Formation Mechanism Of ZnO Research Articles

Formation mechanism of ZnO in dissimilar welding of aluminum alloy to steel

The role of Zn with different existence forms in three kinds of welded joints was discussed in this paper. Net-like zinc oxide cermet structure formed in aluminum alloy/stainless steel fusion-brazed joints, and the thickness of interfacial layer increased after post-weld heat treatment. In aluminum alloy/galvanized steel fusion-brazed welded joints, the thickness of interfacial layer first increased, then decreased from weld toe to root, and block Zn aggregated at the bottom of weld. Zn layer also formed in aluminum alloy/galvanized steel refilled friction stir spot welded joint along the interface of aluminum alloy and steel where the joint fractured.

Structures and emission features of high-density ZnO micro/nanostructure grown by an easy hydrothermal method

Samples of urchin and multipods-like ZnO micro/nanostructure with various morphology, physical, and optical properties are fabricated on glass and silicon substrates through a simple hydrothermal method without any catalyst. The samples demonstrated that high-density ZnO nanorods are assembled to form ZnO micro/nanostructure which has structures that depended on growth time. The influence of growth time and substrate type on the crystalline structure, morphology, and emission response of synthesized ZnO samples were investigated. The samples were characterized by XRD, EDX, FESEM, and PL measurements. A reduction in consumed growth times to produce ZnO micro/nanostructure was achieved. XRD patterns confirmed the wurtzite hexagonal structure of ZnO micro/nanostructure with good crystallinity for (1–4 h) growth time, irrespective of substrate type. Conversely, FESEM images revealed that prolonged growth time of (6–8 h) resulted in destruction of ZnO morphology. EDX patterns showed an oxygen-deficiency- and crystal-defect-mediated growth of ZnO micro/nanostructure on both substrates with different stoichiometric ratios. Optical band-gap energy evaluated from the emission spectra displayed reasonable blue and red shifts depending on growth time (for 1–4 h) and substrate type. The formation mechanism of ZnO micro/nanostructure was demonstrated from the perspective of nucleation and self-assembly of growth unites.

Coating of ZnO nanoparticles onto the inner pore channel surface of SiC foam to fabricate a novel antibacterial air filter material

ZnO nanoparticles layer was successfully and firmly coated onto the surface of the pore channel of SiC foam via a sol–gel method in the presence of a negative pressure suction to fabricate a novel anti-bacterial air filter material. Composition, structure and morphology of the coated ZnO were characterized by scanning electron microscope, X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy and X-ray photoelectronic spectroscopy. A possible formation mechanism of ZnO was proposed. A high crystallized ZnO nanoparticles layer was formed when the calcination temperature exceeds 500°C. The coated ZnO crystallites were hexagonal wurtzite and the grain size was in the range of 20–50nm. No evident N2 permeability difference was detected in gas permeation tests before and after ZnO nanoparticles coating. ZnO-coated SiC foam was found to exhibit an excellent anti-bacterial property with sterilization rate of Escherichia coli exceeding 99.8% for all modified samples.

Mechanisms of self-assembly in solution grown ZnO nanorods

The mechanisms for self-assembly of ZnO nanorods grown by chemical bath deposition are investigated in detail. Using a combination of scanning electron microscopy, x-ray diffraction and transmission electron microscopy, the growth mechanism of ZnO nanostructures from a solution was studied. The study revealed that the mechanism of nucleation is the crucial step in controlling the morphology, orientation and distribution of the nanostructures on a silicon substrate. In the absence of a seed layer, rods initially nucleated from eroded regions in precipitated Zn(OH)2 lead to the formation of flower-like, hemi-spherically arranged nanorods. In the presence of a higher density seed layer, well-aligned nanorods form on the seed layer coated substrate as a result of competition between homogeneous and heterogeneous nucleation. In general, the initial precipitation of Zn(OH)2 in a basic solution followed by its dissolution is suggested as the formation mechanism of ZnO. These findings may contribute to the understanding of the mechanism of self-assembly of ZnO nanorods and help to control and manipulate the ZnO architecture during solution growth.

Large scale synthesis of ZnO nanoparticles via homogeneous precipitation

In order to synthesize ZnO nanoparticles economically, industrial-grade zinc sulfate and urea were utilized to synthesize ZnO precursors in a stirred-tank reactor or a Teflon-lined autoclave at 100–180 °C under complete sealing condition. The ZnO precursors were calcined at 450 °C for 3 h to synthesize ZnO nanoparticles. The composition of the precursors and the formation mechanism of ZnO were studied by thermogravimetric analysis and Fourier transform infrared spectroscopy. The results of X-ray diffraction, transmission electron microscopy and scanning electron microscopy of the ZnO powders demonstrate that high-purity zincite ZnO nanoparticles are synthesized. Orthogonal experiments were performed to find out the optimal conditions for the maximum yield and the minimum size. The effect of temperature on the size of ZnO nanoparticles was investigated. The results show that a higher temperature is propitious to obtain smaller nanoparticles.

Synthesis and photoluminescence of ZnO and Zn/ZnOnanoparticles prepared by liquid-phase pulsed laser ablation

ZnO nanoparticles and Zn/ZnO core/shell structured nanoparticles are synthesized by ablating zinc target in deionized water and sodium dodecyl sulfate (SDS) solutions, respectively, using pulsed laser ablation with 532 nm pulsed infrared laser. The microstructures and photoluminescence properties of the products are characterized by X-ray diffraction, transmission electron microscopy, ultraviolet-visible and PL spectrophotometer. The formation mechanism of ZnO and Zn/ZnO nanoparticles is discussed. The results show that the mean diameters of ZnO nanoparticles are 43 nm and 19 nm, respectively, after ablating the zinc target for 2 and 4 hours in deionized water. The longer-time ablation may lead to the interaction of the ablating laser beam with the ZnO nanoparticles, resulting in the decrease of the mean diameter of ZnO. Zn/ZnO core/shell structured nanoparticles can be obtained in 0.005 mol/L SDS solution due to the enwrapping of SDS to the Zn nanoparticles. A blue photoluminescence at about 450 nm (2.76 eV) and a green one at about 558 nm (2.22 eV) are observed for the colloidal solutions of ZnO and Zn/ZnO nanoparticles.

Electrochemical synthesis of orientation-ordered ZnO nanorod bundles

The high density and orientation-ordered ZnO nanorod bundles with wurtzite structures were prepared on Cu substrates by electrochemical deposition in solution of ZnCl 2 + tartaric acid at a temperature of 90 °C. This approach is a unique and size controlled synthetic method for the large-scale preparation of ZnO nanorod bundles. Cyclic voltammogram measured in solution of the mixture of ZnCl 2 and tartaric acid shows a restraining role of tartaric acid for the electro-reduction of Zn(II). The formation mechanism of ZnO on the surface of the cathode can be explained that the high temperature (⩾90 °C) promotes the corrosion of electrodeposited Zn via reacting with H 2O and O 2 to form the stable passive phase of ZnO. The compositions of the nanorod bundles can be entirely ZnO or Zn and ZnO composites determined by the temperature and deposition rate. The photoluminescence (PL) properties indicate that these ZnO deposits are highly crystallized and of excellent optical quality.