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Wei-Cheng Tian Pang S.W. Chia-Jung Lu Zellers E.T. 《Journal of microelectromechanical systems》2003,12(3):264-272
The design, fabrication, and testing of a preconcentrator-focuser (PCF), consisting of a thick micromachined Si heater packed with a small quantity of a granular adsorbent material are described. The PCF is developed to capture and concentrate vapors for subsequent focused thermal desorption and analysis in a micro gas chromatograph. The microheater contains an array of high-aspect-ratio, etched-Si heating elements, 520 /spl mu/m (h)/spl times/50 /spl mu/m (w)/spl times/3000 /spl mu/m (l), bounded by an annulus of Si and thermally isolated from the remaining substrate by an air gap. This structure is sandwiched between Pyrex glass plates with inlet/outlet ports that accept capillary tubes for sample flow and is sealed by anodic bonding (bottom) and rapidly annealed glass/metal/Si solder bonding (top). The large microheater surface area allows for high adsorption capacity and efficient, uniform thermal desorption of vapors captured on the adsorbent within the structure. The adsorbent consists of roughly spherical granules, /spl sim/200 /spl mu/m in diameter, of a high-surface-area, graphitized carbon. Key design considerations, fabrication technologies, and results of performance tests are presented with an emphasis on the thermal desorption characteristics of several representative volatile organic compounds as a function of volumetric flow rates and heating rates. Preconcentration factors as high as 5600 and desorbed peak widths as narrow as 0.8 s are achieved from 0.25-L samples of benzene at modest heating rates. The effects of operating variables on sensitivity, chromatographic resolution, and detection limits are assessed. Testing of this PCF with a micromachined separation column and integrated sensor array is discussed briefly. 相似文献
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Facile synthesis of ordered nanocrystalline alumina thin films with tunable mesopore structures 总被引:1,自引:0,他引:1
Lijuan Wan Honggang Fu Keying Shi Xiqiang Tian 《Microporous and mesoporous materials》2008,115(3):301-307
Mesoporous alumina layers have attracted attention for their potential use in ultrafiltration of salts, as a heterogeneous catalyst support, an adsorbent in environmental cleanup, and in petroleum refinement. The ability to control the fast hydrolysis rate of the inorganic precursors using simple and inexpensive routes is important for that potential to be realized. Herein, we introduce a novel and facile route to synthesize mesoporous alumina thin films from the combination of inexpensive and commercially available copolymer with aluminum chloride or nitrate (salts) in an EtOH–surfactant–NH3 · H2O–salts (EsNs) system through the evaporation-induced self-assembly (EISA) method. Mesoporous alumina layers obtained utilizing the EsNs system have ordered and tunable pore structures. The ability to easily control the mesophases of the alumina layers within a short time provides distinct advantages over previously reported synthesis procedures. Most importantly, we demonstrate that the binding of surfactant and NH3 · H2O for the formation of hydrogen bond between them in the EsNs system controls the fast hydrolysis rate of the inorganic species. This allows for the synthesis of nanocrystalline alumina layers via the aluminum oxo-clusters’ assembly with the surfactant. Such simple route may be applied in the synthesis of other non-silica mesostructured oxides. 相似文献
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青花装饰是景德镇的传统装饰方法之一,其中的写意青花又以其简约萧疏的艺术特征获得了人们的普遍喜爱。针对时代的变化影响,研究了当今写意青花在题材选择上与传统写意青花的差异。 相似文献
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对于某些容错计算系统,由于成功与故障之间没有明确的界限,用传统的可靠性指标难以准确地评价其容错性能,为此一些学者提出了若干与性能相关的可靠性指标。本文将这些指标概括成三类(即基于瞬时性能的指标、基于累积收益的指标和率模可靠性指标)加以介绍,并简要介绍了它们的求解方法。 相似文献
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金属迁移能导致混合微电路发生灾难性失效。本文介绍一种简单易行的测试方法-水滴试验法,来测量厚膜电路的实际金属迁移率。用引方法测量时,发现Pd-Ag导体的迁移率最大,Pt-Au导体的金属迁移率最小。 相似文献
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