Argon Solutions Research Articles

Infrared spectra and density functional theory calculations of frequencies and intensities of 2-methyl-1,3-butadiene (isoprene) in liquid solutions of xenon (164 K) and argon (86 K)

The mid-infrared spectra of isoprene (2-methyl-1,3-butadiene) dissolved in liquid xenon at temperatures ranging from 164 K to 178 K were obtained using a Fourier transform infrared spectrophotometer and a low temperature cryostat. Additionally, spectra in the C–H region (2800–3200 cm−1) were obtained in liquid argon at 86 K. Spectra in cryogenic liquids show all hidden bands underneath the gas phase spectra. Frequencies of isoprene in liquid argon and liquid xenon solutions are lower with respect to gas phase. Density functional theory (DFT) was employed to calculate vibrational frequencies. Solvent effects were studied using the polarizable continuum model (PCM) demonstrating qualitative agreement with experimental frequency shifts in liquid Ar and Xe. This investigation is important for IR absorption studies of planetary atmospheres where the temperatures are similar (80 K–200 K) and the spectra could resemble the pseudo gas spectra in cryogenic liquids.

Equation of State of an Infinitely Dilute Solution of Argon in Water

A new equation of state is proposed for a solution of gas at infinite dilution, based on considering the interaction between a gas and a solvent at the microscopic level. It is used to describe the properties of an infinitely dilute aqueous solution of argon in a wide range of temperatures and pressures, including the supercritical region of water. It is shown that the resulting equation is capable of predicting the properties of an aqueous solution of an inert gas with high accuracy, based on a limited set of data at moderate temperatures.

Pentamethine sulfobenzoindocyanine dyes with low net charge states and high photostability.

A series of Cy5.5 dye analogs and targeted probes with net charges varied from -3 to 0 were synthesized by an optimized method, followed by comparing their spectral and photostability properties in saturated solutions of air, oxygen, and argon. The Cy5.5 analogs with reduced charge were relatively stable when irridated at their excitation maxima, with a trend of higher stability with lower net charge states. The photostability of dyes was markedly lower in pure oxygen and higher in inert argon relative to ambient atmospheric conditions. The stability of c(RGDyK) conjugates as models of targeted molecular imaging agents mirrored these results and demonstrated the practical utility of the new family of Cy5.5 fluorophores.

Interaction of metals and alloys with gas media under spark discharges

The paper studies the penetration of nitrogen, oxygen, hydrogen, carbon, argon and krypton into copper, nickel, molybdenum, titanium, aluminum, iron and different steels under the action of spark discharges in various media based on radioactive indicators using step-by-step radiometric analysis, macro-, micro-, electron-microscopy and activation autoradiography, Mössbauer and Auger spectroscopy, secondary ion-ionic emission, X-ray diffraction and X-ray microanalysis. The study describes distribution features of penetrating atoms and their concentration profiles. Phase composition of near-surface layers is also determined. It is shown that supersaturated solid solutions of iron in copper and copper in iron are formed during simultaneous iron and oxygen penetration in copper and spinel (Fe6Cu3O4)4. Diffusion of iron and carbon results in supersaturated solid solutions of iron and carbon in copper, copper and carbon in iron, graphite and cementite. Inert gases and nitrogen form solid solutions with copper. Phase composition of near-surface layers in Fe is determined. Iron dioxide FeO, a carbon solid solution in iron with fcc lattice γ-Fe, tetragonal martensite and cementite, two iron (III) hydroxide FeOOH modifications, a supersaturated solid solution of nitrogen and nitride Fe4N, solid solutions of inert gases in iron are formed in the diffusion zone. Simultaneous interaction of molybdenum with iron (the anode material) and various gases results in the formation of substitutional solid solutions of iron in molybdenum and molybdenum in iron, a small amount of interstitial solid solutions of nitrogen and carbon in molybdenum and nitrogen in iron, interstitial phases: molybdenum nitrides and carbides and traces of nitrides of iron (Fe4N, Fe2N) and Fe1,9Mo (λ) phases in the form of needles. Treatment of nickel with a nickel anode in the nitrogen medium promotes formation of a solid solution of nitrogen and nitride Ni3N in the matrix with preserved hexagonal symmetry and lattice parameters that are characteristic of this phase under equilibrium conditions. Atoms of oxygen, nitrogen, carbon and argon are present in the interstitial solid solutions in treatment of nickel in ambient air; however, oxides are not found even on the surface (in the layer ~200 nm). Interaction of titanium with atmospheric gases leads to formation of a solid solution of nitrogen, oxygen, carbon, hydrogen and argon in titanium and titanium nitride Ti2N (ε). Simultaneous saturation of the titanium surface with nickel and nitrogen in the interaction zone causes formation of phases in the following order: nickel nitride; a solid solution of nitrogen and titanium in nickel and a solid solution of both alloying elements in titanium.

Interaction of metals and alloys with gas media under spark discharges

The paper studies the penetration of nitrogen, oxygen, hydrogen, carbon, argon and krypton into copper, nickel, molybdenum, titanium, aluminum, iron and different steels under the action of spark discharges in various media based on radioactive indicators using step-by-step radiometric analysis, macro-, micro-, electron-microscopy and activation autoradiography, Mössbauer and Auger spectroscopy, secondary ion-ionic emission, X-ray diffraction and X-ray microanalysis. The study describes distribution features of penetrating atoms and their concentration profiles. Phase composition of near-surface layers is also determined. It is shown that supersaturated solid solutions of iron in copper and copper in iron are formed during simultaneous iron and oxygen penetration in copper and spinel (Fe6Cu3O4)4. Diffusion of iron and carbon results in supersaturated solid solutions of iron and carbon in copper, copper and carbon in iron, graphite and cementite. Inert gases and nitrogen form solid solutions with copper. Phase composition of near-surface layers in Fe is determined. Iron dioxide FeO, a carbon solid solution in iron with fcc lattice γ-Fe, tetragonal martensite and cementite, two iron (III) hydroxide FeOOH modifications, a supersaturated solid solution of nitrogen and nitride Fe4N, solid solutions of inert gases in iron are formed in the diffusion zone. Simultaneous interaction of molybdenum with iron (the anode material) and various gases results in the formation of substitutional solid solutions of iron in molybdenum and molybdenum in iron, a small amount of interstitial solid solutions of nitrogen and carbon in molybdenum and nitrogen in iron, interstitial phases: molybdenum nitrides and carbides and traces of nitrides of iron (Fe4N, Fe2N) and Fe1,9Mo (λ) phases in the form of needles. Treatment of nickel with a nickel anode in the nitrogen medium promotes formation of a solid solution of nitrogen and nitride Ni3N in the matrix with preserved hexagonal symmetry and lattice parameters that are characteristic of this phase under equilibrium conditions. Atoms of oxygen, nitrogen, carbon and argon are present in the interstitial solid solutions in treatment of nickel in ambient air; however, oxides are not found even on the surface (in the layer ~200 nm). Interaction of titanium with atmospheric gases leads to formation of a solid solution of nitrogen, oxygen, carbon, hydrogen and argon in titanium and titanium nitride Ti2N (ε). Simultaneous saturation of the titanium surface with nickel and nitrogen in the interaction zone causes formation of phases in the following order: nickel nitride; a solid solution of nitrogen and titanium in nickel and a solid solution of both alloying elements in titanium.

Argon–water system at low temperatures

The molecular dynamics method is used to simulate argon solutions in water and a thin water film–argon system at low temperatures. The correlation in motions of two closely spaced argon atoms is of another nature than the correlation of two neon atoms in a neon solid solution in ice II. The structure of hydrate shells of argon atoms contains five-membered rings composed of water molecules. The solubility of argon in a water film at low temperatures is noticeably higher than at room temperature. If a water film is first cooled to the glassy state and then argon atoms are added to it, then approximately as many argon atoms are absorbed on the film surface as they are present in a cooled film in equilibrium with the argon atmosphere. Argon atoms migrate from one pit to another on the rough surface of a solid water film.

Isolated spherical impurity in noble gas crystals

To explain the experimentally observed structural anomalies in diluted solid solutions of argon in krypton, we calculated the positions of atoms in a nine-layer spherical cluster of krypton with an argon atom in the center. The interaction was approximated with the Lenard–Jones potential. The substitution volume ω of an argon atom in the krypton crystal was calculated. It was shown that compared to the generally accepted estimates obtained within the nearest-neighbor approximation, the value of ω is approximately twice as small. This effect is explained by an additional repulsion of the first coordination sphere of krypton atoms arising as the krypton atoms approach each other upon their inward motion.

Experimental and Computational Study on the Solubility of Argon in Propan-2-ol at High Temperatures

An experimental and computational study on the solubility of argon in propan-2-ol at high temperatures and pressures was performed. The following values of the Henry’s law constant for the solution of argon in propan-2-ol were obtained: 58 ± 3 MPa at 480 K, 99 ± 3 MPa at 420 K, and 114 ± 2 MPa at 360 K.

C–H Infrared Absorption and Solubility of Ethylene, Propyne, 2-methyl-2-butene, and 2-methyl-1, 3-butadiene (Isoprene) in Liquid Argon Solutions

The solubility of ethylene (H2C=CH2), propyne (CH3-C≡C-H), 2-methyl-2-butene (CH3-CH=C(CH3)2), and isoprene or 2-methyl-1, 3-butadiene (H2C=C(CH3)-CH=CH2) in liquid argon has been measured using mid-infrared and near-infrared (NIR) absorption. Spectra were recorded in the C-H infrared (IR) region. Spectra were obtained at increasing solution composition until the magnitude of the integrated absorption band reached a maximum value, indicating a saturated solution. The approximate experimental solubilities are: (600 ± 100) ppm at 92 K for ethylene, (22 ± 9) ppm at 100 K for propyne, (9 ± 5) ppm at 100 K for 2-methyl-2-butene, and (12 ± 2) ppm at 86 K for isoprene. The experimental solubility values at the corresponding temperature were used with solubility parameters of two separate models: the perturbed-chain statistical associating fluid theory (PC-SAFT) and the regular solution theory. Solvent-solute interaction parameters k12 (PC-SAFT) and [Formula: see text] (RST) were obtained for each solute in the presence of argon as the solvent. Data from experimental measurements are important for more realistic simulations of solubility of solids in cryogenic liquids.

Features of relaxation processes in methane cryocondensates and weak methane solutions in nitrogen and argon

The paper presents results of IR-spectrometric studies of phase transition peculiarities in thin-film cryodepositsof methane and weak solutions of methane in nitrogen and argon in the temperature range from 12 K to 32 Kand at the deposition pressure of Р=10-4 Torr. The relation between the position of the absorption band ofdeformation vibrations ν4 and α-β phase transition in solid methane is established. Vibrational spectra ofcryodeposited mixtures of methane with argon and nitrogen obtained at various ratios of the componentsdemonstrate a correlation between the nitrogen or argon concentration and the absorption band ν4 position. Thepresence of 5% admixture of argon or nitrogen in the mixture leads to a violation of the reversibility of the α-βtransition. Although the initial heating of the sample from T=16 K to T=26 K clearly shows transition from theβ-phase to the α-phase at T=20 K, further heating and thermal cycling in the same temperature range results inthe spectrometer signal following a new trajectory, distant from the initial heating curve.

Treatment of gastric cancer cells with nonthermal atmospheric plasma generated in water.

Nonthermal atmospheric plasma (NTAP) can be applied to living tissues and cells as a novel technology for cancer therapy. The authors report on a NTAP argon solution generated in deionized (DI) water for treating human gastric cancer cells (NCI-N87). Our findings show that the plasma generated in DI water with 30-min duration has the strongest effect on apoptosis in precultured human gastric cancer cells. This result can be attributed to the presence of reactive oxygen species (ROS) and reactive nitrogen species (RNS) produced in water during treatment. Furthermore, the data show that the elevated levels of RNS may play a more significant role than ROS in the rate of cell death.

Synthesis of hydrophilic carbon nanoparticles from amino acids by pulsed arc discharge over aqueous solution in argon under near-critical pressure

Hydrophilic carbon nanoparticles (CNPs) were synthesized from amino acids using a pulsed arc discharge over an aqueous solution surface under pressurized argon at 4MPa. The CNPs produced using this method were highly dispersible in water because their surfaces were modified by hydrophilic groups derived from the amino acids. The number of carbons in the straight chain of the source amino acids affected the generation of the CNPs, leading to different particle sizes, crystallinities, and nitrogen compositions. The oxygen content in the CNPs was independent of the source amino acid, but the nitrogen content was affected by the atomic ratio of nitrogen in the source amino acid.

Thermal contraction of aqueous glycerol and ethylene glycol solutions for optimized protein-crystal cryoprotection.

The thermal contraction of aqueous cryoprotectant solutions on cooling to cryogenic temperatures is of practical importance in protein cryocrystallography and in biological cryopreservation. In the former case, differential contraction on cooling of protein molecules and their lattice relative to that of the internal and surrounding solvent may lead to crystal damage and the degradation of crystal diffraction properties. Here, the amorphous phase densities of aqueous solutions of glycerol and ethylene glycol at T = 77 K have been determined. Densities with accuracies of <0.5% to concentrations as low as 30%(w/v) were determined by rapidly cooling drops with volumes as small as 70 pl, assessing their optical clarity and measuring their buoyancy in liquid nitrogen-argon solutions. The use of these densities in contraction matching of internal solvent to the available solvent spaces is complicated by several factors, most notably the exclusion of cryoprotectants from protein hydration shells and the expected deviation of the contraction behavior of hydration water from bulk water. The present methods and results will assist in developing rational approaches to cryoprotection and an understanding of solvent behavior in protein crystals.

Magnetic Behavior of Solid Ar–O $$_2$$ 2 Solutions

Solid molecular oxygen presents an interesting example of a low-temperature crystal which exists within several different magnetic phases. When solid solutions of argon and oxygen are formed with molar concentrations of oxygen between 60 and 80 %, a new structural and magnetic phase, known as the \(\delta \)-phase, appears at low temperatures. In order to investigate the nature of the \(\delta \)-phase, we carried out SQUID magnetometry measurements solid argon-oxygen solutions made up of 74 % oxygen and 26 % argon. In particular, we performed measurements of the magnetic susceptibility of the solid solutions over complete temperature cycles and isothermally as a function of time. Taken together, the experimental data demonstrate that that the \(\delta \)-phase is not an equilibrium thermodynamic state of the solid solutions, but is instead only a metastable state.

Investigation of Cold Pressure Welding: Cohesion Coefficient of Copper

Joining materials by forming is an interesting approach to the manufacture of hybrid (multi material) parts. By establishing a cold pressure weld between metallic surfaces, high quality joints with superior properties can be achieved. Reliable cold welding conditions are difficult to set up, however, since the weld initiation requires extraordinary clean, virtually sheer surfaces. Until today such conditions could only be achieved under a high vacuum conditions. Various studies on cold pressure welding reported that under vacuum welds can be established at significantly lower deformation than in a normal atmosphere. Since adverse deformation is currently needed in industrial cold pressure welding processes like the cold roll cladding of metal bands, a new process with in-line electrochemical surface treatment, is investigated. The ECUF process is intended to supply clean and thereby highly activated surfaces to the cold pressure welding process.This paper presents first results on the weld-ability of copper specimens with regard to the influence of the welding environment: air, argon and KCl solution. Butt welds were made by pressure welding of previously fractured specimens.

Characterization of particles made by desolvation of monodisperse microdroplets of analyte solutions and particle suspensions for nanoparticle calibration in inductively coupled plasma spectrometry

Particles produced by low-temperature desolvation of monodisperse microdroplets of analyte standard solution and nanoparticle suspensions in argon were collected on Si-wafers and studied applying scanning electron microscopy and X-ray microprobe techniques. At desolvation temperatures of about 150 °C, the particles from standard solutions are most often spherical and solid with good reproducibility and the analyte elements together with the unavoidable accompanying elements from trace contamination seem to be homogeneously distributed in the particles. However, there are surprising exceptions, particularly at higher temperatures, where analyte elements are separated in the particle by reduction or crystallization, as shown with Au and Ca standard solutions, respectively. Drying droplets of a diluted suspension of 250 nm gold particles at 200 °C revealed another interesting result, the production of relatively stable concave balloons of ∼ 3 µm in diameter including the Au particles. The balloon sheath was formed of compounds made of the contaminant elements in the suspension. The morphology of the particles is discussed in consideration of the Peclet number, the ratio of evaporation rate to analyte diffusion coefficient. The consequences of particle size and morphology for calibration purposes in nanoparticle characterization by ICP spectrometry are discussed.

Molecular Dynamics Simulation of the Vibrational Energy Relaxation of I&lt;SUB&gt;2&lt;/SUB&gt; in Nano-confined Argon Solution

Molecular Dynamics Simulation of the Vibrational Energy Relaxation of I&lt;SUB&gt;2&lt;/SUB&gt; in Nano-confined Argon Solution

Thermal Lens Spectroscopy in Cryogenic Solutions: Analysis and Comparison of Intensities in CH4−N2 and CH4−Ar Liquid Solutions

The C-H (Delta upsilon = 6) absorption spectrum of methane has been obtained in liquid nitrogen and argon solutions using thermal lens spectroscopy. Mathematical models for continuous and periodic excitation were used to describe the concentration dependence of thermal lens intensities. Better fitting of the experimental results was accomplished by taking into account the periodic nature of the excitation. Comparison of thermal lens intensities in nitrogen and argon allowed calculation of relative enhancement factors. In dilute solutions, the intensity in liquid nitrogen was 1.39 +/- 0.08 times higher than that in argon. The literature estimation of this ratio is 1.49 +/- 0.61. In contrast to the estimated value, our result confidently shows actual variation in enhancement factors. This article not only shows the applicability of thermal lensing to cryosamples but also demonstrates that accurate measurements at low temperature are possible.

Thermal Lens Spectroscopy in Liquid Argon Solutions: (Δv = 6) C−H Vibrational Overtone Absorption of Methane

A dual-beam thermal lens technique has been used to obtain the absorption spectrum of the (Deltav = 6) C-H stretch of liquid methane and methane in liquid argon solutions. The lowest concentration detected was 1 x 10(-3) (mole fraction) of CH(4) in liquid Ar with a continuous wave laser power of 20 mW. The thermal lens signal is linear with the mole fraction of methane up to 1 x 10(-2) but not for higher concentrations. Considering the system CH(4)-Ar as an ideal solution, the factors that contribute to the thermal lens signal were calculated as a function of the concentration of methane. A mechanism of energy transfer based on the gas-phase results could explain qualitatively the dependence of the magnitude of the signal on the mole fraction of methane.

Computer simulation of structural properties of dilute aqueous solutions of argon at supercritical conditions

Computer simulation studies of aqueous solutions of argon are performed from ambient to supercritical conditions by using a recent polarizable potential model and the nonpolarizable simple point charge extended model. At T=673 K we compare the water-solute pair correlation functions of the argon-water mixture with recent experimental results obtained from neutron scattering experiments. The comparison shows that the introduction of the polarizable effects decreases the solute-water repulsion and improves the agreement with the experiment at supercritical conditions. In particular we find that the water-solute structure predicted by the polarizable model is in good agreement with the experiment.