactive ion etching (RIE) system is investigated as a function of electron density, residence time, and partial pressure of additive O2 gas. It is found that there is a critical point in the residence time, where the dissociation dominant region and the wall-interaction dominant region are separated. The net flux of chemically reactive species is estimated. The net flux of carbon-inclusive ions is of the order of 1016 cm-2s-1, and is larger than that of CFx radicals. Carbon-inclusive and silicon-inclusive ions dominate the total flux of chemically reactive species. The deposition rate of the fluorocarbon film is strongly dependent on the O2 partial pressure, and is controlled by the chemical etching with oxygen as well as the reduction of fluorocarbon radical density in the gas phase. Based on the estimation of the net flux of chemically reactive species and the effect of added oxygen, dominant chemical species that control the etching reaction in the RIE system are discussed.

Substrate Effects on VOC Emissions from a Latex Paint

Abstract The effects of two substrates - a stainless steel plate and a gypsum board - on the volatile organic compound (VOC) emissions from a latex paint were evaluated by environmental chamber tests. It was found that the amount of VOCs emitted from the painted stainless steel was 2 to 10 times more than that from the painted gypsum board during the 2-week test period. The dominant chemical species emitted were also different between the two substrates. Data analysis indicated that most VOC emissions from the painted stainless steel occurred in the first 100 h via a fast, evaporation-like process. On the other hand, the majority of the gypsum board VOCs were emitted in a later stage via a slow, diffusion-controlled process. There were measurable emissions of VOCs 11 months after paint application on the gypsum board. It is suggested that, instead of the routinely used substrates such as stainless steel plates, real substrates such as wood or gypsum board should be used for the evaluation of emissions in indoor environments.

Effect of negative bias voltage on the microstructures of AlN thin films fabricated by reactive r.f. magnetron sputtering

Aluminium nitride thin films have been fabricated on silicon wafers by reactive r.f. magnetron sputtering in mixed Ar-N2 discharge with variation of negative bias voltage. The effect of negative bias voltage on the microstructures of AlN thin films have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), stress measurement, Auger electron spectroscopy (AES), etc. While the negative bias voltage was varied in the range 0 to −45 V, highly c-axis oriented film can be fabricated at −30 V, and the grain size and compressive stress increase with the negative bias voltage. From the plasma analysis, the dominant positive chemical species is identified as N+2 ions. The above results can be understood considering that at the kinetic energy transfer and flux of N+2 ions increase with increasing negative bias voltage.

Effect of Dry Density on Diffusion of Some Radionuclides in Compacted Sodium Bentonite.

Apparent diffusion coefficients were measured at room temperature under atmospheric condition by one-dimensional non-steady state diffusion for 3H, 90Sr, 99Tc, 129I, 137Cs, 237Np and 241Am in water-saturated compacted sodium-bentonite whose dry densities were 0.2–2.0 (x103kg/m3). Dry density of bentonite affected the diffusivity for the radionuclide and the apparent diffusion coefficient decreased with increasing dry density of bentonite. Small effect of dry density of bentonite on retardation factor which was derived from the apparent diffusion coefficient was indicated for 137Cs, 90Sr, 99Tc and 129I. On the other hand, the retardation factors of 237Np and 241Am showed a tendency of increasing with dry density of bentonite. Dominant chemical species of 237Np and 241Am in the pore water of bentonite were estimated NpO2(CO)3 5- and AmOH(CO3)3 2-, respectively and they possibly formed large anion. Distribution coefficient derived from the apparent diffusion coefficient showed a tendency of decreasing with increasing dry density of bentonite except for 237Np and 241Am whose coefficients were unchanged and were higher than values from Sorption Data Base of OECD/NEA. The decrease of the distribution coefficient may be caused by the change of the ion concentration in the pore water. The higher distribution coefficients of 237Np and 241Am may be caused by sorption, ion exclusion and molecular filtration.

Use of a high volume dichotomous virtual impactor to estimate light extinction due to carbon and related species in the phoenix haze

Size-fractionated atmospheric particulate matter samples were collected in Phoenix, Arizona by the newly developed high volume dichotomous virtual impactor and analyzed for a variety of the major and minor chemical species. From these data, the light extinction budget for the Phoenix aerosol was estimated by applying the visibility model developed for the Denver winter aerosol. The results for Phoenix indicate that scattering by particles plus the additional scattering due to the volume change when water becomes associated with the particles accounts for 56% of the atmospheric light extinction, while light absorption by particles accounts for about 35% of b ext. Elemental carbon appears to be the dominant chemical species responsible for visibility reduction in Phoenix accounting for 41% of b ext. Organic carbon, NH 4NO 3 and NH 4) 2SO 4 each account for only 15% of b ext. Gas absorption and scattering account for less than 10% of the light extinction.

OPTICAL PROPERTIES OF THE URBAN AEROSOL AND THEIR RELATION TO CHEMICAL COMPOSITION

Light extinction and resulting visibility degradation in an unsaturated precipitation-free atmosphere are determined by light absorption and scattering and are caused by a complex mix of natural components and anthropogenic pollutants. The paper reviews correlation studies relating light scattering and light extinction (visibility) to concentrations of sulfate mass, nitrate mass, the remainder of the mass, and in some cases organic aerosol mass, while accounting for variations in relative humidity. It is found that sulfate aerosol mass is the dominant chemical aerosol species affecting light scattering and extinction. The dominant effect of sulfate mass on light scattering and extinction, even when sulfates account for a relatively small fraction of the total mass, results from the fact that sulfates are secondary aerosols and are mostly found in the 0.1-1.0 micron size range (the particular size range that scatters visible light very efficiently).

Chemistry of the Castlereagh River, New South Wales

Preliminary studies of the chemical characteristics of the Castlereagh River were made in 1973. The concentrations of the major ions vary considerably with distance from the head of the river and this variation shows a marked correlation with the geology of the catchment area. The order of dominance for ions within the system was found to be Na+ &gt; Ca2+ &gt; Mg2+ &gt; K+ and HCO3- &gt; Cl- &gt; SO42- for the main river, and creeks in the eastern catchment gave Mg2+ &gt; Ca2+ &gt; Na+ &gt; K+ and Cl- &gt; HCO3- &gt; SO42-. The relative amounts of the dominant chemical species are discussed and suggestions are made for the possible origins of specific components.