Impurity Particles Research Articles

Enhanced Photocatalytic Performance of Visible-Light-Driven BiVO4 Nanoparticles through W and Mo Substituting

Bismuth vanadate (BiVO4), W-doped BiVO4 (BiVO4:W), and Mo-doped BiVO4 (BiVO4:Mo) nanoparticles were synthesized at pH = 4 using a green hydrothermal method. The effects of 2 at% W or Mo doping on the microstructural and optical characteristics of as-prepared BiVO4 nanoparticles and the effect of combining particle morphology modification and impurity dopant incorporation on the visible-light-derived photocatalytic degradation of dilute Rhodamine B (RhB) solution are studied. XRD examination revealed that these obtained BiVO4-based nanoparticles had a highly crystalline and single monoclinic phase. SEM and TEM observations showed that impurity doping could modify the surface morphology, change the particle shape, and reduce the particle diameter to enlarge their specific surface area, increasing the reactive sites of the photocatalytic process. XPS and FL measurements indicated that W- and Mo-doped nanoparticles possessed higher concentrations of oxygen vacancies, which could promote the n-type semiconductor property. It was found that the BiVO4:W and BiVO4:Mo powder samples exhibited better photocatalytic activity for efficient RhB removal than that shown by pristine BiVO4 powder samples under visible light illumination. That feature can be ascribed to the larger surface area and improved concentration of photogenerated charge carriers of the former.

Using SiNx double-layer deposition to reduce electrode incidence of short circuits due to impurity particles in thin film transistor preparation

Aviation safety relies on accurate scope presentation of air navigation displays, and lack of display information due to poor dot line may cause the pilot to misjudge the air conditions. Impurity particles occurred during preparing thin film transistor (TFT) circuit may be a leading reason for poor dot line. This work attempts to replace existing SiNx single-layer deposition with double-layer, so that the incidence risk can be lower through reducing number and size of the impurity particles. Double-layer deposition approach has the dot line structures and performances to that of single-layer, and can meet the requirements of display usage. Results of field test demonstrate that double-layer deposition reduces defect rate of display more efficient than single-layer. Proposed mechanism of double-layer deposition illuminates that 2nd-SiNx can cover holes generated by falling impurity particles to avoid short circuits in both indium tin oxide (ITO) and source-drain (SD) contact.

Assessment of Changes in the Abrasiveness of Solid Particles in Hydraulic Mixtures Pumped with ESPs

The statistics of using downhole electric submersible pump (ESP) units in the oil fields of Eurasia show that hydroabrasive wear is a common cause of ESP emergency failures. The authors of this study theoretically and experimentally investigated the peculiarities of water–abrasive wear of ESP components. The research methodology and construction of the laboratory bench are described, and the results of experimental studies of determination of changes in the abrasivity index of impurity particles contained in the mixture pumped with the working stages of an ESP section are given. It is shown that large particles of mechanical impurities in contact with the metal of the working stages are subjected to intensive grinding of up to 0.25…0.3 mm; after that, particle size remains practically unchanged. An increased abrasiveness index of mechanical impurities causes an increase in the intensity of wear of interstage seals along the flow of a water–abrasive mixture (from the inlet to the outlet of the pumping section). Based on the obtained results, recommendations for selection of devices for formation-fluid cleaning during development and operation of oil wells are given. The relevance of work on improving the design of interstage seals of ESP units is substantiated.

Active Polarization Imaging for Cross-Linear Image Histogram Equalization and Noise Suppression in Highly Turbid Water

The absorption and scattering of impurity particles in turbid water cause the target signal light to be attenuated and to produce backscattered light, resulting in the reduced quality of underwater polarimetric imaging. As water turbidity increases, the effect of backscattered light becomes greater, making polarization imaging in highly turbid water a challenge. Theory and experiment show that the increase in the intensity of backscattered light leads to high noise gain in the underwater active polarization imaging model. In order to enhance image contrast and suppress noise gain in highly turbid water, we propose an underwater imaging enhancement method that appropriately combines the non-physical and physical models. The method uses contrast limited adaptive histogram equalization (CLAHE) for a certain number of cross-linear images (Imin) before calculating their polarization enhancement images, and it constructs joint filtering (multi-frame averaging and bilateral filtering) to suppress the high noise gain introduced by the imaging model and CLAHE. The experimental results in highly turbid water validate the rationality and feasibility of the proposed method, and the comparative processing results (52.7~98.6 NTU) outperform those of the conventional non-physical and physical model methods. The method maintains the complexity of the system and facilitates the application of conventional polarimetric imaging in harsher underwater environments.

Numerical and experimental investigations on enhancement mixing performance of multi-blade stirring system for fluids with different viscosities

Abstract The poor mixing caused by zinc powder deposition in purification process is a serious problem which can’t be avoided in treatment of zinc-containing solid waste. Here, to enhance the purification efficiency of zinc-containing solid waste treatment reactor, two kinds of multi-blade combined stirring systems are compared with single layer four straight-blade and double-layer straight-blade (DFB) stirring systems which are traditionally chosen by industry. This study simulated and explored the flow field characteristics and purification effects of these four kinds of stirred-tank reactor, further proposes the unit ion purification energy (UIPE) as a criterion for purification energy consumption and effect evaluation. The results show that multi-blade combined (MBC) stirring system enhances axial flow by 12.56% in water. Meanwhile it effectively inhibits the growth of isolated mixing region which scope has decreased by 56.25%. In high viscosity Carboxymethylcellulose sodium solution, the fluid axial speed can be increased by up to 1407 times with MBC. MBC can increase the purification rate by 24.79% while the UIPE decreases by 29.45% compared with DFB which is used in industrial purification process. MBC paddle has exhibited a wide range of fluid viscosity applicability and axial velocity improvement effect. The improvement increases collisions between the impurity particles and the zinc powder particles, which increased rate of substitution reactions. The application of MBC solves the purification problem in the process of treating zinc-containing solid waste.

Optimization of Parameters of Two-Beam Laser Twelding of Quartz Raw Materials

In the work , with the help of numerical simulation , the values of technological parameters are established , which provide effective two-beam laser cleaning of quartz raw materials . The optimization of two-beam laser cleaning of quartz raw materials was performed using the MOGA genetic algorithm in the ANSYS Work- bench program . Using the face-centered version of the central compositional plan of the experiment , a regression model of two-beam cleaning of quartz raw materials was obtained . The power density of a laser with the wavelength of 10.6 μm , the power density of a laser with the wavelength of 1.06 μm , the radius of a quartz particle , the radius of an impurity particle , and the processing time were used as variable factors . The maximum temperatures of quartz particles with impurities and quartz particles without impurities were used as responses . The regression model was tested . The results obtained allow us to conclude that there is a necessary correspondence between the regression model and the finite element analysis data . An assessment of the influence of processing parameters on the maximum values of the temperature of quartz particles was made . Optimization of two-beam laser cleaning of quartz raw materials was carried out according to the criterion of minimum processing time when reaching the maximum temperatures of quartz particles with an admixture of the melting temperature and limiting the maximum temperatures of quartz particles without an admixture to values below the melting temperature . Optimization was performed for two combinations of quartz and impurity particle sizes . The parameters obtained as a result of optimization and the parameters obtained as a result of finite element modeling are compared . The maximum relative error of the results obtained using the MOGA algorithm did not exceed 2.5 % when determining the maximum temperatures . As a result of the simulation , processing parameters have been established , the use of which will provide an increase in the productivity of two-beam purification of quartz raw materials .

Modeling colmatation of a porous medium during the injection of water with impurity particles

Modeling colmatation of a porous medium during the injection of water with impurity particles

THEORETICAL ASPECTS OF VIBRATIONAL SPECTROSCOPY OF CONDENSED SYSTEMS WITH IMPURITY PARTICLES

Some problems of vibrational spectroscopy of particles in condensed systems are considered in this work. One of the aspects of theoretical research is the study of the vibrational properties of individual particles in view of the nano-dimension of the molecules of the condensed system surrounding the particle. Using the apparatus of temperature, Green functions of the operators of polarization of condensed systems, two main mechanisms of influence on impurity particles from the medium, solvation and fluctuation, are distinguished. Theoretical results are obtained within the framework of these two mechanisms for calculating changes in the vibrational spectrum of individual particles. The theoretical results are used to analyze the experimental data on the vibrational spectra of the N2O molecule in polar solvents: methanol, ethyl alcohol, acetone, and 1,2-dichloroethane.

Charge transfer processes in granulated Mg3Sb2 particles

In the article, temperature dependence of specific resistance (ρ), concentration of charge carriers (n) and mobility (<) was studied experimentally at T=300-700 K to study charge transfer processes in granulated Mg3Sb2 particles. The research results were explained on the basis of the charge transfer mechanism in Mg3Sb2 particles. In particular, at the initial stage of temperature increase, Т≤375 К, localized traps with energy level Ein appear in the interparticle boundary areas of the heated part of the sample. When charge carriers are trapped in them, ρ increases sharply, and n decreases. In the later stages of temperature increase, the thermal phenomenon increases along the length of the sample. In this process, localized traps with energy level Ein appear successively in the interparticle boundary regions located along the length of the sample. In relation to the charges held in them, the concentration of the generated charge carriers n increases in accordance with the increase in temperature, in this case ρ changes steadily. The increase of the potential barrier height in the interparticle boundary regions from φ ~ 0.411 eV to 0.91 eV confirms the above considerations. In addition, under the influence of temperature, the particle size and impurity ionization in the interparticle boundary areas or thermal fluctuations of the crystal lattice decrease the free movement path of the carriers. This leads to a decrease in µ at T=300-700 K.

Mechanism and kinetics of separation of impurity particles with different densities in a rapid gravity flow of granular material

Mechanism and kinetics of separation of impurity particles with different densities in a rapid gravity flow of granular material

THE INFLUENCE OF TERRAIN, CLIMATIC CONDITIONS AND FACTORS ON THE ATMOSPHERIC AIR MONITORING SYSTEM, BASED ON THE IMPLEMENTATION OF EU LEGISLATION ON THE EXAMPLE OF LVIV REGION

The article is devoted to the influence of terrain, landscapes, and meteorological conditions on the establishment of air quality monitoring points in the relevant territory of the Lviv region. The main factors affecting the distribution of the concentration of pollutants in atmospheric air during the design of air monitoring stations have been determined. It was established that the level of the surface concentration of pollutants increases with an increase in the power of the emission source, the density, and size of impurity particles, and decreases with an increase in the height and radius of the orifice of the emission source, the temperature of the emission, and the rate of release of impurities from the source.

Уточнение модели концентрационной конвекции в пористой среде с учетом иммобилизации примеси и слабой закупорки

The influence of weak clogging on the process of a heavy impurity transport through a horizontal layer of a porous medium is studied. A constant concentration drop is set at the boundaries of the layer, the flow along the layer is maintained by a constant pressure drop. The present problem is a concentration analog of the well-known Horton-Rogers-Lapwood (HRL) problem. The equations describing the transport of the impurity taking into account the deposition (immobilization) of the impurity particles on the porous skeleton are obtained. The deposition process is described in the framework of the well-known linear sorption model (linear MIM model). Clogging is assumed to be weak in the sense that the influence of deposited particles on porosity is considered to be negli-gible and is taken into account only with respect to the reduction of the permeability of the medi-um. It is found that the basic solution to this system admits the regime of stationary filtration along the layer. In this case, the impurity distribution is linear, which coincides with the known HRL so-lution. The stability of the basic state is analyzed numerically. Neutral curves as well as minimum values of critical parameters (Rayleigh-Darcy number, wave number, and frequency) depending on the system parameters are obtained and analyzed. It is shown that the arising instability, as in the HRL problem, is oscillatory by nature. Taking into account the clogging (along with taking into ac-count the deposition) leads to an increase in the stability of the stationary filtration flow and attenu-ation of the oscillations. The study determines the limits of applicability of the linear MIM model, widespread in the literature, that does not taking into account the clogging.

Physicochemical properties of lignin nanoparticles from softwood and their potential application in sustainable pre-harvest bagging as transparent UV-shielding films

Technical lignin can be mainly obtained as a waste by-product from pulp industry, and it exhibits unique properties including ultraviolet adsorption, biodegradable, antibacterial, and antioxidant which can be utilized for bioplastic applications. However, common limitations of technical lignin for plastic applications are compatibility mainly due to poor interfacial adhesion, relatively large particle size and impurity. In this study lignin nanoparticles from softwood (S-LNPs) were successfully produced through a continuous-green-scalable antisolvent precipitation and the suitability of S-LNPs for fabrication of bio-composite polybutylene succinate (PBS) films using conventional blown film extrusion was examined. The attained S-LNPs showed lower ash content, higher phenolic content and higher lignin content compared to pristine softwood kraft lignin (S-lignin). Rheological property including shear viscosity and melt-flow index was determined. The obtained PBS/S-LNP composite films showed improved tensile modulus, higher water vapor transmission rate and excellent UV-shielding ability compared to neat PBS and PBS/S-lignin films. Accelerated weathering testing was conducted to replicate outdoor conditions. Degradation indices including carbonyl, vinyl and hydroxyl of the weathered PBS/lignin composites were evaluated for photo-oxidative stability. The S-LNPs as multifunctional bio-additives in biodegradable composite film exhibited superior performances of transparency, UV-absorption and stiffness with high photo-oxidative stability suitable for outdoor applications.

Preparation of a cationic block copolymer composite coagulant TP(AM-DAC-PPFS) and its coagulation performance for treating oilfield sewage

Efficient purification of oily sewage, recycling, and standard discharge have become key issues for the sustainable development of oil fields. In this study, the surface of PPFS was organically modified by a silane coupling agent. Then, covalently bonded cationic block inorganic-organic composite coagulant was prepared by chosen sodium polyacrylate as the template. This unique structure significantly enhances the positive charge and molecular chain length of the coagulant, thus improving its ability to perform charge neutralisation, adsorption bridging, and sweep coagulation. The characteristic functional groups and thermophysical properties of the composite coagulant were analysed by FTIR and thermogravimetric analysis. The transformation of random copolymers to block copolymers was determined by 1 H NMR, thus confirming the successful synthesis of the cationic block structures. The turbidity removal and oil removal properties of oily sewage were investigated by coagulation experiment. The Zeta potential, dynamic and static light scattering, and field emission scanning electron microscopy (SEM) were used to study the effect of composite coagulants on the microscopic morphology and coagulation of flocs. Finally, the coagulation mechanism of the compound coagulant was analyzed with the dynamic change of the particle size of the flocs. The cationic block structure in TP(AM-DAC-PPFS) can effectively neutralise the negative charges on the surface of impurity particles and emulsified oil. The optimal dosage of TP(AM-DAC-PPFS) was 30 mg·L−1, at which the turbidity and oil removal rates can reach 98.3% and 93.8%, respectively.

Властивості покриттів Cr–Si–B–MgC2 в умовах підвищенних температур

Heat resistance, as well as friction and wear of composite coatings Cr–Si–B–MgC2 under conditions of elevated temperatures implemented in friction pairs, were investigated. The selection of the Cr–Si–B–MgC2 composition and its optimal composition for spraying wear-resistant coatings loaded with friction at high temperatures are substantiated. Indicated the main influence on the properties, structure, and stability of heterogeneous coatings is exerted by alloying elements at certain concentrations, as well as technological parameters of coating application. It has been established that silicon and boron contribute to the formation of complex-alloyed high-temperature formations with increased wear resistance. The microhardness of coatings correction is realized due to the silicon percentage content, while the mechanical properties of the material are increased by additional doping with boron and magnesium carbide. The parameters of sputtering of coatings are also important, on which the formation of a heat-resistant layer directly depends. It was experimentally established that the ratio of consumption of acetylene and oxygen ~20/25 l/min ensures the stability of technological parameters of sputtering, homogeneity of the chemical composition and constancy of coating properties. At a load of up to 5.0 MPa, a sliding speed of up to 1.2 m/s and a temperature of up to 700С, the coatings of the Cr–Si–B–MgC2 system show stable structural adaptability, which ensures the minimization of friction and wear parameters. Metallographic analysis and profilography of the samples indicate that there are no visible damages on the friction surfaces, and individual sticking points are localized in thin film surface layers. It was established that the dependence of the microhardness of the surface structures on the temperature is monotonic, but jumps are also observed if polymorphic transformations or transformations of metastable states into more stable and stable ones during heating and cooling occur. Microhardness indicators are uniform because particles of inclusions and impurities are dissolved in the oxide structures, which significantly affect the microhardness, and therefore, the properties of oxides of both simple and complex compositions. Keywords: protective coatings, surface layer, resistance to oxidation, wear resistance, heat resistance

Particle Contamination in Commercial Lithium-Ion Cells—Risk Assessment with Focus on Internal Short Circuits and Replication by Currently Discussed Trigger Methods

A possible contamination with impurities or material weak points generated in cell production of lithium-ion batteries increases the risk of spontaneous internal short circuits (ISC). An ISC can lead to a sudden thermal runaway (TR) of the cell, thereby making these faults especially dangerous. Evaluation regarding the criticality of an ISC, the development of detection methods for timely fault warning and possible protection concepts require a realistic failure replication for general validation. Various trigger methods are currently discussed to reproduce these ISC failure cases, but without considering a valid basis for the practice-relevant particle properties. In order to provide such a basis for the evaluation and further development of trigger methods, in this paper, the possibilities of detecting impurity particles in production were reviewed and real particles from pouch cells of an established cell manufacturer were analysed. The results indicate that several metallic particles with a significant size up to 1 mm × 1.7 mm could be found between the cell layers. This evidence shows that contamination with impurity particles cannot be completely prevented in cell production, as a result of which particle-induced ISC must be expected and the need for an application-oriented triggering method currently exists. The cause of TR events in the field often cannot be identified. However, it is noticeable that such faults often occur during the charging process. A new interesting hypothesis for this so-far unexplained phenomenon is presented here. Based on all findings, the current trigger methods for replicating an external particle-induced ISC were evaluated in significant detail and specific improvements are identified. Here, it is shown that all current trigger methods for ISC replication exhibit weaknesses regarding reproducibility, which results mainly from the scattering random ISC contact resistance.

Field-Induced Stratification of Goethite Particles in Nematic Matrix

Within the continuum theory, the stratification of colloidal goethite particles in a nematic matrix induced by magnetic and gravitational fields has been studied. The case of a magnetically compensated suspension, which is a liquid crystal analogue of an antiferromagnet, is considered. For a twist structure, the spatial distributions of the fields of the director of the liquid crystal medium and the dispersed phase are studied. The distributions of goethite impurity particles over the layer thickness are calculated for different values of the magnetic field. The obtained equations of orientational and magnetic equilibrium of suspensions of goethite particles in a nematic have a general form and, in limiting cases, can be used to describe liquid crystal suspensions of anisometric ferromagnetic particles and carbon nanotubes.

UIR-Net: A Simple and Effective Baseline for Underwater Image Restoration and Enhancement

Because of the unique physical and chemical properties of water, obtaining high-quality underwater images directly is not an easy thing. Hence, recovery and enhancement are indispensable steps in underwater image processing and have therefore become research hotspots. Nevertheless, existing image-processing methods generally have high complexity and are difficult to deploy on underwater platforms with limited computing resources. To tackle this issue, this paper proposes a simple and effective baseline named UIR-Net that can recover and enhance underwater images simultaneously. This network uses a channel residual prior to extract the channel of the image to be recovered as a prior, combined with a gradient strategy to reduce parameters and training time to make the operation more lightweight. This method can improve the color performance while maintaining the style and spatial texture of the contents. Through experiments on three datasets (MSRB, MSIRB and UIEBD-Snow), we confirm that UIR-Net can recover clear underwater images from original images with large particle impurities and ocean light spots. Compared to other state-of-the-art methods, UIR-Net can recover underwater images at a similar or higher quality with a significantly lower number of parameters, which is valuable in real-world applications.

Mechanism of nodular growth in copper electrorefining with the inclusion of impurity particles under natural convection

Nodular growth behavior with the inclusion of impurity particles in copper electrorefining was investigated herein by quantitative analyses of impurity elements inside nodules, observations of crystal structures, and numerical simulations of natural convection based on the tertiary current distribution. Impurity contents were higher in the upper half of the nodule than in either the lower half or electrolytic copper with non-nodulous growth. Impurity particles, such as suspended slime, were considered to be preferentially taken into the upper part of nodules due to frequent collisions with the upper part as they circulated along the convection vortex that emerged above the nodule. The inclusion of impurity particles changed the electrodeposition morphology and growth direction, and eventually produced granular irregularities and buds of new nodules on the upper surface of the initial nodule.

Vacuum Carbon Reducing Iron Oxide Scale to Prepare Porous 316 Stainless Steel

In order to improve the added value of iron oxide scale and reduce the manufacturing cost of porous stainless steel, steel rolling iron oxide scale as an iron-containing raw material was used to prepare porous 316 stainless steel by high-temperature sintering under vacuum conditions, while carbon was used as a reducing agent and pore-forming agent, and the necessary metal powders were added. In our work, the specific reduction system was confirmed, including the sintering temperature, sintering time, vacuum degree and carbon amount, through thermodynamic calculation combined with experiments. Thermodynamic analysis results showed that the transformation process of the chromium element in the raw materials at 10−4 atm and 300~1600 °C was FeCr2O4 + Cr3O4→Cr2O3 + Cr3O4 + Cr23C6→Cr23C6 + Cr7C3 + FCC→FCC + Cr23C6→FCC→FCC + BCC→Cr(liq). The FCC phase with qualified carbon content could be obtained at 10−4 atm and 1200 °C, while 90.88 g iron oxide scale, 17.17 g carbon, 17.00 g metal chromium, 12.00 g metal nickel and 2.5 g metal molybdenum were necessary to produce 100 g porous 316 stainless steel. The porous 316 stainless steel with a carbon content of 0.025% could be obtained at 10−4 atm and 1200 °C for 180 min, while the chromium element underwent the transformation of metal, Cr→FeCr2O4→Cr23C6→Austenite. The porosity of the porous 316 stainless steel was 42.07%. The maximum size of impurity particles was 5 μm when the holding time reached 180 min. Magnetic separation was an effective method to reduce impurities in the porous stainless steel.