Chemical stability of doped BaCeO_3-BaZrO_3 solid solutions in different atmospheres

BaCe0.45Zr0.45M0.1O3-δ （M=Y, In） and BaCe0.9Y0.1O3-δ were prepared through the conventional solid state reaction route. The chemical stability was investigated in hydrogen, carbon dioxide, and boiling water. Crystalline phase and microsa-ucture of the proton conductor before and after stability test were measured with X-ray diffraction （XRD） and scanning electron microscopy （SEM）, respectively. The results showed that all materials were quite stable in H2 atmosphere. In CO2 atmosphere, BaCe0.45Zr0.45M0.1O3-δ（M=Y, In） were relatively stable, while Bafe0.9Y0.1O3-δ decomposed. In boiling water, BaCe0.9Y0.1O3-δ was quickly decomposed into Ba（OH）2 and corresponding oxide. BaCe0.45Zr0.45M0.1O3-δ slightly reacted with boiling water and some amorphous phases were formed. However, BaCe0.45Zr0.45In0.1O3-δ was observed to exhibit better stability than BaCe0.45Zr0.45Y0.1O3-δ in water. The experimental results were interpreted in terms of thermodynamic data and tolerance factor.

Glass-forming Ability and Chemical Stability of Magneto-optical Glass Heavily Doped with Rare Earth Oxide

The glass-forming region of B2O3-Al2O3-SiO2 （BAS） glass heavily doped with rare earth oxides was investigated by an effective method, and the chemical stability was investigated by powder method. Influences of rare earth oxides on the glass-forming ability and the chemical stability of the BAS glass were also discussed. The experimental results show that the BAS glass-forming region expands firstly with the increase of the Tb2O3 content up to 30mol% and then shrinks. The acid-resistant capacity of the BAS glass doped with rare earth oxides is the lowest, the water-resistant capacity is secondary, and the alkali-resistant capacity is the best. Besides, the glass chemical stability can be improved by doping appropriate amount of rare earth oxides. Moreover, the stronger the ionic polarization ability of the rare earth ions is, the better the chemical stability of the BAS glass will be.

Solid-state reaction synthesis and chemical stability studies in Nd-doped zirconolite-rich ceramics

In this study, Nd-bearing zirconolite-rich ceramics were prepared by solid-state reaction process using CaF2,ZrO2, Ti,TiO2, Fe2 O3 and Nd2O3 as the raw materials. Neodymium was used as trivalent actinide surrogate and designed to substitute the Ca and Zr sites of zirconolite with general stoichiometry of Ca1-xZr1-xNd2 xTi2O7（0≤x≤0.3）. Density of Fe-Nd-O sample reaches a maximum value of 4.13 g/cm^2 after being sintered at 1325 ℃ for 42 h. Three major phases, namely zirconolite, perovskite and pseudobrookite, are observed in all these samples. The EDX result shows that Nd2O3 can be successfully incorporated into the lattice structure of the prepared zirconolite-rich minerals and replace the Ca sites of zirconolite and perovskite with Fe3＋ as the charge-compensating ion. Furthermore, the thermal conductivities are all in the range of 1.51-1.67 W/（m·K）. The normalized elemental leaching rates of Ca and Nd in the Fe-Nd-0.2 sample keep in low values of 6.20 × 10^-2 and 4.86 × 10^-4 g/（m^2·d） after 42 d.

Chemical Stability, Ionic Conductivity of BaCe0.9-xZrxSm0.10O3-α and Its Application to Ammonia Synthesis at Atmospheric Pressure

Dense ceramic samples BaCe0.9-xZrxSm0.10O3-α （x=0.10, 0.15, 0.20, 0.30） were obtained by heat-treating the precursors prepared from a coprecipitation route. The phase structure, chemical stability and conduction behaviors of the ceramic samples have been investigated by X-ray powder diffraction and alternating current impedance spectroscopy methods. All the ceramic samples displayed a single phase of orthorhombic perovskite. The samples with x ≥0.20 were relatively stable after exposed to the flowing mixed gases： CO2 （φ=3%）＋H2O （φ=3%）＋N2 （φ= 94%） at 873 K for 12 h. Among the samples tested, the sample with x=0.20 exhibited both adequate conductivity and better chemical stability. The contribution of different charged species for x=0.20 sample to the conduction in wet hydrogen atmosphere was investigated by means of gas concentration cells. It was found that the sample of x= 0.20 was almost a pure ionic conductor, and the ionic conduction was contributed mainly by proton and partially by oxide ion in wet hydrogen atmosphere at 773--1073 K. The ammonia synthesis at atmospheric pressure in an electrolytic cell based on the sample of x=0.20 was successfully conducted and the peak ammonia formation rate achieved 2.67 × 10 ^-9 molos-locm 2 with direct current of 0.80 mA at 773 K.

Chemical stability and electrical property of Ba_(1.03)Ce_(0.6)Zr_(0.2)Yb_(0.2)O_(3-α) ceramic

Ba1.03Ce0.6Zr0.2Yb0.2O3-α ceramic was prepared by solid state reaction. Phase composition, surface and cross-section morphologies of the material were characterized by using X-ray diffractometer （XRD） and scanning electron microscopy （SEM）, respectively. Its chemical stability against carbon dioxide and water steam at high temperature was tested. Ionic conduction of the material was investigated by ac im-pedance spectroscopy and gas concentration cell methods under different gas atmospheres in the temperature range of 500-900 ℃. Using the ceramic as solid electrolyte and porous platinum as electrodes, the hydrogen-air fuel cell was constructed, and the cell performance at the tem-perature from 500 to 900 oC was examined. The results indicated that Ba1.03Ce0.6Zr0.2Yb0.2O3-α was a single-phase perovskite-type ortho-rhombic system, with high density and good chemical stability under carbon dioxide and water steam atmospheres at high temperature. In wet hydrogen, the material was a pure protonic conductor with the protonic transport number of 1 from 500 to 700 ℃, a mixed conductor of pro-ton and electron with the protonic transport numbers of 0.945-0.916 from 800 to 900 ℃. In wet air, the material was a mixed conductor of proton, oxide ion and electronic hole. The protonic transport numbers were 0.013-0.003, and the oxide ionic transport numbers were 0.346-0.265. Under hydrogen-air fuel cell conditions, the material was a mixed conductor of proton, oxide ion and electron, the ionic trans-port numbers were 0.945-0.848. The fuel cell could work stably, and at 900 ℃, the maximum power output density was 36.5 mW/cm^2.

Conductivity and chemical stability of SrCe_(0.92)Nb_(0.03)Tm_(0.05)O_(3-δ) membrane prepared by modified sol-gel method

SrCe0.92 Nb 0.03 Tm0.05 O 3-δ powders were synthesized by a modified sol-gel method using citrate as a chelating agent.X-ray diffraction（XRD） analysis verified SrCe 0.92 Nb 0.03 Tm 0.05 O 3-δ powders and membranes consisting of a single perovskite phase.The morphologies of the sintered membranes were investigated by using scanning electron microscopy（SEM） technique.Stability tests demonstrated that the Nb introduction into doped strontium cerate greatly enhanced the chemical stability.Electrical conductivities of SrCe 0.92 Nb 0.03 Tm 0.05 O 3-δ and SrCe 0.95 Tm 0.05 O 3-δ were measured by the four-point DC method under 10% H 2 /He atmosphere and temperatures（700-900℃）.With a maximum conductivity of 0.0067 S cm^-1 at 900℃,the total electrical conductivity of SrCe 0.92 Nb 0.03 Tm 0.05 O 3-δ increases with increasing temperature.The H 2 permeation flux of SrCe 0.92 Nb 0.03 Tm 0.05 O 3-δ is 0.035 mL cm-2 min-1 when 40% H 2 /He and Ar were used respectively as the feed and sweeping gases at 900℃.

Physico-Chemical and Microbiological Study for the Stability of Phenytoin Sodium Extemporaneously Compounded Suspension in Saudi Arabia Hospitals

Epilepsy is a chronic and the fourth most common neurological disorder which affects people of all age groups. Recently research and awareness on epilepsy-related deaths have rapidly grown over the past two decades. Many previous studies are attributed to the guidelines that apprise health care professionals in handling these deaths, but there is a relative scarcity of information accessible for clinicians and pharmacists who are responsible for manufacturing or preparing the extemporaneous anti-epileptic suspensions in the hospitals. Mostly in partial seizures, phenytoin is one of the first-choice drugs. In Saudi Arabian hospitals, the extemporaneous preparation of phenytoin suspension is common, but the hot climatic weather in Saudi Arabia possesses stability problems that should be tackled as the prepared suspension should pass all the stability tests to ensure uniform dosage of the extemporaneous formulation. In the current study, the commercial capsules were used to prepare the oral phenytoin sodium extemporaneous suspension. The physical, chemical and microbiological stability of phenytoin sodium suspension is analyzed at various temperatures.

Chemical stability of simulated waste forms Zr1–xNdxSiO4–x/2： Influence of temperature, pH and their combined effects

The chemical stability of simulated waste forms Zr_（1–x）Nd_xSiO_（4–x/2） was investigated using the static leach test（MCC-1） with lixiviants of three pH values（pH=4, 6.7 and 10） at three temperature points（40, 90 and 150 oC） for periods ranging from 1 to 42 d, and the influence of temperature, pH, as well as their combined effects were explored in detail. The results showed that all the normalized release rate of Nd firstly decreased with leaching time and closed to equilibrium after 14 d. As the temperature increased, the normalized release rate of Nd also increased, but it was no more than 3×10^（–5） g/（m^2·d）. And, the normalized release rate of Nd reached the highest values（~5×10^（–5） g/（m^2·d）） when pH=4, whilst the normalized release rate of Nd remained the lowest value（~1×10^（–5） g/（m^2·d）） near neutral environment（pH=6.7）.

NON-EQUILIBRIUM STATIONARY STATE IN CHEMICAL REACTION OF SiO_2/Fe AT INTERFACE OF SLAG/METAL AND ITS STABILITY DURING ARC WELDING

For characteristics of open and far from thermodynamic equilibrium in welding chemical reaction, a new kind of quantitative method, which is used to analyze direction and extent for chemical reaction of SiO2/Fe during quasi-steady state period, is introduced with the concept of non-equilibrium stationary state. The main idea is based on thermodynamic driving forces, which result in non-zero thermodynamic fluxes and lead to chemical reaction far away from thermodynamic equilibrium. There exists certain dynamic equilibrium relationship between rates of diffusion fluxes in liquid phase of reactants or products and the rate equation of chemical reaction when welding is in quasi-steady state. As result of this, a group of non-linear equations containing concentrations of all substances at interface of slag/liquid-metal may be established. Moreover the stability of this non-equilibrium stationary state is discussed using dissipative structure theory and it is concluded theoretically that this non-equilibrium stationary state for welding chemical reaction is of stability.

Epitaxial growth and air-stability of monolayer Cu2Te

A new two-dimensional atomic crystal,monolayer cuprous telluride(Cu2Te)has been fabricated on a grapheneSi C(0001)substrate by molecular beam epitaxy(MBE).The low-energy electron diffraction(LEED)characterization shows that the monolayer Cu2Te forms a √3×√3superstructure with respect to the graphene substrate.The atomic structure of the monolayer Cu2Te is investigated through a combination of scanning tunneling microscopy(STM)experiments and density functional theory(DFT)calculations.The stoichiometry of the Cu2Te sample is verified by x-ray photoelectron spectroscopy(XPS)measurement.The angle-resolved photoemission spectroscopy(ARPES)data present the electronic band structure of the sample,which is in good agreement with the calculated results.Furthermore,air-exposure experiments reveal the chemical stability of the monolayer Cu2Te.The fabrication of this new 2D material with a particular structure may bring new physical properties for future applications.

Mechanical behaviors of warm and ice-rich frozen soil stabilized with sulphoaluminate cement

The warm and ice-rich frozen soil is characterized by high unfrozen water content, low shear strength and large compressibility, which is unreliable to meet the stability requirements of engineering infrastructures and foundations in permafrost regions. In this study, a novel approach for stabilizing the warm and ice-rich frozen soil with sulphoaluminate cement was proposed based on chemical stabilization. The mechanical behaviors of the stabilized soil, such as strength and stress-strain relationship, were investigated through a series of triaxial compression tests conducted at -1.0℃, and the mechanism of strength variations of the stabilized soil was also explained based on scanning electron microscope test. The investigations indicated that the strength of stabilized soil to resist failure has been improved, and the linear Mohr-Coulomb criteria can accurately reflect the shear strength of stabilized soil under various applied confining pressure. The increase in both curing age and cement mixing ratio were favorable to the growth of cohesion and internal friction angle. More importantly, the strength improvement mechanism of the stabilized soil is attributed to the formation of structural skeleton and the generation of cementitious hydration products within itself. Therefore, the investigations conducted in this study provide valuable references for chemical stabilization of warm and ice-rich frozen ground, thereby providing a basis for in-situ ground improvement for reinforcing warm and ice-rich permafrost foundations by soil-cement column installation.

Experimental and numerical interpretation on composite foundation consisting of soil-cement column within warm and ice-rich frozen soil

Affected by climate warming and anthropogenic disturbances, the thermo-mechanical stability of warm and ice-rich frozen ground along the Qinghai-Tibet engineering corridor(QTEC) is continuously decreased, which may delay the construction of major projects in the future. In this study, based on chemical stabilization of warm and icerich frozen ground, the soil-cement column(SCC) for ground improvement was recommended to reinforce the foundations in warm and ice-rich permafrost regions. To explore the validity of countermeasures mentioned above, both the original foundation and the composite foundation consisting of SCC with soil temperature of -1.0℃ were prepared in the laboratory, and then the plate loading tests were carried out. The laboratory investigations indicated that the bearing capacity of composite foundation consisting of SCC was higher than that of original foundation, and the total deformation of original foundation was greater than that of composite foundation, meaning that overall stability of foundation with warm and ice-rich frozen soil can be improved by SCC installation. Meanwhile, a numerical model considering the interface interaction between frozen soil and SCC was established for interpretating the bearing mechanism of composite foundation. The numerical investigations revealed that the SCC within composite foundation was responsible for the more applied load, and the applied load can be delivered to deeper zone in depth due to the SCC installation, which was favorable for improving the bearing characteristic of composite foundation. The investigations provide the valuable guideline for the choice of engineering supporting techniques to major projects within the QTEC.

Crystal Phases and Chemical Stabilities of YSi2 Powders Fabricated from Low and High Purity Si and Y Powders

Y-Si compounds with the composition of Y:Si = 1:2 were fabricated using Yttrium and Silicon raw powders with low and high purity in various atmospheres and temperatures. Although the latest Y-Si phase diagram shows that the α- and β-YSi2 phases are the stable phases for the stoichiometric composition of Y:Si = 1:2, the current experimental results suggest that the high temperature phase with the hexagonal structure, β-Y3Si5, would be the stable phase for this composition, and that the high temperature phase with the orthorhombic structure, β-YSi2, would be the meta-stable phase with high oxygen impurity content. It was demonstrated that YSi2 powders possess much superior chemical stability than Yttrium metal. It was found that the best dispersing solvent was 2-propanol for YSi2 powder.

Improvements of marine clay slurries using chemicale-physical combined method(CPCM)

In this paper, the effectiveness, applicability and validity of chemicalephysical combined methods（CPCMs） for treatment of marine clay （MC） slurries were evaluated. The method CPCM1 combineschemical stabilization and vacuum preloading （VP）, while CPCM2 is similar to CPCM1 but includes boththe application of surcharge and use of geo-bags to provide confinement during surcharge preloading.The key advantage of CPCM2 using geo-bags is that the surcharge can be immediately applied on thechemically stabilized slurries. Two types of geo-bags were investigated under simulated land filling anddyke conditions, respectively. The test results show that the shear strength （cu） of treated slurry byCPCM2 is generally much higher than that by CPCM1. Besides, the use of CPCM2 can significantly reducethe treatment time due to the short drainage paths created by geo-bags. Overall, CPCM2 allows fasterconsolidation and higher preloading that help to achieve higher mechanical properties of the stabilizedslurry. There are consistent relationships between cU and water content of slurries treated by CPCM2.Several important observations were also made based on comparisons of experimental data. 2015 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.

A new fluorescent particle prepared by chemical stabilized phycobilisome

Natural phycobilisomes （PBSs） were isolated and purified from a red macroalga, Polysiphonia urceolata, by multi-step of sucrose gradient centrifugation, and were chemically stabilized by small molecule cross-linker formaldehyde. The stabilized PBSs showed similar absorption and fluorescent properties at room temperature compared to natural PBSs and kept a steady F672/F580 value during more than 3 months of storage in 0.45 mol/L phosphate buffer （pH 6.8） or at low temperature at 77 K. The stabilized PBS migrated as a single band at mild PAGE and in 14-18 h of sucrose gradient centrifugation. All these characters indicated that the stabilized PBSs were stable, soluble, homogenous fluorescent particles with favorable spectroscopic features prepared under present conditions.

Biomimetic chitin hydrogel via chemical transformation

Chitin hydrogel has been recognized as a promising material for various biomedical applications because of its biocompatibility and biodegradability.However,the fabrication of strong chitin hydrogel remains a big challenge because of the insolubility of chitin in many solvents and the reduced chain length of chitin regenerated from solutions.We herein introduce the fabrication of chitin hydrogel with biomimetic structure through the chemical transformation of chitosan,which is a water-soluble deacetylated derivative of chitin.The reacetylation of the amino group in chitosan endows the obtained chitin hydrogel with outstanding resistance to swelling,degradation,extreme temperature and pH conditions,and organic solvents.The chitin hydrogel has excellent mechanical properties while retaining a high water content(more than 95 wt.%).It also shows excellent antifouling performance that it resists the adhesion of proteins,bacteria,blood,and cells.Moreover,as the initial chitosan solution can be feasibly frozen and templated by ice crystals,the chitin hydrogel structure can be either nacre-like or wood-like depending on the freezing method of the precursory chitosan solution.Owing to these anisotropic structures,such chitin hydrogel can exhibit anisotropic mechanics and mass transfer capabilities.The current work provides a rational strategy to fabricate chitin hydrogels and paves the way for its practical applications as a superior biomedical material.

Enhanced H_(2) permeation and CO_(2) tolerance of self-assembled ceramic-metal-ceramic BZCYYb-Ni-CeO_(2) hybrid membrane for hydrogen separation

Perovskite-type mixed protonic-electronic conducting membranes have attracted attention because of their ability to separate and purify hydrogen from a mixture of gases generated by industrial-scale steam reforming based on an ion diffusion mechanism.Exploring cost-effective membrane materials that can achieve both high H_(2) permeability and strong CO_(2)-tolerant chemical stability has been a major challenge for industrial applications.Herein,we constructed a triple phase(ceramic-metal-ceramic)membrane composed of a perovskite ceramic phase BaZr_(0.1)Ce_(0.7)Y_(0.1)Yb_(0.1)O_(3-δ)(BZCYYb),Ni metal phase and a fluorite ceramic phase CeO_(2).Under H_(2) atmosphere,Ni metal in-situ exsolved from the oxide grains,and decorated the grain surface and boundary,thus the electronic conductivity and hydrogen separation performance can be promoted.The BZCYYbNi-CeO_(2)hybrid membrane achieved an exceptional hydrogen separation performance of 0.53 mL min^(-1)cm^(-2) at 800℃ under a 10 vol% H_(2) atmosphere,surpassing all other perovskite membranes reported to date.Furthermore,the CeO_(2) phase incorporated into the BZCYYb-Ni effectively improved the CO_(2)-tolerant chemical stability.The BZCYYbNi-CeO_(2) membrane exhibited outstanding long-term stability for at least 80 h at 700℃ under 10 vol%CO_(2)-10 vol%H_(2).The success of hybrid membrane construction creates a new direction for simultaneously improving their hydrogen separation performance and CO_(2) resistance stability.

Fabrication of sintering-free flexible copper nanowire/ polymer composite transparent electrodes with enhanced chemical and mechanical stability

The thermal decomposition synthesis of long copper nanowires （CuNWs） was achieved by controlling the synthesis parameters. A detailed study was performed to determine the effect of the molar ratio of copper chloride to nickel acetylacetonate, temperature, and stirring rate on the final shape of the products. Transparent electrodes （TEs） were fabricated by wet treatment with acetic acid （AA）, without using a sintering process. The low oxidation stability and high surface roughness are the main disadvantages of the CuNW TEs, which limit their applications. In order to overcome these issues, we prepared CuNW/polymer composite TEs by partial embedding of the CuNWs into poly（methyl methacrylate） （PMMA） on poly（ethylene terephthalate） （PET） substrates. The CuNW/PMMA composite TEs exhibit excellent optoelectronic performance （91.3% at 100.7 ff2/sq）, low surface roughness （4.6 nm in height）, and good mechanical and chemical stability as compared with CuNW TEs. On the basis of these properties, we believe that CuNW-based composite TEs could serve as low-cost materials for a wide range of new optoelectronic devices.

Oxygen permeability and CO_2-tolerance of Ce_(0.8)Gd_(0.2)O_(2-δ)-Ln BaCo_2O_(5+δ) dual-phase membranes

A series of oxygen permeable dual-phase composite oxides 60 wt% Ce0.8Gd0.2O2-δ-40 wt% LnBaCo2O5＋δ （CGO-LBCO, Ln = La, Pr, Nd, Sin, Gd and Y） were synthesized through a sol-gel route and effects of the Ln3＋ cations on their phase structure, oxygen permeability and chemical stability against CO2 were investigated systemically by XRD, SEM, TG-DSC and oxygen permeation experiments. XRD patterns reveal that the larger Ln3＋ cations （La3＋, Pr3＋ and Nd3＋） successfully stabilized the double-layered perovskite structure of sintered LBCO, while the smaller ones （Sm3＋, Gd3＋, and Y3＋） resulted in the partial decomposition of LBCO with some impurities formed. CGO-PBCO yields the highest oxygen permeation flux, reaching 2.8× 10^-7 mol.s-1.cm-2 at 925 ℃ with 1 mm thickness under air/He gradient. The TG-DSC profiles in 20 mol% CO2/N2 and oxygen permeability experiments with CO2 as sweep gas show that CGO-YBCO demonstrates the best chemical stability against CO2, possibly due to its minimum basicity. The stable oxygen permeation flux of CGO-YBCO under CO2 atmosphere reveals its potential application in the oxy-fuel combustion route for CO2 capture.

Preparation of Stable CaS∶Eu^(2+), Tm^(3+) Phosphor

Different fluxes were used to synthesize long persistence phosphors, calcium sulfides activated by Eu 2+ and Tm 3+ , by convenient solid state method. The phosphor using NH 4F as a flux has good crystallinity and large particle size, its stability against water and other atmospheric components is enhanced, and its afterglow is longer and fluorescent intensity is more intense than those of the phosphor using NH 4Cl as flux. Their PL intensities varied with time in moist air were measured, no remarkable change was found for those prepared with NH 4F flux in contrast with NH 4Cl as flux. So using NH 4F as flux is a good method to enhance the stability of alkaline earth sulfides.