The impact of zirconium oxide radiopacifier on the early hydration behaviour of white Portland cement

Zirconium oxide has been identified as a candidate radiopacifying agent for use in Portland cement-based biomaterials. During this study, the impact of 20 wt.% zirconium oxide on the hydration and setting reactions of white Portland cement (WPC) was monitored by powder X-ray diffraction (XRD), ²⁹Si and ²⁷Al magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR), transmission electron microscopy (TEM) and Vicat apparatus.The presence of 20 wt.% zirconium oxide particles in the size-range of 0.2 to 5 μm was found to reduce the initial and final setting times of WPC from 172 to 147 min and 213 to 191 min, respectively. Zirconium oxide did not formally participate in the chemical reactions of the hydrating cement; however, the surface of the zirconium oxide particles presented heterogeneous nucleation sites for the precipitation and growth of the early C-S-H gel products which accelerated the initial setting reactions. The presence of zirconium oxide was found to have little impact on the development of the calcium (sulpho)aluminate hydrate phases.     

Microwave-assisted synthesis and characterization of LaPO4:Re (Re = Ce3+, Eu3+, Tb3+) nanorods

LaPO₄:Re (Re = Ce³⁺, Eu³⁺ and Tb³⁺) nanorods have been successfully synthesized on a large scale by a facile and rapid microwave heating method. The structure, morphology and physical properties of the as-prepared products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence spectroscopy (PL). XRD patterns showed that the as-prepared products had hexagonal structure and high crystallinity and purity. TEM images showed that these LaPO₄:Re nanorods have a high yield and an obvious one-dimensional structure with diameter from 6 nm to 30 nm and length up to 400 nm. The luminescence spectra of the products indicated that different rare-earth ions had been successfully doped in LaPO₄ matrix via the microwave heating method and the actual doping amounts of Re ions were determined by the inductively coupled plasma (ICP).     

Crystalline products and their formation mechanism in thermal hydrolysis of ZrOSO4 solution

Solid products were prepared from mixtures of zirconyl carbonate and sulphuric acid solution under thermal hydrolysis at 240°C. These crystalline products and their formation mechanism were investigated by evaluating the amount of products, and by X-ray diffraction analysis and TEM observation. The solid products precipitated were zirconium oxide sulphates (ZOS, PZOS, ZrOSO₄·H₂O) and m-ZrO₂. The area and thickness of the fine plate-like crystals of ZOS increased with increasing concentration of the solution and hydrothermal treatment time. For thin starting solutions, the precipitation velocity and the amount of PZOS increased. For thick starting solutions, those of ZOS increased. For 0.5 mol/l^–1 ZrOSO₄ solution (ZS0.5) from the thin solution, PZOS crystallized early and m-ZrO₂ crystallized by releasing sulphuric acid ions in PZOS with treatment time. For ZS2.5 from the thick solution, ZrOSO₄·H₂O was crystallized by increasing the proportion of sulphuric acid ions to zirconium ions in the solution, which was caused by ZOS precipitation.     

Molecular structure of preceramic nanozirconooligocarbosilanes

The composition and molecular structure of preceramic nanozirconooligocarbosilanes have been determined using a variety of physicochemical characterization techniques: nuclear magnetic resonance (¹H, ²⁹Si, ¹³C), IR spectroscopy, transmission electron microscopy, gel-permeation chromatography, scanning electron microscopy, thermogravimetry, X-ray photoelectron spectroscopy, and elemental analysis.     

Stability of the structure of compact zirconium nitride ceramics to irradiation with high-energy xenon ions

X-ray diffraction and transmission electron microscopy (TEM) data demonstrate that irradiation with high-energy ⁺²⁴Xe¹³⁶ ions causes no changes in the grain microstructure of compact zirconium nitride ceramics. According to Raman spectroscopy and high-resolution TEM data, the irradiated ceramics may have local distortions of the zirconium nitride lattice within regions on the order of the lattice parameter in size.     

Synthesis of brush-like CdS nanorod arrays through a novel hydrothermal reaction of simultaneous solvent-oxidation-hydrolysis

Brush-like CdS arrays composed of well-arranged nanorods have been successfully synthesized for the first time through a novel chemical reaction under the low-temperature hydrothermal condition. The reaction can be described as the solvent-oxidation-hydrolysis reaction among Cd, H₂O and thiourea. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence (PL). TEM results showed that these nanorods were about 20?nm wide with lengths varying from 1.25?µm to 3.5?µm. XRD pattern indicated that as-obtained CdS was hexagonal phase with good crystallinity. PL spectrum showed the products had novel optical property from the bulk counterpart. The formation mechanism was also explored.     

Solvothermal synthesis and characterization of acicular α-Fe2O3 nanoparticles

Nanometer-sized α-Fe₂O₃ particles have been prepared by a simple solvothermal method using ferric acetylacetonate as a precursor. The products were characterized by X-ray diffraction (XRD), energy dispersive X-ray microanalysis (EDAX), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transition electron microscopy (TEM), infrared spectroscopy (IR) and thermal analysis (TG-DTA). XRD indicates that the product is single-phase α-Fe₂O₃ with rhombohedral structure. Bundles of acicular shaped nanoparticles are seen in TEM images with an aspect ratio ～ 12; typically 8–12 nm wide and over 150 nm long. The α-Fe₂O₃ nanoparticles posses a high thermal stability, as observed on thermal analysis traces.     

Chemical synthesis of environment-friendly nanosized yellow titanate pigments

As yellow pigments, nanosized rutile structured Ni_0.1W_0.1Ti_0.8O₂ and priderite structured BaNiTi₇O₁₆ have been prepared through pyrolysis of precursor solution containing nickel nitrate, dimethyl tungstate, titanium oxalate, triethanolamine (TEA) for the former composition and barium nitrate, nickel nitrate, titanium oxalate, TEA for the later composition, respectively. In the reaction, TEA acts to minimize the agglomeration in the products through formation of a highly branched polymeric framework, which anchors the metal ions for producing nanocrystalline powders. The rutile and priderite structured titanates obtained on heat-treatment of the precursor powders at 800 °C and 850 °C, respectively, have been characterized by XRD, TGA-DTA, BET surface area measurement, UV-vis spectroscopy, CIE L^*a^*b^* colour parameter measurements, TEM and HRTEM. XRD reveals the purity of the resulting rutile and priderite phases. Their crystallite sizes, average particle sizes and specific surface areas determined from XRD, TEM, and BET surface area measurement are found to be in the range between 25 nm and 30 nm, 25-45 nm and 100-120 m²/g, respectively, for both compositions.     

Hydrothermal synthesis of monodisperse CeO2 nanocubes

Monodisperse CeO₂ nanocubes have been fabricated via an acrylamide-assisted hydrothermal route. NH₃ and acrylic acid from the hydrolysis of acrylamide act as OH⁻ provider and capping reagent, respectively. The structure and morphology of the products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), field-emission scanning electron microscopy (FE-SEM) and Fourier transformed infrared (FT-IR). The products have a cubic morphology with a mean size of 200 nm. The possible formation mechanism has been discussed based on the experimental results.     

Single crystalline ZnO nanorods grown by a simple hydrothermal process

Single crystalline ZnO nanorods with wurtzite structure have been prepared by a simple hydrothermal process. The microstructure and composition of the products were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM, energy dispersive X-ray spectrum (EDS) and Raman spectrum. The nanorods have diameters ranging from 100 nm to 800 nm and length of longer than 10 µm. Raman peak at 437.8 cm^− 1 displays the characteristic peak of wurtzite ZnO. Photoluminescence (PL) spectrum shows a blue light emission at 441 nm, which is related to radiative recombination of photo-generated holes with singularly ionized oxygen vacancies.     

Microwave-assisted hydrothermal synthesis of Ni(OH)2 architectures and their in situ thermal convention to NiO

The Ni(OH)₂ architectures with flower-like morphology assembled from nanosheets have been successfully synthesized through a microwave-assisted hydrothermal method using urea as a hydrolysis-controlling agent and polyethylene glycol (PEG) as a surfactant. The NiO architectures with similar morphology were obtained by a simple thermal decomposition process of the precursor Ni(OH)₂. The as-obtained products were well characterized by XRD, TG-DTA, SEM, TEM, FTIR and UV–Vis. The experimental results shown that flower-like Ni(OH)₂ architectures with a diameter of 2.5–4.0 μm are assembled from nanosheets with a thickness of 10–20 nm and width of 0.5–1.5 μm. The UV–Vis experimental results shown that the absorption edge of the NiO architectures have a blue-shift with the increasing of the calcination temperature.     

(Eu-Nb)-codoped TiO2 nanopowders synthesized via Ar/O2 radio frequency thermal plasma oxidation processing: Phase composition and photoluminescence properties through energy transfer

(Eu³⁺-Nb⁵⁺)-codoped TiO₂ nanopowders have been prepared by Ar/O₂ radio frequency (RF) thermal plasma oxidizing liquid precursor mists, with various addition contents of dopants (molar ratio of Eu³⁺:Nb⁵⁺ = 1:1). Characterizations have been performed by the combined studies of XRD, TEM, Raman spectra, UV-vis spectroscopy, and excitation and PL spectra. The plasma-generated nanopowders mainly consist of anatase and rutile polymorphs. Doping Nb⁵⁺ cannot have appreciable influence on Eu³⁺ solubility (0.5 at.%) in the TiO₂ host lattice, but can significantly inhibit the increase of rutile weight fraction for TiO₂. 617 nm PL intensity at 350 nm indirect excitation through energy transfer is considerably weaker than that at 467 nm direct excitation, indicating that a defect state level in the TiO₂ host lattice might be lowered below the excited state of Eu³⁺ by doping Nb⁵⁺, which is conceivable from a relatively large amount of oxygen deficiencies yielded in the TiO₂ host lattice.     

Synthesis of lanthanum zirconium oxide nanomaterials through composite-hydroxide-mediated approach

A novel thermal barrier coating material, lanthanum zirconium oxide (La₂Zr₂O₇) has been synthesized through the composite-hydroxide-mediated method at low temperature. The phase structures, morphology, thermal stability and thermal conductivity of the as-synthesized La₂Zr₂O₇ were investigated systematically. The X-ray diffraction (XRD) patterns revealed a single phase with cubic pyrochlore structure for La₂Zr₂O₇ after treated at 1300 °C for 100 h. The transmission electron microscope (TEM) and scanning electron microscope (SEM) analyses showed that the sample was made up of sphere-like nanoparticles with the size between 50 and 100 nm. Furthermore, the thermal analysis result demonstrated the La₂Zr₂O₇ sample had high thermal stability even at 1300 °C. As the temperature increased to 1200 °C, the thermal conductivity value could be as low as 1.75 W m^?1 K^?1. Due to the high-temperature stability and lower thermal conductivity, the La₂Zr₂O₇ material is expected to be a promising candidate for the use of thermal barrier coatings.     

Iodine-Assisted Solid-State Synthesis and Characterization of Nanocrystalline Zirconium Diboride Nanosheets

A solid-state route was developed to prepare zirconium diboride nanosheets with the dimension of about 500 nm and thickness of about 20 nm from zirconium dioxide, iodine and sodium borohydride at 700°C in an autoclave reactor. The obtained ZrB₂ product was investigated by X-ray diffraction, scanning electron microscope and transmission electron microscopy. The obtained product was also studied by thermogravimetric analysis. It had good thermal stability and oxidation resistance below 400°C in air. Furthermore, the possible formation mechanism of ZrB₂ was also discussed.     

Synthesis of La3+ doped nanocrystalline ceria powder by urea–formaldehyde gel combustion route

Nanocrystalline ceria powders doped with various concentrations of lanthanum oxide have been prepared following gel combustion route using for the first time urea–formaldehyde as fuel. The synthesized products were characterized by XRD, FESEM, TEM, PL and UV–vis spectroscopy. Peak positions of XRD were refined and the lattice parameters were obtained by applying Cohen's method. Unit cell parameter increases with concentration of La³⁺ ion and the variation is consistently linear. XRD calculations showed the dependence of crystallite size on dopant concentrations at lower level. TEM observation revealed unagglomerated particles to be single crystals in the average range of 20–30 nm. Band gap of the La³⁺ doped ceria materials does not change with doping. Spectroscopic experiments proved the existence of Ce³⁺ in the formed powder.     

Deposition of zirconium monoxide glomeruli by laser ablation

 Zirconia is evermore in demand as a thermal barrier coating (TBC) for energy economy and metal protection. Several methods are in use to produce the coatings, including sol-gel, CVD and PVD, however laser ablation, has not been notoriously reported. The present work presents the use of a N₂-SF₆ pulsed laser beam, focused (6 J/cm²) on a metallic zirconium target in a reactor with low pressures of oxygen or helium. Sparks were observed in oxygen atmosphere, which denoted oxidation of laser ablated zirconium. Transmission Electron Microscopy (TEM) and optical interferometric microscopy, identifying small agglomerates of ZrO (cubic phase) studied the crystallographic structure and morphology of the obtained particles. The pyrophorous oxidation phenomenon of ablated Zr droplets is described and interpreted by thermochemical simulations, and the deposited morphology is characterized. Received: 23 March 1998 / Accepted: 30 July 1998     

A novel sol-gel synthetic route to alumina nanofibers via aluminum nitrate and hexamethylenetetramine

Attempts have been made to prepare alumina nanofibers by hydrolyzing aluminum nitrate in the presence of hexamethylenetetramine (HMTA) followed by the supercritical fluid drying (SCFD) process. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and nitrogen physisorption. The results show that δ-Al₂O₃ nanofibers with diameter of 2 nm, length of 50 nm and with BET surface areas of 412.6 m² g^− 1 were successfully synthesized. The thermal evolution of the fibers and the role of hexamethylenetetramine were also briefly discussed.     

Rapid preparation and characterization of Dy2Zr2O7 nanocrystals

Ultrafine fluorite type Dy₂Zr₂O₇ nanocrystals with cubic structure were fabricated at relatively low temperature by stearic acid method (SAM) using zirconium(IV) butoxide and dysprosium nitrate as raw materials, stearic acid as solvent and dispersant. The fabrication process was monitored by thermogravimetric analysis and differential thermal analysis (TG-DTA) and Fourier transform infrared spectroscopy (FT-IR). The obtained products were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectrometer (EDS) and UV-vis absorption spectroscopy. A single phase of Dy₂Zr₂O₇ with high crystallinity was formed at 800 °C. The interplanar distances measured from the HRTEM image were 0.284 and 0.256 nm, respectively, coinciding with the theoretical values.     

A new fluorescent film sensor for Pb(II) ions developed by simulating bio-mineralization process synthesizing of ZnS/CS nanocomposite

Chitosan/zinc sulfide (CS/ZnS) nano-composite films have been prepared by simulating bio-mineralization process. Factors affecting the hydrothermal stability and fluorescence properties of the films have been studied. Furthermore, the sensing properties of nano-composite films to lead ions have been systematically investigated. SEM and TEM observations showed that the size of ZnS particles is 70 nm, and the particles are evenly distributed within the CS films. The fluorescence emission of the nano-composite films indicates that the sizes of real fluorescing ZnS particles are less than 20 nm. This suggests that ZnS particles observed via SEM and TEM may be aggregates of smaller ZnS particles, and the smaller particles may be separated by the organics. The fluorescence emission (363 nm) of the nano-composite films is very sensitive to the presence of Pb ions. C_(Pb²⁺₎ increased from 0 to 664.2 mg L⁻¹ increases the emission dramatically. The emission is hardly affected by common ions in water, except for the iron ions. The films may be developed as excellent sensing films for Pb ions in water.     

Synthesis of nanocrystalline materials through reverse micelles: A versatile methodology for synthesis of complex metal oxides

We have been successful in obtaining monophasic nanosized oxides with varying chemical compositions using the reverse micellar method. Here we describe our methodology to obtain important metal oxides like ceria, zirconia and zinc oxide. The oxalate of cerium, zirconium and zinc were synthesized using the reverse micellar route. While nanorods of zinc oxalate with dimension, 120 nm in diameter and 600 nm in length, could be obtained, whereas spherical particles of size, 4–6 nm, were obtained for cerium oxalate. These precursors were heated to form their respective oxides. Mixture of nanorods and nanoparticles of cerium oxide was obtained. ZrO₂ nanoparticles of 3–4 nm size were obtained by the thermal decomposition of zirconium oxalate precursor. ZnO nanoparticles (55 nm) were obtained by the decomposition of zinc oxalate nanorods. Photoluminescence (PL) studies at 20 K shows the presence of three peaks corresponding to free excitonic emission, free to bound and donor-acceptor transitions. We also synthesized nanoparticles corresponding to Ba_1−x Pb _x ZrO₃ using the reverse micellar route. The dielectric constant and loss were stable with frequency and temperature for the solid solution.