High temperature Superconductors

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MINIREVIEW Hyperthermophilic enzymes ) stability, activity and implementation strategies for high temperature applications Larry D. Unsworth 1,2 , John van der Oost 3 and Sotirios Koutsopoulos 4 1 Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Canada 2 National Research Council ) National Institute for Nanotechnology, University of Alberta, Edmonton, Canada 3 Laboratory of Microbiology, Wageningen University, the Netherlands 4 Center for Biomedical Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA Introduction In general, it is agreed that living organisms can be grouped into four main categories as defined by the temperature range that they grow in: psychrophiles, mesophiles, thermophiles and hyperthermophiles [1]. The origin of extremophilic organisms has long been debated. Based on the analysis of 16S and 18S rRNA gene sequence data, it was shown that, in the evolu- tionary history of the three domains of living organ- isms, bacterial and archaeal hyperthermophiles are closest to the root of the phylogenetic tree of life [2]. Therefore, it has been postulated that hyperthermo- philes actually precede mesophilic microorganisms [3]. Intuitively, this is in agreement with current theories about the environmental conditions on the surface of Earth when life emerged. According to this theory, all biomolecules evolved to be functional and stable at high temperatures, and adapted to low temperature environments. However, another theory suggests that hyperthermophiles arose from mesophiles via adapta- tion to high temperature environments. This hypothe- sis is based on the supposition that ancestral RNA could not be stable at elevated temperatures [4,5]. The first hyperthermophilic organisms from the Sulfolobus species was discovered in 1972 in hot acidic springs in Yellowstone Park [6]. Subsequently, over 50 hyperthermophiles have been discovered in Keywords adsorption; covalent bonding; encapsulation; genomic and proteomic considerations; hyperthermostable enzymes; ion pairs; protein immobilization; structural features Correspondence S. Koutsopoulos, Center for Biomedical Engineering, Massachusetts Institute of Technology, NE47-307, 500 Technology Square, Cambridge, MA 02139-4307, USA Fax: +1 617 258 5239 Tel: +1 617 324 7612 E-mail: sotiris@mit.edu (Received 28 February 2007, accepted 11 May 2007) doi:10.1111/j.1742-4658.2007.05954.x Current theories agree that there appears to be no unique feature responsi- ble for the remarkable heat stability properties of hyperthermostable pro- teins. A concerted action of structural, dynamic and other physicochemical attributes are utilized to ensure the delicate balance between stability and functionality of proteins at high temperatures. We have thoroughly screened the literature for hyperthermostable enzymes with optimal temper- atures exceeding 100 °C that can potentially be employed in multiple bio- technological and industrial applications and to substitute traditionally used, high-cost engineered mesophilic ⁄ thermophilic enzymes that operate at lower temperatures. Furthermore, we discuss general methods of enzyme immobilization and suggest specific strategies to improve thermal stability, activity and durability of hyperthermophilic enzymes. Abbreviations ADH, alchohol dehydrogenase; G-C, guanine-cytosine. 4044 FEBS Journal 274 (2007) 4044–4056 ª 2007 The Authors Journal compilation ª 2007 FEBS environments of extreme temperatures: near or above 100 °C. Examples of environments that, until recently, were considered as being inhospitable to life include volcanic areas rich in sulfur and ‘toxic’ metals and hydrothermal vents in the deep sea (approximately 4 km below sea level) of extremely high pressure High-temperature Superconductors High-temperature Superconductors Bởi: OpenStaxCollege Superconductors are materials with a resistivity of zero They are familiar to the general public because of their practical applications and have been mentioned at a number of points in the text Because the resistance of a piece of superconductor is zero, there are no heat losses for currents through them; they are used in magnets needing high currents, such as in MRI machines, and could cut energy losses in power transmission But most superconductors must be cooled to temperatures only a few kelvin above absolute zero, a costly procedure limiting their practical applications In the past decade, tremendous advances have been made in producing materials that become superconductors at relatively high temperatures There is hope that room temperature superconductors may someday be manufactured Superconductivity was discovered accidentally in 1911 by the Dutch physicist H Kamerlingh Onnes (1853–1926) when he used liquid helium to cool mercury Onnes had been the first person to liquefy helium a few years earlier and was surprised to observe the resistivity of a mediocre conductor like mercury drop to zero at a temperature of 4.2 K We define the temperature at which and below which a material becomes a superconductor to be its critical temperature, denoted by Tc (See [link].) Progress in understanding how and why a material became a superconductor was relatively slow, with the first workable theory coming in 1957 Certain other elements were also found to become superconductors, but all had Tc s less than 10 K, which are expensive to maintain Although Onnes received a Nobel prize in 1913, it was primarily for his work with liquid helium In 1986, a breakthrough was announced—a ceramic compound was found to have an unprecedented Tc of 35 K It looked as if much higher critical temperatures could be possible, and by early 1988 another ceramic (this of thallium, calcium, barium, copper, and oxygen) had been found to have Tc = 125 K (see [link].) The economic potential of perfect conductors saving electric energy is immense for Tc s above 77 K, since that is the temperature of liquid nitrogen Although liquid helium has a boiling point of K and can be used to make materials superconducting, it costs about $5 per liter Liquid nitrogen boils at 77 K, but only costs about $0.30 per liter There was general euphoria 1/4 High-temperature Superconductors at the discovery of these complex ceramic superconductors, but this soon subsided with the sobering difficulty of forming them into usable wires The first commercial use of a high temperature superconductor is in an electronic filter for cellular phones Hightemperature superconductors are used in experimental apparatus, and they are actively being researched, particularly in thin film applications A graph of resistivity versus temperature for a superconductor shows a sharp transition to zero at the critical temperature Tc High temperature superconductors have verifiable Tc s greater than 125 K, well above the easily achieved 77-K temperature of liquid nitrogen One characteristic of a superconductor is that it excludes magnetic flux and, thus, repels other magnets The small magnet levitated above a high-temperature superconductor, which is cooled by liquid nitrogen, gives evidence that the material is superconducting When the material warms and becomes conducting, magnetic flux can penetrate it, and the magnet will rest upon it (credit: Saperaud) The search is on for even higher Tc superconductors, many of complex and exotic copper oxide ceramics, sometimes including strontium, mercury, or yttrium as well as barium, calcium, and other elements Room temperature (about 293 K) would be ideal, but any temperature close to room temperature is relatively cheap to produce and maintain There are persistent reports of Tc s over 200 K and some in the vicinity of 270 K Unfortunately, these observations are not routinely reproducible, with samples losing their superconducting nature once heated and recooled (cycled) a few times (see [link].) They are now called USOs or unidentified superconducting objects, out of frustration and the refusal of some samples to show high Tc even though produced in the same manner as others Reproducibility is crucial to discovery, and researchers are justifiably 2/4 High-temperature Superconductors reluctant to claim the breakthrough they all seek Time will tell whether USOs are real or an experimental quirk The theory of ordinary superconductors is difficult, involving quantum effects for widely separated electrons traveling through a material Electrons couple in a manner that allows them to get through the material without losing energy to it, making it a superconductor High- Tc superconductors are more difficult to understand theoretically, but theorists seem to be closing in on a workable theory The difficulty of understanding how electrons can sneak through materials ...High Temperature Solid Oxide Fuel Cells Fun dam en tals, Desig and Apdirations J; 2 ' cubhash r cinghal and Kevin Kendal h Temperature Solid Oxide Fuel Cells: Fundamentals, Design and Applications ~ High Temperature Solid Oxide Fuel Cells: Fundamentals, Design and Applications Edited by: Subhash C Singhal and Kevin Kendall ELSEVIER UK USA JAPAN Elsevier Ltd, The Boulevard, LangfordLane, Kidlington, Oxford OX5 IGB, UK Elsevier Inc, 360 Park AvenueSouth, New York, NY 10010-1710, USA Elsevier Japan, Tsunashima Building Annex, 3-20-12 Yushima. Bunlryo-ku, Tokyo 11 3, Japan Copyright 0 2003 Elsevier Ltd. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by anj7 means: electronic, electrostatic, magnetic tape, mechanical, photocopying, recording or otherwise, without prior permission in writing from the publishers. British Library Cataloguing in Publication Data High temperature solid oxide fuel cells: fundamentals, design and applications 1. Solid oxide fuel cells I. Singhal, Subhash C. 62 1.3’12429 11. Kendall, Kevin, 1943- ISBN 1856173879 Library of Congress Cataloging-in-Publication Data High temperature solid oxide fuel cells: fundamentals, design and applications / edited by Subhash C. Singhal and Kevin Kendall. p. cm. Includes bibliographical references and index. ISBN 1-85617-387-9 (hardcover) 1. Solidoxidefuelcells. I. Singhal, SubhashC. II.Kendal1, Kevin, 1943- TIC2931 .H54 2002 62 1.3 1’2429-dc2 1 2002040761 No responsibility is assumed by the Publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein. Published by Elsevier Advanced Technology, The Boulevard, Langford Lane, Kidlington Oxford OX5 lGB, UK Tel.: +44(0) 1865 843000 Fax: +44(0) 1865 843971 Typeset by Variorum Publishing Ltd, Lancaster and Rugby Printed and bound in Great Britain by MPG Books Ltd, Bodmin, Cornwall Contents List of Contributors Preface Chapter 1 Introduction to SOFCs 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 1.10 1.11 1.12 1.13 Background Historical Summary Zirconia Sensors for Oxygen Measurement Zirconia Availability and Production High-Quality Electrolyte Fabrication Processes Electrode Materials and Reactions Interconnection for Electrically Connecting the Cells Cell and Stack Designs SOFC Power Generation Systems Fuel Considerations Competition and Combination with Heat Engines Application Areas and Relation to Polymer Electrolyte Fuel Cells SOFC-Related Publications References Chapter 2 History 2.1 2.2 2.3 2.4 Progressin the 1960s 2.5 The Path to the First Solid Electrolyte Gas Cells From Solid Electrolyte Gas Cells to Solid Oxide Fuel Cells First Detailed Investigations of Solid Oxide Fuel Cells On the Path to Practical Solid Oxide Fuel Cells References Chapter 3 Thermodynamics 3.1 Introduction 3.2 The Ideal Reversible SOFC 3.3. Voltage Losses by Ohmic Resistance and by Mixing Effects by Fuel Utilisation xi xv 1 2 4 5 7 8 11 12 14 15 17 18 19 19 23 26 29 32 40 44 53 56 62 vi High Temperature Solid Oxide Fuel Cells: Fundamentals, Design and Applications 3.4 3.5 3.6 3.7 Summary Thermodynamic Definition of a Fuel Cell Producing Electricity and Heat Thermodynamic Theory of [...]... superconductors, deferring any mention of the new high-temperature superconductors (HTSCs) Inevitably, it is necessary to decide what material to include at what point in a presentation, and what to leave out In this explanation of “old superconductivity, ” the classical-physics tools of thermodynamics and Maxwell’s equations are used Not only is this chapter limited to the low-temperature superconductors,... advantage of superconductivity In one of those perverse conspiracies of nature, the crystal- 6 CHAPTER 1 line properties that offer the best chance to circumvent the brittleness problem are the very same properties that tend to degrade flux pinning 1.3 HISTORY Before continuing with what HTSCs may lead to, it is appropriate to look back and see what they have come from The history of high-temperature superconductivity. .. even out to 10 or 15 T The ceramic superconductors do much better Bismuth strontium calcium copper oxide (BSCCO) carries adequate current and remains superconducting well above 20 T, at 20 K Therefore, the best way to obtain very high magnetic fields is to use the ceramic superconductors at low temperatures Of course, in order to wind a coil to produce a magnetic field, the first prerequisite is to make... made of semiconductors A superconductor, in contrast, is a material with no resistance at all A lot of metals, but not all, show modest electrical resistance at ordinary room temperatures, but turn into superconductors when refrigerated very near to absolute zero The first metal discovered to be a superconductor was mercury,1 soon after the invention (in 1908) of a cryogenic refrigerator that could attain... 1957.6 It took 45 years to develop this theory, but it proved to be a very good theory indeed By the early 1960s, superconductivity was considered to be a “mature” science and attention shifted to engineering applications 2.2 THE MEISSNER EFFECT Because the zero-resistance feature of superconductors was discovered first, it is widely believed that this is the most fundamental property of superconductors... intervene must have to do with free energy minimization The free energy is equal to the work done to achieve a particular thermodynamic state In the case of a superconductor, the condition that requires it to have a magnetization The work done on a superconductor moved from infinity to a position r near a permanent magnet7 is the integral over and this is also the increment in free energy dF To calculate... engineering before INTRODUCTION AND OVERVIEW 7 these new superconductors find widespread practical application Serious research managers do not expect to see any large-scale applications until the twenty-first century Some early applications to delicate sensors and electronic devices are beginning to appear in the mid-1990s 1.4 SUPERCONDUCTING MAGNETS A leading use of superconductors is to produce high... compound yttrium barium copper oxide (YBCO) has been found to be superconducting up to 92 K This may not seem like a “high” temperature to most people, but to the engineers figuring the cost of CARBON NANOTUBE ARRAY THERMAL INTERFACES FOR HIGH-TEMPERATURE SILICON CARBIDE DEVICES Baratunde A. Cola 1,2 , Xianfan Xu 1,2 , Timothy S. Fisher 1,2 , Michael A. Capano 1,3 , and Placidus B. Amama 1 1 Purdue University, Birck Nanotechnology Center, West Lafayette, Indiana, USA 2 Purdue University, School of Mechanical Engineering, West Lafayette, Indiana, USA 3 Purdue University, School of Electrical and Computer Engineering, West Lafayette, Indiana, USA Multiwalled carbon nanotube (MWCNT) arrays have been directly synthesized from templated Fe 2 O 3 nanoparticles on the C-face of 4H-SiC substrates by microwave plasma chemical vapor deposition (MPCVD), and the room-temperature thermal resistances of SiC-MWCNT-Ag interfaces at 69–345 kPa as well as the thermal resistances of SiC- MWCNT-Ag interfaces up to 250  C (at 69 kPa) have been measured using a photoacoustic technique. The SiC-MWCNT-Ag interfaces with MWCNTs grown on the C-face of SiC achieved thermal resistances less than 10 mm 2 K/W, which is lower than the resistances of MWCNT interfaces grown using the same catalysis and growth methods on the Si-face of SiC and Ti-coated SiC. The thermal resistances of the SiC-MWCNT-Ag interfaces exhibit weak temperature dependence in the measured range, indicating that the interfaces are suitable for high-temperature power electronics applications. KEY WORDS: carbon nanotube, thermal interface resistance, silicon carbide, high- temperature, photoacoustic INTRODUCTION Silicon carbide (SiC) electronic devices hav e developed such that commercial products are now available. SiC is preferred in high-temperature, high-power, and high-frequency applications because its combination of physical properties enables it to outperform Si under harsh conditions. Under such challenging operating condi- tions, efficient heat flow through the interface from the die to the he at sink or spreader is paramount, and this study considers the use of carbon nanotube arrays to serve this thermal interface function both at room temperature and near the elevated tempera- tures anticipated in practical applications. The possibility of achieving a gradient carbon morphology from the SiC/C-face to the C-C lattice is of particular interest and could enhance interfacial heat conduction. Nanoscale and Microscale Thermophysical Engineering, 12: 228–237, 2008 Copyright Ó Taylor & Francis Group, LLC ISSN: 1556-7265 print / 1556-7273 online DOI: 10.1080/15567260802183015 Address correspondence to Timothy S. Fisher, Purdue University, Birck Nanotechnology Center, 1205 W. State St., W. Lafayette, IN 47907-2057. E-mail: tsfisher@purdue.edu Received 16 February 2008; accepted 5 May 2008. We gratefully acknowledge funding from the Air Force Research Laboratory. B. A. Cola gratefully acknowledges fellowship support from the Intel Foundation and the Purdue University Graduate School. 228 Downloaded by [Purdue University] at 06:09 30 June 2011 Despite the ability of SiC power devices to operate at elevated temperatures as compared to Si devices, thermal issues remain paramount to their performance. In short, excessive thermal loading of a device diminishes the ability to carry current and may lead to catastrophic failure. When defects are present, breakdown of a device is often accelerated. Recent published results examining how SiC Schottky Barrier diodes (SB D) are influenced by defects have demonstrated that forward and revers e characteristics are sensitive to essentially any defect within the active region of the device [1–4]. Defects that are known to degrade diode characteristics include micro- pipes, comets, carrots, inclusions, small-angle boundaries, and screw dislocations. Particularly relevant to NANO EXPRESS Open Access Self-propagating high-temperature synthesis of nano-TiC x particles with different shapes by using carbon nano-tube as C source Shenbao Jin 1,2 , Ping Shen 1,2 , Dongshuai Zhou 1,2 and Qichuan Jiang 1,2* Abstract With using the carbon nano-tube (CNT) of high chemical activity, nano-TiC x particles with different growth shapes were synthesized through the self-propagating high temperature in the 80 wt.% metal (Cu, Al, and Fe)-Ti-CNT systems. The growth shapes of the TiC x particles are mainly octahedron in the Cu- and Al-Ti-CNT systems, while mainly cube- and sphere-like in the Fe-Ti-CNT system. Keywords: self-propagating high-temperature synthesis (SHS), carbon nanotubes, nano-TiC x particles Introduction As known, some ceramic particles, such as titanium car- bide (TiC x ), are usuall y used as the rein forcing phases in the composites due to their unique properties such as high melting point, extreme hardness, and high resistance to corrosion and oxidation. Recently, many experimental and theoretical studies have indicated that decreasing the sizes of the reinforcing ceramic particulates can lead to substantial improvements in mechanical performance of the composites [1-11]. For example, Ma et al. [11] showed that the tensile strength of 1 vol.% Si 3 N 4 (10 nm)/Al com- posite is comparable to that of the 15 vol.% SiC p (3.5 μm)/ Al composite, and the yield strength of the former is much higher than that of the latter. Then, with signifi- cantly increasing intention to develop nanop art icle-rein- forced composites with superior mechanical properties, the demand for nano-sized ceramic powders, including TiC x , has become more urgent. Among the variety of the preparation methods for TiC x , self-propagating high-temperature synthesis (SHS) is noted by us because it is a convenient and efficient way to syn thesize TiC x . However, the SHS is quite chal- lenging to produce the nano-sized ceramic particles because the combustion temperature will lead to consid- erable coarsening of the ceramic particles. At present, the usual method for synthesizing the nano-ceramic par- ticles through the SHS is the addition of volatile diluents such as NaCl into the reactants. Some nano-ceramic particles such as TiB 2 and ZrB 2 have been prepared by adding NaCl to the SHS reactants [12-14], and the nano-TiC x particles (20 to 100 nm) were also obtained by Nersisyan et al. [15] in the 30 wt.% NaCl-Ti-carbon black system. On the other hand, the addition of a second metal (Me) such as Al , Cu, and Fe can also decrease the combustion temperature and thus prevent the ceramic particles from further growth. For example, with the increase in the Al incorporation from 10 to 40 wt.%, the sizes of the TiC x particles decrease from about 3 μm to 400 nm [16]. How- ever, when more Me (≥50 wt.%) is incorporated, the SHS reaction tends to be incomplete or even cannot be ignited. Generally, this situation can be improved through using finer C-source particles because they can enlarge the area of the contact surface between the liquid and the carbon source and decrease the activation energy of the SHS reac- tion. At present, the source of C that are mostly used dur- ing the SHS are graphite (typically 1 to 150 μm) and C black (< 100 nm). In contrast to them, carbon nano-tube (CNT) has much finer size, usually 5 to 20 nm in dia- meter. In fact, CNT has been used to synthesize the nanostructured TiC-TiB 2 [17] and carbide ... lattice structure of a hightemperature superconducting ceramic (credit: en:Cadmium, Wikimedia Commons) 3/4 High- temperature Superconductors Section Summary • High- temperature superconductors are... superconducting at temperatures well above a few kelvin • The critical temperature Tc is the temperature below which a material is superconducting • Some high- temperature superconductors have... into usable wires The first commercial use of a high temperature superconductor is in an electronic filter for cellular phones Hightemperature superconductors are used in experimental apparatus,