Temperature dependent magnetic properties of CoFe2O4/CTAB nanocomposite synthesized by sol–gel auto-combustion technique

A CoFe₂O₄/cetyl trimethylammonium bromide (CTAB) nanocomposite has been fabricated by a sol–gel auto-combustion method. Characterization of the material revealed the composition of the crystalline phase as CoFe₂O₄ while FT-IR confirmed the presence of CTAB on the nanoparticles. From X-ray line profile fitting, average crystallite size was estimated to be 22±6 nm. SEM analysis showed a porous sheet-like morphology with internal nanosize grains of about 30 nm. The room temperature coercive field (H_c) of the CoFe₂O₄/CTAB nanocomposite was found to be 1045 Oe which is close to the previously reported room temperature values for bulk CoFe₂O₄. The H_c was observed to decrease almost linearly with the square root of the temperature (√T) according to Kneller's law. From the linear fit of H_c versus √T, the zero-temperature coercivity (H_c0) and superparamagnetic blocking temperature (T_B) of the CoFe₂O₄/CTAB nanocomposite were found to be ∼9.1 kOe and ∼425 K, respectively. The remanence magnetization (M_r), the reduced remanent magnetization (M_r/M_s), and the effective magnetic anisotropy (K_eff) decrease with increasing temperature. The M_r/M_s value of 0.6 at 10 K higher than the theoretical value of 0.5 for non-interacting single domain particles with the easy axis randomly oriented suggests the CoFe₂O₄/CTAB nanocomposite to have cubic magnetocrystalline anisotropy according to the Stoner–Wohlfarth model.     

Sol–gel synthesis of red-emitting LiEuW2O8 powder as a near-ultraviolet convertible phosphor

LiEuW₂O₈ phosphor with the optical function of color conversion from near-UV to red wavelength was prepared by sol–gel method using inorganic salts as a starting material. Viscous mixing sol was prefired at 300 °C for 120 min in air and then white precursor was finally annealed at 800 °C for 240 min in Ar. Structural and photoluminescent properties of the sample were analyzed by an X-ray diffraction analysis, field emission-scanning electron microscope and a fluorescent spectrophotometer. The main emission peak is ⁵D₀ → ⁷F₂ transitions of Eu³⁺ at 615 nm, other transitions from the ⁵D₀ → ⁷F₁, ⁵D₀ → ⁷F₃ and ⁵D₀ → ⁷F₄ located at 570–700 nm range are weak. The characteristic emission of WO₄²⁻ in LiEuW₂O₈ is quenched absolutely and only red-light emission of Eu³⁺ appears.     

Sol–gel synthesis and characterization of Ce doped-BaTiO3

Barium titanate (BaTiO₃) have been doped “in situ” with 5.5 mol% cerium by a sol–gel method using barium acetate, titanium (IV) isopropoxide, and cerium (III) acetylacetonate as starting materials. The dried gel showed a microstructure consisting of nano-sized grains (∼140 nm) with great tendency to agglomeration. Several thermal analysis techniques were used to study the decomposition process of the gel. The presence of hydroxyls up to 720 °C suggests a strong bonding TiOH that is responsible for the existence of aggregates even at high temperatures. The as-prepared gel powder was found to be amorphous, and then decomposes through oxides and barium carbonate around 500 °C and crystallizes on the perovskite structure of tetragonal BaTiO₃ at 1100 °C for 3h in air. A small influence of the frequency on the dielectric properties of the Ba_0.945Ce_0.055TiO₃ ceramics was observed in 100 Hz to 1 MHz domain. At the Curie temperature point (22 °C) the dielectric constant was 10130 at 100 Hz while the dielectric loss (tan δ) was 0.018.     

Synthesis and characterization of MgAl2O4–ZrO2 composites

Different types of dense 5–97% ZrO₂–MgAl₂O₄ composites have been prepared using a MgAl₂O₄ spinel obtained by calcining a stoichiometric mixture of aluminium tri-hydroxide and caustic MgO at 1300 °C for 1 h, and a commercial yttria partially stabilized zirconia (YPSZ) powder as starting raw materials by sintering at various temperatures ranging from 1500 to 1650 °C for 2 h. The characteristics of the MgAl₂O₄ spinel, the YPSZ powder and the various sintered products were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), BET surface area, particle size analysis, Archimedes principle, and Vickers indentation method. Characterization results revealed that the YPSZ addition increases the sintering ability, fracture toughness and hardness of MgAl₂O₄ spinel, whereas, the MgAl₂O₄ spinel hampered the sintering ability of YPSZ when sintered at elevated temperatures. A 20-wt.% YPSZ was found to be sufficient to increase the hardness and fracture toughness of MgAl₂O₄ spinel from 406 to 1314 Hv and 2.5 to 3.45 MPa m^1/2, respectively, when sintered at 1600 °C for 2 h.     

Agglomeration of α-Al2O3 powders prepared by gel combustion

Ultrafine α-Al₂O₃ powders were prepared by a gel combustion method and the agglomeration characteristic of the resultant powders was studied. A variety of fine crystallite α-Al₂O₃ powders with different agglomeration structures could be obtained by altering the citrate-to-nitrate ratio γ and calcining the precursors at 1050 °C for 2 h. All the powders were of nearly equivalent crystallite size (60–80 nm) except for the P1 powder (113 nm) from the gel with γ = 0.033. The primary crystallites of the obtained α-Al₂O₃ powders were formed into large secondary particles with different degree of agglomeration. Except for the powder P1, the mean particle sizes from specific surface area and particle size distribution measurement increase with increasing citrate-to-nitrate ratio in the fuel-lean condition and decrease in the fuel-rich condition. Densities of alumina ceramics from powders P4 and P5 sintered at different temperatures were relatively low due to the wide particle size distribution.     

Sol–gel preparation and characterization of antibacterial and self-cleaning hybrid nanocomposite coatings

ZnO–TiO₂, SiO₂–TiO₂, and SiO₂–TiO₂–ZnO hybrid nanocomposite coatings were synthesized based on sol–gel precursors including tetramethoxysilane (TMOS), 3-glycidoxypropyl trimethoxysilane (GPTMS), tetra(n-butyl orthotitanate) (TBT), and zinc acetate dihydrate. The hybrid network was characterized by FTIR, FESEM, and EDAX techniques. Results indicated that inorganic particles’ size was of nanoorder (20–30 nm), with very uniform distribution and dispersion. Photocatalytic and self-cleaning activities of these coatings were further investigated by degradation of methylene blue in an aqueous solution (20 ppm) at visible light irradiation, indicating photocatalytic performance of the coatings containing ZnO and TiO₂ nanoparticles. The antibacterial effect of the coatings was investigated for inhibition and inactivation of cell growth, with the results showing the same antibacterial activity for ZnO–TiO₂ and SiO₂–TiO₂–ZnO coatings against Escherichia coli and Staphylococcus aureus; the activity was, however, higher than that of SiO₂–TiO₂ hybrid nanocomposite coatings.     

Facile micro-patterning of ferromagnetic CoFe2O4 films using a combined approach of sol–gel method and UV irradiation

CoFe₂O₄ photosensitive sol was prepared using iron nitrate and cobalt nitrate as precursors, acetyl acetone as a chelating agent, and ethanol as a solvent. CoFe₂O₄ photosensitive sol was used to fabricate smooth and micro-patterned CoFe₂O₄ films. The effects of UV irradiation on the crystallinity, surface morphology and ferromagnetic properties of CoFe₂O₄ films were investigated. For the film prepared using conventional sol-gel process, the crystallization of spinel CoFe₂O₄ phase was completely finished at ~ 600?℃, and no intermediate phase was formed. However, when the sol-gel process was combined with UV irradiation, Fe₂O₃ and CoO intermediate phases were firstly generated, and then reacted to form CoFe₂O₄ phase. Facile micro-patterning of CoFe₂O₄ films can be realized using a combined approach of sol-gel method and UV irradiation without using any photoresist. The structure and functional properties of the CoFe₂O₄ film have not been affected during the patterning process, and its magnetic properties have also not been changed.     

Sol–gel synthesis of Nd-doped BiFeO3 multiferroic and its characterization

Neodymium doped bismuth ferrite (BiFeO₃, BFO) nanoparticles were successfully synthesized by a facile sol–gel route. The influence of annealing temperature, time, Bi content and solvent on the crystal structure of BFO was studied. Results indicated that the optimum processing condition of BFO products was 550–600 °C/1.5 h with excess 3–6% Bi and ethylene glycol as solvent. On the other hand, Nd³⁺ ion was introduced into the BFO system and the effect of Nd³⁺ concentration on the structure, magnetic and dielectric properties of BFO were investigated. It was found that the magnetization of BFO was enhanced significantly with Nd³⁺ substitution, being attributed to the suppression of the spiral cycloidal magnetic structure led by the crystal structure transition. Furthermore, with increasing Nd³⁺ content, the dielectric constant was found to decrease while the dielectric loss was enhanced, which was mainly due to the hoping conduction mechanism with the reduction of oxygen vacancies.     

Magnetic properties of hard (CoFe2O4)–soft (Fe3O4) composite ceramics

Composite ceramics of CoFe₂O₄/Fe₃O₄ with different weight ratios were synthesized by Spark Plasma Sintering (SPS) at a sintering temperature of 500 °C. The X-ray diffraction patterns demonstrate that all samples are composed of CoFe₂O₄ and Fe₃O₄ phases. The magnetization curves for all the composite ceramic are single-step loops indicating the existence of exchange spring effect. Due to the competition between the exchange interaction and the dipolar interaction, magnetic properties like coercivity (H_c) and remanence (M_r) are sensitive to the weight ratio of the soft phase.     

Structural and magnetic evaluation of substituted NiZnFe2O4 particles synthesized by conventional sol–gel method

The aim of this study is to evaluate the structural and magnetic properties of Ni–Zn doped ferrite with trivalent Al³⁺ and Cr³⁺ cations substitution in Ni_0.6Zn_0.4Fe_2−xCr_x/2Al_x/2O₄ (x=0, 0.1, 0.2, 0.3, 0.4 and 0.5) synthesized by employing conventional sol–gel method. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FE-SEM), Mössbauer spectroscopy (MS) and vibrating sample magnetometer (VSM) analysis were carried out in order to characterize the structural and magnetic properties of particles. The XRD results confirmed the formation of single phase of spinel ferrite particles for a whole series of samples. The results of FTIR analysis indicated that the functional groups of Ni–Zn spinel ferrite were formed during the sol–gel process. Furthermore, FE-SEM micrographs revealed that the distribution of particles size is narrow. According to Mössbauer spectra,the doped cations are replaced in iron site occupancy of octahedral sites. It was found that with an increase in substitution contents magnetization decreased due to occupation of Al and Cr cations at low level substitutions in octahedral sites.     

Sol–gel synthesis and sintering of submicronic copper molybdate (α-CuMoO4) powders

A sol–gel method was proposed to prepare copper II molybdate α-CuMoO₄ powders. A gel was first obtained via the polymerizable complex method, using citric acid as complexing and polymerizing agent, dried at 120 °C and decomposed at 300 °C. A calcination in the temperature range 400–500 °C for 2 h led to the pure phase α-CuMoO₄. The different powders obtained were characterized by X ray diffraction analysis and by transmission (TEM) and scanning (SEM) electron microscopies.     

Preparation and characterization of magnetic γ-Al2O3 ceramic nanocomposite particles with variable Fe3O4 content and modification with epoxide functional polymer

Porous γ-alumina (γ-Al₂O₃) is one of widely used ceramic materials. To maximize the application potentials attempt was made to prepare multifunctional γ-Al₂O₃ ceramic composite particles following magnetization and then seeded polymerization with epoxide functional glycidyl methacrylate (GMA). γ-Al₂O₃ particles were first prepared by a modified sol-gel approach and then doped with variable content Fe₃O₄ nanoparticles. At higher Fe₃O₄ content the magnetite nanoparticles were oriented into needle like hairy structure basically grown from the surface of γ-Al₂O₃ particles. Before the seeded polymerization the magnetic γ-Al₂O₃ particles were modified with SiO₂ layer to improve the compatibility with the PGMA layer. The produced multifunctional ceramic particles were named as γ-Al₂O₃/Fe₃O₄/SiO₂/PGMA nanocomposite because one of the phases constituting Fe₃O₄ was in nano-size range. The produced nanocomposite particles possessed superparamagnetic properties and could be isolated from the dispersion medium by external magnetic field. Fourier Transform IR (FTIR) and X-ray photoelectron spectroscopic (XPS) data revealed that final nanocomposite particles contained reactive epoxide groups on or near the surface. The produced multifunctional γ-Al₂O₃ ceramic nanocomposite particles can be useful in biotechnology, catalysis and adsorbents for pollutant removal.     

TEM characterization of spark plasma sintered ZrB2–SiC–graphene nanocomposite

The interfacial behavior of spark plasma sintered ZrB₂–SiC nanocomposite doped with graphene nano-platelets was investigated by transmission electron microscopy (TEM). A powder mixture including ZrB₂ matrix, 20?vol% SiC and 10?vol% graphene was used as the starting material. X-ray diffraction analysis did not exhibit any in situ phase formation in the prepared nanocomposite. TEM observations verified the diffusion-controlled sintering. This study clarifies that graphene nano-platelets additive in the prepared nanocomposite did not engage in reactive sintering process, unlike many previous research studies addressing reactive sintering role for carbon additives.     

Spinelisation and properties of Al2O3–MgAl2O4–C refractory: Effect of MgO and Al2O3 reactants

The effect of particle size of MgO and Al₂O₃ on the spinel formation associated with permanent linear change on reheating (PLCR) and microstructure of Al₂O₃–MgAl₂O₄–C refractory is investigated as a function of heating cycle at 1600 °C with 2 h holding at each cycle. It was found that rate of spinel formation and associated volume expansion is very much dependent on the reactivity and particle size of the reactant. When the reactants are very fine and reactive there is considerable amount of spinel formation, whereas coarser reactants with lower reactivity show negligible formation of spinel phase and associated expansion. Magnesia and alumina with moderate reactivity develops optimum PLCR of the refractory. It continuously increases with the number of heating cycles. The SEM photomicrographs show that in Al₂O₃–MgAl₂O₄–C refractory the spinel phase is formed in between the calcined bauxite grain and the EDX analysis indicates that the spinel phase formed is stoichiometric in nature.     

Fe2O3/CoFe2O4复合光催化剂的制备及性能研究

本文以硝酸钴和氯化铁为主要原料制备了Fe₂O₃∕CoFe₂O₄复合光催化材料。利用X射线衍射仪(XRD)和紫外-可见吸收光谱(UV-VIS)对样品的结构和光吸收性能进行了表征。并在可见光照射下,通过催化降解罗丹明B(RHB)溶液考察各催化材料的催化效果。结果表明,制备的复合催化材料是以CoFe₂O₄为主的面心立方尖晶石结构。在反应时间为8.5 h、反应温度为135℃和煅烧温度为500℃时,制备的Fe₂O₃复合量为3%的复合催化剂性能最好,光催化降解2 h后,罗丹明B降解率可达到96.62%。     

Influence of the synthesis route on sol–gel SiO2–TiO2 (1:1) xerogels and powders

Five different sol–gel routes are used in order to synthesize mixed SiO₂–TiO₂ materials. Simple mixing of the Ti and Si precursors, pre-hydrolyzing of TEOS, modification of the Ti alkoxide with acetic acid, isoamyl alcohol and acetylacetone lead to translucent gels with different time of gelation. Different techniques such as TGA, DTA, XRD and IR spectroscopy are used to characterize each material. IR spectroscopy revealed the presence of Si–O–Ti and Si–O–Si bonds for all the xerogels letting suppose a composite microstructure of the gels. Pre-hydrolyzing of TEOS and modification of Ti alkoxide with isoamyl alcohol are the most appropriate routes to retain the anatase phase up to 1100 °C.     

One-step synthesis of Ni0.5Zn0.5Fe2O4 fine-patterned films via photosensitive sol–gel route

Ni_1−xZn_xFe₂O₄ (NZFO) (x=0.0–0.7) films were prepared by a photosensitive sol–gel route utilizing nickel acetate, zinc acetate and ferric nitrate as starting materials. The saturation magnetization of the NZFO film showed a parabolic tendency with Zn substitution. For Zn substitution of 0.5, the saturation magnetization reached the maximum value of 683 emu/cm³ with a relative low coercivity of 56 Oe at room temperature. The phase constituents and surface morphology of the films were characterized by X-ray diffractometer (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Through a direct patterning process, a fine-patterned Ni_0.5Zn_0.5Fe₂O₄ film was obtained by a photochemical reaction between the chelated complexes and UV light.     

Study of AC electrical properties of V2O5–P2O5–B2O3–Dy2O3 glasses

The AC conductivity of glass samples of composition 60V₂O₅–5P₂O₅–(35−x)B₂O₃–xDy₂O₃, 0.4≤x≤1.2 has been analyzed. The samples were prepared by the usual melt-quench technique. The prepared compounds were analyzed by X-ray diffraction (XRD) and thermo gravimetric–differential thermal analysis (TG/DTA). The activation energies were evaluated using glass transition temperature (T_g) and peak temperature of crystallization (T_c) from TG/DTA. The dependence of activation energy on composition was discussed. The electrical conductance and capacitance were measured over a frequency range of 20 Hz to 1 MHz and a temperature range of 303–473 K; these reveal semiconducting features based predominantly on an ionic mechanism. The dielectric and complex-impedance response of the sample is discussed. The relaxation time was found to increase with increasing temperature. Jonscher's universal power law is applied to discuss the conductivity. The electrode polarization was found to be negligible and confirmed from electrical modulus.     

Crystallographic characterization of silicon nitride ceramics sintered with Y2O3–Al2O3 or E2O3–Al2O3 additions

Silicon nitride ceramics were sintered using Y₂O₃–Al₂O₃ or E₂O₃–Al₂O₃ (E₂O₃ denotes a mixed oxide of Y₂O₃ and rare-earth oxides) as sintering additives. The intergranular phases formed after sintering was investigated using high-resolution X-ray diffraction (HRXRD). The use of synchrotron radiation enabled high angular resolution and a high signal to background ratio. Besides the appearance of β-Si₃N₄ phase the intergranular phases Y₃Al₅O₁₂ (YAG) and Y₂SiO₅ were identified in both samples. The refinement of the structural parameters by the Rietveld method indicated similar crystalline structure of β-Si₃N₄ for both systems used as sintering additive. On the other hand, the intergranular phases Y₃Al₅O₁₂ and Y₂SiO₅ shown a decrease of the lattice parameters, when E₂O₃ was used as additive, indicating the formation of solid solutions of E₃Al₅O₁₂ and E₂SiO₅, respectively.     

Modification of glass ionomer cement by incorporating hydroxyapatite-silica nano-powder composite: Sol–gel synthesis and characterization

A nanohydroxyapatite–silica powder was synthesized using an ethanol based sol–gel technique. The synthesized powder was incorporated into commercial glass ionomer powder (Fuji II GC) and characterized using FTIR, ²⁹Si CP/MAS NMR, EDX and XRD spectroscopy. ²⁹Si CP/MAS NMR results showed the presence of higher degree of cross-linking of silyl species between silica and GIC, which makes the Nano-HA–Silica–GIC composite much stronger. High-resolution transmission electron microscopy (TEM) and scanning electron microscopy (TEM) was employed to investigate the morphology of the synthesized powder. Results revealed that higher content of nanosilica produced a denser and stronger GIC. Thus, the application of nanohydroxyapatite–silica–GIC with improved properties are envisioned to be of great clinical importance, especially in stress bearing areas.