Surface Activity Of Particles Research Articles

A COMPARATIVE STUDY OF ALUMINUM OXIDE NANOPARTICLES SYNTHESIZED IN PLASMA DISCHARGE UNDER ULTRASONIC CAVITATION AND BY LASER ABLATION FOR CREATION OF COMPOSITE MATERIALS

In this work, aluminum oxide nanoparticles were fabricated by two physical methods: laser ablation in liquid medium and plasma discharge under the action of intensive ultrasonic cavitation. Dynamic light scattering, scanning electron microscopy, and electrokinetic potential measurements were employed to comparatively examine the nanoparticles obtained by both methods. It was found that the synthesized particles had spherical shapes with a size range of about 50-70 nm and relatively narrow particle size distributions and were stable to aggregation and sedimentation. The electrokinetic potential values of the pure particles and the effects of the presence of water-soluble polymer polyethylene glycol were used to examine the surface properties of the nanoparticles. This study demonstrates the effect of ultrasonic action on particle surface activity.

Nanoparticles as Potential Agents of Chemical and Biological Weapons

The wide distribution in industry, medicine, agriculture, and other areas of human activity of nanoscale objects raise the question of the possibility of their dual use, which in this work means the use for deliberate mass destruction of people. The aim of the work is to consider nanoparticles as potential agents of chemical and biological weapons. Nanoparticles of any type have been shown to have biological activity. This is due to an increase in the surface activity of particles during the transition from microscale to nanoscale and their ability to penetrate the cell, especially cell nucleus. Being non-biological objects, interacting with cell receptors, distorting intracellular signaling pathways and affecting the genetic regulation of the cell, they can cause a variety of pathological effects (oxidative stress, neuroinflammation, neurodegeneration, etc.). Therefore, with the transition from microscales to nanoscales, essentially remaining chemical compounds, particles of non-toxic materials can transform into potential biological and chemical damaging agents. The existing possibilities of their mass use through the respiratory system, skin, gastrointestinal tract and through the introduction of injectable forms of drugs suggest that based on damaging agents of this type, weapons of mass destruction of a new type that are not subject to the Conventions on the Prohibition of Chemical and Biological Weapons can be developed. It is necessary to start developing methods for detecting nanoparticles and other nanoobjects in various environments surrounding a person, food and dosage forms

Observation of the depassivation effect of attrition on magnesium silicates' direct aqueous carbonation products

The main obstacle to the aqueous carbonation of non-serpentinised magnesium silicates is the formation of surface passivation layers, which severely limits the reaction rate and thus the overall efficiency of the process. A technological solution to overcome this problem is to perform the carbonation process inside a stirred bead mill, which aims to continuously remove the surface by-product layers by attrition. In this work, the aqueous carbonation of ferronickel slag, a mineralogically complex mining waste composed of a Mg/Si rich amorphous phase and a crystalline ferrous forsterite, was studied at 150°C and under 10 bar of CO2 with different operating configurations: carbonation alone (C mode), attrition followed by carbonation (A-C mode) and concomitant attrition and carbonation (AC mode). By careful observation of the mineralogy and the surface of the secondary phases formed using complementary analytical techniques, the article allows a better understanding of the passivation phenomenon inherent to the carbonation of magnesium silicates, and confirms the effectiveness of continuous surface mechanical depassivation for reaching high carbonation rates with this type of material. Comparative analysis of the products obtained with the three operating modes shows that a true synergy takes place between attrition and carbonation due to the combined effect of continuous exfoliation and mechanical activation of particle surface, which goes far beyond the simple increase in surface area due to particle size reduction. While mechanical depassivation is here substantiated by several evidence, the additional mechanochemical activation effect cannot be delineated from experiment; however its beneficial contribution to carbonation is inferred from its observation in A-C mode. The work finds that the synergy between attrition and carbonation also yields very characteristic products. They consist in micrometric agglomerates formed by bound spherical particles a few tens of nanometers in size. These particles themselves contain an entanglement of nanometric grains of carbonates and amorphous silica dispersed inside a magnesium-depleted alumino-siliceous matrix. These results confirm that concomitant attrition and carbonation offers one of the most promising pathways for developing direct aqueous carbonation processes with non-thermally activatable magnesium silicates.

Research perspectives on the photocatalytic activity of titanium dioxide: Catalytic assessment methods in solution and solid-state in relation to particle surface activity

A range of prepared titania nanoparticles were characterised by Brunauer-Emmett-Teller (BET) surface area, X-ray Diffraction (XRD), CPS Disc Centrifuge, Transmission Electron Microscope (TEM), Scanning Electron Micrographs (SEM), Thermogravimetric Analysis (TGA) and Fourier Transform Infrared Measurements (DRIFTS). In addition, the activities of the different catalysts were determined via rapid assessment methodologies like Microwave Dielectric Spectroscopy (MDS), Hydroxyl content, Phosphorescence and Chemiluminescence Spectroscopy and Isopropanol Oxidation Test and the data related to actual weathering properties of the pigments doped in metallocene polyethylene under dry and humid conditions. Quantum size effects, which lead to high surface areas and blue shifts and diminish electron–hole recombination, are used to explain the high activities of the nanoparticle products. In situ FTIR data and OH content determination show the presence of high contents of hydroxyl groups and large amounts of adsorbed water on TiO2 nanoparticles. The Disc Centrifuge results and BET surface area combined with the XRD particle size results show that a careful distinction between the crystal and aggregate sizes must be made in order to properly interpret the activity of TiO2 pigments. Aggregation of TiO2 pigments affects not only the surface area offered by the TiO2 but also the type of interaction between the light and the TiO2. The treatment conditions used for the crystallization of the primary material (precursor) in order to prepare the nanoparticle pigments, not only influenced the anatase crystal size but also other anatase properties (such as the surface hydroxylation, adsorbed water, recombination rate, aggregation state and type of structural defects). Chemiluminescence of the titania particles is discussed in light of potential surface active peroxidic species.

Using colloidal deposition to mobilize immiscible fluids from porous media

Colloidal particles hold promise for mobilizing and removing trapped immiscible fluids from porous media, with implications for key energy and water applications. Most studies focus on accomplishing this goal using particles that can localize at the immiscible fluid interface. Therefore, researchers typically seek to optimize the surface activity of particles, as well as their ability to freely move through a pore space with minimal deposition onto the surrounding solid matrix. Here, we demonstrate that deposition can, surprisingly, promote mobilization of a trapped fluid from a porous medium without requiring any surface activity. Using confocal microscopy, we directly visualize both colloidal particles and trapped immiscible fluid within a transparent, three-dimensional (3D) porous medium. We find that as non-surface active particles deposit on the solid matrix, increasing amounts of trapped fluid become mobilized. We unravel the underlying physics by analyzing the extent of deposition, as well as the geometry of trapped fluid droplets, at the pore scale: deposition increases the viscous stresses on trapped droplets, overcoming the influence of capillarity that keeps them trapped. Given an initial distribution of trapped fluid, this analysis enables us to predict the extent of fluid mobilized through colloidal deposition. Taken together, our work reveals a new way by which colloids can be harnessed to mobilize trapped fluid from a porous medium.

Spontaneous Formation of Double Emulsions at Particle-Laden Interfaces

Traditionally, double emulsions are produced in the presence of both oil-soluble and water-soluble surfactants in sequential droplet formation settings or unique fluidic designs. Micelles, assemblies of surfactants in liquid mediums, can generate single emulsion droplets without requiring input energy. We hypothesize that the synergy between nanoparticles in one phase, and micelles in the other phase can spontaneously generate double emulsions. Nanoparticles can become surface-activated by adsorbing surfactants and form the second type of emulsions from the initially emulsified phase by micelles. We design a thermodynamically-driven emulsification platform where double emulsions are spontaneously formed as soon an aqueous nanoparticle dispersion is placed in contact with an oleic micellar solution. Confocal and cryogenic-scanning electron microscopies are utilized to characterize structure and intensity of emulsions at various concentrations of silica nanoparticle and Span micelles. The rate of particle surface activation and emulsification and the amount of water intake are quantified using dynamic light scattering, dynamic interfacial tension, and density measurements. Nanoscale water droplets nucleate in the oil in form of swollen micelles. Over time, nanoparticles form a water-shell encapsulating the swollen-micelle rich oil phase. The gradual surfaceactivation of nanoparticles is key in self-double emulsification and controlling the emulsion intensity. We build on this new discovery and design a novel system for double emulsification. Incorporating nanoparticles into spontaneous emulsification systems opens novel routes for designing emulsion-based materials.

Modeling study of the bio-dissolution of copper concentrate in a continuous bioreactors system

The objective of the present research was to use two different bacterial cultures in continuous tank bioleaching circuits and to use this knowledge for mathematical modeling of the chalcopyrite bioleaching kinetic. Using three different particle size distributions (PSD) with the indices (d80) of 45, 32 and 16 µm of a chalcopyrite concentrate from the main Iranian copper processing plant and two types of bacteria, one and two-step continuous tests were performed in stirred tanks. In the first phase, tests were performed at 50 ± 2 °C using moderate thermophilic bacteria. The second part consisted of two-step continuous tests at 50 ± 2 °C using moderate thermophilic bacteria in the first reactor and extremely thermophilic bacteria at 65 ± 2 °C in the second reactor. The results of one-step continuous tests indicated that the highest rate of copper dissolution (5.21 g/l·day) resulted from test using feed with d80 = 16 µm. The Field Emission Scanning Electron Microscopy (FE-SEM) analysis of bioleaching residue indicated that the surface of particles was mostly covered with secondary layers. The Energy-dispersive X-ray spectroscopy (EDS) analysis of the formed layer revealed high concentrations of iron, sulfur and a certain amount of potassium. The results of two-step tests showed that under the specified conditions of this study, about 95% of copper was leached and transferred to solution. The analysis of FE-SEM and EDS residue indicated that the particle surface activity at this stage was higher than that of a single-step system probably due to the high temperature of the reaction medium (50 °C for the first reactor and 65 °C for the second reactor) and the presence of Oxidation-Reduction Potential (ORP) of solution in the range between 360 and 480 mV, Ag/AgCl. The results of the mathematical modeling for predicting the PSD of existing particles in the one -step reactor indicated that the maximum rate of size reduction kinetics was related to the first five days. The maximum difference between the experimental and predicted results was 19%. In case of two-step system, the reduction in particle size between the first and fifth days was significantly more than the next days. From the results of this study, it can be pointed out that firstly the two-steps bioleaching of chalcopyrite concentrate is more effective than the one-step and the reduction of particle size distribution can be predicted using the presented mathematical modeling.

Evolution of intermetallic compounds in Ti-Al-Nb system by the action of mechanoactivation and spark plasma sintering

The present study shows promising approach to produce hydrogen-accumulated rechargeable intermetallic compounds (IMC) from three-component powder composition Ti-25Al- 25Nb (at%), through experimentally chosen best modes and combined technological processes. The study includes research results on the effect of mechanoactivation (MA) process and following spark plasma sintering (SPS) technique on structural phase state of intermetallic Ti-Al-Nb composites. It was revealed that upon activation of the initial powder mixtures during their machining, intermetallic phases are formed by the interpenetration of aluminum into titanium and niobium lattices with the formation of solid solutions (Ti, Al) and (Nb, Al). It is found out, that the combination of MA and SPS is good for producing fine-graded predicted micro-structures in Ti-Al-Nb system owing to the activation of particle surface and formation of intermetallic phases at the preparation stage of powder mixture using MA technique as well as due to the effect of fast consolidation using SPS. This points to the fact of prospect for creating metal hydrides by combining MA and SPS techniques that makes it possible to obtain fine-grained IMC containing fair amount of O-phase.

Structure and stabilization mechanism of diesel oil-in-water emulsions stabilized solely by either positively or negatively charged nanoparticles

Two diesel oil-in-water emulsions were formed by using positively charged alumina nanoparticles solely and negatively charged silica nanoparticls solely as emulsifier, respectively. The formal systems are typical Pickering emulsions in which alumina nanoparticles adsorb at oil/water interface endowing droplets very good stability, whereas the later systems are non-Pickering emulsions in which silica nanoparticles do not adsorb at oil/water interface but distribute in aqueous phase surrounding the droplets endowing droplets temporary stability. Trace amounts of anionic surface-active materials in the diesel oil are responsible for the formation of two different emulsions. In the Pickering emulsions they adsorb at alumina particle surface to endow particle surface activity via in situ hydrophobization, whereas in the non-Pickering emulsions they adsorb at oil/water interface constituting a novel emulsion co-stabilized by like charged surfactants and nanoparticles at very low concentrations. By addition of trace amount of extra anionic surfactant, such as 0.1 mM sodium dodecyl benzene sulfate (SDBS), the novel diesel oil-in-water emulsions with good temporary stability can be formed by using silica nanoparticles at a concentration as low as 0.01 wt%. The emulsions can be demulsified easily by addition of trace amount (0.06∼0.1 mM) of a cationic surfactant such as cetyltrimethylammonium bromide (CTAB), or a low concentration (0.6∼3.0 mM) of divalent electrolyte such as CaCl2, and therefore have potential applications in oil transportation. On the other hand the Pickering diesel oil-in-water emulsions are relatively difficult to demulsify, and suitable demulsification protocols need to be developed for their applications in oil transportation.

Dependence of the Internal Structure on Water/Particle Volume Ratio in an Amphiphilic Janus Particle-Water-Oil Ternary System: From Micelle-like Clusters to Emulsions of Spherical Droplets.

Amphiphilic Janus particles (AJP), composed of hydrophilic and hydrophobic hemispheres, are one of the simplest anisotropic colloids, and they exhibit higher surface activities than particles with homogeneous surface properties. Consequently, a ternary system of AJP, water, and oil can form extremely stable Pickering emulsions, with internal structures that depend on the Janus structure of the particles and the system composition. However, the detail of these structures has not been fully explored, especially for the composition range where the amount of the minority liquid phase and AJP are comparable, where one would expect the Janus characteristics to be directly reflected. In this study, we varied the volume ratio of the particles and the minority liquid phase, water, by 2 orders of magnitude around the comparable composition range, and observed the resultant structures at the resolution of the individual particle dimensions by optical microscopy. When the volume ratio of water is smaller than that of the Janus particles, capillary interactions between the hydrophilic hemispheres of the particles induce micelle-like clusters in which the hydrophilic sides of the particles face inward. With increasing water content, these clusters grow into a rodlike morphology. When the water volume exceeds that of the particles, the structure transforms into an emulsion state composed of spherical droplets, colloidosomes, because of the surface activity of particles at the liquid-liquid interface. Thus, we found that a change in volume fraction alters the mechanism of structure formation in the ternary system, and large resulting morphological changes in the self-assembled structures reflect the anisotropy of the particles. The self-assembly shows essential commonalities with that in microemulsions of surfactant molecules, however the AJP system is stabilized only kinetically. Analysis of the dependence of the emulsion droplet size on composition shows that almost all the particles are adsorbed at the water-oil interface; i.e., the particles show ideal surface activity.

Foam stabilisation using surfactant exfoliated graphene

Liquid–air foams have been stabilised using a suspension of graphene particles at very low particle loadings. The suspension was prepared through the liquid phase exfoliation of graphite in the presence of the non-ionic tri-block surfactant, Pluronic® F108. The graphene particles possess an extremely high aspect ratio, with lateral dimensions of between 0.1 and 1.3μm as evidenced by TEM imaging. The particles were shown to exhibit a number of other properties known to favour stabilisation of foam structures. Particle surface activity was confirmed through surface tension measurements, suggesting the particles favour adsorption at the air–water interface. The evolution of bubble size distributions over time indicated the presence of particles yielded improvements to foam stability due to a reduction in disproportionation. Foam stability measurements showed a non-linear relationship between foam half-life and graphene concentration, indicative of the rate at which particles adsorb at bubble surfaces. The wettability of the graphene particles was altered upon addition of alkali metal chlorides, with the stability of the foams being enhanced according to the series Na+>Li+>K+>Cs+. This effect is indicative of the relative hydration capacity of each salt with respect to the surfactant, which is adsorbed along the graphene plane as a result of the exfoliation process. Thus, surfactant exfoliated graphene particles exhibit a number of different features that demonstrate efficient application of high-aspect ratio particles in the customisation and enhancement of foams.

微粒子接合による複合多孔構造の制御とその応用

Smart powder processing stands for novel powder processing techniques that create advanced materials with minimal energy consumption and environmental impacts. Particle bonding technology is a typical smart powder processing technique to make advanced composites. The technology has two main unique features. Firstly, it creates direct bonding between particles without any heat support or binders of any kind in the dry phase. The bonding is achieved through the enhanced particle surface activation induced by mechanical energy, in addition to the intrinsic high surface reactivity of nanoparticles. Using this feature, desired composite particles can be successfully fabricated. The second feature of this technology is its ability to control the nano/micro structure of assembled composite particles. As a result, it can custom various kinds of nano/micro structures and can produce new materials with a simpler manufacturing process. In this paper, particle bonding process developed by the authors will be introduced. New one-pot processes for controlling the microstructure of composite porous materials will be explained. They were developed by making use of particle bonding technology. Furthermore, their applications for high performance thermal insulation materials, electrodes of lithium ion battery and those of solid oxide fuel cells will be explained.

Preliminary characterization of plasma-sintered beryllides as advanced neutron multipliers

Advanced neutron multipliers with low swelling and high stability at high temperatures are desired for pebble bed blankets of demonstration fusion power (DEMO) reactors. Beryllium intermetallic compounds (beryllides) are the most promising advanced neutron multipliers. The plasma sintering method has been selected as a new synthesis method for beryllides because this method is very simple and easy to control. Plasma sintering is a non-conventional consolidation process. The plasma sintering results in starting-powder particle surface activation that enhances sinterability and reduces high temperature exposure. The sintering properties of beryllides were evaluated. Results show that intermetallic beryllide compounds such as Be12Ti, Be17Ti2 and Be2Ti can be directly synthesized by the plasma sintering method from mixed elemental powders of Be and Ti at a temperature below the melting point. The preliminary characterization of plasma-sintered Be–Ti beryllide was carried out including examination of oxidation with water vapor, microstructure analysis, irradiation effects, and deuterium retention compared with beryllium (Be) metal. The preliminary characterization revealed that the plasma-sintered Be–Ti beryllide sample performs well as a neutron multiplier. This beryllide sample has better oxidation resistance, higher radiation resistance and lower deuterium retention than Be metal.

Cementation of copper onto brass particles in a packed bed

The process of copper ion cementation from dilute solution was investigated using a packed bed column filled with brass particles. The influence of initial pH value of the treated solution, particle size and the solution flow rate on the cementation process was determined. It was observed that, in general, the process rate passes through an initial period of particle surface activation; a period of constant rate and a period of decreasing rate. Increasing the initial pH value of treated solution, the rate of cementation has significantly been slowed down and, at pH > 2.6, the process becomes very slow due to an H+-ions consumption and consequently measurable change of pH during the process. Using a packed bed of brass particles, it is possible to remove copper ions from feeding stream to a degree higher than 95% for about 20 - 30 minutes, i.e. an initial copper concentration of about 250 mg/dm3can be reduced to less than 10 mg/dm3. For an hour of the process time the initial level of Cu2+ can reach a value less than 1 ppm, meaning the investigated process is highly efficient. The concentration of zinc in the solution after cementation is about twice higher than the initial copper concentration in the feeding solution. The method of packed bed cementation, using brass particles, which are usually a secondary material for re-melting, could particularly be favorable instead of the conventional one, because zinc dust is being substituted with some less valuable starting material that could be upgraded on copper before its re-melting.

Surface patterning via evaporation of ultrathin films containing nanoparticles

The dewetting dynamics of ultrathin films containing potentially surface-active nanoparticles is considered in the presence of evaporation. Evolution equations for the film height and particle surface and bulk concentration are derived using a lubrication model coupled by a constitutive relation for the dependence of the viscosity on local particle concentration. A linear stability analysis and numerical simulations are used to determine how particle mass distribution depends on the various physical parameters such as equilibrium film separation distance, initial packing concentration, rate of evaporation, and particle surface activity. Our results show that when starting from an initially uniform distribution the particles become aligned into distinct “bands” in rectilinear geometry, or “rings” in cylindrical geometry. The functional dependence of the pattern spacing on relevant system parameters is studied and detailed herein.

Spark plasma sintering as advanced PM sintering method

A short overview of works on spark plasma sintering (SPS) is given in the present paper. SPS is a newly developed rapid sintering technique with a great potential for achieving fast densification results with minimal grain growth in a short sintering time. It is proven by obtained experimental data that enhanced sinterability of powders subjected to SPS mainly associated with particle surface activation and increased diffusion rates on the contact zones caused by applied pulse current. Application of rapid heating results in bypassing of low temperature regions where surface transport controlled sintering is dominant. This preserves the powder surface area to temperature levels where bulk transport is significant. However, the nature of activation effects, especially in its regards to acceleration of diffusion processes, is not clearly established. A lot of research work reports about the occurrence of plasma during the application of pulse current. However, the appearance of thermal plasma during SPS is a controversial issue and plasma-particle interaction is a complex phenomenon. Presently the industrial application of SPS processing is considered mainly in the areas where it is difficult or extremely difficult to obtain high performance materials and where normally HP or hipping processes are applied. Apparently significantly more work is required in this field for better understanding of the entire process and for making a stable ground for more extended industrial application of SPS.

Thin layer activation-based evaluation of tribological behaviour of light ion-implanted metallic samples

In our Cyclotron Laboratory wear and/or corrosion studies of metallic machine parts are performed on a routine basis by using the Charged Particle Surface Activation method, also commonly known as the Thin Layer Activation (TLA) technique. In principle, this method consists of an ion beam irradiation of the surface of interest (typically using proton and deuteron beams), followed by in-situ radioactivity monitoring, on a testing bench or in normal running conditions. The observed changes in radioactivity are then transformed in mass losses, by using a specific calibration procedure. In spite of the high reliability of the method, which allows fast and accurate determinations under real operating conditions, the issue of possible influence of ion bombardment upon the tribologic properties of irradiated components had yet to be clarified. To do that, a dedicated set-up was designed so as to ensure a simultaneous irradiation of the disk-shaped samples at various incident beam energies and doses. Since the expected structural modifications were associated not only to ion-induced damages, but also to the local heating, we tried to outline the contribution of each of the two above-mentioned effects. Consequently, the microstructure effects have been investigated by both electronic and metallography microscopy. The Vickers micro-hardness test has been taken before and after irradiation of each sample. Two main outcomes can be reported: the use of radioactive labelling for wear and corrosion control using MeV beams with doses below 10 17 ions/cm 2 of light particles such as protons and deuterons does not lead to significant changes of the tribologic properties of the studied machine part; and besides, wear diagrams (wear levels vs. running time) for Carbon Steel Alloy (OL-45 in Romanian standard, 0.45% carbon) and Cu 63 Zn 37 brass irradiated at different doses (10 17 – 10 18 ions/cm 2) have been obtained.

Resistance-to-wear testing of metallic machine components by charged particle surface activation

Surface activation, commonly known as Thin Layer Activation (TLA), is an ion beam technique generally employed for wear and/or corrosion monitoring in industrial plants, especially related to applications in engine and machine construction industries. For an efficient industrial application of this technique, one must foresee some specific irradiation set-ups as well as the measuring method, having in mind the diversity of machine components which might be subjects of such studies and the tribological phenomena involved. Some of these aspects are mentioned the paper. In principle, the TLA-based measuring methods exploit the correlation between the loss of material owing to wear and the resulting changes in radioactivity. Two such measuring methods are derived; they will be reviewed briefly in the paper and illustrated by wear diagrams obtained for several parts of running machines such as piston-rings, linear cylinders and bearing crankshafts, together with a study of characteristics of different (unspecified) lubricant oils. An example where a TLA-based method has been successfully applied, for material couple characterisation on Timken testing stands, is also presented. The paper ends with a typical remnant measuring method application executed for the Romanian Railway Company.

Nonconventional pressure-assisted powder consolidation methods

Nonconventional consolidation methods have been developed to minimize the microstructural changes during compaction of metastable powder materials. The methods presented in this article combine short-time high-temperature exposure with either high-pressure application or plasma discharge. The current understanding of pressure sintering was used to identify the densification mechanisms for each process. When high pressure is applied, the contribution of plastic yielding to densification is augmented such that lower temperatures and shorter times than in conventional processes are conceivable for the overall compaction process. Plasma discharge results in particle surface activation that enhances particle sinterability and reduces high-temperature exposure. To illustrate the specifics of these new nonconventional consolidation methods, examples of short-time densification of difficult-to-sinter materials are presented.

Ceramic gas sensors.

Relationship between microstructure and gas sensing characteristics of ceramic gas sensors was described, and highly functional gas sensors using ultrafine particles were reviewed.Using ultrafine particles brings about activation of particle-surface (for adsorption and redox reaction) as well as increases of surface area and contact-points of particles. As a result, a high sensitivity, rapid response and detection of inactive gas species become possible.