H2O Stability Research Articles

Studies on chemical stability in CO2 and H2O and electrical conductivity of perovskite-type Ba3In2Zr1−x Ce x O8 (x = 0, 0.5, 1)

We report the synthesis, structure, microstructure, chemical stability in H2O and CO2, and electrical transport properties of an oxide ion-conducting perovskite-related structure Ba3In2MO8 (M = Zr, Ce, Zr0.5Ce0.5). Powder X-ray diffraction confirmed the formation of a simple cubic perovskite-like structure for Ba3In2ZrO8 (a = 4.205(9) A), Ba3In2CeO8 (a = 4.234(1) A), and Ba3In2Zr0.5Ce0.5O8 (a = 4.285(8) A). The increase in lattice constant is consistent with the Shannon’s ionic radius trend. Among the three samples investigated, Ba3In2ZrO8 was found to be stable against reaction with pure CO2 at elevated temperature, while the Ce and 1:1 Zr and Ce compounds were unstable at 600 °C. Ba3In2ZrO8, Ba3In2CeO8, and Ba3In2Zr0.5Ce0.5O8 were found to be chemically unstable in H2O at about 50 °C. The bulk electrical conductivity of the samples prepared at different temperatures was found to be nearly the same; the total conductivity (bulk + grain–boundary + electrode) seems to change with sintering temperature. Both Ba3In2ZrO8 and Ba3In2CeO8, prepared at 1,400 °C, exhibited comparable electrical conductivity of about 6 × 10−3 S cm−1 at 800 °C, which is comparable to that of conventional Y2O3-doped ZrO2 electrolyte. These compounds are very promising electroltes, provided that their chemical and mechnical stabitities are improved without losing any ionic conductivity.

CO2-Resistant Hydrogen Permeation Membranes Based on Doped Ceria and Nickel

Composite membranes consisting of a proton-conducting ceramic and an electronic conductor are promising in reducing the cost in the separation of hydrogen from CO2. However, the lack of a stable ceramic in CO2 with sufficient proton conductivity remains a great hurdle. In this study, we investigated the hydrogen permeation performance and chemical stability of composite membranes based on doped ceria and Ni. Doped ceria used to be considered as a very poor proton conductor for a long time. However, our results show that ceria heavily doped with rare earth element possesses significant proton conductivity. Compared with membranes based on perovskite-type oxides, hydrogen separation membranes based on fluorite-type ceria show much higher stability in H2O and CO2.

Water Stability and Luminescence of Lanthanide Complexes of Tripodal Ligands Derived from 1,4,7‐Triazacyclononane: Pyridinecarboxamide versus Pyridinecarboxylate Donors

AbstractA series of europium(III) and terbium(III) complexes of three 1,4,7‐triazacyclononane‐based pyridine containing ligands were synthesized. The three ligands differ from each other in the substitution of the pyridine pendant arm, namely they have a carboxylic acid, an ethylamide, or an ethyl ester substituent, i.e., these ligands are 6,6′,6″‐[1,4,7‐triazacyclononane‐1,4,7‐triyltris(methylene)]tris[pyridine‐2‐carboxylic acid] (H3tpatcn), ‐tris[pyridine‐2‐carboxamide] (tpatcnam), and ‐tris[pyridine‐2‐carboxylic acid] triethyl ester (tpatcnes) respectively. The quantum yields of both the europium(III) and terbium(III) emission, upon ligand excitation, were highly dependent upon ligand substitution, with a ca. 50‐fold decrease for the carboxamide derivative in comparison to the picolinic acid (=pyridine‐2‐carboxylic acid) based ligand. Detailed analysis of the radiative rate constants and the energy of the triplet states for the three ligand systems revealed a less efficient energy transfer for the carboxamide‐based systems. The stability of the three ligand systems in H2O was investigated. Although hydrolysis of the ethyl ester occurred in H2O for the [Ln(tpatcnes)](OTf)3 complexes, the tripositive [Ln(tpatcnam)](OTf)3 complexes and the neutral [Ln(tpatcn)] complexes showed high stability in H2O which makes them suitable for application in biological media. The [Tb(tpatcn)] complex formed easily in H2O and was thermodynamically stable at physiological pH (pTb 14.9), whereas the [Ln(tpatcnam)](OTf)3 complexes showed a very high kinetic stability in H2O, and once prepared in organic solvents, remained undissociated in H2O.

Retention behavior of nickel, copper, cadmium and zinc ions from aqueous solutions on silico-titanate and silico-antimonate used as inorganic ion exchange materials

Silico-titanate (SiTi) and silico-antimonate (SiSb) have been synthesized and characterized using X-ray diffraction patterns, infrared and thermal analysis techniques. Divalent cations such as Ni2+, Cd2+, Zn2+ and Cu2+ in the pH range 2 to 8 have been exchanged with the exchangeable active sites of the exchangers using a batch technique. From the results obtained, the equilibrium capacities and distribution coefficient values were calculated indicating high selectivity values for Ni2+, Cd2+, Zn2+ and Cu2+ ions on silico-titanate and silico-antimonate compared to other titanates and antimonates. Also SiTi and SiSb show high chemical stability in H2O, nitric and hydrochloric acids. All these results support the suitability of the prepared materials for the removal of the toxic metals concerned from waste waters. Based on the results obtained, practical separation experiments for the above mentioned cations on SiTi and SiSb columns from aqueous waste solutions were carried out.

Composition and stability of the condensate observed at the Viking lander 2 site on Mars

Surface energy balance and near-surface temperature data from the Viking Lander 2 site taken during the first winter that condensated were observed and analyzed to determine the relative stability of CO2 and H2O frosts. The CO2 frost stability is calculated with an equilibrium surface energy balance model, i.e., the total energy incident on a frost surface is compared with the blackbody energy emitted by the surface. The energy sources considered were IR emission from the atmosphere, sunlight, and the sensible heat flux from the atmosphere. H2O stability was examined as a function of buoyant diffusion and turbulent mixing processes which could remove saturated near-surface gases. The CO2 frost is found to be sufficiently unstable at the time the condensate was observed on the ground, so all CO2 ice deposited at night would boil away in a few hours of sunlight. CO2 ice would not form during a dust storm. Water frost would be stable during the condensate observations, since sublimation would occur at a rate below 1 micron/day. A stable winter thickness of 10 microns is projected for the water ice.