Preparation and characterization of Li2TiO3 ceramic pebbles by modification of the water-based sol–gel method

Li₂TiO₃ is considered as one of the best candidates for breeding materials. This article adopted a modification water-based sol–gel method to synthesize nano-Li₂TiO₃ powders, which overcomes the poor phase purity, coarse grain, and inferior crushing strength described in the previous literature. In this paper, the thermal effect of the precursor, the crystal phase, and the morphology of the powders were characterized by thermogravimetric analysis/differential thermal analysis (TG/DTA), X-ray diffraction (XRD), and transmission electron microscopy (TEM) techniques. The nano-structured Li₂TiO₃ powders with good dispersion and an average particle size of 20–50 nm were successfully synthesized at 600°C by controlling PH and hydrolysis rate. Moreover, the phase transition temperature for the monoclinic phase β-Li₂TiO₃ was as low as 600°C, which is lower than 750°C using the traditional solid-state method. Meanwhile, the morphology, porosity, crushing load, and thermal conductivity of ceramic pebbles are characterized systematically by using scanning electron microscope (SEM), mercury injection meter, compression strength equipment, and laser scattering method, respectively. Experimental results showed that the Li₂TiO₃ ceramic pebbles with a sphericity of .98, crush load of 48.4 N, and relative density of 90.03 % were successfully prepared at 1050°C for 2 h. This method will provide new guidance for the preparation of tritium breeders.     

Synthesis of TiO2–Ag nanocomposite with sol–gel method and investigation of its antibacterial activity against E. coli

TiO₂–Ag nanocomposite was prepared by the sol–gel method and an azeotropic distillation with benzene was used for dehydration of the gel. Because of gel dehydration by distillation method a nanopowder with a surface area of 230 m²/g was produced which decreased to 80 m²/g after calcination. TEM micrographs and XRD patterns showed that spherical nanosized Ag particles (≈ 10 nm) were deposited among TiO₂ particles. The antibacterial activity of calcined powder at 300 and 500 °C was studied in the presence and in the absence of UV irradiation against Escherichia coli as a model for Gram-negative bacteria. The antibacterial tests confirmed the powder calcined at 300 °C possessed more antibacterial activity than the pure TiO₂, amorphous powder and the powder calcined at 500 °C under UV irradiation. In the absence of UV, the reduction in viable cells was observed only with calcinated powder at 300 °C.     

Preparation and dielectric properties of dense and amorphous alumina film by sol–gel technology

Dense and crack-free aluminum oxide films were fabricated by sol–gel spin-coating technology. Aluminum nitrate (Al(NO₃)₃.9H₂O) was used as the precursor material. X-ray diffraction shows that the fabricated films are amorphous. X-ray photoelectron spectroscopy confirms that the thin films are alumina (Al₂O₃). Field-emission scanning electron microscopy images of the films reveal that the films are compact with a dense cross section. Dielectric measurements were carried out on samples with a metal–insulator–metal structure. The electrical characteristics of the films were affected by the thermal sintering temperature of the films. The leakage current density of the films decreases with the increase in the sintering temperature and increases with the increase in the measuring temperature. The leakage current shows a linear dependence on the voltage in the low-electric field-regime. The current density ascends to higher values due to the effect of space charges in the high-electric-field regime. The ionization energy of the top-electrode metals (Au, Pt or Ti–Au) has a strong effect on the leakage current.     

Synthesis of mesoporous SiO2–ZrO2 mixed oxides by sol–gel method

A series of SiO₂–ZrO₂ mixed oxides were prepared by sol–gel method in the presence of directing agent, with variable amounts of ZrO₂ between pure silica and pure zirconia, with the aim to obtain catalytic materials suitable as solid acid catalysts. SiO₂–ZrO₂ mixed oxides differ from the two pure starting oxides. While SiO₂ has a low OH density without peculiar acid character, the introduction of increasing amounts of Zr increases the density of the acid sites in the materials. Furthermore both SiO₂/ZrO₂ molar ratio and drying procedure are able to influence the physico-chemical characteristics (textural properties, acid sites distribution, etc.) of these mixed oxides.     

Optical properties of Nb-doped TiO2 thin films prepared by sol–gel method

In this work, we studied optical properties of pure and Nb-doped TiO₂ synthesized using a sol–gel method and deposited as thin films by spin-coating followed by annealing in air at 500 °C for 1 h. The surface elemental composition was derived from X-ray photoelectron spectra, while structure and surface morphology were investigated using X-ray diffraction and atomic force/scanning electron microscopy. Finally, the optical properties were investigated by means of UV–vis spectrophotometry and spectroscopic ellipsometry.The Nb content was determined from XPS measurements to vary between 1.8 and 4.3 at%. The XRD patterns of the deposited thin films, with a maximum thickness of about 56 nm, showed no diffraction peaks. As proven both by microscopy and spectroscopic ellipsometry studies doping TiO₂ with Nb modified the surface morphology of the samples; the grain size is increasing while the surface roughness decreases with the increase in Nb content. This is accompanied by a decrease in the refractive index and an increase of the extinction coefficient.     

Preparation of nanocrystalline SrTiO3 powder by sol–gel combustion method

In this research a sol–gel combustion route has been presented to synthesize strontium titanate (SrTiO₃:ST) nanocrystalline, using citric acid as fuel. The synthesis procedure was optimized by systematically varying the molar ratios of total metal nitrate to citric acid (MN:CA) from 1:1 to 1:3. The effect was investigated through XRD, SEM and TEM analysis. Analysis of XRD spectrum shows the complete of SrTiO₃ nanocrystalline, however, a minor phase of SrCO₃ impurity was found. Hence, an acid treatment process, with 1 mol/l HNO₃ solution and deionized water, was applied to remove the impurity. The results show that the appropriate condition to prepare the single phase nanocrystalline SrTiO₃ powders is MN:CA molar ratio of 1:3, coupled with an acid treatment process and at the lower calcination temperature of 500 °C. The particle size of powders was in nanometer ranges. The average crystallite size calculated from FWHM was about 23 nm. Morphology of powders was identified by SEM analysis. However, TEM estimated the average particle size about 7.5 nm after applying an acid treatment technique at 600 °C.     

Formation and characterization of p-type semiconductor CuCrO2 thin films prepared by a sol–gel method

This study adopted the sol–gel method to synthesize p-type semiconductor CuCrO₂ films and analyzed the effects of an annealing treatment, under a controlled argon atmosphere by changing the temperature and time, on the phase transformation, micro- and nano-structure, composition, and semiconductor properties of thin films. In the Cu–Cr–O phase transformation system, CuO, Cr₂O₃, and CuCr₂O₄ were the intermediate phases of the reaction for forming CuCrO₂: in the metastable state reaction process, the composite phases changed into a single phase, CuCrO₂; in the stable-state reaction process of CuCrO₂, carbon elements of precursors were released and eliminated; and finally the optoelectronic properties of the CuCrO₂ thin film were adjusted and changed. The CuCrO₂ thin film possessed cell- and polygon-like shaped microstructures. The carbon content in the CuCrO₂ film decreased, so the copper, chromium, and oxygen contents increased accordingly. The optical band gap of CuCrO₂ thin film increased from 2.81 eV to 3.05 eV, while the resistivity decreased. The nanoscale crystal was identified which also of the delafossite CuCrO₂ structure. Using the sol–gel method to prepare the CuCrO₂ thin films, an appropriate annealing temperature and time were helpful in forming the single-phase CuCrO₂; the decrease of precursor elements in the thin film could enhance the band gap and the conductivity of the material.     

The effect of ceramic nanoparticles on tribological properties of alumina sol–gel thin coatings

Thin alumina coatings containing zirconia or alumina nanoparticles having diameter of ～20–30 nm were deposited by the sol–gel dip-coating process on silicon wafers. The mass content of nanoparticles in the alumina coating was fixed at 15% in relation to the theoretical mass of alumina matrix resulted from the amount of the applied precursor. Atomic force microscopy (AFM) was used to image the surface topography of as-made coatings and find out the wear level after frictional tests. Tribological tests were performed with the use of a microtribometer operating in the load range of 30–100 mN. It was found that the presence of α-alumina (corundum) or zirconia nanoparticles enhances the tribological performance of alumina layers annealed at 100 °C by decreasing the average wear rate by 20% and 63% for zirconia and corundum nanoparticles, respectively. No wear was observed for samples containing both types of nanoparticles annealed at 500 °C.     

High-temperature properties of 2.5D SiO2f/SiO2 composites by sol–gel

2.5D SiO_2f/SiO₂ composites were fabricated by sol–gel process. The mechanical and fracture behavior of SiO_2f/SiO₂ composites under higher temperature were discussed. The oxidation behavior at 1200 °C and 1500 °C was investigated. The results showed that SiO_2f/SiO₂ composites had high flexural strength, and the fracture mechanism was a combination of brittle and ductile fracture. After higher temperature oxidation, the fracture mechanism changed to typical brittle/sudden fracture. For long time usage at higher temperature, it was necessary to stabilize SiO₂ fibers and SiO₂ matrix of SiO_2f/SiO₂ composites.     

Preparation of nanocrystalline MoSi2 with enhanced lithium storage by sol–gel and carbonthermal reduction method

Herein nanocrystalline MoSi₂ with enhanced lithium storage was successfully synthesized via a sol-gel and carbonthermal reduction method. Reduction of the gel mixture of Mo precursor and Si precursor by carbon at a desired temperature resulted in the formation of MoSi₂ nanoparticles. The gel mixture was obtained through the hydrolysis of TEOS and ammonium molybdate and the polymerization of hydrolysis products of TEOS. The reducing agent carbon was produced via decarburition of sucrose's hydrolysis products, which have been wrapped in the gel during its formation process. Addition of HCl to the mixed solution controlled the hydrolysis and polymerization rate, and enabled the formation of a gel mixture with homogeneously distributed hydrolysis products of ammonium molybdate, TEOS and sucrose. This achievement likely generates a novel route to synthesize non-oxide compounds such as silicide, carbide through the sol–gel and carbonthermal reduction process. In addition, the as-received MoSi₂ nanoparticles showed considerable activities in the reversible lithiation and delithiation process. When using as an anode for Li-ion batteries, MoSi₂ nanoparticles delivered a specific capacity of 325 mAh g^?1 at C/12 and showed an increasing capacity with cycling.     

Effect of synthesis methods and aging on synthesis of uvarovite garnet by ceramic and sol–gel processes

Abstract

The uvarovite garnet (CaO)₃ (Cr₂O₃ )(SiO₂ )₃ has been synthesised (mineralised with borax to facilitate diffusion of precursors) by several sol–gel methods. Two routes for uvarovite formation have been observed: where CaCrO₄ forms as an intermediate phase; and where metastable pseudowollastonite (α-CaSiO₃ ) forms as an intermediate phase. Synthesis via CaCrO₄ appears to be more reactive in unaged samples. The reactivity of samples can be directly related to the chemical homogeneity of raw powders, and two methods of synthesis, Pechini and alkoxide, were found to stand out for their reactivity. Aging of raw powders for 6 months inhibits nucleation. Consequently, samples without nucleating agents (i.e. chlorides), such as gels from alkoxides, lead to the stabilisation of amorphous material or metastable phases (α-CaSiO₃ ) and, as a result, hinder uvarovite formation. In contrast, aged samples involving heterogeneous nucleation agents, as in the Pechini method with CaCl₂ as precursor, enhance reactivity.     

Preparation and characterization of ultrafine ZrB2–SiC composite powders by a combined sol–gel and microwave boro/carbothermal reduction method

A combined sol–gel and microwave boro/carbothermal reduction technique was investigated and used to synthesize ultrafine ZrB₂–SiC composite powders from raw starting materials of zirconium oxychloride, boric acid, tetraethoxysilane and glucose. The effects of reaction temperature, molar ratios of n(B)/n(Zr) and n(C)/n(Zr+Si) on the synthesis of ultrafine ZrB₂–SiC composite powders were studied. The results showed that the optimum molar ratios of n(B)/n(Zr) and n(C)/n(Zr+Si) for the preparation of phase pure ultrafine ZrB₂–SiC composite powders were 2.5 and 8.0, respectively, and the firing temperature required was 1300 °C. This temperature was 200 °C lower than that require by using the conventional boro/carbothermal reduction method. Microstructures and phase morphologies of as-prepared ultrafine ZrB₂–SiC composite powders were examined by field emission-scanning electron microscopy (FE-SEM) and transmission electron microscope (TEM), showing that SiC grains were formed evenly among the ZrB₂ grains, and the grain sizes of ZrB₂ in the samples prepared at 1300 °C for 3 h were about 1–2 μm. The average crystalline sizes of these two phases in the as-prepared samples were calculated by using the Scherrer equation as about 58 and 27 nm, respectively.     

Preparation and characteristics of sol–gel derived Zn2SiO4 doped with Ni2+

The changing presented during the heating of sol–gel derived Zn₂SiO₄ doped with Ni²⁺ have been investigated by X-ray diffraction (XRD) and differential thermal analysis (DTA). When calcining temperature <700 °C, the XRD patterns of the sample show the characteristic peaks of ZnO crystal and non-crystalline SiO₂. When calcining temperature >900 °C, XRD pattern of the sample shows the characteristic peaks of α-Zn₂SiO₄ crystal phase. Also, the excitation and emission spectra of the undoped and Ni²⁺-doped samples have been investigated. Stable green–yellow–red emission has been observed from Zn₂SiO₄ crystalline phase. A novel photoluminescence (PL) phenomenon has been observed from Ni²⁺-doped Zn₂SiO₄.     

Multilayer zirconium titanate thin films prepared by a sol–gel deposition method

Zirconium titanate multilayer thin films were prepared by an aqueous particulate sol–gel process followed by spin coating. The obtained structures were studied by transmission electron microscope, scanning electron microscope, atomic force microscope, and spectroscopic reflection analyses. According to the results, sound thin films up to three layers were developed, accompanied by an increase in thickness and roughness by increasing the number of the layers. It was also found that the coatings consist of globular nanoparticles with an average diameter of 50 nm. Considering the contribution of roughness to biological responses, the optimization of the surface characteristics to meet an optimal performance seems to be a challenging issue, which demands future studies.     

Preparation of nano-AlN powder by sol–gel foaming and its sintering properties

Uniformly dispersed nano-sized aluminum nitride powders were prepared by the sol–gel foaming method using aluminum nitrate as the aluminum source, sucrose as the carbon source, and ammonium chloride as the foaming agent. The effects of ammonium chloride content on the particle size and the sintering properties of aluminum nitride were investigated. The results showed that when the molar ratio of ammonium chloride to aluminum nitrate was .5, the colloidal foams were uniform, large, and fluffy, and amorphous alumina precursors with uniform particles could be prepared. Aluminum nitride powder with a particle size of 22–27 nm can be obtained by calcining these precursors in nitrogen atmosphere at 1400°C for 2 h. At the same time, aluminum nitride bulk material with a relative density of 95% can be obtained by sintering the compact samples in nitrogen atmosphere at 1700°C for 2 h.     

Preparation of multi-coating PZT thick films by sol–gel method onto stainless steel substrates

PbZr_0.45Ti_0.55O₃ ferroelectric films have been prepared by sol–gel method, using alkoxide precursor compounds and multi-layer technique. The gel films were deposited by spin-coating onto stainless steel substrates. In order to obtain crystallization in the perovskite phase, the samples were annealed at 600–700°C for 1 min. The dependence of the electric properties on the heat-treatment temperature is studied, and the coercive electric field as a function of the material thickness is determined. By SEM photography, the microstructure of the films could be shown to be homogeneous.     

Preparation of Ni1−xMnxFe2O4 ferrites by sol–gel method and study of their cation distribution

The spinel ferrite nanoparticles of the system Ni_1?xMn_xFe₂O₄ with x=0.0, 0.1, 0.3, 0.5, 0.7 and 0.9 were prepared by sol–gel auto combustion technique using chlorides of Ni, Mn and Fe as a source with citric acid as chelating agent. The structure of the ferrite materials and the particle size were determined by XRD, it was observed that the structure was a single phase, face centered cubic with lattice parameter ranging from 8.365 Å to 8.394 Å and the particle size ranging from 23.86 Å to 38.30 Å. The lattice parameter showed a linear dependence on concentration in accordance with the Vegard's law. By analyzing XRD patterns, the cation distribution over A and B-sites was estimated through the R-Factor method. The magnetic moment for each sample was determined from cation distribution on the two sites. An enhancement in the net magnetic moment was observed with gradual increase in the Mn content.     

Effects of annealing temperature on structure and electrical properties of sol–gel derived 0.65PMN-0.35PT thin film

0.65Pb(Mg_1/3Nb_2/3)O₃-0.35PbTiO₃ (0.65PMN-0.35PT) thin films were deposited on Pt/Ti/SiO₂/Si substrates annealed from 550 to 700 °C using sol-gel process. The effects of annealing temperature on microstructure, insulating, ferroelectric and dielectric properties were characterized. The result reveals that 0.65PMN-0.35PT thin films possess a polycrystalline structure, matching well with the perovskite phase despite the existence of a slight pyrochlore phase. The film samples annealed at all temperatures exhibit relatively dense surfaces without any large voids and the grain size increases generally with the increase of the annealing temperature. Meanwhile, pyrochlore phase is considerably generated because of the deformation of perovskite phase caused by volatilization of Pb at an excessive high-temperature. The film annealed at 650 °C exhibits superior ferroelectricity with a remanent polarization (P_r) value of 13.31 μC/cm², dielectric constant (ε_r) of 1692 and relatively low dielectric loss (tanδ) of 0.122 at 10⁴ Hz due to the relatively homogeneous large grain size of 130 nm and low leakage current of approximately 10^-6 A/cm².     

Corrosion protection by zirconia-based thin films deposited by a sol–gel spin coating method

This paper focuses on the structure and corrosion behavior of 316L stainless steel coated by inorganic ZrO₂, hybrid ZrO₂–PMMA, and combined inorganic–hybrid films. The coatings were deposited by a particulate sol–gel spin-coating route, using carboxymethyl cellulose as a nanoparticle dispersant. The electrochemical evaluations were conducted in a simulated body fluid, via potentiodynamic polarization and impedance spectroscopic experiments. According to the results, the hybrid coating presented a better corrosion protection compared to the inorganic coating, due to a lesser density of structural defects. However, the best corrosion resistance was found for a combined coating which consists of an inorganic bottom layer and a hybrid top layer, due to a desirable compromise of good adhesion and low defect density.