ZnO Whiskers Research Articles

Dynamic Compressive Response and Failure Behavior of Basalt Fibers Polymer Functional Composites Embedded with ZnO Whiskers

A type of basalt fibers polymer functional composites embedded with ZnO whiskers was prepared. The as-prepared composites exhibited good microwave absorption properties after the dispersion of ZnO whiskers in resin. The dynamic compressive properties of composites were investigated by the split Hopkinson pressure bar (SHPB) system. The macro- and micro-fracture morphology of composites was obtained by the scanning electron microscope (SEM). The experimental results showed that the as-prepared composites have excellent mechanical properties, and the compressive properties could be significantly affected by the strain rates in the in-plane direction, as well as in the normal direction. As the strain rate increased, the higher strength and elastic modulus are obtained. Under the dynamic compressive load in the normal direction, the main failure mode of composites is pure compression. On the other hand, longitudinal splitting and delamination of composites could be induced when loaded in the in-plane direction. The micro- interfacial crack, fiber fracture and plastic deformation of resin could be observed from the morphology of fractured composites.

Synthesis, characterization and optical properties of multipod ZnO whiskers

Multipod ZnO whiskers were synthesized successfully by two steps: pulsed laser deposition (PLD) and thermal evaporation process. First, a thin layer of Zn films were deposited on Si(1 1 1) substrates by PLD. Then the whiskers grew on Zn-coated Si(1 1 1) substrate by the simple thermal evaporation oxidation of the metallic zinc powder at 900 °C in the air without any catalysts or additives. The pre-deposited Zn films by PLD on the substrate can promote the growth of ZnO multipod whiskers effectively. The as-synthesized ZnO whiskers were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). The results revealed that the whiskers are highly crystalline with the wurtzite hexagonal structure. Room temperature photoluminescence (PL) spectrum of the whiskers shows a UV emission peak at ∼393 nm and a broad green emission peak at ∼517 nm, which was assigned to the near band-edge emission and the deep-level emission, respectively.

Effects of polyethylenimine on morphology and property of ZnO films grown in aqueous solutions

Morphologies and properties of well-aligned ZnO films were controlled using zinc nitrate-hexamethylenetetramine aqueous solutions with the addition of polyethylenimine as a surfactant. Porous and dense ZnO films were fabricated with and without polyethylenimine, respectively. The addition of polyethylenimine proceeded to form porous ZnO whiskers film by preferential adsorption to nonpolar crystal faces and modifications of the surface free energy and growth rate. Dense ZnO film showed high transmittance of 80%, and low intensity of fluorescence and photo-induced current. Porous ZnO whiskers film showed low transmittance of 70%, while high intensity of fluorescence and high photo-induced current were detected because the porous ZnO nanowhisker film possessed a large interior surface area which can capture large amounts of DNA molecules labeled with dye molecules on the surface of ZnO crystals. High performance dye-sensitized sensors can be produced using ZnO whisker films prepared from an aqueous solution.

Tapered ZnO Whiskers: {hkil}-Specific Mosaic Twinning VLS Growth from a Partially Molten Bottom Source

Zn particulates overlaid with wurtzite (W)-type ZnO condensates having nearly orthogonal and facets were found to self-catalyze unusual tapered W-ZnO whiskers upon isothermal atmospheric annealing, i.e., thermal oxidation, at 600 °C. Analytical electron microscopic observations indicated that such whiskers formed tapered slabs having mosaic and twinned domains. The tapered whiskers can be rationalized by an alternative vapor–liquid–solid growth, i.e., {hkil}-specific coalescence twinning growth from the ZnO condensates taking advantage of a partially molten bottom source of Zn and the adsorption of atoms at the whisker tips and ledges under the influence of capillarity effect. The tapered whiskers having strong photoluminescence at 391 nm and with a considerable flexibility could have potential applications.

ZnO Whiskers and Belts in Chestnut Husk-Like Structures: Synthesis and Proof of Chemomechanical Transduction

The preparation of chestnut husk-like ZnO starting from Zn powders is described, pointing out the role of ZnO(1-x) seeds in the self-catalytic liquid-solid growth process. The final architecture is made up of ZnO whiskers stemming from ZnO platelets which are self-assembled into spheroidal agglomerates. Whiskers can be converted into belts by using polyvinylpyrrolidone and configurations exhibiting whiskers and belts on the same husk are obtained through a sequential growth procedure. Polystyrene microspheres are employed in Raman microscopy proof of concept experiments to demonstrate the potential of ZnO whiskers in transduction of chemomechanical interactions, which opens promising perspectives for in-vivo bioapplications.

Preparation and Properties of Calcium Phosphate Cement Containing ZnO Whisker

Calcium phosphate cement (CPC) is a self-hardening material for bone repairing. ZnO whisker is a new type reinforced materials lately, which is acerose single crystal fiber. In this study, ZnO whisker was added into the CPC with different ratios, and each specimen kept at 37 oC in 100% humidity for 24 hrs. The phase and microstructure of the calcium phosphate pastes were investigated using X-ray diffraction and scanning electron microscopy, respectively. It has been found that ZnO whisker could supply nucleating center, TTCP and DCPA could be much easier to form HA around the ZnO whisker. The adding amount of ZnO whisker is a key factor that determines the mechanical properties.

Studies on the Active Oxygen in Zinc Oxides with Different Morphologies

Active oxygen species generated from semiconductor under irradiation play an important role in decomposing and mineralizing pollutants and undesirable compounds in the air and waste water. The production of superoxide anion (O2－) and hydroxyl radical (•OH) generated in the suspension of zinc oxides with different morphologies and particle sizes were studied in the present paper. Three kinds of zinc oxides, which named tetra-needle like ZnO (T-ZnO) whisker with length of 10~20 μm and basal diameter of 1~3 μm, nanosized ZnO (n-ZnO) with particle size of 20~30 nm and commercial ZnO powder (p-ZnO) with particle size of ~1 μm, respectively, were used in this work. Nitroblue tetrazolium (abbr. NBT) was used to determine the amount of super oxide anion generated from the related zinc oxides, in which NBT can be reduced to insoluble purple formazan by super oxide anion. The amount of hydroxyl radicals was determined by detecting the decreased absorption intensity of Fe(phen)32+ (complex of iron (II) with 1,10-phenanthroline) at 510 nm with UV-Vis spectrophotometer. The results indicated that the most amounts of superoxide anion and hydroxyl radical were detected in T-ZnO whiskers and n-ZnO respectively. The difference between the production amount of superoxide anion and hydroxyl radical can be attributed to the different mechanisms for both of the production and transportation of these two kinds of active oxygens.

On-paper synthesis of Au nanocatalysts from Au(III) complex ions for low-temperature CO oxidation

Au nanoparticles (AuNPs) were successfully synthesized in situ on a microstructured paper matrix composed of ceramic fibers as the main framework and ZnO whiskers as a preferential support for AuNPs. The paper-like ceramic fiber/ZnO whisker composites were prepared using a papermaking technique, then soaked in an aqueous solution of the Au(III) complex HAuCl4. AuNPs with size <10 nm were spontaneously formed on the ZnO whiskers in the absence of reducing agents, possibly due to electron transfer from Zn(II) in ZnO whiskers to Au(III) species through Zn–O–Au bonds. As-prepared AuNPs@ZnO whisker-containing paper (AuNPs@ZnO paper) is much like ordinary paper products in being flexible, lightweight and easy to handle. AuNPs@ZnO paper demonstrated excellent catalytic performance in low-temperature CO oxidation. Complete conversion of CO to CO2 was achieved at 20 °C, 140 K lower than the reaction temperature for conventional Au/ZnO catalyst powders. This facile technique has potentially broad wide applications in ‘on-paper’ synthesis of a diverse array of metal NPs. The metal NPs@ZnO paper composites with paper-like flexibility are able to fit various reactor configurations and are thus expected to be promising catalytic materials for improving the practical utility and catalytic performance of these systems, for a wide range of industrial chemical processes.

Properties and field emission characteristics of Ga:ZnO whiskers

Ga:ZnO whiskers were grown by atmospheric chemical vapor deposition on single crystalline silicon (100). By adjusting the concentration of the gallium dopant, the crystallite density and radius of curvature could be varied. The c-axis orientation of the Ga:ZnO crystallite was less than that of the Al:ZnO crystallite. The field emission characteristics of Ga:ZnO whisker emitters were investigated by varying the crystallite density and radius of curvature. Moreover, when the crystallite density was in the range 0.8 × 104-1.6 × 104/mm2 and the crystallite radii of curvature were in the range 46-106 nm, the electric field, E, necessary to obtain a current density, J, of 100 μA/cm2 was in the range 5.3-5.7 V/μm.

Morphology control of ZnO particles via aqueous solution route at low temperature

In this study, monodispersed ZnO whiskers and flower-like ZnO composed of numerous well-aligned nanorods were successfully prepared via a simple solution route at low temperature. To further understand the formation processes of the ZnO particles, scanning electron microscopy (SEM) and X-ray powder diffraction (XRD) analyses of the solid product as well as concentration measurements of Zn(II) remaining in the solution have been made at regular intervals throughout the reaction. Experimental results show that morphology of ZnO depends closely on the precursor before aging step, and regular Zn(OH) 2 are capable of controlling and adjusting the Zn(OH) 4 2− concentration in solution, maintaining it in a suitable range to get one-dimensional ZnO whiskers.

Synthesis of needle- and flower-like ZnO microstructures by a simple aqueous solution route

Needle-like ZnO whiskers and flower-like ZnO microstructures composed of different building blocks were successfully prepared via a simple aqueous solution route at low temperature. To further understand the formation processes of these ZnO microparticles, concentration measurements of Zn(II) remaining in the solution as well as SEM and XRD analyses of the solid product have been made at regular intervals throughout the reactions. It is found that the solution basicity has determinative effects on the morphology of the obtained ZnO products by controlling the composition of the precursor and mediating the nucleation and crystal growth rate of ZnO.

Ferromagnetism in Fe-doped tetra-needle like ZnO whiskers

The Fe-doped tetra-needle like ZnO whiskers (T-ZnOw) were prepared with different loadings of Fe 3+ by a solid solution process. The structures and magnetic properties of the samples were characterized by using X-ray diffraction (XRD) and superconducting quantum interference device (SQUID) magnetometer, respectively. The results indicate that Fe 3+ ions are successfully doped into the crystal lattice of T-ZnOw matrix. The second phase of ZnFe 2O 4 is formed by heavy doping of Fe 3+ ions, and the solid solubility limit of Fe 3+ in T-ZnOw crystal is about 0.7 mol%. The magnetic properties reveal that some of the Fe-doped T-ZnOw exhibits room-temperature ferromagnetic behaviors. The room-temperature ferromagnetism in the Fe-doped T-ZnOw system is ascribed to be originated from the change of the electronic states of ZnOw caused by irons doping.

Conductive mechanism of antistatic poly(ethylene terephthalate)/ZnOw composites

AbstractAntistatic composites of poly(ethylene terephthalate) (PET) and tetrapod‐shaped ZnO whisker (ZnOw), the surface of which was treated with a coupling agent, were prepared by melt‐mixing using a twin screw extruder. The structure and morphology of the blends were examined by FTIR and SEM. Antistatic performance and the effect of ZnOw loading levels were investigated. The conductive mechanism of PET/ZnOw composites is presented, which can be classified into tunnel effect, discharging effect at the pinpoint and conductive network. The simple formula of critical volume fraction (vc) for ZnOw forming conductive network is proposed, based on the actual processing conduction. Comparison of the theory value to the experimental data showed a close agreement. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers

Comparison of tribological behavior of nylon composites filled with zinc oxide particles and whiskers

Mechanical properties and tribological behavior of nylon composites filled with zinc oxides were investigated in this paper. Different effects of ZnO particles and ZnO whiskers filling on the friction and wear behavior of nylon 1010 (PA1010) composites under dry friction condition were observed. The hardness, tensile strength and scratch coefficients of two kinds of nylon composites filled with the ZnO particles and whiskers were measured. Experimental results show that ZnO particles and ZnO whiskers improve the mechanical and tribological properties of nylon composites without affecting the crystallinity of nylon matrix. Hardness, tensile strength and scratch coefficient of composites are increased by the addition of ZnO particles and ZnO whiskers. Filler shape has little effect on the friction coefficients of nylon-based composites. These composites filled with particles and whiskers have nearly the same friction coefficients which locate between 0.4 and 0.45. The wear rates of composites are strongly dependent on filler shape and filler content. Particle-filled composites exhibit the lower wear rates than whisker-filled composites when the content of filler is lower than 10 wt.%. After that, the case is reversed. Ploughing and adhesion are the main wear mechanisms of composites with the addition of both ZnO particles and ZnO whiskers.

Field-Emission Properties of Al:ZnO Whisker Emitters with Various Crystallite Radii of Curvature

The field-emission properties of Al:ZnO whisker emitters were investigated by varying the crystallite radius of curvature. The crystallite radius of curvature could be varied by adjusting the concentration of the reactant of aluminum as a dopant. When the crystallite radius of curvature was decreased from 155 to 46 nm, the electric field necessary to obtain a current density of 100 µA/cm2 decreased from the range of 6.1 to 8.7 to the range of 4.4 to 5.1 V/µm. In addition, when the crystallite radius of curvature was decreased to 25 nm, the electric field necessary to obtain a current density of 100 µA/cm2 decreased to 3.6 V/µm. The crystallite radius of curvature and the crystalline density during the field emission affected the electric field necessary to obtain a cathode current density of 100 µA/cm2.

Highly conductive Al-doped tetra-needle-like ZnO whiskers prepared by a solid state method

Tetra-needle-like zinc oxide whiskers (T-ZnO W) were doped with Al 3+ by a solid state method. In this study, modification conditions were thoroughly investigated to obtain low resistivity T-ZnO W, without destroying the tetra-needle-like structure. The Al-doped T-ZnO W was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transition infrared (FT-IR) spectra and electrical resistance measurement. The SEM and XRD results indicated that the tetra-needle-like structure of ZnO whiskers could be well maintained after modification and the doped (0 0 2) face was preferred. FT-IR results showed that the decrease of resistivity of Al-doped T-ZnO W resulted from formation of [AlO 4] configuration in T-ZnO W bulk. Experiment results showed that the annealing temperature, doping concentration and type of Al sources affected the resistivity of T-ZnO W considerably. The optimum Al-doped concentration was 7.0 at.% and the resistivity of T-ZnO W could be considerably decreased from 10 8 to 10 2 Ω cm.

Field-Emission Properties of Al:ZnO Whisker Emitters with Various Crystallite Lengths and Densities

The field-emission properties of Al:ZnO whisker emitters were investigated by varying the crystallite density and length. The crystallite density could be varied by adjusting the reactant concentration or the substrate temperature under which whiskers were formed. When the crystallite density was decreased from 18 ×104 to 3 ×104/mm2 and the crystallite length was increased from 12 to 19 µm, the electric field necessary to obtain a current density of 100 µA/cm2 decreased from 7.0 to the range of 3.6 to 4.9 V/µm. After the field emission, the crystallite density of some samples decreased. The electric field necessary to obtain a cathode current density of 100 µA/cm2 decreased with increasing geometric electric field enhancement factor β.

WITHDRAWN: Dye-sensitized solar cells applications of ZnO whiskers grown by low-temperature hydrothermal process

This article has been withdrawn consistent with Elsevier Policy on Article Withdrawal ( http://www.elsevier.com/locate/withdrawalpolicy ). The Publisher apologizes for any inconvenience this may cause.

Modification of Electrical Properties of T-ZnO Whisker by Doping Fe

By means of high temperature solid-state reaction process, tetra-pod ZnO whisker (T-ZnOw) was doped with Fe(NO3)3. The doping induced the lattice distortion of the T-ZnOw, and improved its electrical properties significantly. After doping, the volume resistivity of the T-ZnOw decreased from 1010 &amp;·cm to 103 &amp;·cm, and its dielectric constant changed correspondingly.

Synthesis of tetrapod-shaped ZnO whiskers and microrods in one crucible by thermal evaporation of Zn/C mixtures

Tetrapod-shaped ZnO whiskers and microrods were synthesized in one crucible by thermal evaporation of Zn/C mixtures at 930 °C in air without any catalyst. The digital camera, optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction techniques were used to study the morphologies and crystal structures of these tetrapod-shaped ZnO microcrystals. The results show that these two types of ZnO tetrapods are grown at different heights within the same crucible. The legs of these tetrapod-shaped ZnO crystals are hexagonally faceted. Some tetrapod-shaped ZnO whiskers show hierarchical structures. A short button-like hexagonal ZnO microcrystal is observed at the triple junctions of some tetrapod-shaped ZnO whiskers. The tetrapod-shaped ZnO microrods are capped by two sets of hexagonal pyramids with two different groups of crystal planes for the surfaces. These two types of tetrapod-shaped ZnO microcrystals have different side faces and aspect ratio, which are believed to be the result of their different growth behaviors. The octa-twin model was used to discuss the different growth behaviors of these two types of ZnO tetrapods. The crystal planes of the legs and the pyramids were determined.