Physicochemical simulation of fusion processes of basalt and diabase with Na<Subscript>2</Subscript>CO<Subscript>3</Subscript> and Na<Subscript>2</Subscript>CO<Subscript>3</Subscript> + CaO

Fusion processes of basalt and diabase with sodium carbonate and its mixture with calcium oxide are investigated by methods of physicochemical simulation. Equilibrium compositions of the Si-Al-Fe-Ca-Mg-Na system are calculated at various ratios Na₂CO₃: basalt (diabase) and (Na₂CO₃ + CaO): basalt (diabase) in the temperature range of 1270–1470 K. It is shown that, on fusion with sodium carbonate, depending on conditions, the main components of fusion products are sodium metasilicate (Na₂SiO₃) and sodium metaaluminate (NaAlO₂), magnesium orthosilicate (CaMgSiO₄), sodium ferrite(III) (NaFeO₂), iron(III) oxide (Fe₂O₃), and sodium-aluminum orthosilicate (Na₂AlSiO₄). On fusion with the mixture of sodium carbonate and calcium oxide, respectively, the products are sodium metaaluminate, calcium pyrosilicate (Ca₃Si₂O₇), calcium-magnesium orthosilicate, and calcium ferrite (CaFe₂O₄).     

Structural,dielectric and impedance spectroscopy studies of (Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>)(Zr<Subscript>0.025</Subscript>Ti<Subscript>0.975</Subscript>)O<Subscript>3</Subscript> ceramic

Structural, vibrational, dielectric and electrical properties of (Na_0.5Bi_0.5)(Zr_0.025Ti_0.975)O₃ ceramic synthesized by the solid-state reaction technique have been carried out. The X-ray diffraction analysis was indicated as a pure perovskite phase in the rhombohedral structure. The modes of rhombohedral vibrations were appeared in the experimental Raman spectrum at room temperature. The dielectric and electrical properties of the material were investigated by impedance spectroscopy analysis for a broad range of temperatures (50–560 °C) and frequency domain of 10²?10⁶ Hz. The dielectric measurement exhibit two phase transitions: a ferro-antiferroelectric transition followed by an antiferro-paraelectric transition at higher temperatures. Complex impedance analysis was carried out in order to distinct the contribution of the grains and the grain boundaries to the total electrical conduction. The Nyquist plot was proved to be a non-Debye relaxation mechanism. The combined spectroscopic plots of the imaginary part of electric impedance and modulus confirmed the non-Debye type behavior. The frequency dependent ac conductivity obeys the double power law behavior and shows three types of conduction process. The significant decrease of dc conductivity spectrum followed the Arrhenius relationship. The values of calculated activation energy of the compound implied that the electrical conduction is mostly due the high oxygen mobility.     

Dielectric relaxation and ionic conductivity studies of Na<Subscript>2</Subscript>ZnP<Subscript>2</Subscript>O<Subscript>7</Subscript>

The Na₂ZnP₂O₇ compound was obtained by the conventional solid-state reaction. The sample was characterized by X-ray powder diffraction, infrared analysis and electrical impedance spectroscopy. The impedance plots show semicircle arcs at different temperatures and an electrical equivalent circuit has been proposed to explain the impedance results. The circuits consist of the parallel combination of bulk resistance R _p and constant phase elements CPE. Dielectric data were analyzed using complex electrical modulus M* for the sample at various temperatures. The frequency dependence of the conductivity is interpreted in terms of Jonscher’s law. The conductivity σ _d.c. follows the Arrhenius relation. The near value of activation energies obtained from the analysis of M″ and conductivity data confirms that the transport is through ion hopping mechanism, dominated by the motion of the Na⁺ ions in the structure of the investigated materials.     

Removal of lead (II) and nickel (II) ions from aqueous solution using activated carbon prepared from rapeseed oil cake by Na<Subscript>2</Subscript>CO<Subscript>3</Subscript> activation

In this study, rapeseed oil cake as a precursor was used to prepare activated carbons by chemical activation with sodium carbonate (Na₂CO₃) at 600 and 800 °C. The activated carbon with the highest surface area of 850 m² g^?1 was produced at 800 °C. The prepared activated carbons were mainly microporous. The activated carbon having the highest surface area was used as an adsorbent for the removal of lead (II) and nickel (II) ions from aqueous solutions. The effects of pH, contact time, and initial ion concentration on the adsorption capacity of the activated carbon were investigated. The kinetic data of adsorption process were studied using pseudo-first-order, pseudo-second-order kinetic models and intraparticle diffusion model. The experimental data were well adapted to the pseudo-second-order model for both tested ions. The adsorption data for both ions were well correlated with Langmuir isotherm. The maximum monolayer adsorption capacities of the activated carbon for the removal of lead (II) and nickel (II) ions were determined as 129.87 and 133.33 mg g^?1, respectively.     

Photoluminescence properties and charge compensation investigations of novel orange-emitting Eu<Superscript>3+</Superscript> doped Na<Subscript>4</Subscript>Ca<Subscript>4</Subscript>(Si<Subscript>6</Subscript>O<Subscript>18</Subscript>) phosphors

A series of polycrystalline Na₄Ca₄(Si₆O₁₈):Eu³⁺ orange emitting phosphors were synthesized by a conventional high-temperature solid-state reaction. The phase formation was confirmed by X-ray power diffraction analysis. The excitation spectra show a strong host absorption indicating an efficient energy transfer process from O^2? to Eu³⁺ ions. Upon NUV radiation, the phosphors showed strong red emission around 610 nm (⁵D₀ → ⁷F₂) and orange emission around 591 nm (⁵D₀ → ⁷F₁), but the ⁵D_1,2,3 emission nearly can not be seen. Compared with the luminescence properties of Li⁺, Na⁺, and K⁺ co-doped samples, we deduced that Na⁺ ions probably prefer to dope into the intrinsic Na vacancies rather than Ca²⁺ ions vacancies in Na₄Ca₄(Si₆O₁₈) crystal. Thermal stability properties, quantum efficiency and chromaticity coordinates of the phosphors have been investigated for the potential application in white LEDs.     

Enhanced thermal stability in K<Subscript>2</Subscript>O-metakaolin-based geopolymer concretes by Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and SiO<Subscript>2</Subscript> fillers addition

Based on the principle of stability of geopolymer gel as refractory binder, a geopolymeric paste in the K₂O–Al₂O₃–SiO₂ system was developed and used to produce refractory concretes by adding various amount of α-quartz sand (grain size in the range 0.1 μm to 1 mm) and fine powder alumina (grain size in the range 0.1–100 μm). The consolidated samples were characterized before and after sintering using optical dilatometer, DSC, XRD and SEM. The total shrinkage in the range of 25–900 °C was less than 3%, reduced with respect to the most diffused potassium or sodium based geopolymer systems, which generally records a >5% shrinkage. The maximum shrinkage of the basic geopolymer composition was recorded at 1000 °C with a 17% shrinkage which is reduced to 12% by alumina addition. The temperature of maximum densification was shifted from 1000 °C to 1150 or 1200 °C by adding 75 wt% α-quartz sand or fine powder alumina respectively. The sequences of sintering of geopolymer concretes could be resumed as dehydration, dehydroxylation, densification and finally plastic deformation due to the importance of liquid phase. The geopolymer formulations developed in this study appeared as promising candidates for high-temperature applications: refractory, fire resistant or insulating materials.     

Bulk ac conductivity studies of lithium substituted layered sodium trititanates (Na<Subscript>2</Subscript>Ti<Subscript>3</Subscript>O<Subscript>7</Subscript>)

Lithium mixed sodium trititanates with 0.3, 0.5 and 1.0 M percentage of Li₂CO₃ (general formula Na_2−X Li _X Ti₃O₇) have prepared by a high temperature solid-state reaction route. EPR analysis, high temperature range (473–773 K) and variable frequency range (100 Hz–1 MHz) ac conductivity measurements were carried out on prepared sample. The lithium ions are accommodated with the sodium ions in the interlayer space. The EPR specta of lithium mixed sodium Trititanates confirm the partial reduction of Ti⁴⁺ ions to Ti³⁺. Four distinct regions have identified in the LnσT versus 1,000/T plots. Various conduction mechanisms which dependence on concentration, frequency and temperature are reported in this paper for lithium mixed layered sodium Trititanates. The dilation of interlayer space has further been proposed to occur due to inclusion of lithium ions in the interlayer space. The conductivity increases as the concentration of lithium increases. The increase of ionic conductivity in these compounds is due to accommodation of lithium ions with sodium ions in interlayer space.     

Ceramics Based on Powder Mixtures Containing Calcium Hydrogen Phosphates and Sodium Salts (Na<Subscript>2</Subscript>CO<Subscript>3</Subscript>, Na<Subscript>4</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript>, and NaPO<Subscript>3</Subscript>)

Ceramic materials in the Na₂O–CaO–P₂O₅ system have been produced using powder mixtures containing calcium hydrogen phosphates (monetite/brushite: CaHPO₄/CaHPO₄ ? 2H₂O) and sodium salts (Na₂CO₃ ? H₂O, Na₄P₂O₇ ? 10H,O, and NaPO₃). These salts were used as precursors to the following high-temperature phases: Сa₂P₂O₇, Na₂O, Na₄P₂O₇, and NaPO₃. The amount of the salts in the powder mixtures was such that the oxide composition of the ceramics corresponded to 10 mol % sodium oxide for each mixture in the Na₂O–CaO–P₂O₅ system. The powder mixtures were prepared using mechanical activation in acetone, which was accompanied by monetite rehydration to brushite. X-ray diffraction characterization showed that, after firing, the phase composition of the ceramics produced from the powder mixtures thus prepared lay in the Сa₂P₂O₇–NaCaPO₄–Na₂СaP₂O₇–Са(РО₃)₂ phase field. The resultant ceramic materials contain biocompatible and bioresorbable phases and can be recommended for bone implant fabrication.     

High-performance flexible supercapacitors based on C/Na<Subscript>2</Subscript>Ti<Subscript>5</Subscript>O<Subscript>11</Subscript> nanocomposite electrode materials

A new solution method to synthesize Na₂Ti₅O₁₁ with titanium powder is presented, and the C/Na₂Ti₅O₁₁ nanocomposite with high specific surface area and tunnel structure as the electrode material has excellent electrochemical performance. The single electrode composed of the C/Na₂Ti₅O₁₁ nanocomposite based on carbon fiber fabric (CFF) has the highest area capacitance of 1066 mF cm^?2 at a current density of 2 mA cm^?2, which is superior to other titanates and Na-ion materials for supercapacitors (SCs). By scan-rate dependence cyclic voltammetry analysis, the capacity value shows both capacitive and faradaic intercalation processes, and the intercalation process contributed 81.7% of the total charge storage at the scan rate of 5 mV s^?1. The flexible symmetric solid-state SCs (C/Na₂Ti₅O₁₁/CFF//C/Na₂Ti₅O₁₁/CFF) based on different C/Na₂Ti₅O₁₁ mass were fabricated, and 7 mg SCs show the best supercapacitive characteristics with an area capacitance of 309 mF cm^?2 and a specific capacitance of 441 F g^?1, it has a maximum energy density of 22 Wh kg^?1 and power density of 1286 W kg^?1. As for practical application, three SCs in series can power 100 green light-emitting diodes (LEDs) to light up for 18 min, which is much longer than our previous work by Wang et al. lighting 100 LEDs for 8 min. Thus, the C/Na₂Ti₅O₁₁ nanocomposite has promising potential application in energy storage devices.     

Effects of sodium oleate on synthesis and photocatalytic activity of Bi<Subscript>2</Subscript>WO<Subscript>6</Subscript>/Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>@RGO

In this study, the effects of sodium oleate on synthesis of Bi₂WO₆/Bi₂O₃ loaded reduced graphene oxide photocatalyst was studied. The as-prepared composites were characterized by X-ray diffraction, Fourier transform infrared, X-ray photoelectron spectroscopy, UV–visible diffuse reflectance and photoluminescence spectroscopy. The results suggested that addition of sodium oleate not only promoted synthesis of Bi₂O₃, but also enhanced the reduction of GO to graphene. When the amount of sodium oleate was 4 mol (Bi:SO?=?1:1), Bi₂WO₆/Bi₂O₃@RGO to the best visible-light photocatalytic activity can be synthesized by a facile one-step solvothermal process without further reduction reaction. Hence, it indicated that sodium oleate could affect the synthesis of the as-prepared composites and the photocatalytic activity for degradation of RhB. This study did provide not only a facile method to synthesize Bi₂WO₆/Bi₂O₃@RGO, but also a method to reduce graphene oxide to graphene.     

Enhanced electrochemical performance of Na<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>F<Subscript>3</Subscript> for Na-ion batteries with nanostructure and carbon coating

Carbon-coating Na₃V₂(PO₄)₂F₃ nanoparticles (NVPF@C NP) were prepared by a hydrothermal assisted sol–gel method and applied as cathode materials for Na-ion batteries. The as-prepared nanocomposites were composed of Na₃V₂(PO₄)₂F₃ nanoparticles with a typical size of ~?100 nm and an amorphous carbon layer with the thickness of ~?5 nm. Cyclic voltammetry, rate and cycling, and electrochemical impedance spectroscopy tests were used to discuss the effect of carbon coating and nanostructure. Results display that the as-prepared NVPF@C NP demonstrates a higher rate capability and better long cycling performance compared with bare Na₃V₂(PO₄)₂F₃ bulk (72 mA h g^?1 at 10 C vs 39 mA h g^?1 at 10 and 1 C capacity retention of 95% vs 88% after 50 cycles). The remarking electrode performance was attributed to the combination of nanostructure and carbon coating, which can provide short Na-ion diffusion distance and rapid electron migration.     

Conductivity of Sm<Subscript>2</Subscript>TiO<Subscript>5</Subscript> and Sm<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript>

The oxygen-ion conductivity of porous materials, the coarse-grained pyrochlore-like Sm₂Ti₂O₇ and fine-grained Sm₂TiO₅ compounds, produced by mechanical activation of initial oxides is studied at 400–1000 °C. The Sm₂TiO₅ samples contain ～15 wt % of the nanosized pyrochlore-like Sm₂TiO₅ phase in addition to the rhombic phase. As determined by impedance spectroscopy, the ionic conductivities of Sm₂TiO₅ and Sm₂Ti₂O₇ at 1000°C are 1.3 × 10^?3 and 1.8 × 10^?4 S cm^?1, and the activation energies of the bulk and grainboundary conductivities of the materials are 1.04 and 1.24 eV for Sm₂TiO₅ and 1.69 and 1.80 eV for Sm₂Ti₂O₇.     

Luminescence studies on Eu<Superscript>2+</Superscript> and Tb<Superscript>3+</Superscript> doped Ca<Subscript>2</Subscript>MgSi<Subscript>2</Subscript>O<Subscript>7</Subscript> phosphors

Eu²⁺ and Tb³⁺ doped Ca₂MgSi₂O₇ phosphors were synthesized by conventional solid-state reaction. The phase formation was confirmed by X-ray powder diffraction technique and refined lattice parameters were calculated by rietveld refinement process using Celref v3. The photoluminescence (PL) excitation and emission spectra were investigated. The phosphors exhibited broaden green emitting luminescence peaking at 520 nm when excited at 374 nm source. Morphological studies were carried out using Scanning electron microscopy (SEM) images of the sample with optimum PL emission. The dependence of photoluminescence intensity on co-dopant concentration and the kinetic parameters were also reported. Time resolved fluorescence spectroscopy (TRFS) is used to investigate the decay in luminescence signals with respect to time. The sample proved to be a good long lasting material, which makes it useful in emergency signs, textile printing, textile exit sign boards and electronic instrument dial pads etc.     

Multifunctional performance of gC<Subscript>3</Subscript>N<Subscript>4</Subscript>-BiFeO<Subscript>3</Subscript>-Cu<Subscript>2</Subscript>O hybrid nanocomposites for magnetic separable photocatalytic and antibacterial activity

Highly active gC₃N₄-BiFeO₃-Cu₂O nanocomposites were successfully prepared via a facile, cost effective and eco-friendly method of hydrothermally wet precipitation combined with ultrasonic dispersion process. The prepared samples were characterized by XRD, FTIR, HRSEM, EDS, TEM, UV–Vis DRS, PL, VSM, BET and electrochemical properties. By means of these analysis for examine the crystal phase, nanostructure, band gap and light-harvesting properties were carried out. UV-DRS spectra indicate that the bandgap of g-C₃N₄ (2.7 eV) reduced to 2.59 and 2.21 eV by mixed with corresponds to BiFeO₃ and BiFeO₃/Cu₂O nanomaterials. The ideal photocatalytic activity of the gC₃N₄-BiFeO₃-Cu₂O nanocomposites, where RhB dye under visible light irradiation which was up to 4.36 and 2.52 times as the higher photodegradation ability to compare pristine g-C₃N₄ and gC₃N₄-BiFeO₃ catalyst. The magnetization was confirmed by VSM studies, and hence, after the photocatalytic reaction, the magnetically separable catalyst can be quickly separated from the water by an external magnetic field. The superior photocatalytic performance is due to the synergistic effect on the interface of BiFeO₃/Cu₂O in the gC₃N₄-BiFeO₃-Cu₂O nanocomposites has reduced the bandgap which enables high separation efficiency of the charge carrier, suppressed recombination rate and their high surface area. Moreover, the chief gC₃N₄-BiFeO₃-Cu₂O catalyst can exhibited the lesser charge transfer resistance (impedance), enhances of photocurrent responses, whereas exposed to the development of photocatalytic appearance and more charge carrier ability. Also, the antibacterial activity of the gC₃N₄-BiFeO₃-Cu₂O nanocomposite has showing a well deactivation in both G⁺ (S. aureus) and G^? (E. coli) bacteria’s whereas compare to other prepared samples.     

Modulus spectroscopy of lead potassium titanium niobate (Pb<Subscript>0.95</Subscript>K<Subscript>0.1</Subscript>Ti<Subscript>0.25</Subscript>Nb<Subscript>1.8</Subscript>O<Subscript>6</Subscript>) ceramics

The modulus Spectroscopy of Lead Potassium Titanium Niobate (Pb_0.95K_0.1Ti_0.25Nb_1.8O₆, PKTN) Ceramics was investigated in the frequency range from 45 Hz to 5 MHz and the temperature, from 30 to 600 °C. XRD analysis in PKTN indicated a orthorhombic structure with lattice parameters a = 18.0809 Å, b = 18.1909 Å and c = 3.6002 Å. The dielectric anomaly with a peak was observed at 510 °C. Variation of ε^I and ε^II with frequency at different temperatures exhibit high values, which reflects the effect of space charge polarization and/or conduction ion motion. The electrical relaxation in ionically conducting PKTN ceramic analyzed in terms of Impedance and Modulus formalism. The Cole–Cole plots of impedance were drawn at different temperatures. The dielectric modulus, which describes the dielectric relaxation behaviour is fitted to the Kohlrausch exponential function. Near the phase transition temperature, a stretched exponential parameter β indicating the degree of distribution of the relaxation time has a small value. From the AC conductivity measurements the activation energy near phase transition temperature (T _C°C) has been found to different from that of the above and below T _C. The temperature dependence of electrical modulus has been studied and results are discussed.     

Enhanced red-emitting phosphor Na<Subscript>2</Subscript>Ca<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>8</Subscript>:Eu<Superscript>3+</Superscript> by charge compensation

A series of novel red-emitting Na₂Ca_3???x Si₂O₈:xEu³⁺ phosphors were synthesized by solid state reactions. The phosphors can strongly absorb 395 nm light, and show red emission with a good color purity. The excitation and emission spectra properties of Na₂Ca₃Si₂O₈:Eu³⁺ were characterized. Na₂Ca₃Si₂O₈:Eu³⁺ with self-compensated and alkali metal ions charge compensated approaches (2Ca²⁺→Eu³⁺ + M⁺, M?=?Li⁺, Na⁺, K⁺) have investigated, which found that the red emission of luminescent intensity can be greatly enhanced, and shows superior luminescent property to the commercial Y₂0₃S:Eu³⁺. The present work implies that the efficient charge compensated phosphors are promising candidates as red-emitting phosphor for w-LEDs.     

Photoelectrochemical properties of lead-free ferroelectric ceramic Ba(Ti<Subscript>0.96</Subscript>Mg<Subscript>0.013</Subscript>Nb<Subscript>0.026</Subscript>)O<Subscript>3</Subscript>: application to solar conversion of eosin

The lead-free Ba(Ti_0.96Mg_0.013Nb_0.026)O₃ composition has been prepared by solid state reaction. The room temperature X-ray diffraction revealed a perovskite phase with a tetragonal symmetry. The complex dielectric permittivity measured on cooling from 470 to 150 K in the frequency range (10²–10⁶ Hz) indicated a ferroelectric behavior and exhibited a large electromechanical response. This ferroelectric perovskite showed photoelectrochemical properties with an optical gap of 2.90 eV, n-type conduction and a flat band potential of ?0.57 V _SCE . As application, the oxide is successfully tested for the eosin oxidation under solar light. At pH ~ 6.3, 90 % of eosin (15 mg L^?1) disappeared after 6 h of illumination for a catalyst dose of 2.5 g L^?1.     

An Effective Approach to the Synthesis of Nanocrystalline PbMoO<Subscript>4</Subscript> in Na<Subscript>2</Subscript>Mo<Subscript>4</Subscript>O<Subscript>13</Subscript>–PbCO<Subscript>3</Subscript> Melts

This paper presents thermodynamic analysis of reactions of sodium tetramolybdate with Pb₃O₄, PbO₂, PbO, and lead carbonate and describes an effective approach to PbMoO₄ synthesis in melts of the Na₂Mo₄O₁₃–PbCO₃ system, which offers a low synthesis temperature, waste-free character of the process, high rate, and high yield of a reagent-grade synthesis product in a nanocrystalline state. The synthesis product has been identified by chemical analysis, X-ray diffraction, and particle size measurements.     

Frequency and temperature dependence of electrical properties of barium and gadolinium substituted SrBi<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript> ceramics

Barium strontium gadolinium bismuth niobate (Ba_0.1Sr_0.81Gd_0.06Bi₂Nb₂O₉, BSGBN) ceramics were prepared by using the conventional solid-state reaction method. The dielectric permittivity, modulus and impedance spectroscopy studies on BSGBN were investigated in the frequency range, 45 Hz–5 MHz and in the temperature range from room temperature (RT) to 570 °C. The dielectric anomaly with a broad peak was observed at 470 °C. Simultaneous substitution of Ba²⁺ and Gd³⁺ increases the transition temperature of SrBi₂Nb₂O₉ (SBN) from 392 to 470 °C. XRD studies in BSGBN revealed an orthorhombic structure with lattice parameters a = 5.4959 Å, b/a = 1.000, c = 25.0954 Å. Impedance and modulus plots were used as tools to analyse the sample behaviour as a function of frequency. Cole-Cole plots showed a non-Debye relaxation. Also, dc and ac conductivity measurements were performed on BSGBN. The electric impedance which describes the dielectric relaxation behaviour is fitted to the Kohlrausch exponential function. Near the phase transition temperature, a stretched exponential parameter β indicating the degree of distribution of the relaxation time has a small value.     

Spectral diagnostics of vapor composition over molten Na<Subscript>2</Subscript>WO<Subscript>4</Subscript> and Na<Subscript>2</Subscript>O-BaO-B<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The high-temperature Raman spectra recording technique was found applicable also to study luminescence of atoms and individual molecular groups in vapors over some overheated molten compounds. Sodium atomic luminescence excited with a yellow (578.2 nm) copper vapor laser line was detected in vapors over overheated molten Na₂WO₄ and Na₂O-BaO-B₂O₃ system. The possibility of recording the sodium doublet spectrum by excitation with the 578.2 nm copper vapor laser line in vapors of any melts containing sodium was shown. Overheated melts in the Na₂O-BaO-B₂O₃ system disproportionate and lose boron oxide as evidenced by the recording of luminescent spectra of BO₂ molecular radicals in vapors over relevant melts.