Plasma Chemical Method Research Articles

Plasma-Chemical Method of Silicon Carbide Modification to Obtain Particles with Controlled Surface Morphology

Plasma-Chemical Method of Silicon Carbide Modification to Obtain Particles with Controlled Surface Morphology

Екологічні аспекти відновлення довкілля: нанотехнології видалення з води мікро- та нанопластиків

Objective: The goal of the research is to synthesize existing approaches for water purification containing micro- and nanoplastics while also developing a new effective method for such purification to reduce the impact of micro- and nanoplastics on the environment and human health. Materials and Research Methods: The research subject included samples of wastewater from a printing facility, which among other pollutants, contained micro- and nanoplastics. Research methods applied include informational, IR spectroscopy, thermogravimetric analysis, and X-ray diffraction. Results: An analysis of the current state of micro- and nanoplastics removal from contaminated water was conducted. Existing approaches for water purification containing micro- and nanoplastics were summarized. The qualitative composition of nanoplastics was determined, including polyamides, polyimides, polyoxadiazole, and fluoroplastics. The application of thermal treatment allowed the identification of heat-resistant plastics like polyoxadiazole and fluoroplastics. Using either only sorption (with graphite-based sorbents) or only plasma chemical methods was found to be insufficiently effective. The activation mechanism of microplastic particles in the presence of humic acids adsorbed on smectites during high-voltage discharge was examined. A comprehensive plasma chemical method for the purification of contaminated water was developed, effectively removing micro- and nanoplastics from the aquatic environment. Conclusions: The current ecological situation regarding water pollution is highly unfavorable and characterized by an increasing contamination of micro- and nanoplastics combined with various toxic substances. Due to their significant adsorption properties, micro- and nanoplastics exacerbate the toxic effects on the natural environment and human health. The removal of micro- and nanoplastics and associated pollutants is an urgent contemporary issue. The obtained results have led to the development of a comprehensive plasma chemical method for purifying contaminated water from micro- and nanoplastics. This method involves plasma chemical treatment of the contaminated liquid, to which a water dispersion of modified humic substances of high-dispersion smectites is added. This results in the formation of magnetosensitive aggregates incorporating micro- and nanoplastics, which can be removed through magnetic separation. The application of this method holds promise for the purification of water from various micro- and nanoplastics in combination with organic pollutants, heavy metals, and other substances with potential ecological risks.

Surface modification of polyvinyl chloride with sodium alginate/carboxymethyl chitosan and heparin for realizing the anticoagulation

Thrombosis of extracorporeal circuits causes significant morbidity and mortality worldwide. In this study, plasma treatment technology and chemical grafting method were used to construct heparinized surfaces on the PVC substrate, which could not only reduce thrombosis but also decrease the side effects of the direct injection of anticoagulants. The PVC substrate was modified by plasma treatment technology firstly to obtain the active surface with the hydroxyl groups used for grafting. Then, heparin was grafted onto the modified PVC surface using different grafting strategies to prepare different heparinized surfaces. The experimental results indicated that the sodium alginate (SA) and carboxymethyl chitosan (CCS) used as interlayers could significantly increase the graft density of heparin to improve the anticoagulant effects and hemocompatibility of heparinized surfaces. In addition, the modification of heparin can further improve the anticoagulant effects. The CCS/low-molecular-weight heparin (LWMH) surface has the best anticoagulant properties, which can prolong the activated partial thromboplastin time (APTT) values of human plasma for about 35 s, reduce the hemolysis rates to <0.3 %, and perform well in the in-vitro blood circulation test. The heparinized surfaces prepared in this work have great application potential in anticoagulant treatment for medical devices.

EFFECT OF PLASMA CHEMICAL OXIDATION OF ETHYLENE IMPURITIES ON THE EFFICIENCY OF KIWIFRUIT STORAGE

The effectiveness of plasma chemical technology in reducing the concentration of ethylene impurities in order to extend the shelf life of kiwifruit has been studied. Ethylene and mold were controlled by plasma treatment, which slowed the ripening of kiwifruit and significantly inhibited rotting. When storing kiwifruit using the plasma chemical system, the level of ethylene was twice lower than that measured in the control batch. Also, the level of ethylene practically did not change during the entire period of the experiment, since the ethylene released from the fruit was quickly oxidized by ozone. Air treatment of kiwifruit storage environment resulted in the fact that ripening mechanism was delayed and the loss of fruits during their further transportation and storage was almost completely prevented. Thus, high efficiency of plasma-chemical method for extending kiwifruit shelf life was shown as well as the prospects of its application. Storage period can be doubled while preserving the subtle aroma of fruits. The effectiveness of plasma chemical technology in reducing the concentration of ethylene impurities in order to extend the shelf life of kiwifruit has been studied. High efficiency of plasma-chemical method for extending kiwifruit shelf life was shown as well as the prospects of its application. Storage period can be doubled while preserving the subtle aroma of fruits.

Synthesis of thermally stable carbon nanostructures via ethanol pyrolysis in DC plasma jets

Thermostable graphene and carbon nanotubes (CNTs) obtained by the plasma-chemical method were stable when heated to 1300 K. The peculiarity of the obtained materials is associated with the nature of the precursor (ethanol) containing oxygen. It is shown that the composition of the gas phase and the temperature interval for the formation of gaseous precursors depends on the plasma-forming gas used for the pyrolysis of ethanol in a plasma jet: helium, argon, or nitrogen. According to the results of plasma flow simulation, the temperatures of the onset of carbon condensation for helium plasma (2900–2950 K) and argon plasma (2980–3010 K) are quite close, and in the corresponding gas phase the main components are H, H2 and CO, and at lower concentrations there are radicals COOH and OH and HCO+. The nitrogen plasma contains well-represented cyanopolyins responsible for the rearrangement of the gas phase at lower temperatures of 2240–2250 K. It seems that these temperatures are too low for CNT synthesis, so only graphene is formed here. The influence of the combination of H and O in the high-temperature region of plasma flow on the mechanism of formation of precursors of carbon nanostructures has been found.

Fabrication of plane-type axon guidance substrates by applying diamond-like carbon thin film deposition

This research aims to fabricate plane-type substrates for evaluating the axon behaviors of neuronal cells in vitro toward the development of brain-on-chip models by applying the functions of diamond-like carbon (DLC) thin film deposition, which helped to eliminate the costly and time-consuming lithography process by utilizing a shadow mask. The DLC thin films were partially deposited on stretched polydimethylsiloxane (PDMS) substrates covered with a metal mask by the plasma chemical vaper deposition method, and using the substrates culture teats with human neuroblastoma cells (SH-SY5Y) were performed. Three patterns of interconnection structures of axons were created on the substrates with disordered and regular linear wrinkle structures with several μm size formed by the depositions. The patterns were characterized by the structure that the aggregations of axons formed on the linear DLC thin film deposited areas were separately placed in regular intervals and connected each other by plenty of axons, which were individually taut in a straight line at about 100 to over 200 μm in length. The substrates expected of uses for evaluation of axon behaviors are available without fabricating guiding grooves by conventional soft lithographic methods requiring multiple stages and their treating times.

Mechanical and Thermophysical Properties of Epoxy Nanocomposites with Titanium Dioxide Nanoparticles

The introduction of nanoparticles and their homogeneous distribution in the polymer matrix, as well as their size, can have a significant effect on the mechanical properties of composite materials. In this work, we studied the mechanical characteristics of TiO2/epoxy nanocomposites with different contents and sizes of nanoparticles. The preparation of nanocomposites was carried out by a stepwise curing (at 90 and 160 °C) of ED-20 dianic epoxy resin in the presence of an aromatic hardener with the addition of titanium (IV) dioxide nanoparticles preliminarily synthesized by the plasma-chemical method. Ultrasonic dispersion was used to achieve a uniform distribution of nanoparticles in the polymer matrix. The chemical and phase composition, the structure of the as-synthesized TiO2 nanoparticles, and the resulting epoxy nanocomposites were characterized by elemental analysis, X-ray diffraction, transmission and scanning electron microscopy, and infrared spectroscopy. The mechanical properties of the nanocomposites were determined by the static tensile test, and the impact toughness was determined by the Charpy method. The glass transition temperature and thermal stability of the TiO2/epoxy nanocomposites were studied by thermal analysis methods. The formation of an interfacial layer between the TiO2 nanoparticles and an epoxy matrix has been shown for the first time by spectral methods. It is shown that the mode of curing and ultrasonic dispersion used, as well as varying the content and dispersity of the TiO2 nanoparticles, make it possible to obtain epoxy nanocomposites with simultaneously improved deformation-strength characteristics and impact strength values.

Thermal model of a facility for the synthesis of carbon nanotubes by plasma-chemical method

A thermal model of an experimental facility for the synthesis of carbon nanotubes by the plasmachemical method is proposed. The facility contains two thermal zones: in the upper zone, the plasma torch generates thermal power, in the lower zone; heat is removed by using a chiller. Based on the experimental data by using the Matlab tools, the identification of the model parameters is carried out. Keywords mathematical model, nanotube synthesis, experimental facility, empirical method, plasma torch, multidimensional thermal object

In English

In the work, carbon nanostructures (CNS) were synthesized on a plasma chemical plant using graphite electrodes SIGE (Special Impregnated Graphite Electrodes) and FGDG-7 (Fine-grained dense graphite) in a helium environment. In the experiments, it was established that graphite electrodes of the SIGE brand are suitable for the synthesis of CNS by the electric arc plasma chemical method. In addition, the experiments indicate that SIGE graphite in electric arc synthesis in a gas environment allows the creation of centimeter composite rods (deposits), where the core consists of graphene sheets rolled into nanotubes that can withstand extremely high temperatures (&gt;4000 K). Studies using scanning microscopy have shown that the synthetic deposit of SIGE graphite can be divided into blocks, which is important for its use in high voltage stations because it is possible to prepare deposits of the required length without mechanical impact and without violating the integrity of its structure. The structure of the synthesized carbon materials was studied by scanning and transmission electron microscopy and it was shown that carbon nanotubes are formed during the evaporation of SIGE brand graphite even without the use of a catalyst. Experiments have confirmed that the mass yield of wall fullerene-containing carbon black during the evaporation of SIGE grade graphite significantly exceeds the results obtained during the evaporation of FGDG-7 grade graphite electrodes. Such results make SIGE graphite more productive for the synthesis of expensive carbon nanoproducts (fullerenes and fullerene-like structures) by the electric arc method. It was also recorded that during the synthesis of carbon nanostructures, single-walled carbon nanotubes are formed, which have a positive charge and are deposited in the form of a core on the surface of the cathode electrode under the action of an electromagnetic field.

In English

Carbon nanostructures (CNS) were synthesized by the electric arc plasma chemical method during the evaporation of a high-quality graphite electrode of the brand “fine-grained dense graphite” (FGDG-7) filled with a catalyst (Pt), which was evaporated in a helium environment. In the synthesis process, the following were synthesized: multi-walled (MWCNT) and single-walled carbon nanotubes (SWCNT), fullerenes, graphene packets and nanocomposites. A deposit in the form of growth on the cathode electrode was also synthesized. All synthesis products were analyzed at the micro- and nanolevels, which made it possible to analyze the influence of platinum vapors on the formation of carbon nanomaterials (CNM). The non-uniform distribution of catalyst atoms (platinum) in the products of electrochemical synthesis in a gas medium using FGDG-7 graphite was investigated. During the analysis, it was found that platinum is in the state of the face-centered cubic (FCC) lattice and is distributed in the synthesis products as follows: the core of the deposit is less than &lt; 0.001 %, the shell of the deposit is less than &lt; 1 %, the wall soot is more than &gt; 1 %. The morphology and composition of the platinum deposit, which has a hexagonal graphite structure with an admixture of a rhombohedral graphite phase, was studied. In the studies, differential thermal analysis in air (TG, DTG, DTA) was carried out, which made it possible to identify the composition of the synthesis products. It is an established fact that the parts of the deposit with platinum are more heat-resistant compared to the deposit components that do not contain Pt. The resulting carbon nanotubes (CNTs) in diameter (5–25 nm) and length (1.5–2 μm) do not differ from those obtained without the participation of platinum, except for some anomalies. When studying the suitability of platinum-containing carbon nanostructures for 3D printing of CJP (ceramic printing) technology, it was found that for the use of platinum-containing carbon black, it is necessary to carry out a preliminary short-term treatment, namely, grinding in special “ball mills” or rubbing through a fine sieve with minimal effort to create uniformity product. Previous studies have shown that such platinum-containing carbon nanostructures can already be used in 3D printing of CJP technology, or to create new composites for 3D printing technologies of FDM, SLA.

Effect of Conditions of the Pulsed Plasma-chemical Synthesis on Physicochemical Properties of the CuxOy/TiO2 Nanocomposite

Aim: This work presents the study results related to the effect of multipulse electron beam and additional heating of the reaction mixture on the structural and morphological characteristics of the CuxOy/TiO2 nanocomposite prepared by the pulsed plasma-chemical method. Method: The CuxOy/TiO2 nanocomposites were characterized by transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), and X-ray diffraction (XRD). Result: It was found that an increase in the impact of a pulsed electron beam on the synthesized composite affected the degree of its agglomeration and the geometric mean particle diameter. Additional heating of the reaction mixture increased the geometric diameter of the synthesized particles (up to 200 nm). Conclusion: The phase composition of the CuxOy/TiO2 nanocomposite changed depending on the synthesis conditions.

Relationship between the spatial position of the seed and growth mode for single-crystal diamond grown with an enclosed-type holder

The relationship between the spatial position of the diamond seed and growth mode is investigated with an enclosed-type holder for single-crystal diamond growth using the microwave plasma chemical vapor deposition epitaxial method. The results demonstrate that there are three main regions by varying the spatial position of the seed. Due to the plasma concentration occurring at the seed edge, a larger depth is beneficial to transfer the plasma to the holder surface and suppress the polycrystalline diamond rim around the seed edge. However, the plasma density at the edge decreases drastically when the depth is too large, resulting in the growth of a vicinal grain plane and the reduction of surface area. By adopting an appropriate spatial location, the size of single-crystal diamond can be increased from 7 mm × 7 mm × 0.35 mm to 8.6 mm × 8.6 mm × 2.8 mm without the polycrystalline diamond rim.

Optimization of the Conditions for the Synthesis of Zinc Oxide Nanoparticles by Plasma Chemical Method

Zinc oxide nanoparticles (ZnO) have a lot of useful properties, thanks to which they are used in various fields of science, technology and medicine. The properties of such nanoparticles largely depend on the method of their synthesis. This paper presents the results of optimization the conditions for the synthesis of zinc oxide nanoparticles by the plasma chemical method, as well as, clarifying the structure of the obtained samples. It is shown that the lack of air and the duration of the discharge affect the size and structure of the resulting particles. Analysis of the data obtained shows that synthesis in a vacuum chamber on graphite electrodes located inside a galvanived pipe at a pressure of 66, 7 k PA, a voltage of 20 V, DC power of 75 A is optimal for obtaining zinc oxide nanorods by the plasma chemical method.

Plasma-chemical method of silicon carbide modification to obtain particles with controlled surface morphology

A plasma-chemical method for the modification of silicon carbide particles is presented, which makes it possible to obtain particles with a controlled surface morphology. The variable parameter of particle processing was the ratio of the fraction of plasma-forming (Ar) and additional (H) gases. It was shown that at Ar/H = 100/0, the formation of a carbon shell is observed; at Ar/H ratios of 91/9 and 84/16, the particles are characterized by a carbon shell decorated with silicon nanoparticles or nanowires, respectively. The modified particles were analyzed using scanning electron microscopy and Raman spectroscopy. Keywords: silicon carbide, plasma chemistry, surface morphology, nanoparticles, nanowires, carbon shell, core-shell

Improving the Selected Stages of Integrated-Optic Chip Structure Formation and Its Interfacing with Optical Fibers

The paper considers experimental technological regimes at different stages of integrated optical chips creation for modern applications: optoelectronics, fiber-optic sensors, microfluidics. The considered experimental regimes demonstrate not only qualitative, but also quantitative efficiency: at the stage of the ridge waveguides formation, there is a possibility of achieving high etching rates of lithium niobate - up to 950 nanometers per minute in fluorine-containing plasma with an increased consumption of plasma gases without forced thermostating of the sample. Using scanning electron microscope, structural changes in the surface have been demonstrated: clustering of surface etching foci, indicating the uniformity of etching at the macroscale, and changes in the thickness and structure of the near-surface defect layer, indicating the possibility of its complete removal by the plasma-chemical method. The method can be applied both for the manufacturing of ridge waveguides and optical elements based on them, and for microfluidics elements. Then, the efficiency of the waveguides and optical fibers interfacing method has been confirmed with frequency domain reflectometry. The algorithmic details of the interfacing by the modified Newton's method are also described. The modified Newton’s method allowed to simplify the alignment process by performing coarse alignment based on reflections from the far end face of the waveguide, speed up the alignment process at fine mode, and fully automate the alignment of the waveguide and optical fiber at any initial displacements. All the proposed technological process modernization leads to the improvement of technological characteristics and the individual stages production time reduction.

Characterization of iron-doped crystalline silicon nanoparticles and their modification with citrate anions for in vivo applications

Objectives. This paper presents data on the development and study of the structural properties of iron-doped crystalline silicon (nc-Si/SiOx/Fe) nanoparticles obtained using the plasma-chemical method for application in magnetic resonance imaging diagnostics and treatment of oncological diseases. This work aimed to use a variety of analytical methods to study the structural properties of nc-Si/SiOx/Fe and their colloidal stabilization with citrate anions for in vivo applications.Methods. Silicon nanoparticles obtained via the plasma-chemical synthesis method were characterized by laser spark emission spectroscopy, atomic emission spectroscopy, Fouriertransform infrared spectroscopy, and X-ray photoelectron spectroscopy. The hydrodynamic diameter of the nanoparticles was estimated using dynamic light scattering. The toxicity of the nanoparticles was investigated using a colorimetric MTT test for the cell metabolic activity. Elemental iron with different Fe/Si atomic ratios was added to the feedstock during loading.Results. The particles were shown to have a large silicon core covered by a relatively thin layer of intermediate oxides (interface) and an amorphous oxide shell, which is silicon oxide with different oxidation states SiOx (0 ≤ x ≤ 2). The samples had an iron content of 0.8–1.8 at %. Colloidal solutions of the nanoparticles stabilized by citrate anions were obtained and characterized. According to the analysis of the cytotoxicity of the modified nanosilicon particles using monoclonal K562 human erythroleukemia cells, no toxicity was found for cells in culture at particle concentrations of up to 5 µg/mL.Conclusions. Since the obtained modified particles are nontoxic, they can be used in in vivo theranostic applications.

Processing of industrial waste by plasma-chemical method

In this paper, the results of the processing of magnesium fluoride by plasma-chemical method to obtain periclase and a solution of hydrogen fluoride (hydrofluoric acid) were presented. For the industrial implementation of plasma technologies, it is necessary to study the main parameters of plasma processes for obtaining reducing gases and processing metal oxides with them, to solve the issues of their hardware design, to increase the service life of plasma torches for their use in continuous metallurgical processes. The purpose of this work was to determine the conditions for the plasma-chemical process of processing magnesium fluoride. Thermal analysis of magnesium fluoride on a TGA/DSC2 thermogravimetric analyzer was performed. Thermogravimetric analysis showed that in the temperature range under consideration the process is endothermic, and at a temperature of ~1280°C a phase transition of the 1st kind is observed due to the melting of magnesium fluoride. The fractional composition of MgF2 and MgO powders was studied using the Analysette-22 Nanotech laser diffraction analyzer. The results of the evaluation of the fractional composition of powders have a significant difference. At the same time, the convergence of the data obtained using laser diffraction and electron microscopy methods was found.

Effect of the concentration of the starting reagents and the design of the reaction chamber on the morphology and phase composition of the CuxOy@SiO2 nanocomposite synthesized by the pulsed plasma-chemical method

The CuxOy@SiO2 nanocomposite was prepared using a pulsed plasma-chemical method. The regularities of the influence of the concentration of the starting reagents and the design of the reaction chamber on the morphology, phase composition of the CuxOy@SiO2 nanocomposite were revealed. With varying the concentration of the starting reagents, the agglomeration of particles decreased, the particle morphology (particles acquired a spherical shape) and phase composition (the predominant crystalline phases were CuCl2, CuCl, Si, CuO, Cu) changed. Two types of reaction chambers (quartz/copper) were used for the synthesis of the CuxOy@SiO2 nanocomposite. The change in the design of the reaction chamber had an insignificant effect on the phase composition of the CuxOy@SiO2 composites, but had a strong effect on the morphology and average size of the synthesized particles. The morphology of the composite particles prepared in a copper reactor is represented by particles of a fine fraction of an irregular shape.

Heteroepitaxial Growth of Ga2O3 Thin Films of Various Phase Composition by Oxidation of Ga in Hydrogen-Oxygen Plasmas

We describe a novel plasma-chemical method for Ga2O3 thin films synthesis, in which high-purity elemental Ga is delivered by hydrogen flow into the plasma discharge zone to react with O2. Radio Frequency (40 MHz) non-equilibrium low temperature plasma discharge at low pressure (0.01 Torr) is applied for initiation of interaction between these precursors. Optical Emission Spectroscopy together with quantum-chemical calculations was used to determine the main reaction pathways and reacting species appearing in the plasma discharge. For a low growth temperature of 350 °C and high plasma power of 50 W, the Ga2O3 films deposited on basal plane sapphire are textured β-Ga2O3 with (−201) orientation. At low plasma power of 30 W and low growth temperature of 350 °C, the layers are dominated by the polycrystalline ε(k) phase. Increasing the growth temperature under these low plasma power conditions from 350 °C to 550 °C leads to the grains ripening and the conversion of the films into the polycrystalline β-polytype. Electrical measurements on the films grown under high power conditions on sapphire showed them to be semi-insulating, with the Fermi level pinned near Ec−0.7 eV. Films on Si substrates had low donor concentrations of ∼1015 cm−3, most likely due to Si autodoping from the Si substrate.

Plasma-chemical deposition of gallium oxide layers by oxidation of gallium in the hydrogen-oxygen mixture

Gallium oxide is an ultra wide band gap (the width of the band gap is 4.85 eV) transparent semiconducting oxide, that nowadays attracts much attention of scientists and manufacturers. However, the main obstacle, preventing from its massive commercial implementation, is the lack of technological methods to its production; it is supposed to be cheap, reproducible, and scalable. In this work we are developing a novel plasma-chemical method of Ga2O3 thin films’ synthesis; according to this method only high-purity elemental gallium was used as the source of gallium delivered by the hydrogen flow into the plasma discharge zone, where the interaction with oxygen took place. The properties of the solid phase obtained in the conditions of heteroepitaxial growth were studied depending on the experimental parameters.