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1.
The aim of the present investigation is to synthesize mixed sodium potassium alanate (K2NaAlH6) and to explore its hydrogen sorption characteristics. K2NaAlH6 is synthesized through ball milling of KH and NaAlH4 in the molar ratio 2:1 under hydrogen pressure of 10 bar. The temperature programmed desorption experiment shows that the synthesized K2NaAlH6 has peak desorption temperature of ∼352°C and reveals appreciable rehydrogenation kinetics under 6 bar hydrogen pressure at 300°C. The investigations are also focused on the catalytic effect of carbon nanostructures (CNS) namely, the graphene sheet (GS) and single wall carbon nanotube (SWCNT) and titanium halides (TiCl3 and TiF3) on K2NaAlH6. In the case of graphene and SWCNT catalyzed K2NaAlH6, the peak desorption temperature gets reduced to ∼347°C and ∼341°C respectively. The catalytic effects of CNS and titanium halide on K2NaAlH6 are also compared in the investigation. Between the two types of catalysts, halides are found to be better than CNS and out of the two halides, TiF3 is found to be the best catalyst for hydrogen sorption in K2NaAlH6. The peak desorption temperature decreases significantly from 352°C to ∼324°C for TiF3 catalyzed K2NaAlH6. Thus, the desorption activation energy reduces drastically from 124.43 kJ/mol (synthesized K2NaAlH6) to 88.05 kJ/mol for TiF3 catalyzed K2NaAlH6.  相似文献   

2.
Electrical conductivity of pure and SrCO3 doped potassium carbonate has been investigated in the temperature range between 350 and 800 °C. Sintered carbonate mixtures were analysed by X-ray powder diffraction techniques at room temperatures. The conductivity of SrCO3 doped K2CO3 increases nearly linear up to 10 mol.% and decreases in the range between 20 and 50 mol.% continously. X-ray diffraction patterns do not show changes up to 10 mol.% SrCO3 in the host lattice. The compound K2Sr(CO3)2 was found for samples containing 15–50 mol.% SrCO3. The lattice constants of hexagonal crystals which are isotypic with K2Ca(CO3)2 are a0 = (534 ± 1) pm and c0 = (1352 ± 2) pm.  相似文献   

3.
The interactions between YBa2Cu3O7-x and K2CO3 have been studied using thermochemical methods, isothermal annealing of diffusion pairs, optical microscopy, X-ray diffraction, and microprobe analyses. The experiments have shown existence of solubility of YBa2Cu3O7-x or its constituents in both solid and liquid K2CO3. The barium ions are preferably dissolved in K2CO3, whereas potassium cations do not enter massively into the bulk of the YBa2Cu3O7-x-phase. A eutectic-type phase diagram is supposed for the system K2CO3–YBa2Cu3O7-x. The so called “green phase” Y2BaCuO5 and a K–Cu–O compound have been found in the contact zone at 813 °C while a “black phase” layer with nominal composition Y1.6Cu2.8O5.4 has grown at 707 °C.  相似文献   

4.
The thermal behavior of bone mineral samples was investigated in the range from 600 to 900ºC by X‐ray diffraction with line broadening analysis and temperature‐programmed desorption mass spectrometry. At least two stages of CO32‐ release during the thermal evolution were observed, each can be attributed to a different type of carbonate location in the bone mineral. The elimination of CO32‐ occurring without pronounced variations in the substructural parameters of the biomineral nanocrystals is ascribed to the surface carbonate, while the elimination of CO32‐ accompanied by the growth of crystals and disappearance of structural distortions is attributed to the lattice carbonate. The sample of affected immature bone with low bioapatite crystallinity was found to have the surface carbonate content greater than the amount of carbonate in the lattice, while for the mature healthy bone the situation is reverse. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

5.
The electrical conductivity of pure and SrCO3-doped sodium carbonate has been measured in the temperature range 310–800 °C in air using a dc technique. Its concentration dependency is similar to that of the K2CO3–SrCO3 system described recently (GUTH et al. 1986). The maximum conductivity could be observed at ≈ 20 mol.% SrCO3. At temperatures > 440 °C, the conductivity of Na2CO3–SrCO3 mixtures containing up to 80 mol.% SrCO3 is larger than that of pure Na2CO3. X-ray investigations of slowly cooled samples show the mixtures to be heterogeneous. X-ray diffraction patterns of quenched mixtures containing 10 mol.% SrCO3 show reflexes of a high temperature compound. SrCO3, however, could not be detected. The lattice constants of this hexagonal compound Na2Sr4(CO3)5 which is isotyp with Na2Ca2Sr2(CO3)5 described by CHEN and CHAO are a0 = (1066.1 ± 0.4) pm and c0 = (653.2 ± 0.2) pm.  相似文献   

6.
The anomalous wedge‐like shape of KH2PO4‐type single crystal, also called tapering, is discussed in this paper. DKDP single crystals grew on seeds from the solutions containing high concentrations of Al3+, Fe3+ and Cr3+ impurities. The tapering phenomenon occurred on the prismatic {010} faces, and the tapering angle θ was nearly measured as 10°. We adjusted the pD value of the solution from 3.0 to 4.2 by adding K2CO3, the tapering angle of DKDP crystal grown from the same solution at same supercooling was reduced to 0°. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

7.
The new compounds Rb8[Ce(O2)(CO3)3]2 · 12 H2O (1) and Cs8[Ce(O2)(CO3)3]2 · 10 H2O (2) were obtained from the reaction of hydrogen peroxide and Ce(III) in saturated alkali carbonate solutions. The crystal structures and the unit cell parameters of (1) triclinic, P‐1 with a = 8.973(2) Å, b = 10.815(2) Å, c = 11.130(3) Å, α = 66.992(2)°, β = 68.337(2)°, γ = 74.639(2)°, VEZ = 914.7(4) Å3, Z = 2, and (2) orthorhombic, Pbca, a = 19.3840(16) Å, b = 18.528(2) Å, c = 10.487(3) Å, VEZ = 3766.4(13) Å3, Z = 8, were determined. Both compounds contain the bis‐µ‐peroxo‐hexacarbonatodicerate(IV)‐ion, [(CO3)3Ce(O2)2Ce(CO3)3]8‐. IR and Raman spectra were measured and discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

8.
This work deals with the prediction of crystal size distribution (CSD) in a continuous crystallizer for size-dependent growth. Crystal growth rates are described by Abegg, Stevens, and Larson (ASL) model. Stratified Monte Carlo method has been employed to evaluate the integrals involved in the classical moment equation for prediction of CSD. The simulation results have been compared with the available experimental data of K2CO3 · 1.5 H2O crystals in a continuous crystall lizer.  相似文献   

9.
A new double salt K2SiF6·KNO3 was found during determination of the solubility of K2SiF6 in aqueous potassium nitrate solutions. Unit cell parameters (P63/mmc, a = 5.6268(1) Å, c = 14.5186(6) Å, V = 398.09(2) Å3, Z = 2) and crystal structure have been determined. The compound is further characterized by RAMAN spectroscopy and X‐ray powder diffraction. Thermal properties were studied using DTA, DSC and in situ high‐ temperature X‐ray powder diffraction measurements. At 287 °C K2SiF6·KNO3 decomposes into its components KNO3 and K2SiF6 with an enthalpy of decomposition of about + 42 J·g‐1. Further thermal effects could be assigned to phase transformations of KNO3 whereby earlier literature data have been reconfirmed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

10.
A comprehensive experimental study on the effect of fourteen different inorganic salts on the growth rate of NaCl single crystals is presented. The fourteen different inorganic salts are chosen as they are present in Chinese sea water. The impurity content of each salt has been varied according to its presence in the natural sea water. The impurities are differentiated in groups related to their effect on the growth rate of NaCl. The examined impurities are: MgCl2 · 6 H2O, KCl, SrCl2, NaBr, Nal, NaF, Na2SO4, NaBO2 · 4 H2O, Na2CO3, Na2SiO3 · 9 H2O, ZnSO4, CuSO4 · 5 H2O, PbCl2, and K4Fe(CN)6.  相似文献   

11.
The homogeneous (unseeded) precipitation of nesquehonite (MgCO3·3H2O) was studied over the temperature range of 10‐40 °C. Precipitation was triggered by the supersaturation created by mixing MgCl2 solution (0.5‐1.5 M) with Na2CO3 solution in the same concentration range. The Meissner's method was adopted in the calculation of supersaturations during the MgCl2‐Na2CO3 reaction to monitor the precipitation. Solids were identified using X‐ray diffraction (XRD) analysis and scanning electron microscope (SEM) images. In the temperature range of 10‐40 °C, MgCO3·3H2O with needle‐like or gel‐like morphology was precipitated. It was seen that the length, width and surface smoothness of the particles changed with reaction temperature and supersaturation. The supersaturation (S) was in the range of 1.09‐58.68 during titration of Na2CO3 solution. The dimension of the crystals increased with longer addition time (or lower initial concentration of reactant) at the same temperature. Slower addition via titration of 2 h followed by 2 h of equilibration at 40 °C proved successful in producing well developed needle‐like MgCO3·3H2O crystals of 30‐50 μm long and 3‐6 μm wide. MgCO3·3H2O obtained were calcined to produce highly pure magnesium oxide (MgO) at 800 °C. The morphology of MgO was similar to that of their corresponding precursors. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

12.
Ferrierite, a medium-port molecular sieve zeolite, was synthesized as the only crystalline phase from an aqueous gel of composition 1.6 Na2O · 1.6 K2O · Al2O3 · 13.5 SiO2 · 130 H2O · 0.8 CO2 · 2.4 (HCO2)2 at 250 °C in reaction periods ranging from 40 to 95 hours. The crystallization time was reduced with seeding. Ferrierite was a metastable phase in this system and it transformed into tridymite, high sanidine and orthoclase at longer reaction periods. At 200 °C, chabazite was crystallized from the same batch composition at a very slow rate. At temperatures higher than 250 °C and in the absence of carbonates and bicarbonates in the batch mixture, tridymite, high sanidine and orthoclase crystallized directly without the formation of ferrierite. The synthetic ferrierite sorbs benzene, toluene and cyclohexane and behaves as a medium port molecular sieve. The sorption capacity of ferrierite was improved by acid treatments with no deterioration of the crystal structure.  相似文献   

13.
Lithiumcarbonat was treated hydrothermally in the range of temperature from 80 °C to 600 °C. The Li2CO3-crystals of the starting material were monoclinic with the unit cell a = 8.39 Å, b = 5.00 Å, c = 6.21 Å, β = 114.5° and the space group C2/c (Zemann). During the increase of temperature the habit of the Li2CO3-crystals changed in the ranges of higher temperatures that they could be described as pseudocubic. In parallel with this development the electrical conductivity of the crystals also changed.  相似文献   

14.
Electric measurements, including temperature dependencies of direct electrical conductivity and temperature dependencies of complex electrical modulus, have been implemented using Sb2O3–V2O5–K2O glass samples. These glasses absorb ambient humidity but their resistance to water attack depends on composition. The significant decrease of conductivity up to 100 °C can arise from water desorption. Cycling measurements of direct electrical conductivity versus temperature were also implemented. They show that the 30Sb2O3–30V2O5–40K2O and 70Sb2O3–30K2O glasses are irreversibly damaged with the formation of the hydrated layer. In addition, it was observed that the evolution of DC conductivity is ruled by Arrhenius relation, while activation energy decreases as Sb2O3 concentration increases.  相似文献   

15.
Classic composition 8.4Na2O·5K2O·10.8CaO·64SiO2·10.5CaF2·1.3Al2O3 (G1/GC1) and high silicon composition 7.6Na2O·4K2O·8.4CaO·71SiO2·8CaF2·1.0Al2O3 (G2/GC2) canasite-based glass and glass-ceramics were prepared, and the chemical durability and weathering of samples were studied with XRD, ICP-AES, SEM and optical microscopy. Interestingly, a kind of color fringe pattern caused by the acid leaching was directly observed on the glass ceramic surface under optical microscopy. The 20 day weight losses of glass and glass ceramic in acid (1 M HCl) and alkali (1 M NaOH/1 M Na2CO3) solution were measured. Accelerated weathering was used to demonstrate that increasing silicon content contributes to the weathering performance of glass and glass-ceramics. For different micro-structures and compositions, the weight loss of each glass and glass-ceramic is quite different. In general, through increasing the network interconnectivity of residual glass network and suppressing the crystallization of the less durable canasite phase, the addition of SiO2 (from 60 mol% to 71 mol%) enhanced the chemical durability of canasite-based glass and glass ceramic relatively under acid, alkali and weathering conditions.  相似文献   

16.
A novel structure type has been established as a result of studying a non-merohedral microtwin of polyoxovanadate (K2ZnV5O14) by X-ray diffractometry (R = 0.0595). The new compound, synthesized under hydrothermal conditions in the ZnCl2–K2CO3–V2O5–H2O system, is characterized as follows: a = 8.066(5) Å, b = 8.117(5) Å, c = 9.236(5) Å, β = 105.287(5)°, sp. P21/m, Z = 2, ρcalcd = 3.54 g/cm3. Edge-shared five-core “clusters” consisting of vanadium octahedra, between which ZnO4 tetrahedra (sharing vertices with octahedra) are located, form two-dimensional two-layer anion packets of the (ZnV5O14)2– composition, alternating along the c axis with layers of potassium atoms. Structural peculiarities determine the morphology and color of new-phase crystals.  相似文献   

17.
Recrystallization of natural chrysoberyl in multicomponent melts   总被引:1,自引:0,他引:1  
Chrysoberyl and alexandrite crystals have been grown from solutions in melts based on the Li2CO3-MoO3, Bi2O3-MoO3, PbO-V2O5, Na2B4O7, and K2MoO4-MoO3 systems using natural alexandrite and chrysoberyl debris as the initial BeAl2O4 compound. An analysis of the morphology and homogeneity of the crystals grown has revealed the Bi2O3-MoO3 solvent to be the most appropriate. The optimal color characteristics (??quality?? of alexandrite effect) manifest themselves when adding about 5 mol % Cr2O3. The largest crystals (up to 10 mm in size) were obtained from a solution in melt based on PbO-V2O5 at a ratio of the crystal-forming component to the solvent of 9: 91 wt %; These characteristics, along with a relatively low operating temperature (970°C), give grounds to consider this type of solvent promising.  相似文献   

18.
A spinning disk reactor (SDR) was used in this research to prepare Li2CO3 by gas‐liquid reactive crystallization of LiOH and CO2. It was found that the end pH value of the above reaction should be controlled within the range of 9.0‐9.5 to obtain a high yield of Li2CO3. The effects of operational parameters (including the temperature, the concentration of LiOH solution, the rotation rate of the spinning disk, the circulation rate of LiOH slurry, the flow rate of CO2 and the ultrasound field) on the particle size and the yielding rate were investigated by an orthogonal experiment. The results show the significant factors influencing the particle size are the ultrasound field, the temperature and the flow rate of CO2. As for the yielding rate, the temperature, the concentration of LiOH solution and the flow rate of CO2 exert obvious impacts, while the effects of ultrasound field and the rotation rate of the spinning disk are limited. The SEM images show the Li2CO3products are flower‐like particles, which are composed of plate‐like primary crystals. The size analysis shows the volume mean particle size of the Li2CO3products ranges 37‐90 μm depending on the various experimental conditions. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

19.
Abstract

Three methods of synthesizing hydrotalcite(HT) have been developed using magnesium from seawater and dolomite(MgCa(CO3)2). In the first process, 1.0M Na2CO3solution was added to calcium ion free artificial seawater containing AlCl3 with an initial Mg/Al molar ratio of 2.0~3.7 until a pH of 10 was obtained. The solution was then continuously stirred for Ih at 60°C. CO3 2--HT was precipitated as a single phase, and the initial Mg/Al molar ratio, which each recovery of Mg2+and Al3+ from the solution was above 98%, was 2.0–2.3. In the second process, a Ca(OH)2 slurry was added to artificial seawater containing AlCl3 with an initial Mg/Al molar ratio of 1.0~5.0 until a pH of 10.5 was obtained, and then was stirred for Ih at 60°C. HT was also precipitated as a single phase with initial Mg/Al molar ratio 2.0~4.0. The initial Mg/Al molar ratio, which each recovery of Mg2+ and Al3+ from the solution was above 98%, was 2.2~3.3, but SO4 2- and Cl? were contained in the precipitated HT. When HT was produced using initial Mg/Al molar ratio of 3.0 at 25°C, SO4 2- and Cl?in the HT were ion-exchanged with CO3 2- in a 0.05M Na2CO3solution for 24h at 25°C, and SO4 2- and Cl? content of the HT were decreased to 0.5 and 0.05wt%, respectively. In the third process, dolomite calcined at 1000°C was added to an AlCl3 solution with an initial Mg/Al molar ratio of 1.0~2.0, and the solution was stirred for 1~4h at 25~90°C. HT was precipitated with the smallest amount of MgO and Mg(OH)2 when the initial Mg/Al molar ratio was 1.5 and the solution was stirred for 4h at 90°C.  相似文献   

20.
The VPE growth of GaAs in the system GaAs AsCl3 with either H2 or He as the Carrier gas was studied in the range of low deposition temperatures. Down to about 670 °C the growth in the H2-system is limited by the kinetics of chlorine desorption by molecular hydrogen. The increase in growth rate at lower temperatures results from the onset of GaCl3-desorption (disproportionation mechanism). The addition of NH3 to the vapour phase enhances this effect. Below about 700 °C the growth rate in the GaAs AsCl3 H2 NH3 system becomes comparable to that in the GaAs AsCl3 He-system, where the GaCl3 desorption mechanism is the only possible growth mechanism.  相似文献   

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