Hydrothermal synthesis of composites of well-crystallized hydroxyapatite and poly(vinyl alcohol) hydrogel

Composites of hydroxyapatite (HAp) and poly(vinyl alcohol) (PVA) hydrogel were fabricated by the hydrothermal treatment of calcium phosphate powder. Alpha-tricalcium phosphate (α-TCP) or beta-tricalcium phosphate (β-TCP) powder was dispersed in PVA hydrogel and exposed to water vapor at 120 °C, 140 °C or 160 °C for 6 h. Low crystallinity HAp was formed in specimens prepared from α-TCP and PVA hydrogel prior to hydrothermal treatment, which was caused by hydrolysis of α-TCP. This allowed specimen shape to be retained after hydrothermal treatment. β-TCP showed less reactivity in forming HAp in the PVA hydrogel, which led to the formation of large rod-shaped crystals approximately 15 μm in length. Specimens from β-TCP and PVA were too soft to retain their shape after hydrothermal treatment. HAp with controlled morphology was prepared using different types of tricalcium phosphate precursor. The application of α-TCP allowed the in situ fabrication of HAp/PVA composites.     

Template-free synthesis of ZnWO4 powders via hydrothermal process in a wide pH range

ZnWO₄ powders with different morphologies were fabricated through a template-free hydrothermal method at 180 °C for 8 h in a wide pH range. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-visible and luminescence spectrophotometers were applied to study the effects of pH values on crystallinity, morphology, optical and luminescence properties. The XRD results showed that the WO₃ + ZnWO₄, ZnWO₄, and ZnO phases could form after hydrothermal processing at 180 °C for 8 h with the pH values of 1, 3-11, and 13, respectively. The SEM and TEM observation revealed that the morphological transformation of ZnWO₄ powders occurred with an increase in pH values as follows: star anise-, peony-, and desert rose-like microstructures and soya bean- and rod-like nanostructures. The highest luminescence intensity was found to be in sample consisting of star anise-like crystallites among all the samples due to the presence of larger particles with high crystallinity resulted from the favorable pH under the current hydrothermal conditions.     

Fibrous growth of strontium substituted hydroxyapatite and its drug release

The effect of strontium on the crystallization of helical ribbon of hydroxyapatite (HAp) was investigated by single diffusion technique in silica gel matrix at 27 °C and physiological pH. Fibers of HAp were obtained on addition of strontium. The length of the HAp fibers, were found to decrease as the strontium substitution increases. The presence of strontium ion increased the crystallinity as well as crystallite size of HAp. The strontium substituted HAp (Sr-HAp) has similar stoichiometry to that of biological apatite. Sr-HAp was found to have increased surface area (35%) compared to control. Further, strontium substitution leads to an enhancement of in vitro bioactivity. The cumulative in-vitro amoxicillin drug release in phosphate buffer solution (PBS, pH 7.2) showed a prolonged release profile for Sr-HAp.     

Precipitation and its effect on age-hardening behavior of as-cast Mg–Gd–Y alloy

Microstructures evolution of Mg–7Gd–3Y–0.4Zr (wt.%) alloy during aging at 200 °C was investigated by using optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results showed that the alloy could exhibit remarkable age-hardening response by optimum solid solution and aging conditions. Especially, the highest Vickers hardness (HV) of this alloy was obtained when it was aged at 200 °C for 120 h, which was mainly attributed to a dense distribution of β′ precipitation in the matrix.     

Synthesis and conductivity of cerium oxide nanoparticles

Cerium oxide (CeO₂) nanoparticles have been synthesized through composite-hydroxide-mediated approach. The X-ray powder diffraction (XRD) measurement proved that the pure cubic CeO₂ could be obtained at a low temperature region (170-220 °C). The particle size, micrograph morphology and microstructure were investigated by transmission electron microscope (TEM) and environmental scanning electron microscope (ESEM). The conductivity of as-synthesized CeO₂ was measured by a standard four-probe method. The conductivity of CeO₂ increases slightly with the increase of temperature. And the conductivity increases rapidly to 0.02418 s cm^− 1 at 830 °C. The product is a potential material for intermediate temperature solid oxide fuel cells (ITSOFC).     

Characterization and visible light germicidal efficacy of nitrogen doped TiO2 film crystallized by microwave irradiations

The visible light bactericidal ability of nitrogen doped TiO₂ (TiON) film on Si (100) has been enhanced greatly (by 22%) through a single-mode microwave irradiation annealing (f = 2.45 GHz, 20 s) in comparison with the conventional heat treatment at the same temperature (500 °C, 300 s). Analyses of X-ray photoelectron spectroscopy and transmission electron microscopy showed that the microwave annealed TiON film had a higher nitrogen concentration and much better crystallinity, both of which contribute to its prior bactericidal ability under visible light. The optimized annealing parameters of microwave irradiation are 500 °C within 20 s. Increase of annealing temperature and irradiation time resulted in the decrease of nitrogen concentration within the film. The crystallized TiON film has an anatase but not a rutile structure at the annealing temperature up to 800 °C.     

The microstructure evolution and nucleation mechanisms of dynamic recrystallization in hot-deformed Inconel 625 superalloy

Hot compressions tests of Inconel 625 superalloy were conducted using a Gleeble-1500 simulator at different strains between 900 °C and 1200 °C with a strain rate of 0.1 s⁻¹. Optical microscope, transmission electron microscope and electron backscatter diffraction technique were employed to investigate the microstructure evolution and nucleation mechanisms of dynamic recrystallization. It was found that both the size and fraction of dynamically recrystallized grains increase with increasing deformation temperature. However, the size of dynamically recrystallized grains almost remains constant with increasing deformation strain. The dominant nucleation mechanism of dynamic recrystallization in Inconel 625 superalloy deformed at 1150 °C is the discontinuous dynamic recrystallization, which is characterized by the bulging of the original grain boundaries accompanied with twining. The continuous dynamic recrystallization characterized by progressive subgrain rotation occurs simultaneously in dynamic recrystallization process, although it can only be considered as an assistant nucleation mechanism at the early stage of hot deformation.     

Study of alumosilicate porcelains: Sol-gel preparation, characterization and erosion evaluated by gravimetric method

In this paper, the sol-gel synthesis and characteristic properties of kalsilite-type alumosilicates (KAlSiO₄ and K_0.5Na_0.5AlSiO₄) are reported. The polycrystalline powders were characterized by thermal analysis (TG/DTA), powder X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). Single-phase kalsilite oxides have been obtained after annealing precursor gels for 5 h in the temperature range of 750-850 °C. It was demonstrated that crystallinity of the samples slightly depends on the temperature of annealing. From the results obtained, it could be concluded that the KAlSiO₄ solids are composed of the volumetric plate-like grains with no regular size (from 5 μm to 30 μm at 750 °C and around 5-50 μm at 850 °C). Larger crystallites for mixed potassium-sodium kalsilite have formed (from 10 μm to 80 μm at 750 °C and >100 μm at 850 °C) in comparison with potassium kalsilite samples). The erosion of obtained dental porcelain samples stored in saliva, beer and Coca-Cola was compared.     

Preparation of VO2 nanowires and their electric characterization

Large-scale VO₂ nanowires have been synthesized by two-step method. First, we have been obtained (NH₄)_0.5V₂O₅ nanowire precursors by hydrothermal treatment of ammonium metavanadate solution at 170 °C. Secondly, the precursors have been sealed in quartz tube in vacuum and annealed to form VO₂ nanowires at 570 °C. Scanning electron microscope and transmission electron microscope analysis show that the nanowires have self-assembling nanostructure with the diameter of about 80-200 nm, length up to125 μm. Electrical transport measurements show that it is semiconductor with conduction activate energy of 0.128 eV. A metal-semiconductor transition can be observed around 341 K.     

The effect of calcining temperature on the magnetic properties of the ultra-fine NiCuZn-ferrites

In this study, the ultra-fine NiCuZn-ferrite was prepared by a coprecipitation method. The magnetic properties were investigated in terms of calcining temperature. The ferrite powders, Ni_0.206Cu_0.206Zn_0.618Fe_1.94O_4−δ, were initially heat treated at various temperatures of 300-750 °C, and then sintered at the final temperature of 900 °C. The average particle size calculated by a XRD pattern and confirmed by a transmission electron microscope (TEM) micrograph was 7.5 nm. The calcining temperature was an important factor for microstructures and magnetic properties of the sintered ferrite. Scanning electron microscope (SEM) micrographs showed a uniform grain growth with small pores and high densification at the calcining temperature of 450 °C. From the results of magnetic property measurements, the ferrite calcined at 450 °C showed higher initial permeability (170) and quality factor (72) than those of other calcining temperatures.     

Study on the optical property and crystallinity of Ge90Te10 films deposited by electron beam evaporation

Optical property and crystallinity of Ge₉₀Te₁₀ films prepared by electron beam evaporation have been studied. The films grown at different substrate temperatures (Ts) and deposition rates (R) have been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and spectroscopic ellipsometry. The polycrystalline film was obtained at Ts = 300 °C, while the amorphous film was obtained when Ts ≦ 200 °C. However, the film showed the columnar structure when Ts ≦ 100 °C. It was found that Ts had the stronger effect on the crystallinity of the film rather than R. The optical constant in the infrared region was determined. All the film exhibited no absorption, but the refractive index was varied with the change of Ts and R. The relationship between optical constant, the film structure and the deposition parameters were also discussed. In addition, the optimum deposition condition of Ge₉₀Te₁₀ film was found.     

Synthesis and characterization of nanocrystalline La2Mo2O9 fast oxide-ion conductor by an in-situ polymerization method

A nanocrystalline La₂Mo₂O₉ powder was synthesized via the pyrolysis of polyacrylate salt precursor prepared by an in situ polymerization of the metal salts and acrylic acid. The pyrolysis behavior of the polymeric precursor was studied by thermal (TG/DTA) analysis. The obtained product was characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM) analysis. The results revealed that the average particle size is ∼25 nm for La₂Mo₂O₉ with good crystallinity. The synthesized nanocrystalline La₂Mo₂O₉ powder showed good sinterability and reached ∼99% of theoretical density when sintered at 800 °C for 4 h. The La₂Mo₂O₉ sample sintered at 800 °C, yield good microstructure with improved conductivity value of about 0.12 S/cm at 800 °C.     

Growth of carbon with vertically aligned nanoscale flake structure in capacitively coupled rf glow discharge

Carbon nanoflakes (CNFs) have been deposited on Si (1 0 0) wafer substrates at a substrate temperature of 670 °C from a glassy carbon target by capacitively coupled rf (13.56 MHz) glow discharge using a mixture discharge gas of Ar and CH₄ with a total pressure of 14.5 Pa. Microstructures of deposited carbon were investigated by a field emission scanning electron microscope (FESEM) and a high-resolution transmission electron microscope (HRTEM). Under the given conditions, vertically aligned CNFs with a flake length of about 1 μm and thickness of about 20 nm were grown. High intensity and symmetry of electron diffraction pattern indicate that the CNFs deposited by capacitively coupled rf glow discharge have three-dimensionally perfect crystallinity with a graphene interlayer spacing of 335 pm. In particular, there is little disorder in stacking of the layer structure. It was further found that the thickness of the flakes was less dependent of deposition time while the length of the flakes increases to about 1 μm with increasing deposition time to 3 h. The growth rate of a graphite sheet parallel to (0 0 1) stacking layers was much higher than that perpendicular to (0 0 1) stacking layer, resulting in anisotropic growth of a flake-like structure. The formation mechanisms of CNFs are discussed from the viewpoint of the difference in residence time of carbon atoms on CNF surfaces parallel to and perpendicular to (0 0 1) direction and anisotropic heat conductivity of graphite.     

Influence of peak temperature during simulation and real thermal cycles on microstructure and fracture properties of the reheated zones

The objective of this paper is to study the influence of the second peak temperature during real and simulated welding on properties of the subcritically (S), intercritically (IC) and supercritically (SC) reheated coarse grained heat affected (CGHAZ) zones. The X80 high strength pipeline microalloyed steel was subject to processing in a double-pass tandem submerged arc welding process with total heat input of 6.98 kJ/mm and thermal cycles to simulate microstructure of reheated CGHAZ zones. This involved heating to a first peak temperature (T_P1) of 1400 °C, then reheating to different second peak temperatures (T_P2) of 700, 800 and 900 °C with a constant cooling rate of 3.75 °C/s. Toughness of the simulated reheated CGHAZ regions were assessed using Charpy impact testing at 0 °C, −25 °C and −50 °C. The microstructure of the real and simulated reheated CGHAZ regions was investigated using an optical microscope and field emission scanning electron microscope. Morphology of the martensite/austenite (MA) constituent was obtained by the use of a field emission scanning electron microscope. The blocky and connected MA particles, along prior-austenite grain boundaries, act as a brittle phase for the initiation site of the brittle fracture. Charpy impact results indicated that IC CGHAZ had less absorbed energy with higher transition temperature and hardness. The SC CGHAZ region showed higher absorbed impact energy with lower hardness. Design of multipass weld joints with less IC CGHAZ regions can result in a higher toughness property.     

Preparation of hydroxyapatite by the hydrolysis of brushite

The conversion of brushite (CaHPO₂ · 2H₂O; DCPD) into hydroxyapatite (HAp) by hydrolysis has been studied by separating the conversion process into two stages, i.e. the structural change of DCPD into HAp (1) and the subsequent compositional increase in Ca/P ratio of the HAp (II). In Reaction I at 40°C, HAp formed most rapidly at around pH 7.5 to 8.0. The complete conversion was observed within 2.5 h at 40°C, 1 h at 60°C and only 5 min at 80°C. The compositions of HAp thus formed were nonstoichiometric and had a Ca/P ratio below 1.60. It was difficult to increase the Ca/P ratio up to the stoichiometric value 1.67, because the adjustment of pH to higher values and/or the addition of Ca²⁺ ions to accelerate the increase in Ca/P ratio, retarded the proceeding of Reaction I. On the other hand, in Reaction II, such pH adjustment and Ca²⁺ addition were remarkably effective in increasing the Ca/P ratio. Consequently, two-stage processing was reasonable and convenient for the preparation of stoichiometric HAp, because it was possible to manage the controlling factors in both Reactions I and II independently. The resulting HAp powders showed a comparatively low crystallinity similar to precipitated HAp and large weight losses (above 6%) on heating, and were composed of dense aggregates of irregular thin microcrystals.     

Synthesis of stable spherical platinum diphosphide, PtP2/carbon nanocomposite by reacting Pt(PPh3)4 at elevated temperature under autogenic pressure

The synthesis of microsized carbon spheres supporting the semiconductor platinum diphosphide, PtP₂, was conducted by the thermal decomposition of an organometallic precursor. This novel reaction was carried out using the reaction under autogenic pressure at elevated temperature (RAPET) method by dissociating Pt(PPh₃)₄ at 1000 °C. The product was characterized using methods of electron microscopy (scanning electron microscope (SEM), transmission electron microscope (TEM), selected area energy dispersive spectroscopy (SAEDS), elemental analyzer (EA) and energy dispersive X-ray analysis (EDX)) and powder-XRD. Transmission electron microscope images indicate that the particle size of the nanoparticles of PtP₂ coated on the carbon spheres is 50 nm.     

The effects of temperature and pH on the characteristics of corrosion product in CO2 corrosion of grade X70 steel

The effects of temperature and the in situ pH on the composition and morphology of corrosion product layers in the CO₂ corrosion of X70 steel were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses, respectively. The experiments were carried out in a range conditions including temperature 55–85 °C and pH 5.5–6.5 over a period of 72 h. At 55 °C, no corrosion product was formed on the steel surface at any pH conditions. By increasing the temperature to 65 °C, iron carbonate (FeCO₃) phase was formed at all pH conditions with an apparently non-compact morphology. Raising the pH increased the compactness of the layer. At 75 and 85 °C, a compact layer was formed at all pH conditions, while the most compactness was seen at pH 6.5 for both of these temperatures. It was also observed that the thickness of FeCO₃ layer increased with increasing temperature. Therefore, it could be concluded that the optimum conditions for producing a compact and thick layer of FeCO₃ was obtained at temperature of 85 °C and pH 6.5.     

Synthesis of nano-sized hydroxyapatite powders through solution combustion route under different reaction conditions

Calcium hydroxyapatite, Ca₁₀(PO₄)₆(OH)₂ (HAp) was synthesized by combustion in the aqueous system containing calcium nitrate-diammonium hydrogen orthophosphate with urea and glycine as fuels. These ceramics are important materials for biomedical applications. Thermo-gravimetric and differential thermal analysis were employed to understand the nature of synthesis process during combustion. Effects of different process parameters namely, nature of fuel (urea and glycine), fuel to oxidizer ratio (0.6-4.0) and initial furnace temperature (300-700 °C) on the combustion behavior as well as physical properties of as-formed powders were investigated. A series of combustion reactions were carried out to optimize the reaction parameters for synthesis of nano-sized HAp powders. The combustion temperature (T_f) for the oxidant and fuels were calculated to be 896 °C and 1035 °C for the stoichiometric system of urea and glycine respectively. The stoichiometric glycine-calcium nitrate produced higher flame temperature (both calculated and measured) and powder with lower specific surface area (8.75 m²/g) compared to the stoichiometric urea-calcium nitrate system (10.50 m²/g). Fuel excess combustion in both glycine and urea produced powders with higher surface area. Nanocrystalline HAp powder could be synthesized in situ with a large span of fuel to oxidizer ratio (φ) in case of urea system (0.8 < φ < 4) and (0.6 < φ < 1.5) for the glycine system. Calcium hydroxyapatite particles having diameters ranging between 20 nm and 120 nm could be successfully synthesized through optimized process variable.     

Pulsed electron beam deposition of transparent conducting Al-doped ZnO films

Good quality transparent conducting Al-doped ZnO films were deposited on quartz substrates from a high purity target using pulsed electron deposition (PED). Two series of films were made, one deposited at room temperature but at four pressures, viz., 0.7, 1.3, 2.0 and 2.7 Pa of oxygen and one deposited at 1.3 Pa oxygen pressure but at the substrate temperature ranged from room temperature to 600 °C. In order to evaluate the effect of substrate temperature and oxygen pressure on the properties of obtained films, various characterization techniques were employed including X-ray diffraction, stylus profiler, scanning electron microscope, optical spectrophotometer and electrical resistivity. For the first series films, the optimal oxygen pressure of 1.3 Pa was found to bring about the appropriate energetic deposition atoms which results in the best crystallinity. For the second series films, the lowest resistivity was obtained in the film grown at 400 °C. An attempt was made to reduce the resistivity by lowering the oxygen pressure to 0.5 Pa which was the lower limit of working pressure of the PED system. The obtained results indicate that PED is a suitable technique for growing transparent conducting ZnO films.     

Influence of fuels on the morphology of undoped Y3Al5O12 and photoluminescence of Y3Al5O12:Eu prepared by a combustion method

Undoped and Eu-doped yttrium aluminum garnet nano-powders were prepared by a facile combustion method with citric acid/ethylene diamine tetraacetic acid (EDTA) as fuels and nitrates as oxidizers. The precursors and powders calcined at 1030 °C were investigated using thermogravimetric (TG), differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscope (SEM), and Brunauer-Emmett-Teller (BET) surface area measurements. It was found that the powders could be indexed with a garnet structure. The grains were in shape of hemispherical with sizes between 60 nm and 100 nm. With decreasing the citric acid/EDTA ratio, the crystallite size decreased steadily and the specific surface area increased. Investigations of photoluminescence (PL) revealed that as-synthesized YAG:Eu³⁺ phosphor samples exhibited an orange emission band with a main peak at 591 nm under the excitation of 394 nm. As citric acid amounts increased, the quality of crystallinity became higher and the luminescent properties were monotonously enhanced.