Development of hexa- and mono-celsian in the crystallization of banalsite BaNa2Al4Si4O16 (LiF-CaF2-B2O3) glasses

On the basis of the mineral banalsit (BaNa₂Al₄Si₄O₁₆) and the addition of small B₂O₃ concentrations, transparent glasses were prepared. Furthermore, in order to achieve nucleation, LiF and CaF₂ were added. Hexacelsian was formed in bulk crystallized glass samples whereas, monocelsian, as well as small quantities of nepheline and banalsite were crystallized from sintered glass powder. The scanning electron micrographs of the sintered samples show high crystallinity and crystals with sizes from nano to micrometers. The SEM micrographs and the EDX microanalyses show that nano size rods of monocelsian surrounded by micrometer-sized hexagonal nepheline, banalsite or residual glassy phase occur. The coefficient of thermal expansion of the samples sintered at 1000 °C was higher (12.93–9.52 × 10⁻⁶ K⁻¹) in hexacelsian containing samples than in monocelsian (2.24–7.35 × 10⁻⁶ K⁻¹) containing ones. The samples also showed notably different densities of 2.6424 and 2.4718 g/cm³, respectively.     

Zur Bedeutung von V2O3(OH)4(g) für den chemischen Transport von V2O5(s) in Anwesenheit von Wasser. Nachweis des Gasteilchens,thermodynamische Daten und Modellrechnungen

V₂O₃(OH)₄(g), Proof of Existence, Thermochemical Characterization, and Chemical Vapor Transport Calculations for V₂O₅(s) in the Presence of Water By use of the Knudsen-cell mass spectrometry the existence of V₂O₃(OH)₄(g) is shown. For the molecules V₂O₃(OH)₄(g), V₄O₁₀(g), and V₄O₈(g) thermodynamic properties were calculated by known Literatur data. The influence of V₂O₃(OH)₄(g) for chemical vapor transport reactions of V₂O₅(s) with water ist discussed. Δ_BH°(V₂O₃(OH)₄(g), 298) = –1920 kJ · mol^–1 and S°(V₂O₃(OH)₄(g), 298) = 557 J · K^–1 · mol^–1, Δ_BH°(V₄O₁₀(g), 298) = –2865,6 kJ · mol^–1 and S°(V₄O₁₀(g), 298) = 323.7 J · K^–1 · mol^–1, Δ_BH°(V₄O₈(g), 298) = –2465 kJ · mol^–1 and S°(V₄O₈(g), 298) = 360 J · K^–1 · mol^–1.     

Solid electrolytes with cesium cation conductivity in the Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiO<Subscript>2</Subscript>-Cs<Subscript>2</Subscript>O system

Solid solutions based on cesium monogallate CsGaO₂ are synthesized in the Ga₂O₃-TiO₂-Cs₂O system. Their crystalline structure and also temperature and concentration conductivity dependences are studied. The cesium cation character of conductivity is confirmed. The most conducting samples contain an excess of cesium oxide and have the structure of high-temperature γ-modification of KAlO₂. Their specific conductivity is (5.0–6.7) × 10^?3 S cm^?1 at 400 °C, (2.5–5.0) × 10^?2 S cm^?1 at 700°C at the activation energy of 33–35 kJ/mol^?1.     

Methane-fueled SOFC with traditional nickel-based anode by applying Ni/Al2O3 as a dual-functional layer

Novel γ-Al₂O₃ supported nickel (Ni/Al₂O₃) catalyst was developed as a functional layer for Ni–ScSZ cermet anode operating on methane fuel. Catalytic tests demonstrated Ni/Al₂O₃ had high and comparable activity to Ru–CeO₂ and much higher activity than the Ni–ScSZ cermet anode for partial oxidation, steam and CO₂ reforming of methane to syngas between 750 and 850 °C. By adopting Ni/Al₂O₃ as a catalyst layer, the fuel cell demonstrated a peak power density of 382 mW cm^?2 at 850 °C, more than two times that without the catalyst layer. The Ni/Al₂O₃ also functioned as a diffusion barrier layer to reduce the methane concentration within the anode; consequently, the operation stability was also greatly improved without coke deposition.     

Differential scanning calorimetry of RbH2PO4 and CsH2PO4

The high-temperature phase behaviour of RbH₂PO₄ and CsH₂PO₄ have been studied. RbH₂PO₄ undergoes a single quasi-irreversible phase transition with an enthalpy of 4.665 kJ mol^?1. The transition is found to occur over the temperature range 86–111°C. CsH₂PO₄ undergoes two transitions at 149 and 230°C. The lower one is quasi-irreversible and has an enthalpy of 4.284 kJ mol^?1. The one at 230°C is reversible and has an enthalpy of 1.071 kJ mol^?1.     

Use of noncontact dilatometry for the assessment of the sintering kinetics during mullitization of three kaolinitic clays from Cameroon

Noncontact dilatometry, compared to differential scanning calorimetry (DSC), was used together with scanning electron microscopy and densification behavior studies to investigate the parameters that govern the kinetics of transformation of kaolin to mullite during sintering. Three kaolinitc clays from Cameroon, with different SiO₂/Al₂O₃ molar ratio, were examined. The temperatures of mullite nucleation were 973, 979, and 984 °C at 5 °C/min heating rate, respectively, for values of SiO₂/Al₂O₃ molar ratio equal to 4.22, 2.22, and 2.08. At 20 °C/min heating rate, the temperatures are shifted to higher values, 992, 997, and 1,001 °C. The mullitization phenomenon, which includes a first step of nucleation and a second one of crystal growth, presented activation energy in the range of 650–730 kJ/mol, depending on the nature of the sample investigated. These values, obtained by noncontact dilatometer measurements, were comparable to those obtained by means of DSC and are in agreement with literature values. The difference in sintering kinetics for the three kaolinitic clays could explain the different morphologies obtained for the mullite grains.     

Synthesis of ultrafine yttrium aluminum garnet using sol-gel technology

Mesoporous yttrium aluminum garnet Y₃Al₅O₁₂ powders were prepared using sol-gel technology proceeding from solutions of metal alkoxoacetylacetonates. Xerogel microstructure was studied by SEM, and the fact of mesopores being formed was established. The temperature range within which Y₃Al₅O₁₂ crystallizes in a dynamic mode from the xerogel was determined to be 850?C950°C using an SDT Q600 TGA/DTA/DSC analyzer. A 1-h isothermal treatment of the xerogel was shown to reduce the garnet phase formation temperature to 800°C. At lower temperatures (400, 450 or 500°C), even long-term (6-h) calcination yielded X-ray amorphous powders with developed surfaces (specific surface areas were 230?C350 m²/g). Powder particle coarsening was studied upon sintering for 2 and 4 h at 1000, 1200, and 1400°C.     

Solid Reactions of Egyptian Kaolin towards Ni(II). II

The solid reactions between Kaolin of particle size 37 and 74μ and NiO in different mole ratios were performed at two temperatures, viz., 900 and 1100°C. The effect of the three parameters: concentration, particle size and temperature was studied spectrophotometrically and by x-ray diffractometry. The identified resulting phases are mainly the green spinel NiAl₂O₄, together with free SiO₂ and mullite Al₆Si₂O₁₃.     

Temperature factor in interaction of nanotubular magnesium hydrosilicate,Mg3Si2O5(OH)4, with titanium tetrachloride and water vapors

The conditions were found for modification of Mg₃Si₂O₅(OH)₄ nanotubes without altering their inherent chrysolite structure by calcination at 400°C, followed by treatment with TiCl₄ vapor at 150–400°C and vapor-phase hydrolysis at 400°C. The procedure for modification of Mg₃Si₂O₅(OH)₄ nanotubes can be used for the development of high-performance filtration systems, nanocontainers for storage and transportation of substances, supports for heterogeneous catalysts, and modified sorbents.     

Synthesis of Ca<Subscript>3</Subscript>Al<Subscript>6</Subscript>Si<Subscript>2</Subscript>O<Subscript>16</Subscript>: Ce<Superscript>3+</Superscript>, Tb<Superscript>3+</Superscript> phosphors by sol–gel method and optical properties

Ca₃Al₆Si₂O₁₆: Ce³⁺, Tb³⁺ phosphors have been prepared by sol–gel method. The structure and photoluminescence properties were studied with careful. The results indicated that the single-phased Ca₃Al₆Si₂O₁₆ phosphors crystallize at 1,000 °C for 2 h in conventional furnace. With appropriate concentrations of Ce³⁺ and Tb³⁺ ions into Ca₃Al₆Si₂O₁₆ matrix, these materials exhibit blue phosphors and white light under ultraviolet radiation. White-light emission can be achieved because of a 400 nm emission ascribed to transitions of Ce³⁺ ions and three sharp peaks at 487, 543, 585 nm, respectively, resulting from transitions of Tb³⁺ ions.     

Pr4S3[Si2O7] und Pr3Cl3[Si2O7]: Durch weiche Fremdanionen modifizierte Derivate von Praseodymdisilicat

Pr₄S₃[Si₂O₇] and Pr₃Cl₃[Si₂O₇]: Derivatives of Praseodymium Disilicate Modified by Soft Foreign Anions For synthesizing both the disilicate derivatives Pr₄S₃[Si₂O₇] and Pr₃Cl₃[Si₂O₇], Pr, Pr₆O₁₁ and SiO₂ are brought to reaction with S and PrCl₃, respectively, in suitable molar ratios (850 °C, 7 d) in evacuated silica tubes. By using NaCl as a flux, Pr₄S₃[Si₂O₇] crystallizes as pale green, transparent single crystals (tetragonal, I4₁/amd, a = 1201.6(1), c = 1412.0(2) pm, Z = 8) with the appearance of slightly compressed octahedra. On the other hand, Pr₃Cl₃[Si₂O₇] emerges as pale green, transparent platelets and crystallizes monoclinically (space group: P2₁, a = 530.96(6), b = 1200.2(1), c = 783.11(8) pm, β = 109.07(1)°, Z = 2). In both crystal structures ecliptically conformed [Si₂O₇]^6– units of two corner‐linked [SiO₄] tetrahedra with Si–O–Si bridging angles of 131° in the sulfide and 148° in the chloride disilicate are present. In Pr₄S₃[Si₂O₇] both crystallographically independent Pr³⁺ cations show coordination numbers of 8 + 1 (5 S^2– and 3 + 1 O^2–) and 9 (3 S^2– and 6 O^2–). For Pr1, Pr2 and Pr3 in Pr₃Cl₃[Si₂O₇] coordination numbers of 10 (5 Cl^– and 5 O^2–) and 9 (2 ×; 4 Cl^– and 5 O^2– or 3 Cl^– and 6 O^2–, respectively) occur.     

Electron diffraction and X-ray investigation of hydrothermally vitrified 5 A zeolite containing trapped gases

The mechanism of gas fixation by hydrothermal treatment of zeolite type 5 A in the presence of a densified gas has been examined by electron diffraction and X rays. It is shown that gas trapping occurs in an X-ray amorphous phase which is formed within a broad spectrum of fixation conditions. The amorphous matrix recrystallizes at 850°C regardless of the parameter combination selected for vitrification. The recrystallization product consists essentially of anorthite and nepheline phases. In addition some CaAl₂Si₂O₈ was found. Observations made by X rays and by electron diffraction correlate well with leak rate data.     

Acetylation of Glycerol over Highly Stable and Active Sulfated Alumina Catalyst: Reaction Mechanism,Kinetic Modeling and Estimation of Kinetic Parameters

The Langmuir–Hinshelwood–Hougen–Watson (LHHW) kinetic model was developed for acetylation of glycerol over highly stable and active 2 M SO₄²⁻/γ‐Al₂O₃ catalyst. The apparent reaction rate constants were determined by numerically solving the differential rate equations using ode23 tool in MATLAB coupled with the genetic algorithm optimization technique. The estimated rate constants were used to obtain the activation energy and pre‐exponential factor by using the Arrhenius equation. The estimated activation energy for direct acetylation of glycerol to monoacetylglycerol and diacetylglycerol was 7.2 kJ mol⁻¹, for acetylation of monoacetylglycerol to diacetylglycerol was 37.1 kJ mol⁻¹, and for acetylation of diacetylglycerol to triacetylglycerol was 26.6 kJ mol⁻¹, respectively.     

Photo–thermo Catalytic Oxidation over a TiO2-WO3-Supported Platinum Catalyst

Photo–thermo catalysis, which integrates photocatalysis on semiconductors with thermocatalysis on supported nonplasmonic metals, has emerged as an attractive approach to improve catalytic performance. However, an understanding of the mechanisms in operation is missing from both the thermo- and photocatalytic perspectives. Deep insights into photo–thermo catalysis are achieved via the catalytic oxidation of propane (C₃H₈) over a Pt/TiO₂-WO₃ catalyst that severely suffers from oxygen poisoning at high O₂/C₃H₈ ratios. After introducing UV/Vis light, the reaction temperature required to achieve 70 % conversion of C₃H₈ lowers to a record-breaking 90 °C from 324 °C and the apparent activation energy drops from 130 kJ mol⁻¹ to 11 kJ mol⁻¹. Furthermore, the reaction order of O₂ is −1.4 in dark but reverses to 0.1 under light, thereby suppressing oxygen poisoning of the Pt catalyst. An underlying mechanism is proposed based on direct evidence of the in-situ-captured reaction intermediates.     

Composition of the gas phase over Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and the enthalpies of atomization of AlO,Al<Subscript>2</Subscript>O,and Al<Subscript>2</Subscript>O<Subscript>2</Subscript>

The A1, O, AlO, A1₂O, Al₂O₂, WO₂, and WO₃, partial pressures in the vapor over Al₂O₃ in a tungsten Knudsen effusion cell between 2300 and 2600 K were derived from A1⁺, O⁺, AlO⁺, A1₂O⁺, Al₂O₂⁺, WO₂⁺, and WO₃⁺, ion intensities. The mass spectrometer was calibrated against the equilibrium constant of the WO₃(g) = WO₂(g) + O(g) reaction. Refined values of the ionization cross sections of AlO and A1₂O₂ were used in the partial pressure calculations. The enthalpies of atomization of aluminum suboxides were determined to be Δ_at H ^o(AlO, g, 0) = 510.7 ± 3.3 kJ mol⁻¹, Δ_at H ^o(Al₂O, g, 0) = 1067.2 ± 6.9 kJ mol⁻¹, and Δ_at H ^o(Al₂O₂, g, 0) = 1556.7 ± 9.9 kJ mol⁻¹.     

The Si?Sn Chemical Bond: An Integrated Thermochemical and Quantum Mechanical Study of the SiSn Diatomic Molecule and Small Si–Sn Clusters

The silicon–tin chemical bond has been investigated by a study of the SiSn diatomic molecule and a number of new polyatomic Si_xSn_y molecules. These species, formed in the vapor produced from silicon–tin mixtures at high temperature, were experimentally studied by using a Knudsen effusion mass spectrometric technique. The heteronuclear diatomic SiSn, together with the triatomic Si₂Sn and SiSn₂ and tetratomic Si₃Sn, Si₂Sn₂, and SiSn₃ species, were identified in the vapor and studied in the overall temperature range 1474–1944 K. The atomization energy of all the above molecules was determined for the first time (values in kJ mol^?1): 233.0±7.8 (SiSn), 625.6±11.6 (Si₂Sn), 550.2±10.7 (SiSn₂), 1046.1±19.9 (Si₃Sn), 955.2±26.8 (Si₂Sn₂), and 860.2±19.0 (SiSn₃). In addition, a computational study of the ground and low‐lying excited electronic states of the newly identified molecules has been made. These electronic‐structure calculations were performed at the DFT‐B3LYP/cc‐pVTZ and CCSD(T)/cc‐pVTZ levels, and allowed the estimation of reliable molecular parameters and hence the thermal functions of the species under study. Computed atomization energies were also derived by taking into account spin–orbit corrections and extrapolation to the complete basis‐set limit. A comparison between experimental and theoretical results is presented. Revised values of (716.5±16) kJ mol^?1 (Si₃) and (440±20) kJ mol^?1 (Sn₃) are also proposed for the atomization energies of the Si₃ and Sn₃ molecules.     

Crystallization in the SiO2-Al2O3 System from Amorphous Powders

The crystallization of amorphous chemically homogeneous powders in the SiO₂.Al₂O₃ system has been studied by differential scanning calorimetry and X-ray diffraction. Up to 1300°C only one exotherm has been observed. Only mullite crystallizes for compositions ≤69 mol% Al₂O₃ and spinel for those ≤80%. The crystallizations into mullite and spinel are sharp and exothermic, with an enthalpy of 250–300 J/g. The chemical composition of the crystallized mullite regularly increases from 68 to 76 mol% Al₂O₃ with increasing bulk composition from 60 to 75 mol% Al₂O₃.     

The thiomethyl anion: Formation,reactivity, and thermodynamic properties

The thiomethyl anion (1) has been generated by fluorodesilylation of trimethylsilylmethanethiol in a variable-temperature flowing afterglow device. The proton affinity (1649 ± 12 kJ mol^?1) and electron affinity (0.67 ± .13 eV) were determined and compared to a previously reported molecular orbital calculation. Isomerization via a 1,2-proton shift does not take place between ?40° and 100°C despite a 156 kJ mol^?1 driving force. Ion-molecule reactions of 1 were examined with a number of reagents including N₂0, O₂, CS₂, COS, and CO₂, Hydride ion transfer was observed in every case, along with other products, and thermodynamic information has been derived.     

One-pot hydrothermal synthesis of reduced graphene oxide/zinc ferrite nanohybrids and its catalytic activity on the thermal decomposition of ammonium perchlorate

Reduced graphene oxide/Zinc ferrite (rGO/ZnFe₂O₄) nanohybrids are successfully decorated on the surface of the rGO sheets through a simple, one-step hydrothermal method. ZnFe₂O₄ nanoparticles (NPs) are homogeneously anchored on the rGO sheets. The rGO/ZnFe₂O₄ hybrids are characterized by XRD, FT-IR, XPS, TEM, Raman, BET. The rGO/ZnFe₂O₄ hybrids demonstrate amazing catalytic activity on thermal decomposition of ammonium perchlorate (AP), which is better than that of bare ZnFe₂O₄ NPs. TG-DTA results indicate that the ZnFe₂O₄ NPs in the hybrids with increasing ratio (1%, 3%, 5%) could decrease the second decomposition temperature of AP by 42.7?°C, 55.0?°C, 68.1?°C, respectively, and reduce the apparent activation energy of AP from 160.2?kJ?mol^?1 to 103.8?kJ?mol^?1. This enhanced catalytic performance is mainly attributed to the synergistic effect of ZnFe₂O₄ NPs and rGO.     

Photo–thermo Catalytic Oxidation over a TiO2‐WO3‐Supported Platinum Catalyst

Photo–thermo catalysis, which integrates photocatalysis on semiconductors with thermocatalysis on supported nonplasmonic metals, has emerged as an attractive approach to improve catalytic performance. However, an understanding of the mechanisms in operation is missing from both the thermo‐ and photocatalytic perspectives. Deep insights into photo–thermo catalysis are achieved via the catalytic oxidation of propane (C₃H₈) over a Pt/TiO₂‐WO₃ catalyst that severely suffers from oxygen poisoning at high O₂/C₃H₈ ratios. After introducing UV/Vis light, the reaction temperature required to achieve 70 % conversion of C₃H₈ lowers to a record‐breaking 90 °C from 324 °C and the apparent activation energy drops from 130 kJ mol^?1 to 11 kJ mol^?1. Furthermore, the reaction order of O₂ is ?1.4 in dark but reverses to 0.1 under light, thereby suppressing oxygen poisoning of the Pt catalyst. An underlying mechanism is proposed based on direct evidence of the in‐situ‐captured reaction intermediates.