Spark discharge assisted laser induced breakdown spectroscopy

Laser induced breakdown spectroscopy is combined with a spark discharge to operate in a laser triggered spark discharge mode. This spark discharge laser induced breakdown spectroscopy (SD-LIBS) is evaluated for Al and Cu targets in air under atmospheric pressure. Significant enhancement in the measured line intensities and the signal-to-background ratios, which depend on the spark discharge voltage and the laser fluence, is observed in spark discharge laser induced breakdown spectroscopy when compared to laser induced breakdown spectroscopy alone for similar laser conditions. The measured line intensities increase with the applied voltage for both targets, and the ratio of the measured line intensity using spark discharge laser induced breakdown spectroscopy to that using laser induced breakdown spectroscopy is found to increase as the laser fluence is decreased. For Al II 358.56, such intensity enhancement ratio increases from 50 to 400 as the laser fluence is decreased from 48 to 4 J/cm² at an applied voltage of 3.5 kV. Thus, spark discharge laser induced breakdown spectroscopy allows for using laser pulses with relatively low energy to ablate the studied material, causing less ablation, and hence less damage to its surface. Moreover, applying spark discharge laser induced breakdown spectroscopy gives up to 6-fold enhancement in the S / B ratio, compared to those obtained with laser induced breakdown spectroscopy for the investigated spectral emission lines.     

Investigation of the analytical performance of gliding spark source mass spectrometry (GSSMS) for the trace analysis of nonconducting materials

A radiofrequency (rf) spark discharge in vacuum developing across the surface of dielectrics – a so-called gliding spark – has been applied to the direct mass spectrometric trace analysis of nonconducting materials. The special configuration of the electrodes strengthened the electric field over the surface of a nonconducting sample and created optimum conditions for the sputtering and ionization of the sample material. Mass spectrometric investigations of the charge composition of atomic ion and molecular ion formation in radiofrequency gliding spark plasma showed a significant difference to that of the original rf spark discharge between two conducting electrodes. The analytical figures of merit (reproducibility, relative sensitivity factors and detection limits of chemical elements) of gliding spark source mass spectrometry have been studied by using the glass standard reference materials NIST SRM 610 and 611 for the determination of trace elements in glass matrix.     

Einfluß des Gefüges und der Entladungsgase bei der Spektralanalyse von Al-Legierungen

Studies of the spectrochemical behaviour of aluminium alloys subjected to spark discharge at high or medium frequency demonstrate how particularly type and concentration of the alloying element, the discharge gas and structure of the alloy are bearing down on the shape of the analytical curve and influence the quantitative analysis. Changes in the microstructure of Al-alloys, discovered both after spark and general treatment of the samples, shift the analytical curve markedly whenever Cu, Mg or Zn is the alloying element. Spark generating in different ambient gases yields similar effects. Heat developing during spark discharge initiates surface melting on the electrodes with the consequence of metallurgical changes in the original alloy. Proof was given by microprobe analysis that a sample becomes homogeneous in the course of this secondary localized melting process. Depth and nature of the affected zone is solely given by the ambient gas during discharge, if all the other parameters during spark generation are kept constant. The study demonstrates the influence of (A) the thermo-chemical behaviour of the aluminium alloys and (B) of the physical properties of the alloying elements under investigation on the spectroanalytical results.     

Investigation of the analytical performance of gliding spark source mass spectrometry (GSSMS) for the trace analysis of nonconducting materials

A radiofrequency (rf) spark discharge in vacuum developing across the surface of dielectrics – a so-called gliding spark – has been applied to the direct mass spectrometric trace analysis of nonconducting materials. The special configuration of the electrodes strengthened the electric field over the surface of a nonconducting sample and created optimum conditions for the sputtering and ionization of the sample material. Mass spectrometric investigations of the charge composition of atomic ion and molecular ion formation in radiofrequency gliding spark plasma showed a significant difference to that of the original rf spark discharge between two conducting electrodes. The analytical figures of merit (reproducibility, relative sensitivity factors and detection limits of chemical elements) of gliding spark source mass spectrometry have been studied by using the glass standard reference materials NIST SRM 610 and 611 for the determination of trace elements in glass matrix. Received: 31 March 1999 / Revised: 10 May 1999 / Accepted: 13 May 1999     

Improvement of Atmospheric Water Surface Discharge with Water Resistive Barrier

Atmospheric water surface discharge is a promising method for water treatment. The selection of discharge gap distance must take a pair of conflicting aspects into account: the chemical efficiency grows as the discharge gap distance decreases, while the spark breakdown voltage decreases as the gap distance decreases. To raise the spark breakdown voltage and the chemical efficiency of atmospheric pressure water surface discharge, resistive barrier discharge is introduced in this paper. Both the high voltage electrode and the ground electrode are suspended above water surface to form an electrode-water-electrode discharge system. The water layer plays the role of a resistive barrier which inhibits the growth rate of discharge current as voltage increases. Experiments conducted at different discharge gap distances and water conductivities indicate that both the spark breakdown voltage and the chemical efficiency are remarkably raised in comparison with traditional water surface discharge. After parameter optimization, the discharge reactor is scaled up with activated carbon fiber electrodes and advantages of water resistive barrier discharge are kept.     

Recent progress in mass spectrometry for inorganic analysis

Mass spectrometry for inorganic analysis was originally developed with an r.f. spark ion source, a double focussing Mattauch-Herzog mass spectrograph and photographic plate detection. Current equipment is roughly equivalent to that which became available more than 25 years ago, but considerable technological and methodological progress has been achieved recently. Ion bombardment developed into an interesting alternative ionisation method for solid samples. Secondary ion mass spectrometry (SIMS) is widely used for surface inorganic and organic analysis, and localised microanalysis. Other alternative excitation modes have been proposed more recently : the inductively coupled plasma, the hollow cathode discharge and the pulsed laser. The inductively coupled plasma source appears to be promising for the sensitive mass spectrometric analysis of solutions. The laser source is emerging as a viable alternative for the spark source in existing spectrometers because of its more reproducible operating characteristics and the localised nature of the laser-solid interaction. The pulsed laser has led to the development and commercialisation of sensitive microanalysers with a lateral resolution of 1–3 μm. These instruments make use of time-of-flight mass analysers.Advances in the measurement techniques and in the instrumentation are described and a few representative examples of state of the art performance are discussed. Examples are selected from the experience in our own laboratory with SSMS, SIMS with the ion microscope and laser microprobe mass analysis with the transmission type LAMMA instrument. They will be selected from the field of environmental analytical chemistry and from that of the analytical chemistry of pure industrially important materials.     

Mass spectrometric analysis of ceramic components for solid oxide fuel cells

For the determination of trace impurities in ceramic components of solid oxide fuel cells (SOFCs), some mass spectrometric methods have been applied such as spark source mass spectrometry (SSMS), laser ionization mass spectrometry (LIMS), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and inductively coupled plasma mass spectrometry (ICP-MS). Due to a lack of suitable standard reference materials for quantifying of analytical results on La _x Sr _y MnO₃ cathode material a matrix-matched synthetic standard-high purity initial compounds doped with trace elements-was prepared in order to determine the relative sensitivity coefficients in SSMS and LA-ICP-MS. Radiofrequency glow discharge mass spectrometry (rf-GDMS) was developed for trace analysis and depth profiling of thick non-conducting layers. Surface analytical techniques, such as secondary ion mass spectrometry (SIMS) and sputtered neutral mass spectrometry (SNMS), were used to determine the element distribution on surfaces (homogeneity) and the surface contaminants of SOFC ceramic layers.Dedicated to Professor Dr. rer. nat. Hubertus Nickel on the occasion of his 65th birthday     

Comparison of the efficiency of spark source, laser, glow discharge and secondary ion mass spectrometry for bulk analysis

Summary After describing the design and properties of the ion sources, the analytical performances of spark source, laser, glow discharge and secondary ion mass spectrometry are compared. The criteria are the sample requirements, the detectable elements, the detection limits, element sensitivity factors and the achievable accuracy. Typical areas of use for these methods are derived from these properties.

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Vergleich der Leistungsfähigkeit von Funkenquellen, Laser, Glimmentladungs- und Sekundärionen-Massenspektrometrie für die Bulk-Analyse

     

Redox processes induced in methemoglobin solution by mercury lamp UV light and spark-discharge plasma radiation

The buildup of–SH groups in methemoglobin by irradiation with emission of spark discharge plasma in air and UV light from a low-pressure mercury lamp (λ = 253.7 nm) has been studied. The concentration of–SH groups increases the during spark discharge treatment, with the methionine amino acid residue in the methemoglobin molecule being reduced by nitrous and peroxynitrous acids; the bonds in the methemoglobin molecule are destroyed within 20 minutes of the spark treatment. By the action of UV radiation, methionine is reduced through chromophores (tryptophan, tyrosine) and methemoglobin is reduced by O₂^.- radical ions to oxy- and deoxyhemoglobin.     

Quantitative distribution analysis of alumina inclusion particles in ferritic stainless steels by using laser‐induced breakdown optical emission spectrometry

This paper describes an analytical method for determining the spatial distribution of alumina inclusion particles in several ferritic stainless steels by laser‐induced breakdown optical emission spectrometry with a single‐shot laser scanned on the sample surface. For this purpose, an irradiation system, which comprised a Q‐switched Nd:YAG laser with an average energy of 50 mJ/pulse and a precisely driven X‐Y‐Z sample stage, was prepared. A Czerny–Turner‐mounting spectrograph equipped with an ICCD detector was employed for a time‐resolved measurement of the laser‐induced breakdown optical emission spectrometry signal. The intensity ratio of Al I 396.152 nm to Cr I 396.368 nm was measured each for the single shot, while the irradiation positions were step‐wise moved in the X‐Y direction and then the same sampling area was repeatedly irradiated by subsequent laser shots in the Z direction. The number of alumina particles was mapped from the intensity ratio of Al/Cr each for the irradiation points in both the lateral and in‐depth directions, enabling the distribution of alumina particles to be presented. The resolution of our measuring system was 40 μm in the lateral position and 6–7 μm in the depth direction, which were mainly determined by the crater size of a laser shot. A typical size of the alumina particles (several μm) was smaller than their resolutions; nevertheless, the suggested method would be still more effective to give the distribution of alumina particles, especially the coarse ones, because of its rapid response for the analytical result. Copyright © 2017 John Wiley & Sons, Ltd.     

火花放电原子发射光谱法测定钛及钛合金中主要元素

采用火花放电原子发射光谱法测定了钛及钛合金中碳、铁、铝和钒的含量。通过对钛合金样品的表面处理方式、氩气流量和压力、类型标准化等参数的摸索,确立了一套系统的分析方法。结果表明,4种元素测定的相对标准偏差在0.40%~6.8%,测定结果和化学湿法分析结果相比基本一致,比较适合批量检测。     

Degradation of Formic Acid in Different Oxidative Processes

Abstracts—The decomposition of formic acid by OH radicals produced upon UV irradiation of hydrogen peroxide or in a spark corona discharge between solid electrodes and water surface was studied. Experimental data for both processes are rationalized in terms of the same scheme of transformation of formic acid and various schemes of interaction of active species. The degradation yields in these processes are compared with those obtained in a radiation-chemical process. The yields with reference to the efficiency of the devices were shown to be close in value in all cases.     

火花放电原子发射光谱法测定钛及钛合金中主要元素

采用火花放电原子发射光谱法测定了钛及钛合金中碳、铁、铝和钒的含量。通过对钛合金样品的表面处理方式、氩气流量和压力、类型标准化等参数的摸索,确立了一套系统的分析方法。结果表明,4种元素测定的相对标准偏差在0.40%～6.8%,测定结果和化学湿法分析结果相比基本一致,比较适合批量检测。     

Study of Spark Discharge Assisted to Enhancement of Laser-Induced Breakdown Spectroscopic Detection for Metal Materials

In this work, laser triggered spark discharge was combined with laser-ablation under Air and Ar gases to investigate the characteristics of laser-ablated plasma emission. The experimental results show that the optical emission intensity is significantly enhanced by electric discharge compared to without discharge and the spectral emission time of plasma is much longer than that without discharge. The enhancement effect is more apparent in the presence of Ar ambient. In addition, the plasma temperature and electron density as well as limits of detections (LOD) have been determined. The better LOD can be attributed to the improvement of plasma. The higher plasma temperature and electron density indicate that the enhanced mechanism in emission intensity is predominated by the further excitation/ionization of the laser-ablated material by the spark discharge due to the energy deposition in the plasma.     

Evaporation of material and influence of auxiliary spark gap on the spectral excitation by means of laser emission spectroscopy for local analysis of graphite

For the determination of impurities in graphite, laser-micro-emission spectroscopy allows the analysis of much smaller sample areas than possible by spectroscopic analysis of arc or spark discharges.Because the maximum quantity of material which can be evaporated by a laser beam is only approximately 8μg, it was found necessary to introduce a spark gap above the evaporation pit to provide additional excitation of the plasma, thereby increasing the sensitivity of the analysis. In this way, the radiation intensity of the plasma was increased by two orders of magnitude.The effects of the spark gap parameters, voltage, capacitance and inductance, on the spectral excitation were investigated. Voltage and capacitance determine the energy supplied to the spark gap, whereas capacitance, together with inductance, controls the duration and characteristic of the discharge. To obtain the optimum additional excitation, the duration of the spark discharge had to be matched with the time taken for the material to evaporate.The catalytic effect of some impurity elements on the corrosion of graphite was identified by using the technique to analyse material in the corrosion pits of irradiated graphite fuel elements.     

Nonthermal Activation of Oxidation Reactions on Piezocatalytic Sensors in Determining Flammable Gases in Air

Experimental approaches to improving analytical characteristics of piezocatalytic sensors were described. Nonthermal activation of the oxidation of flammable gases in air was proposed for these purposes. Nonthermal activation of a system can be attained using either UV irradiation or a corona discharge. For both activation methods, mechanisms of the formation of analytical signals were considered. The analytical characteristics of procedures using corona discharge were significantly better than those of procedures using UV irradiation.     

Electrode phenomena in a medium voltage spark

The surface of aluminium samples containing approximately 5 % copper has been studied by means of high speed photography while it was being struck by single medium voltage spark discharges under atmospheric pressure. The formation of cathode spots was found to be dependent on the condition of the sample electrode surface and changed during the duration of one single discharge. Cathode spots have been observed under the impact of oscillating and damped spark discharges.     

Thermomechanical properties of polytetrafluoroethylene in different zones of impact of continuous CO2 laser radiation

The pseudo-network structure of the amorphous block of polytetrafluoroethylene is formed by branching points, the crystallites of low- and high-melting crystalline polymorphs and the cluster segments of macromolecules. The polymer treated by laser irradiation is amorphized, with the degree of amorphization and other changes depending on the radiation fluence. A depression of the molecular flow onset and initial melting temperatures of the crystalline polymorphs, a decrease in the molecular mass, and the disappearance of the crystalline branching points characteristic of the original polymer have been observed in the irradiated polymer. Areas with different degrees of modification of the molecular structure appear in the dynamic mode with moving boundaries during continuous CO₂ laser irradiation. The difference in absorbance of the crystalline and amorphous portions of the polymer at the laser emission wavelength and a relatively high transmittance make laser-induced degradation differ from thermolysis in contact with a hot surface.     

Influence of surface melting effects and availability of reagent ions on LDI‐MS efficiency after UV laser irradiation of Pd nanostructures

In this study, the influence of surface morphology, reagent ions and surface restructuring effects on atmospheric pressure laser desorption/ionization (LDI) for small molecules after laser irradiation of palladium self‐assembled nanoparticular (Pd‐NP) structures has been systematically studied. The dominant role of surface morphology during the LDI process, which was previously shown for silicon‐based substrates, has not been investigated for metal‐based substrates before. In our experiments, we demonstrated that both the presence of reagent ions and surface reorganization effects – in particular, melting – during laser irradiation was required for LDI activity of the substrate. The synthesized Pd nanostructures with diameters ranging from 60 to 180 nm started to melt at similar temperatures, viz. 890–898 K. These materials exhibited different LDI efficiencies, however, with Pd‐NP materials being the most effective surface in our experiments. Pd nanostructures of diameters >400–800 nm started to melt at higher temperatures, >1000 K, making such targets more resistant to laser irradiation, with subsequent loss of LDI activity. Our data demonstrated that both melting of the surface structures and the presence of reagent ions were essential for efficient LDI of the investigated low molecular weight compounds. This dependence of LDI on melting points was exploited further to improve the performance of Pd‐NP‐based sampling targets. For example, adding sodium hypophosphite as reducing agent to Pd electrolyte solutions during synthesis lowered the melting points of the Pd‐NP materials and subsequently gave reduced laser fluence requirements for LDI. Copyright © 2015 John Wiley & Sons, Ltd.