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Showing papers on "Ceramic published in 2007"


Journal ArticleDOI
05 Oct 2007-Science
TL;DR: A high level of ordering of the nanoscale building blocks, combined with dense covalent and hydrogen bonding and stiffening of the polymer chains, leads to highly effective load transfer between nanosheets and the polymer.
Abstract: Nanoscale building blocks are individually exceptionally strong because they are close to ideal, defect-free materials. It is, however, difficult to retain the ideal properties in macroscale composites. Bottom-up assembly of a clay/polymer nanocomposite allowed for the preparation of a homogeneous, optically transparent material with planar orientation of the alumosilicate nanosheets. The stiffness and tensile strength of these multilayer composites are one order of magnitude greater than those of analogous nanocomposites at a processing temperature that is much lower than those of ceramic or polymer materials with similar characteristics. A high level of ordering of the nanoscale building blocks, combined with dense covalent and hydrogen bonding and stiffening of the polymer chains, leads to highly effective load transfer between nanosheets and the polymer.

1,489 citations


Book
04 Apr 2007
TL;DR: In this article, the authors discuss the role of point defects, charge and diffusion in the process of phase transformation in polycrystalline polycrystals, and propose a phase diagram for each point defect.
Abstract: Introduction.- Some History.- What You Already Know.- Bonds and Energy Bonds.- Models, Crystals and Chemistry.- Binary Compounds.- Complex Crystal and Glass Structures.- Equilibrium Phase Diagrams.- Furnaces.- Characterizing Structure, Defects and Chemistry.- Point Defects, Charge and Diffusion.- Are Dislocations Unimportant?- Surfaces, Nanoparticles and Foams.- Interfaces in Polycrystals.- Phase Boundaries, Particles and Pores.- Mechanical Testing.- Deforming: Plastic.- Fracturing: Brittleness.- Raw Materials.- Powders, Fibers, Platelets and Composites.- Glass and Glass-Ceramics.- Gels, Sols and Organic Chemistry.- Sintering and Grain Growth.- Solid-State Phase Transformations and Reactions.- Processing Glass and Glass-Ceramics.- Coatings and Thick Films.- Thin Films and Vapor Deposition.- Growing Single Crystals.- Shaping and Forming.- Conducting Charge or Not.- Locally Redistributing Charge.- Interacting With and Generating Light.- Storing Data Using Magnetic Fields.- Responding to Temperature Changes.- Bioceramics and Biomimetics.- Minerals and Gems.- Industry and the Environment.

742 citations


Journal ArticleDOI
TL;DR: In this paper, the formation of regular patterns is a common feature of many solidification processes involving cast materials, and regular patterns can be obtained in porous alumina by controlling the freezing of ceramic slurries followed by subsequent ice sublimation and sintering.

683 citations



Book
10 Dec 2007
TL;DR: In this paper, the authors present a classification of Materials Materials Materials of Importance-Carbonated Beverage Containers 1.5 Advanced Materials 1.6 Modern Materials Needs 1.7 Processing/Structure/Properties/Performance Correlations.
Abstract: Chapter 1 - Introduction. 1.1 Historical Perspective 1.2 Materials Science and Engineering 1.3 Why Study Materials Science and Engineering? 1.4 Classification of Materials Materials of Importance-Carbonated Beverage Containers 1.5 Advanced Materials 1.6 Modern Materials Needs 1.7 Processing/Structure/Properties/Performance Correlations Chapter 2 - Atomic Structure and Interatomic Bonding. 2.1 Introduction 2.2 Fundamental Concepts 2.3 Electrons in Atoms 2.4 The Periodic Table 2.5 Bonding Forces and Energies 2.6 Primary Interatomic Bonds 2.7 Secondary Bonding or van der Waals Bonding Materials of Importance-Water (Its Volume Expansion Upon Freezing) 2.8 Molecules Chapter 3 - Structures of Metals and Ceramics 3.1 Introduction 3.2 Fundamental Concepts 3.3 Unit Cells 3.4 Metallic Crystal Structures 3.5 Density Computations-Metals 3.6 Ceramic Crystal Structures 3.7 Density Computations-Ceramics 3.8 Silicate Ceramics 3.9 Carbon Materials of Importance-Carbon Nanotubes 3.10 Polymorphism and Allotropy Material of Importance-Tin (Its Allotropic Transformation) 3.11 Crystal Systems 3.12 Point Coordinates 3.13 Crystallographic Directions 3.14 Crystallographic Planes 3.15 Linear and Planar Densities 3.16 Close-Packed Crystal Structures 3.17 Single Crystals 3.18 Polycrystalline Materials 3.19 Anisotropy 3.20 X-Ray Diffraction: Determination of Crystal Structures 3.21 Noncrystalline Solids Chapter 4 - Polymer Structures 4.1 Introduction 4.2 Hydrocarbon Molecules 4.3 Polymer Molecules 4.4 The Chemistry of Polymer Molecules 4.5 Molecular Weight 4.6 Molecular Shape 4.7 Molecular Structure 4.8 Molecular Configurations 4.9 Thermoplastic and Thermosetting Polymers 4.10 Copolymers 4.11 Polymer Crystallinity 4.12 Polymer Crystals Chapter 5 - Imperfections in Solids 5.1 Introduction 5.2 Point Defects in Metals 5.3 Point Defects in Ceramics 5.4 Impurities in Solids 5.5 Point Defects in Polymers 5.6 Specification of Composition 5.7 Dislocations-Linear Defects 5.8 Interfacial Defects Materials of Importance-Catalysts (and Surface Defects) 5.9 Bulk or Volume Defects 5.10 Atomic Vibrations 5.11 Basic Concepts of Microscopy 5.12 Microscopic Techniques 5.13 Grain Size Determination Chapter 6 - Diffusion 6.1 Introduction 6.2 Diffusion Mechanisms 6.3 Steady-State Diffusion 6.4 Nonsteady-State Diffusion 6.5 Factors That Influence Diffusion 6.6 Diffusion in Semiconducting Materials Material of Importance-Aluminum for Integrated Circuit Interconnects 6.7 Other Diffusion Paths 6.8 Diffusion in Ionic and Polymeric Materials Chapter 7 - Mechanical Properties 7.1 Introduction 7.2 Concepts of Stress and Strain 7.3 Stress-Strain Behavior 7.4 Anelasticity 7.5 Elastic Properties of Materials 7.6 Tensile Properties 7.7 True Stress and Strain 7.8 Elastic Recovery after Plastic Deformation 7.9 Compressive, Shear, and Torsional Deformation 7.10 Flexural Strength 7.11 Elastic Behavior 7.12 Influence of Porosity on the Mechanical Properties of Ceramics 7.13 Stress-Strain Behavior 7.14 Macroscopic Deformation 7.15 Viscoelastic Deformation 7.16 Hardness 7.17 Hardness of Ceramic Materials 7.18 Tear Strength and Hardness of Polymers 7.19 Variability of Material Properties 7.20 Design/Safety Factors Chapter 8 - Deformation and Strengthening Mechanisms 8.1 Introduction 8.2 Historical 8.3 Basic Concepts of Dislocations 8.4 Characteristics of Dislocations 8.5 Slip Systems 8.6 Slip in Single Crystals 8.7 Plastic Deformation of Polycrystalline Metals 8.8 Deformation by Twinning 8.9 Strengthening by Grain Size Reduction 8.10 Solid-Solution Strengthening 8.11 Strain Hardening 8.12 Recovery 8.13 Recrystallization 8.14 Grain Growth 8.15 Crystalline Ceramics 8.16 Noncrystalline Ceramics 8.17 Deformation of Semicrystalline Polymers 8.18 Factors That Influence the Mechanical Properties of Semicrystalline Polymers Materials of Importance-Shrink-Wrap Polymer Films 8.19 Deformation of Elastomers Chapter 9 - Failure 9.1 Introduction 9.2 Fundamentals of Fracture 9.3 Ductile Fracture 9.4 Brittle Fracture 9.5 Principles of Fracture Mechanics 9.6 Brittle Fracture of Ceramics 9.7 Fracture of Polymers 9.8 Fracture Toughness Testing 9.9 Cyclic Stresses 9.10 The S-N Curve 9.11 Fatigue in Polymeric Materials 9.12 Crack Initiation and Propagation 9.13 Factors That Affect Fatigue Life 9.14 Environmental Effects 9.15 Generalized Creep Behavior 9.16 Stress and Temperature Effects 9.17 Data Extrapolation Methods 9.18 Alloys for High-Temperature Use 9.19 Creep in Ceramic and Polymeric Materials Chapter 10 - Phase Diagrams 10.1 Introduction 10.2 Solubility Limit 10.3 Phases 10.4 Microstructure 10.5 Phase Equilibria 10.6 One-Component (or Unary) Phase Diagrams 10.7 Binary Isomorphous Systems 10.8 Interpretation of Phase Diagrams 10.9 Development of Microstructure in Isomorphous Alloys 10.10 Mechanical Properties of Isomorphous Alloys 10.11 Binary Eutectic Systems Materials of Importance-Lead-Free Solders 10.12 Development of Microstructure in Eutectic Alloys 10.13 Equilibrium Diagrams Having Intermediate Phases or Compounds 10.14 Eutectoid and Peritectic Reactions 10.15 Congruent Phase Transformations 10.16 Ceramic Phase Diagrams 10.17 Ternary Phase Diagrams 10.18 The Gibbs Phase Rule 10.19 The Iron-Iron Carbide (Fe-Fe3C) Phase Diagram 10.20 Development of Microstructure in Iron-Carbon Alloys 10.21 The Influence of Other Alloying Elements Chapter 11 - Phase Transformations 11.1 Introduction 11.2 Basic Concepts 11.3 The Kinetics of Phase Transformations 11.4 Metastable versus Equilibrium States 11.5 Isothermal Transformation Diagrams 11.6 Continuous-Cooling Transformation Diagrams 11.7 Mechanical Behavior of Iron-Carbon Alloys 11.8 Tempered Martensite 11.9 Review of Phase Transformations and Mechanical Properties for Iron-Carbon Alloys Materials of Importance-Shape-Memory Alloys 11.10 Heat Treatments 11.11 Mechanism of Hardening 11.12 Miscellaneous Considerations 11.13 Crystallization 11.14 Melting 11.15 The Glass Transition 11.16 Melting and Glass Transition Temperatures 11.17 Factors That Influence Melting and Glass Transition Temperatures Chapter 12 - Electrical Properties 12.1 Introduction 12.2 Ohm's Law 12.3 Electrical Conductivity 12.4 Electronic and Ionic Conduction 12.5 Energy Band Structures in Solids 12.6 Conduction in Terms of Band and Atomic Bonding Models 12.7 Electron Mobility 12.8 Electrical Resistivity of Metals 12.9 Electrical Characteristics of Commercial Alloys Materials of Importance-Aluminum Electrical Wires 12.10 Intrinsic Semiconduction 12.11 Extrinsic Semiconduction 12.12 The Temperature Dependence of Carrier Concentration 12.13 Factors that Affect Carrier Mobility 12.14 The Hall Effect 12.15 Semiconductor Devices 12.16 Conduction in Ionic Materials 12.17 Electrical Properties of Polymer 12.18 Capacitance 12.19 Field Vectors and Polarization 12.20 Types of Polarization 12.21 Frequency Dependence of the Dielectric Constant 12.22 Dielectric Strength 12.23 Dielectric Materials 12.24 Ferroelectricity 12.25 Piezoelectricity Chapter 13 - Types and Applications of Materials 13.1 Introduction 13.2 Ferrous Alloys 13.3 Nonferrous Alloys Materials of Importance-Metal Alloys Used for Euro Coins 13.4 Glasses 13.5 Glass-Ceramics.

524 citations


Journal ArticleDOI
TL;DR: The high density and slow biodegradability of ceramics is not beneficial for tissue engineering purposes, so macroporosity can be introduced often in combination with osteoinductive growth factors and cells to address these issues.

521 citations


Journal ArticleDOI
TL;DR: In this article, the state-of-the-art processing methods, structures and mechanical properties of the metal matrix composites reinforced with ceramic nanoparticles are summarized and reviewed, showing that in-situ nanocomposites with very low loading levels of nanoparticles exhibit higher yield strength and creep resistance than their microcomposite counterparts filled with much higher particulate content.
Abstract: This paper summarizes and reviews the state-of-the-art processing methods, structures and mechanical properties of the metal matrix composites reinforced with ceramic nanoparticles. The metal matrices of nanocomposites involved include aluminum and magnesium. The processing approaches for nanocomposites can be classified into ex-situ and in-situ synthesis routes. The ex-situ ceramic nanoparticles are prone to cluster during composite processing and the properties of materials are lower than the theoretical values. Despite the fact of clustering, ex-situ nanocomposites reinforced with very low loading levels of nanoparticles exhibit higher yield strength and creep resistance than their microcomposite counterparts filled with much higher particulate content. Better dispersion of ceramic nanoparticles in metal matrix can be achieved by using appropriate processing techniques. Consequently, improvements in both the mechanical strength and ductility can be obtained readily in aluminum or magnesium by adding ceramic nanoparticles. Similar beneficial enhancements in mechanical properties are observed for the nanocomposites reinforced with in-situ nanoparticles.

510 citations


Journal ArticleDOI
Hideo Nakajima1
TL;DR: Heat sinks are a promising application of lotus metals due to the high cooling performance with a large heat transfer and the remarkable anisotropy in the mechanical strength is attributed to the stress concentration around the pores aligned perpendicular to the loading direction.

463 citations


Journal ArticleDOI
TL;DR: The use of the MDP-containing composite resin Panavia F on air abraded zirconia ceramic can be recommended as promising bonding method.

431 citations


Journal ArticleDOI
TL;DR: In this paper, the influence of nanostructured materials on important areas, such as, thermal barrier coatings (TBCs) and biomedical coatings was investigated, and it was determined that by controlling the distribution and character of the semi-molten nanozones embedded in the coating microstructure, it was possible to engineer coatings that exhibited high toughness for anti-wear applications or highly friable for use as abradable, exhibiting abradability levels equivalent to those of metallic-based abradables.
Abstract: Thermal spray coatings produced from nanostructured ceramic agglomerated powders were tailored for different applications, some of which required almost completely opposite performance characteristics (e.g., anti-wear and abradable coatings). The influence of nanostructured materials on important areas, such as, thermal barrier coatings (TBCs) and biomedical coatings was also investigated. It was determined that by controlling the distribution and character of the semi-molten nanostructured agglomerated particles (i.e., nanozones) embedded in the coating microstructure, it was possible to engineer coatings that exhibited high toughness for anti-wear applications or highly friable for use as abradables, exhibiting abradability levels equivalent to those of metallic-based abradables. It is shown that nanozones, in addition to being very important for the mechanical behavior, may also play a key role in enhancing and controlling the bioactivity levels of biomedical coatings via biomimetism. This research demonstrates that these nanostructured coatings can be engineered to exhibit different properties and microstructures by spraying nanostructured ceramic agglomerated powders via air plasma spray (APS) or high velocity oxy-fuel (HVOF). Finally, in order to present readers with a broader view of the current achievements and future prospects in this area of research, a general overview is presented based on the main papers published on this subject in the scientific literature.

405 citations


Journal ArticleDOI
TL;DR: In this paper, a review of the various ceramic nanofiber systems that have been fabricated so far is presented, and the physical and chemical properties enhancements due to the nanosize have been discussed in detail and the various applications they fi...
Abstract: Nanostructured ceramics are attractive materials that find potential uses ranging from simple everyday applications like paints and pigments to sophisticated ones such as bioimaging, sensors, etc. The inability to economically synthesize nanoscale ceramic structures in a large scale and simultaneously achieve precise control of their size has restricted their real time application. Electrospinning is an efficient process that can fabricate nanofibers on an industrial scale. During the last 5 years, there has been remarkable progress in applying this process to the fabrication of ceramic nanorods and nanofibers. Ceramic nanofibers are becoming useful and niche materials in several applications owing to their surface dependant and size dependant properties. These advances are reviewed here. The various ceramic nanofiber systems that have been fabricated so far are presented. The physical and chemical property enhancements due to the nanosize have been discussed in detail and the various applications they fi...

Journal ArticleDOI
TL;DR: In this paper, the authors proposed a method to increase the dielectric constant of polymer-based capacitors by using conductive fillers (e.g., metal particles).
Abstract: The mechanical flexibility and tunable properties of polymer-based materials make them attractive ones for a lot of applications. Exploring polymer-based dielectrics, such as ones used for capacitors and charge-storage applications, with high dielectric constant (high-j) has recently aroused considerable interest. Especially, motivated by higher function and further miniaturization of electronics, embedding (or integrating) polymer-based capacitors into the inner layers of organic printed circuit boards (PCBs) allows packaging substrate miniaturization and better electrical performance, which is a key for organic-based system-on-package technologies. But as capacitors, the relative dielectric constant j of general polymers (being good insulators) is too low (e.g., j< 5).Thus, a key issue is to substantially raise the dielectric constant of the polymers while retaining low dielectric loss. A few strategies have been developed to raise the j of polymer-based materials. A common approach is to add high-j ceramic fillers (e.g., BaTiO3) into a polymer. High loading of the ceramic fillers in the polymer composite, usually over 50 vol %, can increase j by about ten times relative to the polymer matrix, but dramatically decreases the adhesion of the composite (and increases its porosity) thus deteriorating the adaptability between the composite and the organic circuit boards. Another strategy is to fabricate percolative composite capacitors by using conductive fillers (e.g., metal particles). As the volume fraction f of the fillers increases to the vicinity of the percolation threshold fc, j of the composites can be dramatically enhanced as described by the well-known power law

Book
07 May 2007
TL;DR: In this article, the authors present an overview of the literature on porous fiber contactors and their application in the diffusion of gases in porous fiber membranes, including the following: 1.1 Introduction. 2.2.
Abstract: Chapter 1. Ceramic Membranes and Membrane Processes. 1.1 Introduction. 1.2 Membrane Processes. 1.2.1 Gas separation. 1.2.2 Pervaporation. 1.2.3 Reverse osmosis and nanofiltration. 1.2.4 Ultrafiltration and microfiltration. 1.2.5. Dialysis. 1.2.6 Electrodialysis. 1.2.7 Membrane contactor. 1.2.8 Membrane reactors. References. Chapter 2. Preparation of Ceramic Membranes. 2.1 Introduction. 2.2 Slip casting. 2.3 Tape casting. 2.4 Pressing. 2.5 Extrusion. 2.6 Sol-gel process. 2.7 Dip-coating. 2.8 Chemical vapour deposition (CVD). 2.9 Preparation of hollow fibre ceramic membranes. 2.9.1 Preparation of spinning suspension. 2.9.2 Spinning of ceramic hollow fibre precursors. 2.9.3 Sintering. 2.9.4 Example 1: Preparation of porous Al2O3 hollow fibre membranes. 2.9.5 Example 2: Preparation of TiO2/Al2O3 composite hollow fibre membranes. 2.9.6 Example 3: Preparation of dense perovskite hollow fibre membranes. Appendix 2.1: Surface forces. References. Chapter 3. Characterisation of Ceramic Membranes. 3.1 Introduction. 3.2 Morphology of membrane surfaces and cross sections. 3.3 Porous ceramic membranes. 3.3.1 Gas adsorption/desorption isotherms. 3.3.2 Permporometry. 3.3.3 Mercury porosimetry. 3.3.4 Thermoporometry. 3.3.5 Liquid displacement techniques. (a) Bubble point method. (b) Liquid displacement method. 3.3.6 Permeation method. (a) Liquid permeation. (b) Gas permeation. 3.3.7 Measurements of solute rejection. 3.4 Dense ceramic membranes. 3.4.1 Leakage test. 3.4.2 Permeation measurements. 3.4.3 XRD. 3.4.4 Mechanical strength. Notation. References. Chapter 4. Transport and Separation of Gases in Porous Ceramic Membranes. 4.1 Introduction. 4.2 Performance indicators of gas separation membranes. 4.3 Ceramic membranes for gas separation. 4.4 Transport Mechanisms. 4.4.1 Knudsen and slip flow. 4.4.2 Viscous flow. 4.4.3 Surface flow. 4.4.4 Capillary condensation. 4.4.5 Configurational or micropore diffusion. 4.4.6 Simultaneous occurrence of different mechanism. 4.5 Modification of porous ceramic membranes for gas separation. 4.6 Resistance model for gas transport in composite membranes. 4.6.1 Effect of support layers. 4.6.2 Effect of non-zeolitic pores. 4.6.3 Effect of coating. 4.7 System design. 4.7.1 Operating Schemes. (a) Perfect mixing. (b) Cross flow. (c ) Parallel plug flow. 4.7.2 Design equations for membrane processes in gas separation. (a) Perfect mixing. (b) Cross flow. (c) Cocurrent flow. (d) Countercurrent flow. Notation. References. Chapter 5. Ceramic Hollow Fibre Membrane Contactors for Treatment of Gases/Vapours. 5.1 Introduction. 5.2 General review. 5.3 Operating modes and mass transfer coefficients. 5.3.1 Nonwetted mode. 5.3.2 Wetted mode. 5.3.3 Mass transfer coefficients determined from experiments. 5.4 Mass transfer in hollow fibre contactors. 5.4.1 Mass transfer in hollow fibre lumen. 5.4.2 Mass transfer across membrane. 5.4.3 Mass transfer in shell side of a contactor. 5.4.4 Nonwetted, wetted, and partially wetted conditions in a hollow fibre contactor. 5.5 Effect of chemical reaction. 5.5.1 Instantaneous reaction. 5.5.2 Fast reaction. 5.6 Design equations. Notation. References. Appendix A. Chapter 6. Mixed Conducting Ceramic Membranes for Oxygen Separation. 6.1 Introduction. 6.2 Fundamentals of mixed conducting ceramic materials. 6.2.1 Structure of peroviskite-type of materials. 6.2.2 Doping strategies. 6.2.3 Properties of materials. 6.3 Current status in oxygen permeable membranes. 6.3.1 Pervoskite-type oxides. Sr(Co,Fe)O3-d (SCFO). La(Co,Fe)O3-d (LCFO). LaGaO3(LGO). 6.3.2 Non-perovskite-type oxides. 6.3.3 Summary of ceramic oxygen permeable materials. 6.4 Dual phase membranes. 6.5 Oxygen transport. 6.5.1 Transport mechanism. 6.5.2 Transport equations. 6.5.3 Transport analysis. 6.6 Air separation. 6.6.1 Design equations. Cocurrent flow. Countercurrent flow. 6.6.2 Performance analysis. Effect of operating pressures and temperatures. Effect of flow patterns. Effect of feed flow rate. Effect of membrane area. Comparison with experimental data. Production of oxygen using hollow fibre modules. 6.7 Further development-challenges and prospects. Notation. References. Chapter 7. Mixed Conducting Ceramic Membranes for Hydrogen Permeation. 7.1 Introduction. 7.2 Proton and electron (hole) conducting materials and membranes. 7.2.1 Pervoskite-type oxides. 7.2.2 Non-pervoskite-type oxides. 7.3 Dual phase membranes. 7.4 Proton transport. 7.4.1 Transport mechanism. 7.4.2 Transport equations for mixed proton-hole conducting membranes. 7.4.3 Transport analysis. Effect of membrane thickness. Effect of temperature. Effect of partial pressure of oxygen. Comparison with experimental data. 7.5 Applications of proton conducting ceramic membranes. 7.5.1 Hydrogen production. 7.5.2 Dehydrogenation reactions. Notation. References. Chapter 8. Ceramic Membrane Reactors. 8.1 Introduction. 8.2 Membranes as product separators. 8.2.1 Microporous membrane reactors. 8.2.2 Dense ceramic membrane reactors. 8.2.2.1 Experimental investigation of a dense ceramic membrane reactor for methane coupling reaction. 8.3 Membranes as a reactant distributor. 8.3.1 Porous membrane reactors. 8.3.1.1 Techniques in modification of membrane pores. 8.3.1.2 Applications of porous ceramic membrane reactors. 8.3.1.3 Analysis of membrane reactors for elimination of DO from water. 8.3.2 Dense ceramic membranes. 8.3.2.1 Configurations of the dense ceramic membrane reactors. 8.3.2.2 Applications of the dense ceramic membrane reactors. 8.3.2.3 Experimental investigation of a dense membrane reactor for oxidative methane coupling (OMC). Notation. References.

Journal ArticleDOI
TL;DR: The use of ceramic foams as structured catalyst supports has been extensively studied in the past decade as discussed by the authors, and many applications involving important reactions have appeared in the open and patent literature, especially for catalytic processes that suffer certain limitations.
Abstract: This paper reviews the use of ceramic foams as structured catalyst supports. They are open-cell ceramic structures that may be fabricated in a variety of shapes from a wide range of materials, and they exhibit very high porosities with good interconnectivity. These characteristics result in a lower pressure drop than that observed with packed beds and high convection in the tortuous megapores, which, in turn, enhances mass and heat transfer. They are easily coated with high-surface-area catalytic components, using well-established techniques. Research in the past decade has produced a large amount of fundamental information that elucidates the desirable properties of ceramic foams. In addition, many applications involving important reactions have appeared in the open and patent literature, especially for catalytic processes that suffer certain limitations, such as those encountered in relieving high pressure drop with low-contact-time reactions at high space velocities or with narrow reactors in heat-tran...

Journal ArticleDOI
TL;DR: In this article, a morphotropic phase boundary between orthorhombic and tetragonal ferroelectric phases was identified in the composition range of 0.02
Abstract: Highly dense (1−x)(Na0.5K0.5)NbO3–x(Bi0.5Na0.5)TiO3 (NKN-BST) solid solution piezoelectric ceramics have been fabricated by ordinary sintering. All compositions show pure perovskite structures, showing room-temperature symmetries of orthorhombic at x⩽0.02, of tetragonal at 0.03⩽x⩽0.09, of cubic at 0.09 0.20. A morphotropic phase boundary (MPB) between orthorhombic and tetragonal ferroelectric phases was identified in the composition range of 0.02

Journal ArticleDOI
TL;DR: In this paper, the exotic effects of metal particles embedded into matrix ceramics due to the dissimilar properties of the components, percolation laws, and the nature of the interfaces are discussed.

Journal ArticleDOI
TL;DR: In this article, the influence of silicon carbide (SiC) particle size on the microstructure and mechanical properties of Zirconium diboride-silicon carbide-SiC ceramics was investigated.
Abstract: The influence of silicon carbide (SiC) particle size on the microstructure and mechanical properties of zirconium diboride–silicon carbide (ZrB2–SiC) ceramics was investigated. ZrB2-based ceramics containing 30 vol.% SiC particles were prepared from four different α-SiC precursor powders with average particle sizes ranging from 0.45 to 10 μm. Examination of the dense ceramics showed that smaller starting SiC particle sizes led to improved densification, finer grain sizes, and higher strength. For example, ceramics prepared from SiC with the particle size of 10 μm had a strength of 389 MPa, but the strength increased to 909 MPa for ceramics prepared from SiC with a starting particle size of 0.45 μm. Analysis indicates that SiC particle size controls the strength of ZrB2–SiC.

Journal ArticleDOI
TL;DR: In this paper, the influence of the powder layer thickness on laser sintering/melting is studied for different laser beam velocity V (V = 1250-2000mm/s), defocalisation (−6 to 12mm), distance between two neighbour melted lines (so-called “vectors”) (20-40μm), vector length and temperature in the furnace.

Journal ArticleDOI
TL;DR: In this paper, a direct-foaming method was proposed to produce macroporous ceramics using particles instead of surfactants as stabilizers of the wet foams.
Abstract: We present a novel direct-foaming method to produce macroporous ceramics using particles instead of surfactants as stabilizers of the wet foams. This method allows for the fabrication of ultra-stable wet foams that resist coarsening upon drying and sintering. Macroporous ceramics of various chemical compositions with open or closed cells, average cell sizes ranging from 10 to 300 μm and porosities within 45% and 95%, can be easily prepared using this new approach. The sintered foams show high compressive strengths of up to 16 MPa in alumina foams with porosities of 88%.

Journal ArticleDOI
TL;DR: In this paper, it was shown that a low heating rate has an effect on the densification and transparency of alumina for sintering at 1150°C with a heating rate of 8°C/min.

Journal ArticleDOI
TL;DR: The polycrystalline sample of NaBa2V5O15 (NBV), a member of tungsten bronze family, is prepared by a mixed oxide-technique and X-ray diffraction analysis shows the formation of single phase compound with an orthorhombic structure at room temperature.

Journal ArticleDOI
TL;DR: This Letter demonstrated unusually large strain plasticity of ceramic SiC nanowires (NWs) at temperatures close to room temperature that was directly observed in situ by a novel high-resolution transmission electron microscopy technique.
Abstract: Large strain plasticity is phenomenologically defined as the ability of a material to exhibit an exceptionally large deformation rate during mechanical deformation. It is a property that is well established for metals and alloys but is rarely observed for ceramic materials especially at low temperature ( approximately 300 K). With the reduction in dimensionality, however, unusual mechanical properties are shown by ceramic nanomaterials. In this Letter, we demonstrated unusually large strain plasticity of ceramic SiC nanowires (NWs) at temperatures close to room temperature that was directly observed in situ by a novel high-resolution transmission electron microscopy technique. The continuous plasticity of the SiC NWs is accompanied by a process of increased dislocation density at an early stage, followed by an obvious lattice distortion, and finally reaches an entire structure amorphization at the most strained region of the NW. These unusual phenomena for the SiC NWs are fundamentally important for understanding the nanoscale fracture and strain-induced band structure variation for high-temperature semiconductors. Our result may also provide useful information for further studying of nanoscale elastic-plastic and brittle-ductile transitions of ceramic materials with superplasticity.

Journal ArticleDOI
TL;DR: In this article, the interaction of water and the alumina surface is comprehensively reviewed and the role of surface charge on the adsorption of processing additives is briefly discussed, and the influence of these forces on suspension properties such as rheological behavior is outlined.
Abstract: The interaction of water and the alumina surface is comprehensively reviewed. Water can be incorporated in the alumina crystal structure resulting in the formation of aluminum hydroxides such as gibbsite. Alumina dissolves into water to an extent that depends primarily upon the solution pH and temperature. The soluble Al (III)aq species (hydrolysis products) likewise depend upon the solution pH, temperature, aluminum, and other salt concentrations. The development of charge on the surface of alumina is controlled by amphoteric surface ionization reactions. The charging behavior of both alumina powders and single crystal faces is compared. The differences can be explained by the reactivities of different types of surface hydroxyl groups. The substantial difference in surface charging behavior of single crystal sapphire and alumina powders indicates that experiments and modeling conducted on single crystals is of limited use in predicting suspension behavior. The atomic scale structure of the hydroxylated sapphire (0001) basal plane is nearly identical to the gibbsite (001) basal plane. The observed surface structures are consistent with the charging behavior of the surfaces. The role of surface charge on the adsorption of processing additives is briefly discussed. How surface charge and processing additives at the alumina aqueous solution interface influence surface forces between particles is reviewed. The influence of these forces on suspension properties such as rheological behavior is outlined. The importance of controlling these behaviors to improve colloidal ceramic powder processing is stressed.

Journal ArticleDOI
TL;DR: Cercon Zirconia core material showed high values of biaxial flexural strength and indentation fracture toughness when compared to the other ceramics studied, which showed significant differences in strength and toughness values.
Abstract: Statement of problem Many different strengthened all-ceramic core materials are available. In vitro study of their mechanical properties, such as flexural strength and fracture toughness, is necessary before they are used clinically. Purpose The purpose of this study was to evaluate and compare the mechanical properties of 6 commonly used all-ceramic core materials using biaxial flexural strength and indentation fracture toughness tests. Material and methods Specimens of 6 ceramic core materials (Finesse, Cergo, IPS Empress, In-Ceram Alumina, In-Ceram Zirconia, and Cercon Zirconia) were fabricated (n=25) with a diameter of 15 mm and width of 1.2 ± 0.2 mm. For each group, the specimens were tested to compare their biaxial flexural strength (piston on 3 balls) (n=15), Weibull modulus, and indentation fracture toughness (n=10) (IF method). The data were analyzed with 1-way ANOVA test (a=.05). The Tamhane multiple comparison test was used for post hoc analysis. Results Mean (SD) of biaxial flexural strength values (MPa) and Weibull modulus ( m ) results were: Finesse (F): 88.04 (31.61), m =3.17; Cergo (C): 94.97 (13.62), m =7.94; IPS Empress (E): 101.18 (13.49), m =10.13; In-Ceram Alumina (ICA): 341.80 (61.13), m =6.96; In-Ceram Zirconia (ICZ): 541.80 (61.10), m =10.17; and Cercon Zirconia (CZ): 1140.89 (121.33), m =13.26. The indentation fracture toughness results showed that there were significant differences between the tested ceramics. The highest fracture toughness values (MPa × m 0.5 ) were obtained with the zirconia-based ceramic core materials. Conclusions Significant differences were found in strength and toughness values of the materials evaluated. Cercon Zirconia core material showed high values of biaxial flexural strength and indentation fracture toughness when compared to the other ceramics studied.

Journal ArticleDOI
TL;DR: In this paper, the structure transformation and magnetic properties of Bi1−xLaxFeO3 (x=0.0 − 0.15) ceramics prepared by a conventional solid-state reaction processing were analyzed.
Abstract: The authors present the structure transformation and magnetic properties of Bi1−xLaxFeO3 (x=0.0–0.15) ceramics prepared by a conventional solid-state reaction processing. Magnetic measurements reveal that remnant magnetization of 15% La-doped BiFeO3 has enhanced about 20 times as compared to pure BiFeO3. It is the structural phase transition (R3c–C222) near x=0.15 that destructs the spin cycloid, and thus enhances the ferromagnetic properties significantly. In these Bi1−xLaxFeO3 ceramic samples, besides the known antiferromagnetic Neel temperature TN1∼615K, another Neel temperature TN2∼260K can be observed due to the trace impurity phase of Bi2Fe4O9 in these ceramic samples.


Journal ArticleDOI
TL;DR: In this article, LiSbO3 (LS) modified KNN based ceramics were sintered at atmospheric pressure and high density (>96% theoretical) was obtained, and detailed elastic, dielectric, piezoelectric and electromechanical properties were characterized by using the resonance technique combined with the ultrasonic method.

Journal ArticleDOI
TL;DR: Barium strontium titanate glass-ceramics were successfully produced with one major crystalline phase when Al2O3 was added to the melt as mentioned in this paper, achieving a dielectric constant of 1000 and a breakdown strength of 800 kV/cm.
Abstract: Barium strontium titanate glass-ceramics were successfully produced with one major crystalline phase when Al2O3 was added to the melt. A dielectric constant of 1000 and a breakdown strength of 800 kV/cm was achieved; however the energy density was only measured to be 0.3–0.9 J/cm3. These energy density values were lower than anticipated due to the presence of dendrites and pores in the microstructure. Using BaF2 as a refining agent improved the microstructure and doubled the energy density for BST 80/20 samples. However, no refining agent reduced the increasing amount of hysteresis that developed with increasing applied electric field. This phenomenon is believed to be due to interfacial polarization.

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TL;DR: LiNbO3-doped lead-free piezoelectric ceramics were prepared by normal sintering, and the electrical properties were investigated with a special emphasis on the influence of sinting temperature as discussed by the authors.
Abstract: LiNbO3-doped (Na,K)NbO3 lead-free piezoelectric ceramics were prepared by normal sintering, and the electrical properties were investigated with a special emphasis on the influence of sintering temperature. The ceramics synthesized at 1020–1080°C showed a phase transition from orthorhombic to tetragonal symmetry, which is similar to the morphtropic phase boundary (MPB). Because of such MPB-like behavior, a high piezoelectric coefficient d33 (314pC∕N) was obtained in the nominal composition 0.058LiNbO3–0.942[(Na0.535K0.480)NbO3] ceramic sintered at 1060°C; however, this high d33 value was reported previously only in the Li-modified (Na,K)NbO3-based ceramics with codopants of Ta and Sb to B site.

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TL;DR: In this paper, the effects of target composition on the film's surface topology, crystallinity, and optical transmission have been investigated for various oxygen partial pressures in the sputtering atmosphere, while their preferential crystalline growth orientation revealed by X-ray diffraction remains always the (002).