Showing papers in "International Materials Reviews in 2008"
TL;DR: In this paper, the authors present a review of low temperature co-fired ceramic (LTCC) technologies for high frequency applications, which will be of immense help to researchers and technologists all over the world.
Abstract: Small, light weight and multifunctional electronic components are attracting much attention because of the rapid growth of the wireless communication systems and microwave products in the consumer electronic market. The component manufacturers are thus forced to search for new advanced integration, packaging and interconnection technologies. One solution is the low temperature cofired ceramic (LTCC) technology enabling fabrication of three-dimensional ceramic modules with low dielectric loss and embedded silver electrodes. During the past 15 years, a large number of new dielectric LTCCs for high frequency applications have been developed. About 1000 papers were published and ∼500 patents were filed in the area of LTCC and related technologies. However, the data of these several very useful materials are scattered. The main purpose of this review is to bring the data and science of these materials together, which will be of immense help to researchers and technologists all over the world. The comme...
968 citations
TL;DR: In this article, the authors highlight recent advances in X-ray microcomputed tomography (microCT) as applied to materials, specifically advances made since the first materials microCT review appeared in Internati...
Abstract: This review highlights recent advances in X-ray microcomputed tomography (microCT) as applied to materials, specifically advances made since the first materials microCT review appeared in Internati...
470 citations
TL;DR: In this article, the high strain rate dependence of the flow stress of metals and alloys is described from a dislocation mechanics viewpoint over a range beginning from conventional tension/compression testing through split Hopkinson pressure bar (SHPB) measurements to Charpy pendulum and Taylor solid cylinder impact tests and shock loading or isentropic compression experiment (ICE) results.
Abstract: The high strain rate dependence of the flow stress of metals and alloys is described from a dislocation mechanics viewpoint over a range beginning from conventional tension/compression testing through split Hopkinson pressure bar (SHPB) measurements to Charpy pendulum and Taylor solid cylinder impact tests and shock loading or isentropic compression experiment (ICE) results. Single crystal and polycrystal measurements are referenced in relation to influences of the crystal lattice structures and nanopolycrystal material behaviours. For body centred cubic (bcc) metals, the strain rate sensitivity (SRS) is in the yield stress dependence as compared with the face centred cubic (fcc) case of being in the strain hardening property. An important consequence is that an opposite ductility influence occurs for the tensile maximum load point strain that decreases with strain rate for the bcc case and increases with strain rate for the fcc case. Different hexagonal close packed (hcp) metals are shown to foll...
293 citations
TL;DR: In this article, the effect of the initial grain growth cannot be ignored because that it is sufficient to cause the material to lose nanocrystalline characteristics and it is generally found that the sintering temperatures of nanosized particles are dramatically lower than that of their micrometre or submicrometer sized counterparts.
Abstract: The sintering of nanosized particles is a scientific and technological topic that affects the manufacture of bulk nanocrystalline materials and the understanding of the stability of nanoparticles. Owing to their extremely small size and the high surface to volume ratio, nanoparticles during sintering exhibit a number of distinctively unique phenomena compared to the sintering of coarse powders. Particularly, it is generally found that the sintering temperatures of nanosized particles are dramatically lower than that of their micrometre or submicrometre sized counterparts. Research has also shown that the grain growth during nanosintering consists of an initial dynamic grain growth stage that occurs during heating up and the normal grain growth stage that occurs mostly during isothermal holding. For nanoparticles, the effect of the initial grain growth cannot be ignored because that it is sufficient to cause the material to lose nanocrystalline characteristics. This review aims to bring to focus th...
219 citations
TL;DR: In this paper, a critical review of metallic interconnects for SOFCs with a focus on recent progress in materials development, as well as advances in understanding materials degradation and interfacial phenomena under the SOFC operating conditions.
Abstract: With the reduction in solid oxide fuel cell (SOFC) operating temperatures into the range 650–800°C, cost effective metallic materials, in particular high temperature oxidation resistant alloys, have become promising candidates, in place of ceramic counterparts, for construction of interconnects in SOFC stacks. For a lifetime of thousands of hours, the alloys must demonstrate excellent surface, structural and electrical stability, and compatibility with other components in SOFC stacks in a very challenging environment. The present paper provides a critical review of metallic interconnects for SOFCs with a focus on recent progress in materials development, as well as advances in understanding materials degradation and interfacial phenomena under the SOFC operating conditions. It also attempts to provide guiding principles for the development of optimised, cost effective metallic interconnect materials that can demonstrate satisfactory life time stability and performance.
206 citations
Abstract: With the advent of high performance thermoplastic polymers, structural applications for thermoplastic composites are increasing rapidly. Thermoplastic matrix composites possess distinct advantages vis-a-vis thermoset matrix composites in terms of recyclability, high specific strength and specific stiffness, corrosion resistance, enhanced impact toughness, cost effectiveness, and flexibility of design. Since 1990s, the number of material forms and combinations in fibre reinforced thermoplastic polymers has increased exponentially, thereby expanding application avenues in transportation, automotive, mass transit, marine, aerospace, military and construction sectors. In this paper we review the state of the art in processing of fibre reinforced thermoplastics. We start with a brief description of thermoplastic polymers used in structural applications followed by material forms and methods of impregnation of the reinforcement with polymer. Long fibre based processing methods are described next. A desc...
201 citations
TL;DR: In this paper, a fundamental survey of the electrospinning process (apparatus, governing parameters) and of recent improvements of the technique, including structural modifications of polymeric nanofibre meshes, is provided.
Abstract: Electrospinning has attracted tremendous interest in the research community as a simple and versatile technique to produce synthetic polymeric ultrafine fibres with diameters ranging from a few micrometres to tens of nanometres. Recently, some natural origin polymers have also been successfully electrospun. Owing to their very small diameter, polymeric nanofibres exhibit unusual properties such as high specific surface area, flexibility in surface functionalities and superior mechanical properties. In addition, electrospun non-woven meshes could physically mimic the extracellular matrix structure of native tissues. These remarkable properties render electrospun nanofibres useful for many applications, particularly those related to the field of biomedical engineering. The first part of this review is intended to provide a fundamental survey of the electrospinning process (apparatus, governing parameters) and of recent improvements of the technique, including associated structural modifications of polymeric nanofibre meshes. The prospective tissue engineering/biomedical applications of electrospun polymeric nanofibres are then reviewed, namely, wound dressings, medical prostheses, drug delivery systems, DNA release and tissue engineering scaffolds. The essential properties of scaffolds in terms of the structural features of electrospun nanofibre meshes are discussed. Finally, the future perspectives for applications of electrospun nanofibres, particularly in the field of tissue engineering, are considered.
160 citations
TL;DR: In this article, a review examines the fundamental factors underlying nanoceramic sintering and the approaches to effectively utilize these factors to improve the performance of the sintered grains.
Abstract: There are two challenges in nanoceramic sintering: fully densifying the sintered body and maintaining the sintered grains at <100 nm size. This review examines the fundamental factors underlying nanoceramic sintering and the approaches to effectively utilise the sintering factors to advantage. Nanoceramic sintering techniques are divided into four categories: pressureless sintering, pressure sintering, electrically assisted sintering, and other sintering related techniques. Pressureless sintering has mainly evolved around modifying sintering schedules, improving nanoparticle packing characteristics, and using additives to tailor the diffusion rates. Pressure sintering, which includes hot pressing, hot isostatic pressing, and sinter forging, can effectively achieve full densification for nanostructured ceramics but microstructural inhomogeneity and sintered shape limitation are difficult to overcome. For electrically assisted sintering, many nanoceramics have been sintered to full density with spar...
146 citations
TL;DR: In this article, the authors reviewed the approaches commonly used to quantify creep and fracture behaviour and pointed out the limitations of these approaches, as well as their limitations when applied to comprehensive long-term data sets.
Abstract: The approaches commonly used to quantify creep and creep fracture behaviour are critically reviewed. Their limitations are illustrated by reference to information openly available for three martensitic steels, namely, grades 91, 92 and 122. Adopting traditional procedures, the creep design strengths of these 9–12% chromium steels have been reduced substantially as continuing experimental programmes have increased the maximum test durations from ∼30 000 towards 100 000 h. Moreover, even when applied to comprehensive long-term data sets, the estimated 100 000 h strengths vary considerably, depending on the detailed method selected to perform the calculations. In contrast, by normalising the applied stress through the appropriate ultimate tensile strength (UTS) value, new relationships allow the multi-batch stress rupture properties at various creep temperatures to be superimposed onto sigmoidal 'master curves' using the activation energy for lattice diffusion in the alloy steel matrixes (300 kJ mol−...
123 citations
TL;DR: In the past ten years, ∼20 novel processes have been investigated as possible low-cost routes for titanium, based upon electrolytic processes, both anodic and cathodic, and variations of the Hunter and Kroll processes as mentioned in this paper.
Abstract: Titanium ores are very plentiful in the earth crust but the demand for titanium metal is restricted by its high cost in spite of its excellent mechanical properties, corrosion and oxidation resistance and low density. Titanium was first produced by the Hunter process but this has been superseded, except for special applications, by the Kroll process which entails carbochlorination of rutile and ilmenite to obtain titanium tetrachloride followed by metallothermic reduction with magnesium. In the past ten years, ∼20 novel processes have been investigated as possible low cost routes for titanium, based upon electrolytic processes, both anodic and cathodic, and variations of the Hunter and Kroll processes. The anodic processes use a conducting anode consisting of Ti–O–C and the titanium is essentially electrorefined, in a molten salt, from the anode. The cathodic routes rely on either the electrodeposition of calcium or the electro-deoxidation of the oxide. The variations on the Hunter and Kroll proce...
97 citations
TL;DR: In this paper, the authors present the advancement in synthesis and characterisation techniques of one-dimensional nanostructures (ODNS) as well as their potential for novel applications.
Abstract: This review presents the advancement in synthesis and characterisation techniques of one-dimensional nanostructures (ODNS) as well as their potential for novel applications. In the first section of the review, the authors describe the synthesis techniques of one-dimensional nanostructures, i.e. template based synthesis, vapour phase growth, solution based growth and other innovative techniques. Various characterisation techniques such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are described in detail, followed by a comprehensive review of the unique material properties of one-dimensional nanostructures. The final section of this paper presents current state of the art chemical and biological sensing applications as well as other potential technologies which may emerge due to the advantage nanomaterials have over their bulk counterparts.
TL;DR: Genetic algorithms (GAs) belong to the broader family of generic population based metaheuristic optimisation algorithms called evolutionary algorithms as mentioned in this paper, and have been successfully applied in many fields such as polymer production, polymer design, polymer processing, polymer laminates and other polymers.
Abstract: Genetic algorithms (GAs) belong to the broader family of generic population based metaheuristic optimisation algorithms called evolutionary algorithms. These are one of the biology inspired computing techniques that emulate the basic Darwinian concept of natural selection. Because of their many positive attributes such as ease of use, versatility and robustness, GAs have become important in materials research very rapidly since their inception. Though going through a major stage of theoretical development, GAs have been successfully applied in many fields such as polymer production, polymer design, polymer processing, polymer laminates and other polymers, as well as non-polymer applications in recent times. The present review attempts to present the state of the art in this area. The review is broadly divided into three sections: fundamentals of GAs, the use of GAs in polymeric materials and the use of GAs in non-polymer applications. First, the fundamentals of GAs are presented to provide some gl...
TL;DR: In this paper, a brief review of the literature on liquid transport into and through polymer matrices is presented, which attempts to point out the accuracy of experimental observations and the ability of different theories to explain them.
Abstract: The purpose of this brief review is not to provide a comprehensive cover of the field, but only to open a discussion on some important issues. Many well established procedures are rarely challenged, and it may be useful to revisit them in the light of new experimental evidence. The review deals specifically with liquid transport into and through polymer matrices. It attempts to point out the accuracy of experimental observations and the ability of different theories to explain them. Most often the rates of diffusion (or time dependence of diffusion distance) are measured. The results are usually interpreted using Fick's law. This gives a good correlation for thick samples; however, for thin samples, the Case II theory provides a better correlation with experimental data. The combination of these two mechanisms, or the dependence of the diffusion distance on time to an exponent different than 1 or 1/2, however, requires inhomogeneous material. The best correlation can be obtained by considering the...
TL;DR: A critical review of dynamic compaction as a means to densify metal powders is presented in this paper, focusing on the powder metallurgical aspects of the process and highlighting the key powder related factors and processing parameters.
Abstract: This paper is a critical review of dynamic compaction as a means to densify metal powders Dynamic compaction was discovered in the 1960s Most of the investigations since then have focused mainly on the physics dealing with energy, motion and force aspects of the process Owing to this, there is a lack of knowledge of the effects of preprocessing and processing factors on this process This knowledge gap has created skepticism in the PM community about this process' practice This review attempts to bridge this gap and highlights the powder metallurgical aspects of dynamic compaction by emphasising the key powder related factors and processing parameters affecting dynamic compaction Powder related factors include powder characteristics and the processing parameters including the machine operating parameters Attention has been given to iron, aluminium and copper powders Through this review, this article paves the way to design of high density dynamic compaction systems based on the final PM com
TL;DR: In this article, a review of methods to improve the hydration resistance of lime-based materials is presented, which includes densification of the lime aggregate by addition of sintering aids and surface treatment.
Abstract: Studies to improve the hydration resistance of lime-based materials are reviewed. The methods described include densification of the lime aggregate by addition of sintering aids and surface treatment. Methods for assessing hydration resistance are also reviewed. Additions of ZrO2, TiO2 (including Ti chelating compounds) and rare earth oxides can improve the hydration resistance of CaO aggregate by, it is believed, enhancing solid state sintering without sacrificing refractoriness via formation of hydration resistant solid solutions. Fe2O3, Al2O3 (as well as Al chelating compounds and Al metal), CuO and V2O5, act as liquid forming aids. These additives improve the sintering of lime and subsequently the hydration-resistance via formation of liquids at high temperature which cool to produce hydration-resistant solids surrounding the lime polycrystals. However, the liquids formed may significantly reduce the refractoriness of lime materials, thus eroding their particular advantage. The same problem is...