Low Argon Research Articles

Determination of Ni in Fe-based Alloys using Low Pressure Laser-Induced Argon Plasma Emission Spectrometry

In order to evaluate the analytical precision in low pressure laser-induced argon plasma emission spectrometry (LIPS), we conducted the determination of Ni in Fe-based alloys to consider the most suitable measurement condition, in particular, a gas pressure of argon and several measuring parameters for time-resolved observation. The selection of emission lines was an important factor to obtain a liner calibration curve depending on the concentration of Ni. The precision was generally inferior to analytical results in XRF and ICP-OES. However, the analytical value of Ni was obtained with good reliability, by averaging during replicate measurements. It was further shown the Ni content in Fe-Ni-X alloys would be determined by using calibration curves estimated from binary Fe-Ni alloys.

Synthesis, Crystal and Electronic Structures, and Magnetic Properties of LiLn9Mo16O35 (Ln=La, Ce, Pr, and Nd) Compounds Containing the Original Cluster Mo16O36

The new compounds LiLn(9)Mo(16)O(35) (Ln=La, Ce, Pr, and Nd) were synthesized from stoichiometric mixtures of Li(2)MoO(4), Ln(2)O(3), Pr(6)O(11) or CeO(2), MoO(3), and Mo heated at 1600 °C for 48 h in a molybdenum crucible sealed under a low argon pressure. The crystal structure, determined from a single crystal of the Nd member, showed that the main building block is the Mo(16)O(36) unit, the Mo(16) core of which is totally new and results from the fusion of two bioctahedral Mo(10) clusters. It can also be viewed as a fragment of an infinite twin chain of edge-sharing Mo(6) octahedra. The Mo(16)O(36) cluster units share some oxygen atoms to form infinite chains running parallel to the b axis, which are separated by the rare-earth and lithium cations. (7)Li-NMR experiments, carried out at high field on the nonmagnetic LiLa(9)Mo(16)O(35), provided insights into the local environment of the lithium ions. Magnetic susceptibility measurements confirmed the trivalent oxidation state of the magnetic rare-earth cations and indicated the absence of localized moments on the Mo(16) clusters. The electronic structure of the LiLn(9)Mo(16)O(35) compounds was analyzed using molecular and periodic quantum calculations. The study of the molecular orbital diagrams of isolated Mo(16)O(36) models allowed the understanding of this unique metallic architecture. Periodic density functional theory calculations demonstrated that few interactions occur between the Mo(16) clusters, and predicted semiconducting properties for LiLn(9)Mo(16)O(35) as a band gap of 0.57 eV was computed for the lanthanum phase.

Multiple scattering causes the low energy–low angle constant wavelength topographical instability of argon ion bombarded silicon surfaces

We show that holes and perpendicular mode ripples that are generated at low argon ion beam energies and incidence angles on room temperature silicon targets (C.S. Madi, et al., Phys. Rev. Lett. 101 (2008) 246102; C.S. Madi, et al., J. Phys. Condens. Matter 21 (2009) 224010) are caused by multiple scattering events from the impingement of the primary ion beam on adjacent silicon shields. We show that in a geometry that minimizes these multiple scattering events, only ultra-smooth stable silicon surfaces are for incidence angles <50° from normal. We present a revised topographical phase diagram of 250–1000eV Ar+ ion bombarded silicon surfaces in the linear regime of surface dynamics in the absence of secondary scattering effects. It is characterized only by a diverging wavelength phase transition from parallel mode ripples to a flat stable surface as the incidence angle falls below about 50° from normal incidence, and a crossover to perpendicular mode ripples as the incidence angle crosses above about 80°.

Development of a Small Size Spark Chamber by use of Automobile Spark Plug for the Purpose of Educational Demonstration

We constructed a small size spark chamber for use in educational demonstration at Korean high school. For produce required high voltage electrical pulses in the spark chamber, we used an commercial automobile spark plug. A 10 kV DC high voltage power supply which was needed also to operate spark chamber was made by use of Cockroft-Walton circuit. As a spark chamber inner gas, we used low cost argon gas. Finally, we observed electrical sparks which were happened by the incident cosmic muon particles in the spark chamber.

Raman characterization of the structural evolution in amorphous and partially nanocrystalline hydrogenated silicon thin films prepared by PECVD

AbstractHydrogenated silicon (Si:H) thin films were obtained by plasma‐enhanced chemical vapor deposition (PECVD). Raman spectroscopy was used to investigate the structural evolution in phosphor‐doped n‐type amorphous hydrogenated silicon thin films, which were prepared under different substrate temperatures and gas pressures. Meanwhile, the effect of nitrogen doping on the structure of P‐doped thin films was also investigated by Raman spectroscopy. Moreover, the transition from the amorphous state to the nanocrystalline state of undoped Si:H films deposited through low argon dilution was studied by Raman spectroscopy, X‐ray diffraction, and transmission electron microscopy. The results show that Raman spectroscopy can sensitively detect the structural evolution in hydrogenated silicon thin films deposited under different conditions in a PECVD system. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Influence of reactive gas and temperature on structural properties of magnetron sputtered CrSiN coatings

CrSiN coatings were deposited on stainless steel (Grade: SA304) and silicon Si(100) substrates, with varying argon–nitrogen gas proportions and deposition temperature, using reactive magnetron sputtering technique in the present work. The influence of sputtering (Ar) and reactive gas proportions (N2) and temperature on the structural properties of the CrSiN coating was investigated. A small amount of silicon content (3.67at.% Si) plays a crucial role in addition to the nitrogen content for the formation of different phases in the CrSiN coatings as observed in the present work. For example, the coating with comparatively low nitrogen content, 40% N2, during deposition, formed a crystalline structure consisting of nano-crystalline CrN which is separated by an amorphous SiN phase, as evident from X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The formation of CrN(111) and Cr2N(111) phases has occurred at 30% N2 with 3.67% Si content, which transformed in to CrN(111) and CrN(200) with increase in N2 content but with same Si content. The surface topography and morphology of the coatings were analyzed by atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM), respectively. A less columnar growth is observed in CrSiN coatings deposited at low argon content, Ar:N2 (20:80), and with 3.67at.% Si in the coatings. However, it becomes dense with increase in nitrogen content and temperature. The XRD analysis showed that the intensity of a dominating peak (111) is decreasing from (80:20) to (60:40) argon:nitrogen environment. With a further increase of nitrogen content, from (60:40), in the sputtering gas mixture, to (40:60) argon–nitrogen, there is a sudden increase in (111) peak and above (40:60), the peak reduction rate is very slow than the previous one. The (111) and (200) peak intensity variations are very limited due to high nitrogen content, above 50%, and considerable amount of Si atoms, 3.67at.%, present in the CrN coatings.

Effects of Specimen Surface Condition and Atmosphere on Small Punch Creep Property of Low Alloy Steel

The effects of various factors such as the surface finish condition of specimens, lubricant and argon gas flow rate on both the creep deformation behavior and time to rupture for 2.25Cr-1Mo low alloy steel used for boilers by small punch testing were studied. There was little difference in both the small punch creep deformation behavior and time to rupture due to the difference in surface roughness between #1200 polished specimens and those in mirror polished condition. The application of BN lubricant to the specimen surface resulted in the decrease in time to rupture, due to the lowering of friction coefficient. Furthermore, the time to rupture increased according to the increase of argon gas flow rate. The depth analysis by μ-ESCA for surface oxide film formed in an argon gas atmosphere demonstrated that the formation of Fe-rich oxide film with a low friction coefficient produced a decrease in time to rupture under a low argon gas flow rate condition. The formation of Cr-rich oxide film with high friction coefficient produced the increase in time to rupture under high argon gas flow rate condition. This suggests that the reliable control of argon gas flow rate is very important in order to evaluate the life of material by small punch creep testing.

Low Power Argon Laser-Induced Thermal Therapy for Subcutaneous Ehrlich Carcinoma in Mice Using Spherical Gold Nanoparticles

The present study examines the feasibility of a low power argon laser-induced thermal therapy to Ehrlich carcinoma, employing a direct administration of spherical gold nanoparticles (GNPs). This modality utilizes the advantage of strong surface plasmon resonance exhibited by spherical GNPs in the visible range. Ehrlich tumors were grown in female balb mice by subcutaneous injection of Ehrlich ascites carcinoma cells. GNPs with an average diameter 13 +/- 1.2 nm and optical density (ODlambda:518 nm = 3) were directly injected within the tumor interstitium. Tumors were then illuminated with a continuous-wave (CW) argon ion laser with irradiance 55 mW cm-2 for 45 min. All laser-GNPs treated tumors exhibited a significant suppression in tumor growth throughout 15 days. On the contrary, sham-treated group (laser treatment without GNPs injection) and control group (neither laser nor GNPs treatment) showed a progressive increase in tumor growth during the same period. Histopathological examination demonstrated extensive necrotic percentage in laser-GNPs treated group (90%) in comparison with sham (35%) or control group (3-7%). A wide-angle X-ray scattering also revealed detectable changes in tumor protein structure exposed to both laser and GNPs. It can be concluded from this study that the intense surface plasmon resonance exhibited by spherical GNPs in the visible range could be very useful as a noninvasive technique for photothermal therapy of skin or near-surface type tumors that need much less laser energy and lower concentrations of GNPs.

Surface studies of diamond‐like carbon films grown by plasma‐enhanced chemical vapor deposition

AbstractThe influence of plasma pressure on the surface morphology of diamond‐like carbon (DLC) films, synthesized by plasma enhanced chemical vapour deposition (PECVD) has been investigated. The DLC films have been grown at different methane–argon ratios. The grain size and the surface roughness have been studied as a function of plasma pressure. The morphology and surface roughness of the films have been inspected by atomic force microscopy. The film surface has also been characterized by Raman spectroscopy to study the hybridization of carbon in the film so as to evaluate its carbon composition. The results confirm that the film grown at low argon pressure has more uniform distribution on the substrate. The Raman spectrum indicates that increase in plasma pressure leads to a proportional increase in the amount of sp3 hybridized carbon in the grown film. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Oral bacterial deactivation using a low-temperature atmospheric argon plasma brush

Objective To study the plasma treatment effects on deactivation effectiveness of oral bacteria. Methods A low temperature atmospheric argon plasma brush were used to study the oral bacterial deactivation effects in terms of plasma conditions, plasma exposure time, and bacterial supporting media. Oral bacteria of Streptococcus mutans and Lactobacillus acidophilus with an initial bacterial population density between 1.0 × 10 8 and 5.0 × 10 8 cfu/ml were seeded on various media and their survivability with plasma exposure was examined. Scanning electron microscopy was used to examine the morphological changes of the plasma treated bacteria. Optical absorption was used to determine the leakage of intracellular proteins and DNAs of the plasma treated bacteria. Results The experimental data indicated that the argon atmospheric plasma brush was very effective in deactivating oral bacteria. The plasma exposure time for a 99.9999% cell reduction was less than 15 s for S. mutans and within 5 min for L. acidophilus. It was found that the plasma deactivation efficiency was also dependent on the bacterial supporting media. With plasma exposure, significant damages to bacterial cell structures were observed with both bacterium species. Leakage of intracellular proteins and DNAs after plasma exposure was observed through monitoring the absorbance peaks at wavelengths of 280 nm and 260 nm, respectively. Conclusion The experimental results from this study indicated that low temperature atmospheric plasma treatment was very effective in deactivation of oral bacteria and could be a promising technique in various dental clinical applications such as bacterial disinfection and caries early prevention.

Low power capacitively coupled plasma microtorch for simultaneous multielemental determination by atomic emission using microspectrometers

A new, low power capacitively coupled plasma microtorch (30 W, 13.56 MHz, 0.5 L min −1 Ar) was investigated in conjunction with commercially available microspectrometers for the simultaneous multielemental analysis by atomic emission spectrometry of liquid samples without desolvation. Emission spectrum is simpler than in ICP-AES, the resonance lines are the most intense, so that a microspectrometer with FWHM of at least 1.5 nm is satisfactory for the record. The deviation from the Boltzmann distribution for Fe I has demonstrated the departure from the LTE in plasma. The non-spectral matrix effects of Li, Na, K, Ca and Mg on analytes emission are depressive and depend on matrix volatility, ionization potential of the interferent and analyte excitation energy. The detection limits (μg mL −1) are in the range 0.003 (Li) and 1.5 (Mn). The use of the standard additions method allowed the simultaneous determination of elements in environmental certified reference materials with overall recovery of 95 ± 10% and relative standard deviation of 1.7–8.2%. Compared to the traditional ICP, the microtorch has a simple construction, runs at low argon flow and can be integrated in a portable system suitable for in-situ simultaneous determination of elements.

Synthesis of Aluminum Nanoparticles by Electromagnetic Levitational Gas Condensation Method

A novel electromagnetic levitational gas condensation (ELGC) system was designed and manufactured for the synthesis of aluminum nanoparticles. Both liquid and membrane filtration systems were used for collecting the nanoparticles. Effects of induction coil design, input power and gas flow rate were investigated. It was found that the wet collection in toluene resulted in a smaller particle size than the dry collection on membrane filter. While using low argon flow rate, coarser particles were produced, high argon flow rate intensified the particle coalescence. The best argon flow rate for the synthesis of aluminum nanoparticles was found about 10-15 lit/min.

A global (volume averaged) model of a Cl2/Ar discharge: I. Continuous power

A global (volume averaged) model is applied to a low pressure (1–100 mTorr) high density chlorine discharge diluted with argon. The model is found to be in fair agreement with measurements reported in the literature. Atomic chlorine is the dominating chlorine species at low pressures and low argon content, but with increasing pressure the discharge becomes less dissociated. As the argon content is increased the chlorine dissociation fraction increases and the decrease with pressure becomes less pronounced. The electronegativity was found to decrease proportionally to the argon dilution for a wide range of discharge conditions. The pressure dependence of the Cl+/n+ fraction was found to vary with argon content, from peaking at low pressures in a pure chlorine discharge to peaking at high pressures in an argon dominated discharge. The electron temperature increases with argon content at low and intermediate pressures but decreases at high pressures. Argon–chlorine reactions generally have only a small effect on the creation or destruction of chlorine particles, even at high argon content, except for the loss of Cl− which is rapidly neutralized by Ar+ ions in an argon dominated discharge. Surface losses are most important for positive ion loss at low pressures and become increasingly important when the chamber is made larger or argon is added to the discharge. Volume losses always dominate the loss of neutral Cl atoms at low pressures, but at moderate to high pressures as well when the chamber is either large or small. Argon dilution benefits the neutral surface losses in small chambers but the volume losses in large chambers.

High frequency microwave characteristics of amorphous FeCoNiB–SiO 2 thin films

A series of FeCoNiB–SiO 2 thin films were synthesized by RF magnetron sputtering. Effects of the Ni addition to FeCoB–SiO 2 system and the sputter pressure on microstructure and electromagnetic characteristics were investigated. It is found that appropriate increment of Ni content and suitable low argon pressure is of advantage to the high-frequency characteristics. High permeability and high magnetic loss in the GHz frequency range are achieved in the optimum process parameters. Both μ′ and μ″ are larger than 85 until 2.0 GHz and larger than 400 at 2.1 GHz, and the resistivity reaches 682 μΩ cm. These results show that the presented films possess potential in designing microwave absorbers or synthesizing EMI shielding materials.

Study of Ni2–Mn–Ga phase formation by magnetron sputtering film deposition at low temperature onto Si substrates and LaNiO3∕Pb(Ti,Zr)O3 buffer

Film deposition of Ni2MnGa phaselike alloy by radio frequency (rf) magnetron sputtering was performed onto bare Si(100) substrates and LaNiO3∕Pb(Ti,Zr)O3 (LNO/PZT) ferroelectric buffer layer near room temperature. The prepared samples were characterized using conventional x-ray diffraction (XRD), superconducting quantum interference device, and electron dispersive x-ray spectroscopy from scanning electron microscope observations. The optimized films deposited under high rf power and low argon pressure present good surface quality and highly textured phase crystallization. The positioning distance between the substrate and the target-holder axis has some limited effect on the film’s composition due to the specific diffusion behavior of each element in the sputtering plasma. Extended four pole high resolution XRD analysis allowed one to discriminate the intended Ni–Mn–Ga tetragonal martensitic phase induced by the (100) LNO/PZT oriented buffer. This low temperature process appears to be very promising, allowing separate control of the functional layer’s properties, while trying to achieve high electromagnetoelastic coupling.

Collisionless wave damping in neutral loop discharges

Heating mechanisms in a low pressure magnetized argon radio-frequency neutral loop discharge (NLD) are investigated. Results obtained in the NLD are compared with results obtained in an azimuthally isotropic m = 0 helicon discharge operated in the same setup. B-dot probe measurements are carried out showing that helicon waves are excited in the NLD. Phase resolved optical emission spectroscopic measurements demonstrate that electrons oscillate effectively not in the neutral loop (NL) but in a toroidal cusp located above the NL. In a simple transformer model we consider a diamagnetic current induced from the antenna windings into this cusp. The resulting calculated fields reproduce qualitatively well the measured helicon-NLD field. Furthermore, standing wave and beat patterns emerge in the axial direction. Depending on the dc magnetic field strength and plasma density different damping of the axial wave takes place. At strong damping, measured and calculated wave phase velocities approach the electron thermal velocity. Observed optical emission patterns corroborate the hypothesis of electron Landau damping being the main heating mechanism in both discharges.

Separation of Argon and Oxygen by Adsorption on a Titanosilicate Molecular Sieve

A titanosilicate molecular sieve adsorbent, Ba-RPZ-3, was synthesized and tested for its use in the separation of O2+Ar mixtures at room temperature. A clean resolution of both gases was achieved in pulse chromatographic experiments using a standard column (0.25″ OD, 3.5 grams of adsorbent). In another experiment, using a column containing 30 grams of adsorbent and a continuous O2+Ar feed at 10 cm3/min, argon breakthrough was detected more than 5 minutes before the oxygen breakthrough, and the separation was sufficiently sensitive to achieve quantitative separation of mixtures with low argon content (5% Ar). Equilibrium adsorption isotherms and isosteric heats of adsorption for oxygen and argon were found to be almost identical at room temperature. The thermodynamic selectivity was found to be mildly in favor of oxygen (∼1.1–1.2). However, the adsorption of oxygen was observed to be much faster than argon, indicating that the separation of the O2+Ar mixtures was based on the sieving properties of the adsorbent and the difference in sizes of O2 molecules and Ar atoms. This indicates that a suitably-oriented oxygen is physically smaller than argon, despite the fact that many references assume that oxygen is larger than argon.

Optical diagnostics of a low power—low gas flow rates atmospheric-pressure argon plasma created by a microwave plasma torch

We employ a suite of optical techniques, namely, visual imaging, optical emission spectroscopy and cavity ringdown spectroscopy (CRDS), to characterize a low power, low gas flow rates, atmospheric-pressure argon microwave induced plasma. The plasma is created by a microwave plasma torch, which is excited by a 2.45 GHz microwave with powers ranging from 60 to 120 W. A series of plasma images captured in a time-resolution range of as fine as 10 µs shows that the converging point is actually a time-averaged visual effect and the converging point does not exist when the plasma is visualized under high time resolution, e.g. <2 ms. Simulations of the emission spectra of OH, N2 and in the range 200–450 nm enable the plasma electronic excitation temperature (Texc) to be determined at 8000–9000 K, while the vibrational temperature (Tv), the rotational temperature (Tr) and the gas temperature (Tg) at different locations along the axis of the plasma column are all determined to be in the range 1800–2200 K. Thermal equilibrium properties of the plasma are discussed. OH radical concentrations along the plasma column axis are measured by CRDS and the concentrations are in the range 1.6 × 1013–3.0 × 1014 cm−3 with the highest density at the tail of the plasma column. The upper limit of electron density ne is estimated to be 5.0 × 1014 cm−3 from the Lorentzian component of the broadened lineshape obtained by ringdown spectral scans of the rovibrational line S21 of the OH A–X (0–0) band.

Investigation on Argon–Oxygen Plasma Induced Blood Compatibility of Polycarbonate and Polypropylene

Surface properties of polycarbonate and polypropylene were modified using low pressure radiofrequency argon–oxygen mixture plasma in order to increase their wettability and make them useful for biomedical applications. The effects of process variables on wettability and weight loss were studied statistically using response surface methodology. Increased surface energies were observed for both argon–oxygen plasma treated polycarbonate and polypropylene. Formation of aldehyde and hydroxyl groups on polycarbonate and hydroxyl group on polypropylene were the surface chemistry changes observed by means of Fourier transform infrared spectroscopy. Qualitative analysis of surface morphology was performed through scanning electron microscopy. A statistical model was developed relating the process variables with the responses: surface energy and percentage weight loss. The obtained statistical models were optimized to maximize the surface energy and minimize the percentage weight loss. Blood compatibility of the polymers was tested for control sample and polymers treated with argon–oxygen plasma at optimized conditions by measuring the partial thromboplastin time. Increased partial thromboplastin time (PTT) was observed for both polycarbonate (144 s) and polypropylene (149 s) after plasma treatment compared to both control samples (128 s).

Synthesis of Nanowires by Spray Pyrolysis

Nanowires of carbon as well as nickel‐carbon (Ni‐C) were synthesized by spray‐pyrolysis. The carbon nanowires were synthesized using methanol as a precursor while the Ni‐C nanowires were obtained by using nickel chloride methanol solution as feed. It was found that low argon carrier gas flow rates (&lt;100 cm3/min) and suitable reaction temperatures (∼700∘C) were found to be critical for the formation of wired structures. The formation of nanowires was quite sensitive to reaction temperature. Nanowires could not form at temperatures higher than 900∘C in the presence of hexane. Ruthenium chloride and nickel chloride dissolved in hexane and methanol resulted in carbon coated binary metallic nanoparticles. Morphological differences of carbon nanowires, Ni‐C wires and carbon coated binary nanoparticles were characterized by scanning electron microscopy (SEM) and energy‐dispersive X‐ray analysis (EDS). The formation mechanism for the wired structures is proposed to explain the structural results obtained.