Hengde Li

Preparation of nanocrystalline metal oxide powders with the surfactant-mediated method

Abstract Nanocrystalline metal oxides (ZnO, NiO, and SnO2) powders with an average particle diameter of 18–55 nm have been successfully prepared with the surfactant-mediated method. The cationic surfactant (cetyltrimethylammonium bromide, CTAB) and the hydrous metal chlorides (ZnCl2·2H2O, NiCl2·6H2O, and SnCl4·5H2O) appear to be the good candidates for obtaining a high yield of nanoparticles. The resultant products have been characterized by thermogravimetric analysis (TGA), X-ray powder diffraction (XRD), and transmission electron microscopy (TEM). The resulting powders are highly crystalline and largely monodisperse oxide particles. The surfactant-mediated method turned out to be suited for the preparation of the nanocrystalline oxide powders. Through this method, it is possible to obtain nanocrystalline metal oxide powders.

Preparation and characterization of SnO2 nanoparticles with a surfactant-mediated method

Using a surfactant-mediated method, tin dioxide nanoparticles with a high surface area were generated within the template of the cationic surfactant (cetyltrimethylammonium bromide) micelle assembly from the hydrous metal chloride (SnCl4 ? 5H2O). The as-synthesized product was amorphous and transformed into crystalline calcined at 500?C for 2 h, and exhibited a higher Brunauer?Emmet?Teller surface area of 69.2 m2 g?1. The resulting particles were highly crystalline and largely monodisperse oxide particles in the nanometre range (15?25 nm). Thermogravimetric analysis, x-ray powder diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy and x-ray photoelectron spectroscopy were used to characterize the final products.

Structure and properties of carbon nitride films synthesized by low energy ion bombardment

Carbon nitride films have been synthesized at low substrate temperature by Ar + sputtering a graphite target with concurrent N + assisted bombardment. It was disclosed that N + bombardment with low energies of 150–400 eV and beam densities of 0.16–0.23 mA cm −2 was favorable to grow carbon nitride films with high N/C atomic composition ratios of 0.47–0.56. The spectra of x-ray photoelectron spectroscopy and infrared spectroscopy show that the low energy N + bombardment activates nitrogen atoms to combine carbon atoms in unpolarized covalent bonds. Under the 150–300 eV and 0.16–0.23 mA cm −2 N + assisted bombardment, the formed films are identified by transmission electron microscopy to possess the β–C 3 N 4 microcrystalline structure. The films exhibit an extremely high hardness of 5260 kgf/mm 2 , a high resistivity of 4.8 × 10 12 Ω × cm, and excellent optical transmittance. Friction and wear tests show that carbon nitride films on steel substrate can perform the even wear in low friction coefficients of 0.05–0.16 while raising wear loads up to 20 N.

Structure and performance of γ-alumina washcoat deposited by plasma spraying

Abstract An alumina–titania coating and an alumina composite coating was deposited on a FeCrAl metal support as a washcoat by a plasma spraying technique, and an alumina-dipped coating was prepared for comparison. The microstructures and performances of the coatings were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), the Brunauer–Emmett–Teller method (BET), as well as an ultrasonic vibration simulation. The results showed that the combined properties of the alumina composite sprayed coating were comparatively optimized in three kinds of samples. Due to the high-temperature stabilizers of CeO 2 , La 2 O 3 , SiO 2 and ZrO 2 , its surface phase was mainly composed of γ-Al 2 O 3 with some α-Al 2 O 3 . With a large number of nanoscale particles stacked on the honeycomb framework, this complex structure provided a firmer cohesive ability between the alumina composite sprayed coating and metal support, as well as a much higher resistance to mechanical vibration and thermal shock than the dipped coating. Moreover, it was supplied with a high geometric specific surface area of 32.1 m 2 /g. Thus, it has great possibilities for the alumina composite sprayed coating deposited by plasma spraying to be used directly as a washcoat of metal-supported catalysts on controlling motorcycle exhaust gas emission.

Preparation and characterization of MnOOH and β-MnO 2 whiskers

Abstract MnOOH and β-MnO 2 whiskers are obtained for the first time in our work. MnOOH whiskers are chemically synthesized in the presence of cationic surfactant cetyltrimethylammonium bromide (CTAB). The product is obtained under extremely low surfactant concentrations under basic conditions, using MnSO 4 ·H 2 O as the manganese source and ethylamine as the alkali source. After the subsequent heat treatment of MnOOH at 300 °C for 1 h, β-MnO 2 whiskers retaining the similar morphologies are obtained. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and thermogravimetry analysis (TGA) are used to characterize the products.

Synthesis of mesoporous structured material based on tin oxide

Abstract Mesoporous structured tin oxide with high specific surface area was synthesized under acidic conditions at ambient temperature in this study. The synthesis of this material was accomplished using a cationic surfactant (cetyltrimethylammonium bromide: CH 3 (CH 2 ) 15 N + (CH 3 ) 3 Br − ) as the organic supramolecular template and the hydrous tin chloride (SnCl 4 ·5H 2 O) and NH 4 OH as the inorganic precursor and counterion source. X-ray diffraction, thermogravimetric analysis and transmission electron microscopy have been used to characterize the mesostructures formed at room temperature as well as calcined at different temperature. The synthesis procedure strongly influenced the formation of the mesophase. The pore diameters and the surface areas of materials, evaluated from the N 2 -sorption isotherms, indicate average pore diameters of about 22 and 24 A and surface areas about 368 and 343 m 2 /g for calcination at 300 and 350 °C respectively. The formation of the tin oxide mesostructured material was proposed due to the presence of the hydrogen-bonding interactions between supramolecular template and inorganic precursors Sn 4+ and OH − , which were supposed to self-assemble around the cationic surfactant molecules.

Synthesis and characterization of amorphous TiO2 with wormhole-like framework mesostructure

Abstract Using neutral amine surfactant (dodecylamine) as an organic template and neutral inorganic material (tetrabutyl titanate) as a precursor, amorphous TiO2 with wormhole-like framework mesostructure was synthesized with the variation of surfactant-to-Ti alkoxide ratios. Powder X-ray diffraction (XRD), thermogravimetric analysis, Fourier transformed infrared spectra, transmission electron microscopy (TEM), nitrogen adsorption–desorption, and X-ray photoelectron spectroscopy (XPS) have been used to characterize the TiO2 mesostructure. The interaction between surfactant and titanium dioxide was displayed by XPS. The samples exhibit a wormhole-like framework from XRD patterns and TEM images, and high surface area (221 m2/g) for the sample calcined at 450 °C for 2 h. The formation of the titanium oxide mesostructure is proposed to be due to the presence of the interactions between surfactant head group and inorganic precursors prior to hydrolysis, and the condensation under condition favorable for liquid crystal formation.

Oriented growth of hydroxyapatite on (0001) textured titanium with functionalized self-assembled silane monolayer as template

A highly (0001) textured hydroxyapatite [Ca 10 (PO 4 ) 6 (OH) 2 , HA] coating on polycrystalline titanium plate is successfully synthesized by a biomimetic process mimicking biomineralization. To simulate the first stage of biomineralization, that is, supramolecular preorganization, a template surface with highly organized arrangement of carboxyl (–COOH) and alcoholic hydroxyl (–1OH) groups is prepared through self-assembly of vinyltriethoxysilane [(C 2 H 5 O) 3 SiCH=CH 2 , VTS] on hydroxylated titanium with strong (0001) texture, followed by oxidation of the vinyl groups (–1CH=CH 2 ) with dilute KMnO 4 solution into alcoholic hydroxyl and then into carboxyl groups. The functionalized substrate can induce oriented nucleation and growth of HA with (0001) planes parallel to the substrate surface from supersaturated HA solution through interfacial molecular recognition. The mechanisms of molecular recognition are also discussed.

Effect of inorganic–organic interface adhesion on mechanical properties of Al2O3/polymer laminate composites

Abstract Al2O3/polymer laminate composites were studied by using different surface treatment techniques and different resins. The silane coupling agent TEVS (triethoxyvinylsilane: CH2CHSi(OC2H5)3) was used to enhance the inorganic–organic interface adhesion. The inorganic-organic interface shear strength, the flexural strength, and the work of fracture of the laminate composites were measured through tensile test and three-point bending test. The morphology of inorganic surface and crack propagation was examined by SEM and AFM. The relationship between inorganic-organic interface shear strength and the work of fracture of the laminate composites was investigated. The experimental results suggest that the toughness of the laminate composites related closely to surface status of the matrix, couping agent, and resin. The maximum value of the work of fracture of the laminate composites was 6.1 times that of monolithic alumina. The work of fracture of the laminate composites, which alumina matrices were coated with a layer of epoxy vinyl ester resin (UPR 3201), increased gradually with increasing the interface shear strength. The work of fracture of the laminate composites, on which alumina matrices were coated with a layer of toughened epoxy vinyl ester resin (T-UPR 3201), decreased greatly as the interface shear strength increased.

The functionalization of titanium with EDTA to induce biomimetic mineralization of hydroxyapatite

A new process is developed to functionalize an inorganic substrate with an organic polycarboxylic chelating agent to obtain a biomimetic template for mimicking biomineralization for the synthesis of films or coatings. A titanium plate is first placed in ethylenediaminetetracetic acid (EDTA) solution to effect chemisorption and self-assembly of EDTA molecules on the plate. The plate is then aged in supersaturated hydroxyapatite [(Ca 10 (PO 4 ) 6 (OH) 2 , HA] solution to mimic biomineralization. The functionalization process is found to be very effective in creating a surface with an organized arrangement of carboxylate ions (–COO – ) with the orientation of lone pairs of electrons on O perpendicular to or radiating from the substrate surface. The coating is formed through the plate-like outgrowth of HA grains along the [001] direction under the mediation of the functionalized surface, giving rise to the coexistence of two kinds of microstructural patterns in coating. One is a parallel arrangement of the plate-like HA grains with (001) planes preferably parallel to the substrate surface, the other is a radial arrangement of the plate-like HA grains with the [001] direction radiating from one surface core and the (111) planes preferably parallel to the surface. The mineralization mechanism is discussed on the basis of the conformation of the self-assembled EDTA molecules and the interfacial molecular recognition, analogous to the biomineralization, including electrostatic interactions, hydrogen bonding, stereochemical arrangement and geometrical correspondence.