Radioanalytical investigation on rhodium extraction behaviour with tri-N-butylphosphate from iodide solutions

Radioanalytical techniques are used in this work to investigate the extraction behaviour with TBP of rhodium (III) chloride solutions to which a large excess of iodide is added. Extraction yields and distribution coefficients are determined as a function of HClO₄ or H₂SO₄ content in the aqueous phase. Rhodium-stripping from the organic phase with ammonia solutions is also tested.     

Techniques used to study the chemistry of gas phase elemental clusters

Recent studies of the chemistry of elemental clusters (such as C _n , Si _n , and Fe _n ) in the gas phase have revealed a number of fascinating results. This review article discusses and compares the various techniques that have been used to investigate the chemical properties of gas phase elemental clusters. Examples are provided of the often complimentary information that can be obtained from the different methods.     

Preparation of Y2Ba4Cu7O15-δ Superconductor without High Oxygen Pressure

The synthesis of bulk Y₂Ba₄Cu₇O_15-δ superconductor at atmospheric oxygen pressure via solid state sintering is reported. Temperature ranging from 860 to 890 °C as well as time interval over 2 to 15 days were used to investigate the formation of the Y₂Ba₄Cu₇O_15-δ phase. A time-temperature profile characterizing the conditions for the preparation of Y₂Ba₄Cu₇O_15-δ phase suggests the optimal condition to be sintering at 890 °C for over 10 days. Detailed results of X-ray diffraction, electrical resistivity, iodometric titration and magnetization measurements are described.     

Detection of the reversibility of an excited-state reaction by phase-modulation fluorometry

We used phase and modulation fluorometry to investigate the excited-state proton transfer from 2-naphthol. Phase-sensitive detection of fluorescence allows determination of the phase angles of the two-excited species, naphthol and naphtholate. If the steady-state spectra of the individual species are known and are not identical, then this general procedure yields the phase angles irrespective of the extent of the spectral overlap. The phase difference (Δφ) between the naphthol and naphtholate emission is given by tan Δφ = ω/(Γ_R + k₂ where ω is the circular modulation frequency, Γ_R the decay rate of naphtholate fluorescence and k₂ the rate of the reverse reaction. Hence, Δφ reflects both the decay rate of the reaction product and the rate of the reverse action. This back reaction was also detected by comparison of phase shift (φ) and demodulation (m) values for the initially excited state. Specifically, the reverse reaction results in a double exponential decay of naphthol fluorescence, which is revealed by m/cosφ < 1. The concepts described herein are generally applicable to determination of the reversibility of excited-state reactions.     

Crystal chemistry on a lattice: The case of BZN and BZN-related pyrochlores

This paper uses a diagnostic, highly structured diffuse intensity distribution to investigate the local crystal chemistry of (Bi_1.5Zn_0.5−δ)(Zn_0.5Nb_1.5)O_7−δ (BZN) as well as Sn⁴⁺ and Ti⁴⁺, B site substituted, BZN-related pyrochlore phases. The structured diffuse distribution of the B site substituted material is found to be remarkably similar to that observed for BZN itself. In the special case of (Bi_1.5Zn_0.5)(Ti_1.5Nb_0.5)O₇ (BZNT), the continuous G±〈10l〉* type diffuse streaking characteristic of BZN-related pyrochlores has virtually condensed out to give just G±〈001〉* “satellite reflections” and a P-centred, close to a superstructure phase of average pyrochlore unit cell dimensions. Bond valence sum considerations are used to investigate the local crystal chemistry of this BZNT phase and to derive a plausible model for this superstructure phase. Monte Carlo modelling is used to confirm the plausibility of the model proposed. The underlying crystal chemistry of BZN and BZN-related pyrochlores is shown to result from strong local Bi/Zn ordering rules and associated large amplitude structural relaxation.     

The use of the High-Temperature Gas-Balance (HTGB) for thermogravimetric measurements

Several methods are established in thermal analysis to investigate phase formation, phase transition, and decomposition reactions. The analysis of phase equilibria with volatile components is particularly feasible by using standard method of thermogravimetry. Hardly any investigations of phase formation reactions are possible to realize if one of the components is lost by vaporization. By using the ??High-Temperature Gas-Balance?? (HTGB), the vapor phase is enclosed in a silica ampoule and thus forms an equilibrium gas phase in permanent contact with the solid phase. The measurement signal ??m _meas is caused by change of the leverage of the horizontal balance support during evaporation and condensation. The application of the HTGB allows the analysis of solid?Cgas equilibria in the working range from 0.01 till 15?bar at temperatures up to 1,100?°C. The first comparison of evaporation reactions determined by standard thermogravimetric analyses and by measurements using the HTGB is given for the inorganic systems: P, As, SeO₂, PtI₂, and Hg/I.     

Thermal investigations of reactive powder mixtures as precursors for melt-processing of YBa2Cu3O7−x

DTA and XRD measurements were carried out with reactive precursors taken from the YO_1.5-BaO-CuO system in order to investigate mechanisms of YBa₂Cu₃O_7–x formation. The reactions taking place depend strongly on phase composition, phase purity, powder size and heating rate. Among the examined reactive precursors a mixture of 7Y₂O₃+22BaCuO₂+10CuO turned out as the most suited for melt-processing.     

Modulated DSC studies of Pb1−X Ca X TiO3 ferroelectric ceramics

The polycrystalline ceramic samples of general formula Pb_1?X Ca _X TiO₃ with X = 0.00, 0.1, 0.2 and 0.3 have been synthesized by standard high temperature solid state reaction method using high purity oxide and carbonates. The formation of the single phase compounds have been checked by X-ray diffraction technique. The Modulated Differential Scanning Calorimetry has been used to investigate the effect of substitution on the phase transition temperature and the corresponding change on the enthalpy and other thermal parameters of the substituted compound/solid solutions. It was observed that the phase transition temperature (T _c ) decreases linearly with the increase of substitution concentration. The linear decrease in T _c with increase of substitution concentration may be useful for the eventual functionality of the materials for different ferroelectric devices. The results are discussed in detail.     

Use of high-temperature differential scanning calorimetry to investigate the β–α transition in calcium pyrophosphate

High-temperature differential scanning calorimetry was used to investigate the thermodynamic parameters of the γ–β and β–α transitions in calcium pyrophosphate (Ca₂P₂O₇). The measured enthalpy of transition compared well with previous results when higher heating rates (≥20 K min^?1) were used. Recommendations for optimal use of HTDSC in high-temperature phase transition measurements are presented.     

Zinc(II) oxide solubility and phase behavior in aqueous sodium phosphate solutions at elevated temperatures

A platinum-lined, flowing autoclave facility is used to investigate the solubility/phase behavior of zinc(II) oxide in aqueous sodium phosphate solutions at temperatures between 17 and 287°C. ZnO solubilities are observed to increase continuously with temperature and phosphate concentration. At higher phosphate concentrations, a solid phase transformation to NaZnPO₄ is observed. NaZnPO₄ solubilities are retrograde with temperature. The measured solubility behavior is examined via a Zn(II) ion hydrolysis/complexing model and thermodynamic functions for the hydrolysis/complexing reaction equilibria are obtained from a least-squares analysis of the data. The existence of two new zinc(II) ion complexes, Zn(OH)₂(HPO₄)^2– and Zn(OH)₃(H₂PO₄)^2–, is reported for the first time. A summary of thermochemical properties for species in the systems ZnO–H₂O and ZnO–Na₂O–P₂O₅–H₂O is also provided.     

A mechanism for the photochemical transformation of nitrate in snow

Photochemical reactions of trace compounds in snow have important implications for the composition of the atmospheric boundary layer in snow-covered regions and for the interpretation of concentration profiles in snow and ice regarding the composition of the past atmosphere. One of the prominent reactions is the photolysis of nitrate, which leads to the formation of OH radicals in the snow and to the release of reactive nitrogen compounds, like nitrogen oxides (NO and NO₂) and nitrous acid (HONO) to the atmosphere. We performed photolysis experiments using artificial snow, containing variable initial concentrations of nitrate and nitrite, to investigate the reaction mechanism responsible for the formation of the reactive nitrogen compounds. Increasing the initial nitrite concentrations resulted in the formation of significant amounts of nitrate in the snow. A possible precursor of nitrate is NO₂, which can be transformed into nitrate either by the attack of a hydroxy radical or the hydrolysis of the dimer (N₂O₄). A mechanism for the transformation of the nitrogen-containing compounds in snow was developed, assuming that all reactions took place in a quasi-liquid layer (QLL) at the surface of the ice crystals. The unknown photolysis rates of nitrate and nitrite and the rates of NO and NO₂ transfer from the snow to the gas phase, respectively, were adjusted to give an optimum fit of the calculated time series of nitrate, nitrite, and gas phase NO_x with respect to the experimental data. Best agreement was obtained with a ∼25 times faster photolysis rate of nitrite compared to nitrate. The formation of NO₂ is probably the dominant channel for the nitrate photolysis. We used the reaction mechanism further to investigate the release of NO_x and HONO under natural conditions. We found that NO_x emissions are by far dominated by the release of NO₂. The release of HONO to the gas phase depends on the pH of the snow and the HONO transfer rate to the gas phase. However, due to the small amounts of nitrite produced under natural conditions, the formation of HONO in the QLL is probably negligible. We suggest that observed emissions of HONO from the surface snow are dominated by the heterogeneous formation of HONO in the firn air. The reaction of NO₂ on the surfaces of the ice crystals is the most likely HONO source to the gas phase.     

Activation‐Dependent Breathing in a Flexible Metal–Organic Framework and the Effects of Repeated Sorption/Desorption Cycling

A non‐interpenetrated metal–organic framework with a paddle‐wheel secondary building unit has been activated by direct thermal evacuation, guest exchange with a volatile solvent, and supercritical CO₂ drying. Conventional thermal activation yields a mixture of crystalline phases and some amorphous content. Exchange with a volatile solvent prior to vacuum activation produces a pure breathing phase with high sorption capacity, selectivity for CO₂ over N₂ and CH₄, and substantial hysteresis. Supercritical drying can be used to access a guest‐free open phase. Pressure‐resolved differential scanning calorimetry was used to confirm and investigate a systematic loss of sorption capacity by the breathing phase as a function of successive cycles of sorption and desorption. A corresponding loss of sample integrity was not detectable by powder X‐ray diffraction analysis. This may be an important factor to consider in cases where flexible MOFs are earmarked for industrial applications.     

Activation-Dependent Breathing in a Flexible Metal–Organic Framework and the Effects of Repeated Sorption/Desorption Cycling

A non-interpenetrated metal–organic framework with a paddle-wheel secondary building unit has been activated by direct thermal evacuation, guest exchange with a volatile solvent, and supercritical CO₂ drying. Conventional thermal activation yields a mixture of crystalline phases and some amorphous content. Exchange with a volatile solvent prior to vacuum activation produces a pure breathing phase with high sorption capacity, selectivity for CO₂ over N₂ and CH₄, and substantial hysteresis. Supercritical drying can be used to access a guest-free open phase. Pressure-resolved differential scanning calorimetry was used to confirm and investigate a systematic loss of sorption capacity by the breathing phase as a function of successive cycles of sorption and desorption. A corresponding loss of sample integrity was not detectable by powder X-ray diffraction analysis. This may be an important factor to consider in cases where flexible MOFs are earmarked for industrial applications.     

NMR study of phase separation in D2O/ethanol solutions of poly(N-isopropylmethacrylamide) induced by solvent composition and temperature

¹H and ¹³C NMR spectroscopies were applied to investigate phase separation in solutions of poly(N-isopropylmethacrylamide) (PIPMAm) in D₂O/ethanol (EtOH) mixtures induced by solvent composition (cononsolvency) and temperature. Effects of EtOH content in D₂O/EtOH mixtures and temperature on the appearance and extent of the phase separation were characterized. Differences in mesoglobules formed during the phase separation induced by cononsolvency and temperature were found. For temperature-induced phase separation, ¹³C spin-spin relaxation times showed that besides the free EtOH expelled from the PIPMAm mesoglobules, there are also EtOH molecules bound in these mesoglobules. On the other hand, virtually no bound EtOH molecules were detected for mesoglobules formed as a consequence of the cononsolvency. For PIPMAm random copolymers containing negatively charged methacrylate units the phase separation induced by solvent composition was not observed.     

Formation of scandium carbides and scandium oxycarbide from the elements at high-(P, T) conditions

Synchrotron diffraction experiments with in situ laser heated diamond anvil cells and multi-anvil press synthesis experiments have been performed in order to investigate the reaction of scandium and carbon from the elements at high-(P,T) conditions. It is shown that the reaction is very sensitive to the presence of oxygen. In an oxygen-rich environment the most stable phase is ScO_xC_y, where for these experiments x=0.39 and y=0.50-0.56. If only a small oxygen contamination is present, we have observed the formation of Sc₃C₄, Sc₄C₃ and a new orthorhombic ScC_x phase. All the phases formed at high pressures and temperatures are quenchable. Experimentally determined elastic properties of the scandium carbides are compared to values obtained by density functional theory based calculations.     

Automated screening of reversed‐phase stationary phases for small‐molecule separations using liquid chromatography with mass spectrometry

There are various reversed‐phase stationary phases that offer significant differences in selectivity and retention. To investigate different reversed‐phase stationary phases (aqueous stable C₁₈, biphenyl, pentafluorophenyl propyl, and polar‐embedded alkyl) in an automated fashion, commercial software and associated hardware for mobile phase and column selection were used in conjunction with liquid chromatography and a triple quadrupole mass spectrometer detector. A model analyte mixture was prepared using a combination of standards from varying classes of analytes (including drugs, drugs of abuse, amino acids, nicotine, and nicotine‐like compounds). Chromatographic results revealed diverse variations in selectivity and peak shape. Differences in the elution order of analytes on the polar‐embedded alkyl phase for several analytes showed distinct selectivity differences compared to the aqueous C₁₈ phase. The electron‐rich pentafluorophenyl propyl phase showed unique selectivity toward protonated amines. The biphenyl phase provided further changes in selectivity relative to C₁₈ with a methanolic phase, but it behaved very similarly to a C₁₈ when an acetonitrile‐based mobile phase was evaluated. This study shows the value of rapid column screening as an alternative to excessive mobile phase variation to obtain suitable chromatographic settings for analyte separation.     

Lithium insertion into YBa2Cu3O7

Atomistic computer simulation techniques are used to investigate the effects of lithium insertion into YBa₂Cu₃O₇. Attention is focused on various possible lattice sites occupied by the inserted lithium ions and pathways for their migration. The square-planar position in the Cu(2) layer is calculated to be the most energetically favorable. This is supported by the structural modeling of the ordered lithiated phase Li_0.33YBa₂Cu₃O₇. The calculated activation energies derived from migration profiles are in accord with experimental values and suggest fairly mobile lithium ions.     

Phase equilibria in Cu-Al-Zr system at 1073 K and aluminum concentration of less than 55 at %

X-ray diffraction and electron probe microanalysis were used to investigate phase equilibria in the ternary Cu-Al-Zr system at 1073 K in the Zr-rich region. The fragment of the isothermal section of the system was plotted. The regions of homogeneity of the ternary ZrCu₂Al and ZrCu _x Al_{2 ? x} phases were investigated. The type of phase equilibria between binary and ternary compounds of the Al-Cu-Zr system was established. It was found out that, at a Zr concentration above 55 at %, ternary compounds are not formed, and the Zr₃Al and Zr₂Cu phases were in equilibria with ??-Zr at 1073 K.     

Solubility and phase behavior of nickel oxide in aqueous sodium phosphate solutions at elevated temperatures

A platinum-lined, flowing autoclave facility was used to investigate the solubility/phase behavior of nickel oxide (NiO) in aqueous sodium phosphate solutions between 290 and 560 K. A layer of hydrous nickel oxide was concluded to exist on the nickel oxide surface below 468 K; only at higher temperatures did the anhydrous nickel oxide phase control the nickel ion solubility behavior. The measured solubility behavior was examined via a nickel(II) ion hydrolysis/complexing model and thermodynamic functions for the hydrolysis/complexing reaction equilibria were obtained from a least-squares analysis of the data. The existence of two new nickel ion complexes are reported for the first time: Ni(OH)₂(HPO₄)⁼ and Ni(OH)₃(H₂PO₄)⁼. The positive entropy change associated with the formation of Ni(OH)₃(H₂PO₄)⁼ leads to its dominance in alkaline phosphate solutions at elevated temperatures.     

Nucleation and Crystal Formation in Lithium Disilicate‐Apatite Glass‐Ceramic from a Combined Use of X‐Ray Diffraction,Solid‐State NMR,and Microscopy

Glass‐ceramics are multi‐phase materials that are comprised of one amorphous phase and at least one crystalline phase. Their versatile performance and properties can be engineered by alterations of the three fundamental steps – formulation and production of the amorphous base glass, nucleation, and crystallization. Efforts have been made on syntheses of glass‐ceramics with different components, yet little is known about the details of nucleation and crystallization processes that are essential for tailoring glass‐ceramic properties. Herein, we investigate the nucleation and crystallization mechanisms of a multi‐component, that is SiO₂‐Al₂O₃‐CaO‐Li₂O‐K₂O‐P₂O₅‐F, glass‐ceramic system by a combined use of powder X‐ray diffraction (pXRD), solid‐state nuclear magnetic resonance (NMR), and electron microscopic (EM) techniques. The role of P₂O₅ in the nucleation and crystallization processes is particularly studied. We show that the formation of lithium silicate crystals being independent of the P₂O₅‐associated crystals, and the separation of P₂O₅ phases into individual growth domains of lithium orthophosphate and fluorapatite. We also observe the non‐uniform distribution of fluorapatite particles that explains the opalescence effect of this glass‐ceramic.