Papers by Keyword: Growth Mechanism

Abstract: Highly-ordered nanoleaf sodium titanate were successfully synthesized on high-purity titanium surface by catalyst oxidation method. Sodium metaborate powder was coated on titanium substrates, heated in an electric furnace at 650°C for 5 hours and then subjected to a water bath rinse. The structure and morphology of oxide coatings were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results showed that the fabricated coatings were composed of rutile and sodium titanium, providing the excellent biocompatibility and nanoscale even gap structure between bamboo-shaped sodium titanate. The mechanism about the growth of highly-ordered nanoleaf sodium titanate also discussed in the current work.

Abstract: In this work, Bi₂Fe₄O₉ superfine particles were prepared by hydrothermal method and effects of hydrothermal conditions on the microstructure of Bi₂Fe₄O₉, especially the concentration of OH^- ([OH^-]) in initial solutions, were investigated. The results showed that [OH^-] had obvious influences on the growth of Bi₂Fe₄O₉ under the same hydrothermal temperature and hydrothermal time. Phase structure of Bi₂Fe₄O₉ unchanged with the increase of [OH^-] and maintained orthorhombic structure. Besides, the microstructure of Bi₂Fe₄O₉ was carefully studied through transmission electron microscopy (TEM). The results suggested that the mechanism of Bi₂Fe₄O₉ growth was Ostwald ripening. In conclusion, Bi₂Fe₄O₉ superfine particles with good morphology and microstructure can be successfully synthesized when the concentration of OH^- is 2 mol/L and hydrothermal conditions are 240 °C for 6h.Keywords: Bi₂Fe₄O₉, hydrothermal method, phase structure, growth mechanism Topic code numbers: C2

Abstract: The foaming and nucleation and growth mechanism of soybean oil-based polyurethane (SPU) were determined by the degree of hydrogen bonding, and isocyanate groups. New types of SPU were prepared by the different NCO/OH molar ratio (isocyanate index) from 1.0 to 2.0 in a soy polyol/polyether polyol (MDI) system. Foaming and nucleation and growth mechanisms of SPU were studied by fluorescence microscope (FM), scanning electron microscope (SEM), energy disperse spectroscopy (EDS) and Fourier transform infrared spectroscopy (FT-IR). It indicated that the isocyanate index affected remarkably the velocity of foaming and the critical nucleation radius of SPU and the ester functional group increased with the increase of isocyanate index. The nucleation and growth phase transition were dominated by the diffusion controlled nucleation and isocyanate content was the key factor of foam formation.

Abstract: Tuning high density nanostructures by simple and economic method may contribute towards the development of solid oxide fuel cells. Copper oxide nanowires grown on Cu foil by thermal oxidation at relative low operating temperature from 400°C are characterized by using x-ray diffraction (XRD), energy dispersive x-ray spectroscopy (EDX), atomic force morphology (AFM), conductive-AFM (C-AFM), and field emission scanning electron microscopy (FESEM). The role of oxidizing temperature and time on structural and electrical properties are studied. The formation of nanowires is confirmed by X-Ray diffraction pattern with the presence of copper oxide. The electrical conductivity of the nanowires was ranging from 0.2x10⁵ S m^-1 to 0.8x10⁵ S m^-1are determined from conductive atomic force microscopy. The oxidation time strongly influence the morphology and chemical composition of the nanowires. Field emission scanning electron microscopy reveals the growth mechanism of copper nanowires formation is based on vapour-solid (VS) mechanism. Herein, the successfully growth of CuO nanowire are directly from Cu foil to overcome the mismatching stress between the substrate and the oxide layer. Optimum parameters are studied to make better electrolyte performance in the applications of solid oxide fuel cell (SOFC).

Abstract: The marker method in studying the formation mechanism and defect structure of higher oxide during oxidation of lower oxide has been discussed. The approach to this problem needs specific treatment, both in experimental procedure and in the interpretation of results. It has been shown that the correct results of marker experiments in the case of highly defected substrates can be obtained, if these substrates before the marker deposition process are submitted to homogenization under highest oxidant activity, at which they remain stable at a given temperature. In addition, the nonstoichiometry must be considered in formulating appropriate chemical reactions, being the basis for foreseeing the location of markers in the interior of reaction product. The other very important problem consists in the possibility of the formation of reaction product not only on the surface of oxidized substrate but also inside of this substrate. In such a situation, the formulation of final conclusions concerning the crystalline lattice disorder from marker position should be combined with considerations of chemical reactions and transport processes occurring in a given substrate.

Abstract: The effect of carrier gas flow rate on the morphologies of In₂O₃ nanostructures was studied in a horizontal tube furnace via chemical vapor deposition method. Under low carrier gas flow rate, there appeared randomly oriented nanorods on the substrate, while the high carrier gas flow rate resulted in the nanocubes growth. The insufficient understanding of the role of the argon carrier gas flow rate motivated us to systematically research the transportation of the grown species during the growth processes and its effect on the nanostructure growth. COMSOL simulations were applied to evaluate the distribution of the growth species in the reactor versus the carrier gas flow rate, based on the geometry of our chemical vapor deposition system and a variety of actual growth conditions. The vapor species partial along with different carrier gas rate could cause the different super saturation condition, which is mainly to be responsible for the structural transformation. A combined VLS–VS mechanism was proposed to describe the growth of the Au-catalyzed In₂O₃ nanorods, while the nanocubes were governed by catalyst free VS growth mechanism.

Abstract: Mg-doped GaN nanowires have been successfully synthesized on Si (111) substrates by magnetron sputtering deposition through ammoniating Ga₂O₃/Au thin films at 900 °C for 15 min. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and photoluminescence (PL) spectrum were carried out to characterize microstructure, morphology, and optical property of GaN sample. The results demonstrate that the nanowires are single-crystal Mg-doped GaN with hexagonal wurtzite structure and high crystalline quality, which have the size of 40 nm in diameter and several tens of microns in length and good emission property. The growth procedure mainly follows the VLS mechanism, and Au plays an important role as catalyst, and more defect energy is formed due to metallic Au and thus promote the growth of GaN nanowires.

Abstract: In this Letter, we reported the facile synthesis of manganese (III) oxide (Mn₂O₃) nanowires via the facile hydrothermal treatment in the presence of ammonia, which were prepared simply by hydrothermal treatment of commercial bulky Mn₂O₃ crystals at 160 ^oC for 24 h. The obtained Mn₂O₃ products consist a large quantity of nanwires with the diameters of 30-90 nm, and lengths ranging from 1 to 10 μm. Such high quality nanowires with high aspect ratio have a variety of promising applications. The simplicity of hydrothermal process, cheapness, and availability of raw materials, without the need of catalyst or template, are advantages favoring industrial manufacturing in scaled-up process by the novel method. X-ray and transmission electron microscopy, electron diffraction, and scanning electron microscopy have been employed to characterize these materials. In addition, the possible growth mechanism of the Mn₂O₃ nanowires was also proposed. The growth of Mn₂O₃ nanowires occurred via a dissolution-recrystallization process.

Abstract: The ultralong copper nanowires (Cu NWs) with diameter of 90±10 nm and length over 20 μm were synthesized by the self-assembly growth process, in which the copper ions were reduced with hydrazine in an aqueous solution containing NaOH and ethylenediamine (EDA). The prepared Cu NWs were characterized by XRD, SEM and TEM. The results indicate that the ultralong Cu NWs product almost containing no particles can be obtained at 80 °C for 1 h with a proper concentration of EDA. During the growth of Cu NWs, as the EDA moleculars are possibly preferentially absorbed onto the crystal plane of (110), the gowth of Cu NW will be oriented along the crystal plane of (111).

Abstract: Because of the characteristics of both one dimensional nanostructure and excellent physical and chemical properties, the kinds of novel nanomaterials-tungsten carbide nanowires, have important academic significance and practical meaning. The research development of one-dimensional nanostructured tungsten carbide is reviewed. The production methods of one-dimensional nanostructured tungsten carbide, such as nanotubes, nanorods, nanowires and nanoneedles by thermal decomposition technique, vapour deposition technique, magnetron sputtering technique, Eruptive heating technique and template technique respectively are systematically introduced. This paper summarizes the growth mechanisms and the problems involved in the existing synthesis methods. The research tendency is also forecasted.