Estimation of the solubility product of hydrocalumite–hydroxide,a layered double hydroxide with the formula of [Ca2Al(OH)6]OH·nH2O

From aqueous NaOH/Ca(OH)₂/NaAl(OH)₄ mixtures, after allowing short reaction times we observed the precipitation of Ca(OH)₂(s) at lower, and a mixture of Ca(OH)₂(s) and a layered double hydroxide, hydrocalumite (HC) at higher aluminate concentrations. From the maximum aluminate concentration, at which the equilibrium solid phase is still portlandite (i.e., further increase in the aluminate concentration results in HC appearing in the precipitate beside the portlandite), the concentration based solubility products of two polymorphs of HC with the formula of [Ca₂Al(OH)₆]OH·nH₂O (differing in n) has been estimated and was found to be log L_HC=−11.4 at 25 °C and −12.1 at 75 °C, respectively (where L_HC=[Ca²⁺]²[Al(OH)₄⁻][OH⁻]³) and at constant ionic strength (I=1 M NaCl). To the best of our knowledge, this is the first published estimate for the solubility product of hydrocalumite. Additionally, from the composition obtained for NaOH/Ca(OH)₂/NaAl(OH)₄ mother liquors in equilibrium with Ca(OH)₂(s), attempts were made to extract the formation constant of the ion pair CaAl(OH)₄⁺. It was found, that the effects caused by the supposed formation of this solution species are too small to be reliably determined, which allowed an upper estimate for its formation constant, K, to be suggested in the temperature range of 25–75 °C (K<200 and 40 M⁻¹ at 25 and 75 °C, respectively).     

Biomimetic apatite induction on Ca-containing titania

To understand the apatite induction mechanism in SBF, Ca-containing titania film without CaTiO₃ phase was fabricated by micro-arc oxidation (MAO) at low voltage (230 V) in an electrolytic solution containing calcium acetate monohydrate. Macro-porous, Ca-containing titania film was formed on the titanium substrate and the oxidized layer was composed of anatase and rutile phase. When immersed in 1.5SBF, no apatite was induced in the MAO specimen similar to the CaTiO₃-containing titania. However, after hydrothermal treatment at 250 °C for 2 h, numerous precipitates, presumably calcium phosphates, were formed on the surface of the titania after 7 day immersion and titania surface was entirely covered with apatite after 14 days of immersion. This study clearly showed that Ca-containing titania has the capability to induce apatite in SBF and hydrothermal treatment plays a decisive role in apatite induction, particularly producing surface hydroxyl groups such as Ca–OH or Ti–OH.     

Sintering kinetics and oxide ion conduction in Sr-doped apatite-type lanthanum silicates,La9Sr1Si6O26.5

These last past years, a major interest has been devoted to decrease the working temperature of solid oxide fuel cells (SOFCs) down to about 700 °C.Apatite materials (La_10 ? xSr_xSi₆O_27?x/2) are attractive candidates for solid electrolytes, with a high ionic conductivity at these intermediate temperatures. An apatite powder (x = 1) with a 0.75 µm mean particle size, produced by solid state reaction, was tape cast to obtain green sheets with a thickness of about 260 µm.On one hand, the densification mechanism of the apatite ceramic during the intermediate solid state sintering has been approached. It appeared from the kinetical tests performed under isothermal conditions between 1250 and 1550 °C, that densification could be controlled by the diffusion at grain boundaries of the rare-earth element, La, with an activation energy of 470 kJ/mol.On the other hand, conductivity measurements were performed on apatite samples sintered at 1400 and 1500 °C. The ionic conductivity was mainly sensitive to the presence of secondary phases at 1400 °C. The ionic conductivity of the apatite sintered at 1500 °C (mean grain size = 3.9 µm) is equal to 1.2 × 10^? 2 S/cm at 700 °C.     

Novel clays: Solid-state synthesis,characterization and cation exchange selectivity

Several novel swelling mica-type clays have been synthesized by solid-state processes. Synthetic clays of ideal compositions such as Na₂Si₆Al₂Mg₆O₂₀F₄ · xH₂O (Na-2-mica), Na₃Si₅Al₃Mg₆O₂₀F₄ · xH₂O (Na-3-mica) and Na₄Si₄Al₄Mg₆O₂₀F₄ · xH₂O (Na-4-mica) have been prepared and characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and ²⁷Al and ²⁹Si solid-state magic angle spinning nuclear magnetic resonance (MASNMR) spectroscopy. Powder XRD showed that all syntheses yielded water swollen micas with c-axis spacing of ∼1.2 nm except in the case of Na-2-mica which also showed a small peak of anhydrous mica phase with a c-axis spacing of 0.96 nm. Solid-state ²⁷Al MASNMR spectroscopy revealed that almost all the Al is present in the tetrahedral environment of the different micas. Solid-state ²⁹Si MASNMR spectroscopy revealed different Si (Al) nearest neighbor environments depending upon the composition of the various micas. Selective cation exchange studies were performed on the various micas using 0.5 N NaCl solution containing 12.9 ppm Sr²⁺ or 8.12 ppm of La³⁺. The results showed, for the first time, that Na-3-mica has a high selectivity for the trivalent cation tested. The previously reported high selectivity of these synthetic micas for the divalent cations has been confirmed. These selective cation exchange studies are of relevance in cation separations from drinking and waste waters.     

Influence of Cu doping on the microstructure,optical properties and photoluminescence features of Cd0.9Zn0.1S nanoparticles

Cd_0.9−xZn_0.1Cu_xS (0≤x≤0.06) nanoparticles were successfully synthesized by a conventional chemical co-precipitation method at room temperature. Crystalline phases and optical absorption of the nanoparticles have been studied by X-ray diffraction (XRD) and UV–visible spectrophotometer. XRD confirms the phase singularity of the synthesized material, which also confirmed the formation of Cd–Zn–Cu–S alloy nanocrystals rather than separate nucleation or phase formation. Elemental composition was examined by the energy dispersive X-ray analysis and the microstructure was examined by scanning electron microscope. The blue shift of absorption edge below Cu=2% is responsible for dominance of Cu⁺ while at higher Cu concentration dominated Cu²⁺, d–d transition may exist. It is suggested that the addition of third metal ion (Cu²⁺/Cu⁺) is an effective way to improve the optical property and stability of the Cd_0.9Zn_0.1S solid solutions. When Cu is introduced, stretching of Cd–Zn–Cu–S bond is shifted lower wave number side from 678 cm⁻¹ (Cu=0%) to 671 cm⁻¹ (Cu=6%) due to the presence of Cu in Cd–Zn–S lattice and also the size effect. The variation in blue band emission peak from 456 nm (∼2.72 eV) to 482 nm (∼2.58 eV) by Cu-doping is corresponding to the inter-band radiation combination of photo-generated electrons and holes. Intensity of red band emission centered at 656 nm significantly increased up to Cu=4%; beyond 4% it is decreased due to the quenching of Cu concentration.     

Formation of nickel and nickel,zinc-bearing ferrite in aqueous suspension by air oxidation

Stoichiometric Ni-bearing ferrite was formed by air oxidation of an iron(II) hydroxide suspension at an initial Ni : Fe_tot mol ratio (r_Ni) of 0.20 : 2.80 at pH 10.0 and 65°C. Most of products formed at r_Ni=0.40 : 2.60 and 0.60 : 2.40 were Ni-bearing ferrites, of which vacancies of Fe³⁺ ion on the lattice points may be considered. Only Ni, Zn-bearing ferrites were formed in the suspensions at initial (Ni + Zn)  : Fe_tot mol ratios (r_{Ni + Zn}) of 0.20 : 2.80–0.60 : 2.40 at pH 10.0 and 65°C. At higher r_Ni or r_{Ni + Zn} by-products containing Ni, Fe and O₄²⁻ were formed. The formation of the by-products was depressed in the suspensions containing chloride ions in the place of sulfate ions.     

Magnetic properties and formation of Sr ferrite nanoparticle and Zn,Ti/Ir substituted phases

Strontium hexaferrite nanoparticles are prepared by the chemical sol–gel route. Specific saturation magnetization σ_s and coercive field strength H_c are determined depending on the heat treatment of the gel and iron/strontium ratio in the starting solution. These ultrafine powders with single-domain behavior have specific saturation magnetization σ_s=74 emu/g and coercive field strength H_c=6.4 kOe. Experimental results show that it is necessary to preheat the gel between 400 and 500°C for several hours . It can prevent the formation of intermediate γ-Fe₂O₃ and help to obtain ultrafine strontium ferrite single phase with narrow size distribution at a low annealing temperature. Additionally, the magnetic properties of sol–gel derived strontium ferrite with iron substituted by Zn²⁺, Ti⁴⁺ and Ir⁴⁺ are discussed. For an amount of substitution 0<x⩽0.6, the (Zn, Ti)_x substituted strontium ferrite shows higher values of both coercive field strength and saturation magnetization than the (Zn, Ir)_x substituted phase.     

Critical current density in MgB2 bulk samples after co-doping with nano-SiC and poly zinc acrylate complexes

The co-doped MgB₂ bulk samples have been synthesized using an in situ reaction processing. The additives is 8 wt.% SiC nano powders and 10 wt.% [(CH₂CHCOO)₂Zn]_n poly zinc acrylate complexes (PZA). A systematic study was performed on samples doped with SiC or PZA and samples co-doped with both of them. The effects of doping and co-doping on phase formation, microstructure, and the variation of lattice parameters were studied. The amount of substituted carbon, the critical temperature (T_c) and the critical current density (J_c) were determined. The calculated lattice parameters show the decrease of the a-axis, while no obvious change was detected for c-axis parameter in co-doped samples. This indicates that the carbon was substituted by boron in MgB₂. The amount of substituted carbon for the co-doped sample shows an enhancement compared to that of the both single doped samples. The co-doped samples perform the highest J_c values, which reaches 3.3 × 10⁴ A/cm² at 5 K and 7 T. It is shown that co-doping with SiC and organic compound is an effective way to further improve the superconducting properties of MgB₂.     

Improved critical current density in Zn doped YBCO single crystals

Magnetic measurements were made using pure YBCO and Zn doped YBa₂(Cu_1?xZn_x)₃O_7?σ. Single crystals with Zn concentration of 0.5%, 1.5%, 3.0% and 4.3%. The magnetic hysteresis loops for these samples were measured in the temperature range 0.1 ? T/T_c ? 0.96 under magnetic fields of 5 T using SQUID. It was found that the critical current density J_c increased for low Zn content samples up to 3% Zn concentration compared to pure YBCO sample and decreased for the higher Zn content samples. These values varied consistently when compared at magnetic fields of 1 T and 3 T. Moreover Zn doped samples showed significant values of J_c in the temperature range of 0.7–0.9T_c, close to critical temperature compared to pure YBCO sample. The irreversibility field H_irr was also enhanced in this temperature range showing consistent decrease with increase of Zn concentration. The peak field H_p above H_c1 and irreversibility field H_irr, both show power law dependence of the form H = m₁(1 ? T/T_c)^m2 in the temperature range of 0.75–0.96T_c. The values of parameter m₂ increased from 1.44 to 1.95 for the samples up to 3% Zn content and decreased to 1.37 for higher Zn contents. The ratio H_irr/H_p was found to be 3–4 for the lower Zn content samples and was 7–8 for the sample with high Zn content indicating more disorder for higher Zn content samples. The region between peak field H_p and irreversibility field H_irr was broadened with the increase of Zn concentration. The strong effect of Zn substitution in modifying behavior of these samples even at elevated temperatures is possibly due to the changes in the anisotropy of our samples with the increase of Zn concentration and also due to the locally induced changes in magnetic moments by Zn substitution.     

Maximum magnetic entropy change modulated toward room temperature in perovskite manganites La0.7−xNdx(Ca,Sr)0.3MnO3

With Nd³⁺ doping and Ca²⁺, Sr²⁺ modulating in the sol–gel technique, a series of polycrystalline perovskite samples La_0.7?xNd_x(Ca,Sr)_0.3MnO₃ (x = 0, 0.05, 0.1, 0.15, 0.20, 0.25) was prepared, their maximum magnetic entropy changes were tuned to room temperature (ΔS_H = ?1.47 J/kg K at 298 k for La_0.45Nd_0.25(Ca,Sr)_0.3MnO₃), an enhancement of the maximum magnetic entropy change (ΔS_H = ?1.89 J/kg K at 315 k) and its refrigerant capacity (about 45.3 J/kg) had also been obtained under 9 kOe magnetic field variation for La_0.55Nd_0.15(Ca,Sr)_0.3MnO₃ contrast to La_0.7(Ca,Sr)_0.3MnO₃.     

Band overlap via chemical pressure control in double perovskite (Sr2−xCax)FeMoO6 (0 ⩽ x ⩽ 2.0) with TMR effect

The chemical pressure control in (Sr_2−xCa_x)FeMoO₆ (0 ⩽ x ⩽ 2.0) with double perovskite structure has been investigated systematically. We have performed first-principles total energy and electronic structure calculations for x = 0 and x = 2.0. The increasing Ca content in (Sr_2−xCa_x)FeMoO₆ samples increases the magnetic moment close to the theoretical value due to reduction of Fe/Mo anti-site disorder. An increasing Ca content results in increasing (Fe²⁺ + Mo⁶⁺)/(Fe³⁺ + Mo⁵⁺) band overlap rather than bandwidth changes. This is explained from simple ionic size arguments and is supported by X-ray absorption near edge structure (XANES) spectra and band structure calculations.     

Ionic conductivity and phase transition in Pb4.8Bi1.6Na3.6(PO4)6, an apatite-type compound

Bismuth sodium lead phosphate, Pb_4.8Bi_1.6Na_3.6(PO₄)₆, a compound having an apatite structure, was obtained via a solid-state reaction. Determination of the structure by X-ray diffraction on a single crystal gave the following results: hexagonal, P6₃/m, a = 9.6545(11) Å, c = 7.1457(5) Å, R = 0.03 and R_w = 0.09. The presence of Bi³⁺ and Pb²⁺ ions, carrying a lone electron pair, at (6h) sites helped to stabilize the apatite structure in spite of the anionic vacancies in the center of the tunnel. The compound was characterized by chemical analysis, differential thermal analysis, thermal expansion of the cell, and infrared, impedance and ²³Na NMR spectroscopy. The thermal behavior revealed two breaks attributed to order–disorder transitions. One of them was ascribed to a reordering of cations from the (6h) site to the center of the tunnel. Conductivity was dominated by hopping mechanisms.     

Thermal and sonochemical synthesis of porous (Ce,Zr)O2 mixed oxides from metal β-diketonate precursors and their catalytic activity in wet air oxidation process of formic acid

Porous (Ce_0.5Zr_0.5)O₂ solid solutions were prepared by thermolysis (T = 285 °C) or sonolysis (20 kHz, I = 32 W cm⁻², P_ac = 0.46 W mL⁻¹, T = 200 °C) of Ce(III) and Zr(IV) acetylacetonates in oleylamine or hexadecylamine under argon followed by heat treatment of the precipitates obtained in air at 450 °C. Transmission Electron Microscopy images of the samples show nanoparticles of ca. 4–6 nm for the two synthetic approaches. The powder X-ray diffraction, scanning electron microscopy, energy dispersive X-ray and μ-Raman spectroscopy of solids obtained after heat treatment indicate the formation of (Ce_0.5Zr_0.5)O₂ solid solutions with a metastable tetragonal crystal structure for the two synthetic routes. The specific surface area of the samples varies between 78 and 149 m² g⁻¹ depending on synthesis conditions. The use of Barrett–Joyner–Halenda and t-plot methods reveal the formation of mixed oxides with a hybrid morphology that combines mesoporosity and microporosity regardless of the method of preparation. Platinum nanoparticles were deposited on the surface of the mixed oxides by sonochemical reduction of Pt(IV). It was found that the materials prepared by sonochemistry exhibit better resistance to dissolution during the deposition process of platinum. X-ray photoelectron spectroscopy analysis shows the presence of Pt(0) and Pt(II) on the surface of mixed oxides. Porous (Ce_0.5Zr_0.5)O₂ mixed oxides loaded with 1.5 %wt. platinum exhibit high activity in catalytic wet air oxidation of formic acid at 40 °C.     

High adsorption capacity of two Zn-based metal–organic frameworks by ultrasound assisted synthesis

Micro- and nano-rods and plates of two 3D, porous Zn(II)-based metal–organic frameworks [Zn(oba)(4-bpdh)_0.5]_n·(DMF)_1.5 (TMU-5) and [Zn(oba)(4-bpmb)_0.5]_n (DMF)_1.5 (TMU-6) were prepared by sonochemical process and characterized by scanning electron microscopy, X-ray powder diffraction and IR spectroscopy. These MOFs were synthesized using a non-linear dicarboxylate (H₂oba = 4,4-oxybisbenzoic acid) and two linear N-donor (4-bpdh = 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene and 4-bpmb = N¹,N⁴-bis((pyridin-4-yl)methylene)benzene-1,4-diamine) ligands by ultrasonic irradiation. Sonication time and concentration of initial reagents influencing size and morphology of nano-structured MOFs, were also studied. Calcination of TMU-5 and TMU-6 at 550 °C under air atmosphere yields ZnO nanoparticles. TMU-5 and TMU-6 exhibited maximum percent adsorption of 96.2% and 92.8% of 100 ppm rhodamine B dye, respectively, which obeys first order reaction kinetics.     

Structural investigation of Te-based chalcogenide glasses using Raman spectroscopy

Structural changes of metals (Zn, Sb, In, Ga) and metal halides (AgI, ZnI₂, CdI₂, PbI₂, BiI₃) modified GeTe₄ glasses were investigated with the aid of Raman spectroscopy. The Raman spectra of these glasses in the frequency region between 100 cm^?1 and 300 cm^?1 display four main bands at about 124, 140, 159 and 275 cm^?1 which are contributed by Ge–Te, Te–Te, Te–Te and Ge–Ge vibration modes. The intensity of 159 cm^?1 and 275 cm^?1 bands vary with the addition of different glass modifiers. While the relative intensity of the 124 cm^?1 and 140 cm^?1 bands are insensitive to composition changes. Glass modifiers like Zn, In and Sb act as glass network unstabilizer which will disorganize the glass network by opening up the chain structures of Ge–Te and Te–Te. In the case of Ga and metal halides, Ga can open up Ge–(Te–Te)_4/2 tetrahedra and form Ga–(Te–Te)_3/2 triangle. Iodine can form covalent bonds with tellurium and decrease the tendency of microcrystal formation. Thus both Ga and iodine ultimately act as glass network stabilizer.     

Aqueous polymer–nitrate solution deposition of YBCO films

High critical current density YBa₂Cu₃O_7?x (YBCO) films were prepared by solution deposition of aqueous non-fluorine precursors. Non-fluorine polymer-assisted deposition (PAD) processes utilizing rheology modifiers and chelating agents were used to produce 50 nm films with a critical current density (J_c) over 3 MA/cm² and 400 nm films with J_c > 1 MA/cm²_. T_c measurements indicated that films have T_c values near 90 K. The total heat treatment time to produce these high performance films was less than 4 h. Rheology modifiers such as polyvinyl alcohol (PVA) and hydroxyethyl cellulose (HEC) were used to increase the thickness of deposited films independent of the solution cation concentration. Chelating agents such as polyethylene glycol (PEG) and sucrose increased the barium ion solubility. Nitrate crystallization during deposition was controlled through rapid drying with vacuum and coating with hot solutions.     

Enhanced nonvolatile holographic properties in Zn,Ru and Fe co-doped LiNbO3 crystals

A series of LiNbO₃ crystals doped with various concentrations of ZnO and fixed concentrations of RuO₂ and Fe₂O₃ have been grown by the Czochralski method from the congruent melts. The type of charge carriers was determined by Kr⁺ laser (476 nm) and He–Ne laser (633 nm). The results revealed that the holes were the dominant charge carriers at blue light irradiation. Dual-wavelength and two-color techniques were employed to investigate the nonvolatile holographic storage properties of Ru:Fe:LiNbO₃ and Zn doped Ru:Fe:LiNbO₃ crystals. The essential parameters of blue nonvolatile holographic storage in Zn:Ru:Fe:LiNbO₃ crystals were enhanced greatly with the increase of Zn concentration. This indicates that the damage resistant dopants Zn²⁺ ions enhance the photorefractive properties at 476 nm wavelength instead of suppressing the photorefraction. The different mechanisms of blue photorefractive and nonvolatile holographic storage properties by dual wavelength recording in Zn:Ru:Fe:LiNbO₃ crystals were discussed.     

Mechanoluminescence,thermoluminescence and photoluminescence studies on Al2O3:Tb phosphors

Terbium activated Al₂O₃ phosphors were synthesized by combustion technique using hydrazine as a reductive non-carbonaceous fuel. X-ray diffraction (XRD) patterns of the samples were recorded to confirm the formation of the sample. Scanning electron microscope (SEM) images were taken to study the surface morphology of the sample. The photoluminescence (PL), thermoluminescence (TL) and mechanoluminescence (ML) properties of the γ-ray irradiated samples were studied. ML was excited impulsively by dropping a piston on the sample. In ML glow curves one peak with a shoulder was observed. ML intensity increases with activator concentration. Optimum ML was observed for the sample having 0.5 mol% of Tb ions. In the TL glow curve two distinct peaks, one around 222 °C and another around 280 °C, were observed for the samples having 0.5 mol% of activator concentration. In the PL spectra the ⁵D₄→⁷F₅ line at 544 nm in the green region is observed, which is the strongest in Al₂O₃ system. It is suggested that de-trapping of trapped charge carriers followed by recombination is responsible for ML and TL in this system.     

A comparative study of different concentrations of pure Zn powder effects on synthesis,structure, magnetic and microwave-absorbing properties in mechanically-alloyed Ni–Zn ferrite

In this study, a powder mixture of Zn, Fe₂O₃ and NiO was used to produce different compositions of Ni_1−xZn_xFe₂O₄ (x=0.36, 0.5 and 0.64) nanopowders. High-energy ball milling with a subsequent heat treatment method was carried out. The XRD results indicated that for the content of Zn, x=0.64 a single phase of Ni–Zn ferrite was produced after 30 h milling while for the contents of Zn, x=0.36 and 0.5, the desired ferrite was formed after sintering the 30 h-milled powders at 500 °C. The average crystallite size decreased with increase in the Zn content. A DC electrical resistivity of the Ni–Zn ferrite, however, decreased with increase in the Zn content, its value was much higher than those samples prepared by the conventional ceramic route by using ZnO instead of Zn. This is attributed to smaller grains size which were obtained by using Zn. The FT-IR results suggested two absorption bands for octahedral and tetrahedral sites in the range of 350–700 cm⁻¹. The VSM results revealed that by increasing the Zn content from 0.36 to 0.5, a saturation magnetization reached its maximum value; afterwards, a decrease was observed for Zn with x=0.64. Finally, magnetic permeability and dielectric permittivity were studied by using vector network analyzer to explore microwave-absorbing properties in X-band frequency. The minimum reflection loss value obtained for Ni_0.5Zn_0.5Fe₂O₄ samples, about −34 dB at 9.7 GHz, making them the best candidates for high frequency applications.     

Sonication enhances polyphenolic compounds,sugars, carotenoids and mineral elements of apple juice

A study was initiated with the objective of evaluating the effects of sonication treatment on quality characteristics of apple juice such as polyphenolic compounds (chlorogenic acid, caffeic acid, catechin, epicatechin and phloridzin), sugars (fructose, glucose and sucrose), mineral elements (Na, K, Ca, P, Mg, Cu and Zn), total carotenoids, total anthocyanins, viscosity and electrical conductivity. The fresh apple juice samples were sonicated for 0, 30 and 60 min at 20 °C (frequency 25 kHz and amplitude 70%), respectively. As results, the contents of polyphenolic compounds and sugars significantly increased (P < 0.05) but the increases were more pronounced in juice samples sonicated for 30 min whereas, total carotenoids, mineral elements (Na, K and Ca) and viscosity significantly increased (P < 0.05) in samples treated for 60 min sonication. Losses of some mineral elements (P, Mg and Cu) also occurred. Total anthocyanins, Zn and electrical conductivity did not undergo any change in the sonicated samples. Findings of the present study suggest that sonication technique may be applied to improve phytonutrients present naturally in apple juice.