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V.M. Gun’ko V.V. Turov D. Palijczuk S.V. Kerus E.M. Pakhlov 《Applied Surface Science》2008,254(10):3220-3231
The behaviour of water and water/organic mixtures adsorbed onto activated microporous carbons or a carbon adsorbent with narrow intraparticle micropores and broad mesopores and macropores between nanoparticles was studied using low-temperature adsorption method and 1H NMR spectroscopy with layer-by-layer freezing-out of liquids at 190-273 K. These investigations revealed concentration-dependent effects of benzene, DMSO, acetone, chloroform, methane and acetonitrile on the characteristics of adsorbed water and the influence of this water on the interfacial behaviour of adsorbed organics. The influence of organics causes the structural and energetic differentiations of adsorbed water. The latter can be displaced by organics from micropores into broader pores and/or form mixture with polar solvents in meso and macropores. Freezing of adsorbed water can affect the adsorbent structure because ice crystallites have a larger size than that of liquid water droplets that lead to changes in the behaviour of adsorbed water/organic mixtures observed by the 1H NMR and adsorption methods. 相似文献
14.
Fine-sized ZnO–B2O3–CaO–Na2O–P2O5 glass powders with spherical shape were directly prepared by high temperature spray pyrolysis. The ZnO–B2O3–CaO–Na2O–P2O5 powders prepared by spray pyrolysis at temperatures above 1200 °C had broad peaks at around 30° in the XRD patterns. The glass transition temperatures (Tg) of the glass powders obtained by spray pyrolysis at preparation temperatures between 900 °C and 1400 °C were near 480 °C regardless of the preparation temperatures. The dielectric layers formed from the glass powders prepared by spray pyrolysis at preparation temperatures above 1300 °C had clean surface and dense inner structure at the firing temperature of 580 °C. The transmittance of the dielectric layer formed from the glass powders obtained by spray pyrolysis at preparation temperature of 1400 °C was 90% at the firing temperature of 580 °C, in which the thickness of the dielectric layer was 13 μm. The UV cutoff edges gradually shift towards longer wavelength with increasing the preparation temperature of glass powders and the firing temperature of dielectric layers. 相似文献
15.
Titanium diboride ultrafine powder was prepared from sucrose, tetrabutyl titanate and boric acid by the sol–gel and microwave
carbothermal reduction method. The influence of reaction temperature, ratio of Ti to C and Ti to B on the synthesis of titanium
diboride was studied. The results indicated that the carbothermal temperature, the content of carbon and the amount of H3BO3 show obvious effects on the formation of TiB2. 1,300 °C was the optimum synthesis temperature and pure TiB2 could be prepared. The microstructure of prepared TiB2 was investigated by field emission-scanning electron microscopy (FE-SEM), which results showed that the crystalline size
of the prepared titanium diboride at 1,300 °C was about 3–5 μm. The quantities of the crystalline phases of the powders prepared
at different temperatures were analyzed by Rietveld refinement method.
An erratum to this article can be found at 相似文献
16.
Haijun Zhang Faliang Li Quanli Jia Guotian Ye 《Journal of Sol-Gel Science and Technology》2008,46(2):217-222
Titanium carbide ultrafine powders were prepared from tetrabutyl titanate and sucrose by sol–gel and microwave carbothermal
reduction. The influences of reaction temperature and molar ratio of Ti to C on the synthesis of titanium carbide were studied.
The results show that excess amount of carbon plays a positive effect on the carbothermal reduction of TiO2 at low temperature. The inceptive carbothermal reduction temperature of TiO2 and formation of titanium oxycarbide was below 900 °C, and pure TiC can be prepared at 1,200 °C, which was considerably lower
compared to that by conventional carbothermal reduction using a mixture of TiO2 and carbon powders as raw materials. The morphology and particle size of synthesized TiC powder were examined by field emission-scanning
electron microscopy (FE-SEM) and the quantities of the phases of the powders were analyzed by Rietveld refinement method,
the particle sizes of the TiC powders synthesized at 1,300 °C distribute over 0.1–0.5 μm. 相似文献
17.
M. Novellani R. Santini L. Tadrist 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(3):571-578
The aim of this work is to study the porosity of three-dimensional and two-dimensional packing of stiff cylindrical fibres
according to their aspect ratio. First, we have carried out an experimental study of the porosity for 3D and 2D packing. In
this last case, the elementary representative surfaces have been determined. Then, an attempt of interpretation of the porosity
variations for 2D stacks has been realized on the basis of the excluded volume theory and a variation law has been proposed.
To conclude, we have studied the relevance of a simplified packing model based on a single geometry of the defects.
Received 12 April 1999 and Received in final form 4 August 1999 相似文献
18.
Y. Grasselli H.J. Herrmann 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(4):673-679
Experimental investigations on the shape of a heap formed in a Hele Shaw cell either on a flat base or in a two-dimensional
silo are presented. We have focused our attention on the shape dependence on mass flux and initial energy of particles poured
into the cell. Two kinds of granular media are considered: glass beads and sand and we shall point out their different behaviors.
We described the variations of the angle of repose and of the size of the tail as a function of the experimental parameters.
We also report the time evolution of the angle of repose during the formation of the heap.
Received 28 September 1998 and Received in final form 20 January 1999 相似文献
19.
Planarization machining of sapphire wafers with boron carbide and colloidal silica as abrasives 总被引:1,自引:0,他引:1
XiaoKai Hu Zhitang Song Zhongcai Pan Weili Liu LiangCai Wu 《Applied Surface Science》2009,255(19):8230-8234
The as-cutted sapphire wafers are planarized by the grinding and polishing two-step machining processes with micrometer B4C and nanometer silica as abrasives, respectively. The material removal rates (MRRs) of two processes are measured. During the polishing process, the MRR increases with the down-pressure increased, whereas the rotational speeds have less effect on the MRR. The alkaline colloidal silica is more favorable than the acidic to polish sapphire wafer. The ground and polished surfaces of the substrate are compared by scanning electron microscopy, atomic force microscopy, and X-ray rocking curves. Our results show that B4C abrasives are effective in elimination of the ununiformity in thickness within a wafer. The colloidal silica can achieve a nanoscale flatness of wafer, but the lasting polishing time seems unfavorable. The polishing process is also analyzed in terms of chemical mechanical polishing mechanism. 相似文献
20.
金属表面耐腐蚀性能与其微观结构密切相关。以金为分析对象,采用不同粒径氧化铝抛光粉抛光处理金片表面,经扫描电镜和原子力显微镜观察,表明金片表面具备与实际工件类似的微观结构,在此基础上,研究金片表面微观划痕结构对表面增强拉曼散射(SERS)以及耐腐蚀性能的影响。以罗丹明B为探针分子,对不同特征尺寸的微观划痕进行SERS分析,获得了罗丹明B的SERS信号强度随划痕平均特征尺寸的变化规律。通过改变拉曼激发光偏振方向与划痕方向的夹角大小,发现SERS信号主要归因于激发光与划痕相互作用产生的横向表面等离激元。划痕平均特征尺寸在50 nm附近时,横向表面等离激元最强,之后随着划痕平均特征尺寸增加,横向表面等离激元逐渐变弱。另一方面,对具有不同特征尺寸微观划痕的金片进行电化学极化测试,获得了各样品的自腐蚀电位,发现金片的自腐蚀电位随着划痕平均特征尺寸增大而降低。结果表明,当划痕平均特征尺寸大于50 nm,金表面的SERS信号与自腐蚀电位间存在良好的线性对应关系,这为SERS技术用于工件耐蚀性分析提供了依据。通过在工件表面滴涂探针分子并使用便携式拉曼光谱仪测量有望可以对工件耐蚀性进行现场快速预判。 相似文献