Proton transport in a binary biomimetic solution revealed by molecular dynamics simulation

We report the simulation results of the proton transport in a binary mixture of amphiphilic tetramethylurea (TMU) molecules and water. We identify different mechanisms that either facilitate or retard the proton transport. The efficiency of these mechanisms depends on the TMU concentration. The overall picture is more complicated than a recent suggestion that the presence of amphiphilic molecules suppresses the proton mobility by slowing down the reorientation of the surrounding water molecules. It has also been suggested that the hydronium ion induces local water orientational order, which results in an ordered region that has to move along with the proton potentially slowing down the proton transport as suggested by experiment. We find that water-wire like structures formed at low amphiphile concentrations facilitate proton transfer, and reduction of the hydrogen bond connectivity induced at high concentrations retards it.     

Novel nano-structured Pd+yttrium doped ZrO2 cathodes for intermediate temperature solid oxide fuel cells

Novel nano-structured Pd+yttrium doped ZrO₂ (YSZ) electrodes have been developed as cathodes of intermediate temperature solid oxide fuel cells (IT-SOFCs). Nano-sized Pd particles were introduced into the rigid and porous YSZ structure by PdCl₂ solution impregnation. The results show that Pd nanoparticles (20–80 nm) were uniformly distributed in the porous YSZ structure; and such nano-structured composite cathodes were highly active for the O₂ reduction reaction, with polarization resistances (R_E) of 0.11 and 0.22 Ω cm² at 750 and 700 °C and activation energy of 105 kJ mol⁻¹ that is significantly lower than those for the conventional perovskite-based cathodes (130–201 kJ mol⁻¹).     

Monte-Carlo simulation of copolymer mass spectra

A computer program, MACO5, was developed which employs the Monte-Carlo approach to simulate the time-variation of the mass spectral peak intensities of a copolymer sample during the synthesis of an A/B copolyester via reactive blending of a mixture of homopolyesters A and B or when a copolymer undergoes partial degradation. The program was first used to simulate literature data consisting of a series of mass spectra of a butadiene/styrene copolymer subjected to partial ozonolysis. It was also used to investigate the role of terminal groups in reactive blending processes. Two models were developed: the first one describes inner-group ester-ester exchange reactions, the second describes the process in which and active terminal groups attacks an ester group. The predictions of the two models are compared with recent experimental mass spectral data concerning a poly(ethylene adipate-co-ethylene terephalate) copolyester.     

Monte-Carlo simulation of microwave noise in n-type InSb

Numerical Monte Carlo calculations of the electron noise temperature dependence on the electric field strength in n-type InSb are presented. It is established that hot electron noise temperature in strongly compensated InSb increases with the increase of electron density due to more intensive electron–electron scattering stimulating delocalization of electrons from the bottom of the conduction band. For low electron density, when the electron–electron scattering is negligibly small, the electron noise temperature is found to become close to the lattice temperature in a wide range of electric field strength in which the electron gas cooling effect takes place. Satisfactory agreement between calculations of the electron noise temperature and available experimental data has been obtained.     

Proton conductivity of potassium doped barium zirconates

Potassium doped barium zirconates have been synthesized by solid state reactions. It was found that the solubility limit of potassium on A-sites is between 5% and 10%. Introducing extra potassium leads to the formation of second phase or YSZ impurities. The water uptake of barium zirconates was increased even with 5% doping of potassium at the A-site. The sintering conditions and conductivity can be improved significantly by adding 1 wt% ZnO during material synthesis. The maximum solubility for yttrium at B-sites is around 15 at% after introducing 1 wt% zinc. The conductivity of Ba_0.95K_0.05Zr_0.85Y_0.11Zn_0.04O_3−δ at 600 °C is 2.2×10⁻³ S/cm in wet 5% H₂. The activation energies for bulk and grain boundary are 0.29(2), 0.79(2) eV in wet 5% H₂ and 0.31(1), 0.74(3) eV in dry 5% H₂. A power density of 7.7 mW/cm² at 718 °C was observed when a 1 mm thick Ba_0.95K_0.05Zr_0.85Y_0.11Zn_0.04O_3−δ pellet was used as electrolyte and platinum electrodes.     

Studies on monodispersed colloidal particles of doped yttrium compounds

Monodispersed particles of doped yttrium basic carbonates were prepared at aging at elevated temperature corresponding salts solutions in the presence of urea. Coprecipitation in mixed solutions of yttrium, lanthanum and neodymium salts under similar experimental conditions yielded composite particles of basic carbonates. The content of the three metals in the solids followed closely the initial composition of the reacting solutions. On calcination all prepared solids converted to their corresponding oxides while retaining their particle morphology. The so-prepared powders were characterized by various techniques.     

Synthesis and surface characterization of yttrium doped boehmite nanofibers

Yttrium doped boehmite nanofibers with varying yttrium content have been synthesized at low temperatures using a soft-chemistry route in the presence of polyglycol ether surfactant. The effect of yttrium content, hydrothermal temperature on the growth of boehmite nanostructures was systematically studied. Nanofibers were formed in all samples with varying doped Y% treated at 100 °C; large Y(OH)₃ crystals were also formed at high yttrium doping. Treated at an elevated temperatures resulted in a remarkable changes in size and morphology for samples with the same doped Y content. The resultant nanofibers were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), energy-dispersive X-ray analysis (EDX), N₂ adsorption and thermogravimetric analysis. The detailed characterization and discussion on the Y doped nanostructures are presented.     

A Monte-Carlo simulation of diffusion and reaction in zeolites

Investigations of two-dimensional models to simulate diffusion and reaction in zeolites with a Monte-Carlo method are presented herein. New results of the simulation of single component diffusion and binary diffusion and a possible method to rescale the obtained diffusion coefficients in real units is presented. The estimation of an accurate activation energy was found to be the most important factor, the other parameters were estimated by simple assumptions.Complex reactions such as a consecutive reaction and xylene isomerisation were simulated with a new model. With this model the selective behaviour of the two reactions was investigated. A Type-III selectivity according to Wheeler was found for the consecutive reaction. For xylene isomerisation, reaction paths were simulated and compared with experimental reaction paths. The composition of the thermodynamic equilibrium was obtained for high transition probabilities and the relative rate constants from the literature could be confirmed. According to the results of the simulations one can conclude that a ratio of the diffusion coefficients of o-, m-, and p-xylene=1:1:1000 is too large to explain the experimentally observed distribution of the xylene isomers and a difference of only one order of magnitude was found.     

Li+ transport in lithium sulfonylimide-oligo(ethylene oxide) ionic liquids and oligo(ethylene oxide) doped with LiTFSI

The Li+ environment and transport in an ionic liquid (IL) comprised of Li+ and an anion of bis(trifluoromethanesulfonyl)imide anion (TFSI-) tethered to oligoethylene oxide (EO) (EO(12)TFSI-/Li+) were determined and compared to those in a binary solution of the oligoethylene oxide with LiTFSI salt (EO(12)/LiTFSI) by using molecular dynamics (MD) simulations and AC conductivity measurements. The latter revealed that the AC conductivity is 1 to 2 orders of magnitude less in the IL compared to the oligoether/salt binary electrolyte with greater differences being observed at lower temperatures. The conductivity of these electrolytes was accurately predicted by MD simulations, which were used in conjunction with a microscopic model to determine mechanisms of Li+ transport. It was discerned that structure-diffusion of the Li+ cation in the binary electrolyte (EO(12)/LiTFSI-) was similar to that in EO(12)TFSI-/Li+ IL at high temperature (>363 K), thus, one can estimate conductivity of IL at this temperature range if one knows the structure-diffusion of Li+ in the binary electrolyte. However, the rate of structure-diffusion of Li+ in IL was found to slow more dramatically with decreasing temperature than in the binary electrolyte. Lithium motion together with EO(12) solvent accounted for 90% of Li+ transport in EO(12)/LiTFSI-, while the Li+ motion together with the EO(12)TFSI- anion contributed approximately half to the total Li+ transport but did not contribute to the charge transport in IL.     

Photodissociation of yttrium and lanthanum oxide cluster cations

Transition metal oxide cations of the form M n O m (+) (M = Y, La) are produced by laser vaporization in a pulsed nozzle source and detected with time-of-flight mass spectrometry. Cluster oxides for each value of n form only a limited number of stoichiometries; MO(M2O3)x(+) species are particularly intense. Cluster cations are mass selected and photodissociated using the third harmonic (355 nm) of a Nd:YAG laser. Multiphoton excitation is required to dissociate these clusters because of their strong bonding. Yttrium and lanthanum oxides exhibit different dissociation channels, but some common trends can be identified. Larger clusters for both metals undergo fission to make certain stable cation clusters, especially MO(M2O3) x (+) species. Specific cations are identified to be especially stable because of their repeated production in the decomposition of larger clusters. These include M3O4(+), M5O7(+), M7O10(+), and M9O13(+), along with Y6O8(+). Density functional theory calculations were performed to investigate the relative stabilities and structures of these systems.     

Thermodynamic stability and hydration enthalpy of strontium cerate doped with yttrium

The standard molar enthalpy of formation of SrY_0.05Ce_0.95O_2.975 has been derived by combining the enthalpy of solution in 1 M HCl + 0.1 KI with auxiliary literature data, Δ_fH° (SrY_0.05Ce_0.95O_2.975, s, 298.15 K) = −1720.4 ± 3.4 kJ/mol. The formation enthalpy of SrY_0.05Ce_0.95O_2.975 from the mixture of binary oxides is Δ_oxH° (298.15 K) = −45.9 ± 3.4 kJ/mol and the enthalpy of reaction of SrY_0.05Ce_0.95O_2.975 with water forming Sr(OH)₂, CeO₂, and Y₂O₃ is Δ_rH° (298.15 K) = −85.5 ± 3.4 kJ/mol. Our data and the entropies of different substances show that SrY_0.05Ce_0.95O_2.975 is thermodynamically stable with respect to a mixture of SrO, Y₂O₃, CeO₂ and that the reaction of SrY_0.05Ce_0.95O_2.975 with water is thermodynamically favourable.     

Self-diffusion of yttrium in monocrystalline yttrium oxide: Y2O3

Yttrium self-diffusion in monocrystalline yttrium oxide (Y₂O₃) is studied by means of the classical radio tracer technique. The few reliable diffusion data obtained in the temperature range 1600–1700°C lead to the following diffusion coefficient

$\text{D=3.5×10}{}^{\mathrm{?9}}\text{exp}\text{?}\text{72}\text{RT}\text{(}\text{kcal/mole}\text{)}\text{m}{}^2\text{sec}{}^{\mathrm{?1}}$

.Experimental errors on the above numerical values are large and give, for the preexponential and energy terms, respectively:

$\text{2.10}{}^{\mathrm{?7}}\text{<D}{}_0\text{<3.10}{}^{\mathrm{?10}}\text{m}{}^2\text{sec}{}^{\mathrm{?}}$

$\text{62<Q<82}\text{kcal/mole}$

.Nevertheless these results seem in good agreement with those deduced from high-temperature and low-stress creep experiments. The theoretical aspect of self-diffusion of yttrium in Y₂O₃ is studied in terms of point defects and lattice disorder due to the equilibrium between the oxide and its environment. This last part is confined to the restricted range of high oxygen partial pressure in which oxygen interstitials are supposed to be majority defects. Intrinsic and extrinsic diffusion behavior are both considered on the basis of a vacancy diffusion mechanism.     

Concentration of yttrium subgroup impurities in high-purity yttrium oxide by TBP-NH(4)SCN extraction chromatography

Separation factors for all the yttrium subgroup elements and yttrium, extracted with TBP from 0.45M NH(4)SCN solution at 24-42 degrees have been determined and found to be 1.9. Eight yttrium subgroup impurities in high-purity yttrium oxide have been concentrated by means of TBP-NH(4)SCN extraction chromatography at 32 degrees before spectroscopic determination. Analysis of one real sample and two synthetic samples gave average recoveries of 80-100%.     

Sol–gel combustion synthesis of chromium doped yttrium aluminum perovskites

A water-based sol–gel combustion synthesis was optimized in order to achieve pure yttrium aluminium perovskite (YAlO₃, YAP). The method involved three main steps: xerogel formation, combustion treatment and calcination of the combusted precursors. TG DTA, FTIR and XRPD, used to investigate the precursor phase evolution, confirmed the strong influence of gel synthesis conditions, combustion temperature and calcination rate on YAP purity. Both stoichiometry and kinetics control during all the preparation steps are crucial in order to avoid the formation of undesired Y₃Al₅O₁₂ (YAG) and Y₄Al₂O₉ (YAM) stable phases. This method allowed to synthesize, for the first time from an aqueous sol–gel process, single phase samples of YAP. A series of samples with composition: YAl_(1−x)Cr_(x)O₃ where x is 0, 0.035, 0.135, 0.250, 0.500, 0.750 was obtained. A consistent decrease of calcination temperature, with respect to conventional solid state synthesis, was achieved by sol–gel combustion, avoiding polyphase materials even without the use of mineralizers. This is an important result in several applications like the synthesis of ceramic pigments.     

Anion exchange separation and determination of yttrium in uranium oxide — Yttrium oxide mixture

A procedure has been developed for quantitative separation of yttrium from uranium by anion exchange from nearly saturated NH₄Cl solution in 0–2N HCl medium. Apparently no organic matter is leached out during the separation as yttrium could be determined by EDTA titration without resorting to fuming with perchloric acid before titration. The precision obtained in the analysis of yttrium in a mixture containing about 12 mg of yttrium and about 300 mg of uranium was ±0.3% (27 determinations).