Sol–gel combustion synthesis of BNBT powders

Ba-modified bismuth sodium titanate with composition 0.94[(Bi_0.5Na_0.5)TiO₃]-0.06BaTiO₃ (BNBT) was prepared by a citrate nitrate sol–gel combustion method. The sol was obtained using barium acetate, bismuth nitrate, sodium nitrate and a peroxo-citrate complex of titanium isopropoxide as starting precursors. Various molar ratios of citrate/nitrate (C/N) were considered for the sol production. The corresponding gels were fired at different temperatures (300, 400, 500 °C) in order to evaluate the conditions necessary to obtain the decomposition of the precursors and the formation of the pure BNBT perovskitic phase in a single step. The best conditions to obtain the desired phase are: (C/N) = 0.2, and combustion temperature of 500 °C. Ball milled powders were densified at a temperature 100 °C lower than the one generally used for powder produced with the conventional mixed oxide route. The electrical properties are comparable to those reported for conventionally prepared materials.     

Thermal stability of anatase TiO2 aerogels

Titanium dioxide (TiO₂) aerogels were prepared with sol–gel ambient pressure drying method by using titanium tetrachloride (TiCl₄) as precursor and tetraethoxysilane as modifier, calcinated at different temperature and characterized by X‐ray diffraction, transmission electron microscopy and small angle X‐ray scattering. The results showed that the TiO₂ aerogels remained amorphous under 500 °C, changed to anatase from 600 °C and further changed to rutile from 900 °C. Between 60 °C and 500 °C, the primary particles within the samples concentrated mainly upon small sizes, enlarged and diverged remarkably above 600 °C. The crystalline grains grew and agglomerated with the rise of the calcination temperature. The TiO₂ aerogels at a temperature higher than 800 °C have better stability than anatase because of the formation of partial Ti―O―Si bonds. Copyright © 2016 John Wiley & Sons, Ltd.     

Graphene Nanosheets as a Platform for the 2D Ordering of Metal Oxide Nanoparticles: Mesoporous 2D Aggregate of Anatase TiO2 Nanoparticles with Improved Electrode Performance

Graphene nanosheets are successfully applied as an effective platform for the 2D ordering of metal oxide nanoparticles. Mesoporous 2D aggregates of anatase TiO₂ nanoparticles are synthesized by the heat treatment of the uniformly hybridized nanocomposite of layered titanate–reduced graphene oxide (RGO) at elevated temperatures. The precursor layered titanate–RGO nanocomposite is prepared by self‐assembly of anionic RGO nanosheets and cationic TiO₂ nanosols. The calcination of the as‐prepared layered titanate–RGO nanocomposite at 500 °C induces a structural and morphological change of layered titanate nanoplates into anatase TiO₂ nanoparticles without significant modification of the RGO nanosheet. Increasing the heating temperature to 600 °C gives rise to elimination of the RGO component, leading to the formation of sheetlike porous aggregates of RGO‐free TiO₂ nanoparticles. The nanocomposites calcined at 500–700 °C display promising functionality as negative electrodes for lithium ion batteries. Among the present calcined derivatives, the 2D sheet‐shaped aggregate of TiO₂ nanoparticles obtained from calcination at 600 °C delivers the greatest specific discharge capacity with good capacity retention for all current density conditions applied. Such superior electrode performance of the nanocomposite calcined at 600 °C is attributable both to the improved stability of the crystal structure and crystal morphology of titania and to the enhancement of Li⁺ ion transport through the enlargement of mesopores. The present findings clearly demonstrate the usefulness of RGO nanosheets as a platform for 2D‐ordered superstructures of metal oxide nanoparticles with improved electrode performance.     

On the existence of bivalent ions in the apatite channels: A new example—Phosphocalcium cyanamido-apatite

A new apatite, phosphocalcium cyanamido-apatite Ca₁₀(PO₄)₆ CN₂ □, is obtained by treatment under low pressure at high temperature (900–1000°C) of a mixture of the corresponding hydroxyapatite and calcium cyanamide. In this apatite, one CN^2?₂ ion associated with a vacancy replaces two hydroxyl ions in the channels. The formation of a cyanamide-containing apatite also occurs by treatment of an A-type carbonated apatite by ammonia at 600–900°C: in the latter case, the reaction seems more difficult and more limited than in the former. The cyanamido apatite is decomposed by heating in air, and it gives rise first to an A-type carbonated apatite, with release of both ammonia and nitrogen oxide and second to hydroxyapatite by hydrolysis of the A-type carbonated apatite.     

Thermal decomposition of nickel aluminium mixed hydroxides and formation of nickel aluminate spinel

Various nickel aluminium mixed hydroxide samples of different compositions were prepared by co-precipitation from their nitrate solutions using dilute NH₄OH. Additional samples were prepared by impregnation of hydrated Al₂O₃, preheated at 600 and 900°C, with nickel nitrate solution in an equimolar ratio. The thermal decomposition of different mixed solids was studied using DTA. The X-ray investigation of thermal products of the mixed solids was also studied.The results obtained revealed that the presence of NiO up to 33.3 mole % with aluminium oxide much enhanced the degree of crystallinity of the γ-Al₂O₃ phase. In contrast, the presence of Al₂O₃ much retarded the crystallization process of the NiO phase. With the exception of samples containing 20 mole% NiO, all the mixed hydroxide samples, when heated in air at 900°C, led to the formation of well-crystalline Ni Al₂O₄ spinel, alone, or together with either NiO or γ-Al₂O₃, depending on the composition of the mixed oxide samples. The solid containing 20% NiO and heated at 900°C was constituted of amorphous NiO dispersed in γ-Al₂O₃. Heating the nickel nitrate-impregnated Al₂O₃ in air at 800–1000°C led to the formation of Ni Al₂O₄ together with non-reacted NiO and γ-Al₂O₃. The degree of crystallinity of the spinel was found to increase by increasing the calcination temperature of the impregnated solids from 800 to 1000°C and by increasing the preheating temperature of the hydrated Al₂O₃ employed from 600 to 900°C.     

Influence of Temperature and Time on the Stability of Silver in Silica Sol-Gel Glasses

The darkening of silica sol-gel glasses doped with 0.05 mol% silver was studied. Six sols were prepared from TEOS and silver nitrate. Different additives were used, to influence the chemical and physical states of silver: oxidizing or reducing agents (H₂O₂, As₂O₅), colloid stabilizer (sodium citrate) and network modifiers (Li₂O, CaO). Sols were gelified at 60°C and densified at 600°C. The samples without additives and those prepared with H₂O₂ at room temperature even if they were protected from light. With increased temperature, the darkening became samples were heated above, 400°C, reversible bleaching took place. This darkening-bleaching is of thermal nature (“thermochromic effect”) and seems to be determined by a reversible aggregation-disaggregation of tiny silver particles. The presence of sodium citrate, as an additive delayed the darkening effect and the presence of CaO delayed it even further. Lithium oxide inhibited it totally.     

Excess capacity on compound phases of Li2FeTiO4 composite cathode materials synthesized by hydrothermal reaction using optional titanium sources to boost battery performance

Li₂FeTiO₄ composites have been produced using commercial LiAC, FeCl₂ and different titanium sources by hydrothermal synthesis (HS) at 175 °C and subsequent annealing at 700 °C. Impure phase TiO₂, Fe₂O₃ and FeTiO₄ were detected out among the Li₂FeTiO₄ composites with different titanium sources. Micron and nano-sized particles of Li₂FeTiO₄ were prepared from various titanium raw materials, with nano-sized particles predominating when titanium raw materials were layered hydrogen titanate nanowire (H₂Ti₃O₇NW, HTO-NW) and titanium oxide nanotubes (TiO₂NB). The Li₂FeTiO₄ composites synthesized by HTO-NW shows a primary particle size of 50−200 nm of high crystallinity staggered with undissolved nanowire with a diameter size of about 100 nm. The samples using one-dimensional nanometer titanium oxide (TiO₂ NB) as the raw material can get a super high initial discharge capacity of 367.8 mAh/g at the rate of C/10 and excellent cycling stability. The selection of raw materials and adopting multi-phase modification can be considered as an effective strategy to improve the electro-chemical properties of Li₂FeTiO₄ composite cathode materials for the lithium secondary battery.     

Synthesis and Characterization of Uniform Fine Particles of Iron(III) Hydroxide/Oxide

Iron(III) hydroxide was precipitated from the homogeneous solutions, containing variuos amounts of iron(III) nitrate, potassium sulfate, and urea, by heating at 85 °C for different periods of time (5‐30 min). The precipitated solids were either in the form of gel or dispersed particles of different shapes and sizes, depending upon the composition of the reactant mixtures. The as‐prepared solids were amorphous in nature and were formulated as Fe(OH)₃.H₂O. On calcinations at 800 °C for 1 h, the latter converted into crystalline compound, composed of α‐Fe₂O₃ (hematite). The calcined particles retained the original features of their precursors to a maximum extent.     

Nanostructured polymer–titanium composites and titanium oxide through polymer swelling in titania precursor

Polymer (XAD7HP)/Ti⁴⁺ nanocomposites were prepared through the swelling of polymer in titanium (IV) ethoxide as a titanium dioxide precursor. The nanocomposite beads exhibit relatively high porosity different than the porosity of the initial polymer. Thermal treatment of composite particles up to 200 °C in vacuum causes the change of their internal structure. At higher temperature, the components of composite become more tightly packed. Calcination at 600 °C and total removal of polymer produce spherically shaped TiO₂ condensed phase as determined by XRD. Thermally treated composites show the substantial change of pore dimensions within micro- and mesopores. The presence of micropores and their transformation during thermal processing was studied successfully by positron annihilation lifetime spectroscopy (PALS). The results derived from PALS experiment were compared with those obtaining from low-temperature nitrogen adsorption data.     

Synthesis and mechanism research of an ethylene glycol-based sol-gel method for preparing PZT nanopowders

Lead zirconate titanate nanopowders Pb(Zr_0.52Ti_0.48)O₃ (PZT) were prepared by modified sol-gel process in ethylene glycol system with zirconium nitrate as the zirconium source. The research showed that it was critical to add lead acetate after the reaction of zirconium nitrate and tetrabutyl titanate in ethylene glycol system for preparing PZT of exact titanium content. The reaction mechanisms of the sol synthesis, preparation of xerogel and agglutinating process were characterized through using FT-IR, NMR, TG-FTIR, and GC-MS. The experiment proved that ethylene glycol system did not rely on hydrolysis and condensation reactions in the process of the sol formation, but on the formation of chain or network large molecules from complexation of ethylene glycol and all Ti and minor Pd, Zr. In the preparation of xerogel, the complexation reaction was so completed that it formed large molecules network composed of metal and dioxyethyl. Bulk weight loss happened before 350°C in the process of sintering xerogel to prepare PZT nanopowders. Volatile matters and vapor phase decomposition resultants were primarily oxy-compounds including ethylene glycol, aldehyde-ketone compounds, carbon dioxide and nitrate radical conversion matters. After 350°C, primary vapor phase decomposition resultants were carbon dioxide and minor carbonyl compound.     

Preparation of nano and microcrystals of silver using titania xerogel matrix as template

Ag-doped TiO₂ wet gels were prepared by sol?Cgel process using a mixture of titanium isopropoxide and silver nitrate as precursor solution, with Ag:Ti molar ratio of 1:6. After drying, the titanium oxide xerogels were used as template in the preparation of nano and microcrystals of metallic silver. The porous network and the structure of the titania matrix influenced the type and distribution of silver crystal produced on the composite surface. Silver nanoparticles segregated to the surface of titania xerogel during the heating step, giving rise to nanocrystals that coalesced forming microcrystals with different shapes and faceting. The microcrystals grew on the composite surface, reaching sizes between 5 and 20 microns and self-organized of different ways. The xerogel heated at 600 °C formed by anatase, rutile and silver nanoparticles exhibited considerable photocatalytic activity to degrade methylene blue.     

Synthesis and phosphorescence properties of Dy3+ and (Pr3+–Dy3+) in MgTiO3

Using tetra-n-butyl titanate and magnesium nitrate as raw materials, Dy³⁺ and Pr³⁺ ions in the matrix of magnesium titanate (MgTiO₃) was successfully synthesized by a modified solid-state reaction. The mixtures to achieve a solid-state reaction were heated in porcelain crucibles at 600?°C for 2?h, 900?°C for 6?h, and 1000.0?°C for 2?h. The reaction products obtained in an air atmosphere were characterized by X-ray powder diffractions. The optimization of reaction conditions were carried out by thermal gravimetry and differential thermal analysis methods. Surface and elemental analyses were performed by using on SEM instrument. The excitation and emission spectra were recorded by photoluminescence spectrophotometer.     

Synthesis of nanostructured nickel oxide

The process of formation of nickel oxide nanostructured powders by annealing nickel hydroxide in the temperature range 200–700°C was studied. Nickel hydroxide was prepared by precipitation with alkali from nickel nitrate solutions. The annealing process was shown to be multi-step. In the first stage the hydrogel Ni (OH)₂·nH₂O decomposes and partial dehydration of hydroxide occurs. Sizes of the formed particles decrease. At the temperatures above 230°C, further hydrogel decomposition and coalescence of NiO particles proceed. In view of the structural rearrangement of powder at the high temperatures 400–700°C, dehydration process is monitored by the decrease of NiO particles surface area at their coalescence. According to the change in the dehydration mechanism, the hierarchically nanostructured material forms, whose particle sizes are in the range 4–5, 9–12, and 18–40 nm.     

A kinetics-controlled coating method to construct 1D attapulgite @ amorphous titanium oxide nanocomposite with high electrorheological activity

A new kind of one-dimension attapulgite (APG) @ titanium oxide nanoparticles was prepared via kinetics-controlled coating method. By simply altering the ammonia content and reaction time to control the kinetics of hydrolysis and condensation of tetra-n-butyl titanate (TBOT) in ethanol/ammonia mixtures, amorphous titanium oxide nanoparticles can adhere to the APG rods firmly, and the thickness of uniform amorphous titanium oxide shells can be adjusted from 0 to 40 nm. The obtained APG@ titanium oxide nanorods were applied as a new electrorheological (ER) fluid, which showed a promising ER activity. The yield stresses of the APG@ titanium oxide nanorod (40-nm shell thickness) ER fluid under electric field was 2.1 times of the granular titanium oxide ER fluid and 4.1 times of the APG ER fluid. And, the APG@ titanium oxide nanorod ER fluid also exhibited distinctly improved suspended stability.     

Effect of synthesis conditions on the preparation of titanium dioxides from peroxotitanate solution and their photocatalytic activity

Nanosized TiO₂ particles were prepared by the hydrothermal method from the amorphous powders which were precipitated in an aqueous peroxotitanate solution. The physical properties of the nanosized TiO₂ particles prepared were investigated. We also examined the activity of TiO₂ particles as a photocatalyst on the decomposition of orange II. The titania sol can be successfully crystallized to the anatase phase through hydrothermal aging at temperatures higher than 160°C. The particle size increases from 18 to 26 nm as the synthesis temperature increases from 140 to 200°C. Titania particles prepared at 180°C show the highest activity, and titania particles calcined at 400°C show also the highest activity on the photocatalytic decomposition of orange II.     

Sol–gel reactions of titanium alkoxides and water: influence of pH and alkoxy group on cluster formation and properties of the resulting products

In this work the effect of pH and the titanium precursor on the cluster and particle formation during titanium alkoxide based sol–gel processes was investigated using electrospray ionization mass spectrometry (ESI-MS) and dynamic light scattering (DLS). The influence of pH and the titanium precursor on the particle size, morphology, crystallinity and chemical composition of the resulting particles were investigated using differentiel scanning calometry (DSC), X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FT-IR), BET-adsorption isotherms and high resolution transmission electron microscopy (HR-TEM). ESI-MS investigation of the titanium clusters present during the nucleation and growth period showed that the number of titanium atoms in the clusters varied dependent on the alkoxide used. Moreover, it was found that the titanium clusters formed using titanium tetraethoxide (TTE) were smaller than the clusters formed by titanium tetraisopropoxide (TTIP) and titanium tetrabutoxide (TTB) under similar conditions. pH was not found to influence the nature of the titanium clusters present in the sol–gel solution. HR-TEM investigation of the TiO₂ particles prepared at pH 7 and 10 showed that the primary particle size of the particles was around 3 nm. However, it was found that these primary particles aggregated to form larger secondary particles in the size order of 300–500 nm range. At pH 3 the particles grew significantly during the drying process due to destabilization of the colloidal solution leading to the formation of a gel. The highest specific surface area was found for particles synthesized under neutral or alkaline conditions based on TTIP. XRD analysis of the TiO₂ particles showed that the particles synthesized at 25 °C were amorphous. First after heating the samples to above 300 °C the formation of anatase were observed.     

The differential thermal analysis behavior of lead zirconate titanate materials

Differential thermal analysis has been used to examine the reactions involved in the formation of lead zirconate titanate and related materials. The reaction of PbO and TiO₂ produced an exothermic peak near 600°C, while mixtures of PbO and ZrO₂ gave endothermic peak at 760°C. Lead titanate and lead zirconate mixtures showed no evidence of reaction below 900°C. Evidence is presented which suggests that PbO and PbTiO₃ react in the vicinity of 750°C. For ternary mixtures of PbO, titanate, the thermograms indicate a complicated behavior between 600–800°C, depending on the ratios of the reactant materials. The results suggest that the calcination reaction to form lead zirconate titanate is a more complex process than has been recognized. Data on the various phase transitions for the lead zirconate titanate materials are also presented.     

The effect of annealing temperatures on surface properties,hydroxyapatite growth and cell behaviors of TiO2 nanotubes

Well‐ordered TiO₂ nanotubes were prepared by the electrochemical anodization of titanium in an ethylene glycol electrolyte containing 1 wt% NH₄F and 10 wt% H₂O at 20 V for 20 min, followed by annealing. The surface morphology and crystal structure of the samples were examined as a function of the annealing temperature by field emission scanning electron microscopy (FE‐SEM) and X‐ray diffraction (XRD), respectively. Crystallization of the nanotubes to the anatase phase occurred at 450 °C, while rutile formation was observed at 600 °C. Disintegration of the nanotubes was observed at 600 °C and the structure vanished completely at 750 °C. Electrochemical corrosion studies showed that the annealed nanotubes exhibited higher corrosion resistance than the as‐formed nanotubes. The growth of hydroxyapatite on the different TiO₂ nanotubes was also investigated by soaking them in simulated body fluid (SBF). The results indicated that the tubes annealed to a mixture of anatase and rutile was clearly more efficient than that in their amorphous or plain anatase state. The in vitro cell response in terms of cell morphology and proliferation was evaluated using osteoblast cells. The highest cell activity was observed on the TiO₂ nanotubes annealed at 600 °C. Copyright © 2010 John Wiley & Sons, Ltd.     

Heat treatment of rapidly solidified Fe−Cr−Zr−B alloys

The crystallization behaviour of amorphous melt spun Fe_82?x?yCr₁₈Zr_xB_y (x=0–8, y=10–20) ribbons have been investigated using differential scanning calorimetry. The crystallization temperature and crystallization behaviour change with varzing Zr and B content. The microstructural development during annealing of amorphous Fe₆₄Cr₁₈Zr₈B₁₀ has been investigated by a combination of transmission electron microscopy and energy dispersive X-ray microanalysis. Isothermal annealing for 2 h at temperatures in the range 600–1000°C produces a variety of different microstructures depending on the annealing temperature. At 600°C, the amorphous alloy partially crystallizes to a form a microstructure consisting of 9 nm sized bee ferrite grains embedded in an amorphous matrix. At temperatures in the range 700–900°C, the alloy microstructure transforms into a mixture of bee ferrite, faulted fcc MB₁₂ boride particles and tetragonal M₃B boride particles. At 1000°C, the faulted fcc MB₁₂ boride particles are replaced by orthorhombic M₄B boride particles.     

Sol–gel synthesis of macroporous TiO2 from ionic precursors via phase separation route

Monolithic macroporous titanium dioxide (TiO₂) derived from ionic precursors has been successfully prepared via the sol–gel route accompanied by phase separation in the presence of formamide (FA) and poly(vinylpyrrolidone) (PVP). The addition of FA promotes the gelation, whereas PVP enhances the polymerization-induced phase separation. Appropriate choice of the starting compositions allows the production of cocontinuous macroporous TiO₂ monoliths in large dimensions, and controls the size of macropores. The resultant dried gel is amorphous, whereas anatase and rutile phases are precipitated at 500 and 900 °C respectively, without spoiling the macroporous morphology. Nitrogen adsorption–desorption measurements revealed that the dried gels exhibits mesostructure with a median pore size of about 3 nm and BET surface area of 228 m²/g, whereas 15 nm and 73 m²/g for the gels calcined at 600 °C.