Solid-state Growth Mechanism Research Articles

Unraveling the growth mechanism of W18O49nanowires on W surfaces

This work unravels the solid-state growth mechanism of 1dW18O49nanowires on W surfaces under a water vapor atmosphere. Such growth was understood to be the intermediate WO3layer formation and its reduction induced planar faults driven 1dsolid-state growth.

Formation mechanism of the outer layer of duplex scales on stainless steels in oxygenated supercritical water

The dependence on water density of the formation and growth of the outer scale layer was revealed by using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) to analyze the effects of additive phosphates on morphology and composition of oxide scales formed on 316 stainless steel in supercritical water (SCW) with an initial dissolved oxygen of 100 mg·L−1 at 400 °C and 600 °C. In 400 °C SCW with a high density (exceeding 100 kg·m−3) the outer layer thickens via a precipitation process, hence the promotion of pre-existent phosphates in cationic precipitation results in the presence of smaller product particles and phosphorus on the scale surface. In 600 °C SCW with a low density, the formation of the outer scale layer follows a solid-state growth mechanism.

Corrosion Mechanism of Inconel 600 in Oxidizing Supercritical Aqueous Systems Containing Multiple Salts

The corrosion behavior and mechanism of Inconel 600 exposed to the oxidizing high-salinity supercritical water (SCW) containing chlorides, sulfates, and phosphates at 450, 500, and 580 °C were investigated and proposed. The corrosion film had an outer layer dominated by NiO, Fe₂O₃, and eutectic phosphate deposit and an inner layer consisting of Cr-rich oxides. Some produced oxides may generate ionic reactions with the low-melting phosphates precipitated out from SCW, triggering the generation of the eutectic FePO₄–Ni₃(PO₄)₂–Na₃PO₄–Na₂HPO₄ salts in the outer layer. The formation and thickening of the outer layer results from the eutectic phosphate disposition and the common solid-state growth mechanism. Nonmolten chlorides and sulfates in SCW predominantly exist on the outmost surface and are easily washed off, being supported by the absence of S and Cl on sample surfaces. Based on this investigation, a comprehensive corrosion mechanism, involving the solid-state growth of oxide scales, salt precipitation, and phosphate melting processes, was proposed and discussed.

Solid-state graphene formation via a nickel carbide intermediate phase

Direct formation of graphene with a controlled number of graphitic layers on dielectric surfaces is achieved with an in-depth understanding of the solid-state growth mechanism.

Corrosion Behavior of Ni–20Cr–18W–1Mo Superalloy in Supercritical Water

The corrosion behavior of Ni–20Cr–18 W–1Mo superalloy in supercritical water 500 °C/25 MPa for 200 h is investigated using gravimetry, SEM/EDS, XPS, and TEM. The oxide films show a layered structure with Ni rich in the outer layer, and Cr rich in the inner layer, consisting of an outer Ni(OH)2 and NiO layer, including some Cr(OH)3, and an inner Cr2O3, NiCr2O4, and WO3 layer. Mo elements are not oxidized. The oxide films grow via a mixed mechanism, namely metal dissolution/oxide precipitation mechanism and solid-state growth mechanism. The effects of secondary and primary carbides on the weight-gain trend and oxide formation are discussed.

Preparation of copper germanate nanowires with good electrochemical sensing properties

AbstractTernary copper germanate nanowires have been synthesized by the hydrothermal deposition route in an autoclave using germanium dioxide and copper oxide powders as the starting materials as well as the copper germanate nanowires have been investigated for cysteine sensing characteristics. The nanowires with the length of several dozens of micrometers are mainly composed of single crystalline orthorhombic CuGeO3, which are supported by X‐ray diffraction, selected area electron diffraction, high‐resolution transmission electron microscopy and X‐ray photoelectron spectrum. Room temperature photoluminescence spectrum exhibits strong green light emission ability at 535.4 nm with a broad emission band. The copper germanate nanowires may be controlled grown by controlling the growth conditions of the nanowires. The nanowire growth process is explained using a solid state growth mechanism. The electrochemical analysis demonstrates that the copper germanate nanowires serve as a good electrochemical sensor with excellent electrochemical sensing ability for cysteine and catalytic ability for electron‐transfer process. The electrochemical result of the copper germanate nanowires presents an important advance toward the application for electrochemical sensors operating at room temperature. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Low temperature growth of single crystalline germanium nanowires

Ge nanowires have been prepared at a low temperature by a simple hydrothermal deposition process using Ge and GeO 2 powders as the starting materials. These as-prepared Ge nanowires are single crystalline with the diameter ranging from 150 nm to 600 nm and length of several dozens of micrometers. The photoluminescence spectrum under excitation at 330 nm shows a strong blue light emission at 441 nm. The results of the pressure and GeO 2 content dependences on the formation and growth of Ge nanowires show that the hydrothermal pressure and GeO 2 content play an essential role on the formation and growth of Ge nanowires under hydrothermal deposition conditions. The growth of Ge nanowires is proposed as a solid state growth mechanism.

Corrosion behavior of Hastelloy C-276 in supercritical water

The corrosion behavior of a nickel-based alloy Hastelloy C-276 exposed in supercritical water at 500–600 °C/25 MPa was investigated by means of gravimetry, scanning electron microscopy/energy dispersive X-ray spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. An oxide scale with dual-layer structure, mainly consisting of an outer NiO layer and an inner Cr 2O 3/NiCr 2O 4-mixed layer, developed on C-276 after 1000 h exposure. Higher temperature promoted oxidation, resulting in thicker oxide scale, larger weight gain and stronger tendency of oxide spallation. The oxide growth mechanism in SCW seems to be similar to that in high temperature water vapor, namely solid-state growth mechanism.

Characterization of oxide films grown on 316L stainless steel exposed to H 2O 2-containing supercritical water

The characterization of microstructure and chemical compositions of oxide films formed on surfaces of stainless steels is necessary for understanding of corrosion processes and environmentally assisted cracking. In this study, the morphologies, microstructure and chemical compositions of oxide films grown on 316L stainless steel exposed to H 2O 2-containing supercritical water (SCW) were investigated using a scanning electron microscope equipped with an energy-dispersive X-ray spectrometer (EDX), an X-ray photoelectron spectroscopy (XPS) analyzer and an X-ray diffraction (XRD) analyzer. A duplex-layer structure was identified in the oxide films. The loose outer layer was rich in Fe, while the compact inner layer was rich in Cr and Fe. In addition, Ni enrichment was observed at the interface between the metal matrix and oxides. The surface oxides tended to change with an increase in water temperature. The possible growth mechanism of the oxide films on 316L stainless steel in SCW environments is believed to be similar to that in high-temperature water, namely metal dissolution/oxide precipitation mechanism and solid-state growth mechanism.

Synthesis of copper oxide nanomaterials and the growth mechanism of copper oxide nanorods

A novel and simple solid-state reaction in the presence of a nonionic surfactant, NP9, has been developed to synthesize copper oxide (CuO) nanoparticles with different diameters. CuO nanorods were synthesized in the circumstances of different molten salts and heat treatment temperatures. The CuO nanoparticles and nanorods were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The influence of molten salts and temperature to the growth of CuO nanorods and the effect of NP9 on the size and morphology of CuO particles were discussed. A solid-state growth mechanism was put forward and applied to explain the growth of CuO nanorods.

Multi-method Analysis of the Metal/Electrolyte Interface: Scanning Force Microscopy (SFM), Quartz Microbalance Measurements (QMB), Fourier Transform Infrared Spectroscopy (FTIR) and Grazing Incidence X-ray Diffractometry (GIXD) at a Polycrystalline Copper Electrode

The successful application of various in situ and ex situ analytical techniques has been demonstrated at the buried interface between a metal and an electrolyte. Scanning force microscopy (SFM), electrochemical quartz microbalance measurements (EQMB), grazing incidence x-ray diffractometry (GIXD), Fourier transform infrared spectroscopy (FTIR) in the specular reflection absorption mode and electrochemical charge measurements proved complementary in the characterization of a polycrystalline copper electrode in alkaline 0.1 M sulphate, perchlorate, fluoride and chloride electrolyte contact at pH 12. The surface exhibited a mixture of Cu(111) and Cu(200) grains of the order of 100 nm. Repeated potential scanning in the double layer and passive oxide region, between -1.4 and +0.1 VMSE, resulted in a complete reorganization of the surface morphology but no detectable corrosion. The electrochemical exchange of H2O and OH− between the electrolyte and the oxide film took place reversibly in accordance with a solid-state growth mechanism. The copper atoms were redeposited at crystallographically preferred sites, generating comparatively homogeneously oriented, narrow Cu(111)-edged grain ridges of length 200 nm. In the Cu(I) potential range, the formation of several monolayers of amorphous Cu2O could be confirmed. Only after extended time periods in the Cu(II) oxide potential region, Cu2O recrystallized to a (111) phase accompanied by Cu2O(200) and Cu2O(110). In this region, one observed the formation of amorphous Cu(OH)2 concurrent with further growth of Cu2O. Strong CuOH IR stretching bands excluded the existence of CuO. At corrosive potentials of +0.25 VMSE, high anodic currents and substantial mass losses led to an electropolished surface with isolated features of <300 nm width and <70 nm height.© 1997 John Wiley & Sons, Ltd.

Multi‐method Analysis of the Metal/Electrolyte Interface: Scanning Force Microscopy (SFM), Quartz Microbalance Measurements (QMB), Fourier Transform Infrared Spectroscopy (FTIR) and Grazing Incidence X‐ray Diffractometry (GIXD) at a Polycrystalline Copper Electrode

The successful application of various in situ and ex situ analytical techniques has been demonstrated at the buried interface between a metal and an electrolyte. Scanning force microscopy (SFM), electrochemical quartz microbalance measurements (EQMB), grazing incidence x-ray diffractometry (GIXD), Fourier transform infrared spectroscopy (FTIR) in the specular reflection absorption mode and electrochemical charge measurements proved complementary in the characterization of a polycrystalline copper electrode in alkaline 0.1 M sulphate, perchlorate, fluoride and chloride electrolyte contact at pH 12. The surface exhibited a mixture of Cu(111) and Cu(200) grains of the order of 100 nm. Repeated potential scanning in the double layer and passive oxide region, between -1.4 and +0.1 VMSE, resulted in a complete reorganization of the surface morphology but no detectable corrosion. The electrochemical exchange of H2O and OH− between the electrolyte and the oxide film took place reversibly in accordance with a solid-state growth mechanism. The copper atoms were redeposited at crystallographically preferred sites, generating comparatively homogeneously oriented, narrow Cu(111)-edged grain ridges of length 200 nm. In the Cu(I) potential range, the formation of several monolayers of amorphous Cu2O could be confirmed. Only after extended time periods in the Cu(II) oxide potential region, Cu2O recrystallized to a (111) phase accompanied by Cu2O(200) and Cu2O(110). In this region, one observed the formation of amorphous Cu(OH)2 concurrent with further growth of Cu2O. Strong CuOH IR stretching bands excluded the existence of CuO. At corrosive potentials of +0.25 VMSE, high anodic currents and substantial mass losses led to an electropolished surface with isolated features of <300 nm width and <70 nm height.© 1997 John Wiley & Sons, Ltd.