Creep-sintering of polycrystalline ceramic particulate composites

The sintering of particulate composites consisting of a polycrystalline zinc oxide matrix with 10 vol % zirconia inclusions of two different sizes (3 and 14 m) was investigated at a constant heating rate of 4 °C min^–1 under an applied stress of 300 kPa. The presence of the inclusions produced a decrease in both the creep rate and the densification rate but the ratio of the densification to creep rate remained constant during the experiment. The ratio of the densification rate to creep rate for the composites was 1.5 times greater than that of the unreinforced matrix regardless of inclusion size. The creep viscosity of the composites was higher than that of the unreinforced matrix and increased slightly with decreasing inclusion size.     

Interaction of zinc oxide with bismuth oxide

The lattice parameters of polycrystalline ZnO in mixtures of ZnO-Bi₂O₃ and their dependence on Bi₂O₃-concentration were determined. Simultaneously the influence of ZnO presence on the origin of various modifications of Bi₂O₃ was observed. On the grounds of the measured decrease of the elementary cell volume the supposition about the interaction of Zn-intersititals with overstoichiometric oxygen atoms in Bi₂O₃ was accepted. In accordance with this idea the changes of free carrier concentration of samples ZnO+5 mol% Bi₂O₃ in the dependence on annealing temperature were found.     

氨法浸出氧化锌烟尘制取活性氧化锌

为实现冶锌废渣中锌资源的再利用,以商洛炼锌厂冶锌过程中产生的氧化锌烟尘为原料,采用氨法浸出-微波蒸氨-火法焙解工艺制得粒度分布均匀的球状活性氧化锌.对锌的浸出工艺及氧化锌前驱体的热解工艺进行研究,并利用TG/DTA、XRD、SEM等测试手段对产品进行结构及物相表征.研究表明,氨法浸出过程中总氨浓度为8 mol/L、pH为10.0、液固比为4∶1、浸出温度为40℃时,锌的浸出率最高可达92.05%.浸出液经两段净化除杂后,80℃下蒸氨25 min时,制得前驱体碱式碳酸锌.在400℃焙解120 min制得平均粒径约为3μm,六方晶系的球状活性氧化锌.此法对设备要求不高,生产成本低,工艺流程短,具有较强的实用性.     

Bicrystalline zinc oxide nanocombs

Bicrystalline ZnO nanocombs have been prepared by zinc powder evaporation at 650 degrees C. Structural analysis showed that as-synthesized samples are composed of two crystals that form a twin structure parallel to the (113) plane with the growth direction of the branching nanowires and the main stem closely parallel to (0001) and (0110), respectively. Due to the unique twin structures, both sides of the main stems could be Zn-terminated ZnO(0001) polar surfaces. The chemically active surfaces make the aligned branching nanowires grow from both sides of the main stems, which is consistent with the structure of the obtained bicrystalline nanomaterials. The growth of bicrystalline ZnO nanocombs can be explained by polar-surface dominated growth and twins induced growth mechanisms.     

Doughnut-shaped zinc oxide particles

Zinc oxide doughnut-shaped particles were synthesized using a chemical route. A possible growth model has been proposed from a detailed experiment in which samples were picked from the reaction chamber at various time intervals and characterized using scanning electron microscopy (SEM). Particles were also characterized using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).     

纳米氧化锌的制备

以硫酸锌和碳酸铵为原料,直接沉淀法制得纳米氧化锌的前驱体,然后煅烧得到纳米氧化锌.采用 TG-DTG、XRD和TEM等测试手段对其进行了表征.结果表明,前驱体为Zn4(OH)6CO3.通过控制煅烧温度、反应温度和反应物浓度可以得到不同粒径的球形纳米氧化锌.得出了最佳制备工艺条件.     

Pyramidal nanostructures of zinc oxide

Zinc oxide (ZnO) nanostructures have been prepared by pulsed laser deposition of the oxide onto Si(100) substrate at 600 degrees C. An examination of the morphology using atomic force microscopy and scanning electron microscopy reveals well formed pyramidal structures consistent with the growth habit of ZnO. A domain matched epitaxy across the interface makes the ZnO pyramids orient along the axes of Si(100) surface. The pyramidal nanostructures signify an intermediate state in the growth of hexagonal nanorods of ZnO. The hardness of the nanostructures as well as their response to oxygen gas have been investigated using nanoindentation and conducting probe methods respectively. ZnO nanostructures are much harder than their bulk. The hardness of ZnO pyramids obtained by nanoindentation is 70 +/- 10 GPa which is about one order more that of bulk ZnO. Besides, the nanostructures exhibit high sensitivity towards oxygen. A 70% increase in the resistance of ZnO nanostructures is observed when exposed to oxygen atmosphere.     

纳米ZnO的制备

本文研究了以Zn (No3 ) 2 、尿素为原料 ,加入表面活性剂改性制备纳米氧化锌粉体的方法。实验讨论了Zn (NO3 ) 2 浓度、尿素浓度、pH值、焙烧温度对纳米氧化锌粒径的影响。用扫瞄电镜和粒度分析仪确定纳米氧化锌的形貌和粒径     

Development of zinc oxide varistors

Grain growth kinetics of ZnO ceramics containing 6% additives of Bi₂O₃, CoO and MnO in equal molar ratios has been studied in the temperature range 1000 to 1350°C. It has been observed that the grain growth data fits theD ²=kt law and the activation energy computed from the rate constants is 65 kcal/mol.     

Optical properties of amorphous-like indium zinc oxide and indium gallium zinc oxide thin films

The paper presents the optical properties of amorphous-like indium zinc oxide and indium gallium zinc oxide thin films with various In/(In + Zn) ratios obtained by Pulsed Laser Deposition. Thickness results obtained from simulations of X-ray Reflectivity and Spectroscopic Ellipsometry data were very similar. The dependence of density on stoichiometry resembles the corresponding dependence of the refractive index in the transparency range. A free carrier absorption was noted in the visible spectral range, leading to a weak absorbing thin transparent conductive oxide. On the other hand, the refractive index is smaller than those of based oxides (ZnO and In₂O₃), and counterbalance therefore the weak light absorption.     

Optical and electrical properties of zinc oxide/indium/zinc oxide multilayer structures

Zinc oxide/indium/zinc oxide multilayer structures have been obtained on glass substrates by magnetron sputtering. The effects of indium thickness on optical and electrical properties of the multilayer structures are investigated. Compared to a single zinc oxide layer, the carrier concentration increases from 8 × 10¹⁸ cm⁻³ to 1.8 × 10²⁰ cm⁻³ and Hall mobility decreases from 10 cm²/v s to 2 cm²/v s for the multilayer structure at 8 nm of indium thickness. With the increase of indium thickness, the transmittance decreases and optical band gap shifts to lower energy in multilayer structures. Results are understood based on Schottky theory, interface scattering mechanism and the absorption of indium layer.     

Preparation of extrapure zinc oxide and zinc acetate from diethylzinc

We have developed a process for the preparation of extrapure zinc oxide and zinc acetate from diethylzinc, which includes ultrapurification of this compound through low-pressure fractional distillation, oxygen oxidation of the purified diethylzinc in combustion mode, and heat treatment of the resultant zinc oxide. Zinc acetate was obtained by dissolving the zinc oxide in acetic acid. The content of regulated metallic impurities (iron, copper, aluminum, silicon, cadmium, nickel, cobalt, tin, lead, chromium, molybdenum, and magnesium) in the zinc oxide and zinc acetate was 10^?5 to 10^?6 wt %, and their net content was <5 × 10^?4 wt %.     

L-Histidine-modified biocompatible zinc oxide nanocrystals

In this article, we report a new method of preparing size-controlled and well-dispersed ZnO nanocrystals using L-histidine as the capping agent. The synthesis and properties of ZnO nanocrystals capped with L-histidine prepared by the wet chemical route are presented. The structural properties of L-histidine-capped nanocrystals are investigated by XRD, TEM, EDAX and FTIR spectroscopy. The optical characterisation of the nanocrystals is carried out on the basis of UV-Vis absorption and photoluminescence spectroscopy. The size of the L-histidine-capped ZnO nanocrystals is less than 10?nm as confirmed from TEM images. The elemental composition detected from EDAX establishes the presence of the capping agent in the samples. For L-histidine-modified ZnO nanocrystals, the UV absorption edge shifts towards the blue region compared to pure ZnO, suggesting the formation of nanocrystals of smaller size. The intense photoluminescence emission observed around 527?nm for L-histidine-capped ZnO offers high prospects in bio-imaging applications. The colloidal stability of the capped nanocrystals is very good as it remains stable without settling down for more than three weeks. Nanocrystals of different sizes have also been synthesised and their properties studied. The present synthesis route is of low cost and easy to control offering high purity to the products, using only bio-compatible materials. The functionalised nanoparticles are suitable for biological applications.     

Flame synthesis of zinc oxide nanocrystals

Distinctive zinc oxide (ZnO) nanocrystals were synthesized on the surface of Zn probes using a counter-flow flame medium formed by methane/acetylene and oxygen-enriched air streams. The source material, a zinc wire with a purity of ～99.99% and diameter of 1 mm, was introduced through a sleeve into the oxygen rich region of the flame. The position of the probe/sleeve was varied within the flame medium resulting in growth variation of ZnO nanocrystals on the surface of the probe. The shape and structural parameters of the grown crystals strongly depend on the flame position. Structural variations of the synthesized crystals include single-crystalline ZnO nanorods and microprisms (ZMPs) (the ZMPs have less than a few micrometers in length and several hundred nanometers in cross section) with a large number of facets and complex axial symmetry with a nanorod protruding from their tips. The protruding rods are less than 100 nm in diameter and lengths are less than 1 μm. The protruding nanorods can be elongated several times by increasing the residence time of the probe/sleeve inside the oxygen-rich flame or by varying the flame position. At different flame heights, nanorods having higher length-to-diameter aspect-ratio can be synthesized. A lattice spacing of ～0.26 nm was measured for the synthesized nanorods, which can be closely correlated with the (0 0 2) interplanar spacing of hexagonal ZnO (Wurtzite) cells. The synthesized nanostructures were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution TEM (HR-TEM), X-ray energy dispersive spectroscopy (EDS), and selected area electron diffraction pattern (SAED). The growth mechanism of the ZnO nanostructures is discussed.     

Vapour growth of single-crystal zinc oxide

A vapour technique is described by which single-crystal zinc oxide may be grown. Sintered, polycrystalline zinc oxide, contained in a tube furnace, is first reduced by hydrogen to zinc vapour, which is then re-oxidised to form single-crystal zinc oxide in the furnace hot-zone. The effect of temperature and gas flow on the crystal type is reported, together with some crystal properties, including resistivity and drift mobility.     

Low-temperature sintering of zinc oxide varistors

High-field varistors in the system ZnO-CoO-MnO-Bi₂O₃ were fabricated using powders prepared by a previously developed coprecipitation process. Following calcination, the powders were compacted and densified by conventional pressureless sintering at temperatures below 750° C in air, The effects of sample green density, sintering temperature, and grain-growth inhibitor on densification and microstructure development were investigated. Addition of aluminium at the 125 p.p.m level was used to inhibit grain growth. Samples with densities >0.98 theoretical and grain sizes <1m were fabricated by high-pressure cold-isostatic pressing followed by sintering at 730° C. For comparison, typical commercial varistor devices have grain sizes of about 20 m and switching fields of approximately 2 kV cm^–1 after sintering at 1200 to 1400° C. As a result of the fine grain size, our high-field varistors had switching fields of 45 kV cm^–1 at a current density of 10 A cm^–2. Consistent with earlier work on extremely high-density varistors (>0.98 theoretical) prepared from similar powders, nonlinearity coefficients of about 10 were measured for current densities between 2.5 and 10 A cm^–2.     

Microstructure of nanoscale zinc oxide crystallites

Nanosized ZnO particles were prepared using a simple precipitation method. First, hydrozincite was obtained by adding Na₂CO₃ aqueous solutions with different concentrations to a zinc acetate precursor, previously dissolved in ethanol. We observed that the starting concentration of the precursors and the water content used for the hydrolysis influenced the size of the hydrozincite particles. The formation of the ZnO nanoparticles began after heating the hydrozyncite to 200 °C, and even when heating to 600 °C nanosized ZnO particles of 20-50 nm were obtained without agglomeration. The morphology and crystallinity of the obtained solids were characterized using XRD, SEM and TEM.     

Secondary emission of nanocrystalline zinc oxide

The Raman and photoluminescence (PL) spectra of nanocrystalline zinc oxide produced by mechanochemical synthesis were measured using a pulsed nitrogen laser (337.1 nm) and xenon lamp (360 nm) as excitation sources in PL measurements and a cw Nd:YAG laser in Raman measurements. PL was observed in the range 400–800 nm. The Raman spectrum of nanocrystalline (90 nm) ZnO was compared to that of coarsegrained ZnO. The Raman bands of nanocrystalline zinc oxide were found to be shifted to lower frequencies and broadened. Laser radiation was shown to cause local heating of zinc oxide up to 1000 K, resulting in photoinduced formation of zinc nanoclusters. Mixtures of zinc oxide and sodium chloride powders are heated to substantially lower temperatures. Under nitrogen laser excitation, the green PL band (535 nm), characteristic of bulk ZnO, is shifted to longer wavelengths by 85 nm. The results are interpreted in terms of light confinement in zinc oxide microclusters consisting of large number of nanocrystallites. The photoinduced processes in question may be a viable approach to producing metal-insulator structures in globular photonic crystals, opals, filled with zinc oxide.