Determination of the dissociation constant of molten Li2CO3/Na2CO3/K2CO3 using a stabilized zirconia oxide-ion indicator

An Li₂CO₃/Na₂CO₃/K₂CO₃ eutectic melt has been selected as an example of a molten-carbonate system and the suitability of a stabilized zirconia—air electrode as an oxide-ion concentration indicator for this melt has been confirmed.With this indicator, the dissociation constant of the reaction CO₃^2? (?) = CO₂(g) + O^2? (?) in this melt has been determined to be K_d = P_CO2 [O^2?] = 4.03 × 10^?3 Pa at 873 KReproducible measurements were obtained throughout the experiment and this method might find further application in the study of reactions related to the oxide ion in carbonate melts.     

Pitting corrosion of Type 430 stainless steel under chloride solution droplet

To clarify the critical relative humidity (RH) to initiate pitting corrosion and the rusting mechanism in a marine atmospheric environment, pitting corrosion of Type 430 stainless steels under drops of MgCl₂ solutions were investigated. A pitting corrosion test was performed at different relative humidities under droplets with various diameters and thicknesses. The probability of pitting decreased as the diameter and thickness decreased. Pitting progressed only when the chloride concentration exceeded 4 M, which is the equilibrium concentration at 80% RH. Accordingly, pitting of Type 430 could be initiated when the RH was less than 80%. Additionally, a pitting corrosion mechanism of Type 430 stainless steel under droplets containing chloride ions is proposed.     

Evaluation of experimentally obtained permeance based on module simulation: How should permeance be evaluated?

Permeance and permeance ratio in binary separation generally are obtained from experimental data using an analytical permeance equation consisting of the logarithmic average of the partial pressure difference (hereafter, approximate permeance equation). The aim of the present study was to clarify the applicable range for this equation. First, the separation performance of a membrane module was calculated with various given membrane properties (permeance, permeance ratio) and operation conditions (pressure, flow rate) via numerical computation. The obtained concentrations and flow rates in the retentate and permeate were used to calculate permeances via approximate permeance equation, and the validity was discussed by comparing permeances used for numerical computation with obtained ones. The present work clarifies the validity of the approximate permeance equation, and yields a general guideline stipulating that the partial pressure difference across the membrane at the inlet and outlet should maintain more than 60% to obtain the correct permeance.     

Characteristics of ammonia permeation through porous silica membranes

A sol–gel method was applied for the preparation of silica membranes with different average pore sizes. Ammonia (NH₃) permeation/separation characteristics of the silica membranes were examined in a wide temperature range (50–400°C) by measurement of both single and binary component separation. The order of gas permeance through the silica membranes, which was independent of membrane average pore size, was as follows: He > H₂ > NH₃ > N₂. These results suggest that, for permeation through silica membranes, the molecular size of NH₃ is larger than that of H₂, despite previous reports that the kinetic diameter of NH₃ is smaller than that of H₂. At high temperatures, there was no effect of NH₃ adsorption on H₂ permeation characteristics, and silica membranes were highly stable in NH₃ at 400°C (i.e., gas permeance remained unchanged). On the other hand, at 50°C NH₃ molecules adsorbed on the silica improved NH₃‐permselectivity by blocking permeation of H₂ molecules without decreasing NH₃ permeance. The maximal NH₃/H₂ permeance ratio obtained during binary component separation was ～30 with an NH₃ permeance of ～10^?7 mol m^?2 s^?1 Pa^?1 at an H₂ permeation activation energy of ～6 kJ mol^?1. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Zeolite nanocrystals prepared from zeolite microparticles by a centrifugation-assisted grinding method

Different sizes of zeolite nanocrystals were fabricated from zeolite microparticles using a centrifugation-assisted grinding method. The zeolite nanocrystal formation can be attributed to the Al₂O₃ bowl mill generation of mechanical stress that fractured zeolite microparticles into smaller fragments. In the present study, the smaller fragments had a wide distribution of size and morphology. Therefore, different sizes of zeolite nanocrystals could be recovered from these smaller fragments by varying the centrifugation process. Zeolite nanocrystal product yields were measured by periodically recovering the nanocrystals from the smaller fragments based on milled zeolite powder. The larger crystals of zeolite were typically irregular in shape, whereas the smaller zeolite nanocrystals tended to be spherical. High product yield of the zeolite nanocrystals was obtained by periodically removing nanocrystals from the milled zeolite powder and recycling the large zeolite particles. Thus, the results from this new hybrid process suggest that it can be used to fabricate differing sizes of zeolite nanocrystals. In addition, the size of the recovered zeolite nanocrystal products was narrow, and the initial zeolite nanocrystal structure was not destroyed by the mechanical stress.     

Structural Characterization and Protein Adsorption Property of Hydroxyapatite Particles Modified With Zinc Ions

Zinc-containing hydroxyapatite particles (Zn/HAp) were prepared by an ion exchange reaction process involving hydroxyapatite (HAp) particles with aqueous solutions containing various amounts of zinc nitrate. The Zn²⁺ ion was partially substituted for the Ca²⁺ ion position in the HAp lattice, and hence, the obtained samples had changed little in crystallinity, particle size, and specific surface area. Adsorption of bovine serum albumin (BSA) and β₂-microglobulin (β₂-MG) in solutions containing both BSA and β₂-MG was examined. As the Zn²⁺ ion content in the apatites increased, the adsorbed amount of BSA was almost constant, whereas that of β₂-MG increased.     

Thermodynamic properties of neptunium nitride: a first principles study

The thermal and mechanical properties of neptunium nitride (NpN) were investigated by first principles calculations. From the Helmholtz free energy equilibrium lattice constants, thermal expansion coefficients, bulk moduli and specific heat capacities were calculated for temperatures up to 1500 K. The electronic specific heat capacity was also calculated from the electronic density of states at the Fermi energy. The obtained specific heat capacity reproduced the experimental data well. It was thus clarified that the specific heat capacity of NpN consists of the lattice and electronic specific heat capacities and the contribution of the lattice dilatation to the specific heat capacity.     

Preparation of a novel bimodal catalytic membrane reactor and its application to ammonia decomposition for COx-free hydrogen production

A novel bimodal catalytic membrane reactor (BCMR) consisting of a Ru/γ-Al₂O₃/α-Al₂O₃ bimodal catalytic support and a silica separation layer was proposed. The catalytic activity of the support was successfully improved due to enhanced Ru dispersion by the increased specific surface area for the γ-Al₂O₃/α-Al₂O₃ bimodal structure. The silica separation layer was prepared via a sol–gel process, showing a H₂ permeance of 2.6 × 10⁻⁷ mol Pa⁻¹ m⁻² s⁻¹, with H₂/NH₃ and H₂/N₂ permeance ratios of 120 and 180 at 500 °C. The BCMR was applied to NH₃ decomposition for CO_x-free hydrogen production. When the reaction was carried out with a NH₃ feed flow rate of 40 ml min⁻¹ at 450 °C and the reaction pressure was increased from 0.1 to 0.3 MPa, NH₃ conversion decreased from 50.8 to 35.5% without H₂ extraction mainly due to the increased H₂ inhibition effect. With H₂ extraction, however, NH₃ conversion increased from 68.8 to 74.4% due to the enhanced driving force for H₂ permeation through the membrane.