Novel fabrication of monodispersed peanut-type celestine particles using Sr-EDTA chelating precursors

Novel monodispersed peanut-type SrSO₄ (celestine) particles have been prepared using a facile precipitation reaction of Sr-EDTA chelating precursors at ambient temperature. The as-formed products were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), nitrogen absorption–desorption and differential scanning calorimetry–thermogravimetry (DSC–TG) measurement. The monodispersed SrSO₄ particles with an average length of 1.7 μm and an aspect ratio of 1.4 appear unusual peanut-type morphology. These SrSO₄ particles have a relatively large Brunauer–Emmett–Teller (BET) surface area of about 20.9 m² g⁻¹ and contain mesopores with a mean pore size of about 34.3 nm. The SrSO₄ particles exhibit an excellent thermal stability from room temperature to 1400 °C with a structural transformation at 1158.3 °C. The growth mechanism of the monodispersed peanut-type celestine particles was discussed to obtain a better understanding on their formation process.     

Synthesis of GaN nanorods by ammoniating Ga2O3 films on TiO2 (rutile) layer deposited on Si(111) substrates

GaN nanorods have been synthesized by ammoniating Ga₂O₃ films on a TiO₂ middle layer deposited on Si(111) substrates. The products were characterized by X-Ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transformed infrared spectra (FTIR) and high-resolution transmission electron microscopy (HRTEM). The XRD analysis indicates that the crystallization of GaN film fabricated on TiO₂ middle layer is rather excellent. The FTIR, SEM and HRTEM demonstrate that these nanorods are hexagonal GaN and possess a rough morphology with a diameter ranging from 200 nm to 500 nm and a length less than 10 μm, the growth mechanism of crystalline GaN nanorods is discussed briefly.     

Solid-state reaction synthesis of sodium niobate (NaNbO<Subscript>3</Subscript>) powder at low temperature

A modified solid-state reaction was applied to produce lead-free piezoelectric sodium niobate (NaNbO₃) powders. The mixture of Na₂C₂O₄ and Nb₂O₅ was identified by thermo gravimetric analysis (TGA) and differential thermal analysis (DTA). The powders were characterized using a scanning electron microscope (SEM) and the X-ray diffraction technique (XRD). The SEM image suggested that the particle size of the powders obtained ranged from 180 to 360 nm. The XRD pattern showed that the pure perovskite phase of NaNbO₃ could be synthesized at the low temperature of 475 °C for 1 h, with an average crystallite size of 31.45 ± 5.28 nm. This temperature was about 300 °C lower than that when using the conventional solid-state method with Na₂CO₃ as reactant, which resulted in a cost-, energy-, and time-saving method.     

Formation of SrTiO3 from Sr-oxalate and TiO2

SrTiO₃ powder has been prepared from Sr-oxalate and TiO₂ precursors, instead of using titanyl-oxalate. Sr-oxalate was precipitated from nitrate solution onto the surface of suspended TiO₂ powders. Crystallization of SrTiO₃ from the precursor was investigated by TGA, DTA and XRD analysis. It is evident that precursor, upon heating, dehydrates in two stages, may be due to the presence of two different types of Sr-oxalate hydrates. Dehydrated precursor then decomposes into SrCO₃ and TiO₂ mixture. Decomposition of SrCO₃ and simultaneous SrTiO₃ formation occur at much lower temperature, from 800 °C onwards, due to the fine particle size of the SrCO₃ and presence of acidic TiO₂ in the mixture. The precursor completely transforms into SrTiO₃ at 1100 °C. About 90 nm size SrTiO₃ crystallites are produced at 1100 °C/1 h, due to the lower calcination temperature and better homogeneity of the precursor.     

Synthesis and characterization of pure anatase TiO<Subscript>2</Subscript> nanoparticles

Pure anatase TiO₂ nanoparticles were synthesized by microwave assisted sol–gel method and further characterized by powder X-ray diffraction (XRD), energy dispersive x-ray analysis (EDAX), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV–Visible spectrophotometer, SEM images showed that TiO₂ nanoparticles were porous structure. The XRD patterns indicated that TiO₂ after annealed at 300 °C for 3 h was mainly pure anatase phase. The crystallite size was in the range of 20–25 nm, which is consistent with the results obtained from TEM images. Microwave heating offers several potential advantages over conventional heating for inducing or enhancing chemical reactions.     

Thermal behavior of SrSO4–SrCO3 and SrSO4–SrCO3–Al2O3 mixtures

The high temperature behavior of SrSO₄, SrCO₃ and Al₂O₃ mixtures was studied. A mixture of 1:1 mole of SrSO₄ and mechanically activated SrCO₃ was mixed and characterized using thermal gravimetric analysis. Some samples were uniaxially pressed and sintered at 1100, 1200 and 1300 °C for 8 h and then analyzed using X-ray diffraction and scanning electron microscopy. Additionally, a mixture of SrSO₄:SrCO₃:Al₂O₃ was uniaxially pressed and sintered at 1500 °C. The decomposition temperature of SrCO₃ was decreased 18° by milling for 180 min. Samples sintered at 1300 °C showed a microstructure free of porosity. X-ray diffraction analysis showed the presence of SrO and SrSO₄ after sintering at 1100, 1200 and 1300 °C. The mixture containing alumina showed the formation of a strontium aluminum oxide sulfate compound in addition to strontium aluminate.     

Solid phase preparation of submicron-sized SrTiO3 crystallites from SrO2 nanoparticles and TiO2 powders

Submicron-sized SrTiO₃ crystallites were prepared by a low temperature solid state method. The proposed preparation method involved two simple steps: firstly, SrO₂ nanoparticles of 35–90 nm were precipitated from the reaction of Sr(NO₃)₂ and H₂O₂ in an alkalescent aqueous solution (pH = 8) under the ambient condition; secondly, perovskite phase SrTiO₃ with a minor amount of SrCO₃ impurity were produced by heating the mixture of excessive SrO₂ nanoparticles and commercial TiO₂ powders in air at 700 °C for 10 h, which could be easily washed with 1 mol/l HNO₃ aqueous solution and distilled water to yield pure SrTiO₃ crystallites with the size of about 125–320 nm. The phase, purity and size of the as-obtained product were characterized by means of powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (FESEM).     

Low-temperature synthesis of Li2TiO3 tritium breeder ceramic pebbles by water controlled-release solvothermal process

In this work, the water-controlled release solvothermal process (WCRSP) method was selected to synthesize nanostructured β-Li₂TiO₃ tritium breeder ceramic pebbles using anhydrous lithium acetate (LiOAc) as lithium source and tetrabutyl titanate (TBOT) as titanium source. The effects of the reaction system, temperature, and amount of acetic acid on the crystal structure and morphology of Li₂TiO₃ power were systematically investigated by using XRD, SEM, and TEM techniques, respectively. The urea or acetone in the reaction system affects the composition of Li₂TiO₃ in the water-controlled release solvothermal process at 550 °C. Initially, the nanostructured single-phase Li₂TiO₃ powders with good dispersion and an average particle size of 35 nm were successfully synthesized at 550 °C when the acetic acid content was 15 vol%. Moreover, the phase transition temperature for the monoclinic phase β-Li₂TiO₃ was as low as 450 °C. The morphology of Li₂TiO₃ powder presents two different shapes, one is micro-spherical, the other is spherical nanoparticles in different content acetic acid. The results indicate that using ethanol/acetic acid mixture as a reaction system is favorable for obtaining nanostructured Li₂TiO₃ powder. Finally, Li₂TiO₃ ceramic pebbles with grain size of 1.4 μm were successfully fabricated at 950 °C for 2 h at room temperature, and the crush load and relative density (theoretical density, T.D) of the pebbles reach 53 N and 85.2%, respectively.     

Preparation and characterization of high surface area nanosheet titania with mesoporous structure

High surface area nanosheet TiO₂ with mesoporous structure were synthesized by hydrothermal method at 130 °C for 12 h. The samples were characterized by XRD, SEM, TEM, SAED, and BET surface area. The nanosheet structure was slightly curved and approximately 50–100 nm in width and several nanometers in thickness. The as-synthesized nanosheet TiO₂ had an average pore diameter about 3–4 nm. The BET surface area and pore volume of the sample are about 642 m²/g and 0.774 cm³/g, respectively.     

Preparation of SrTiO3 nanoparticles by the combination of solid phase grinding and low temperature calcining

Spherical SrTiO₃ nanoparticles with diameters of 15-35 nm were successfully synthesized by a solid phase grinding followed by low-temperature (400-600 °C) calcination method, using strontium hydroxide and tetrabutyl titanate as reactants. The as-synthesized samples were characterized by XRD, FT-IR, SEM and TEM, and the formation process of the products was investigated by means of TG-DTA. The results show that the as-synthesized SrTiO₃ nanoparticles with uniform sizes belong to cubic perovskite structure. The crystallite size and crystallinity increase with the increasing of calcination temperature. In the meantime, the crystal water contained in the reactant of strontium hydroxide also affects the crystallinity of products.     

Low temperature molten salt synthesis of SrTiO3 submicron crystallites and nanocrystals in the eutectic NaCl-KCl

An eutectic NaCl-KCl molten salts method has been developed for the synthesis of SrTiO₃ submicron crystallites and nanocrystals from SrO₂ and two kinds (submicron and nano-sized) of TiO₂ powders at 700 °C, which was much lower than that (generally > 1000 °C) of the conventional solid state reactions. The characterization results from X-ray diffraction and X-ray photoelectron spectroscopy revealed that the obtained products were pure perovskite phase SrTiO₃ without any contamination of Na, K, and Cl ions. The scanning electronic microscopy and transmission electron microscopy images disclosed that the starting TiO₂ played an important role in the morphology and size of the obtained SrTiO₃: while the product derived from TiO₂ submicron crystallites comprised faceted submicron crystallites of about 95-184 nm, that derived from TiO₂ nanocrystals comprised quadrate nanocrystals of about 20-61 nm. Besides, based on the experiments without the molten NaCl-KCl eutectic, at different temperatures and times, and using different kinds of TiO₂, the possible formation mechanism of SrTiO₃ submicron crystallites and nanocrystals was proposed.     

Mechanochemical synthesis of nanocrystalline titanium monoxide

Nanocrystalline cubic titanium monoxide, TiO_x (0.92 < x < 1.19), with mean crystallite size of ≈ 6 nm, was synthesized by mechanochemical treatment of Ti and TiO₂ (rutile) powder mixtures with molar ratios of 1:1, 1.10:1 and 1.25:1. The mechanochemical solid state reaction in a high-energy planetary ball mill was completed for 2 h in either air or argon atmosphere. During heating in vacuum at 900 and 1000 °C for 24 h, nanocrystalline TiO_x transforms to a well-crystallized, cubic or monoclinic TiO_x. The materials prepared were characterized by XRPD, TGA/DSC and SEM/EDS analysis.     

RBS,XRR and optical reflectivity measurements of Ti–TiO2 thin films deposited by magnetron sputtering

Single-, bi- and tri-layered films of Ti–TiO₂ system were deposited by d.c. pulsed magnetron sputtering from metallic Ti target in an inert Ar or reactive Ar + O₂ atmosphere. The nominal thickness of each layer was 50 nm. The chemical composition and its depth profile were determined by Rutherford backscattering spectroscopy (RBS). Crystallographic structure was analysed by means of X-ray diffraction (XRD) at glancing incidence. X-ray reflectometry (XRR) was used as a complementary method for the film thickness and density evaluation. Modelling of the optical reflectivity spectra of Ti–TiO₂ thin films deposited onto Si(1 1 1) substrates provided an independent estimate of the layer thickness. The combined analysis of RBS, XRR and reflectivity spectra indicated the real thickness of each layer less than 50 nm with TiO₂ film density slightly lower than the corresponding bulk value. Scanning Electron Microscopy (SEM) cross-sectional images revealed the columnar growth of TiO₂ layers. Thickness estimated directly from SEM studies was found to be in a good agreement with the results of RBS, XRR and reflectivity spectra.     

SrTiO3-SrZrO3 solid solution: Phase formation kinetics and mechanism through solid-oxide reaction

The perovskite solid solution composition Sr(Ti_0.5Zr_0.5)O₃ (STZ (ss)) has been synthesized from the mixture of SrCO₃, TiO₂ and ZrO₂ powders through solid-state reaction. The phase formation mechanism and kinetics were investigated using TG/DSC, XRD. SrCO₃ in the precursor decomposes at relatively lower temperature than pure powder decomposition, due to the presence of acidic TiO₂. Upon calcinations of the precursor SrTiO₃ (ST) and SrZrO₃ (SZ) were formed separately in the system. Then ST defuses in to SZ to form STZ (ss). ST formation started at lower temperature (800 °C) with lower activation energy (47.274 kcal/mol) than SZ. SZ formation started at 1000 °C with high activation energy (65.78 kcal/mol). STZ (ss) formation started from 1500 °C with very high activation energy (297.52 kcal/mol). It is concluded that solid solution formed coherently with SZ lattice by the diffusion of Ti in to the SZ.     

Large-scale synthesis of nanocrystals of barium titanate and other titanates through solution-phase processes

We reported a large-scale synthesis of nanocrystals of BaTiO₃, SrTiO₃, PbTiO₃, Sr_xBa_1−xTiO₃ through low-temperature and solution-phase processes without any surfactant. The series of samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Samples obtained were of high purity, consisting of nanoparticles with fine crystallinity and uniformity as well as good dispersibility in ethanol. This method might also offer an effectively new way to synthesis other titanate nanocrystals with perovskite structure in the future.     

Effects of sintering temperature on the microstructure and dielectric properties of titanium dioxide ceramics

Nanostructured (~200 nm grain size) titanium dioxide (TiO₂) ceramics were densified at temperature as low as 800 °C by pressureless sintering in a pure oxygen atmosphere. Phase transition and microstructural development of sintered samples were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Dielectric properties including d.c. conductivity, dielectric constant, loss tangent, and dielectric breakdown strength (BDS) were determined for samples sintered at various temperatures. The influence of sintering temperature on the microstructural development, defect chemistry, and dielectric properties of TiO₂ is discussed. Nanostructured TiO₂ ceramics with high sintering density (>98%) lead to improved dielectric properties; high BDS (~1800 kV/cm), low electrical conductivity (~5 × 10⁻¹⁵ S/cm), high dielectric constant (~130), and low loss tangent (~0.09% at 1 kHz), which is promising for application in high energy density capacitors.     

Synthesis of titanium carbide and TiC–SiO2 nanocomposite powder using rutile and Si by mechanically activated sintering

High-energy ball milling was applied with subsequent heat treatment for synthesizing nanoparticles of TiC powders by the carbothermic and carbosilisisothermic reduction of titanium oxide (rutile type). The milling procedure involved milling of TiO₂/C and TiO₂/Si/C powders at room temperature in an argon atmosphere. The progress of the mechanically induced solid state reaction was monitored using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results showed that TiC nanoparticles were duly synthesized in the TiO₂/C system at 1700 °C in 60-h milled samples. In the non-milled samples, although heated at the same temperature, only a minor amount of a lower degree of titanium oxide (Ti₃O₅) was observed to form. Further, in other non-milled samples, but with Si initially present, despite heating to 1550 °C no TiC phase was detected. However, using Si as a reducing agent accompanied by graphite, after 60 h ball milling, only Si remained as a distinguishable crystalline phase. Further, heat treatment of activated powders by forming the interphase compounds (such as Ti₃Si₅ and Ti₅Si₃) remarkably decreased the synthesis temperature to 900 °C for the 60 h milled samples.     

The effect of sputtering gas pressure on structure and photocatalytic properties of nanostructured titanium oxide self-cleaning thin film

Titanium oxide thin films were deposited by DC reactive magnetron sputtering on ZnO (80 nm thickness)/soda-lime glass and SiO₂ substrates at different gas pressures. The post annealing on the deposited films was performed at 400 °C in air atmosphere. The results of X-ray diffraction (XRD) showed that the films had anatase phase after annealing at 400 °C. The structure and morphology of deposited layers were evaluated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The surface grain size and roughness of TiO₂ thin films after annealing were around 10-15 nm and 2-8 nm, respectively. The optical transmittance of the films was measured using ultraviolet-visible light (UV-vis) spectrophotometer and photocatalytic activities of the samples were evaluated by the degradation of Methylene Blue (MB) dye. Using ZnO thin film as buffer layer, the photocatalytic properties of TiO₂ films were improved.     

Characterization and optical properties of m-Li2ZrO3 prepared by optimized solid-state reaction

m-Li₂ZrO₃ powders were successfully prepared by solid-state reaction method using Li₂CO₃ and ZrO₂ as raw materials. The synthesis was optimized by varying the ball-milling time (0–96 h); Li₂CO₃ excess (0 or 5 wt%), reaction temperature (700, 800, 900 or 1000 °C), and reaction time (3, 6, 9 or 12 h). The structural, morphological and optical properties of m-Li₂ZrO₃ powders were examined by X-Ray Diffraction, Thermogravimetric and Differential-Thermal analysis, Scanning Electron Microscopy, High-Resolution Transmission Electron Microscopy, Laser Diffraction, Dynamic Light Scattering and UV–Vis Diffuse Reflectance Spectroscopy. The results show that precursors suitable for the synthesis of fine powders require ball-milling times longer than or equal to 6 h. Highly crystalline m-Li₂ZrO₃ was synthesized under two distinctive calcination conditions as follows: 900 °C/6h without Li₂CO₃ excess or 1000 °C/12 h using 5 wt% of Li₂CO₃ excess. Particle size of as-synthesized powders was found to be in the range from 200 nm to 1 µm. m-Li₂ZrO₃ was found to be a wide band gap material with apparent optical band gap of 5.5 eV (direct) and 5.1 eV (indirect), which can be used in UV-C applications.     

Titanium and iron oxides produced by sol–gel processing of [FeCl{Ti2(OPri)9}]: structural,spectroscopic and morphological features

The first structurally characterised titanium and iron isopropoxide, [FeCl{Ti₂(OPrⁱ)₉}] (1), has been used as a single-source precursor for TiO₂/Fe₂TiO₅ composites prepared by the sol–gel route. Two distinct hydrolysis and condensation conditions were employed, followed by drying and thermal treatment up to 1000 °C. Product composition and oxide phase transitions were characterised by powder X-ray diffractometry and Raman, electron paramagnetic resonance, Mössbauer and Fourier-transformed infrared spectroscopies. A mixture of nanometric-size TiO₂ (anatase, 3.6–5.8 nm) and amorphous iron(III) oxide was obtained up to 500 °C, while TiO₂ (rutile), α-Fe₂O₃ (hematite) and Fe₂TiO₅ (pseudobrookite) were found at 700 °C. At 1000 °C, only rutile and pseudobrookite were observed. These results suggest that 1 behaves as a type III single-source precursor. Powders calcined at 1000 °C were analysed for surface morphology, microstructure and elemental composition by scanning electron microscopy/energy dispersive X-ray spectroscopy. Results suggest no phase segregation on a sub-micrometer level. Different morphologies were observed for the materials produced by the N₂ route, and this could relate to early crystal growth in an oxygen-deficient environment.