Structural Properties and Thermal Behavior of Li2CO3–BaCO3 System by DTA,TG and XRD Measurements

The binary system Li₂CO₃–BaCO₃ was studied by means of differential thermal analysis (DTA), thermogravimetry (TG) and X-ray phase analysis. The composition of carbonate and CO₂ partial pressure influence on the thermal behavior of carbonate were examined. It was shown that lithium carbonate does not form the substitutional solid solution with barium carbonate, however the possible formation of diluted interstitial solid solutions is discussed. Above the melting temperature the mass loss is observed on TG curves. This loss is the result of both decomposition of lithium carbonate and evaporation of lithium in Li₂CO₃–BaCO₃ system. Increase of CO₂ concentration in surrounding gas atmosphere leads to slower decomposition of lithium carbonate and to increase the melting point. This revised version was published online in July 2006 with corrections to the Cover Date.     

Conductivity Studies of Glasses in the System WO3−P2O5

Russian Journal of Applied Chemistry - Quenching method was used to obtain glasses in the system xWO3-(100-x)P2O5 (x = 70, 75, 80, 82 mol %). The electrical conductivity of the compositions was...     

Thermodynamic Model for SnO2(cr) and SnO2(am) Solubility in the Aqueous Na+–H+–OH−–Cl−–H2O System

The solubility of SnO₂(cassiterite) was studied at 23±2?°C as a function of time (7 to 49 days) and pH (0 to 14.5). Steady state concentrations were reached in <7 days. The data were interpreted using the SIT model. The data show that SnO₂(cassiterite) is the stable phase at pH values of 10 K ⁰ value of ?64.39±0.30 for the reaction (SnO₂(cassiterite) +2H₂O?Sn⁴⁺+4OH^?) and values of 1.86±0.30, ≤?0.62, ?9.20±0.34, and ?20.28±0.34 for the reaction ( $\mathrm{Sn}^{4+} + n\mathrm{H}_{2}\mathrm{O} \rightleftarrows \mathrm{Sn}(\mathrm{OH})_{n}^{4 - n} + n\mathrm{H}^{+}$ ) with values of “n” equal to 1, 4, 5, and 6 respectively. These thermodynamic hydrolysis constants were used to reinterpret the extensive literature data for SnO₂(am) solubility, which provided a log?₁₀ K ⁰ value of ?61.80±0.29 for the reaction (SnO₂(am)+2H₂O?Sn⁴⁺+4OH^?). SnO₂(cassiterite) is unstable under highly alkaline conditions (NaOH concentrations >0.003 mol?dm^?3) and transforms to a double salt of SnO₂ and NaOH. Although additional well-focused studies will be required for confirmation, the experimental data in the highly alkaline region (0.003 to 3.5 mol?dm^?3 NaOH) can be well described with log?₁₀ K ⁰ of ?5.29±0.35 for the reaction Na₂Sn(OH)₆(s)?Na₂Sn(OH)₆(aq).     

Studies on Oxidation of Active α-H of Aromatic Hydrocarbon by CAN/NaBrO3/H2O System

Cerium ammonium nitrate (CAN) is an expensive and powerful selective oxidant. It has played an important role in organic synthesis. Because it is a single electron oxidant,many organic reactions need large quantities of it. The application of CAN in organic synthesis in the oxidation of alkyl aromatics has so far been limited. In this paper, we wish to report a new method of oxidation of active α-H of aromatic hydrocarbon by CAN/NaBrO₃/H₂O system. Only catalytic amount of CAN was needed in this method and the selectivity was improved as well.     

Structural Aspect of a Thermal Activation Effect in the MnO x /γ-Al2O3 System

Solid-phase reactions in the aluminum–manganese oxide system, including the structural mechanism of the thermal activation of catalysts, were studied at temperatures up to 1100°C. It was found that the solid-phase reaction at 900–1000°C occurred via two pathways because of the diffusion of manganese ions to aluminum oxide and aluminum ions to manganese oxide. Nanoheterogeneous state of the active component, which was observed in the range 25–600°C, is the product of incomplete decomposition of the high-temperature aluminum–manganese phase Mn_{2.1 – x} Al_{0.9 + x} O₄ (0 x 0.6) with a cubic spinel structure; this phase was equilibrium at the synthesis temperature but metastable below 650°C.     

Study of the oxygen distribution in YBa2Cu3O7−x ceramics by (n, α) radiography technique

A technique to determine the oxygen distribution in high T_c superconducting YBa₂Cu₃O_7–x ceramics has been developed which is based on the (n, ) radiography method. The technique enables the non-destructive study of superconducting ceramics as well as monocrystal samples with spatial resolution not worse than 1 m at a relative standard deviation of 1.5%. This technique is used to study the influence of radiation-stimulated diffussion of oxygen on the formation of the superconducting phase in an yttrium ceramic. The oxygen distribution in the samples with a narrow transition (T1 K) and with a transition widened (T10 K) by thermal and thermo-radiative treatment is compared in the experiment. The oxygen distribution radiographs of irradiated and unirradiated samples provide strong evidence for the influence of irradiation on the ordering of superconducting ceramics structure.     

Degradation Mechanism of Phenol in C/PTFE O2-Fed Cathode by Determining the Product of Oxygen Electroreduction

A terylene membrane which kept pH〉12 in cathode compartment was used to construct a divided cell with a carbon/polytetrafluoroethylene（C/PTFE） O2-fed cathode. The concentrations of hydrogen peroxide （H2O2） and hydroxyl radical （HO^-）in the catholyte were 8.3 mg/L and 2.15 μmol/L, respectivel.y, which were determined by permanganate titration, electron spin resonance （ESR） spectrum and the fluorescence spectra. ;The efficiency of the removal of phenol achieved 100% as a result of these two kinds of stronger oxidizer.     

Phase-field Determination of NaSICON Materials in the Quaternary System Na2O−P2O5−SiO2−ZrO2: The Series Na3Zr3–xSi2PxO11.5+x/2

Two types of solid electrolytes have reached technological relevance in the field of sodium batteries: ß/ß”-aluminas and NaSICON-type materials. Today, significant attention is paid to room-temperature stationary electricity storage technologies and all-solid-state Na batteries used in combination with these solid electrolytes are an emerging research field besides sodium-ion batteries. In comparison, NaSICON materials can be processed at lower sintering temperatures than the ß/ß”-aluminas and have a similarly attractive ionic conductivity. Since Na₂O−SiO₂−ZrO₂−P₂O₅ ceramics offer wider compositional variability, the series Na₃Zr_3–xSi₂P_xO_11.5+x/2 with seven compositions (0≤x≤3) was selected from the quasi-quaternary phase diagram in order to identify the predominant stability region of NaSICON within this series and to explore the full potential of such materials, including the original NaSICON composition of Na₃Zr₂Si₂PO_l2 as a reference. Several characterization techniques were used for the purpose of better understanding the relationships between processing and properties of the ceramics. X-ray diffraction analysis revealed that the phase region of NaSICON materials is larger than expected. Moreover, new ceramic NaSICON materials were discovered in the system crystallizing with a monoclinic NaSICON structure (space group C2/c). Impedance spectroscopy was utilized to investigate the ionic conductivity, giving clear evidence for a dependence on crystal symmetry. The monoclinic NaSICON structure showed the highest ionic conductivity with an optimum ionic conductivity of 1.22×10⁻³ at 25 °C for the composition Na₃Zr₂Si₂PO₁₂. As the degree of P⁵⁺ content increases, the total ionic conductivity is initially enhanced until x=1 and then decreases again. Simultaneously, the increasing amount of phosphorus leads a decrease in the sintering temperatures for all samples, which was confirmed by dilatometry measurements. The thermal and microstructural properties of the prepared samples are also evaluated and discussed.     

Synthesis and Evaluation of Graphene Aerogel-Supported MnxFe3−xO4 for Oxygen Reduction in Urea/O2 Fuel Cells

Graphene aerogel-supported manganese ferrite (Mn_xFe_3−xO₄/GAs) and reduced-graphene oxide/manganese ferrite composite (MnFe₂O₄/rGO) were synthesized and studied as cathode catalysts for oxygen reduction reactions in urea/O₂ fuel cells. MnFe₂O₄/GAs exhibited a 3D framework with a continuous macroporous structure. Among the investigated Fe/Mn ratios, the more positive oxygen reduction onset potential was observed with Fe/Mn=2/1. The half-wave potential of MnFe₂O₄/GAs was considerably more positive than that of MnFe₂O₄/rGO and comparable with that of Pt/C, while the stability of MnFe₂O₄/GAs significantly higher than that of Pt/C. The best urea/O₂ fuel cell performance was also observed with the MnFe₂O₄/GAs. The MnFe₂O₄/GAs exhibited an OCV of 0.713 V and a maximum power density of 1.7 mW cm⁻² at 60 °C. Thus, this work shows that 3D structured graphene aerogel-supported MnFe₂O₄ catalysts can be used as an efficient cathode material for alkaline fuel cells.     

Studies on Kinetic Properties of Active Oxygen on the Surfaces of V_2O_5/SiO_2, V_2O_5-MoO_3/SiO_2 and V_2O5-P_2O5/SiO_2 Catalysts

Applying the TPD-MS with a high sensitivity of determination, the TPD spectrum of surface oxygen of V2O5/SiO2, V2O5-MoO3/SiO2 and V2O6-P2O5/SiO2 catalysts was obtained. The surface oxygen of these catalysts can be divided into three groups according to the desorption temperature. O2- desorbs mainly from 373K. to 423K, O- from 673K to 873K and O2- at above 873K. The activation energy and frequency factor of all the three kinds of oxygen species were calculated. Based on these results, the mechanism of oxygen desorption and the influence of P2O5 and MoO3 on the properties of oxygen supply of V2O5/SiO2 catalst were investigated. MoO3 and a small amount of P2Os increase the number of supplying oxygen and increase the activity of O- species. A large amount of P2O5 increases the number of supplying oxygen and restrains the activity of O- species.     

Thermal studies on Li(CH3CN)4PF6 and Li(C4H10O2)2PF6 complexes by the TG–DTA–MS and DSC

Journal of Thermal Analysis and Calorimetry - Li(CH3CN)4PF6 and Li(C4H10O2)2PF6 complexes are important intermediates created in the synthetic process of high-purity LiPF6 electrolyte via...     

Reductive Cyclodimerization of Arylidenecyanoacetates Promoted by Sm/InCl_3·4H_2O System in Aqueous Media

Metal-mediated reactions in aqueous media have received considerable attention in the last decade1. Such aqueous reactions offer a number of advantages over conventional organometallic reactions in organic solvent in that they are practically convenient, environmentally benign and do not require strict anhydrous conditions2. In recent years, besides zinc and tin, indium has been found to be the metal of choice for promoting organic reactions in aqueous media3. Indium is considered to be mor…     

Dta/TG study of the formation of the (Bi,Pb)2Sr2Ca2Cu3O10+δ superconductor

In order to get insight in some of the yet unanswered questions about the formation process of the (Bi,Pb)₂Sr₂Ca₂Cu₃O₁₀₊ superconducting compound, coupled DTA-TG measurements have been performed in parallel with other techniques such as X-ray diffraction, Scanning Electron Microscopy and Energy Dispersive X-ray Microanalysis. The path leading to the formation of the (Bi,Pb)₂Sr₂Ca₂Cu₃O₁₀₊ compound, starting from coprecipitated oxalates powders was studied. The activation energy of some of the involved transformation processes were determined. Relationships between the differences induced in the DTA traces by various sample nominal compositions and the intergranular magnetic properties of the superconductor will be discussed.     

Distribution and Transfer of Gatifloxacin Between Two Microemulsion Phases with Different Structures in SDS/n-C5H11 OH/H2O System

At a weight ratio of n‐C₅H₁₁OH/H₂O=50/50, when the total content of sodium dodecyl sulfate (SDS) was less than 6.0%, the ternary mixture of SDS/n‐C₅H₁₁OH/H₂O coexisted in two immiscible microemulsions. The distribution and transfer of gatifloxacin (GTFX) between the two phases were studied using UV‐Vis and electrochemistry AC impedance spectra. The results show that GTFX transferred from the upper phase (W/O) to the lower phase (O/W or bicontinuous microemulsion), but a small amount of SDS transferred from the lower phase to the upper phase correspondingly with the increase of the total SDS content at a total GTFX concentration of 1.0×10^?5 mol/L. The addition of GTFX did not change the structures of the two different phases fundamentally, but resulted in the transfer and redistribution of GTFX and SDS, so the electric properties of the system were changed correspondingly.     

Optical Resolution of 2-(3-Chloro-phenyl)-3,4a,5,6,7,7a-hexahydro-cyclopentapyrimidin-4-one with O,O′-Dibenzoyl-2R,3R-tartaric Acid in Water-Chloroform Two Phase Solvent System

Optical resolution of racemic 2-(3-chloro-phenyl)-3.4a. 5.6.7.7a-hexahydrocyclopentapyrimidin-4-one with O.O′-dibenzoyl-2R,3R-tartaric acid in an unusual solvent combination, in water-chloroform two phase solvent system was accomplished. During enantiomeric enrichment of the resulted raw base the optically active base can be recovered from the ethanolic mother liquor.     

Enhanced photoactivity of antimony phosphates by substitution of H+, Cu2+ and N3− in the K3Sb3P2O14·xH2O crystal lattice

Research on Chemical Intermediates - Substitutional doping of framework heteroatoms in photocatalysis is one of the approaches for harvesting visible light. Tunnel structure potassium antimony...     

Studies of Copper(II) Thiosemicarbazide Complexes and their Reactivities. X-Ray Structure of Two Unusual Reaction Products, [Cu(bpy)(H2O)2SO4] and [(bpy)2Cu2(C2O4)Cl2]·H2O

A number of ternary complexes of Cu²⁺ with thiosemicarbazide (TSC) including [Cu(bpy)(TSC)₂]Cl₂, [Cu(o-phen)(TSC)₂]Cl₂ and [Cu(bpy)(TSC)₂][CuCl₄] [Cu(o-phen)(TSC)₂] [CuCl₄] have been synthesised and characterized. Their reactivities in aqueous and DMF solutions were studied. It was observed that while on coordination to Cu²⁺ thiosemicarbazide is converted to thiocyanate in aqueous solution, in DMF solution the thiocyanate is further aerially oxidised to sulfate. In the presence of hydrogen peroxide, oxidation to sulfate is rapid and from the mother liquor we could isolate [(bpy)₂Cu₂(C₂O₄)Cl₂]·H₂O whose structure was determined by X-ray crystallography. X-ray crystal structure of [Cu(bpy)(H₂O)₂SO₄] is also discussed.*     

Investigation and characterization by TG/DTG–DTA and DSC of the fusion of Riboflavin,and its interaction with the antibiotic norfloxacin in the screening of cocrystal

This work synthesized and characterized the NOR-RIB 1:1 (mol–mol) cocrystal. During a study of the reagents, Riboflavin (RIB) melted at 304 °C, which is different from the temperature previously reported in the literature (280–290 °C); therefore, this compound was characterized individually. Subsequently, the cocrystal was synthesized with the active pharmaceutical ingredient (API) norfloxacin (NOR) with the RIB coformer, and the mechanochemical synthesis route was adopted. NOR, RIB, and the cocrystal were characterized by thermogravimetry–differential thermal analysis (TG–DTA), differential scanning calorimetry (DSC), DSC coupled to a microscope (photo-DSC), mid-infrared spectroscopy (MIR), and powder X-ray diffraction. The results of thermal analysis showed that the RIB starts decomposition process (260 °C) and then melts (304 °C). The MIR found that beginning at 295 °C, the RIB passes into the form of a decomposition intermediate; therefore, the melting point observed in the DSC curve is related to this decomposition material. The cocrystal presented thermal stability (200 °C) lower than the API (235 °C) and the coformer (260 °C). The DSC curve did not contain a melting peak. The bands at 1726 cm^?1 (C=O of the carboxylic acid) for the NOR, and the band at 3326 cm^?1 (stretch O–H), among others, were not visible for the cocrystal in the MIR spectrum, indicating interactions in these regions. The X-ray diffractograms showed a new diffraction pattern, which proved the obtainment of a new phase and cocrystal formation.