Synthesis and fabrication of (1 − x)ZnAl2O4–xSiO2 thin films to be applied as patch antennas

Zinc aluminate compounds have been dispersed in silica matrix prepared by sol-gel method with different compositions for (1 ? x)ZnAl₂O₄–xSiO₂. Continuous stirring of ethylene glycol solution contained zinc nitrate, aluminium nitrate and silicon dioxide to produces gel precursor. Structural and morphological studies of (1 ? x)ZnAl₂O₄–xSiO₂ thin films were examined by field emission scanning electron microscopy (FESEM) and X-ray diffractometer (XRD) analysis. The FESEM images showed the spherical structures with porosity for (1 ? x)ZnAl₂O₄–xSiO₂ thin films. XRD analysis indicated that the crystallite size for (1 ? x)ZnAl₂O₄–xSiO₂ increased from 39.79 to 44.34 nm. Fourier transform infra-red analysis showed that the existence of H₂O molecules and the presence of nitrate group within the samples. Dielectric permittivity (ε _r ) of (1 ? x)ZnAl₂O₄–xSiO₂ samples were measured within frequency range from 1 Hz to 1 MHz. The dielectric permittivity, ε _r decreased as frequency was applied to the sample. The performance of the patch antenna can be measured using return loss analysis. The highest result shows that the patch antenna resonated at frequency 3.46 GHz and gives ?14.25 dB return loss bandwidth.     

Thermal stability of Li2O–SiO2–TiO2 gels evaluated by the induction period of crystallization

To evaluate the thermal stability of materials, various criteria have been used. Not only the simple parameters, as characteristic temperatures, but also the combined criteria E/RT _p , k _f (T) and criterion based on the length of induction period of crystallization have been taken into account. Four gels with the composition Li₂O–2SiO₂–nTiO₂ (n = 0.00, 0.03, 0.062, and 0.1) were prepared and the validity of the criteria was tested by applying them to these gels. The results indicate that thermal stability of the studied gels decrease with amount of TiO₂.     

Characterization of anti-reflective and self-cleaning SiO2–TiO2 composite film

Sol–gel dip-coating technique can be used to fabricate SiO₂–TiO₂ composite film with self-cleaning and anti-reflectance properties from low-cost SiO₂ colloid solution and Ti(OC₄H₉)₄. The physical and structural properties have been investigated by UV–visible spectrophotometer, contact angle meter, XRD, FT-IR, FESEM. UV–vis spectra and methyl orange photodegradation experiments showed that the SiO₂–TiO₂ composite film had high light transmittance and photocatalytic activity.     

Thermal stability of ZrO2–SiO2 aerogel modified by Fe(III) ion

ZrO₂–SiO₂ aerogel modified by Fe(III) ion was prepared and the stability of the samples under high temperature was investigated. The structure and properties of modified aerogels were characterized by N₂ adsorption–desorption, FT-IR, XRD and TEM. The samples still contain a specific surface area about 228 m²/g after 1,000 °C 0.5 h calcinations. The inhibition of ZrO₂ particle growth is attributed to the Fe(III) ion modified aerogel surface, which strongly retards the ZrO₂ tetragonal phase transformation as well.     

Structural and electrical properties of sol–gel grown (1 − x) (ZnO) + (x) (SnO2) (x = 0, 0.25, 0.5) nanocomposites

Journal of Sol-Gel Science and Technology - Semiconducting oxide nanocomposites of ZnO/SnO2 with different weight ratio, i.e. (i) ZnO:SnO2?=?100:0 (ZnO0), (ii)...     

Thermal behavior and effect of SiO2 and PVA-SiO2 matrix on formation of Ni–Zn ferrite nanoparticles

Journal of Thermal Analysis and Calorimetry - The paper presents the synthesis of ZnFe2O4/SiO2, NiFe2O4/SiO2, Ni0.4Zn0.6Fe2O4/SiO2 and Ni0.4Zn0.6Fe2O4/PVA-SiO2 nanocomposites by a modified...     

Aggregation Stability of SiO2, FeOOH, ZrO2, CeO2, and Natural Diamond Sols and Their Binary Mixtures: 2. The Photometric Study of Heterocoagulation of SiO2–FeOOH, SiO2–ZrO2, SiO2–CeO2, and CeO2–Natural Diamond Binary Systems in KCl Solutions

The aggregation stability of 1 : 1 and 3 : 1 (by volume) binary mixtures of two hydrophobic (SiO₂–FeOOH), one hydrophobic and one hydrophilic (SiO₂–ZrO₂, SiO₂–CeO₂), and two hydrophilic (CeO₂–natural diamond) sols was studied by photometry over a wide range of KCl concentrations at pH 6 and 3. The stability of the mixed binary sols was determined by the stability of the sol with a predominant particle number concentration. In the SiO₂–FeOOH system, the phenomenon of heteroadagulation stabilization was caused by the electrostatic factor of the stability of adsorbed SiO₂ particles and, in the SiO₂–ZrO₂ system, by the structural factor of the stability of adsorbed hydrophilic ZrO₂ particles. The stability of binary mixtures containing one or two hydrophobic components is qualitatively explained in terms of the Derjaguin theory of heterocoagulation of hydrophobic colloids. The stability of the binary system of two hydrophilic components (CeO₂–natural diamond) is determined by the structural component of the interaction energy of particles.     

Preparation and characterization of crack-free sol–gel based SiO2–TiO2 hybrid nanoparticle film

Owing to the diverse potential applications of hybrid silica–titania thin films, the synthesis and characterization of these films have been carried out with a special focus on application as a medium index layer for multilayered functional coatings. For synthesis, tetraethylorthosilicate and titanium tetraisopropoxide were chosen as precursors for the formation of silica-titania hybrid thin films/nano-composites through an in situ sol–gel process. These films were sequentially obtained on Cu substrate utilizing spin coating. The hybrids were characterized by field emission scanning electron microscope, energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction, atomic force microscopy and Fourier transform infrared spectroscopy (FTIR). Field emission scanning electron microscope morphology displayed a smooth, densified and crack- free layer of silica-titania hybrid nanoparticles in the range of 20–71 nm after calcinations at low temperature of 300ºC for 1 h. X-ray diffraction pattern confirms the phases of titania with higher crystallinity and phase transformation at low temperature. The prepared films were uniform with low 8.852 nm RMS value. The stoichiometry of films was confirmed by EDX results. The FTIR spectroscopy indicated the establishment of heterogeneous chemical bonding between the Ti and Si surfaces through oxygen.     

Formation of (C x H2x+1)4NBr·nH2O (x = 1–3) hydrate

The phase diagram of the binary system tetramethylammonium bromide-water was studied by the differential thermal analysis. In the stable region two phases, ice and the salt itself, were detected, and in the metastable region, three tetramethylammonium bromide hydrates (bromide-water, 1 : 4, mp 68.8°C, 1 : 5, mp 36.0°C, 1 : 7.5, mp ?19.5°C) were found. Formation of (C _x H_2x+1)₄NBr·nH₂O (x = 1–3, n = 4, 5, 7.5) hydrates was revealed.     

Theoretical study of group 11 metal–silonyl complexes: M–SiO and M–(SiO)2 (M = Cu, Ag, or Au)

 The spectroscopic properties of M–SiO and M–(SiO)₂ (1–1 and 1–2 complexes with M = Cu, Ag, or Au) have been theoretically studied. It has been shown that both M–SiO and M–(SiO)₂ compounds in their ground state are bent with a metal–Si bonded structure. The calculated M(ns) spin density agrees well with the electron spin resonance experimental data. From a topological analysis, it has been shown that a rather large charge transfer occurs from the metal towards the SiO moiety, and that the M–Si bond energy correlates with the electron density located at the M–Si bond path (bond critical point). Received: 6 July 2000 / Accepted: 11 October 2000 / Published online: 19 January 2001     

Synthesis,characterization and visible-light photocatalytic activity of TiO2–SiO2 composite modified with zinc porphyrins

Three types of silica gel supported titanium dioxide particles immobilizing Zn(II) carboxylphenyl porphyrins appending p-CH₃, p-H and p-Cl phenyl substituents (designated as ZnMP–TiO₂–SiO₂, ZnPP–TiO₂–SiO₂ and ZnCP–TiO₂–SiO₂, respectively) have been synthesized and characterized using SEM, XRD, IR, AFS, DRS, UV–Vis, XPS and TG. The photodegradation of α-terpinene in aqueous suspension was used to determine the photocatalytic activity of TiO₂–SiO₂ samples which had been impregnated with Zn(II) porphyrins, as sensitizers. The experimental results confirmed that the photocatalytic activitys of these composites are much higher than those of the nonmodified TiO₂–SiO₂ under visible light irradiation and follow the order of ZnMP–TiO₂–SiO₂ > ZnPP–TiO₂–SiO₂ > ZnCP–TiO₂–SiO₂.     

Thermal behavior of the mixed composition xSb2O3–(1 − x)Bi2O3–6(NH4)2HPO4

The study of the system xSb₂O₃–(1 ? x)Bi₂O₃–6(NH₄)₂HPO₄ has been carried out to identify the phases and simulate the mechanisms of their formation, using the technique of thermal analysis in association with X-ray diffractometry. The main stages observed during thermal treatment of the samples include: (1) elimination of water and ammonia leading to the formation of (NH₄)₅P₃O₁₀; (2) reaction of the latter with M ₂ ^III O₃ and the formation of acidic polyphosphates M ₂ ^III H₂P₃O₁₀; (3) their dehydration with the formation of the polyphosphates M^III(PO₃)₃. Then Sb(PO₃)₃ decomposes giving SbPO₄ and P₂O₅. In the presence of excessive P₂O₅, two moles of Bi(PO₃)₃ condensate into oxophosphates Bi₂P₄O₁₃ and BiP₅O₁₄. The data of thermal analysis match with the composition of intermediate and final products. The hygroscopicity of the samples diminishes with growing bismuth content.     

Fabrication of hollow SiO2 and Au (core)–SiO2 (shell) nanostructures of different shapes by CdS template dissolution

Core–shell silica (SiO₂) coated CdS nanorods (NR) and nanospheres (NS) were prepared (SiO₂@CdS) by deposition of a Si–O–Si amorphous layer over the CdS surface through the hydrolysis of 3-mercaptopropyltrimethoxysilane and tetraethylorthosilicate. Nanoporous SiO₂ matrix (NPSM), hollow SiO₂ nanotubes (HSNT) and nanospheres (HSNS) useful for efficient adsorption and catalytic processes were prepared by chemical dissolution of CdS–NS (size: 9–10 nm) and CdS–NR (length: 116–128 nm and width: 6–11 nm) template from SiO₂@CdS with 2 M HNO₃. These SiO₂ nanostructures were characterized by optical absorption, TEM, EDX, SAED and BET surface area analysis. TEM images revealed the fabrication of slightly distorted HSNS (size: 9–12 nm) and closed HSNT (length: 30–45 nm and diameter: 9–14 nm) of shorter dimensions than the CdS–NR template used. The BET surface area (112–134 m² g^?1) of NPSM and HSNS is found to be larger than the surface area (29–51 m² g^?1) of SiO₂@CdS composites indicating hollow SiO₂ morphology. Silica coated Au (SiO₂@Au) composites formed by CdS dissolution from Au (2 wt%) deposited CdS–NR core-encapsulated into SiO₂ shell (SiO₂@Au–CdS–NR) exhibited a surface plasmon band at 550 nm and displayed high catalytic activity for 4-nitrophenol reduction by Au nanoparticle.     

Development of polybenzoxazine–silica–titania (PBZ–SiO2–TiO2) hybrid nanomaterials with high surface free energy

In the present work, silica and titania reinforced polybenzoxazine (PBZ–SiO₂–TiO₂) hybrid nanomaterial possessing high surface free energy have been developed using dimethylol-functional benzoxazine monomer (4HBA-BZ), tetraethoxysilane (TEOS), 3-(isocyanatopropyl)triethoxysilane (ICPTS), titaniumisopropoxide (TIPO) through an in situ sol–gel process. Data obtained from the contact angle measurement indicate that the hybrid materials are hydrophilic in nature and possess a high surface free energy. For example, hybrid PBZ obtained from 1:1:0.6:0.4 (m:m:w:w) ratio of 4HBA-BZ:ICPTS:TEOS:TIPO (PBST₄) exhibit a high surface free energy of 38.2 mJm^?2 which is higher than that of neat polybenzoxazine (29.5 mJm^?2). Further data resulted from thermal studies indicate that the hybrid PBZ possess higher values of T_g, thermal stability and char yield than those of neat PBZ.     

Thermal properties and structure of (As2S3)100−x(Sb4S4)x glassy system

Thermal properties and structure of bulk glasses of (As₂S₃)_1?x(Sb₄S₄)_x system (x varies from 0 to 60 mol%) were studied by differential scanning calorimetry and Raman spectroscopy. It was found that with increasing Sb content the glasses can be sorted out to the three groups. The structure of glasses with x ≤ 10 is build-up mainly from AsS_3/2 pyramidal units and the well-known crystallization resistance of As₂S₃ can explain the reluctance of these undercooled liquids against crystallization. In glasses with a higher content of antimony, i.e., 10 < x ≤ 30 mol%, the vibration characteristics of As₄S₄ clusters appear. Undercooled melts of these glasses crystallize forming both β-As₄S₄ and high-temperature phases of Sb₂S₃. Structure of glasses with the highest antimony content (x > 30 mol%) is based on SbS_3/2 structural units significantly lowering stability of their undercooled melts from which only Sb₂S₃ crystallizes.     

Synthesis and characterization of SiO2–CrO3, SiO2–MoO3, and SiO2–WO3 mixed oxides produced using the non-hydrolytic sol–gel process

Silica-based mixed oxide xerogels, namely SiO₂–CrO₃, SiO₂–MoO₃, and SiO₂–WO₃, were prepared using the non-hydrolytic sol–gel process. The materials were synthesized using metal chloride:tetraethoxysilane (TEOS) molar ratios of 0.1:2; 0.2:2 and 0.4:2 for each metal chloride and 1:2 SiCl₄:TEOS molar ratio. All of the xerogels containing Cr, Mo or W had considerably greater surface areas than that of SiO₂. The small angle X-ray scattering experiments suggest that the surface roughness of the aggregates in SiO₂–CrO₃ is less than that of SiO₂–MoO₃ and SiO₂–WO₃. The morphological characteristics of the silica-based mixed oxide xerogels were not affected by the nature and amount of metal chloride employed in the synthesis. An irregular morphology was observed for SiO₂–CrO₃, SiO₂–MoO₃ and SiO₂–WO₃, but a lamellar structure was observed for SiO₂. X-ray photoelectron spectroscopy analysis suggests that tungsten species were preferentially distributed on the outmost part of the grain. The resulting particle diameter was shown to be lower for the mixed oxides compared to that of bare silica. Furthermore, the presence of metals (Cr, Mo and W) on silica caused a decrease in the size of the particles as the atomic radii of these metals increased. According to the Fourier transform infrared spectroscopy and Raman, Cr, Mo and W were incorporated within the silica framework.     

Determination of the stability constants of Pb–(DIPSO)x–(OH)y and Pb–(AMPSO)x–(OH)y systems

In this work, complexation between lead ion and the ligands 3-[N,N-bis(2-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid (DIPSO) and N-(1,1-dimethyl-2-hydroxyethyl)-3-amino-2-hydroxypropanesulfonic acid (AMPSO), which are commercial pH buffers, is presented. Both ligands form complexes with lead in their pH buffer range (between pH 6.5 and 8.5 for DIPSO and between pH 8.0 and 9.0 for AMPSO). The final models and the overall stability constants, which are reported here, were determined by direct current polarography and glass electrode potentiometry [only for the Pb–(DIPSO)_x–(OH)_y system] at 25.0 °C and 0.1 M KNO₃ ionic strength. For the Pb–(DIPSO)_x–(OH)_y system, the proposed final model contains PbL, PbL₂, PbL₂(OH), and PbL₂(OH)₂ with stability constants, as log β, of 3.4 ± 0.1, 6.35 ± 0.15, 12.8 ± 0.2, and 18.0 ± 0.3, respectively. For the Pb–(AMPSO)_x–(OH)_y system, the species observed are PbL, PbL(OH), and PbL(OH)₂ with stability constants, as log β, of 2.9 ± 0.5, 9.4 ± 0.1, and 14.5 ± 0.2, respectively. For AMPSO, the possible adsorption of the ligand at the mercury electrode surface was evaluated by alternating current polarography through calculation of the capacitance of the double layer.     

Effect of the variation of metal and cerium loadings on CeO2x–TiO2(100−x) supports in the complete catalytic oxidation of formaldehyde

Research on Chemical Intermediates - Formaldehyde has been successfully converted into CO2 and H2O at low temperature in the presence of CeO2x–TiO2(100?x) mixed oxides prepared by the...     

New polymolecular bismuth monohalides. Synthesis and crystal structures of Bi4BrxI4–x (x = 1, 2, or 3)

New mixed bismuth monohalides Bi₄Br_xI_4–x (x = 1, 2, or 3) were prepared for the first time by the reactions of bismuth metal with bismuth trihalides taken in stoichiometric amounts. Their crystal structures were established by single-crystal X-ray diffraction analysis. The Bi₄Br₃I and Bi₄BrI₃ compounds are isostructural and crystallize in the orthorhombic system, and Bi₄Br₂I₂ crystallizes in the monoclinic system. The crystal structures of all three phases contain one-dimensionally infinite molecular chains consisting of the [Bi₄X₄] fragments whose structures are identical with those of the individual Bi₄I₄ and Bi₄Br₄ molecules. The molecules are packed in layers. Different packing modes of the layers were found for different bismuth monohalides. The Bi₄ClI₃ compound, which is apparently structurally similar to Bi₄Br₃I and Bi₄BrI₃, was also prepared.