Showing papers in "Current Opinion in Solid State & Materials Science in 1999"
TL;DR: In this paper, the authors investigated the properties and modes of action of an ideal PEG coating and found that PEG surfaces with very short chains are capable of rejecting proteins, while other, very similar coatings appear less able to resist bio-adhesion.
Abstract: The search for surfaces that resist bioadhesion has continued with the pursuit of a number of avenues. A large part of the studies has investigated PEG coatings. Nevertheless, there is still controversy about what exactly the properties and modes of action of an ‘ideal’ PEG coating should be. While some studies have reported no irreversible protein adsorption, other, very similar coatings appear less able to resist bioadhesion. Of great interest are results showing that PEG surfaces with very short chains are capable of rejecting proteins. As it is very difficult to obtain direct information about the microstructure of the coatings, studies typically employ plausible models to interpret observations. New analytical techniques and the direct measurement of interfacial forces between proteins and surfaces open up the possibility of improved, guided design and feedback in the optimization of surfaces intended to resist bioadhesion.
374 citations
TL;DR: In this paper, the specific mechanisms that contribute to failure of thermal barrier coatings are described, with the motivation that this understanding can be used to design TBCs having greater reliability and durability.
Abstract: Thermal barrier coatings (TBCs) are now used on hot section components in most commercial turbine engines. They are used to enhance the temperature differential between the gas and the underlying metal surfaces. They comprise several layers designed to simultaneously provide thermal and oxidation protection. They have microstructures which afford sufficient strain tolerance that they remain attached despite severe thermomechanical cycling. Eventually, they spall. This happens because a thin, highly stressed, thermally grown oxide (TGO) develops beneath the TBC. In this article, the specific mechanisms that contribute to failure are described, with the motivation that this understanding can be used to design TBCs having greater reliability and durability.
363 citations
TL;DR: In the past several decades, membrane separation has gone from a laboratory curiosity to commercial reality as discussed by the authors, and these membranes often have a separating layer thickness varying from 1.5 to 3.5 mm.
Abstract: In the past several decades, membrane separation has gone from a laboratory curiosity to commercial reality These membranes often have a separating layer thickness
278 citations
TL;DR: In this article, nonlinear limiters may protect optical sensors against pulsed lasers of any wavelength and new nonlinear materials have been produced, offering increased nonlinear sensitivity and reduced visual loss.
Abstract: Nonlinear limiters may protect optical sensors against pulsed lasers of any wavelength. New nonlinear materials have been produced, offering increased nonlinear sensitivity and reduced visual loss. Particle suspensions, macrocyclic dyes, and two-photon absorbers are particularly promising. Issues surrounding incorporation into optical systems are under study.
172 citations
TL;DR: In this article, the chemical structures of hybrid inorganic-organic polymers and their modified sol-gel processing method are described and an overview is given for the control of various properties (mechanical, electrical, optical) of the materials on a molecular scale.
Abstract: Hybrid inorganic-organic polymers based on organically modified heteropolysiloxanes have found widespread attention and application as materials with adjustable properties using tailor-made precursors. The chemical structures of monomers and their modified sol-gel processing method are described. An overview is given for the control of various properties (mechanical, electrical, optical) of the materials on a molecular scale. Successful material developments and industrial applications are described.
166 citations
TL;DR: The main advantages of the use of hybrid organic-inorganic nanocomposites result from their high versatility in offering a wide range of possibilities to fabricate tailor-made materials in terms of their chemical and physical properties, and macroscopic shape molding.
Abstract: In the course of the recent development of new sol-gel derived materials for optics, organically modified metal oxide matrices have widely demonstrated their great potential. Most of the work performed in this area has been concentrated on embedding organic or organo-metallic chromophores in an oxide network to make optical devices. The main advantages of the use of hybrid organic—inorganic nanocomposites result from their high versatility in offering a wide range of possibilities to fabricate tailor-made materials in terms of their chemical and physical properties, and macroscopic shape molding. Such materials emerging in this field are known as ‘sol-gel photonics’. There have been some striking examples of the use of room temperature processed hybrids to design materials with emission, absorption, second-order nonlinear optical and photochromic properties.
133 citations
TL;DR: In the past 18 months, new and unique examples have been synthesized; enhanced performance characteristics have been realized; and improved descriptions of physical properties have been developed as discussed by the authors. And these advances will likely increase the overall scope of applicability for these materials.
Abstract: Crystalline inorganic borates comprise a structurally intriguing, technologically important class of solid-state oxides. During the past 18 months, new and unique examples have been synthesized; enhanced performance characteristics have been realized; and improved descriptions of physical properties have been developed. Combined, these advances will likely increase the overall scope of applicability for these materials.
122 citations
TL;DR: In this article, the authors proposed a thin-film rechargeable lithium battery with a low discharge power and a long cycle life, which relies on the amorphous lithium phosphorus oxynitride electrolyte, known as Lipon, deposited by magnetron sputtering.
Abstract: Thin-film rechargeable lithium batteries, less than 15 μm thick, are being developed as micro-power sources. Batteries with long cycle lives have been constructed with a variety of electrode materials and cell configurations onto thin ceramic, metal, and Si substrates. Improvements in the properties of several well-known cathode thin-film materials have been reported, while several novel thin-film anode materials have been introduced in recent papers. All recent thin-film batteries with moderate discharge powers and cycle lives rely on the amorphous lithium phosphorus oxynitride electrolyte, known as Lipon, deposited by rf magnetron sputtering.
121 citations
86 citations
TL;DR: A review of the literature on the synthesis of supported catalysts can be found in this article, with the use of carbon nanotubes and new heteropolyanions as examples of novel supports and of novel precursors of active components, respectively.
Abstract: Research reports on the synthesis of supported catalysts during the review period (1997–1998) have shown the use of carbon nanotubes and new heteropolyanions as examples of novel supports and of novel precursors of active components, respectively. Studies of adsorption and precipitation chemistry reveal new molecular details of the extensive interactions between precursors and supports in an aqueous environment. Progress is being made in the use of chemical vapor deposition for the synthesis of supported catalysts. Combinatorial techniques have made their first contributions to solid catalyst synthesis.
85 citations
TL;DR: In this paper, the photoinduced electron transfer in solid composite films of fullerenes embedded into conjugated polymers is shown to be reversible, ultrafast with a quantum efficiency approaching unity, and metastable.
Abstract: Recent developments in conjugated polymer-based photovoltaic elements have been reviewed. The photophysics of such photoactive devices is based on the photoinduced electron transfer from donor-type semiconducting conjugated polymers onto acceptor-type conjugated polymers or acceptor molecules such as Buckminsterfullerene, C60. Photoinduced electron transfer in solid composite films of fullerenes embedded into conjugated polymers is reversible, ultrafast (within 300 fs) with a quantum efficiency approaching unity, and metastable. Similar to the first step in natural photosynthesis, this photoinduced electron transfer leads to a number of potentially interesting applications, which include sensitization of the photoconductivity and photovoltaic phenomena. Furthermore, using the conjugated polymer donors in polymer blends with another conjugated polymer acceptor, similar photovoltaic elements have been realized. Examples of photovoltaic architectures are discussed with their potential in terrestrial solar energy conversion.
TL;DR: In this paper, a novel Mg-based amorphous alloy, MgNi, and its hydride was synthesized by ball milling, which showed lower dehydrogenation temperatures than intermetallic Mgbased alloys.
Abstract: Improvement of hydrogen capacity in hydrogen-absorbing alloys has been achieved in recent years. Mg-based alloys which were synthesized by ball milling showed lower dehydrogenation temperatures than intermetallic Mg-based alloys. This technique is also effective for preparing a novel Mg-based amorphous alloy, MgNi, and its hydride. Besides conventional intermetallic compounds such as LaNi5, solid solution alloy, ‘Laves phase related BCC solid solution’ with body-centered-cubic structure showed a hydrogen capacity of 2.2 mass% at room temperature. Alanate, which is not an interstitial hydride, was found to react with gaseous hydrogen reversibly with a catalyst, and its hydrogen capacity was more than 3 mass%.
TL;DR: In this paper, single-wall carbon nanotubes exhibit many properties analogous to quantum dots and wires at very low temperatures: Coulomb blockade and single-electron charging, and these properties may be exploited in constructing active electronic devices of unprecedentedly small size.
Abstract: Single-wall carbon nanotubes exhibit many properties analogous to quantum dots and wires at very low temperatures: Coulomb blockade and single-electron charging. These and other phenomena may be exploited in constructing active electronic devices of unprecedentedly small size. Bulk material may be chemically doped to yield mass-normalized electrical conductivity higher than that of copper.
TL;DR: In this paper, the stability and kinetics of ordering in perovskite-related structures have been investigated, including the ordering of structural slabs and formation of modulated intergrowth structures.
Abstract: Several recent papers have addressed the fundamental aspects of the stability and kinetics of ordering in complex oxides, and investigated systems where the properties are mediated by the degree of order. Cation ordering reactions have been shown to induce large alterations in the dielectric, ferroelectric, magnetic, and electronic response of many complex oxides. The majority of the cited publications focus on ion ordering in perovskite-related structures; however, additional examples include the ordering of structural slabs and formation of modulated intergrowth structures.
TL;DR: In this paper, the gamma Ti aluminide has been used in non-aerospace applications to reduce the power consumption of exhaust valves and turbocharger turbines for automotive engines.
Abstract: Attempts to utilize gamma Ti aluminide in non-aerospace applications have centered on components for which weight reduction would improve overall equipment performance, namely exhaust valves and turbocharger turbines for automotive engines. As a result of extensive research that has recently been conducted on materials, manufacturing processes, and application tests for those two types of components, both have reached the point of practical utilization. However, the development of low-cost manufacturing processes is still needed for expanded practical application in the future.
TL;DR: For about 40 years living anionic polymerization has been the premier technique for the synthesis of model polymers of controlled architecture and narrow molecular weight distribution (MWD) as mentioned in this paper.
Abstract: For about 40 years living anionic polymerization has been the premier technique for the synthesis of model polymers of controlled architecture and narrow molecular weight distribution (MWD). Nowadays, despite the continuing development of new strategies for the synthesis of well-defined polymers and copolymers (e.g. group transfer polymerization, living radical polymerization, etc.), anionic polymerization continues to be the most reliable and versatile method for the synthesis of a wide variety of model polymers. The main reason for the broad utility of living anionic polymerization is that the conditions necessary for the efficient generation of polyanions that do not undergo termination or chain transfer reactions are well established for many monomers [Hsieh HL, Quirk RP. Anionic polymerization: principles and practical applications, New York: Marcel Dekker, 1996]. Despite these successes, significant challenges remain in the field of anionic polymerization. These challenges include extension of the strategies for anionic synthesis of polymers with controlled architectures (such as star and graft copolymers), further development of strategies for chain end functionalization, and mastering control over polymerization of (meth)acrylates. Recent advances in these areas are summarized in this article.
TL;DR: In this paper, it has been shown that the optical properties of organic films under electrical excitation are affected by the formation of polarons, imposing yet another obstacle for realization of these devices.
Abstract: Lasing action in optically pumped thin films of organic semiconductors has recently been demonstrated in a variety of materials employing a variety of cavity configurations. The excitation intensities required for lasing in optically pumped films are comparable to the electrical current densities achievable in light emitting devices based on these materials, opening the door to the possible realization of organic diode lasers. However, the design of diode laser structures is complicated by the relatively low charge carrier mobilities of organics. It has also been shown that the optical properties of organic films under electrical excitation are affected by the formation of polarons, imposing yet another obstacle for realization of these devices. The continuing research on organic diode lasers is motivated by the unique properties of these devices, such as narrow spectral emission linewidth and the temperature independence of laser output power and emission wavelength, which may be advantageous in a number of applications.
TL;DR: The ability to control both the length scale and the spatial organization of block copolymer morphologies makes these materials particularly attractive candidates for use as templates in the synthesis of functional nanocomposites as mentioned in this paper.
Abstract: There are applications and devices which require controlled distribution of material functionality (electrical, optical, catalytic, magnetic) in two or three dimensions. At the nanometer length scale, attempts to meet this challenge have included template-mediated materials chemistry [1] in which track-etched membranes, porous alumina and zeolites serve as the nanoscale reaction vessels for the synthesis of the functional materials. The ability to control both the length scale and the spatial organization of block copolymer morphologies makes these materials particularly attractive candidates for use as templates in the synthesis of functional nanocomposites. Appropriate choices of the repeat units of the block sequences renders them capable of selectivity sequestering preformed inorganic nanoclusters or selectively solubilizing inorganic reagents for in-situ cluster synthesis. Methods exist to produce nanoscale voids which percolate through the structure, leading to processes which coat or backfill the channels with functional materials.
TL;DR: Several methods for the preparation of di-and triblock copolymers are described in this paper. But, their methods are not suitable for the synthesis of block copolymars, and they do not support the use of polycyclic polymers.
Abstract: The efficient synthesis of structurally well-defined block copolymers is exciting and important area of research. This article describes several methods for the preparation of di- and triblock copolymers. Examples are taken from the literature and include anionic, cationic, free-radical and metal-catalyzed polymerizations that are useful for the preparation of these hybrid materials. In addition, examples that combine these polymerization mechanisms are described.
TL;DR: In this paper, the authors used a specially designed procedure to reproduce a catalysts for the selective synthesis of ethylene from methanol and showed that the relationship between catalyst properties and reaction performances is clearer than ever before.
Abstract: The past year has seen remarkable advances both in methanol to olefin process development and in understanding the catalysts and reactions involved. The methanol to olefin process is now on the way to being commercialized locally with economic advantages in comparison with other natural gas utilization technologies and conventional naphtha cracking processes. Using a specially designed procedure, a catalyst for the selective synthesis of ethylene from methanol has been reliably reproduced. The relationships between catalyst properties and reaction performances are clearer than ever before.
TL;DR: The field of bioactive ceramic implant materials is surveyed in this paper for the period 1997-1998, with a focus on the use of calcium phosphate materials for dental and orthopedic applications.
Abstract: The field of bioactive ceramic implant materials is surveyed, for the period 1997–1998. Literature on the use of calcium phosphate materials for dental and orthopedic applications is discussed. The use of bioactive bone cements and the recent introduction of bioactive glasses into clinical use are discussed.
TL;DR: In this paper, a new technology is implemented when the perceived technical risks are outweighed by the perceived marketing risks of not using the technology, and considerable uncertainty remains regarding the economic and marketing issues.
Abstract: New technology is implemented when the perceived technical risks are outweighed by the perceived marketing risks of not using the technology. Although great strides have been made in reducing the technical risks of gamma titanium aluminide, considerable uncertainty remains regarding the economic and marketing issues.
TL;DR: In this article, the synthesis of metal sulfides with controlled architecture, exemplified by microporous and mesostructured materials, intercalates, nanowires, and nanotubes, is described.
Abstract: Recent advances in the synthesis of metal sulfides with controlled architecture, exemplified by microporous and mesostructured materials, intercalates, nanowires, and nanotubes are described. These illustrate a paradigm shift from traditional solid-state methods to rational, directed assembly of materials with hierarchical design.
TL;DR: In the absence of effective lean NOx catalysts, NOx sorption systems are emerging as the alternative method for clean NOx control in gasoline engines as mentioned in this paper, but no catalysts have surfaced that meet all the desired requirements for lean burn gasoline or diesel engines.
Abstract: The past year has seen a wealth of published articles from around the world related to automobile exhaust emission control. The applied automotive catalysis work continues in response to the need for robust systems that comply with new, stricter regulations for the control of nitric oxides (NOx), hydrocarbons and carbon monoxide under an expanded range of driving conditions that includes higher speeds and air conditioner operation. The search also continues for catalysts that effectively reduce nitric oxide levels in lean feed streams. Although promising results continually emerge, no catalysts have surfaced that meet all the desired requirements for lean burn gasoline or diesel engines. In the absence of effective lean NOx catalysts, NOx sorption systems are emerging as the alternative method for lean NOx control in gasoline engines.
TL;DR: In this paper, solid free-form fabrication (SFF) is an extension of conventional manufacturing technology (made possible by advances in computing and automated shaping machinery), and the key process control variables that arise when SSF is applied to ceramics are of a character that is familiar to ceramic processing in general.
Abstract: In this review, the author suggests that solid freeform fabrication is an extension of conventional manufacturing technology (made possible by advances in computing and automated shaping machinery). That is, the basic unit operations and the layered-assembly strategy have long histories, what is new is the automation thereof. It is further suggested that the key process control variables that arise when SSF is applied to ceramics are of a character that is familiar to ceramic processing in general. It is speculated that thoughtful extension of green machining practices may erode the current position of assembly-based approaches to SFF. Lastly, one under-explored application area for SFF is identified as the production of test specimens with unique and highly-controlled microstructure for scientific testing.
TL;DR: In this article, the temperature-dependent dielectric behavior of (Ba, Sr)TiO 3 films as a function of strain, composition, and thickness was studied and a direct link between the thin film and bulk electrical properties was made.
Abstract: Recent developments in ferroelectric films have been made in terms of their application in nonvolatile memories and dynamic random access memories. One highlight is the report of a complete description of the temperature-dependent dielectric behavior of (Ba, Sr)TiO 3 films as a function of strain, composition, and thickness. For the first time, a direct link has been made between the thin film and bulk electrical properties.
TL;DR: The processing advantages associated with heterogeneous catalysis have led to the development of many new chiral heterogeneous catalysts for a variety of important asymmetric reactions, such as site isolation, stability against leaching, and mass transfer to the active sites.
Abstract: The processing advantages associated with heterogeneous catalysis have led to the development of many new chiral heterogeneous catalysts for a variety of important asymmetric reactions. Established systems, such as chirally modified metals, have been further developed, while new strategies for the creation of chiral polymer catalysts and oxide systems, such as zeolites containing chelate complexes, are being explored. Important issues, such as site isolation, stability against leaching, and mass transfer to the active sites, have been addressed. Advances have been made in chiral zeolite frameworks and porous hybrid solids, chiral modifiers in porous hosts, asymmetric catalysts occluded in membranes and dissolved in supported liquid films, and modular chelate complexes on polymer beads.
TL;DR: The most intriguing recent development in the field of silicon nitride ceramics has undoubtedly been the discovery of a cubic form of silicon oxide as discussed by the authors, which is known as α-SiAlON.
Abstract: The most intriguing recent development in the field of silicon nitride ceramics has undoubtedly been the discovery of a cubic form of silicon nitride. Major advances were made in α-SiAlON ceramics, including the development of thermally stable, in situ reinforced grades. Significant achievements were reported in tailoring the mechanical properties of silicon nitride ceramics through control of secondary phase chemistry and grain morphology.
Journal Article•
TL;DR: In this paper, the authors consider the use of chalcogen-based infrared glasses for the development of optical waveguides such as channel or fiber-laser emission.
Abstract: Driven by applications in hot fields such as optical communications, lasers, sensors, etc. infrared glasses have to be considered as key components in the development of devices for telecom signal amplification, fibre-laser emission as well as for passive functions related to IR remote spectroscopy or thermal imaging. Stable vitreous materials with low-phonon energies are found in the family of fluorides and chalcogenides glasses; they offer the advantage of excellent transparency in the mid-IR and weak nonradiative relaxation when doped with rare earth elements. Despite the number of candidates only a very limited number of glass compositions can be shaped into good optical waveguides such as channel or fibre. When possible, this led to remarkable amplification in the 1.3 μm region and lasing emission in the blue or mid-IR. Non-linear optical properties of chalcogen-based glasses are also of special interest for fast all optical switching and photo-induced effects.