Preparation of uniform porous hydroxyapatite biomaterials by a new method

In this paper, a new method of preparation of uniform porous hydroxyapatite biomaterials was reported. In order to obtain uniform porous biomaterials, disk samples were formed by the mixture of hydroxyapatite (HAP) powders and monodispersed polystyrene microspheres, and then HAP uniform porous materials with different diameter and different porosity (diameter: 436 ± 25 nm, 892 ± 20 nm and 1890 ± 20 nm, porosity: 46.5%, 41.3% and 34.7%, respectively) were prepared by sintering these disk samples at 1250 °C for 5 h. The pure phase of HAP powders fabricated by the hydrothermal technology was confirmed by X-ray diffraction (XRD). The surface and size distribution of pores in HAP biomaterials were observed by scanning electron microscopy (SEM), and the pore size distribution in porous HAP biomaterials was tested by mercury intrusion method.     

Homogeneous ZnO Nanoparticles by Flame Spray Pyrolysis

Zinc oxide (ZnO) nanoparticles were made by flame spray pyrolysis (FSP) of zinc acrylate–methanol–acetic acid solution. The effect of solution feed rate on particle specific surface area (SSA) and crystalline size was examined. The average primary particle diameter can be controlled from 10 to 20nm by the solution feed rate. All powders were crystalline zincite. The primary particle diameter observed by transmission electron microscopy (TEM) was in agreement with the equivalent average primary particle diameter calculated from the SSA as well as with the crystalline size calculated from the X-ray diffraction (XRD) patterns for all powders, indicating that the primary particles were rather uniform in diameter and single crystals. Increasing the solution feed rate increases the flame height, and therefore coalescence and/or surface growth was enhanced, resulting in larger primary particles. Compared with ZnO nanoparticles made by other processes, the FSP-made powder exhibits some of the smallest and most homogeneous primary particles. Furthermore, the FSP-made powder has comparable BET equivalent primary particle diameter with but higher crystallinity than sol–gel derived ZnO powders.     

Effect of calcination temperature on porous titania prepared from industrial titanyl sulfate solution

Porous titania with anatase phase was prepared via thermal hydrolysis of industrial titanyl sulfate solution, and subsequent calcination at different temperature. The as-prepared powders were characterized by TG, DSC, XRD, particle size distribution test, N₂ adsorption-desorption isotherm and SEM. Raising calcination temperature could accelerate the crystal growth, enlarge its specific surface area, pore diameter, and improve its photocatalytic activity. While too high temperature could destroy the pore structure even collapse. The optimal calcination temperature is 550 °C, and the obtained sample showed good thermal stability and high photocatalytic activity, with specific surface area of 189.3 m²/g and higher degree of crystallinity, and its photocatalytic degradation rate of methylene blue was of 95.76%.     

Gas-phase Crystallization of Titanium Dioxide Nanoparticles

We have investigated the development of crystal morphology and phase in ultrafine titanium dioxide particles. The particles were produced by a droplet-to-particle method starting from propanolic titanium tetraisopropoxide solution, and calcined in a vertical aerosol reactor in air. Mobility size classified 40-nm diameter particles were conveyed to the aerosol reactor to investigate particle size changes at 20–1200°C with 5–1-s residence time. In addition, polydisperse particles were used to study morphology and phase formation by electron microscopy. According to differential mobility analysis, the particle diameter was reduced to 21–23-nm at 600°C and above. Precursor decomposition occurred between 20°C and 500°C. The increased mobility particle size at 700°C and above was observed to coincide with irregular particles at 700°C and 800°C and faceted particles between 900°C and 1200°C, according to transmission electron microscopy. The faceted anatase particles were observed to approach a minimized surface energy by forming {101} and {001} crystallographic surfaces. Anatase phase was observed at 500–1200°C and above 600°C the particles were single crystals. Indications of minor rutile formation were observed at 1200°C. The relatively stable anatase phase vs. temperature is attributed to the defect free structure of the observed particles and a lack of crystal–crystal attachment points.     

Physical Characteristics and Sintering Behavior of MgO-Doped ZrO2nanoparticles

Nanosized particles of 13mol% MgO-doped ZrO₂ with a narrow distribution of pore sizes were prepared by the coprecipitation technique using optimized parameters of synthesis. Transmission electron microscopy analysis of the calcined powder reveals that the majority of the particles have grain sizes in the 10–20nm range. From nitrogen adsorption analysis an average particle size of 13nm was estimated, which is similar to the average pore size diameter (12nm). Besides the unimodal distribution of pore sizes, the linear shrinkage curve of a powder compact exhibits several inflexions indicating different rates of densification up to 1600°C. After sintering at 1600°C for 2h, the microstructure features of a compact are characteristics of the intermediate stage with interconnected porosity preferentially observed at grain boundaries. These results are explained as a size effect of nanoparticles of magnesia-doped zirconia during sintering.     

Microstructure and mechanical characteristics of nanodiamond-SiC compacts

Superhard nanodiamond-SiC ceramics are prepared by infiltrating liquid Si into porous nanodiamond compacts under pressure. Synthesized samples are 2.2 mm thick and 3–4 mm in diameter. The effect of particle size of dynamically synthesized nanodiamond powders on silicon infiltration and SiC phase formation is studied. It is established that silicon does not penetrate into the pores of nanodiamond powders if the original particle size is smaller than 0.5–1.0 μm. The critical pore size for infiltration is 100–200 nm. A study of the microstructure of the samples showed the presence of the nanometer-and submicron-scale SiC phase. The ultrasound velocities are measured in the prepared compacts, and the elastic moduli are calculated. __________ Translated from Fizika Tverdogo Tela, Vol. 46, No. 4, 2004, pp. 734–736. Original Russian Text Copyright ? 2004 by Ekimov, Gromnitskaya, Mazalov, Pal’, Pichugin, Gierlotka, Palosz, Kozubowski.     

Effect of Hydrolysis Conditions on the Direct Formation of Nanoparticles of Ceria–Zirconia Solid Solutions from Acidic Aqueous Solutions

The effect of the cation concentration, hydrolysis temperature, and composition in the CeO₂–ZrO₂ system on the direct precipitation of ceria–zirconia solid solutions and the structure of the precipitates from acidic aqueous solutions of (NH₄)₂Ce(NO₃)₆ and ZrOCl₂ by hydrolysis under hydrothermal conditions were investigated. Nanometer-sized (8–10 nm) ceria–zirconia solid solution particles in a composition range of 0 to 60 mol% ZrO₂ were directly precipitated from the solutions with total metal cation concentration less than 0.2 mol/dm³ by simultaneous thermal hydrolysis at 150–240°C. The crystalline phase of the precipitates gradually changed from cubic and/or tetragonal to monoclinic with increasing the cation concentration of the solution from 0.2 to 0.8 mol/dm³ at the starting composition of 50 mol% ZrO₂ under hydrolysis condition of 150°C for 48 h, which was attributed to decrease in the supply of hydrolyzed Ce component caused by decrease in the hydrolysis ratio of (NH₄)₂Ce(NO₃)₆. Ceria–zirconia solid solutions containing large amount of ZrO₂ maintained high specific surface area and small-sized crystallite after heat-treatment at 900–1000°C for 1 h.     

Study of latent and etched tracks by a charged particle transmission technique

A recently suggested technique for non-destructive investigation of inhomogeneities in thin objects, which is based on the measurement of the energy spectra of charged particles transmitted through the object, is used for the study of thermal annealing of 10–20 μm thick polyethylene terephtalate, polypropylene and polycarbonate foils irradiated with 1–10 MeV/amu heavy ions. At elevated temperature a foil linear contraction is observed on pristine and irradiated material. Also the foil roughness increases with increasing temperature. On the same foils with etched pores 0.5–1.0 μm in diameter, the thermal annealing results in gradual closing of the pores up to about 30% of their initial diameter at the temperatures of 150–175°C. At higher temperatures the pore diameter increases and achieves its initial value.     

Characterization of nanosized TiO2 synthesized inside a porous glass-ceramic monolith by metallo-organic decomposition process

This work reports the preparation of TiO₂ by decomposition of a metallo-organic precursor (MOD process) in the pores of an α-NbPO₅ glass-ceramic monolith (PGC-NbP) and the study of the TiO₂ anatase-rutile transition phase. The impregnation of titanium di-(propoxy)-di-(2-ethylhexanoate) in the PGC-NbP was confirmed by diffuse reflectance infrared spectroscopy. In the restrictive porous environment the decomposition of the metallo-organic compound exhibits a lower initial decomposition temperature but a higher final decomposition temperature, in comparison to the free precursor. The pure TiO₂ rutile phase is formed only above 700 °C when the titanium precursor is decomposed outside the pores. The TiO₂ anatase obtained inside the PGC-NbP was stabilized up to 750 °C and exhibits a smaller average crystallite size in comparison with the MOD process performed without PGC-NbP. Furthemore, the temperature of the TiO₂ anatase-rutile transformation depends on crystallite size, which was provided by XRD and Raman spectroscopy. The precursor impregnation-decomposition cycle revealed a linear mass increment inside PGC-NbP. Micro-Raman spectroscopy shows the presence of a gradient concentration of the TiO₂ inside the PGC-NbP. The use of the MOD process in the PGC-NbP pores has several advantages: control of the amount and the nature of the phase formed and preservation of the pore structure of PGC-NbP for subsequent treatments and reactions.     

Aerosol Synthesis of Fullerene Nanocrystals in Controlled Flow Reactor Conditions

Fullerene nanocrystals in the size range 30–300 nm were produced starting from atomized droplets of C₆₀ in toluene. The experiments were carried out under well-controlled conditions in a laminar flow reactor at temperatures of 20–600°C. Particle transformation and crystallization mechanisms of polydisperse and monodisperse (size classified) fullerene aerosol particles were studied. The results show that fullerene particles are roughly spherical having pores and voids at temperatures of 300°C and below. Particles are already crystalline and likely fine-grained at 20°C and they are polycrystalline at temperatures up to 300°C. At 400°C monodisperse particles evaporate almost completely due to their low mass concentration. Polydisperse particles are crystalline, but sometimes heavily faulted. At 500°C most of the particles are clearly faceted. In certain conditions, almost all particles are hexagonal platelets having planar defects parallel to large (111) faces. We suggest that at 500°C fullerene particles are partially vaporized forming residuals with lamellar defects such as twins and stacking faults, which promote crystal growth during synthesis. Subsequently fullerene vapor is condensed on faces with defects and hexagonal particles are grown by a re-entrant corner growth mechanism. At 600°C particles are single crystals, but they have a less distinct shape due to higher vaporization of fullerene. The final size and shape of the particles are mainly determined at the reactor outlet in the short time when the aerosol cools.     

Synthesis and thermal stability of gold nanowires within monolithic mesoporous silica

This paper describes the preparation, by a novel and simple method, and the thermal stability of gold nanowires within monolithic mesoporous silica, involving soaking monolithic mesoporous silica in HAuCl₄ aqueous solution, followed by drying and subsequent step-annealing. It has been shown that reduction of Au³⁺ within silica pores can occur during the drying process at 80 °C without any special reduction treatment. After initial annealing at 300 °C, Au nanowires are formed within the pores and are stable at temperatures up to 500 °C. Increasing the annealing temperature leads to a wire-to-rod-to-sphere morphological transformation of the Au nanowires. The surface-mediated reducing groups (-OH) on the silica pore are responsible for the low-temperature reduction of Au³⁺ ions, and the formation of Au nanowires is attributed to the uni-directional diffusion of Au atoms and the confinement of the pore channels. Spheroidization and breaking at some defects in the Au nanowires during annealing at elevated temperature result in the wire-to-rod-to-sphere transformation, accompanied by a blue-shift of the surface plasmon resonance over a very wide region in the optical spectrum. PACS 81.07.-b; 81.40.-z; 81.05.Rm     

Elaboration of nanostructured Eu3+-doped Gd2O3 phosphor fine spherical powders using polyol-mediated synthesis

Red-emitting Eu³⁺-doped Gd₂O₃ spherical powders were directly precipitated using a polyol method. The as-synthesized powders consist of agglomerates with a spherical shape and a size ranging between 0.4 and 0.6 μm. Each agglomerate is nanostructured and consists of a packing of nanocrystallites (3–5 nm) of a bcc oxide phase whose luminescence presents original features in comparison with bulk materials. The powders were further calcinated and the size of both crystallites and agglomerates, the crystalline structure and the luminescence were studied as a function of the annealing temperature. For temperatures lower than 900 °C, the samples obtained are highly crystalline and possess the classical Eu³⁺ red luminescence. For optimized temperature, the morphology of the particles can be preserved leading to spherical, dense, luminescent and almost monodisperse oxide powders, 0.5 μm in size. PACS 81.07.Bc; 81.07.Wx; 81.16.Be; 75.50.-y; 42.70.-a     

Electromagnetic radiation and variations in the conductivity of muscovite specimens during dehydration

The authors give experimental results on the measurement of electromagnetic radiation and electrical conductivity of muscovite specimens during heating or cooling in the temperature range from 20 to 600°C. It was established that at some temperatures there were variations in the electrical conductivity with the attendant onset of pulsed electromagnetic radiation in the radio-frequency range from 247.5 kHz to 35.8 MHz. The oscillations in the conductivity and the maximum intensity of electromagnetic radiation coincide with the boiling points of weakly bound water at about 100°C, the electrical activity of centers on the surface of micas (20–450°C), the temperatures of crystallization of muscovite in a hydrothermal process from 480 to 160°C, and phase transitions at 550–590°C. The electromagnetic radiation is probably due to fluctuations in the defects in the mineral under thermal excitation and adhesion processes as a result of dehydration of the muscovite.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 27–33.     

Low temperature growth and dimension- dependent photoluminescence efficiency of semiconductor nanowires

Low temperature growth and dimension dependent photoluminescence (PL) efficiency of semiconductor nanowires were investigated with CdS as a model system. The CdS nanowires were prepared with a simple, low temperature metal-organic chemical vapor deposition (MOCVD) process via the vapor–liquid–solid (VLS) mechanism. The low growth temperature of 360 °C was made possible with a newly developed single-source precursor of CdS and by using sputtered Au as the catalyst for the VLS growth. The length and diameter of the nanowires were adjusted by reaction time and sputtering conditions of Au, respectively. Nanowires of up to several μm in length and 20 to 200 nm in diameter were obtained. The PL quantum yield of the nanowires was found to decrease with increasing wire length, but to increase with decreasing wire diameter. This dimension-dependent PL efficiency of one-dimensional nanostructure, unlikely resulting from the quantum size confinement effect, appears to be a new observation that carries application significance. PACS 74.25.Gz; 78.55.Et; 78.67.Lt     

Microstructural characterization of nanosized YMnO<Subscript>3</Subscript> powders: the size effect

Nanosized YMnO₃ powders of grain size below 100 nm were prepared and characterized by various techniques to understand the size effect of the microstructures and the stoichiometry of the as-prepared powders. It is revealed that the grain surface oxidization state depends on grain size, with a lower oxidization state for the smaller grains. Raman and infrared spectroscopy studies show a remarkable broadening of the reflection peaks with decreasing grain size, identifying the significant surface structure relaxation effect for small-size powders. The ferromagnetic–antiferromagnetic transition around 65–68 °C is determined by the specific-heat measurement, also indicating the remarkable size dependence. PACS 75.47.Lx; 81.07.Wx; 74.62.Yb     

Dynamics of plastic and liquid cyclohexane in bulk and in porous glasses studied by NMR methods

Cyclohexane was investigated both in bulk and in porous glasses with pore diameters between 4 and 208 nm in the temperature range 136 K≤T≤300 K. The methods involved were field-cycling NMR relaxometry, field-gradient NMR diffusometry, transverse-relaxation spectroscopy, and differential scanning calorimetry (DSC). The field-cycling data for the bulk material can best be described assuming translational modulation of intermolecular dipole-dipole coupling. This interpretation is confirmed by experiments with different degrees of deuteration, and is in accordance with diffusion coefficients determined with the aid of field-gradient diffusometry. The confinement in pores produces substantial changes in the phase behaviour and in molecular dynamics. For pore diameters of 30 nm and above, a non-frozen two monolayers thick film on the surface retains a diffusivity about one order of magnitude lower than in the bulk liquid, but two orders of magnitude larger than in the bulk plastic phase. Experiments indicate an exchange mechanism between this layer and the crystallite inside the pore. In glass with a pore diameter of 4 nm, all applied methods corroborate DSC results of the virtual absence of a phase transition and reveal a continuously decreasing translational mobility down to temperatures more than 100 K below the bulk liquid/cubic phase transition temperature.     

Melting mechanism of monolayers adsorbed in cylindrical pores: An influence of the pore wall roughness

We have analyzed the mechanism of melting of layers adsorbed in cylindrical pores of porous materials. The goal was to understand the melting mechanism of simple fluids adsorbed in pores with heterogeneous wall surface. The studied system was a monolayer of methane molecules adsorbed in MCM-41 pore of diameter d = 4 nm. Both experimental (neutron scattering) and simulation (Monte Carlo) results proved extremely strong influence of the wall roughness on the melting mechanism. The most striking difference between melting on smooth and rough surfaces was in the temperatures of the transition. The transformation between solid-like and liquid-like monolayer phases adsorbed on a rough surface was observed in a very large temperature range and the solid like properties were observed even above the bulk methane melting temperature.     

Free-standing and vertically aligned InP nanowires grown by metalorganic vapor phase epitaxy

Metalorganic vapor phase epitaxial technique has been used to grow surface mounted vertical and uniform cross-sectional InP nanowires on a wafer scale basis. The growth was carried out under the vapor–liquid–solid mechanism using Au colloidal nanoparticles of nominal diameters of 10 and 20 nm, and their properties were compared. The effect of the pre-growth anneals and growth temperatures on the stability of the nanowires were studied in detail. Scanning electron microscopy and transmission electron microscopic studies showed average diameter of the nanowires in the range of 20–35 nm, and of length 700 nm with growth direction of 1 1 1. Room temperature photoluminescence measurements of the nanowires grown on 10 and 20 nm Au particles showed strong peaks, which were blue shifted by 25 and 32 meV, respectively, compared to bulk InP.     

Rapid thermal annealing and titanium silicide formation

Titanium silcides have been formed on monocrystalline (111) silicon substrates by rapid thermal annealing (RTA) of Ti layers deposited on Si at 700–800 °C for 1 to 240 s. The phase composition is dependent on the annealing temperature and time: at 700° and 750 °C for short annealing, TiSi and TiSi₂ are observed. At 800 °C and by increasing the exposure time at 700 ° and 750 °C, only TiSi₂ is detected. The growth of the total silicide thickness is found to be faster for RTA than for conventional furnace annealing and governed by two different mechanisms depending on the phases formed: in the range 700–750 °C, and 750–800 °C, activation-energy values of 2.6 ± 0.2 and 1.5 ±0.2 eV are found, respectively.For a thin deposited Ti layer (< 100 nm), the whole Ti is finally transformed into TiSi₂ with 20@ cm resistivity. For thicker Ti thicknesses, titanium oxide stops the reaction.     

Disorder-dependent photoluminescence in Ba0.8Ca0.2TiO3 at room temperature

The photoluminescence (PL) emission in structurally disordered Ba_0.8Ca_0.2TiO₃ (BCT20) powders was observed at room temperature with laser excitation at lines 355 and 460 nm. The structural evolution perovskite-like titanate BCT20 powders prepared by a soft chemical processing at different annealing temperatures were accompanied by X-ray diffraction (XRD) and X-ray absorption near-edge structure (XANES). Intermediate oxycarbonate phase was identified and your influence with PL emission was discarding. BCT20 annealed at 500 °C displays intense PL emission. The results indicate relationship between broad PL band and order-disorder degree.