Phase content,tetragonality, and crystallite size of nanoscaled barium titanate synthesized by the catecholate process: effect of calcination temperature

A modified catecholate process has been applied to synthesize high purity barium titanate powders in the submicron range. A barium titanium-catechol complex, Ba[Ti(C₆H₄O₂)₃] was prepared from TiCl₄, C₆H₄(OH)₂ and BaCO₃, freeze-dried, and calcined for 3 h at temperatures between 600 and 1300 °C. Phase transformation and crystallite size of the calcined powders were investigated as a function of the calcination temperature by X-ray diffraction methods, and particle morphology and size were studied by scanning electron microscopy. With increasing calcination temperature, BaTiO₃ transformed from the (pseudo)cubic to the ferroelectric tetragonal phase. The tetragonality (c/a-1) increases with increasing calcination temperature and increasing crystallite size, respectively. Higher temperatures clearly favoured particle growth and the formation of large and hard agglomerates. The crystallite size of the tetragonal phase increased from <60 nm at 600–800 °C to 1237±344 nm at 1300 °C.     

Modified Sol–Gel Based Nanostructured Zirconia Thin Film: Preparation,Characterization, Photocatalyst and Corrosion Behavior

In this work, AISI 316L stainless steel was coated by nanostructured zirconia using the sucrose assisted sol–gel dip-coating route. Then, the effect of different calcination temperatures and the thickness of the coating on the corrosion protection of 316L stainless steel was investigated. Here, Zr(acac)₄ and sucrose were used as starting materials and gelation agents, respectively. Thermogravimetry and differential thermal analysis, X-ray powder diffraction (XRD), Fourier transform infrared, scanning electron microscopy and energy dispersive X-ray spectroscopy were used to characterize the coatings. XRD revealed that the pure tetragonal phase of zirconia was obtained at the calcination temperature of 300–500 °C. However, the mixture of monoclinic (m) and tetragonal (t) phase found in the zirconia coating calcined at 650 °C. Also, by increasing the calcination temperature from 300 to 650 °C, the mean of the crystallite size of structures was increased from 7 to 27 nm. AFM result show that the average roughness value of the sample calcined at 300 °C is 10.5 nm and the dimensions of the particles on the surface of this sample smaller than 50 nm. The potentiodynamic polarization and electrochemical impedance spectroscopy results revealed that the as-synthesized nanostructured sol–gel zirconia coatings exhibited a barrier property for the protection of the substrate. However, the highest corrosion resistance was obtained by the zirconia coating calcined at 300 °C. This was as a result of the desirable compromise of good adhesion, low defect density, and high barrier behaviour. Furthermore, zirconia nanoparticles were synthesized by calcination of the gel at the different temperature. The photocatalytic activity of samples was tested for degradation of methyl orange solutions. It is found that ZrO₂ nanoparticles calcined at 500 °C have higher photocatalytic activity than the other samples under UV light.     

Fluorination synthesis of MgF2 nanoparticles synthesized for manufacturing IR windows by hot-pressing

In this study, magnesium fluoride (MgF₂) nanoparticles were synthesized through the fluoridation method, by dissolving magnesium chloride and hydrofluoric acid (HF) in deionized water. The influences of some parameters, including pH, concentration ratio of reactants, F:Mg mole ratio, washing method and calcination temperature were investigated on the particle size, morphology, chemical purity and phase purity of MgF₂ nanoparticles. In order to study the impact of pH on the properties of MgF₂ nanoparticles, different samples at pH values of 1, 5 and 9 were synthesized. The obtained results revealed that as pH value increased from 1 to 9, the morphology of MgF₂ nanoparticles changed from rod to spherical shape. The effect of mole ratio of fluorine ions to magnesium ions on the MgF₂ nanoparticles at three ratios of 2, 6 and 12 also demonstrated that by increment of F:Mg mole ratio, the particle size was decreased from 150 nm to 30 nm. In addition, it was figured out that by the increment of F:Mg mole ratio, the MgO phase was eliminated. Afterwards, by decreasing the HF:MgCl₂ molar ratios from 0.1 to 0.03 the particle size reduced from 300 nm to 30 nm. After determining the optimal synthesis conditions, magnesium fluoride nanoparticles were calcined at 470, 530 and 600 °C. Regarding the results, the powder that was calcined at 600 °C with a particle size of about 30–40 nm was selected as the optimal sample. Ultimately, the resulting powder was sintered using hot-press (HP) at a temperature of 700 °C for 45min in the vacuum pressure of 10^?3 bar. After polishing the sintered piece, its inferred (IR) transparency was over 90% in the wavelength ranges of 3–5 μm.     

Low-cost synthesis of nano-hydroxyapatite from carp bone waste: Effect of calcination time and temperature

The aim of this study was to synthesize Hydroxyapatite (HA) from carp bone waste by calcination treatment. The effects of calcination temperature and time on crystallite size, crystallinity%, powder size and morphology, formed phases, and Ca/P ratio were analyzed. The XRD analyses indicated that for 1 h calcination time, HA was the only phase produced at all temperatures. However, for 5 h calcination time, temperatures other than 700ºC resulted in formation of TCP+HA. The HA obtained at 700ºC at both times had less crystallinity compared to other temperatures. Crystallite size increased by increase in temperature at 1 h calcination time. The smallest and largest particulate sizes were obtained at 800ºC for 1 h and 900ºC for 5 h, respectively. The Ca/P ratio close to theoretical value (1.67) was obtained for 5 h calcination time. Finally, the results showed the usefulness of the methodology used in natural HA production that can be used in orthopedics and dentistry.     

Synthesis and Thermal Treatment of Pd-Cr@Carbon for Efficient Oxygen Reduction Reaction in Proton-Exchange Membrane Fuel Cells

A nanostructured Pd-Cr catalyst was deposited on a supported carbon surface using the modified borohydride reduction method for the oxygen reduction reaction (ORR) to be utilized as an efficient catalyst in the proton-exchange membrane fuel cell. The crystal structure and feature nanostructure of the Pd-Cr@carbon were established through the use of X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). Meanwhile, its catalytic activity was studied using the cyclic voltammetry and electrochemical polarization techniques. Based on the XRD analysis, it was observed that the Pd phase with the fcc crystal structure was dominant, while the Pd-Cr phase with tetragonal crystal structure was detected only for the as-prepared sample and samples calcined at 573 K. The estimated average crystallite size of the Pd phase increased from 9.66 to 37.54 nm as the calcination temperature increased to 973 K, and the calcination time had a slight effect on the crystallite size. On the other side, the average crystallite size for the formed Pd-Cr phase slightly increased from 43.74 nm for the as-prepared sample to 44.90 nm for the sample calcined at 573 K for 3 h. The TEM examination revealed the uniform distribution of the Pd and Pd-Cr nanoparticles upon the carbon surface. The calcination temperature and time played an important role in controlling the structural and morphology parameters of Pd-Cr@carbon. The adsorption/desorption potentials were found to be dependent on the calcination temperature and time and hence the particle and crystallite sizes. The optimum ORR activity and chemical stability were observed for samples calcined at 773 K for 3 h.

     

Critical Particle Size and Phase Transformation in Zirconia: Transmission Electron Microscopy and X-ray Diffraction Studies

A study was undertaken to examine the crystallite size effect on the low-temperature transformation of tettragonal zirconia. Zirconia weas prepared by precipitation from a solution of zirconium tetrachloride by adding ammonium hydroxide to produce a pH of 2.95. Portions of the sample, after drying, were calcined at 500°C for various time intervals. Phase transformation was followed by X-ray diffraction; the data show that the tetragonal phase was initially formed and it was transformed to the monoclinic phase at longer periods of calcination. It was observed by TEM particle size and XRD crystallite size that the transformation does not appear to be due to a critical particle size effect.     

Influence of temperature,ripening time and calcination on the morphology and crystallinity of hydroxyapatite nanoparticles

Nano-sized hydroxyapatite (HA) particles were prepared by chemical precipitation through aqueous solutions of calcium chloride and ammonium hydrogenphosphate. The influence of temperature, ripening time and calcination on the crystallinity and morphology of the HA nanoparticles were investigated. It was found that the crystallinity and crystallite size increased with the increase of synthetic temperature and ripening time. XRD and TEM results showed that the morphology change of HA nanoparticles was related to their crystallinity. High crystallinity of HA led to regular shape and smooth surface of the nanoparticles. The crystallinity of HA powders increased greatly after calcination at 650 °C for 6 h but the change of the crystallite size after calcination was dependent on the crystallinity and crystallite size of “as prepared” HA nanoparticles.     

Phase Characterization of Lead Zirconate Titanate Obtained from Organic Solutions of Citrates

Lead zirconate titanate (PZT) with several Zr/Ti ratios was prepared by the organic solution of citrates of the respective cations. The Rietveld method was applied to perform quantitative analysis of the coexisting phases. The ratio of tetragonal/rhombohedral phases increased with calcination temperature. For the composition where Zr/Ti = 53/47, the tetragonal quantity varied from 25% to 35% for temperatures ranging from 600° to 800°C. For the powder with Zr/Ti = 57/43, only the rhombohedral phase was observed after calcination at 700°C. For the powder with Zr/Ti = 49/51, only the tetragonal phase was observed after calcination at 800°C. The amount of tetragonal phase was controlled in Zr/Ti = 55/45 by seeding the powder with the tetragonal phase of PZT.     

Preparation of Monodisperse and Spherical Zirconia Powders by Heating of Alcohol–Aqueous Salt Solutions

A novel method is demonstrated which yields a spherical ZrO₂ powder of narrow size distribution through heating of a zirconyl chloride solution with an alcohol–water mixture as the solvent. The kind and composition of the solvent mixture greatly influenced the behavior of the precipitation and the morphology of the resulting particles. When 1-propanol or 2-propanol was employed as the alcohol of the solvent mixture, the resulting particles had a spherical shape and a narrow size distribution. The particle size and the particle agglomeration level could be controlled by the amount of hydroxypropyl cellulose (HPC) in the solution. As-prepared amorphous powder was crystallized to a mixture of metastable tetragonal phase and monoclinic phase at about 460°C. The metastable tetragonal phase was converted to the monoclinic phase as the calcination temperature was increased. After calcination, the spherical shape of the zirconia powder was retained, while its particle size was decreased slightly.     

Synthesis and characterization of nano-LiMn2O4 powder by tartaric acid gel process

Polycrystalline nano-LiMn₂O₄ spinel powder was synthesized by the tartaric acid gel process and developed without any detectable minor phase at 300 °C. The powders synthesized by the tartaric acid gel process had a relatively smaller particle size, larger specific surface area and narrower particle size distribution than those prepared by the conventional solid state reaction. The average valence of manganese decreased with increasing synthesis temperature and resulted in an increase of the lattice parameter with calcination temperatures. As temperatures were increased to above 500 °C, LiMn₂O₄ underwent phase transition from a cubic to a tetragonal phase by removing oxygen ion in the lattice. From the results of MAS NMR, LiMn₂O₄ spinels formed at 300–800 °C had a large Knight shift of ∼520 and 560 ppm in reference to LiC1.     

Hydrothermal synthesis of titanium dioxide using acidic peptizing agents and their photocatalytic activity

We have prepared TiO₂ nanoparticles by the hydrolysis of titanium tetraisopropoxide (TTIP) using HNO₃ as a peptizing agent in the hydrothermal method. The physical properties of nanosized TiO₂ have been investigated by TEM, XRD and FT-IR. The photocatalytic degradation of orange II has been studied by using a batch reactor in the presence of UV light. When the molar ratio of HNO₃/TTIP was 1.0, the rutile phase appeared on the titania and the photocatalytic activity decreased with an increase of HNO₃ concentration. The crystallite size of the anatase phase increased from 6.6 to 24.2 nm as the calcination temperature increased from 300 °C to 600 °C. The highest activity on the photocatalytic decomposition of orange II was obtained with titania particles dried at 105 °C without a calcination and the photocatalytic activity decreased with increasing the calcination temperature. In addition, the titania particles prepared at 180 °C showed the highest activity on the photocatalytic decomposition of orange II. This paper was prepared at the 2004 Korea/Japan/Taiwan Chemical Engineering Conference held at Busan, Korea between November 3 and 4, 2004.     

Coprecipitation and Hydrothermal Synthesis of Ultrafine 5.5 mol% CeO2-2 mol% YO1.5ZrO2 Powders

Ultrafine 5.5 mol% CeO₂—2 mol% YO_1.5ZrO₂ powders with controllable crystallite size were synthesized by two kinds of coprecipitation methods and subsequent crystallization treatment. The amorphous gel produced by ammonia coprecipitation and hydrothermal treatment at 200°C for 3.5 h results in an ultrafine powder with a surface area of 206 m²/g and a crystallite size of 4.8 nm. The powder produced by urea hydrolysis and calcination exhibits a purely tetragonal phase. In addition, the powders crystallized by hydrothermal treatment exhibit high packing density and can be sintered at lower temperature (,1400°C) with nearly 100% tetragonal phase achieved.     

Synthesis,structural and optical properties of ZnS,CdS and HgS nanoparticles from dithiocarbamato single molecule precursors

Dithiocarbamate complexes of Zn(II), Cd(II) and Hg(II) were synthesize and characterized by elemental analysis, thermogravimetric analysis, UV–Vis, FTIR, ¹H- and ¹³C-NMR spectroscopy. The complexes were thermolyzed at 180°C to prepare HDA-capped ZnS, CdS and HgS nanoparticles. The optical properties of the nanoparticles showed absorptions that are blue shifted with respect to the bulk and narrow emissions. The ZnS nanoparticles are in the cubic phase with average crystallite sizes of 3–5 nm. The CdS nanoparticles consist of a mixture of cubic and hexagonal phases with particle sizes of 8–22 nm, while the HgS nanoparticles are in the cubic phase with average crystallite sizes of 7–14 nm.     

Characterization of perovskite LaFeO3 synthesized by microwave plasma method for photocatalytic applications

Perovskite LaFeO₃ nanoparticles were successfully synthesized by microwave plasma method combined with high temperature calcination at 700–1000?°C. The influences of calcination temperature on morphology, crystalline structure, purity and the atomic compositions of samples were studied. The photocatalytic performance of LaFeO₃ was evaluated though the photodegradation of Rhodamine B (RhB) under visible light. In this research, the orthorhombic LaFeO₃ nanoparticles showed band gaps in the range of 2.15–2.30?eV. The particle size increased with increasing in the calcination temperature, leading to the decreasing in the surface area. The LaFeO₃ sample calcined at 900?°C showed the highest photodegradation of 77.8% and the apparent rate constant of 0.0077?min^?1 within 180?min because of the narrower of band gap and the higher crystalline degree and oxygen adsorption.     

Synthesis of (Ni,Mn,Co)O4 nanopowder with single cubic spinel phase via combustion method

(Ni,Mn,Co)O₄ nanopowders with single cubic phase were successfully synthesized using combustion methods. Particle size of the as-burnt nanopowders after combustion was about 20 nm. Crystallization behavior of the NMC was investigated using various techniques such as X-ray diffraction (XRD), thermogravimetric (TG), Fourier transform infrared (FT-IR) spectroscopy, and transmission electron microscopy (TEM). Calcination at different temperature from 400 °C to 700 °C provides the powders with increased crystallinity and grain size. However, further increasing temperature above 800 °C for calcination, cubic spinel phase of NMC partly transformed to tetragonal spinel phase, which implies that cubic spinel phase of NMC nanopowder synthesized by combustion method becomes unstable above 800 °C.     

Crystallite Size and Microstrain of Thermally Aged Low-Ceria- and Low-Yttria-Doped Zirconia

The final phases of zirconia powders depend on the synthesis method employed, and the amounts of stabilizer present. In this study, ceria- and yttria-doped zirconia powders were prepared by urea hydrolysis and subsequent hydrothermal treatment. The amount of tetragonal ( t ) vs monoclinic ( m ) phase in the powders increased with increasing stabilizer content, while the tetragonal phase size decreased and the microstrain of t crystals remained unchanged. The thermal degradation behavior of the metastable t phase in zirconia containing a low CeO₂ or YO_1.5 doping level was explored during aging treatment by means of X-ray line profile broadening analysis. Both ultrafine yttria- and ceria-doped zirconia powder pellets exhibit isothermal t → m transformation after aging at 900°C for various times. It is argued that a crystallite size effect, rather than the dopant valence, dictates the occurrence of the t → m transformation in ultrafine zirconia powders. The change in crystallite sizes of both t and m phases during aging depends significantly on the amount of stabilizer, aging time, and mechanism of t → m phase transformation. However, the change of microstrain in both t and m phases is related to the amount of stabilizers present and the matrix constraints.     

Effect of stoichiometry and milling processes in the synthesis and the piezoelectric properties of modified KNN nanoparticles by solid state reaction

Nanoparticles in the system (K,Na,Li)(Nb,Ta,Sb)O₃, modified KNN, were synthesized following a solid state reaction procedure. Milling of the individual carbonate and oxide raw materials was carried out before mixing of the components to optimize particle size. These mixtures were calcined at 700 °C for 2 h, obtaining nanoparticles with size ranging between 50 and 200 nm. The optimization of the raw materials particle size and the particle refinement of the carbonates during their decomposition play a key role in the formation of the modified KNN nanoparticles by solid state route. The obtained nanoparticles show tetragonal and orthorhombic phases coexistence that could be attributed in part to the lack of homogeneity of cations distribution confirmed by EDS analysis. The K⁺ cation excess on the modified KNN system produces a displacement of Li⁺ cations from the perovskite structure that is the origin of the stabilization of the orthorhombic symmetry. These nanoparticles are used to sintered ceramics with good piezoelectric properties without needing of anisotropic preparation methods. The sintered ceramics show resistance to hygroscopicity and deliquescence.     

Effect of Composition and Size of Crystallite on Crystal Phase in Lead Barium Titanate

Lead titanate, barium titanate, and lead barium titanate powders (>99.9% pure), the particle size of which varied from 0.03 to 0.15 μm depending on the calcination temperature and the composition, was prepared from barium lead titanyl oxalate, which was previously prepared by reacting high-purity ammonium titanyl oxalate with barium and lead acetate. The critical crystallite size of BaTiO₃ powder from the cubic to the tetragonal phase is around 1 μm. Pb_0.3Ba_0.7TiO₃ powder with an average size of 0.057 μm showed the tetragonal phase.     

Synthesis and characterization of nanocrystalline zirconia powder by simple sol–gel method with glucose and fructose as organic additives

The present study has devised the sol–gel method using glucose and fructose as two organic additives so as to synthesize zirconia nanoparticles. The presence of these organic additives has produced some positive effect on the phase transition from tetragonal to monoclinic and played an important role in the morphology and crystallite size of the nanoparticles. Fourier transform infrared (FT-IR) spectra have shown Zr–O–Zr bond. Crystal phase and crystallite size have been determined by X-ray Diffraction (XRD) analysis. Besides, the morphology of the samples has been investigated by field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM). The optical properties of the samples have been analyzed using photoluminescence (PL) spectroscopy, too. All the analyses consistently have shown fairly uniform nanoparticles with small size, containing both tetragonal and monoclinic phases with crystallite size between 10 and 30 nm.     

Some new observations on the structural and phase evolution of nickel titanate nanofibers

In this study, we report for the first time the synthesis of nickel titanate (NTO) nanofibers containing a mixture of ilmenite and spinel phases of NTO, at an atypical low temperature. Precursor nanofibers produced by sol-gel electrospinning were calcined at three different temperatures to produce the NTO nanofibers. Thermal analysis along with X-ray photoelectron spectroscopy confirmed the formation of non-crystalline stable phases of TiN and Ti-O-N that restrained the formation of ilmenite NTO, and the Ni-rich environment pushed the Ti atoms to tetrahedral sites to form a defective spinel structure. The crystallite size of spinel NTO was observed to increase as a function of the calcination temperature above 700 °C, as the activation energy for coalescence and growth of spinel NTO was favorable. NTO nanofibers obtained above the calcination temperature of 700 °C exhibited new band gap energy around 2.5 eV in Tauc plot. Oxygen vacancies in these ceramic nanofibers decreased as the calcination temperature was increased. A hypsochromic shift of 20 nm in the photoluminescence spectra suggested that the material had a Ni²⁺ rich NTO (spinel).