Improved electrical and thermal conductivities of polysiloxane-derived silicon oxycarbide ceramics by barium addition

The electrical and thermal conductivities of bulk barium-added silicon oxycarbide (SiOC-Ba) ceramics are investigated. The SiOC-Ba ceramics exhibited improved electrical and thermal conductivities upon increasing the sintering temperature from 1450 °C to 1650 °C. Precipitation of graphitic carbon clusters observed by Raman spectroscopy and high-resolution transmission electron microscopy is attributed to the phase separation during the fabrication process. The increase in the electrical conductivity can be rationalized in terms of an increase in the density of the sp² CC bonds within the carbon clusters. The increase in the thermal conductivity is mainly attributed to the formation of interconnected graphitic clusters in the SiOC matrix and SiC embedded in the clusters. The electrical and thermal conductivities of the SiOC-Ba ceramics sintered at 1650 °C are 14.0 Ω^?1 cm^?1 and 5.6 W/m K, respectively, at room temperature. The electrical conductivity of SiOC-Ba sintered at 1550 °C is 5.3 Ω^?1 cm^?1 and 7.0 Ω^?1 cm^?1 at 2 and 300 K, respectively.     

Carbon-coated Li2S cathode for improving the electrochemical properties of an all-solid-state lithium-sulfur battery using Li2S-P2S5 solid electrolyte

Li₂S is coated with carbon to improve the electrical conductivity of the composite cathode in all-solid-state lithium-sulfur batteries. Carbon is applied by thermal evaporation from a polyacrylonitrile (PAN) source at 600 °C for 5 h. It is shown that the carbon coating is impurity free, and the crystallinity of Li₂S is well maintained. The electronic conductivity of Li₂S is dramatically improved from 9.21 × 10^?9 S cm^?1 to 2.39 × 10^?2 S cm^?1 upon carbon coating. An all-solid-state battery prepared with the carbon-coated Li₂S shows a high initial capacity of 585 mAh g^?1 (g of Li₂S) that increases up to 730 mAh g^?1 (g of carbon-coated Li₂S) by the 10th cycle. This high capacity is stable throughout the 25 cycles tested, with an excellent coulombic efficiency of 99%. Carbon-coated Li₂S is advantageous for all-solid-state batteries due to the increased electrical conductivity, while allowing a reduction of the total carbon content present in the composite cathode.     

The effect of graphite oxide on the thermoelectric properties of polyaniline

Graphite oxide (GO)/ordered polyaniline (PANI) composites have been prepared through an in situ polymerization. TEM, XRD, FTIR and XPS analyses show that the PANI grew along the surface of exfoliated GO as a template to form a more ordered structure with high crystallinity during polymerization. Compared with pure PANI, both higher electrical conductivity and higher Seebeck coefficient of GO/PANI composites result from the increased carrier mobility, which is confirmed by Hall measurement. Strong interactions exist between graphene oxide and PANI, including electrostatic forces, hydrogen bonding and π–π stacking. There is no significant difference in thermal conductivity between GO/PANI composites and PANI. The maximum electrical conductivity and Seebeck coefficient of the composites reach 751 S m^?1 and 28.31 μV K^?1, respectively. The maximum thermoelectric figure of merit is up to 4.86 × 10^?4, 2 orders of magnitude higher than that of pure PANI.     

DC electrical conductivity of nano-composite polystyrene–titanium–arsenate membrane

In continuation to our previous work with nano-composite polystyrene–titanium–arsenate (PS–Ti–As), we further extended the characterization by means of DSC, TEM and mercury porosimetry measurements. In addition to the extended characterization, we also investigated the DC electrical conductivity behaviour of the PS–Ti–As composite membrane under different time, temperature and electrolyte conditions. The conductivity of the membrane investigated in the temperature region of 30–200 °C using a four-in-line probe DC measurement and in the semi-conductor region of 10^?5–10^?3 S cm^?1, found to obey the Arrhenius equation. From the time and temperature dependent conductivity studies on the HCl doped composite, it was observed that the conductivity increases with increase of temperature until 100 °C and further decreased with time during 120–160 °C, which can be attributed to the loss of HCl dopant molecules and blocking of the chemical reactions associated with the dopant. Further, we studied the stability of DC electrical conductivity retention in an oxidative environment by two slightly different techniques viz. isothermal and cyclic.     

Graphene nanoplatelet paper as a light-weight composite with excellent electrical and thermal conductivity and good gas barrier properties

Paper forms (i.e. thin free-standing films) of carbon-based materials have received increasing attention. Here we present a novel approach to fabricating a binder free, self-standing flexible paper consisting of exfoliated graphite nanoplatelets (GNPs). It is found that the electrical conductivity of the GNP paper can be as high as 2200 S cm^?1 and the thermal conductivity reaches 313 W m^?1 K^?1. Both thermoset and thermoplastic matrices were used to impregnate the porous GNP paper and an extremely high tensile modulus was attained. Even with 30 vol.% polymer, the GNP paper composite can still exhibit ～700 S cm^?1 electrical conductivity thanks to the highly continuous GNP network formed in the paper making process. The impregnated GNP paper was also investigated as a component in carbon fiber composite. It is found that when inserted into a layered laminate composite construction, gas permeability can be severely reduced and electrical and thermal conductivity can be greatly enhanced.     

Chemical stability and electrical properties of Nb doped BaCe0.9Y0.1O3−δ as a high temperature proton conducting electrolyte for IT-SOFC

BaCe_0.9?xNb_xY_0.1O_3?δ (where x=0, 0.01, 0.03 and 0.05) powders were synthesized by solid-state reaction to investigate the influence of Nb concentration on chemical stability and electrical properties of the sintered samples. The dense electrolyte pellets were formed from the powders after being uniaxially pressed and sintered at 1550 °C. The electrical conductivities determined by impedance measurements in temperature range of 550–750 °C in different atmospheres (dry argon and wet hydrogen) showed a decreasing trend with an increase of Nb content. For all samples higher conductivities were observed in the wet hydrogen than in dry argon atmosphere. The chemical stability was enhanced with increasing of Nb concentration. It was found that BaCe_0.87Nb_0.03Y_0.1O_3?δ is the optimal composition that satisfies the opposite demands for electrical conductivity and chemical stability, reaching 0.8×10^?2 S cm^?1 in wet hydrogen at 650 °C compared to 1.01×10^?2 S cm^?1 for undoped electrolyte.     

Estimating the permeability of cement pastes and mortars using image analysis and effective medium theory

A method to estimate permeability of cement-based materials using pore areas and perimeters from SEM images is presented. The pore structure is idealised as a cubic lattice having pores of arbitrary size. The hydraulic conductance of each pore is calculated using the hydraulic radius approximation, and a stereological factor is applied to account for the random orientation of the image plane. A ‘constriction factor’ is applied to account for variations in pore radius along the pore axis. Kirkpatrick's effective medium equation is then used to obtain an effective pore conductance, from which the macroscopic permeability is derived. The method was tested on forty-six pastes and mortars with different w/c ratio, cement, age and sand content. The permeabilities ranged from 3 × 10^? 18 m² to 5.8 × 10^? 16 m². It was found that 76% of the permeabilities were predicted to within a factor of ± 2, and 98% within a factor of ± 5 from measured values.     

Role of the effective electrical conductivity of nanosuspensions in the generation of TiO2 agglomerates with electrospray

Suspensions with varying volume fraction of TiO₂ nanoparticles and ionic strength were electrosprayed to obtain agglomerates of different characteristics, which were then deposited to produce films with tailored morphology, thickness, and porosity. The role of the nanoparticle volume fraction in both the effective electrical conductivity of TiO₂ nanosuspensions and the control of the size of agglomerates produced by electrospray was investigated. A simple modified equation for the effective electrical conductivity of TiO₂ nanoparticle suspensions was derived. The equation, which accounted for nanoparticles' diffuse ionic layer and their agglomeration in a liquid, showed that the effective electrical conductivity is not only a function of the liquid and particle conductivities, and the particle volume fraction but also a function of both the thickness of the adsorbed ionic layer on the particles and the particle size. Gradual increase of particle volume fraction resulted in an increase in the suspension's effective electrical conductivity, when the initial liquid conductivity was in the range of 10^?4–10^?3 S m^?1. When the liquid conductivity was in the range of 10^?3–10^?2 S m^?1; however, addition of particles did not have any significant effect on the effective electrical conductivity. Control over the size of the TiO₂ nanoparticle agglomerates was achieved by electrospraying suspensions with liquid electrical conductivity of the order of 10^?3 S m^?1 and by varying the particle volume fraction. Electrospray deposition of suspensions with TiO₂ volume fraction=0.04% resulted in a more compact film with lower porosity and showed better water-splitting performance.     

Uranyl ion-selective optical test strip

A novel, optical sensor, test strip has been developed for the spectrophotometric determination of trace amounts of uranyl ions, UO₂²⁺, based on immobilization of C.I. Mordant Blue 29 (Chromazurol S)/cetyl N,N,N-trimethyl ammonium bromide ion pair on a triacetyl cellulose membrane. Optimization of the sensor for the detection of low levels of uranyl ion is described. The test strip responded linearly to uranyl ions between 3.0 × 10^?7 and 6.0 × 10^?5 mol L^?1; the reproducibility of the sensor at a medium level of UO₂²⁺ activity was ±0.55%. The optical sensor can be regenerated using 0.01 mol L^?1 HCl or 0.01 mol L^?1 NaF solution after 10 min. The developed test strip was used in the determination of UO₂²⁺ in ground water samples.     

Flow injection analysis of free glycerol in biodiesel using a copper electrode as an amperometric detector

The main goal of this work was to develop a simple analytical method for quantification of glycerol based on the electrocatalytic oxidation of glycerol on the copper surface adapted in a flow injection system. Under optimal experimental conditions, the peak current response increases linearly with glycerol concentration over the range 60–3200 mg kg^?1 (equivalent to 3–160 mg L^?1 in solution). The repeatability of the electrode response in the flow injection analysis (FIA) configuration was evaluated as 5% (n = 10), and the detection limit of the method was estimated to be 5 mg kg^?1 in biodiesel (equivalent to 250 μg L^?1 in solution) (S/N = 3). The sample throughput under optimised conditions was estimated to be 90 h^?1. Different types of biodiesel samples (B100), as in the types of vegetable oils or animal fats used to produce the fuels, were analysed (seven samples). The only sample pre-treatment used was an extraction of glycerol from the biodiesel sample containing a ratio of 5 mL of water to 250 mg of biodiesel. The proposed method improves the analytical parameters obtained by other electroanalytical methods for quantification of glycerol in biodiesel samples, and its accuracy was evaluated using a spike-and-recovery assay, where all the biodiesel samples used obtained admissible values according to the Association of Official Analytical Chemists.     

Effect of carbonaceous matter contents on the fire resistance and mechanical properties of coal fly ash enriched mortars

In this paper, the thermal and mechanical behaviors of mortars mainly composed of coal fly ash (80 wt%) are studied with the aim of analyzing the influence of the unburned matter of the ash on the fire resistance and mechanical strength characteristics of mortars potentially used for passive protection against fire. All the properties have been evaluated after 28 days of setting time, comparing the properties of mortars containing ashes with different loss on ignition (LOI) contents and studying the behavior of mortars in which fly ash has been submitted to a pre-treatment aimed at removing the unburned matter. The insulating properties of the mortars have been analyzed by means of thermal analysis techniques; also the standard fire resistance test has been reproduced on 200 mm-height, 50 mm-diameter cylindrical test probes. Different mechanical properties such as compressive and flexural strength of the probes (before and after the fire resistance test), superficial hardness and dynamic elasticity modulus have been measured. The results obtained show a slight influence of the ash unburned matter content on the insulating capacity and mechanical properties of the mortars. On the other hand, the thermally-treated ash mortars showed better mechanical and insulating properties, although presumably the cost of the thermal pre-treatment does not justify the improvement achieved.     

Influence of Y2O3 addition on electrical properties of β-SiC ceramics sintered in nitrogen atmosphere

The influence of Y₂O₃ addition on electrical properties of β-SiC ceramics has been investigated. Polycrystalline SiC samples obtained by hot-pressing SiC–Y₂O₃ powder mixtures in nitrogen (N) atmosphere contain Y₂O₃ clusters segregated between SiC grains. Y₂O₃ forms a Y–Si-oxycarbonitride phase during sintering by reacting with SiO₂ and SiC and by dissolution of N from the atmosphere; this induces N doping into the SiC grains during the process of grain growth. The SiC samples exhibit an electrical resistivity of ～10^?3 Ω cm and a carrier density of ～10²⁰ cm^?3, which are ascribed to donor states derived from N impurities. The increase in defect density with increasing Y₂O₃ content is likely to be a main limiting factor of the electrical conductivity of SiC ceramics.     

Pre-treatment of adsorbents for waste water treatment using adsorption coupled-with electrochemical regeneration

With the aim to address waste water treatment problems, a novel and economic water treatment technology was introduced at the University of Manchester. It comprised of a unique combination of adsorption and electrochemical regeneration in a single unit. This process successfully eliminated a number of organic pollutants by using an electrically conducting adsorbent material called Nyex? which was a modified form of synthetic graphite. To expand the scope of other graphite types in waste water treatment applications, natural vein and recycled vein graphite materials were selected for electrochemical surface treatment (pre-treatment) in order to evaluate their adsorptive and electrical properties. New graphite based adsorbents were developed and characterized using a laser diffraction particle size analyser, BET surface area, SEM analysis, X-ray (EDS) elemental analysis, X-ray powder diffraction, Boehm surface titration, Zeta potential electrical bed conductivity and bulk density measurements. Boehm surface titration and EDS (X-ray) elemental analysis showed a significant increase in oxygen containing surface functional groups. Although, no significant improvement in bed electrical conductivity was found to occur after electrochemical surface treatment, however, natural vein and recycled vein graphite materials presented highest bed electrical conductivity amongst competing graphite materials. Aqueous solution of acid violet 17 as a standard pollutant was used to evaluate the comparative performance of these adsorbents. The investigations revealed that electrochemical surface treatment contributed to an increase in the adsorption capacity by a factor of two only for natural vein graphite. Un-treated recycled vein graphite adsorbent delivered the same adsorptive capacity (3.0 mg g^?1) to that of electrochemically treated natural vein graphite. The electrochemical regeneration efficiency at around 100% was obtained using a treatment time of 60 and 30 min, current density of 14 mA cm^?2, charge passed of 36 and 18 C g^?1 for synthetic graphite, natural and recycled vein graphite materials respectively. Relatively a small consumption of electrical energy, 24 J g^?1 for regenerating natural vein graphite adsorbent versus 36 J g^?1 for synthetic graphite adsorbent, was found to be required for destruction/oxidation of adsorbed acid violet 17. Multiple adsorption/regeneration cycles presented no loss in adsorptive capacity over 5 adsorption/regeneration cycles. The use of natural and recycled vein graphite adsorbents offered some advantages over graphite intercalation based adsorbents with reduced electrical energy consumption during regeneration and simpler separation of particulate adsorbent.     

The influence of structure order on the kinetics of dehydroxylation of kaolinite

The structural order of kaolinite is an important factor that shows a substantial effect on the processes which take place during the thermal treatment of kaolin. The influence of structural order on the dehydroxylation process was investigated by simultaneous thermogravimetry and differential thermal analysis (TG-DTA). The thermal analysis was performed on the samples with gradually decreasing structural order prepared by milling procedure. The apparent activation energy of dehydroxylation process decreases with decreasing structural order according to the exponential function. The extrapolation of experimental data leads to the estimation of apparent activation energy of 76.6 kJ mol^?1 and of frequency factor of 0.12 × 10⁴ s^?1 related to completely disordered form of kaolinite, while the ordered form shows the apparent activation energy of 216.17 kJ mol^?1 and the frequency factor of 9.26 × 10⁴ s^?1. The relationships between features such as the infrared pattern of treated material, the degree of structural order and the apparent activation energy were established.     

The use of an electric field in the preparation of glass fibre/epoxy composites containing carbon nanotubes

This paper focuses on the use of electric field for the alignment of carbon nanotubes in glass fibre reinforced thermosetting composites and the associated infusion processing and property modifications. A satisfactory dispersion leads to high quality infusions with uniform distribution and infiltration of intrafibre microchannels by the nanofiller. Field application causes a reduction of resistivity during the process. The resistivity reduction follows an exponential decay with relaxation times in the 100–300 s range. This process is attributed to preferential aggregation in the field direction, whilst indications of individual nanotube alignment are found. The through thickness conductivity of the composite increases by an order of magnitude with the application of the field reaching a value of 1.4 × 10^?3 S/m for 0.1 wt.% nanotubes. The in plane conductivity remains unaffected. The interlaminar toughness increases slightly but statistically significantly upon the addition of nanotubes. A high field leads to a further increase of strain energy release rate to 520 J/m², which corresponds to a value 20% higher than the control. The effects observed on electrical properties are attributed mainly to preferential network formation in the field direction, whilst improvements in interlaminar toughness are linked to the nanotube alignment.     

Synthesis and properties of heptadecane-functionalized poly(propylene oxide) based single-ion polymer electrolytes

Lithium methacrylate and heptadecane-functionalized poly(propylene oxide) (PPO) methacrylate based single-ion polymer electrolytes have been synthesized by radical copolymerization and neutralization. The thermal and electrical properties of the polymer electrolyte have been characterized by differential scanning calorimetry (DSC) and AC impedance spectroscopy, respectively. The results showed that the crystalline melting behavior of PPO segment was changed significantly by the presence of lithium ion due to the coordinative interaction and enhanced crystallinity. The ionic conductivity was 1.8 × 10^?7 S cm^?1 at 25 °C in the case of the lithium ion concentration of [PO]:[Li] = 30:1 due to the single-ion nature but its transference number reached roughly 1, indicating no migration of counter anions. Inspection with control sample suggested that the polymer electrolyte with ion conduction channel formed by a self-assembly is favored to realize relatively high ionic conductivity and decoupled lithium ion motion. The contact angle measurement onto the polymer electrolyte surface showed a strong hydrophobic wetting behavior due to the integrated hydrophobic nature of PPO and heptadecane alkyl chains.     

The effect of silica doping on neodymium diffusion in yttrium aluminum garnet ceramics: implications for sintering mechanisms

The Nd³⁺ cation diffusion into transparent polycrystalline YAG (Y₃Al₅O₁₂) was investigated as a function of temperature and silica content. Thin neodymium oxide layers were deposited on sintered YAG substrates prior to annealing under air at temperatures from 1400 to 1600 °C. Bulk and grain boundary neodymium diffusion coefficients were measured by secondary ion mass spectrometry. The experimental results show that silica addition increases the diffusivity of Nd³⁺ by a factor 10 whatever the diffusion path, probably as a result of extrinsic point defects formation, especially rare-earth vacancies.The experimental diffusion data were used to elucidate the sintering mechanism of Nd:YAG ceramics in the temperature range 1450–1550 °C. Firstly, it appeared that the intermediate stage of solid-state sintering should be controlled by the rare-earth diffusion along the grain boundary with an activation energy of about 600 kJ mol^?1. Secondly, grain growth mechanism at the final stage of liquid-phase sintering was investigated for silica-doped Nd:YAG samples. Thus, the grain growth should be limited by the reaction at interfaces at a temperature lower than 1500 °C, with an activation energy of about 880 kJ mol^?1. At higher temperature, it seems to be limited by the ionic diffusion through the intergranular liquid phase, with an activation energy of 250 kJ mol^?1.     

Metakaolin and fly ash alkali-activated mortars compared with cementitious mortars at the same strength class

Alkali-activated and cementitious mortars belonging to R1 ≥ 10 MPa, R2 ≥ 15 MPa and R3 ≥ 25 MPa strength classes were tested and compared in terms of workability, dynamic modulus of elasticity, porosimetry, and water vapor permeability. Capillary water absorption, drying shrinkage, resistance to sulfate attack, and corrosion behavior of embedded bare and galvanized reinforcements were also investigated.In alkali-activated mortars, drying shrinkage is higher than that of cementitious mortars but restrained shrinkage is lower due to lower modulus of elasticity. Pore dimensions affect water vapor permeability, more pronounced in alkali-activated mortars, and capillary water absorption, much lower in fly ash ones. The high alkalinity of fly ash and metakaolin mortars delayed the achievement of the passive state in particular for the galvanized reinforcements but after 1 month of curing they reached the same corrosion rates of those embedded in cementitious mortars.     

Thermal and electrical conductivity of array-spun multi-walled carbon nanotube yarns

The electrical resistivity of CNT yarns of diameters 10–34 μm, spun from multi-walled carbon nanotube arrays, have been determined from 2 to 300 K in magnetic fields up to 9 T. The magnetoresistance is large and negative at low temperatures. The thermal conductivity also has been determined, by parallel thermal conductance, from 5 to 300 K. The room-temperature thermal conductivity of the 10 μm yarn is (60 ± 20) W m^?1 K^?1, the highest measured result for a CNT yarn to date. The thermal and electrical conductivities both decrease with increasing yarn diameter, which is attributed to structural differences that vary with the yarn diameter.     

Coupled strain rate and temperature effects on the tensile behavior of strain-hardening cement-based composites (SHCC) with PVA fibers

This paper reports the experimental findings on the tensile behavior of Strain-hardening cement-based composites (SHCC) subjected to elevated temperatures and different strain rates and to combinations of these parameters. Uniaxial tension tests with in-situ temperature control were performed at 22 °C, 60 °C, 100 °C and 150 °C. In addition, the effect of loading rate was investigated using the strain rates of 10^? 5 s^? 1, 3 × 10^? 4 s^? 1 and 10^? 2 s^? 1 at all four temperatures considered. It was shown that tensile strength decreases both with an increase in temperature and with a decrease in the strain rate. The strain capacity increases with decreasing strain rate at temperatures of 22 °C and 60 °C, but for the temperature of 100 °C this material property increases when the strain rate increases. At 150 °C the investigated SHCC loses its ductility and no noticeable strain rate effect can be observed. Furthermore, the residual properties of SHCC were evaluated using uniaxial tensile tests at room temperature on the specimens which were previously heated to 60 °C, 100 °C or 150 °C. The residual tests showed that the strength, strain capacity, and work-to-fracture decrease with increasing pre-treatment temperature. However, in comparison with the results of the in-situ tests with elevated in-situ temperatures, the residual tests on SHCC yielded higher tensile strength and lower ductility. These results and possible mechanisms leading to changes in mechanical performance are discussed on the basis of the observed crack patterns on the specimens' surfaces as well as the microscopic investigations of the condition of fibers on fracture surfaces.