Flexible and Robust Functionalized Boron Nitride/Poly(p‑Phenylene Benzobisoxazole)Nanocomposite Paper with High Thermal Conductivity and Outstanding Electrical Insulation

With the rapid development of 5G information technology,thermal conductivity/dissipation problems of highly integrated electronic devices and electrical equipment are becoming prominent.In this work,“high-temperature solid-phase&diazonium salt decomposition”method is carried out to prepare benzidine-functionalized boron nitride(m-BN).Subsequently,m-BN/poly(pphenylene benzobisoxazole)nanofiber(PNF)nanocomposite paper with nacremimetic layered structures is prepared via sol–gel film transformation approach.The obtained m-BN/PNF nanocomposite paper with 50 wt%m-BN presents excellent thermal conductivity,incredible electrical insulation,outstanding mechanical properties and thermal stability,due to the construction of extensive hydrogen bonds andπ–πinteractions between m-BN and PNF,and stable nacre-mimetic layered structures.Itsλ∥andλ_(⊥)are 9.68 and 0.84 W m^(-1)K^(-1),and the volume resistivity and breakdown strength are as high as 2.3×10^(15)Ωcm and 324.2 kV mm^(-1),respectively.Besides,it also presents extremely high tensile strength of 193.6 MPa and thermal decomposition temperature of 640°C,showing a broad application prospect in high-end thermal management fields such as electronic devices and electrical equipment.

Saturation Estimation with Complex Electrical Conductivity for Hydrate-Bearing Clayey Sediments:An Experimental Study

Clays have considerable influence on the electrical properties of hydrate-bearing sediments.It is desirable to understand the electrical properties of hydrate-bearing clayey sediments and to build hydrate saturation(S_(h))models for reservoir evaluation and monitoring.The electrical properties of tetrahydrofuran-hydrate-bearing sediments with montmorillonite are characterized by complex conductivity at frequencies from 0.01 Hz to 1 kHz.The effects of clay and Sh on the complex conductivity were analyzed.A decrease and increase in electrical conductance result from the clay-swelling-induced blockage and ion migration in the electrical double layer(EDL),respectively.The quadrature conductivity increases with the clay content up to 10%because of the increased surface site density of counterions in EDL.Both the in-phase conductivity and quadrature conductivity decrease consistently with increasing Sh from 0.50 to 0.90.Three sets of models for Sh evaluation were developed.The model based on the Simandoux equation outperforms Archie’s formula,with a root-mean-square error(E_(RMS))of 1.8%and 3.9%,respectively,highlighting the clay effects on the in-phase conductivity.The fre-quency effect correlations based on in-phase and quadrature conductivities exhibit inferior performance(E_(RMS)=11.6%and 13.2%,re-spectively)due to the challenge of choosing an appropriate pair of frequencies and intrinsic uncertainties from two measurements.The second-order Cole-Cole formula can be used to fit the complex-conductivity spectra.One pair of inverted Cole-Cole parameters,i.e.,characteristic time and chargeability,is employed to predict S_(h) with an E_(RMS) of 5.05%and 9.05%,respectively.

Extrusion 3D printing of carbon nanotube-assembled carbon aerogel nanocomposites with high electrical conductivity

Carbon nanotubes(CNTs)with high aspect ratio and excellent electrical conduction offer huge functional improvements for current carbon aerogels.However,there remains a major challenge for achieving the on-demand shaping of carbon aerogels with tailored micro-nano structural textures and geometric features.Herein,a facile extrusion 3D printing strategy has been proposed for fabricating CNT-assembled carbon(CNT/C)aerogel nanocomposites through the extrusion printing of pseudoplastic carbomer-based inks,in which the stable dispersion of CNT nanofibers has been achieved relying on the high viscosity of carbomer microgels.After extrusion printing,the chemical solidification through polymerizing RF sols enables 3D-printed aerogel nanocomposites to display high shape fidelity in macroscopic geometries.Benefiting from the micro-nano scale assembly of CNT nanofiber networks and carbon nanoparticle networks in composite phases,3D-printed CNT/C aerogels exhibit enhanced mechanical strength(fracture strength,0.79 MPa)and typical porous structure characteristics,including low density(0.220 g cm^(-3)),high surface area(298.4 m^(2)g^(-1)),and concentrated pore diameter distribution(~32.8nm).More importantly,CNT nanofibers provide an efficient electron transport pathway,imparting 3D-printed CNT/C aerogel composites with a high electrical conductivity of 1.49 S cm^(-1).Our work would offer feasible guidelines for the design and fabrication of shape-dominated functional materials by additive manufacturing.

GLOBAL UNIQUE SOLUTIONS FOR THE INCOMPRESSIBLE MHD EQUATIONS WITH VARIABLE DENSITY AND ELECTRICAL CONDUCTIVITY

We study the global unique solutions to the 2-D inhomogeneous incompressible MHD equations,with the initial data(u0,B0)being located in the critical Besov space■and the initial densityρ0 being close to a positive constant.By using weighted global estimates,maximal regularity estimates in the Lorentz space for the Stokes system,and the Lagrangian approach,we show that the 2-D MHD equations have a unique global solution.

Fabrication of Graphene/Cu Composite by Chemical Vapor Deposition and Effects of Graphene Layers on Resultant Electrical Conductivity

Graphene(Gr)has unique properties including high electrical conductivity;Thus,graphene/copper(Gr/Cu)composites have attracted increasing attention to replace traditional Cu for electrical applications. However,the problem of how to control graphene to form desired Gr/Cu composite is not well solved. This paper aims at exploring the best parameters for preparing graphene with different layers on Cu foil by chemical vapor deposition(CVD)method and studying the effects of different layers graphene on Gr/Cu composite’s electrical conductivity. Graphene grown on single-sided and double-sided copper was prepared for Gr/Cu and Gr/Cu/Gr composites. The resultant electrical conductivity of Gr/Cu composites increased with decreasing graphene layers and increasing graphene volume fraction. The Gr/Cu/Gr composite with monolayer graphene owns volume fraction of less than 0.002%,producing the best electrical conductivity up to59.8 ×10^(6)S/m,equivalent to 104.5% IACS and 105.3% pure Cu foil.

GaInX_3(X=S,Se,Te):Ultra-low thermal conductivity and excellent thermoelectric performance

Seeking intrinsically low thermal conductivity materials is a viable strategy in the pursuit of high-performance thermoelectric materials.Here,by using first-principles calculations and semiclassical Boltzmann transport theory,we systemically investigate the carrier transport and thermoelectric properties of monolayer Janus GaInX_(3)(X=S,Se,Te).It is found that the lattice thermal conductivities can reach values as low as 3.07 W·m^(-1)·K^(-1),1.16 W·m^(-1)·K^(-1)and 0.57 W·m^(-1)·K^(-1)for GaInS_(3),GaInSe_(3),and GaInTe_(3),respectively,at room temperature.This notably low thermal conductivity is attributed to strong acoustic-optical phonon coupling caused by the presence of low-frequency optical phonons in GaInX_(3) materials.Furthermore,by integrating the charac teristics of electronic and thermal transport,the dimensionless figure of merit ZT can reach maximum values of 0.95,2.37,and 3.00 for GaInS_(3),GaInSe_(3),and GaInTe_(3),respectively.Our results suggest that monolayer Janus GaInX_(3)(X=S,Se,Te)is a promising candidate for thermoelectric and heat management applications.

Boron nitride silicone rubber composite foam with low dielectric and high thermal conductivity

Silicone rubber(SR)is widely used in the field of electronic packaging because of its low dielectric properties.In this work,the porosity of the SR was improved,and the dielectric constant of the SR foam was reduced by adding expanded microspheres(EM).Then,the thermal conductivity of the system was improved by combining the modified boron nitride(f-BN).The results showed that after the f-BN was added,the dielectric constant and dielectric loss were much lower than those of pure SR.Micron-sized modified boron nitride(f-mBN)improved the dielectric and thermal conductivity of the SR foam better than that of nano-sized modified boron nitride(f-nBN),but f-nBN improved the volume resistivity,tensile strength,and thermal stability of the SR better than f-mBN.When the mass ratio of f-mBN and fnBN is 2:1,the thermal conductivity of the SR foam reaches the maximum value of 0.808 W·m^(-1)·K^(-1),which is 6.5 times that before the addition.The heat release rate and fire growth index are the lowest,and the improvement in flame retardancy is mainly attributed to the high thermal stability and physical barrier of f-BN.

Continuous changes in electrical conductivity of sodium aluminate solution in seeded precipitation

The mechanism of seeded precipitation of sodium aluminate solution was studied by measuring the seeded-precipitation rate and electrical conductivity online, as well as calculating the activity and fraction of ion pair. The results show that the electrical conductivity of sodium aluminate slurry linearly decreases with increasing aluminum hydroxide addition. Moreover, both the electrical conductivity of slurry and the difference in electrical conductivity between sodium aluminate solution and slurry remarkably decline in the first 60 min before gradually increasing in the preliminary 10 h and finally reaching almost the same level after 10 h. In low Na2 O concentration solution the activities of Na OH and Na Al（OH）4 in seeded precipitation are high, which can enlarge the difference in conductivity between slurry and solution. Additionally, more ion pairs exist in solution in preliminary seeded precipitation, and the adsorption of Na＋Al（OH）4- on seed surface is likely to break the equilibrium of ion pair formation and to decrease the difference in conductivity in preliminary seeded precipitation.

Electrical conductivity of NaF-AlF_3-CaF_2-Al_2O_3-ZrO_2 molten salts

The electrical conductivity of NaF-AlF3-CaF2-Al2O3-ZrO2 system was studied by a tube-type cell with fixed cell constant. The results show that the electrical conductivity of NaF-AlF3-3%Al2O3-3%CaF2-ZrO2 molten salt system decreases with increase of ZrO2 content in an interval of 0-5%. The increase of 1%ZrO2 results in a corresponding electrical conductivity decrease of 0.02 S/cm, and the equivalent conductivity increases with the increase of molar ratio of NaF to AlF3. When the temperature increases by 1 °C, the electrical conductivity increases by 0.004 S/cm. At last, the regression equations of electrical conductivity relative to temperature and ZrO2 are obtained by quadratic regression analysis.

Mechanical properties,electrical conductivity and microstructure of CuCrZr alloys treated with thermal stretch process

CuCrZr alloys were treated with the thermal stretch process at various temperatures from 100 to 300℃.The results reveal that the thermal stretch process is successfully developed to manufacture the precipitation hardening CuCrZr alloys with a good combination of microhardness and electrical conductivity.By increasing the tensile elongations at each temperature from 100 to 300℃,the microhardness increases whereas the electrical conductivity decreases slightly.Cr-containing precipitate phases with a Nishiyama-Wasserman orientation relationship to the copper matrix were observed by TEM.The achievement of high micro-hardness and acceptable electrical conductivity in the thermal stretch treated alloys is ascribed to the interactions of the heteroatom solution,dislocation increment,grain refinement and dispersive precipitation effect.

Ambient electrical conductivity of carbon cathode materials for aluminum reduction cells

The ambient electrical conductivity (AEC) of carbon cathode materials was investigated in respect to their open porosity, crystal structure and graphite content using hydrostatic method, four-probe technique and X-ray diffraction (XRD), respectively. The AEC is proportional to the specific conductivity (σ0) and the exponential of (1?ε) (ε is porosity) by a quasi-uniform formula based on the percolation theory. Theσ0 can reflect the intrinsic conductivity of the carbon cathodes free of pores, and it depends on the mean crystallite size parallel to the layer (002). The exponentn is dependent on the materials nature of the cathode aggregates, while an averaged value, 4.65, can practically work well with 5 types of cathode materials. The calculation ofσ0 can be extended to the graphitic cathodes containing different aggregates using the simple rule of mixture.

Electrical conductivity of MO(MO=FeO,NiO)-containing CaO-MgO-SiO_2-Al_2O_3 slag with low basicity

As a fundamental study on recovery of valuable metals from nonferrous metallurgical slags,electrical conductivity values of MO（MO=FeO,NiO）-containing CaO-MgO-SiO2-Al2O3 slag with a low basicity were measured at different temperatures using AC impedance spectroscopy.The result shows that the electrical conductivity increased from 1.4 S/m to 14.4 S/m with the increase of the temperature from 1 573 to 1 773 K and the content of MO which is less than 12% under the constant mass ratio of （CaO＋MgO） to （SiO2＋Al2O3） of 0.47.Moreover,the increase magnitude of the electrical conductivity was also promoted with the increase of the content of MO.The electrical conductivity of FeO-containing slags was close to that of NiO-containing slags when the content was less than 8%;however,it was obviously larger than that of NiO-containing slags when the content was 12%.The activation energy of the electrical conductivity decreased with the increase of MO content.

Effective thermal and electrical conductivity of graphite nanoplatelet composites

The relationship between the thermal/electrical conductivity enhancement in graphite nanoplatelets （GNPs） composites and the properties of filling graphite nanoplatelets is studied. The effective thermal and electrical conductivity enhancements of GNP-oil nanofluids and GNP-polyimide composites are measured. By taking into account the particle shape, the volume fraction, the thermal conductivity of filling particles and the base fluids, the thermal and electrical conductivity enhancements of GNP nanofluids are theoretically predicted by the generalized effective medium theory. Both the nonlinear dependence of effective thermal conductivity on the GNP volume fraction in nanofhiids and the very low percolation threshold for GNP-polyimide composites are well predicted. The theoretical predications are found to be in reasonably good agreement with the experimental data. The generalized effective medium theory can be used for predicting the thermal and electrical properties of GNP composites and it is still available for most of the thermal/electrical modifications in two-phase composites.

Electrical properties of dry polycrystalline olivine mixed with various chromite contents: Implications for the high conductivity anomalies in subduction zones

Chromite,a crucial high-conductivity mineral phase of peridotite in ophiolite suites,has a significant effect on the electrical structure of subduction zones.The electrical conductivities of sintered polycrystalline olivine containing various volume percents of chromite(0,4,7,10,13,16,18,21,23,100 vol.%)were measured using a complex impedance spectroscopic technique in the frequency range of 10^(−1)-10^(6) Hz under the conditions of 1.0-3.0 GPa and 873-1223 K.The relationship between the conductivities of the chromite-bearing olivine aggregates and temperatures conformed to the Arrhenius equation.The positive effect of pressure on the conductivities of the olivine-chromite systems was much weaker than that of temperature.The chromite content had an important effect on the conductivities of the olivine-chromite systems,and the bulk conductivities increased with increasing volume fraction of chromite to a certain extent.The inclusion of 16 vol.%chromites dramatically enhanced the bulk conductivity,implying that the percolation threshold of interconnectivity of chromite in the olivine-chromite systems is-16 vol.%.The fitted activation enthalpies for pure polycrystalline olivine,polycrystalline olivine with isolated chromite,polycrystalline olivine with interconnected chromites,and pure polycrystalline chromite were 1.25,0.78-0.87,0.48-0.54,and 0.47 eV,respectively.Based on the chemical compositions and activation enthalpies,small polaron conduction was proposed to be the dominant conduction mechanism for polycrystalline olivine with various chromite contents.Furthermore,the conductivities of polycrystalline olivine with interconnected chromite(10-1.5-100.5 S/m)provides a reasonable explanation for the high conductivity anomalies in subduction-related tectonic environments.

Electrical conductivity and viscosity of cryolite electrolytes for solar grade silicon(Si-SoG) electrowinning

Electrical conductivity of molten binary and ternary mixtures based on the system NaF-AlF3-SiO2 was investigated by means of a tube–cell （made of pyrolytic boron nitride） with stationary electrodes. Viscosity of the binary system Na3AlF6-SiO2 was measured by computerized torsion pendulum method. It was found that conductivity and viscosity varied linearly with temperature in all investigated mixtures. Obtained content dependence of electrical conductivity （isotherms） was divided into two parts. First, one represented the content region up to 10%（mole fraction） of SiO2;second, the region was with a higher content of SiO2 （from 10%up to 40%）. While the conductivity considerably decreased with content of SiO2 in the second part; it surprisingly rose in the low content range. A small addition of SiO2 to the molten cryolite （up to 10%） could slightly increase viscosity, but had no influence on the slope of this dependence since it is responsible for a glassy-networks formation in the melt. Further addition of SiO2 to the molten cryolite had a huge effect on the viscosity.

Bacterial Cellulose/Zwitterionic Dual-network Porous Gel Polymer Electrolytes with High Ionic Conductivity

Bacterial cellulose(BC)was innovatively combined with zwitterionic copolymer acrylamide and sulfobetaine methacrylic acid ester[P(AM-co-SBMA)]to build a dual-network porous structure gel polymer electrolytes(GPEs)with high ionic conductivity.The dual network structure BC/P(AM-co-SBMA)gels were formed by a simple one-step polymerization method.The results show that ionic conductivity of BC/P(AM-co-SBMA)GPEs at the room temperature are 3.2×10^(-2) S/cm@1 M H_(2)SO_(4),4.5×10^(-2) S/cm@4 M KOH,and 3.6×10^(-2) S/cm@1 M NaCl,respectively.Using active carbon(AC)as the electrodes,BC/P(AM-co-SBMA)GPEs as both separator and electrolyte matrix,and 4 M KOH as the electrolyte,a symmetric solid supercapacitors(SSC)(AC-GPE-KOH)was assembled and testified.The specific capacitance of AC electrode is 173 F/g and remains 95.0%of the initial value after 5000 cycles and 86.2%after 10,000 cycles.

Improving thermal conductivity of Mg-Si-Zn-Cu alloy through minimizing electron scattering at phase interface

The primary cause of the decrease in thermal conductivity of conventional thermal conductive magnesium alloys is electron scattering brought on by solute atoms.However,the impact of phase interface on thermal conductivity of magnesium alloys is usually disregarded.This study has developed a Mg-Si-Zn-Cu alloy with high thermal conductivity that is distinguished by having a very low solute atom content and a significant number of phase interfaces.The thermal conductivity of the Mg^(-1).38Si-0.5Zn-0.5Cu alloy raises from its untreated value of 133.2 W/(m·K)to 142.2 W/(m·K),which is 91%of the thermal conductivity of pure Mg.This is accomplished by subjecting the alloy to both 0.8wt%Ce modification and T6 heat treatment.The morphology of eutectic Mg_(2)Si phase is changed by Ce modification and heat treatment,and as a result,the scattering of electrons at the Mg_(2)Si/Mg interface is reduced,resulting in increase of the alloy’s thermal conductivity.

Effect of Cerium on Mechanical Performance and Electrical Conductivity of Aluminum Rod for Electrical Purpose

The effect of rare earth element Ce on mechanical performance and electrical conductivity of aluminum rod for electrical purpose were studied under industrial production condition. Using optical microscope, SEM, TEM, EDS and X-ray diffractometer, the microstructure and phase composition of aluminum rod were measured and analyzed. The results indicate that the content of rare earth element Ce is between 0.05% -0.16% in the aluminum rod for electrical purpose. Its tensile strength is enhanced to some extent. The research also discovers that the tensile strength is enhanced remarkably with impurity element Si content increases. Because influence of Si is big to the conductivity, the Si content should be controlled continuously strictly in the aluminum for electrical purpose. Adding rare earth element Ce reduces the solid solubility of Si in the aluminum matrix, and the negative effect of Si on the aluminum conductor reduces effectively. So the limit of in Si content in aluminum rod for electrical purpose can be relaxed moderately.

Effects of physical properties on electrical conductivity of compacted lateritic soil

Natural soils of various types have different electrical properties due to the composition,structure,water content,and temperature.In order to investigate the electrical properties of lateritic soil,electrical conductivity experiments have been conducted on a self-developed testing device.Test results show that the electrical conductivity of laterite increases with the increase of water content,degree of saturation and dry density.When the water content is below the optimum water content,the electrical conductivity of soils increases nonlinearly and the variation rate increases dramatically.However,when the water content,degree of saturation,or dry density increases to a certain value,the electrical conductivity tends to be a constant.In addition,soil electrical conductivity increases with the increase of temperature,and it is observed that the electrical conductivity decreases with the increase of the number of wetting–drying cycles.

Electrical Conductivity in Soil Extracts: Chemical Factors and Their Intensity

The electrical conductivity （EC） of 1：5 soil-water extract （EC1：5） was studied utilizing path coefficient analysis. The study focused on revealing the main chemical factors contributing to EC of soil extracts and their relative importance. Results showed that the most important factors influencing the EC1：5 of coastal salt-affected soils were the concentration of salt in 1：5 soil-water extract （So）, Cl^-, and the sodium adsorption ratio （SAR）, while effects of pH, CO3^2-, HCO3^, soluble sodium percentage （SSP）, and sodium dianion ratio （SDR） were very weak. Though the direct path coefficients between EC1：5 and SO4^2- , Ca^2＋, Mg^2＋, K^＋, or Na^＋ were not high, influence of other chemical factors caused the coefficients to increase, making the summation of their direct and indirect path coefficients relatively high. Evidences showed that multiple regression relations between EC1：5 and most of the primary factors （So, Cl^-, and SAR） had sound reliability and very good accuracy.