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21.
Jeffrey R. Wank 《Powder Technology》2004,142(1):59-69
Experiments are conducted with alumina (Al2O3) deposition on a wide size range of hexagonal boron nitride (BN) platelet-like particles. Successful deposition of alumina films on these particles, with film thickness controllable at the Angstrom level, is observed based upon TEM imaging, ICP-AES, particle size distributions, and surface area analysis. While fluidizing, fine BN particles aggregate in the bed. The aggregates are the entities fluidizing, not the primary particles. However, individual particles are coated using Atomic Layer Deposition (ALD), not aggregates. Since ALD is a surface chemistry phenomenon, the films grow uniformly on every primary particle. BN particles are small platelets with different functional groups on the basal planes and edge planes. A small exposure to reagents [2.5×106 Langmuir (L) per reagent per cycle], will only coat the edge planes of uncoated BN particles. A larger dose of 1×108 L will coat the entire uncoated BN particle (edge and basal planes). After 10 ALD cycles of the 1×108 L dose, the exposures can be reduced to 1×106 L as the film is then growing on alumina and not BN. Peel strength data indicate that adhesion between the coated particles and a cured epoxy in a filled composite is ∼25% stronger than that of uncoated particles and the epoxy. The overall thermal conductivity drops ∼17% for an identical filler loading as expected due to the additional thermal resistance added by the film. However, the viscosity of an epoxy resin loaded with coated BN is as much as five times lower than that of the resin loaded with the same amount of uncoated BN. These results indicate that the loading of Al2O3 nanocoated BN particles in an epoxy matrix can be substantially increased relative to that of uncoated particles. The thermal conductivity of the more highly filled composite will be increased without adversely impacting filled resin viscosity or the peel strength of the cured material. This is the first reported study indicating that cohesive primary particles that fluidize as aggregates in a fluidized bed can be individually coated with a nano-thick ceramic film using ALD. 相似文献
22.
Flemming Jappe Frandsen 《Fuel》2005,84(10):1277-1294
Through the years, Danish utilities have gained significant knowledge on how to minimize or even avoid ash deposition problems in utility boilers, firing a worldwide suite of high-volatile bituminous coals. In the early 1990s, the Danish Government decided on a 20% reduction in the CO2-emission before the year 2005, based on the 1988-level. Biomass is considered CO2-neutral due to its short time of regeneration, compared to fossil fuels. Thus, the Danish power producers are enjoined to burn 1.0 Mtonnes of straw, 0.2 Mtonnes of wood chips and 0.2 Mtonnes of straw/wood chips (free choice) every year beyond year 2005. As a consequence of this, the CHEC Research Centre, Department of Chemical Engineering, Technical University of Denmark, being partly funded by the Danish power utilities, has during the last decade, investigated ash and deposit formation, and corrosion, in utility boilers fired with coal, petcoke, orimulsion, and different types of biomass (straw (barley, rape and wheat), wood (beech, spruce, fibreboard, bark and waste wood), shea nuts, olive stones, etc.). A number of reviews of these full-scale measuring campaigns have been provided in the open literature. Recently, a project on the formation of ash and deposits in waste incinerators has been initiated.This paper summarizes our findings, including recent activities on: (1) deposit formation during coal-wheat straw co-firing in suspension-fired boilers; (2) a pilot-scale study of ash and deposit formation in the Sandia Multi-Fuel Combustor (MFC); (3) a full-scale measuring campaign dealing with the effect of co-firing of biomass on the ash and deposit formation; (4) a full-scale measuring campaign addressing low-temperature corrosion of tubes in the air pre-heater of a straw-fired utility boiler; (5) a lab-scale study of the corrosion of superheater materials in straw-fired utility boilers, and, finally; (6) a fundamental study on ash and deposit formation in municipal solid waste incinerators. The paper provides insight into the experience gained on ash, deposit and corrosion formation in thermal fuel conversion systems fired with solid non-fossil fuels, and focuses attention on how these results fit into our current understanding of this subject. A complete and updated list of references covering our research activities within this area during the last decade is provided. In addition, a brief overview of current and future research activities is provided. 相似文献
23.
石墨颗粒表面化学镀铜研究 总被引:15,自引:2,他引:15
为了充分利用Cu的导电性能,碳石墨的润滑性能,改善Cu/C的润湿性,用化学镀铜的方法成功地对石墨颗粒表面进行镀覆,详细地研究了镀铜液组分及工艺与石墨颗粒表面镀铜层厚度、沉积速率的关系,并得出较好的组分工艺方案,采用优化工艺可以得到平均厚度约7.1μm的镀铜层。同时应用X射线、金相显微镜、扫描电镜及电子探针对镀铜层的厚度、表面形貌、镀铜层与基体的界面进行了全面观察。分析表明,Cu/C界面存在过渡层,界面成锯齿状,机械冶金结合的特征十分明显,改善了铜碳界面的相溶性。 相似文献
24.
25.
Kaupo Kukli Mikko Ritala Timo Sajavaara Timo Hnninen Markku Leskel 《Thin solid films》2006,500(1-2):322-329
Calcium oxide and calcium hafnium oxide thin films were grown by atomic layer deposition on borosilicate glass and silicon substrates in the temperature range of 205–300 °C. The calcium oxide films were grown from novel calcium cyclopentadienyl precursor and water. Calcium oxide films possessed refractive index 1.75–1.80. Calcium oxide films grown without Al2O3 capping layer occurred hygroscopic and converted to Ca(OH)2 after exposure to air. As-deposited CaO films were (200)-oriented. CaO covered with Al2O3 capping layers contained relatively low amounts of hydrogen and re-oriented into (111) direction upon annealing at 900 °C. In order to examine the application of CaO in high-permittivity dielectric layers, mixtures of Ca and Hf oxides were grown by alternate CaO and HfO2 growth cycles at 230 and 300 °C. HfCl4 was used as a hafnium precursor. When grown at 230 °C, the films were amorphous with equal amounts of Ca and Hf constituents (15 at.%). These films crystallized upon annealing at 750 °C, showing X-ray diffraction peaks characteristic of hafnium-rich phases such as Ca2Hf7O16 or Ca6Hf19O44. At 300 °C, the relative Ca content remained below 8 at.%. The crystallized phase well matched with rhombohedral Ca2Hf7O16. The dielectric films grown on Si(100) substrates possessed effective permittivity values in the range of 12.8–14.2. 相似文献
26.
X. Darok V. Bhat L. Aymard L. Dupont L. Laffont J.-M. Tarascon 《Thin solid films》2006,515(4):1299-1306
Mg-Ni thin films were grown using Pulsed Laser Deposition. In situ optical changes from shiny metallic to transparent states were observed for films deposited in vacuum and under an Ar/H2 gas mixture (93/7%), respectively. Optical changes were also achieved by ex situ hydrogenation under hydrogen gas pressure of 15 bars at 200 °C. However, after ex situ hydrogenation, the optical transmittance of the Mg-based hydrogenated thin films did not exceed 25%. Such limitation was attributed to oxygen contamination, as deduced by High Resolution Transmission Electron Microscopy observations, showing the co-existence of both Mg-based and MgO phases for as-deposited films. A significant decrease in oxygen contamination was successfully achieved with the addition of carbon, leading to the preparation of (Mg-based)-Cx (x < 20%) thin films showing a faster and easier hydrogenation. 相似文献
27.
In this paper we present the results of XPS study of the surface chemistry of L-CVD SnO2 thin films onto Si(100) before and after subsequent additional oxidation. Moreover, the ageing effect was also studied in order to check the influence of ambient oxidation. As-deposited L-CVD SnO2 thin films exhibit evident nonstoichiometry with the relative concentration [O]/[Sn] equal to 1.29 ± 0.1. After in situ oxidation at high temperature (800 K) the relative concentration [O]/[Sn] increases to 1.95 ± 0.05 which corresponds to the almost stoichiometric SnO2. Almost the same relative concentration [O]/[Sn] of L-CVD SnO2 thin films has been obtained after long term exposure to air. The oxidation states of L-CVD SnO2 thin films in both cases were confirmed by the shape analysis of corresponding XPS O1s and Sn3d5/2 peaks using the decomposition procedure. For the as-deposited L-CVD SnO2 thin films a mixture of SnO and SnO2 was observed, while for the oxidized L-CVD SnO2 thin films the domination of SnO2 was determined. 相似文献
28.
氟化类金刚石(FDLC)薄膜是在传统类金刚石膜基础上发展起来的一种新型表面改性材料.本文简述了FDLC薄膜的结构、性能,重点介绍了其制备工艺,讨论了源气体的种类和退火工艺对薄膜的影响. 相似文献
29.
ZnO thin films were prepared on Si(0 0 1) substrates using a pulsed laser deposition (PLD) technique and then their growth and properties were investigated particularly as a function of ambient O2 pressure during film growth. It was found that the microstructure, crystallinity, orientation and optical properties of the films grown are strongly dependent on the O2 pressures used. Completely c-axis oriented ZnO films are grown in a low O2 pressure regime (5×10−4-5×10−2 Torr), whereas a randomly oriented film with a much lower crystallinity and a rougher grained-surface is grown at an O2 pressure of 5×10−1 Torr. This deterioration in film quality may be associated with the kinetics of atomic arrangements during deposition. Our results suggest that ambient O2 pressure is an important processing parameter and should be optimized in a narrow regime in order to grow a ZnO film of good properties in PLD process. 相似文献
30.
The deposition rate and the thickness uniformity of chemical vapor deposition (CVD) titanium nitride films depend on wafer temperatures. The heater surface conditions, such as flatness, roughness, and surface imperfections, can greatly affect heat transfer efficiency from the heater surface to the wafer, and the process performance. Because heater surface imperfections or “hot spots” that caused poor uniformity had to be eliminated, the origin of “hot spots” was identified by a detailed study of heater surface profiles. A better visualization of “hot spots” could be obtained by comparing wafer-chucking patterns with deposition patterns. Thus, the time needed to locate “hot spots” could be shortened. The manufacturing process was revised to prevent “hot spots” and improve heater performance. 相似文献