Decrease In Electrical Conductivity Research Articles

INVESTIGATION OF FLUORINATED DOUBLE-WALL CARBON NANOTUBES

Experimental results of investigation of the original and fluorinated ultra-long double-walled carbon nanotubes (DWCNTs) with a length of at least 1000 μm are presented. The degree of fluoridation did not exceed 27 at.%. It has been shown that the process of fluorination of samples of double-walled carbon nanotubes deforms the outer surface of the nanotube wall although does not destroy its internal concentric structure, while the diameter of the fluorinated nanotube increases by 1.5-2 times. In addition, the fluorinated samples, which were thermochemically purified from iron particles and other forms of carbon before fluorination, demonstrated many split/cut ends of nanotubes. The effect of fluorination on the electrical properties of initial and purified samples of double-walled carbon nanotubes was studied. It was revealed that with an increase in temperature from 80 to 300 K for non-fluorinated and fluorinated purified nanotube samples, the resistivity decreases, which corresponds to the semiconductor nature of the conductivity. It was also revealed that when a sample of initial DWNT is fluorinated, a change in the nature of conductivity from semiconductor to metallic is observed. With an increase in temperature from 80 to 300 K, the resistance of the non-fluorinated sample of the original DWNTs decreased by 45%, while the resistance of the fluorinated sample increased by 11%. Despite the decrease in electrical conductivity as a result of fluorination of the purified samples, all samples remained conductors, which presumably indicates partial fluorination of the outer wall of the DWNTs while maintaining the structure of the inner wall. Thus, fluorination of double-walled carbon nanotubes with a well-aligned and concentric structure leads to the formation of fluorocarbon nanostructures, which can be promising materials for electronic nanodevices. For citation: Karaeva A.R., Khaskov M.A., Kurzhumbaev D.Zh., Kulnitskiy B.A., Mordkovich V.Z. Investigation of fluorinated double-wall carbon nanotubes. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 10. P. 38-48. DOI: 10.6060/ivkkt.20246710.4y.

Significant ductility enhancement for high thermal conductivity Mg-2Sn-2.3La alloy via Zn addition

Herein, we introduced a trace amount of Zn into a high-thermal conductivity (HTC) MgSnLa-based alloy and prepared HTC MgSnLaZn alloy with large ductility as well as high strength by a carefully-designed rolling and annealing process. The elongation and strength of the as-annealed MgSnLaZn alloy are 28 % and 215 MPa, respectively, which are increased by 60 % and 16.9 %, respectively, compared with the MgSnLa-based alloy. Addition of Zn converts the Mg12La phase into the τ1 phase and partly dissolved into the matrix, resulting in slight decrease in electrical conductivity (about 3.5 W/(m-K)), but effectively enhancing the tensile properties. The purity of matrix and the fine dispersed precipitation phases ensure that the electrical and thermal conductivity is close to that of pure magnesium. Non-basal texture characteristics and weak texture intensity are the key factors for improvement in ductility.

Effect of CaCO3, SrCO3 and BaCO3 additions on the microstructure and electrical characteristics of SnO2-based varistor ceramics

The ceramic varistors SnO2–Co3O4–Nb2O5–Cr2O3 with the addition of CaCO3, SrCO3 or BaCO3 were sintered at temperatures 1250 and 1350°C, then their structures and electrical properties were studied. In all samples, the SnO2 cassiterite phase with a rutile-type structure and the Co2SnO4 phase with a spinel-type structure were observed. All materials exhibited a highly nonlinear dependence of the current density on the electric field with the nonlinearity coefficient 24–50. When alkaline earth metal carbonates were added, the grain size of all samples decreased and the electric field E1 increased. The addition of CaCO3 lead to the decrease of the low-field electrical conductivity of varistors. The lowest low-field conductivities 4·10-13 and 6·10-13 Ω-1 cm-1 were found in the samples with CaCO3 addition baked at 1250 and 1350°C, respectively. The observed effect is due to the increase of the potential barrier height at the SnO2 grain boundaries by 7 and 13%, respectively, and the decrease of the grain size by 26 and 28% compared to SnO2-based varistor ceramics without CaCO3 addition.

Refinement of eutectic structure and precipitates of Cu–20Ag alloy due to Y microalloying

Copper-silver alloy rod with high mechanical properties and stable conductivity are the key materials for the preparation of microfilaments used in endoscopy and other medical fields. In this paper, the microstructure of Cu–20Ag rod was regulated by adding trace rare earth Y in order to improve the comprehensive performance of copper-silver alloy further. and studies the distribution and existence of rare earth Y as well as the influence on the performance of copper-silver alloy rod billet. The results of research show that: rare earth Y mainly exists in the branching nodes of the eutectic organization, so that the alloy in the solidification of constitutional supercooling increases, thus refining the eutectic structure, and make it uniformly distributed. After addition of 0.01 wt%Y, Cu4Y was precipitated in the eutectic structure of the rod. After adding 0.03 wt%Y, the precipitates types increased to trace intermetallic compound AgY and nanoparticles Cu4Y. The increase of the interface between eutectic structure and Cu matrix decreases the electron scattering probability. This is the main factor to lead to the decrease of electrical conductivity. The precipitation hardening of precipitated phase and the increase of interface between eutectic structure and Cu matrix are the main factors for the increase of tensile strength of bar billet. The main factor of the decrease in the conductivity of rod billet is the increase of Ag phase dissolved in eutectic structure and the interface between eutectic structure and Cu matrix.

Polyaniline/graphitic carbon nitride/reduced graphene oxide ternary nanocomposite film for flexible thermoelectric application

The present study outlines the preparation of a ternary nanocomposite film comprising of polyaniline doped with camphor sulfonic acid (PANI), reduced graphene oxide (rGO), and graphitic carbon nitride (g-C3N4), and delves into its thermoelectric performance. PANI is known to possess high electrical conductivity (σ) and poor thermal conductivity (κ). However, its potential for thermoelectric applications is constrained by the low value of the Seebeck coefficient (S). The incorporation of g-C3N4in PANI has been demonstrated to result in an improvement of the Seebeck coefficient. Furthermore, the addition of rGO to the PANI/g-C3N4sample counteracts the decrease in electrical conductivity. The PANI/g-C3N4/rGO ternary nanocomposite film exhibits an enhanced Seebeck coefficient of ∼2.2 times when compared to the PANI sample. The Seebeck coefficient of the PANI/g-C3N4/rGO nanocomposite is enhanced by the energy filtering effect that occurs at the interfaces between g-C3N4/PANI and PANI/rGO. Theπ-πinteraction between the PANI chains and rGO is responsible for the increased electrical conductivity resulting from the well-ordered polymer chain arrangement on the g-C3N4and rGO surfaces. The ternary nanocomposite sample demonstrated a synergistic improvement in both electrical conductivity and Seebeck coefficient, resulting in a remarkable ∼4.6-fold increment in power factor and an ∼4.3-fold enhancement in the figure of merit (zT), as compared to the pristine PANI film.

Synergistic biochar and Serratia marcescens tackle toxic metal contamination: A multifaceted machine learning approach

Metal contamination in soil poses environmental and health risks requiring effective remediation strategies. This study introduces an innovative approach of synergistically employing biochar and bacterial inoculum of Serratia marcescens to address toxic metal (TM) contamination. Physicochemical, enzymatic, and microbial analyses were conducted, employing integrated biomarker response (IBR) and machine-learning approaches for toxicity estimation. The combined application significantly reduced the Cd, Cr, and Pb concentrations by 71.6, 31.2, and 57.1%, respectively, while the Cu concentration increased by 85% in the individual Serratia marcescens treatment. Biochar enhanced microbial biomass by 33–44% after 25 days. Noteworthy physicochemical improvements included a 44.7% increase in organic content and a decrease in pH and electrical conductivity. The K⁺ and Ca2⁺ concentrations increased by 196.9 and 21.6%, respectively, while the Mg2⁺ content decreased by 86.4%. Network analysis revealed intricate relationships, displaying direct and indirect negative correlations between metals and soil physicochemical parameters. The IBR index values indicated effective mitigation of TM toxicity in Serratia marcescens and biochar with individual and combined treatments. Binary classification demonstrated high sensitivity (80.1%) and specificity (80.5%) in identifying TM-contaminated soil. These findings indicate significant biochar- and Serratia marcescens-induced impacts on toxic metal availability, physicochemical properties, and enzymatic activities in metal-contaminated soil, suggesting that blending soil with biochar and microorganisms is an effective remediation strategy.

Enhancing the thermoelectric properties of PEDOT:PSS films through the incorporation of g-C3N4 nanosheets and carbon nanotubes

Present study focuses on the synthesis of flexible nanocomposite film made of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS), graphitic carbon nitride (g-C3N4) nanosheets, and carbon nanotubes (CNTs) and how the g-C3N4 nanosheets and CNTs affect the thermoelectric properties of PEDOT:PSS. Incorporating 10 wt% of g-C3N4 nanosheets to PEDOT:PSS improved the Seebeck coefficient to 74.3 μVK−1, ∼5 times higher than the PEDOT:PSS film. However, this led to a decrease in electrical conductivity, limiting the power factor to 335.4 μWm−1K−2. In order to address this, CNTs were added as conductive fillers. The resulting PEDOT:PSS composite, with 10 wt% of g-C3N4 and 10 wt% CNTs, showed a significant power factor of 589.8 μWm−1K−2, an electrical conductivity of 810.6 Scm−1, and a Seebeck coefficient of 84.5 μVK−1, indicating a substantial improvement in the thermoelectric performance of pristine PEDOT:PSS. The increased Seebeck coefficient in the PEDOT:PSS and g-C3N4 composite is due to reduced carrier concentration and energy filtering at the interfaces. The enhancement in electrical conductivity and the Seebeck coefficient after adding CNTs is attributed to the formation of conductive networks, increased mobility, and energy filtering at the interfaces between PEDOT:PSS and CNTs. The study suggests that combining g-C3N4 nanosheets and CNTs with PEDOT:PSS could enhance the thermoelectric performance of PEDOT:PSS-based materials.

Impact of titanium modification on the performance improvement and phase change mechanism of ZnSb thin film

Phase change memory has emerged as a promising option for neuro-inspired and data-intensive AI applications, attracting significant attention from the semiconductor field recently. The performance of the device relies on the phase change material, aiming for enhanced thermal stability along with low power consumption. Nanocomposite ZnSb thin films with titanium dopant were prepared and their crystallization properties and mechanisms were investigated. Compared to pure ZnSb material, the addition of titanium can significantly enhance the temperature of crystallization and the 10-year data retention ability, both of which surpassing 16 °C. The obvious enhancement in thermal stability may be ascribed to the ionic bond formation between titanium and antimony elements, as indicated by differential charge calculations. Also, phase change memory cells with a diameter of 190 nm were fabricated using standard CMOS technology. The Ti-doped ZnSb thin film demonstrates rapid crystallization and amorphization within 50 ns while consuming low power at approximately 1.5 × 10−10 J. The decrease in power consumption may stem from the increase in band gap energy and a decrease in electrical conductivity, as confirmed by first-principles calculations. Both experimental and theoretical results prove that titanium doping can remarkably improve the physical properties of ZnSb thin film, facilitating the exploration and design of novel phase change materials with high thermal stability, low power consumption, as well as fast switching speed.

Direct Writing of SiC-polymer nanocomposites for humidity sensing with enhanced performance

Humidity sensors are essential for monitoring humidity levels in various fields. This paper investigates the development and optimization of humidity sensitive SiC-Fe3O4 polymer nanocomposites with varying Fe3O4 concentrations fabricated using Direct Writing (DW) process. The inks were evaluated for flow behavior to ensure proper extrudability through the nozzle. The rheological behavior was then correlated with the printing parameters to optimize the printing accuracy of the nanocomposites. It was observed that all the inks exhibited shear-thinning behavior, enabling a smooth extrusion process. To ensure high-resolution features, a new image analysis method was introduced to quantify corner rounding in printed features, enabling the optimization of printing parameters. In terms of humidity sensing performance, all the inks displayed a change in electrical properties with humidity adsorption. The fabricated nanocomposites showed a decrease in electrical conductivity with increasing humidity, suggesting potential for humidity-sensing applications. Notably, the humidity sensitivity of the nanocomposites was highly dependent on the Fe3O4 concentration in the inks. These findings provide valuable insights into the DW of SiC-Fe3O4 polymer nanocomposites for humidity sensing applications.

Exogenous melatonin alleviates sodium chloride stress and increases vegetative growth in Lonicera japonica seedlings via gene regulation

Melatonin (Mt) functions as a growth regulator and multifunctional signaling molecule in plants, thereby playing a crucial role in promoting growth and orchestrating protective responses to various abiotic stresses. However, the mechanism whereby exogenous Mt protects Lonicera japonica Thunb. (L. japonica) against salt stress has not been fully elucidated. Therefore, this study aimed to elucidate how exogenous Mt alleviates sodium chloride (NaCl) stress in L. japonica seedlings. Salt-sensitive L. japonica seedlings were treated with an aqueous solution containing 150 mM of NaCl and aqueous solutions containing various concentrations of Mt. The results revealed that treatment of NaCl-stressed L. japonica seedlings with a 60 µM aqueous solution of Mt significantly enhanced vegetative plant growth by scavenging reactive oxygen species and thus reducing oxidative stress. The latter was evidenced by decreases in electrical conductivity and malondialdehyde (MDA) concentrations. Moreover, Mt treatment led to increases in the NaCl-stressed L. japonica seedlings’ total chlorophyll content, soluble sugar content, and flavonoid content, demonstrating that Mt treatment improved the seedlings’ tolerance of NaCl stress. This was also indicated by the NaCl-stressed L. japonica seedlings exhibiting marked increases in the activities of antioxidant enzymes (superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase) and in photosynthetic functions. Furthermore, Mt treatment of NaCl-stressed L. japonica seedlings increased their expression of phenylalanine ammonia-lyase 1 (PAL1), phenylalanine ammonia-lyase 2 (PAL2), calcium-dependent protein kinase (CPK), cinnamyl alcohol dehydrogenase (CAD), flavanol synthase (FLS), and chalcone synthase (CHS). In conclusion, our results demonstrate that treatment of L. japonica seedlings with a 60 µM aqueous solution of Mt significantly ameliorated the detrimental effects of NaCl stress in the seedlings. Therefore, such treatment has substantial potential for use in safeguarding medicinal plant crops against severe salinity.

Self-assembly of mixed surfactants sodium dodecylsulfate and polyethylene glycol dodecyl ether in aqueous solutions

The thermodynamic behavior of mixed systems containing the anionic surfactant sodium dodecyl sulfate (SDS) and the nonionic surfactant polyethylene glycol dodecyl ether (Brij L4) in aqueous solutions was investigated. Electrical conductivity and interfacial tension measurements were employed to investigate the concentration-dependent properties of these surfactant mixtures. Two main experiments were conducted: i) constant ratio experiment: the overall surfactant concentration was varied while maintaining a fixed ratio between SDS and Brij L4. It was shown that the critical micelle concentration (CMC) determined from electrical conductivity measurements does not indicate the formation of the first mixed micelles as observed using tensiometry, but the point from which the adsorption of counterions by the existing micelles became important. By using the Regular Solution Theory (RST), it was found that the interaction between SDS and Brij L4 is synergistic, driven by dipole-ion interactions of the hydrophilic regions of the two surfactants. ii) Fixed SDS concentration while increase the Brij L4 concentration: the resulting electrical conductivity exhibited non-trivial behavior which complexity arose from simultaneous phenomena of incorporation of free SDS molecules into the micelles as Brij L4 concentration increased, leading to a decrease in electrical conductivity; liberation of some adsorbed counterions from the mixed micelles to the solution, which increases the conductivity and increase of viscosity due to Brij L4 further addition that leads to a sequential decrease in electrical conductivity.

RADIATION-STIMULATED CONVERSION TO SUPERIONIC STATE OF TlSe AND TlS CRYSTALS

The electrical properties of TlSe and TlS compounds were studied in a constant and alternating measuring field when exposed to various doses of gamma radiation in the temperature range of 300…400 K. In a constant electric field, a decrease in electrical conductivity with time was detected. Complex impedance spectra were measured in the frequency range 20…106 Hz. It is shown that in the studied range of temperatures, frequencies and doses of γ-radiation, conductivity is ionic in nature. The electrical properties of TlSe and TlS crystals are determined by the conductivity of Tl+1 ions and the accumulation of charge carriers near the blocking silver electrodes.

Mitigating the detrimental impacts of low- and high-density polyethylene microplastics using a novel microbial consortium on a soil-plant system: Insights and interactions

The accumulation of polyethylene microplastics (PE-MPs) in soil has raised considerable concerns; however, the effects of their persistence and mitigation on agroecosystems have not been explored. This study aimed to assess the detrimental effects of PE-MPs on a soil-plant system and evaluate their mitigation using a novel microbial consortium (MC). We incorporated low-density polyethylene (LDPE) and high-density polyethylene (HDPE) at two different concentrations, along with a control (0 %, 1 %, and 2 % w/w) into the sandy loam soil for a duration of 135 days. The samples were also treated with a novel MC and incubated for 135 days. The MC comprised three bacterial strains (Ralstonia pickettii (MW290933) strain SHAn2, Pseudomonas putida strain ShA, and Lysinibacillus xylanilyticus XDB9 (T) strain S7–10F), and a fungal strain (Aspergillus niger strain F1–16S). Sunflowers were subsequently cultivated, and physiological growth parameters were measured. The results showed that adding 2 % LDPE significantly decreased soil pH by 1.06 units compared to the control. Moreover, adding 2 % HDPE resulted in a more significant decrease in soil electrical conductivity (EC) relative to LDPE and the control. A dose-dependent increase in dissolved organic carbon (DOC) was observed, with the highest DOC found in 2 % LDPE. The addition of higher dosages of LDPE reduced soil bulk density (BD) more than HDPE. The addition of 2 % HDPE increased the water drop penetration time (WDPT) but decreased the mean weight diameter of soil aggregates (MWD) and water-stable aggregates (WSA) compared to LDPE. The results also revealed that higher levels of LDPE enhanced soil basal respiration (BR) and microbial carbon biomass (MBC). The interaction of MC and higher MP percentages considerably reduced soil pH, EC, BD, and WDPT but significantly increased soil DOC, MWD, WSA, BR, and MBC. Regarding plant growth, incorporating 2 % PE-MPs significantly reduced physiological responses of sunflower: chlorophyll content (Chl; −15.2 %), Fv/Fm ratio (-25.3 %), shoot dry weight (ShD; −31.3 %), root dry weight (RD; −40 %), leaf area (LA; −38.4 %), and stem diameter (StemD; −25 %) compared to the control; however, the addition of novel MC considerably reduced and ameliorated the harmful effects of 2 % PE-MPs on the investigated plant growth responses.

Nanostructuring of AlSiCrMnFeNiCu High‐Entropy Alloy via Cryomilling: Exploring Structural, Magnetic, and Thermoelectric Properties

Efforts are made to understand the influence of milling intensity on structure, morphology, magnetic and thermoelectric properties of nonequiatomic nanostructured AlSiCrMnFeNiCu high‐entropy alloy (HEA) powders prepared by cryomilling. These powders are cryomilled with different ball‐to‐powder ratios (BPR) and present a dual‐phase structure containing a major B2‐type and a minor Cr5Si3‐type phase. An increase in BPR enhances the refinement of crystallite size, grain size, and particle size accompanied by a decrease in the phase fraction of the minor Cr5Si3‐type phase. Magnetic measurements revealed that at room temperature, sufficient increase in BPR leads to a transition from multi‐domain behavior to single‐domain behavior which leads to enhancement in soft magnetic properties. Thermal measurements show the presence of different magnetic phase transitions which vary with an increase in BPR. A change of charge carrier type from p to n‐type was observed as the grain size is reduced. The figure of merit decreases with the decrease in grain size from 2 × 10–5 for as‐cast powders and is lowest for the smallest grain‐sized sample due to a decrease in electrical conductivity. This study shows the possibility of exploring nonequiatomic low‐density HEAs whose functional properties can be tailored, offering flexibility in material design for specific applications.

Evolution of thermoelectric transport properties of Sb2Te3–Sb2Se3 solid-solution alloys depending on phase formation behavior

Sb2Te3-based alloys exhibit decent thermoelectric transport properties in the mid-temperature range above 550 K. However, the study on Sb2Te3 alloys has been limited in simple doping approach. Herein, evolution in the thermoelectric transport properties associated with the phase formation of solid solution alloys of Sb2(Te1−xSex)3 (x = 0, 0.25, 0.33, 0.5, 0.75, and 1.0) compositions is investigated to widen the strategy to solid solution alloying. A single phase of the Sb2Te3 rhombohedral structure formed from x = 0 to 0.5, whereas mixed phases with an orthorhombic structure of Sb2Se3 was observed at x = 0.75. The electrical conductivity weighted mobility were gradually decreased as Se content increases to x = 0.75. Consequently, the power factor was decreased gradually and significantly to 0.076 mW/mK2 for x = 0.75 (Sb2(Te0·25Se0.75)3) compared with 2.6 mW/mK2 of the pristine sample. The total thermal conductivity of 2.0 W/mK for the Sb2Te3 was significantly reduced gradually to 0.64 W/mK for x = 0.75 owing to simultaneous decrease in electrical and lattice thermal conductivities. The reduction in lattice thermal conductivity is mainly owing to the addition point defect scattering caused by the Se addition. Nevertheless, thermoelectric figure of merit zT of Sb2Te3 is gradually decreased from 0.64 to 0.11 for x = 0.75 at 650 K due to the degradation in electrical transport properties. Furthermore, the theoretical zT was estimated for all samples with varying carrier concentration based on single parabolic band model.

Effect of particle size and concentration on foodborne pathogen inactivation by pulsed ohmic heating in tomato sauce

This research investigated the effects of the size and concentration of diced tomato particles in tomato sauce on the performance of pulsed ohmic heating (POH). Samples were prepared by adding 5 and 10 g of tomato particles (square shapes with sides of 2.5, 5, 10, and 15 mm) to 20 and 15 g of tomato sauces, and tomato sauce without particles was used as the control group. As the size and concentration of tomato particles increased, the passage of electric current was hindered, resulting in a decrease in electrical conductivity and consequently a deceleration in the heating rate of POH. Through infrared camera image analysis, it was determined that tomato particles formed cold areas in the tomato sauce, inhibiting uniform heating of POH. Because particles reduced efficiency of POH, there was an inverse relationship between the size and content of particles and the reduction of pathogens. At 20% tomato particles, the reduction levels of Escherichia coli O157:H7 were 1.60, 1.85, 2.12, 2.28, and 3.07 log CFU/ml for tomato sauces with particle sizes of 2.5, 5, 10, and 15 mm and without particles, respectively. When the size of the tomato particles was the same, increasing the particle concentration in the sauce from 20 to 40% resulted in an average reduction of 0.47 in the inactivation levels of E. coli O157:H7 by POH. Therefore, the size and concentration of particles dispersed in food should be contemplated when designing a POH process to inactivate harmful bacteria in food.

Effect of Intermediate Annealing on Microstructure and Cold Rolling Hardness of AlFeMn Alloy

The microstructure and texture of an AlFeMn alloy were studied under different intermediate annealing processes, and the changes in microhardness during cold rolling were analyzed. After annealing at 420 °C with a slow heating rate, the alloy showed a high number of small dispersed particles and recrystallization textures dominated by R texture, with deformation textures of 23.5%. Annealing at 610 °C with a rapid heating rate resulted in a significant decrease in the number of small-sized particles and an increase in recrystallization texture contents, with CubeND being the majority. The deformation texture contents decreased to 14.9%. The electrical conductivity of the 420 °C annealed sheet was higher than before annealing, whereas the sheet annealed at 610 °C showed a decrease in electrical conductivity after annealing. This indicated that annealing at 610 °C led to a higher degree of recrystallization and the development of Cube/CubeND due to the dissolution of dispersed particles. During the subsequent cold rolling process, the microhardness of both annealed sheets initially increased and then decreased. However, the microhardness of the 420 °C annealed sheet with varying cold rolling reductions consistently remained lower than that of the 610 °C annealed sheet, as was the cold rolling reduction corresponding to the peak microhardness. The results showed that the precipitation at 420 °C facilitated work softening, while the dissolution at 610 °C promoted work hardening.

Influence of the presence of ions on the dielectric properties of reverse micelle systems

AOT/isooctane/water reverse micelle solution was doped with ionic salts solutions: sodium chloride, potassium chloride, tetramethylammonium chloride, tetramethylammonium bromide, sodium butyrate and sodium benzoate. Each system was investigated for the influence of ionic additives on dielectric properties: electric permittivity, conductivity and nonlinear dielectric effect (NDE). Studies showed that addition of salts noticeably changes the dielectric parameters. Based on the salts used in this research, the most common effect is a decrease of electric permittivity, conductivity and NDE effect. However, addition of some ions can lead to their increase, which was proved in the case of sodium benzoate. The registered changes were explained based on the percolation effect and changes in rigidity of the micellar surfactant shell due to the incorporation of the dissolved ions into the micellar structure.

Improved strength-plasticity-conductivity of graphene/copper layered composites by vacuum hot rolling

The method used to strengthen copper matrix composites generally results in a significant decrease in ductility and electrical conductivity. In this work, multilayer graphene was grown on both sides of copper foil using chemical vapor deposition process and graphene/copper layered composites were prepared by stacking copper foils and hot rolling under vacuum. The microstructures, mechanical properties and electrical conductivity of hot rolled graphene/copper layered composites with different reduction amounts were investigated. Results showed that the grain size increased while the dislocation density did not change much with the reduction amounts from 30% to 50%. The size of graphene decreased and the spacing of graphene increased with the reduction amounts. When the reduction amounts increased from 30% to 50%, the tensile strength decreased from 223 MPa to 163 MPa, the elongation decreased from 45% to 31% and the electrical conductivity decreased from 101.52 %IACS to 89.73 %IACS. The optimized combination of properties was obtained when the hot rolled reduction amount was set as 30% because of the grain refining and the change in graphene size and spacing. Combining the analysis of microstructures and properties of the unreinforced copper matrix at 30% reduction amount, it can be concluded that the tensile strength of the composite increased from 179 MPa to 223 MPa, elongation increased from 38% to 45% and electrical conductivity increased from 98.02 %IACS to 101.52 %IACS. Long and distributed continuously graphene were beneficial to the improvement of strength, elongation and electrical conductivity by playing an obvious role in the load transfer strengthening mechanism, refining the grain size of the composites, and preventing the crack propagation.

SODIUM, MONOETHANOLAMMONIUM AND POLYETHYLENE POLYAMMONIUM CITRATES AQUEOUS SOLUTIONS ELECTROCHEMICAL PROPERTIES

pH and conductometric study of aqueous (0.1 ÷ 9.0)⋅10-3 mol/l solutions of sodium (Na3Cit), monoethanolammonium (H3Cit⋅3MEA) and polyethylenepolyammonium (kH3Cit⋅3PEPA) citrates was carried out. Features of the electrochemical behavior of monoethanolamine and polyethylenepolamine ammonium citrates aqueous solutions were revealed in comparison with Na3Cit. As the temperature increases from 293 to 303 K, the pH values and Na3Cit solutions molar electrical conductivity increase. Due to hydrolytic processes, when diluting H3Cit⋅3MEA solutions, a change in pH is observed from slightly acidic to slightly alkaline, in contrast to Na3Cit. An increase in temperature (in the region of 293–308 K) leads to an increase in the medium acidity, in contrast to sodium citrate solutions, which is accompanied by an atypical decrease in molar electrical conductivity at the same H3Cit⋅3MEA content. It has been shown that an increase in temperature in the range of 293-308 K leads to a decrease in H3Cit⋅3MEA aqueous solutions pH, in contrast to Na3Cit and kH3Cit⋅3PEPA solutions, which is accompanied by an atypical decrease in molar electrical conductivity at the same H3Cit⋅3MEA content. The component composition of Na3Cit, H3Cit⋅3MEA and kH3Cit⋅3PEPA aqueous solutions was calculated. The probability of the existence of negatively charged ion-molecular complexes in H3Cit⋅3MEA and kH3Cit⋅3PEPA aqueous solutions is shown. The concentration and temperature dependence of citrate ions hydrolysis constant was obtained. The concentration and temperature dependence of these complexes was assessed. The atypical negative effect of heating on H3Cit⋅3MEA aqueous solutions molar electrical conductivity is associated with a change in the radius of the ion-molecular complex and its stability. The value of the limiting molar electrical conductivity of sodium, monoethanolammonium and polyethylenepolyammonium citrates aqueous solutions in the range of 293–313 K was estimated. Correlations were revealed between the values of the limiting electrical conductivity and ion-molecular complexes formation constants in H3Cit⋅PEPA aqueous solutions. The values of energy, enthalpy and entropy of activation of molar electrical conductivities of aqueous solutions were calculated. For the solutions studied, compensation effects were noted in the activation parameters of molar electrical conductivity.