Description of a high-performance density cell. Application to new investigations in the field of polymers studies

A new density cell based on the vibrating tube principle is described. This cell provides an accuracy of density measurements of 2 × 10^?6 g/cm³ and presents a great stability with respect to temperature and time variations. In two experiments—measurement of self-diffusion coefficient of heavy water through membrane and determination of partial specific volume of polymers in very dilute solutions—it is shown that such a precision leads to new types of investigations.     

Permeation of water vapor through cellulose triacetate membranes in hollow fiber form

A modification of the carrier gas method for measuring permeability of a hollow fiber to a vapor is described with particular application to water vapor permeation through asymmetric cellulose triacetate in hollow fiber from. Conventional methods are inadequate because the high flux of permeation vapor combined with its low pressure on the permeate side and the small diameter of the fiber lead to an excessive buildup of pressure in the permeate stream—in some cases so great as to render much of the fiber length ineffective. The method described in this paper involves the permeation from the outside to the inside of the fiber of a binary mixture consisting of the water vapor and a fairly highly permeable carrier (helium). There is a significant pressure drop along the fiber, but a theoretical treatment is presented to take this into account and to permit a determination of the vapor permeability. Experiments at 35°C over a range of water vapor pressures up to 1.7 cm Hg gave a water flux of 9 × 10^?3 cc(S.T.P.)/cm²-sec-cm Hg, with an apparent slight decrease with increasing pressure. Over the same range of water vapor pressure the helium flux decreased from 2.3 × 10^?4 to 1.85 × 10^?4 cc(S.T.P.)/cm²-sec-cm Hg.     

An Evaluation of the Thermophysical Properties of Stoichiometric CeO2 in Comparison to UO2 and PuO2

The thermal conductivity of stoichiometric CeO₂ was determined through measurement of thermal expansion from 313 to 1723 K, thermal diffusivity from 298 to 1473 K, and specific heat capacity from 313 to 1373 K. The thermal conductivity was then calculated as the product of the density, thermal diffusivity, and specific heat capacity. The thermal conductivity was found to obey an (A + BT)^?1 relationship with A = 6.776×10^?2 m·K·W^?1 and B = 2.793 × 10^?4 m·W^?1. Extrapolations of applied models were made to provide suggested data for the specific heat capacity, thermal diffusivity, and thermal conductivity data up to 1723 K. Results of thermal expansion and heat capacity measurements agreed well with the limited low‐temperature data available in the literature. The thermal conductivity values provided in the current study are significantly higher than the only high‐temperature data located for CeO₂. This is attributed to the tendency of CeO₂ to rapidly reduce at elevated temperatures given the available partial pressure of O₂ in air at ambient pressure. The CeO₂ data are compared to literature values for UO₂ and PuO₂ to evaluate its suitability as a surrogate in nuclear fuel systems where thermal transport is a primary criterion for performance     

Thermophysical properties of Devonian shales

A detailed study of the thermophysical properties of Devonian shales from the central and eastern United States has been carried out. Thermal conductivity, thermal diffusivity, specific heat and dielectric constant data are presented. A Michigan shale sample with an oil yield of 28 litres per metric ton (1 t^?1) and a Kentucky shale (oil yield: 52 l t^?1) were selected. The specific heats of these shales are in the range 0.20–0.30 cal gm^?1 °C^?1, and increase with increasing temperature. The thermal conductivity (κ) of the two shale samples are comparable (ca. 1 W m^?1 °C^?1). The κ values show only a weak temperature dependance. The thermal diffusivity (α) of these shales range from 0.3–0.5 × 10^?2 cm² s^?1 and tend to decrease with increasing temperature. The dielectric constants show anomalously high values at temperatures above 200 °C. This effect is indicative of interfacial polarization mechanisms presumably arising from loss of water and onset of pyrolysis of the shale organic matter. Comparison of the trends in thermophysical behaviour of Devonian shales with data obtained previously on Green River oil shales is presented. The importance of thermophysical measurements in on-field applications in oil shale technology is highlighted.     

Voltage relaxation measurements of the electron and hole mobilities in yttria-doped zirconia

The voltage relaxation of galvanic cells with zirconia electrolytes polarized between an inert silver electrode and either a Pt/air or a Fe/FeO electrode has been analysed to obtain the mobilities of both electronic minority charge carriers. At 900°C the mobility of the electrons is 2.4 × 10^?2 cm²/Vs, that of the holes is 2 orders of magnitude lower, 1.6 × 10^?4 cm²/Vs. The activation enthalpy is 0.55 eV for the electrons and 1.4 eV for the holes. From conductivity data, the concentrations of electrons and holes at 900°C and 1 atm oxygen partial pressure are calculated to be 3 × 10¹⁰ and 6 × 10¹⁷ cm^?3 respectively. With the use of platinum inert electrodes the formation of intermetallic Pt—Zr compounds appears at an oxygen partial pressure of 2.3 × 10^?22 atm at 900°C. From this the Gibbs formation energy of yttria-doped zirconia is calculated to be ?9.1 eV at 900°C.     

Preparation and characterization of sulfonated block‐graft copolyimide/sulfonated polybenzimidazole blend membranes for fuel cell application

Polymer electrolyte blend membranes composed of sulfonated block‐graft polyimide (S‐bg‐PI) and sulfonated polybenzimidazole (sPBI) were prepared and characterized. The proton conductivity and oxygen permeability coefficient of the novel blend membrane S‐bg‐PI/sPBI (7 wt%) were 0.38 S cm^?1 at 90 °C and 98% relative humidity and 7.2 × 10^?13 cm³(STP) cm (cm² s cmHg)^?1 at 35 °C and 76 cmHg, respectively, while those of Nafion^® were 0.15 S cm^?1 and 1.1 × 10^?10 cm³(STP) cm (cm² s cmHg)^?1 under the same conditions. The apparent (proton/oxygen transport) selectivity calculated from the proton conductivity and the oxygen permeability coefficient in the S‐bg‐PI/sPBI (7 wt%) membrane was 300 times larger than that determined in the Nafion membrane. Besides, the excellent gas barrier properties based on an acid ? base interaction in the blend membranes are expected to suppress the generation of hydrogen peroxide and reactive oxygen species, which will degrade fuel cells during operation. The excellent proton conductivity and gas barrier properties of the novel membranes promise their application for future fuel cell membranes. © 2015 Society of Chemical Industry     

Thermal Insulation Characteristics of Polybenzoxazine Aerogels

Polybenzoxazine (PBO) aerogels with low densities and low thermal conductivities are prepared from Bisphenol A (BPA) benzoxazine monomers by ring‐opened polymerisation using HCl as a catalyser at 10 °C. The obtained PBO aerogels have cross‐linked and 3D network structures with the densities ranging from 0.084 to 0.526 g cm^?3. The thermal conductivities under different pressures (3–10⁵ Pa, air) and different atmospheres (N₂, Ar, and CO₂, 10⁵ Pa) are investigated. The thermal conductivities are in the range of 0.0335–0.0652 W m K^?1 under ambient pressure and 0.0098–0.0571 W m K^?1 at 3 Pa. The thermal transfer mechanism under different gas pressures is analyzed with increasing pressure. Under different atmospheres, the thermal conductivities decrease as the molecular weight of the gas increases. Compared with the traditional organic foam insulating materials of phenolic foam, polyurethane and polystyrene, which have similar apparent densities, PBO aerogels exhibit lower thermal conductivity of 0.0335 W m K^?1 than that of traditional organic foam at room temperature.     

Measurement of the permeability of thick membranes to liquefied hydrocarbons by a radioactive tracer technique

A radioactive tracer technique has been devised to measure the permeability of thick membranes and layers of synthetic rubbers and glass-fibre laminates to liquefied hydrocarbons. The technique involves the use of the tritium-labelled hydrocarbon, prepared by treating the appropriate Grignard reagent with tritiated water. The labelled hydrocarbon is transferred to a thermostatted permeability cell. Permeate is trapped in a vial which contains liquid scintillation phosphor and is cooled in liquid air. The trapped permeate is measured by liquid scintillation counting of the sealed vial. Such measurements, made over an appropriate period, allow permeability constants to be calculated. Propane transfer rates down to 10^?10 g/h have been measured, with membranes of thickness ranging from about 0·5 to 1·5 mm, giving permeability constants of the order of 10^?11 g cm^?1 h^?1 atm^?1. Abnormal rate/time curves have been found for some membranes. Factors affecting the accuracy of the measurements, and the safety precautions necessary, are discussed. Finally, extension of the technique to the study of hydrocarbons of low boiling point such as methane is considered.     

Permeabilität galvanisch beschichteter Polymerfolien. I. Methode zur Messung der Gaspermeabilität

The construction and function of an apparatus for the determination of gas permeability through metallized polymer films is described. The test gases N₂, O₂, and CO₂ penetrate under pressure differences from 100 torr to 20 bar through galvanized ABS films (acrylonitrile–butadiene–styrene copolymer). The metallic layers consists of chemically deposited Ni and a galvanic deposited Cu having a thickness of 2–30 μm. The quantity of permeated gases is determined by gas chromatography. The lowest permeability coefficient obtained is 10^?17 (cm³ cm/cm² sec torr). Leak effects can be measured quantitatively. The permeability of gas mixtures (i.e., air) can also be investigated. The apparatus allows the determination of extremely low permeability rates as well as those for conventional polymer systems.     

Phthalonitrile end-capped sulfonated polyarylene ether nitriles for low-swelling proton exchange membranes

A series of phthalonitrile end-capped sulfonated polyarylene ether nitriles are synthesized via K₂CO₃ mediated nucleophilic aromatic substitution reaction at various molar ratios. The as-prepared polymer structures are confirmed by ¹H NMR and FTIR spectroscopy. The properties of membranes cast from the corresponding polymers are investigated with respect to their structures. The membranes exhibit good thermal and mechanical properties, low methanol permeability (0.01?×?10^?6–0.58?×?10^?6 cm²·s^?1 at 20 °C), and high proton conductivity (0.021–0.088 S·cm^?1 at 20 °C). The introduction of phthalonitrile is proved to increase intermolecular interaction, mainly contributing to the reduction in water uptake, swelling ratio, and methanol permeability. More importantly, its introduction does not decrease the proton conductivity, but there is a slight increase. Furthermore, the selectivity of SPEN-CN-50 can reach 4.11?×?10⁵ S·s·cm^?3, which is about nine times higher than that of Nafion 117. All the data show that the as-prepared membranes may be potential proton exchange membrane for DMFCs applications.     

Electrolytic characteristics of mixed solvent electrolytes for lithium secondary batteries

Measurements on conductivity and Li charge-discharge efficiency in various propylene carbonate (PC)-based electrolytes were carried out to obtain electrolytes for Li secondary batteries. Among the electrolytes examined, 2 M LiClO₄—PC—THF (PC/THF volume ratio = $\text{4}\text{6}$) showed 1.6 times higher conductivity of 9.8 × 10^?3 Ω^?1 cm^?1 and also ca. 10% higher Li charge-discharge efficiency of 81.3% at 5 mA cm^?2 (0.3 C cm^?2) than those in 1 M LiClO₄—PC. Generally, Li cycling efficiency increases with increase in electrolyte conductivity. From the analysis made on electrolytic parameters, such as transport number of Li⁺ ion, it was concluded that conductivity and Li cycling efficiency increases were caused by the total effects of lower chemical reactivity of THF to Li and smaller practical Li⁺ ion radius based on Li⁺—THF complex formation.     

New organic–inorganic hybrid membranes based on sulfonated polyimide/aminopropyltriethoxysilane doping with sulfonated mesoporous silica for direct methanol fuel cells

A series of novel composite methanol‐blocking polymer electrolyte membranes based on sulfonated polyimide (SPI) and aminopropyltriethoxysilane (APTES) doping with sulfonated mesoporous silica (S‐mSiO₂) were prepared by the casting procedure. The microstructure and properties of the resulting hybrid membranes were extensively characterized. The crosslinking networks of amino silica phase together with sulfonated mesoporous silica improved the thermal stability of the hybrid membranes to a certain extent in the second decomposition temperature (250–400°C). The composite membranes doping with sulfonated mesoporous silica (SPI/APTES/S‐mSiO₂) displayed superior comprehensive performance to the SPI and SPI/APTES membranes, in which the homogeneously embedded S‐mSiO₂ provided new pathways for proton conduction, rendered more tortuous pathways as well as greater resistance for methanol crossover. The hybrid membrane with 3 wt % S‐mSiO₂ into SPI/APTES‐4 (SPI/A‐4) exhibited the methanol permeability of 4.68 × 10^?6 cm² s^?1at 25°C and proton conductivity of 0.184 S cm^?1 at 80°C and 100%RH, while SPI/A‐4 membrane had the methanol permeability of 5.16 × 10^?6 cm² s^?1 at 25°C and proton conductivity of 0.172 S cm^?1 at 80°C and 100%RH and Nafion 117 exhibited the values of 8.80 × 10^?6 cm² s^?1 and 0.176 S cm^?1 in the same test conditions, respectively. The hybrid membranes were stable up to about 80°C and demonstrated a higher ratio of proton conductivity to methanol permeability than that of Nafion117. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

The effect of anionic surfactant on the properties of polythiophene/chitosan composites

Polythiophene/chitosan (PT/Ch) composites and PT homopolymers were chemically synthesized in the presence of anthraquinone‐2‐sulfonic acid sodium monohydrate, ACS anionic surfactant. Conductivity, FTIR, SEM, TGA, and XRD measurements were used to study the properties of the composites. The effect of the ratio of the surfactant to the Ch onto structural and physical properties of the composites was also investigated. Our experimental data show that the properties of the composites depend on the amount of both surfactant and Ch used. The highest conductivity of 9.62 × 10^?3 S/cm^?1 was measured for the PT/Ch2 sample. When measurements were taken for PT/Ch/ACS samples with different Ch and surfactants content, the highest conductivity and initial decomposition temperature were recorded for the PT/Ch2/ACS10 sample as 3.49 × 10^?4 S/cm^?1, 223°C, respectively. POLYM. ENG. SCI., 54:2632–2640, 2014. © 2013 Society of Plastics Engineers     

Fabrication,Physicochemical Characterizations and Electrical Conductivity Studies of Modified Carbon Nanofiber-Reinforced Epoxy Composites: Effect of 1-Butyl-3-Methylimidazolium Tetrafluoroborate Ionic Liquid

This study presents the fabrication of carbon nanofiber-reinforced epoxy nanocomposites using 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid as filler dispersant. FTIR and XRD measurements were utilized to assess structural attributes and crystallographic change in the composites. In addition, morphological studies were performed by field emission scanning electron microscope while the extent of miscibility between epoxy and IL was computed by Accelrys Materials Studio Software. The conductivity measurement was performed by two point impedance analyzer and result demonstrated increase in the electrical conductivity from ～10^?7 to ～10^?5?S?cm^?1 compared to pristine epoxy composite.     

Influence of Sulfonated Graphene Oxide on Sulfonated Polysulfone Membrane for Direct Methanol Fuel Cell

Novel proton exchange membranes consisting of an inorganic filler, namely sulfonated graphene oxide, embedded in sulfonated polysulfone were fabricated. The membrane performance depended on the sulfonated graphene oxide content possessed the functional groups to provide the interfacial interaction with sulfonated polysulfone through ionic channels and blocking effect. The membrane with 3% v/v sulfonated graphene oxide content embedded in the matrix was shown to be suitable for direct methanol fuel cell applications. The membrane exhibited the highest proton conductivity of 4.27?×?10^?3 S cm^?1 which was higher than that of Nafion117. Moreover, the membrane provided the lowest methanol permeability of 3.48?×?10^?7?cm²/s which was lower than that of Nafion117.     

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.     

Synthesis and characterization of acid–base polyimides bearing pendant sulfoalkoxy groups for direct methanol fuel cell applications

A series of acid–base polyimides with sulfonic acid groups in the side chains have been prepared, based on a new synthesized sulfonated diamine monomer containing pyridine functional group. The effect of the introduction of pyridine groups into copolymer backbone on the properties of membrane were evaluated through the investigation of membrane parameters. The copolymers produced flexible, tough, and transparent membranes by solvent casting method. All the prepared membranes displayed high thermal stability, great oxidative stability and good mechanical properties. They exhibited appropriate water uptake (15.8–30.2 wt % at 80°C) and remarkable dimensional stability (2.5–6.9% at 80°C). The proton conductivity of SPI‐80 was 1.01 × 10^?2 S cm^?1 at room temperature. Moreover, the methanol permeability of SPI‐80 membrane was 1.22 × 10^?7 cm² s^?1, which was lower than 23.8 × 10^?7 cm² s^?1 of Nafion 117. Therefore, these acid‐base polyimides materials have a promising prospect for direct methanol fuel cell applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42238.     

Evaluation of mixed‐conducting lanthanum‐strontium‐cobaltite ceramic membrane for oxygen separation

In this study, La_0.4Sr_0.6CoO_3‐δ (LSC) oxide was synthesized via an EDTA‐citrate complexing process and its application as a mixed‐conducting ceramic membrane for oxygen separation was systematically investigated. The phase structure of the powder and microstructure of the membrane were characterized by XRD and SEM, respectively. The optimum condition for membrane sintering was developed based on SEM and four‐probe DC electrical conductivity characterizations. The oxygen permeation fluxes at various temperatures and oxygen partial pressure gradients were measured by gas chromatography method. Fundamental equations of oxygen permeation and transport resistance through mixed conducting membrane were developed. The oxygen bulk diffusion coefficient (D_v) and surface exchange coefficient (K_ex) for LSC membrane were derived by model regression. The importance of surface exchange kinetics at each side of the membrane on oxygen permeation flux under different oxygen partial pressure gradients and temperatures were quantitatively distinguished from the oxygen bulk diffusion. The maximum oxygen flux achieved based on 1.6‐mm‐thick La_0.4Sr_0.6CoO_3‐δ membrane was ～4.0 × 10^?7 mol cm^?2 s^?1at 950°C. However, calculation results show theoretical oxygen fluxes as high as 2.98 × 10^?5 mol cm^?2 s^?1 through a 5‐μm‐thick LSC membrane with ideal surface modification when operating at 950°C for air separation. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Electrical characterization of multidoped ceria ceramics

Ceria ceramics was obtained from multi-doped nanosized ceria powders prepared by both modified glycine nitrate procedure (MGNP) and self-propagating reaction at room temperature (SPRT). Rare earth elements such as Nd, Sm, Gd, Dy, Y, Yb were used as dopants. The overall mole fraction of dopants was 0.2. One-hour long sintering of powder compacts was performed at 1500 °C in oxygen atmosphere. Phase composition, microstructure and ionic conductivity of sintered samples were analysed. Single-phase ceria was detected in all samples. In general, the increase in the number of dopants improved the ionic conductivity. The samples doped simultaneously with five dopants had the highest ionic conductivity, as evidenced by the impedance measurements. At 450 °C, the conductivity of sample obtained by MGNP was 3.94×10^?3 Ω^?1 cm^?1 whereas the conductivity of sample obtained by SPRT was 2.61×10^?3 Ω^?1 cm^?1. The conductivity activation energy for MGNP and SPRT samples was measured to be 0.348 and 0.385 eV, respectively. Finally, the conductivity decreased as the number of dopants increased to six.