Sun-Ju Song

Defect chemistry modeling of high-temperature proton-conducting cerates

The appropriate equations governing proton incorporation into perovskite oxides with an emphasis on high-temperature proton conductors (HTPCs) are reviewed. The prototypical compound SrCe0.95Y0.05O3−δ is considered in detail. The mathematical approach of Poulsen is applied and the defect concentrations are modeled with a C language routine. A cluster-defect model is not considered here. Defect concentrations are calculated as a function of water vapor pressure and oxygen partial pressure. The solutions are presented in the form of two- and three-dimensional graphs of defect concentrations versus water vapor and oxygen partial pressures. Their physical meanings are explained by pertinent proton incorporation equations. Effects of water vapor pressure and A/B ratio on the n–p transition point are simulated.

Chemical constitution, physical properties, and biocompatibility of experimentally manufactured Portland cement.

INTRODUCTION An experimental Portland cement was manufactured with pure raw materials under controlled laboratory conditions. The aim of this study was to compare the chemical constitution, physical properties, and biocompatibility of experimentally manufactured Portland cement with those of mineral trioxide aggregate (MTA) and Portland cement. METHODS The composition of the cements was determined by scanning electron microscopy (SEM) and energy-dispersive x-ray analysis (EDAX). The setting time and compressive strength were tested. The biocompatibility was evaluated by using SEM and XTT assay. RESULTS SEM and EDAX revealed the experimental Portland cement to have a similar composition to Portland cement. The setting time of the experimental Portland cement was significantly shorter than that of MTA and Portland cement. The compressive strength of the experimental Portland cement was lower than that of MTA and Portland cement. The experimental Portland cement showed a similar biocompatibility to MTA. CONCLUSIONS The experimental Portland cement might be considered as a possible substitute for MTA in clinical usage after further testing.

Pyro-Synthesis of Functional Nanocrystals

Despite nanomaterials with unique properties playing a vital role in scientific and technological advancements of various fields including chemical and electrochemical applications, the scope for exploration of nano-scale applications is still wide open. The intimate correlation between material properties and synthesis in combination with the urgency to enhance the empirical understanding of nanomaterials demand the evolution of new strategies to promising materials. Herein we introduce a rapid pyro-synthesis that produces highly crystalline functional nanomaterials under reaction times of a few seconds in open-air conditions. The versatile technique may facilitate the development of a variety of nanomaterials and, in particular, carbon-coated metal phosphates with appreciable physico-chemical properties benefiting energy storage applications. The present strategy may present opportunities to develop “design rules” not only to produce nanomaterials for various applications but also to realize cost-effective and simple nanomaterial production beyond lab-scale limitations.

Highly functional nano-scale stabilized bismuth oxides via reverse strike co-precipitation for solid oxide fuel cells

Nano-scale erbia stabilized bismuth oxides (ESBs) were successfully synthesized by a wet chemical reverse strike co-precipitation. Due to homogenous, molecular level mixing, the desired cubic fluorite structure was formed at a dramatically reduced temperature of 500 °C, which was confirmed by X-ray diffraction and Raman spectroscopy. Moreover, this low calcine temperature led to nano-scale ESB powders with a crystallite size of ∼20 nm and a specific surface area of ∼13.2 m2 g−1. Due to the high surface area, the nano-sized ESB powders show high functionality for solid oxide fuel cell (SOFC) applications. As an SOFC electrolyte, the high sinterability of the co-precipitated ESB was demonstrated, achieving over 98% density after sintering at only 750 °C for 30 min. Moreover, the total conductivity of the sample was identical to that obtained by conventional methods after sintering at 890 °C (for 16 h), regardless of the different grain boundary densities. In addition, the co-precipitated ESB was used in a composite cathode with lanthanum strontium manganite (LSM), achieving significantly reduced cathodic ASRs, 0.55 and 0.03 Ω cm2, at 550 and 700 °C by extending triple phase boundary (TPB) lengths in the cathode bulk and at the cathode–electrolyte interface.

Electrical Conductivity and Thermoelectric Power of La2NiO4+δ

The electrical conductivity, Seebeck coefficient, and thermal chemical expansion properties of La 2 NiO 4+δ were measured as a function of temperature and oxygen partial pressure (pO 2 ). The electronic conductivity was analyzed in relation to the thermoelectric power (thermopower) data to elucidate the positive deviation of the activity coefficient of hole on the basis of the delocalized electron model by using the Joyce-Dixon approximation of the Fermi-Dirac integral from the partition function in the quasi-free-particle approximation with the regular solution model. The electrical conductivity and thermopower vs oxygen activity were all explained consistently in the logical frame of the degenerate p-type conductor across the entire experimental range investigated. Like other K 2 NiF 4 -type oxides, the chemical diffusion coefficient was slightly higher than the surface exchange coefficient, suggesting the need for further work to enhance the sluggish surface exchange kinetics of oxygen. The best-estimated mobility values were in reasonable agreement with the reported values and the very weak temperature dependence of hole mobility suggested a band conduction.

Determination of Oxygen Chemical Diffusivity from Chemical Expansion Relaxation for BaCo0.7Fe0.22Nb0.08O3 − δ

The thermal and chemical expansion properties of BaCo 0.7 Fe 0.22 Nb 0.08 O 3-δ , a potential candidate for oxygen permeable membranes and cathodes in solid oxide fuel cells, are reported here. The average thermal expansion coefficient is about 14 × 10- 6 K -1 below 500°C, about 19 × 10- 6 K -1 between 600 and 900°C, and about 29 × 10- 6 K -1 between 900 and 1000°C, which consists of the previous weight change in a thermal gravimetric analysis experiment. The transient behavior in the thermochemical expansion can be best fitted with Ficks second law for a small displacement from the equilibrium. The chemical diffusivity of oxygen and the surface exchange kinetics are successfully extracted.

An Enhanced High-Rate Na3V2(PO4)3-Ni2P Nanocomposite Cathode with Stable Lifetime for Sodium-Ion Batteries

Herein, we report on a high-discharge-rate Na3V2(PO4)3-Ni2P/C (NVP-NP/C) composite cathode prepared using a polyol-based pyro synthesis for Na-ion battery applications. X-ray diffraction and electron microscopy studies established the presence of Na3V2(PO4)3 and Ni2P, respectively, in the NVP-NP/C composite. As a cathode material, the obtained NVP-NP/C composite electrode exhibits higher discharge capacities (100.8 mAhg-1 at 10.8 C and 73.9 mAhg-1 at 34 C) than the NVP/C counterpart electrode (62.7 mAhg-1 at 10.8 C and 4.7 mAhg-1 at 34 C), and the composite electrode retained 95.3% of the initial capacity even after 1500 cycles at 16 C. The enhanced performance could be attributed to the synergetic effect of the Ni2P phase and nanoscale NVP particles, which ultimately results in noticeably enhancing the electrical conductivity of the composite. The present study thus demonstrates that the Na3V2(PO4)3-Ni2P/C nanocomposite is a prospective candidate for NIB with a high power/energy density.

Oxygen excess nonstoichiometry and thermodynamic quantities of La2NiO4 + δ

The oxygen excess nonstoichiometry of La2NiO4 + δ is measured as a function of temperature and oxygen partial pressure (pO2) by coulometric titration method. A positive deviation from the ideal dilution solution behavior is exhibited, and the partial molar thermodynamic quantities of La2NiO4 + δ are calculated from the Gibbs–Helmholtz equation for regular solution by introducing the activity coefficient of the charge carriers. The activity coefficient of holes is successfully calculated by using the Joyce–Dixon approximation of the Fermi–Dirac integral. The effective mass of holes (

An in-situ gas chromatography investigation into the suppression of oxygen gas evolution by coated amorphous cobalt-phosphate nanoparticles on oxide electrode

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