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81.
Scaling Effects in Perovskite Ferroelectrics: Fundamental Limits and Process‐Structure‐Property Relations 下载免费PDF全文
Jon F. Ihlefeld David T. Harris Ryan Keech Jacob L. Jones Jon‐Paul Maria Susan Trolier‐McKinstry 《Journal of the American Ceramic Society》2016,99(8):2537-2557
Ferroelectric materials are well‐suited for a variety of applications because they can offer a combination of high performance and scaled integration. Examples of note include piezoelectrics to transform between electrical and mechanical energies, capacitors used to store charge, electro‐optic devices, and nonvolatile memory storage. Accordingly, they are widely used as sensors, actuators, energy storage, and memory components, ultrasonic devices, and in consumer electronics products. Because these functional properties arise from a noncentrosymmetric crystal structure with spontaneous strain and a permanent electric dipole, the properties depend upon physical and electrical boundary conditions, and consequently, physical dimension. The change in properties with decreasing physical dimension is commonly referred to as a size effect. In thin films, size effects are widely observed, whereas in bulk ceramics, changes in properties from the values of large‐grained specimens is most notable in samples with grain sizes below several micrometers. It is important to note that ferroelectricity typically persists to length scales of about 10 nm, but below this point is often absent. Despite the stability of ferroelectricity for dimensions greater than ~10 nm, the dielectric and piezoelectric coefficients of scaled ferroelectrics are suppressed relative to their bulk counterparts, in some cases by changes up to 80%. The loss of extrinsic contributions (domain and phase boundary motion) to the electromechanical response accounts for much of this suppression. In this article, the current understanding of the underlying mechanisms for this behavior in perovskite ferroelectrics is reviewed. We focus on the intrinsic limits of ferroelectric response, the roles of electrical and mechanical boundary conditions, grain size and thickness effects, and extraneous effects related to processing. In many cases, multiple mechanisms combine to produce the observed scaling effects. 相似文献
82.
Mahder?Tewolde Gaosheng?Fu David?J.?Hwang Lei?Zuo Sanjay?Sampath Jon?P.?LongtinEmail author 《Journal of Thermal Spray Technology》2016,25(3):431-440
Thermoelectric generators (TEGs) are solid-state devices that convert heat directly into electricity. They are used in many engineering applications such as vehicle and industrial waste-heat recovery systems to provide electrical power, improve operating efficiency and reduce costs. State-of-art TEG manufacturing is based on prefabricated materials and a labor-intensive process involving soldering, epoxy bonding, and mechanical clamping for assembly. This reduces their durability and raises costs. Additive manufacturing technologies, such as thermal spray, present opportunities to overcome these challenges. In this work, TEGs have been fabricated for the first time using thermal spray technology and laser micromachining. The TEGs are fabricated directly onto engineering component surfaces. First, current fabrication techniques of TEGs are presented. Next, the steps required to fabricate a thermal spray-based TEG module, including the formation of the metallic interconnect layers and the thermoelectric legs are presented. A technique for bridging the air gap between two adjacent thermoelectric elements for the top layer using a sacrificial filler material is also demonstrated. A flat 50.8 mm × 50.8 mm TEG module is fabricated using this method and its performance is experimentally characterized and found to be in agreement with expected values of open-circuit voltage based on the materials used. 相似文献
83.
Méndez Susana Arenas María Ángeles Niklas Andrea González Rodolfo Conde Ana Sertucha Jon de Damborenea Juan José 《Oxidation of Metals》2019,91(1-2):225-242
Oxidation of Metals - The use of high silicon ductile irons is increasing as they offer some advantages with respect to conventional pearlitic–ferritic grades such as high elongation at... 相似文献
84.
Natalia Remirez de Esparza Nerea Cocera Lexuri Vazquez Jon Alkorta Ibon Ocaña Jose M. Sanchez 《Journal of the American Ceramic Society》2014,97(12):3958-3966
The oxidation of highly porous ceramic matrix composites (PCMCs) based on different Tyranno® fibers has been analyzed by means of thermogravimetry and electron microscopy. Both uncoated fibers and PCMC materials exhibit parabolic kinetics between 900°C and 1250°C, these being faster for Ti‐doped than for Zr‐doped Tyranno fibers. Oxide layers in Ti‐doped fibers are porous and partially crystalline, whereas in Zr‐doped materials a significant fraction of relatively coarse β‐SiC grains is still found embedded in the amorphous silica matrix. On the other hand, the CVD‐SiC coatings exhibit higher oxidation rates from the outer surface than from the inner one, a phenomenon that has been associated not only with the more difficult access of oxygen to the inner face but also with the highly <111> textured structure of these coatings, for which very different oxidation rates have been published for the inward and outward directions. Cracking phenomena observed above 1100°C for long dwelling times do not lead to an acceleration of the oxidation process, which could be due to the simultaneous crystallization of the amorphous silica layers. 相似文献
85.
Ian Mabbett Jon Elvins Catherine Gowenlock Carol Glover Paul Jones Geraint Williams David Worsley 《Progress in Organic Coatings》2014
Near infrared (NIR) is becoming a popular option for rapid cure of coatings in the coil coating industry particularly where fast line speeds are required. The technology has the potential to reduce the cure time of a 20 μm polyester coating on a galvanised steel substrate from around 30 s via conventional heating methods down to <10 s under the lamps. Previous work suggested that the ideal situation in this case is to have a topcoat which is slightly transparent to NIR and an absorbing substrate to heat the coating from the substrate outwards in a two stage process which separates solvent removal from cross linking and film formation. This can be taken further by tinting the primer layer with a pigment that absorbs in the NIR region. In this study spectroscopy was used to show that a coated steel system could appear white in the visible region because of the reflectance of TiO2 but the NIR absorption could be altered by adding absorbing pigments such as carbon black. Lamp settings could be reduced by 20% to achieve equivalent cure with tinted primer systems. The potential degradation in corrosion protection afforded by carbon-black containing pigments at various loadings was assessed for model organic coatings applied to galvanised steel specimens. In situ scanning Kelvin probe studies showed that rates of corrosion-driven coating delamination by cathodic disbondment remained unchanged by pigment loadings of up to 3.5 wt%. 相似文献
86.
Jon Pearson 《电子产品世界》2006,(22):25-26
在嵌入式设计中,即便进行了周密的计划,完全按照最严格的程序进行工作,项目也可能会遭遇理查三世一样的失败:比方说,您所选用的处理器可能不具备足够的引脚,导致目标难以实现.在选择芯片、驱动LED时,总难做到全面,人们总是事后才失望地发现,本应选择引脚更多的另一款处理器.即便进行了前期计划,为设计上的问题预留了空间,但还是不能确保得到你想要的引脚(还要考虑到安全性),因为市场或公司的市场营销策略总是要求尽可能降低成本.即便您全力以赴,总算得到批准采用具有10个额外引脚的处理器,能够按时完成设计工作,但这样做只能造成公司下一步肯定采取降低成本的措施. 相似文献
87.
In the paper we present a framework for partitioning data parallel computations across a heterogeneous metasystem at runtime. The framework is guided by program and resource information which is made available to the system. Three difficult problems are handled by the framework: processor selection, task placement and heterogeneous data domain decomposition. Solving each of these problems contributes to reduced elapsed time. In particular, processor selection determines the best grain size at which to run the computation, task placement reduces communication cost, and data domain decomposition achieves processor load balance. We present results which indicate that excellent performance is achievable using the framework. The paper extends our earlier work on partitioning data parallel computations across a single-level network of heterogeneous workstations. 相似文献
88.
Jon L. Maienschein Albert L. Nichols Jeffrey F. Wardell 《Propellants, Explosives, Pyrotechnics》1995,20(6):287-293
The reactions of combustion products (CO, H2O) from the insensitive high explosive LX-17 (92.5 wt% 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), 7.5 wt% Kel-F 800 binder) with molten metal (75 a%Nd, 25 a% Fe) were studied, to determine their contribution to the energy release rate of deflagrating LX-17, Kinetic data taken with gas mixtures of CO and H2O, and larger-scale tests with LX-17, showed that the reactions were slow and incomplete and that there was no significant contribution to the energy release rate. From the tests with JX-17, the effective flame temperature and burn velocity were dependent on confinement of gas products. LX-17 preheated to 500 K - 510 K showed effective flame temperatures of 1100 K - 1400 K and burn rates of 0.08–0.11 mm/s, depending on the extent of gas confinement by the molten metal. 相似文献
89.
Jon Volden Grethe Iren A. Borge Gunnar B. Bengtsson Magnor Hansen Ingrid E. Thygesen Trude Wicklund 《Food chemistry》2008
The effects of various thermal processing treatments (blanching, boiling and steaming) of red cabbage, Brassica oleracea L. ssp. capitata f. rubra cv. ‘Autoro’, were assessed for the levels of glucosinolates (GLS), total phenols (TP), total monomeric anthocyanins (TMA), l-ascorbic acid (L-AA) and soluble sugars, as well as for the antioxidant potential by the ferric reducing ability power (FRAP) and oxygen radical absorbance capacity (ORAC) assays. Individual native GLS were determined by ion-pair HPLC-MS/DAD. There were significant (p < 0.05) losses in blanched red cabbage: TP, 43%, TMA 59%, FRAP 42%, ORAC 51%, L-AA 48% and soluble sugars 45%. Boiling gave less extensive reductions: TP 16%, TMA 41%, FRAP 17%, ORAC 19%, L-AA 24% and soluble sugars 19%. Steaming caused no losses for TP, ORAC, FRAP or soluble sugars. However, significant reductions were found for TMA and L-AA, with 29% and 11%, respectively. In general losses were accounted for in the processing waters; however, TMA was not fully recovered, indicating degradation. Total GLS were severely affected by processing, with reductions of 64%, 38% and 19% in blanched, boiled and steamed red cabbage, respectively. Total aliphatic and indole GLS were similarly affected. Lost GLS were partially recovered in the processing water. 相似文献
90.
Lappi VR Thimothe J Walker J Bell J Gall K Moody MW Wiedmann M 《Journal of food protection》2004,67(6):1163-1169
Two ready-to-eat crawfish processing plants were monitored for 2 years to study the impact of Listeria control strategies, including employee training and targeted sanitation procedures, on Listeria contamination. Environmental, raw material, and finished product samples were collected weekly during the main processing months (April to June) and tested for Listeria spp. and Listeria monocytogenes. Before implementation of control strategies (year 1), the two processing plants showed Listeria spp. prevalences of 29.5% (n = 78) in raw, whole crawfish, 5.2% (n = 155) in the processing plant environment, and 0% (n = 78) in finished products. In year 2, after plant-specific Listeria control strategies were implemented, Listeria spp. prevalence increased in raw crawfish (57.5%, n = 101), in the processing plant environment (10.8%, n = 204), and in the finished product (1.0%, n = 102). Statistical analysis showed a significant increase in Listeria spp. prevalence (P < 0.0001) and a borderline nonsignificant increase in L. monocytogenes prevalence (P = 0.097) on raw material in year 2. Borderline nonsignificant increases were also observed for Listeria spp. prevalence in environmental samples (P = 0.082). Our data showed that Listeria spp. prevalence in raw crawfish can vary significantly among seasons. However, the increased contamination prevalence for raw materials only resulted in a limited Listeria prevalence increase for the processing plant environment with extremely low levels of finished product contamination. Heat treatment of raw materials combined with Listeria control strategies to prevent cross-contamination thus appears to be effective in achieving low levels of finished product contamination, even with Listeria spp. prevalences for raw crawfish of more than 50%. 相似文献