Synthesis of ultrafine zeolites by dry-gel conversion without any organic additive

ZSM-5, mordenite, cancrinite and Y zeolites were successfully crystallized by the dry-gel conversion (DGC) without any organic additive (or template), in which the crystal particles of ZSM-5, mordenite and Y zeolite were well controlled in the range of ultrafine size. With a molar ratio of SiO₂/Al₂O₃ ≤40, the pure ZSM-5 zeolite was obtained at 170 °C at the Na₂O/SiO₂ molar ratio <0.2, but the pure mordenite was formed at 150 °C at the Na₂O/SiO₂ molar ratio >0.25. When the dry-gel with a composition of 5.0Na₂O:Al₂O₃:5.0SiO₂ was crystallized at 140 °C for 24 h, pure cancrinite phase was obtained. TEM images showed that thus-crystallized zeolites consisted of ultrafine particles ranging 35-150 nm for ZSM-5, 50-200 nm for mordenite and 120-200 nm for zeolite Y, respectively. Different from ZSM-5, mordenite and cancrinite zeolites, the DGC synthesis of Y zeolite required more water in the dry-gel before crystallization.     

Synthesis of zeolite Li-ABW from fly ash by fusion method

The zeolite Li-ABW was synthesized by fusion method using fly ash as raw material. It comprised alkaline fusion followed by hydrothermal treatment in LiOH·H₂O medium. Crystallinity of zeolite as high as 97.8% was attained under the following conditions: LiOH·H₂O concentration, 3 M; hydrothermal temperature, 180 °C; the corresponding aging time, 12 h. The content of Li-ABW increased at the expense of lithium aluminum silicate or quartz with an increase of LiOH·H₂O concentration. With increasing hydrothermal temperature and aging time, the soluble species re-crystallized and crystalline phase transformation between different zeolites was observed. Scanning electron microscopy (SEM) observation revealed that the obtained zeolite Li-ABW was a rod-like crystal. The pore size distribution curve indicated the presence of mesopores.     

Formation of Na-A and -X zeolites from waste solutions in conversion of coal fly ash to zeolites

Na-A and -X zeolites were synthesized from waste solutions in conversion of coal fly ash (Fa) to zeolite. The amorphous SiO₂ and Al₂O₃ of Fa were completely dissolved to form Po, Pt, and Pc type zeolites in NaOH solutions at 85°C. Only 24% of Si⁴⁺ eluted from Fa were converted to the zeolites and the remaining waste solutions contained high Si⁴⁺ concentrations. When molar ratio SiO₂/Al₂O₃ of the waste solutions was modified at 1.0≤SiO₂/Al₂O₃≤2.0 by addition of NaOH-NaAlO₂ solutions and the solutions were agied at 85°C, a single phase of Na-A zeolite was formed. The Na-X zeolite was formed at SiO₂/Al₂O₃≥2.5 and its crystallinity was increased with increasing the SiO₂/Al₂O₃ ratio, whereas the crystallinity of Na-A zeolite was decreased. At SiO₂/Al₂O₃=7.3, a single phase of Na-X zeolite was produced.     

Analyses of nano-crystalline LiCoVO4 prepared by solvothermal reaction

LiOH·H₂O, Co(NO₃)₂·6H₂O and NH₄VO₃ were used to prepare nano-crystalline LiCoVO₄ by 150 °C solvothermal reaction in isopropanol for 10–360 h and subsequent calcination at 300–500 °C for 6 h. XRD, TEM and selected area electron diffraction (SAED) revealed the presence of nano-crystalline LiCoVO₄ with inverse spinel structure. The V–O stretching vibration modes of VO₄ tetrahedrons were detected by FTIR over the range 617–835 cm^− 1 and by Raman spectrometer at 805.7 and 783.1 cm^− 1. Co, V and O were detected by EDX. TGA of solvothermal products shows weight loss due to the evaporation and decomposition processes at 40–648 °C.     

Effective removal and fixation of Cr(VI) from aqueous solution with Friedel's salt

Friedel's salt (3CaO·Al₂O₃·CaCl₂·10H₂O or Ca₄Al₂(OH)₁₂Cl₂(H₂O)₄) is a calcium aluminate hydrate formed by hydrating cement or concrete in seawater at a low cost. In the current study, we carefully examined the adsorption behaviors of Friedel's salt for Cr(VI) from aqueous solution at different concentrations and various initial pHs. The adsorption kinetic data are well fitted with the pseudo-first-order Lageren equation at the initial Cr(VI) concentration from 0.10 to 8.00 mM. Both the experimental and modeled data indicate that Friedel's salt can adsorb a large amount of Cr(VI) (up to 1.4 mmol Cr(VI)/g) very quickly (t_1/2 = 2–3 min) with a very high efficiency (>99% Cr(VI) removal at [Cr] < 4.00 mM with 4.00 g/L of adsorbent) in the pH range of 4–10. In particular, the competitive adsorption tests show that the Cr(VI) removal efficiency is only slightly affected by the co-existence of Cl⁻ and HCO₃⁻. The Cr(VI)-fixation stability tests show that only less than 0.2% adsorbed Cr(VI) is leaching out in water at pH 4–10 for 24 h because the adsorption/exchange of Cr(VI) with Friedel's salt leads to the formation of a new stable phase (3CaO·Al₂O₃·CaCrO₄·10H₂O). This research thus suggests that Friedel's salt is a potential cost-effective adsorbent for Cr(VI) removal in wastewater treatment.     

Conventional hydrothermal synthesis of Na-A zeolite from cupola slag and aluminum sludge

Na-A type zeolites were prepared from two industrial wastes: the solid by-product of cupola slag and aluminum sludge from an aluminum plating plant. Two preparation methods using the same starting material compositions were carried out. In the first method, alkaline fusion was introduced, followed by the hydrothermal treatment to obtain sodium aluminosilicate which was then crystallized in NaOH solution under the condition of 90 ± 3 °C for 1–9 h with different H₂O/SiO₂ ratios. The result shows that higher H₂O/SiO₂ ratio increases the rate of crystallization. The largest amount of crystallinity for Na-A was found at 3 h. In the second method, alkaline hydrothermal treatment without fusion was carried out in the same condition as the first method. No Na-A zeolite was obtained by this method. The changes of the dissolved amounts of Si⁴⁺ and Al³⁺ in 3 M NaOH were investigated during the hydrothermal reaction.     

Lead clustering in a zeolite X

Single-crystal structure analyses of a Pb-exchanged zeolite X of ideal formula Pb₅₄(H₃O)₁₂(OH)₃₂Al₈₈Si₁₀₄O₃₈₄ · nH₂O (h-Pb-X), its dehydrated form (d-Pb-X), and its partially Cs-exchanged form (h-(Pb,Cs)-X), of ideal formula Pb₃₇Cs₄₆(OH)₃₂Al₈₈Si₁₀₄O₃₈₄ · nH₂O, are reported. The structures were refined in space group Fd3 (no. 203) to final R values of 0.077, 0.071, and 0.050, using 287, 253,and 426 independent reflections with I > 4σ (I). No significant change in the framework of the three structures was observed. The position and coordination of the cation sites are discussed. Structural analysis of the three zeolites strongly supports the hypothesis that [Pb(OH)]₄⁴⁺ clusters fully occupy the sodalite cages in the hydrated forms, whereas upon dehydration about one third of Pb²⁺ migrates from the sodalite cages into the large cavities.     

Simultaneous synthesis of high crystalline manganese oxides with layered and tunnel structures

High crystalline manganese oxides with birnessite-type (H-BirMO) and large 2 × 4 tunnel-type (Na-2 × 4) were synthesized simultaneously using a low crystalline Na-form birnessite (NaBir) as a precursor in a 2 M NaOH solution at low temperature (150 °C) and autogenous pressure. The weight ratio of the obtained Na-2 × 4 to H-BirMO was about 50. Elemental analyses indicated that Na-2 × 4 had a formula in one unit cell of Na₈Mn₂₇O₅₃·9H₂O, and the manganese average oxidation state was 3.63. H-BirMO had a formula of Na_0.31Mn_2.04O₄·0.66H₂O and the manganese average oxidation state of 3.77. H-BirMO contained a set of basal reflections with d values that correspond to a minimum periodicity along c equal to 7.06 Å. H-BirMO belonged to a monoclinic system, and the lattice parameters were a = 5.18 Å, b = 2.85 Å, c = 7.35 Å, and β = 103.3°, respectively. Na-2 × 4 showed that the first peak appeared at a d spacing of 12.07 Å in the [0 0 2] direction, and the second peak had a similar d spacing of 7.16 Å in the [2 0 0] direction with Na-birnessite in the [1 0 0] direction. FE-SEM image of H-BirMO showed a very large plate-like morphology, while SEM photograph of Na-2 × 4 consisted of nanofibers with a thickness of about 80 nm and lengths ranging between 6 and 10 μm.     

Empirical correlation for ejector designCorrélation empirique pour la conception des éjecteurs

In the present study, two empirical correlations from the test results of 15 ejectors are derived for the performance prediction of ejectors using R141b as the working fluid. The ratio of the hypothetical throat area of the entrained flow to the nozzle throat area A_e/A_t, the geometric design parameter of the ejector A₃/A_t, and the pressure ratios P_g/P_e and P_c*/P_e are used to correlate the performance of the ejector. The prediction of the entrainment ratio ω using the correlations is within ±10% error. A method of calculation for the ejector design using the correlations is also developed. R141b is shown in the present study to be a good working fluid for an ejector. The measured ω for the ejectors used in the present study can reach as high as 0.54 at P_g=0.465 MPa (84°C), P_c^*=0.087 MPa (28°C) and P_e=0.040 MPa (8°C). For P_g=0.538 MPa (90°C), P_c^*=0.101 MPa (32°C) and P_e=0.040 MPa (8°C), ω reaches 0.45.

Résumé

Dans cette étude, on a établi deux corrélations empiriques à partir des résultats expérimentaux obtenus utilisant 15 éjecteurs; ces corrélations ont été utilisées ensuite pour prédire la performance d'éjecteurs utilisant le R141b comme fluide frigorigène. Les rapports A_e/A_t (section de passage du fluide entraîné rapporté à la section théorique du col de l'éjecteur), et A₃/A_t (section de sortie de l'éjecteur rapporté à la section théorique du col de l'éjecteur) et les relations entre pressions P_g/P_e et P_c*/P_e sont utilisés pour trouver la corrélation de la performance de l'éjecteur. La prévision du taux d'entraînement à partir des corrélations est précise à la hauteur de ±10%. Les auteurs ont également développé une méthode de calcul permettant de concevoir des éjecteurs à partir des corrélations. On a montré dans cette étude que le R141b s'avère être un fluide actif efficace pour cette utilisation. Le ω mesuré des éjecteurs utilisés dans cette étude peuvent atteindre 0.54 à P_g=0.465 MPa (84°C), P_c^*=0.087 MPa (28°C) et P_e=0.040 MPa (8°C). Pour P_g=0.538 MPa (90°C), P_c^*=0.101 MPa (32°C) et P_e=0.040 MPa (8°C), ω atteint 0.45.     

Thermochemical preparation of W–25%Cu nanocomposite powder through a CVT mechanism

In order to produce a W–25%Cu nanocomposite powder manufactured by a thermochemical procedure a novel pair of precursors were used. Cu₂WO₄(OH)₂ and CuWO₄·2H₂O precipitates were first produced by reacting the copper nitrate and sodium tungstate aqueous solutions under certain pH and temperature. The precipitates were then dried and calcined in order to prepare CuWO_4 − x, CuO, and WO₃ oxide powders for the next step reduction. The reduction was carried out under a H₂ atmosphere to form the final W–Cu metal nanocomposite powder. Characteristics of the final powder such as distribution, uniformity and size were then discussed based thoroughly on the dominant mechanism of reduction; Chemical Vapor Transport. It was found that the average particle size of the reduced powder is 35 nm for W and 54 nm for Cu.     

High-temperature stability of the mechanical and optical properties of Si–B–C–N films prepared by magnetron sputtering

Quaternary Si–B–C–N materials are becoming increasingly attractive due to their possible high-temperature and harsh-environment applications. In this work, amorphous Si–B–C–N films with two compositions (Si₃₄B₉C₄N₄₉ and Si₃₆B₁₃C₇N₄₀) and low contamination level (H + O + Ar < 4 at.%) were deposited on silicon substrates by reactive dc magnetron co-sputtering using two different targets and gas mixtures. Thermal stability of these films was investigated in terms of composition, bonding structure, as well as mechanical and optical properties after annealing in helium up to a 1300°C substrate limit. Films with a high nitrogen content (Si₃₄B₉C₄N₄₉, i.e. N/[Si + B + C]~ 1.0) were found to be stable up to 1300°C. After annealing, the hardness and elastic recovery of those films slightly increased up to 27 GPa and 84%, respectively, and the reduced Young's modulus remained practically constant (~ 170 GPa). The refractive index and the extinction coefficient at 550 nm were evaluated at 2.0 and 5 × 10^− 4, respectively, and the optical band gap was approximately 3.0 eV. In contrast, films with a lower nitrogen content (Si₃₆B₁₃C₇N₄₀, i.e. N/[Si + B + C]~ 0.7) were stable only up to 1200°C. Both Si–B–C–N materials studied here exhibited extremely high oxidation resistance in air up to the 1300°C substrate limit.     

New powellite type oxides in Ca–R–Nb–Mo–O system (R = Y, La, Nd, Sm or Bi)—Their synthesis, structure and dielectric properties

New complex oxides having powellite (CaMoO₄) type structure in the Ca–R–Nb–Mo–O system (R = Y, La, Nd, Sm or Bi) were prepared employing the method of solid state reaction between the component oxides at high temperature (1000–1100 °C). The new compounds, CaRNbMoO₈ (R = Y, La, Nd, Sm, Bi) are colorless and electrical insulators. The dielectric constants (K at 1 MHz) of these compounds are in the range 14–33 and K shows very little variation in the temperature range 30–100 °C. Their temperature coefficient of dielectric constant (TCK) is negative, which varies from − 21 to − 220 ppm/°C.     

Mechanochemical Synthesis of Double Hydroxides

It has been demonstrated that the formation of magnesium-aluminium double hydroxides [Mg_{(1 – X)}Al _X (OH)₂] ^X+(A ^n– _X/n ) m H₂O, (A–Cl^–, NO^– ₃, SO^2– ₄) occurs during mechanical activation of the mixture of magnesium hydroxide (brucite) with aluminium chloride, nitrate and sulphate in high-energy planetary-type activators. The effect of activation time on the formation of the double hydroxide has been investigated. Thermal decomposition of the chloride form of the double hydroxide has been studied.     

FAU-type zeolite membranes synthesized by microwave assisted in situ crystallization

FAU-type zeolite membranes were prepared by an “in situ aging-microwave synthesis” (AM) method using a clear solution with the molar composition of 70Na₂O: 1Al₂O₃: 20SiO₂: 2000H₂O. After two-stage AM synthesis, a defect-free FAU zeolite layer consisted of uniform zeolite crystals was formed on the support surface. The Si/Al ratio was ca. 1.5. The single-gas permeation and single-liquid vapor permeation properties of the as-synthesized zeolite membranes were investigated. The permselectivity of H₂ and N₂ was as high as 4.25 for FAU-type zeolite membranes. Pervaporation measurements were carried out for the dehydration of ethanol and isopropanol aqueous solutions. FAU-type zeolite membranes displayed relatively high permeation flux and water-selectivity.     

Preparation of nanoplates assembled 4CaO·5B2O3·7H2O oval-like microspheres via a hydrothermal method

4CaO·5B₂O₃·7H₂O uniform oval-like microspheres morphology has been prepared at 120 °C by a simple hydrothermal method with the help of the surfactant polyethylene glycol(PEG-300). The result indicates that 4CaO·5B₂O₃·7H₂O oval-like microspheres are constructed by ladder-like layers, and each layer is made up of numerous densely packed nanoplates with the thickness of 50–100 nm and the diameter of several microns. The nanoplates in each layer are interconnected with the nanoplates in next layer, which leads to form the multilayered structural oval-like microspheres. The PEG-300 plays an important role in the formation of this oval-like microspheres morphology.     

Physical properties of transparent conducting Cd–Te–In–O thin films: Outlining a thermodynamic system for transparent conducting oxides

Cd–Te–In–O thin films are grown by pulsed laser deposition using a composite target of CdTe powder embedded in an indium matrix. Oxygen pressures range from 2.00 to 6.67 Pa at a substrate temperature of 420 °C. The structure, optical transmission and sheet resistance of the films are measured. Substitutional compounds with In_2 − 2x(Cd,Te)_2xO₃ stoichiometry are found at high oxygen pressures. A ternary phase diagram of the CdO–In₂O₃–TeO₂ system shows the relationship between the structure and the stoichiometry of the films. To evaluate film performance, a figure of merit is proposed based on the relationship between the integral photonic flux and the sheet resistance. The best figure of merit values corresponds to a sample prepared at 3.8 Pa O₂ that consists of (In₂O₃)_0.3(CdTe₂O₅)_0.7 and exhibits an optical band gap of 3.0 eV. This sample is a suitable substrate for electrodeposition due to its good electrochemical stability.     

A hydrothermal method to prepare the spherical ZnS and flower-like CdS microcrystallites

The spherical ZnS and flower-like CdS microcrystallites are prepared by a convenient hydrothermal process through the reactions of Zn(CH₃COO)₂·2H₂O or Cd(CH₃COO)₂·2H₂O with S and NaH₂PO₂·H₂O in aqueous solution at 180 °C for 12 h. Powder X-ray diffraction (XRD) is used to confirm the cubic phases of the ZnS and CdS microcrystallites. Their chemical compositions are characterized by X-ray photoelectron spectroscopy (XPS). Scanning electron microscope (SEM) images show the morphologies of the as-synthesized ZnS and CdS. The photoluminescence spectra (PL) exhibit their optical properties.     

Effect of stirring on the dissolution of coal fly ash and synthesis of pure-form Na-A and -X zeolites by two-step process

Using the coal fly ash (FA), pure-form Na-A and -X zeolites were synthesized by two-step process. The FA was pretreated in aqueous NaOH solution under stirring condition at 85 °C for 18 h. The amorphous aluminosilicate of FA was dissolved during pretreatment. Increasing the stirring speed accelerated the dissolution of FA and increased Si⁴⁺ and Al³⁺ concentrations in the solution. This fact indicated that the stirring during pretreatment significantly affected on the dissolution of FA. After pretreatment, remaining FA was removed and aqueous NaAlO₂ solution was added to the residual solution to control the molar ratio SiO₂/Al₂O₃ of 0.5–4.5. After aging the resultant at 85 °C for 24 h, white precipitates were generated over the whole SiO₂/Al₂O₃ range. Increment of Si⁴⁺ concentration by stirring during pretreatment increases the yield of the product. At SiO₂/Al₂O₃ = 0.5, the material was identified as Na-A zeolite with a trace amount of hydroxysodalite. A single phase Na-A zeolite was obtained at SiO₂/Al₂O₃ = 1.0. The Na-X zeolite was emerged at SiO₂/Al₂O₃ ? 2.0. At SiO₂/Al₂O₃ = 4.5, a single phase Na-X zeolite was formed. The cation exchange capacity of synthetic single phase Na-A and -X zeolites was respectively 4.78 and 3.88 meq./g.     

Si diffusion in magnetron sputtered silicon carbide films deposited on silicon and carbon substrates

Self-diffusion of silicon in magnetron sputtered silicon carbide films deposited on different substrates (crystalline silicon and glassy carbon) is investigated. Since crystallization of amorphous silicon carbide films strongly depends on the substrate, the diffusivity of silicon is expected to depend on the substrate as well. Isotope hetero-structures and secondary ion mass spectrometry were used for analysis. For amorphous samples an upper limit of the diffusivity of 1 × 10^− 21 m²/s is derived at 1100 C°. For crystallized films diffusivities between 1350 °C and 1600 °C are found to be not significantly different for the two types of substrates. For samples deposited on glassy carbon substrates an activation enthalpy ΔH_D = (8.7 ± 0.9) eV was found for the self-diffusion of Si. The consequences of our findings for crystallization are discussed.