Cathode Glow Discharge Research Articles

Liquid Cathode Glow Discharge as an Excitation Source for the Analysis of Complex Water Samples with Atomic Emission Spectrometry.

A liquid cathode glow discharge (LCGD) was developed as a low-power and miniaturized excitation source of atomic emission spectrometry (AES) for the determination of K, Na, Ca, and Mg in water samples from rivers and lakes. The discharge stability and parameter influencing the analytical performance of LCGD-AES were systematically examined. Moreover, the measurement results of water samples using LCGD-AES were verified by ion chromatography (IC). The results showed that the optimized operating parameters are a 660 V discharge voltage, pH = 1.0 HNO3 as the supporting electrolyte, and a 4.0 mL min–1 solution flow rate. High concentrations of some metals may interfere with the detection of Ca and Mg. Low-molecular-weight organic substances do not have a remarkable enhancement on signal intensity. With the addition of 0.5% cetyltrimethylammonium chloride (CTAC), the emission intensity of elements can enhance significantly. However, it is not used to further evaluate the analytical performance due to instability of plasma after adding CTAC. The maximum power of LCGD is 52 W. The limits of detection and precision (RSD, in 1 mg L–1) of K, Na, Ca, and Mg are 0.20, 0.02, 0.01, and 0.01 mg L–1 and 0.9, 1.5, 0.6, and 1.2%, respectively. The measurement results of K, Na, Ca, and Mg in water samples by LCGD-AES are basically in agreement with the reference values measured by IC. The recovery of samples ranged from 84 to 113% except for Na, suggesting that the measurement results have high accuracy and reliability. All the results indicated that the LCGD-AES can provide an alternative analytical method for in situ, real-time, on-line determination of K, Na, Ca, and Mg in water samples from rivers and lakes.

Evaluation of a sampling system coupled to liquid cathode glow discharge for the determination of rubidium, cesium and strontium in water samples

A simple sample introduction system has been successfully developed, and then integrated with liquid cathode glow discharge (LCGD) to form atomic emission spectrometry (AES) for the detection of rubidium (Rb), cesium (Cs) and strontium (Sr) in water samples by using a fiber-optic spectrometer, in which a buffer bottle was employed to improve the stability of microplasma, and a six-port valve equipped with sample loop was used to reduce the sample consumption and enhance the analytical precision and speed. The effects of flow rate, discharge voltage, supporting electrolyte and solution pH on signal intensity were examined systemically. The matrix interferences of major cations and anions in aqueous solution were also evaluated. The results indicated that the optimal operating conditions are 2.4 mL min−1 flow rate, 660 V discharge voltage and pH = 1.0 HNO3 as supporting electrolyte. Only Al3+ ions interfere with the determination of Rb, Cs and Sr. The limits of detection (LODs) of Rb, Cs and Sr are 0.18, 0.17 and 0.21 mg L−1, respectively, which are basically inferior to those of the closed-type electrolyte cathode atmospheric discharge (ELCAD). The relative standard deviation (RSD) is 2.7% for Rb, 2.0% for Cs and 2.5% for Sr, the correlationcoefficients (R2) of Rb, Cs and Sr are over 0.999, and the power is below 50 W. The measuredresults of Rb, Cs and Sr are in agreement well with the spiked values, and the satisfactory recoveries of standard addition are obtained between 97 and 111%. The advantages of small size, low sample and power consumption and high stability suggested that the LCGD-AES isa promising technique for the detection of Rb, Cs and Sr in water samples.

Sensitivity improvement of solution cathode glow discharge-optical emission spectrometry by external magnetic field for optical determination of elements

A method has been developed to improve elemental determination by solution cathode glow discharge (SCGD) optical emission spectrometry. The introduction of a 0.65 T external magnetic field to the plasma discharge cell considerably enhanced the metal signal. Compared with the field-free case under the same voltage condition (400 V), the net intensities of the atomic emission lines of Cd, Cu, Pb, and Zn are enhanced by a factor of 2.9, 2.3, 2.1, and 3.2 in the presence of the external magnetic field, respectively. Moreover, the external magnetic field improved signal stability and extended the discharge voltage range from 300–420 V to 340–510 V. When the voltage was 490 V with a 0.65 T magnetic field, the emission intensity can be further enhanced by a factor of 4.2, 3.7, 3.1, and 5.0 for Cd, Cu, Pb, and Zn, respectively. The established limits of detections (LODs) are several times better as those obtained without a magnetic field at 400 V. The accuracy of the proposed method was demonstrated by the determination of elements in the standard water samples.

In vitro antibacterial properties of MoO3/SiO2/Ag2O nanocomposite coating prepared by double cathode glow discharge technique

To obtain a self-disinfecting surface to combat nosocomial infections, in situ synthesis of the MoO3-SiO2-Ag2O nanocomposite antibacterial coating was prepared onto Ti–6Al–4V substrate via a double cathode glow discharge technique conducted in a Ar + O2 gas mixture. The phase composition, microstructure and chemical structure of the as-prepared coating were systematically characterized by means of a series of microscopic examination methods. The microstructure of the coating exhibited an amorphous/nanocrystalline architecture, and both the MoO3 and Ag2O crystallites were evenly embedded in an amorphous SiO2 matrix. Photocatalytic activities of the coating were evaluated by photodegradation of rhodamine B (RhB) dye. The results showed that the introduction of Ag2O enhanced photocatalytic activity of the MoO3-SiO2 nanocomposite coating. In vitro antibacterial activity of the MoO3-SiO2-Ag2O coating against Gram-negative bacteria, Gram-positive bacteria and fungi were investigated and compared with that of the MoO3-SiO2 coating under both dark and visible light conditions. The MoO3-SiO2-Ag2O coating possessed higher bactericidal activities than the MoO3-SiO2 coating, due to the combined effects of surface hydrophobicity, the release of Ag+ ions, surface acidic reaction and photocatalytic activity.

Plasma electron source for generating a ribbon beam in the forevacuum pressure range.

We describe a plasma-cathode electron beam source based on a hollow cathode glow discharge and operating in the forevacuum pressure range that produces a steady-state ribbon beam. The electron beam is generated in the pressure range of 10-30 Pa. A multi-aperture electron extraction and beam formation system is used to provide beam stability and enhanced uniformity of beam current density, allowing the use of this kind of device for beam-plasma surface modification over relatively large areas.

Investigation of slurry erosion-corrosion behavior of Ta(Si1−xAlx)2 nanocrystalline coatings

To enhance the erosion-corrosion resistance of titanium alloys, two Ta(Si1−xAlx)2 coatings with different Al content were deposited on Ti−6Al−4V alloy by double cathode glow discharge method. The coatings consist of single hexagonal C40 structured TaSi2 phase, which forms an equiaxed grain structure with an average diameter of ∼5 nm. Al addition was found to enhance the values of H/E and adhesive strength between the substrate and coating. The erosion–corrosion behavior of the coatings was studied in a liquid–solid acid slurry flow (specifically a medium of 5 wt% HCl solution that contained a 10 wt% concentration of silica-based sand) using electrochemical measurements, weight loss tests and SEM observation. The results indicated that the ternary Ta(Si0.875Al0.125)2 coating provided better protection, compared to the binary TaSi2 coating, against the combined attack of mechanical erosion and electrochemical corrosion in a liquid–solid acid slurry flow. This is attributable to high self-healing ability of the surface passive film and a higher H/E ratio.

Synthesis of spindle-like CuO nanoparticles by using cathode glow discharge electrolysis plasma

Spindle-like CuO nanoparticles (NPs) were prepared in a single-step approach by using a cathode glow discharge electrolysis plasma (CGDEP) technique with 2.5 g L−1 NaNO3 as an electrolyte and 1.0 g L−1 cetyltrimethylammonium bromide (CTAB) as a stabilizer. When a sufficiently high voltage (>280 V) was applied, plasma was generated around the Pt needle point cathode. The copper foil anode was gradually consumed and black CuO NPs appeared. The active species formed during the CGDEP process were recorded on an optical fiber spectrometry. The structure and morphology of the CuO NPs were characterized by XRD and SEM. The results showed that spindle-like CuO NPs with the length of 250–350 nm were formed at 300 V discharge voltage.

Ultra-sensitive determination of antimony valence by solution cathode glow discharge optical emission spectrometry coupled with hydride generation

An ultra-sensitive solution cathode glow discharge-optical emission spectrometry (SCGD-OES) method coupled with hydride generation (HG) for the determination of antimony valence is described.

Theoretical Study of Plasma Using Different Dimension of Hollow Cathode

This article deals about the theoretical study on DC hollow cathode glow discharge using different hollow cathode geometry. The mechanism of discharge is analyzed at various gas pressure and radial configuration. The dependence of temperature on gas pressure has been elucidated with the help of Scotty limit. Discharge behavior with radius has also been explained. It is revealed that floating potential increases as gas pressure increases whereas plasma potential decreases as gas pressure increases. This theoretical work resembles with the experimentally measured results. This work might be useful for the plasma processing for industrial purposes.

A novel method for producing NH4+ reagent ions in the hollow cathode glow discharge ion source of PTR-MS instruments

Proton-transfer-reaction mass spectrometry (PTR-MS) is seeing an increased use of NH4+ ions for the detection of amines and labile oxygenated organic compounds. NH4+ ions are usually generated from ammonia or ammonium-containing chemicals. We herein present a simple method for generating NH4+ reagent ions in the hollow cathode glow discharge ion source that nowadays most proton-transfer-reaction mass spectrometry (PTR-MS) instruments are equipped with. We show that NH4+ ions can be generated in high purity and yield by simply introducing a mixture of water vapor and nitrogen in the ion source. We also show that rapid switching (∼10 s loss of data) between the H3O+ and NH4+ operation modes is possible. Our new method can be easily implemented in most PTR-MS instruments that are currently in use, thus opening the possibility to easily operate the PTR-MS analyzer in the NH4+ chemical ionization mode.

Influence of the hole diameter in the perforated electrode on the parameters of electron beam generated by a forevacuum plasma electron source

We present experimental results on geometry optimization of the emission electrode in a plasma cathode electron source operating in the forevacuum range of pressure. For the 2-mm thick emission electrode, we have determined an optimal diameter of the emission aperture that provides the most efficient electron extraction from a hollow cathode glow discharge plasma in helium. At the working pressure of helium in the vacuum chamber 30 Pa, the beam power during emission from a single aperture can vary from 2 to 6 kW, while the beam diameter does not exceed 0.5 mm.

Influence of Ag alloying on the antibacterial properties, bio-corrosion resistance and biocompatibility of α-Nb5Si3 nanocrystalline coating

To improve the corrosion resistance and impart the bioactivity and antibacterial functionalities to titanium alloys for biomedical applications, α-(Nb1-xAgx)5Si3 compounds, with three different Ag contents, were deposited on Ti–6Al–4V by double cathode glow discharge method. The new α-(Nb1-xAgx)5Si3 coatings, each about 16 μm in thickness, exhibited a compact uniform structure, composed of equiaxed nanocrystalline grains. Nanoindentation measurements revealed that Ag alloying reduced the hardness (H) and elastic modulus (E) values of the α-(Nb1-xAgx)5Si3 coatings. Compared to Ti–6Al–4V, the α-(Nb1-xAgx)5Si3 coatings exhibited improved corrosion resistance in Ringer’s physiological solution, as well as newly added in-vitro bioactivity and antibacterial ability against both E. coli and S. aureus. A MTT assay experiment shows that the two α-(Nb1-xAgx)5Si3(x = 0 and 0.05) coatings were as non-cytotoxic as bare Ti-6Al-4V. However, the MC3T3-E1 osteoblast-like cell viability for the α-(Nb0.9Ag0.1)5Si3 coating was slightly reduced, suggesting that the proliferation of MC3T3-E1 osteoblast-like cell was affected to some degree by excess Ag added to α-Nb5Si3. Overall, the α-(Nb0.95Ag0.05)5Si3 coating provides an attractive combination of good bioactivity, high corrosion resistance and new antibacterial function, and thus demonstrates great potential for applications in orthopedic devices.

Determination of trace cadmium in zinc concentrate by liquid cathode glow discharge with a modified sampling system and addition of chemical modifiers for improved sensitivity

In this work, a sampling system of liquid cathode glow discharge (LCGD) was developed for the highly sensitive determination of Cd in digested Zn concentrate samples, in which buffer bottle was used to eliminate the pulsation of peristaltic pump and increase the stability of discharge, and six-port valve injection system was employed to ensure the continuity of discharge and improve the precision and speed of analysis. The results showed that the flow rate of modified LCGD is reduced to 2.4 mL min−1 from the previous 4.5 mL min−1. The presence of anions and cations does not significantly interfere with the detection of Cd. Compared with the addition of no chemical modifier, the net intensity of Cd with 0.15% hexadecyltrimethylammonium bromide (CTAB) and 18% formic acid is improved by 2.4- and 2.7-fold, respectively. The relative standard deviations with 18% formic acid, 0.15% CTAB and no chemical modifier are 0.87%, 2.01% and 2.39%, respectively. The sensitivity of Cd is improved with the addition of chemical modifiers by factors of 4.5 for 18% formic acid and 2.6 for 0.15% CTAB. The LOD with 18% formic acid for Cd is arrived at 0.0049 mg L−1 which improved by 2.7 times. The results measured by modified LCGD-AES are in accordance with the reference value as well as verification values measured by ICP-AES. In addition, the recoveries are in the range of 96.5–105.4%. The accuracy, reliability and practicality can satisfy the requirements of monitoring of trace Cd in complex samples.

A reactive-sputter-deposited TiSiN nanocomposite coating for the protection of metallic bipolar plates in proton exchange membrane fuel cells

To meet the needs of corrosion resistance and electrically conductivity for metallic bipolar plates that are employed in proton exchange membrane fuel cells (PEMFCs), a TiSiN nanocomposite coating was fabricated on to a Ti–6Al–4V substrate using reactive sputter-deposition through the double cathode glow discharge plasma technique. The microstructure of the TiSiN coating comprised nanocrystallite TiN grains embedded in an amorphous Si3N4 matrix. Electrochemical measurements were employed to investigate the corrosion behavior of the TiSiN coating in the simulated operating environments of a PEMFC, specifically 0.5 M H2SO4 solution containing different HF concentrations (namely 2, 4 and 6 ppm) at 70 °C pumped with H2 at the anode and air at the cathode. With increasing HF concentration, a higher corrosion current density and lower corrosion potential were observed from both the coating and the uncoated substrate, indicating that the addition of HF accelerated their corrosion rates under these conditions. Compared to the uncoated substrate, the TiSiN coating showed a markedly higher corrosion resistance at all HF concentrations. The passive film that formed on the TiSiN coating, with a resistance of the order of magnitude of ~107 Ω cm2, displayed good electrochemical stability and was less affected by changes in HF concentration. For the TiSiN coating, the values of interfacial contact resistance (ICR) were 14.7 mΩ cm−2 and 18.3 mΩ cm−2, respectively, before and after 2.5 h potentiostatic polarization with 6 ppm HF under cathodic conditions under a compaction pressure of 140 N cm−2. Both values are much lower than those for the bare substrate. Moreover, the TiSiN coating was shown to improve the hydrophobicity of Ti–6Al–4V that would help facilitate water management in the PEMFC operating environment. This coating, which exhibited excellent corrosion resistance, electro-conductivity and hydrophobicity, is therefore a promising material for protecting metallic bipolar plates from corrosive attack.

Analytical Performance of Hollow Anode-Solution Cathode Glow Discharge-Atomic Emission Spectrometry

A hollow anode-solution cathode glow discharge (HA-SCGD) was designed as a plasma excitation source for optical emission spectrometry. The operation parameters such as the discharge current, argon flow rate and solution flow rate were investigated. The spatial distribution profiles of normalized results of spectral bands and spectral lines were investigated and analyzed. The detection limits of Na, Li, K, Ca, Mg, Pb, Sr, Mn, Rb, Cs and Zn were 0.22, 0.69, 1.33, 240.37, 21.55, 529, 619.43, 209.51, 2.94, 7.13 and 206.95 µg L−1, respectively. The repeatability, expressed as the relative standard deviation for these elements, was determined to be within the range from 0.53 to 2.70%. The Ca, Fe, K, Mg and Na concentrations in a certified reference material were quantitatively analyzed, and the results obtained by the HA-SCGD system agreed well with the reference values. The results show that the HA-SCGD system accurately and stably determined metals in aqueous solution.

Classification of bottled mineral waters using solution cathode glow discharge optical emission spectroscopy and chemometrics methods

Water is the most important substance for daily life and contains minerals which play an important role in nutrition. In this study, seven kinds of bottled water in Chinese market were analysed and identified by the solution-cathode glow discharge optical emission spectroscopy (SCGD-OES) combined with chemometrics methods. The score matrix was obtained by principal component analysis (PCA), and the back propagation artificial neural network (BP-ANN) model was established to identify the kind of the brands of the bottled water based on their spectral properties. The average classification accuracy based on BP-ANN is 99.74%, support vector machine (SVM) model and linear discrimination analysis (LDA) model were also employed to classify the kind of the brands of the bottled water based on the PCA analysis results, and the correct identification rate based on SVM model and LDA model are 99.50% and 98.00%, respectively. It is confirmed that SCGD-OES combined with chemometrics methods is promising for automatic real time, reliable and robust measurement, and can be integrated into a simplified form for non-specialist users.

Spatially Resolved Characteristics of Solution Cathode Glow Discharge Source Coupled with an Interference Filter Wheel as Spectral Discrimination Device

Solution cathode glow discharge-atomic emission spectrometry (SCGD-AES) has attracted wide attention globally in recent years. The technology has the advantages of on-line detection of various metal elements, small volume, and convenience. In this work, the original spectrometer based on SCGD-AES technology was replaced by filter-wheel, photomultiplier tube (PMT) and picoammeter, which was named FPP spectral discrimination device. Analytical performance of the device with narrow-band monochromator (0.08 nm) was compared to its performance with wide-bandpass filters (10 nm) with optimized spatial. The relative standard deviation of SCGD-FPP for Na, K, Ca, Li, Sr, Rb, and Cs ranged from 0.2 to 0.8%, comparable to the 0.6 to 1.4% with the monochromator. With optimized spatial resolution, the detection limits ranged from 0.15 to 350 μg/L, and the optimal plasma spectral collected points of Na, K, Ca, Li, Sr, Rb, and Cs at 0.8 mm, 0.8 mm, 0.6 mm, 0.4 mm, 0.2 mm, 0.6 mm, and 0.6 mm, respectively. The deviation analysis of the samples containing Na, K, Ca, and Li were analyzed under optimal conditions. The results show that a SCGD-FPP source with spatial resolution improved the detection performance.

Effect of the Geometric of (Al) Hollow Cathode on Paschen Curves in Nitrogen

In this paper, an experimental study of DC hollow cathode glow discharge plasma at different nitrogen pressures ranged from (0.065 to 0.75Torr) has been proposed. Investigated was carried out under the influence of the hollow cathode geometry such as diameter and depth of hollow cathode on the breakdown voltage of the nitrogen gas, the discharge system consists of two electrodes, the cathode forms various geometrical shapes and anode as a disc- shaped with diameter (8.8cm). The electrodes are enclosed in a large cylindrical glass chamber of pyrex filled with nitrogen gas. Three important physical parameters affecting the condition of the discharge are the gas pressure, constant inter-electrode distance and the cathode geometry. We used the hollow cathode with geometric shapes such as Cylindrical, conical, oppressive and variable dimensions. The cylindrical and conical shapes have inner diameters (3 & 6) cm and repressive shapes have inner diameter (1 & 2) cm. The breakdown voltage Vb is shown to depend on the product (p.d), for lower values of pressure, p or gap, d. This work represents the investigation of the dependence of the breakdown voltage on the gas pressure and on the distance between electrodes and the cathode geometry. The minimum value of breakdown voltage increases with increases gap d or increase the diameter of the hollow cathode with the length of the cavity is fixed.

Battery-operated portable high-throughput solution cathode glow discharge optical emission spectrometry for environmental metal detection

In this study, miniaturized optical emission spectrometry (OES) based on solution cathode glow discharge (SCGD) was developed for the determination of metal elements in samples.

Determination of gallium in water samples by atomic emission spectrometry based on solution cathode glow discharge

A novel and rapid method was established for gallium determination by a home-made solution cathode glow discharger coupled with a portable fiber-optic spectrometer. Plasma was generated by the discharger and the emission line at 417 nm for gallium was observed with a portable fiber-optic spectrometer, whose spectral resolution was 1.1 nm based on the peak width of half height using a 10 mg/L gallium standard solution. The analytical conditions and instrumental parameters were optimized. The results showed acidity turned to be significantly influential for the emission intensity of the same sample. Therefore, acidity control of the testing solution was crucial. Under the optimized conditions, the limit of detection (LOD) for gallium was 0.47 mg/L calculated by 3SDblank/S. The stability was evaluated by the seven replicates of 10 mg/L gallium standard solution, and the relative standard deviation (RSD) was 2.1%. This method was applied to the analysis of gallium for river and waste water available in Beijing. The recoveries in the range of 92.0%–113.1% were acquired while the RSD values were below 7% (n = 5), which showed this method was feasible for gallium determination of real water samples. Moreover, only 1% HNO3 is demanded while the whole instrument is portable and works under ordinary atmospheric pressure so that the field test demand can be satisfied.