Preparation and characterization of dicalcium phosphate dihydrate coating on enamel

A coating of 60-80 μm in thickness had been prepared on the surface of enamel by rapid growth of highly crystalline dicalcium phosphate dihydrate crystal (DCPD). The DCPD coating was formed by conversion of calcium-deficient hydroxyapatite (CDHA) in strong acidic conditions. The characterization of the coating was performed using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD). No obvious gap between the coating and the enamel was detected by SEM observation, which suggested that the coating adhered well to the enamel. Analysis of FT-IR and XRD revealed that the coating was a good match to DCPD. Moreover, the mean Vicker hardness number (VHN) of the coating was approximately 125, as measured by a microhardness tester.     

Facile synthesis and crystal growth dynamics study of MgAl2O4 nanocrystals

Well-dispersed MgAl₂O₄ nanocrystalline was prepared by a convenient salt-assistant combustion process using low-toxic glycine as fuel, low-cost Mg(NO₃)₂·6H₂O and Al(NO₃)₃·9H₂O as raw materials. By changing the reaction condition such as glycine dosage, the amount of inert-salt, inert-salt types and calcinations temperature, the optimal conditions to synthesize MgAl₂O₄ nanocrystalline were explored. The obtained results showed that parameters inert-salt and fuel dosage in the process have an important effect on the structure properties of samples. The obtained products were characterized by XRD and TEM. TEM images revealed that the products were composed of well-dispersed cube-like nanocrystals with the size of 60–80 nm. The synthesis mechanism of MgAl₂O₄ nanocrystals was discussed. The crystal growth dynamics of MgAl₂O₄ nanocrystals was studied and the activation energy of MgAl₂O₄ nanocrystals was 39.1 kJ/mol.     

Hydrothermal synthesis, characterization, and influence factors of PbTe nanocrystals

In the present paper, we successfully prepared PbTe nanocrystals in a simple aqueous system via the hydrothermal route employing PbO, Te powders and N₂H₄·H₂O as the starting reactants at 150 °C for 14 h. Some factors affecting the morphologies of the PbTe nanocrystals, such as the reaction temperature, time, the amount of NaOH, sorts of reductants and Pb²⁺ ion sources, were systematically investigated. Experimental results indicated that, under keeping the other experimental conditions constant: raising the reaction temperature, the shapes of the as-obtained PbTe hardly changed, while decreasing the temperature, some PbTe dendrites were obtained; the short reaction time availed to obtain cubes with a hole in the center of each face; more amounts of NaOH were favorable to the formation of regular PbTe nanocuboids. When NaBH₄ was used as the reductant, a large amount of near spherical PbTe nanocrystals was produced; while NaH₂PO₂ was used, many PbTe crystals with hollow framework structures were obtained. When Pb(CH₃COO)₂ was used as the Pb²⁺ ion source, some dendrites made of many irregular particles were generated; while PbSO₄ was employed, many PbTe nanocuboids were produced. A possible formation mechanism of PbTe nanocrystals was proposed based on the experimental results.     

Simultaneous uptake of ammonium and phosphate ions by composites of γ-alumina/potassium aluminosilicate gel

The simultaneous uptake of ammonium and phosphate ions from solution by composites of γ-alumina/potassium aluminosilicate (KAS) gel has been investigated. The composites were prepared by selective leaching of calcined kaolinite (Al₂Si₂O₅(OH)₄) using KOH solution, followed by neutralization of the leachate at pH 5.5 with nitric acid. The composites were reacted with solutions containing various concentrations of (NH₄)₂HPO₄ at pH 5, 7 and 10 at room temperature for 24 h to examine their uptake of ammonium and phosphate ions. Simultaneous uptake of ammonium and phosphate ions was found, the uptake of ammonium ions being greater than for phosphate ions, especially at pH=7. This observation is considered to result mainly from the porous properties of the composites, which should therefore be controlled to enhance the simultaneous uptake of both ions, especially phosphate ion.     

Hydrothermal synthesis of HgTe rod-shaped nanocrystals

HgTe nanorods composed of crystalline particles with the diameter of 100-300 nm and length of up to 2-3 μm have been prepared by a hydrothermal method, and characterized by means of X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transition electron microscopy (TEM) and energy-dispersive X-ray analysis (EDX). It was found that ammonia played a key role in the formation of HgTe nanorods.     

Microwave-hydrothermal synthesis of perovskite bismuth ferrite nanoparticles

Hydrothermal microwave method (HTMW) was used to synthesize crystalline bismuth ferrite (BiFeO₃) nanoparticles (BFO) in the temperature of 180 °C with times ranging from 5 min to 1 h. BFO nanoparticles were characterized by means of X-ray analyses, FT-IR, Raman spectroscopy, TG-DTA and FE-SEM. X-ray diffraction results indicated that longer soaking time was benefit to refraining the formation of any impurity phases and growing BFO crystallites into almost single-phase perovskites. Typical FT-IR spectra for BFO nanoparticles presented well defined bands, indicating a substantial short-range order in the system. TG-DTA analyses confirmed the presence of lattice OH⁻ groups, commonly found in materials obtained by HTMW process. Compared with the conventional solid-state reaction process, submicron BFO crystallites with better homogeneity could be produced at the temperature as low as 180 °C. These results show that the HTMW synthesis route is rapid, cost effective, and could be used as an alternative to obtain BFO nanoparticles in the temperature of 180 °C for 1 h.     

A novel route to ZnO nanorods with small diameters of 20 nm

The ZnO nanorods with small diameters of 20 nm were prepared successfully by an easy “in situ consumed template” route. In the synthesis, Zn(Ac)₂ were used as Zn source and dodecanethiol (DT) was used as coordinated agents in ethanol solvent. The samples were characterized detailed by XRD, TEM and IR techniques. The results indicated that the ZnO rods were uniform in diameters with good crystallinity. Time-dependent experiments indicated that the ZnO rods are grown within the Zn–DT complex (a complex composed of Zn and DT) that was formed at the beginning of the reaction. With prolonging the reaction time, the Zn–DT “template” was gradually in situ consumed and transformed into ZnO, and finally, the ZnO nanorods with diameters of 20 nm were obtained. The method here provides the new route for ZnO nanorods with small diameters.     

Morphology controllable synthesis of ZnO crystals—pH-dependent growth

ZnO crystals were grown through a solution-based chemical route at ambient pressure and low temperature. It was found that the solution pH is a dominative factor in determining the morphology of crystals: Rod-like ZnO crystals are apt to be formed at near neutral condition, whereas flower-like structured ZnO crystals are preferred to be formed at higher solution pH. By monitoring the reaction intermediates during the ZnO growth process, it was realized that the crucial role of solution pH in determining the morphology of ZnO crystals is to control the structure of the primary reaction intermediates at the early stage of ZnO growth. Moreover, by appreciate controlling the solution pH together with Zn²⁺ concentration, various ZnO crystals of rod-like, dumbbell-like and even more complex flower-like structures were obtained without any template, and a pH-dependent morphology controllable growth mechanism is suggested.     

A facile synthesis of ordered ultralong silver nanobelts

Large-scale ordered ultralong silver nanobelts, which built a beautiful chrysanthemum-like structure, are prepared on the interface between dibutyl sebacate (DBS) and silver nitrate solution by a chemical electro-deposition technique. The influences of chemical circumvent of interface, concentration of silver nitrate solution and applied voltage on the formation of silver nanobelts are investigated. It is shown that the silver nanobelts possess a perfect single crystal structure and well-defined nanobelt-like morphology with a length of 5 mm, width 80-150 nm, and thickness 20 nm, respectively. The growth mechanism of the nanobelts is discussed. Furthermore, UV-vis spectra of the silver nanobelts show similar surface plasmon resonance properties to silver nanowires.     

Selective synthesis of copper nanoplates and nanowires via a surfactant-assisted hydrothermal process

A facile solution-phase process has been demonstrated for the selective preparation of single-crystalline Cu nanoplates and nanowires by reducing Cu⁺ with ascorbic acid (VC) in the presence of cetyltrimethylammonium bromide (CTAB) or cetyltrimethylammonium chloride (CTAC). To study the formation process of nanoplates and nanowires, samples obtained at various stages of the growth process were studied by TEM and XRD. The possible mechanism was discussed to elucidate the formation of different morphologies of Cu nanostructures. UV–vis spectra of the Cu nanoplates and nanowires were recorded to investigate their optical properties, which indicated that the as-prepared Cu nanostructures exhibited morphology-dependent optical property.     

Properties of size-tuned PbS nanocrystals stabilized in a polymer template

Nanoclusters of PbS embedded in polymer matrices have recently been shown to have interesting optical properties with the capability of tuning the effective band gap over a wide spectral range. The results of a systematic investigation of the preparation and characterization of size-tuned PbS nanocrystals stabilized in the polymer nanotemplate of Nafion and their size-dependent physical properties are presented in this paper. These nanocrystals exhibit large characteristic blueshift in optical absorption from the bulk absorption onset value of 3020 nm. XRD and HRTEM measurements indicate the presence of PbS nanocrystals in the size range of 2-6 nm, in the regime of strong quantum confinement. Thermal and electrical properties of the polymer are found to be influenced to a great extent by the embedded PbS nanocrystals.     

Citrate gel route for synthesis of dense pyrochlores

The solid solution of pyrochlore oxides, Nd₂Zr_xTi_2−xO₇ (x = 0.2, 0.4, 0.6, 0.8 and 1.0) was synthesized by citrate gel method and the conventional ceramic method. The results indicate that the citrate gel method gives pyrochlore phase formation at a much lower temperature and better morphology of the product oxides as compared with the ceramic method. The dc conductivity study was carried out on some samples to understand the defects, if any, in the lattice of the solid solution Nd₂Ti_xZr_2−xO₇ (x = 0.2, 0.4, 0.6, 0.8 and 1.0) on substitution of Zr by Ti. The formation of defects in the lattice on substitution of Zr by Ti, was explained on the basis of XPS studies.     

Thermokinetic study on growth process of CdS nanocrystals by in situ microcalorimetry

In situ microcalorimetry was used to investigate the energy evolution during CdS nanocrystal growth process. It can provide important information for controlling crystal growth. The CdS nanospheres were synthesized in the glycol-water system at room temperature. The energy change of CdS nanocrystal growth process was measured by a microcalorimeter. The microcalorimetric curve shows a strong exothermic peak. On the basis of the experimental result, the rate constant and the activation Gibbs energy have been obtained. The CdS nanocrystals were characterized by X-ray diffraction, scanning electron microscope and photoluminescence spectra. The morphology evolution can be well connected with the energy change.     

Centrifugal effects on combustion synthesis of (Ti-B-C) compound system

A centrifugal force plays an important role on the control of combustion synthesis. In the present work, the data of reaction propagation rates obtained by changing the direction of reaction propagation and centrifugal force are evaluated in order to make clear the effect of centrifugal force on reaction propagations and product formation. As a result, the reaction propagation rate in the case of the direction of centrifugal force inverse to reaction propagation is larger than that in the case of the same direction, and product grains become smaller in size. It is confirmed that the centrifugal effect is much larger for the present combustion synthesis process in the case that the reaction propagates inversely to the direction of centrifugal force. Since molten titanium near combustion front tends to coalesce into larger drops in that case, reactants of boron and carbon would diffuse more sufficiently into titanium.     

Aqueous combustion synthesis and characterization of ZnO powders

New organic fuels (β-alanine, valine, zinc acetate and acrylamide) have been successfully tested for the preparation of nanocrystalline ZnO powders via aqueous combustion synthesis. In all cases, ZnO resulted directly from the combustion process and no subsequent annealing was required. Properties of the as-prepared ZnO powders were investigated and it was found that morphology, specific surface area, crystallite size and cumulative volume of pores are determined by the used fuel. A correlation has been found between the total volume of generated gases, adiabatic temperature, the amount of ZnO and the characteristics of the resulting powders. Largest surface area (42.0 m² g⁻¹) and smallest ZnO crystallite size (21 nm) were obtained for acrylamide.     

One-pot template-free synthesis of mesoporous boehmite core-shell and hollow spheres by a simple solvothermal route

Uniform-sized and monodispersed boehmite core-shell and hollow spheres have been successfully synthesized using a template-free solvothermal route. The experimental parameters such as reaction duration, the trisodium citrate amounts and solvents are shown to play important roles in the formation of the AlOOH core-shell and hollow spheres. X-ray diffraction, Fourier transform IR, thermal gravimetric analysis, N₂ adsorption/desorption, scanning electron microscopy, transmission electron microscopy, and high-resolution TEM were used to characterize the products. The results show that the prepared polycrystalline hollow spheres are composed of well-aligned AlOOH nanowires and have an orthorhombic structure. Finally, a dissolution-renucleation mechanism was proposed for the formation of boehmite hollow structures.     

Adsorption of vitamin E on mesoporous titania nanocrystals

Tri-block nonionic surfactant and titanium chloride were used as starting materials for the synthesis of mesoporous titania nanocrystallite powders. The main objective of the present study was to examine the synthesis of mesoporous titania nanocrystals and the adsorption of vitamin E on those nanocrystals using X-ray diffraction (XRD), transmission electron microscopy, and nitrogen adsorption and desorption isotherms. When the calcination temperature was increased to 300 °C, the reflection peaks in the XRD pattern indicated the presence of an anatase phase. The crystallinity of the nanocrystallites increased from 80% to 98.6% with increasing calcination temperature from 465 °C to 500 °C. The N₂ adsorption data and XRD data taken after vitamin E adsorption revealed that the vitamin E molecules were adsorbed in the mesopores of the titania nanocrystals.     

Colloidal synthesis of Cu2SnSe3 nanocrystals

While Cu₂SnSe₃ material has various potential applications including acousto-optics and photovoltaics, preparation methods of this material only in a bulk form or a thin film have been reported so far. In this work, for the first time, we demonstrate that highly crystalline Cu₂SnSe₃ nanoparticles can be prepared via colloidal synthesis. The Cu₂SnSe₃ nanocrystals have a cubic crystal structure with a lattice parameter of 5.68 Å, an average diameter of 18 nm, and an atomic ratio of approximately 2:1:3. The nanocrystals can be stably suspended in solution for several months. The suspended nanocrystalline form of Cu₂SnSe₃ could potentially be useful for printable acousto-optic and photovoltaic applications.     

Solution synthesis and electrochemical capacitance performance of Mn3O4 polyhedral nanocrystals via thermolysis of a hydrogen-bonded polymer

Hausmannite Mn₃O₄ polyhedral nanocrystals have been successfully synthesized via a simple solution-based thermolysis route using a three-dimensional hydrogen-bonded polymer as precursor. The as-obtained product was characterized by means of powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Possible formation mechanism of polyhedral nanocrystals was proposed based on the role of organic ligand dissociation from the polymer precursor at elevated temperature. The electrochemical capacitance performance of Mn₃O₄ electrode was investigated by cyclic voltammetry and galvanostatic charge/discharge measurements. A maximum specific capacitance of 178 F g⁻¹ was obtained for the nanocrystals in a potential range from −0.1 to 0.8 V vs. SCE in a 0.5 M sodium sulfate solution at a current density of 0.2 A g⁻¹.     

Double electrodeposition and heat treatment process for the fabrication of superconducting oxides on the intensified {1 1 3} <1 2 1> Ag substrate

The Tl-1223 coated conductor (Tl_0.8Pb_0.2Bi_0.2Sr_1.8Ba_0.2Ca_2.2Cu₃O_δ) was synthesized by using electrodeposition on the intensified {1 1 3} <1 2 1> Ag substrate applying the new method of the repeating electrodeposition/heat treatment. The films were fabricated conducting the first electrodeposition and then heat treatment, after that the second electrodeposition on the first electrodeposition/heat treatment coated conductors. The second electrodeposition on the first electrodeposition/heat treatment/the first electrodeposition/heat treatment coated conductor showed the better quality of the Tl-1223 phases than that of the first electrodeposition/heat treatment coated conductor, showing more compact and dense grains on the films. The thin Tl-1223 films caused by the thinning process were discussed by considering the properties of Tl and the epitaxial growth aspects. The purer Tl-1223 grains obtained at the double electrodeposition/heat treatment are due to the growth from Tl-1223 grains already synthesized during the first electrodeposition/heat treatment, facilitating the epitaxial growth easier than that of the Ag substrate. The second electrodeposition process was successfully performed, obtaining 1.9 × 10⁵ A/cm² of J_c at 0 T at 10 K.