Low Carrier Gas Flow Research Articles

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 (<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.

Simultaneous Desulfurization and Deoxidation of Molten Steel with in Situ Produced Magnesium Vapor

A new simultaneous desulfurization and deoxidation process of molten steel with magnesium vapor produced in situ by aluminothermic reduction of magnesium oxide is proposed. The pellets composed of MgO and Al are charged into an immersion tube and the magnesium vapor produced in situ by aluminothermic reduction of magnesium oxide is injected directly into molten steel to react with the dissolved sulfur and oxygen in it. Effects of various operating parameters on desulfurization and deoxidation are discussed.In the case of the high initial oxygen concentration, deoxidation of molten steel proceeds preferentially, and desulfurization does not take place. When the oxygen concentration in the melt is low enough, desulfurization of molten steel with magnesium vapor can proceed.A higher initial sulfur concentration increases the desufurization ratio of molten steel. The sulfur concentration in the melt tends to be in equilibrium with the magnesium partial pressure in the Mg–Ar bubble rather than the dissolved magnesium concentration in the melt. Increasing pellet mass promoted desulfurization of molten steel. The maximum desulfurization ratio of molten steel can be obtained at a relatively low argon carrier gas flow rate. In both cases of the porous magnesia and the dense alumina immersion tubes with injecting holes, addition of lime onto the melt surface increases the desulfurization ratio. The desulfurization using the dense alumina tube is accompanied by resulfurization more significantly at the later stage than that using the porous magnesia tube.

Investigation of copper layers deposited by CVD using Cu(I)hfac(TMVS) precursor

Chemical vapour deposition (CVD) of copper on titanium-coated substrates was performed in a stainless steel reactor using copper(I) hexafluoroacetylacetonate trimethylvinylsilane (Cu(I)hfac(TMVS)) as a precursor and nitrogen (N2) as carrier gas. Film resistivity, film composition and surface morphology were studied in relation to deposition temperature, process pressure and process gas flow ratio. The lowest resistivity value obtained was around 2 μΩcm. In addition, cross-sectional examination of the copper films, using a LEO SEM imaging system, indicated increased film porosity at higher deposition temperatures. An optimum carrier gas flow rate was determined: higher carrier gas flow rates caused excessive dilution of the copper precursor, whilst lower carrier gas flow rates weakened the transport of the copper precursor to the substrate. XRD data revealed formation of copper oxide (Cu2O) if annealing temperatures exceeded 450∘C for a period of 30 min.

The Characterization of an Electrothermal Vaporization‐Direct Current Plasma Atomic Emission Spectrometer for the Determination of Boron, Cadmium, Copper, Iron, and Lead

A graphite rod electrothermal vaporizer used to introduce microliter‐sized samples into a direct current plasma (DCP) atomic emission spectrometer is reported in this work. Several important experimental conditions were found to be important in achieving good analytical performance from the electrothermal vaporization (ETV‐DCP) system. A combination of lowered plasma electrode sleeve gas flow rates, when compared to that commonly used in the DC plasma jet, and relatively low carrier gas flow rates resulted in very good analytical performance. Relative precision for the ETV‐DCP instrument using B, Cd, Cu, Fe, and Pb solutions ranged between 4% and 10%. Limits of detection (LOD) lower than 100 pg were achieved for these elements, roughly an order of magnitude better than other ETV‐DCP studies that used commercial graphite boat/furnace combinations. In addition, good calibration linearity was observed, with 2–4 orders of magnitude linearity for the elements investigated.

Novel setup for investigation of the plasma conditions in direct sample insertion inductively coupled plasma atomic emission spectrometry (DSI-ICP-AES)

Insertion of a sample probe into the inductively coupled plasma (ICP) for direct sample insertion (DSI) could change the plasma excitation conditions. In this study, a novel setup is proposed for the investigation of the probe effects. A hollow graphite tube was used as a stand-in for the DSI sample probe to exert probe effects on the plasma. Laser-ablated testing elements (Fe, Zn and Mg) were introduced separately into the central channel of the plasma via the hollow graphite tube for measurement of plasma excitation temperature and electron number density. A relatively low Ar carrier gas flow rate (0.42 L min−1) was used to minimize perturbation to the plasma due to the gas flow. The study shows that the extent of reduction in plasma excitation temperature and electron number density increases with probe insertion position at all observation heights. In addition, the probe effects strongly depend on the relative distance of the observation position to the tip of the probe. The probe effects are the strongest near the tip of the probe and reduce at observation positions further away from the tip. Signal-to-background ratios (SBR) of the testing elements also depend strongly on the probe insertion position and the relative distance of the observation position to the tip of the probe. The SBR peaks at 5–10 mm above the tip of the sample probe. The vertical profile of SBR depends on analyte diffusion in the plasma and the plasma excitation conditions.

Combining single-element stored spectra for the simulation of experimental spectra using multichannel detection-based ICP-AES

Simple, linear combination of single-element stored spectra can simulate an experimental sample spectrum to facilitate line and background selection, taking into account the expected concentrations in the sample. Acquisition of UV–visible spectra with wavelength reproducibility is possible with the use of solid-state detectors, in this case an assembly of linear CCD array detectors set up on a Rowland circle. The feasibility of the procedure is illustrated with Co line selection in stainless steel at a 0.07% concentration. Because an Fe matrix does not produce significant non-spectral interferences, the influence of the operating parameters on the agreement between experimental and simulated spectra is not important, provided that the same conditions are used. In this case, it is sufficient to use the expected concentration for the computation. In contrast, for a matrix leading to non-spectral interferences, such as Na, robust plasma conditions are recommended, i.e., high power and low carrier gas flow rate, because they provide a flat change in the line intensity, regardless of the excitation energy. Instead of the concentration, a simple correction factor may be then used in the spectral combination, and may serve as an indicator of the presence of a non-spectral interference effect.

Comparison of matrix effects in inductively coupled plasma using laser ablation and solution nebulization for dry and wet plasma conditions

Matrix effects of calcium in inductively coupled plasma-atomic emission spectrometry were investigated. Matrix effects were studied by monitoring the excitation conditions of the plasma using Zn ionic to atomic spectral line intensity ratios. Dry and wet inductively coupled plasmas with robust and non-robust conditions were compared. Laser ablation and solution nebulization sample introduction were used to produce the dry and wet plasma conditions, respectively. Low (0.6 l/min) and high (1.0 l/min) carrier gas flow rates were used to produce the robust and non-robust conditions, respectively. No differences in the trend of matrix effects for dry and wet plasmas were observed at vertical positions above normal observation height (>8 mm height above load coil) for low and high carrier gas flow rates. However, matrix effects in the lower part of the plasma (<8 mm height above load coil) were significantly different between dry and wet plasmas when a high carrier gas flow was used. The differences are likely due to the desolvation process.

Effects of Particle Size Distribution on Inductively Coupled Plasma Mass Spectrometry Signal Intensity during Laser Ablation of Glass Samples

The relation between laser-generated particles and ICPMS signal intensity was investigated using single-pulse laser ablation sampling of solids. The particle size distribution of glass samples was measured using an optical particle counter for different laser ablation conditions. Ablation of a new surface produced fewer particles and lower ICPMS signal intensity than a preablated surface. Laser power density of 0.4−0.5 GW/cm2 was found to be a threshold value, across which particle size distribution changed. Laser beam diameter was a more influential parameter than power density in efficient particle generation. Particle loss during transport from the ablation chamber to the ICPMS was significant for a low carrier gas flow rate of 0.1 L/min, while almost no loss was observed for a higher flow rate of 0.26 L/min. The onset of ICPMS intensity time profiles decreased as more large particles were generated. ICPMS intensity data were calibrated with respect to the particle mass entering the ICPMS. Particle ent...

Effect of sodium during the aerosol transport and filtering in inductively coupled plasma atomic emission spectrometry

Robust conditions, i.e. high R.F. power and low carrier gas flow rate were used to minimize the role of the plasma and to emphasize the contribution of the sample introduction system in the effect of Na in ICP-AES. Two combinations of pneumatic nebulizers and spray chambers were selected to obtain different Na effects. A conespray nebulizer was used with a cyclone spray chamber, and a cross-flow nebulizer was coupled to a double-pass spray chamber. A decrease in the ICP-AES analyte signal was observed with Na solutions under so-called robust conditions, irrespective of the sample introduction system employed. The cross-flow nebulizer associated with the double-pass spray chamber was more sensitive to Na presence than the other combination. These observations can be partially explained by a decrease in the solvent transport rate observed in presence of Na. It has been found that, in every case, the presence of Na did not modify the characteristics of the primary aerosol, while the tertiary aerosol is significantly modified. Finer droplets were obtained at the exit of the spray chamber when Na was present. Also, recirculation of the aerosol led to a significant element enrichment of the largest droplets for the Na solutions. It can be concluded that the effect of Na occured during the aerosol transport and filtering through the spray chamber.

Comparison of the effect of acetic acid with axially and radially viewed inductively coupled plasma atomic emission spectrometry: influence of the operating conditions

Acetic acid was selected as a highly perturbing matrix for the comparison of matrix effects between axial and radial viewing modes in ICP-AES. The effect of acetic acid (5 and 10% v/v) on the intensities of various ionic lines in ICP-AES was studied under extreme operating conditions,i.e., robust and non-robust conditions. A cross-flow nebulizer associated with a double-pass spray chamber was chosen as a sample introduction system. The influence of the operating conditions on the Mg II 280 nm/Mg I 285 nm line intensity ratio was also studied. This work confirmed that, under so-called robust conditions, i.e., high rf power and low carrier gas flow rate, the acetic acid caused an enhancement of the signal intensity, regardless of the energy line and the viewing mode, which could be assigned to a change in the aerosol formation and transport. An increase in the solvent transport rate and a significant modification of the primary, and especially the tertiary, aerosol drop size distributions were observed in the presence of acetic acid. Hence, finer aerosols were obtained when acetic acid was present.

Revisitation of the matrix effects in inductively coupled plasma atomic emission spectrometry: the key role of the spray chamber

The level of matrix effects observed in ICP-AES linked to a change in the matrix concentration is usually low, with the matrix being either the major element or a reagent such as an acid. However, the magnitude of the matrix effects depends on the ICP operating conditions. Under so-called robust conditions,i.e., high power and low carrier gas flow rate, matrix effects resulting from a change in the plasma conditions, i.e., temperature, electron number density and spatial distribution of the various species, are minimized to the same extent, regardless of the element and line. Robust conditions can be verified by using the ratio of an ionic line intensity to an atomic line intensity, the Mg II/Mg I ratio being commonly used. The remaining depressive effect is assigned to the sample introduction system, and it can be demonstrated that the effect occurs during aerosol transport and filtering. This phenomenon emphasizes the key role of the spray chamber in the matrix effects.

Comparison of Axially and Radially Viewed Inductively Coupled Plasma Atomic Emission Spectrometry in Terms of Signal-to-Background Ratio and Matrix Effects

A comparison was made of axial and radial viewing modes in terms of the signal-to-background ratio for several commercially available ICP-AES systems. The average improvement factor was found to be in the range of 2–3 for ionic lines when the axial viewing mode was used. To obtain higher improvement factors, other modifications of the ICP systems must be associated with axial viewing, such as better practical resolution of the dispersive system and better efficiency of the sample introduction system. Matrix effects with axial viewing, such as those resulting from the presence of Na, can be minimized to the same extent as for radial viewing provided that a high rf power and a low carrier gas flow rate are used to optimize the exchange of energy between the surrounding plasma and the central channel. An increase in the id of the torch injector is also beneficial for this purpose.

Effect of power and carrier gas flow rate on the tolerance to water loading in inductively coupled plasma atomic emission spectrometry

The effects of the carrier gas flow rate and the power on the amount of water that can be tolerated by the plasma have been studied by ICP-AES. Pneumatic nebulization, ultrasonic nebulization associated with desolvation and laser ablation have been used to obtain wet, partially desolvated and dry aerosols. It has been found that water is beneficial in improving the plasma electron number density and the excitation temperature when so-called robust conditions are used, i.e. high power and low carrier gas flow rate. This can be explained by the release of hydrogen. Under these conditions, desolvation had almost no effect on the plasma characteristics. When non-robust conditions were used, the plasma was highly sensitive to water loading. Desolvation led to an improvement in the plasma conditions. In this instance, the addition of hydrogen was most useful to restore the properties of the plasma and to act as a load buffer to minimize the matrix effects. The plasma characteristics have been evaluated based on simple diagnostics such as the Mg II/Mg I line intensity ratio, the Fe excitation temperature, the Ar line and the Ar continuum.

Dissociation of analyte oxide ions in inductively coupled plasma mass spectrometry

Analyte oxide ions have been studied in inductively coupled plasma mass spectrometry as a function of the sampling position, the carrier gas flow rate and the efficiency of the energy transfer from the plasma to the sample, in order to support the hypothesis of analyte oxide formation in the plasma. Lanthanum was selected as the test species owing to its high oxide bond strength, and its behaviour was compared to that of Pb as this element has a low oxide bond strength. A prototype ICP mass spectrometer was used. The LaO+: La+ ratio was found to be in the 0.2–13 000% range under the operating conditions used. Energy transfer was either degraded by adding a sheathing gas or improved by adding hydrogen. The LaO+: La+ ratio was minimized for low carrier gas flow rates and an efficient energy transfer. This was corroborated by temperature optical measurements. The results are in good agreement with those found in other recent work. In any instance, the role of the sampling position was found to be crucial in studying analyte oxide ion behaviour and optimizing analytical performance.

Beta -diketonate precursors for the chemical vapour deposition of YBaCuO

The quality of the starting materials, especially of the Ba compounds, is highly important in the CVD process for YBaCuO. The authors describe details of the preparation, the handling and the transport rates of 2,2,6,6-tetramethyl-3,5-heptanedionates of Y, Ba and Cu. A major problem with the Ba precursor is found in an aging process at room temperature that can be overcome by storage at low temperature. The vapour pressures of the precursors are derived from the transport rates at low carrier gas flow rates and compared with published data.

Application of the “cooled needle” technique to split and splitless sampling onto capillary columns

AbstractCooled needle sampling using syringes was applied to splitless injection and to simulated distillation analyses. Slight changes of the construction of the previous device are also described. The changes concern the temperature profile within the injector and especially the vaporization insert. Even with the low carrier gas flow through the injector during splitless injection, discrimination by component volatility can be avoided. Precision and accuracy of simulated distillation data obtained with split sampling also can be improved by the cooled needle technique.

A study of the interference of cesium and phosphate in the low power inductively coupled radiofrequency argon plasma using spatially resolved emission and absorption measurements

The literature on interferences in the radio frequency inductively coupled atmospheric argon plasma (ICP) is reviewed. Even for the most extensively investigated interferences of aluminium, phosphate and alkali elements on calcium, the studies are mostly descriptive. Interpretation of these data is impeded by conflicting results, the absence of thermal equilibrium and the lack of radially resolved observations. The present study of a low-power ICP (0.5 kW) utilizes the Abel inversion technique for emission and absorption measurements of atom and ion lines to clarify the mechanism of interferences on calcium and magnesium due to phosphate and cesium. Under conditions of large carrier gas flow (4.5 1/min) the pronounced interferences are the result of three combined effects: volatilization interference, a change in excitation temperature and a shift in the ionization equilibrium. At lower carrier gas flow (1.4 1/min) the interferences are markedly reduced but still due to the same three effects. The relative preponderance of a particular type of interference depends upon the height of observation and upon the particular combination of analyte and interferent considered.

The negative alkali flame detector response

Under certain conditions, the alkali flame detector will give negative response (inverted peaks) for organic compounds containing halogen, nitrogen, or other elements. With a modification of the alkali flame detector particularly suited for such a study, the range and magnitude of negative response was defined in terms of alkali bead bore, hydrogen flow, carrier gas flow, electrode height, and other parameters. Organic compounds containing chlorine, bromine, iodine, and nitrogen, were used as test substances; an organophosphate was studied under the same conditions for purposes of comparison. Cl, Br, I, N, and C can show either positive or negative response and each can be distinguished from the others by proper choice of parameters. Both halides and carbon compounds show stronger response in the negative mode than in the positive mode. The use of two different carrier gases, nitrogen and helium, did not cause significant differences, except in its effect on the response of nitrogen compounds. In general, a large bead bore, a high hydrogen supply and/or a low carrier gas flow favor negative response. These are also the conditions which establish a large area of contact between flame and alkali surface and, consequently, a large background current. In order to obtain reproducible response of adequate magnitude, the Rb 2SO 4 salt surface must be smooth and homogenous. The described detector functions can be used for qualitative microanalysis of hetero-organic compounds by gas—liquid chromatography.

Deposition and Microstructure of Vapor‐Deposited Silicon Carbide

Vapor deposition of Sic from methyltrichlorosilane in a fluidized bed and the microstructure of the deposit were studied over a range of deposition temperatures, carrier gas flow rates, and reactant fluxes. The rate‐determining factor for the deposition of Sic was the rate of supply of reactant. The microstructure of vapor‐deposited Sic was primarily dependent on the deposition temperature; however, carrier gas flow rate and reactant flux had a secondary influence on microstructure. At low temperatures and high carrier gas flow rates, laminar deposits containing excess silicon were produced. At higher temperatures and lower carrier gas flow rates deposits were characterized by faulted columnar grains. The grain diameter increased from about LP at 1400°C to about 15 μ at 1800°C. The grain size also increased, but less markedly, with increasing reactant flux. The deposits characterized by columnar grains were predominantly β‐Sic with traces of a‐SiC and excess carbon.