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1、Nanomaterials (1-100 nm) offer a host attractive properties that are different fromthose associated with coarse particles. With the growing number of applications for thisnew nanomaterials, several techniques have evolve
2、d over the past several years for thesynthesis of Zn and ZnO powders. The unique challenges associated with processingsuch fine structures are discussed together with each technique. Major obstacles haveincluded the diff
3、iculty (now largely overcome) of producing sufficient quantities ofnanometer powders and the strong tendency of nanomaterials powders to agglomerate. While it is virtually impossible to avoid agglomeration (particle adhe
4、sion) in pristinenanopowders due to the enormous van der Waals forces of attraction, the extent of agglomeration and aggregation (particle sintering) depends on the synthesis technique used to produce nanomaterials and p
5、rocessing parameter.Reactive and gas evaporation syntheses are described in which nanomaterials Zn and ZnO powders are directly produced by evaporating Zn powder of an average particle size of 370 μm from an alumina cruc
6、ible using an electric furnace. The experimental geometry is described, and the effects of experimental parameters are characterized.Samples are collected from the inner wall of the work chamber as well as from special c
7、ollector set in the work chamber. The suitable conditions for obtaining nano-ZnO synthesized by reactive evaporation method is determined as: evaporation temperature 1100 ℃, air flow-rate 0.6m3/h, amount of powder charge
8、d 5g, distance from evaporation source 10cm. On the other hand, the optimal synthetic conditions for obtaining nano-Zn particles is determined as: evaporation temperature 1200℃, argon flow-rate 0.4 m3/h,amount of powder
9、charged 5 g, distance from evaporation source 10 cm.ZnO particles are also produced by gas evaporation method in O2-Ar mixture. The mechanism of producing nano-ZnO particles from Zn powder in either air or O2-Ar isformed
10、 by the oxidation of the evaporated zinc vapor. Zn vapor formed at 1000 ℃ andfollowed towards the open end of the outer alumina tube where Zn oxidation took place.It is shown that ZnO fourlings almost certainly nucleate
11、as fourfold twins. X-ray diffraction (XRD) and electron diffraction (ED) show the powders to be highly pure ZnO and the tetrapod-like is hexagonal (wurtzite) structured ZnO with lattice parameters of a = 0.3249 nm and c
12、= 0.5205 nm. TEM images indicate that nano-ZnO particles are structurally uniform with regular shapes. The nano-ZnO particles as whole are individual or single ones and mainly have the shape of a tetrapod-like of hexagon
13、al (wurtzite)structure. These particles consist of three or four needle-shaped crystals united at a common juncture. Such needles or particles are called "fourlings or tetrapod-like.Nanoparticles with a tetrapod-shaped c
14、rystal are expected to possess properties having applications in shock-resistance, sound insulation, photosensitization, fluorescence, gas sensitization, and catalyst. In same cases tetrapod with broken legs are also pre
15、sented.ZnO formed well-defined crystals as verified by ED. As determined by ED, the growth direction of ZnO nanoparticles is [11 ~ 0], which consists of strong spots of zinc oxide.Under various conditions, the range of p
16、article sizes is remarkably uniform (70 to 109 nm in diameter). The agreement between XRD measurement and TEM is good. Comparison is made between the particles prepared by reactive evaporation method and those obtained i
17、n gas evaporation method (O2-Ar), which are showed similar structural features.On the other hand, twinned particles are mainly observed among particles prepared in O2-Ar mixture. Twining is a common crystallographic phen
18、omenon in which two or more crystals are united in some symmetrical manner characteristic of the particular substances.The crystallite with these habits has also the wurtzite structure. By controlling the evaporation con
19、ditions, high surface area nanoparticles of ZnO are produced with minimal aggregation. Air flow-rate and amount of metal charged have strong effect on the particle size of ZnO, while argon flow-rate and evaporation tempe
20、rature play key role in controlling particle size of Zn, although they are made at nearly identical parameter conditions. The size of Zn particles increases linearly with the height where no metal vapor exists. The relat
21、ion is verified by measuring the size of Zn particles in a different height due to the zinc particles grow remarkably by coalescence. In the case of nano-Zn,the particles are covered with epitaxially grown oxide during r
22、emoval from chamber,which slows down the growth of nanoparticles, is deleterious to their mechanical properties and diminishes their density. Another problem that is crucial to Zn nanopowders is their ability to self-sin
23、ter when they come to rest, to form agglomerates during condensation. However, Zn with definite crystal habits (hexagonal) is sometimes observed among those with irregular ones and has a particle size of 12 to 99 nm in d
24、iameter. The oxide formed on the zinc particles even when these are produced under the cleanest possible conditions. XRD measurement yields smaller particles compared to TEM image analysis, which can be attributed to the
25、 manner of agglomerated particles.The manner of aggregation has been found to be independent of the argon pressure. The aggregation, however, changed markedly when small amount of air is present. The mixture particles of
26、 Zn and ZnO are formed when evaporation is carried out in an atmosphere containing a small amount of air in the work chamber. Electron as well as Xray patterns from the particles are consistent with a mixture of Zn and Z
27、nO. It is shown by TEM that smoke particles grew by coalescence in which two or more single particles joined in definite orientation. Oxide rings are usually broad and continuous whereas the metal rings are grainy. This
28、implies that the oxide crystals are very small.Nano-ZnO particles produced by the reactive evaporation have higher density because of their discrete tetrapod structure. The densities resulting from nanomaterials consolid
29、ation have ranged up to about 3.523 g/cra3 for nano-Zn and up to 4.865 g/em3 for nano-ZnO, i.e., 87 % of the theoretical density of ZnO.On the other side of some applications, nanoscale particles are deliberately fabrica
30、ted into a specific morphology to obtain the required functionality. During the last few years the development of inert anodes for the aluminum industry has advanced considerably and announcements of progress have influe
31、nced the stock market. This work result of tests on anodes is made of nano-ZnO and normal ZnO in aluminum industry. The study examines solubility in (Na3AlF6, AlF3, Al2O3, CaF2) electrolysis test.These anodes can be used
32、 to replace carbon anodes for the production of aluminum that are resistant to attack by molten bath, yet exhibits good electrical conductivity. NanoZnO is produced by reactive evaporation method while normal ZnO is obta
33、ined from Shenyang Chemicals Factory. Raw materials are agglomerated with a binder to give green strength to the cold compact. Cold uniaxial pressing at 10 MPa, drying at 110 ℃for 2 hours and sintering temperature in atm
34、osphere furnace at 1200 to 1300 ℃ at 5 to 10hours are made inert anodes materials. The effects of variable operations are discussed.Laboratory solubility tests reveal that the weight loss ratio of nano-ZnO anode is muchl
35、ower than the normal one made from ordinary-ZnO (6.67~10.18) provided to be better suited than normal ZnO for resistance towards cryolite. When the sintering temperature increases up to 1300 ℃, the weight loss ratio of n
36、ano-ZnO and normal ZnO get up to 5.01~7.33% and up to 6.67~10.18% respectively.Photocatalytic degradations of p-nitrochlorbenzene (P-NCB) with distilled water are also investigated with ZnO crystals (catalyst) of 70 nm i
37、n diameter under UV irradiation. The suitable experimental conditions are determined as: ZnO 0.25 g, pH 7, PNCB concentration 30 mg/L. We have discussed these variables in terms of the degradation rate that we defined as
38、 the rate of the initial degradation to the final degradation of P-NCB. When all of the experimental degradation rate values are plotted as a function of irradiation time, all of the points appeared on a single line for
39、wide range of P-NCB degradations. On the basis of these results, we have concluded that at lower ZnO catalyst amount, much of the light is transmitted through the slurry in the container beaker, while at higher catalyst
40、amount, all the incident photons are observed by the slurry. Degradation rates of P-NCB are found to decrease with increasing solution pH.We have also concluded that the maximum degradation rate values of P-NCB under pri
41、ncipally the same experimental conditions mentioned above are 97.4%, 98.8%, and 95.5% at 100.0 min respectively. The results suggest that the photocatalytie degradation is initiated by an oxidation of the P-NCB through Z
42、nO surface- adsorbed hydroxyl radicals. Absorption spectra are recorded using spectrophotometer before and after UVirradiation in the wavelength range 200-400 nm at room temperature. It is found that the variation of irr
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