Showing papers on "Ceramic published in 2012"

Engineering of Micro‐ and Nanostructured Surfaces with Anisotropic Geometries and Properties

Abstract: Widespread approaches to fabricate surfaces with robust micro- and nanostructured topographies have been stimulated by opportunities to enhance interface performance by combining physical and chemical effects. In particular, arrays of asymmetric surface features, such as arrays of grooves, inclined pillars, and helical protrusions, have been shown to impart unique anisotropy in properties including wetting, adhesion, thermal and/or electrical conductivity, optical activity, and capability to direct cell growth. These properties are of wide interest for applications including energy conversion, microelectronics, chemical and biological sensing, and bioengineering. However, fabrication of asymmetric surface features often pushes the limits of traditional etching and deposition techniques, making it challenging to produce the desired surfaces in a scalable and cost-effective manner. We review and classify approaches to fabricate arrays of asymmetric 2D and 3D surface features, in polymers, metals, and ceramics. Analytical and empirical relationships among geometries, materials, and surface properties are discussed, especially in the context of the applications mentioned above. Further, opportunities for new fabrication methods that combine lithography with principles of self-assembly are identified, aiming to establish design principles for fabrication of arbitrary 3D surface textures over large areas.

Effect of filler size and concentration on the structure and properties of poly(vinylidene fluoride)/BaTiO3 nanocomposites

Abstract: The effect of filler size and content in the thermal, mechanical, and electrical response of poly(vinylidene fluoride) (PVDF)/BaTiO3 nanocomposites has been investigated Dielectric constant increases significantly with increasing filler content and decreasing filler size Space charge effects at the interface between BaTiO3 and PVDF strongly influence the dielectric response The electroactive β-phase of PVDF is nucleated by the presence of the ceramic filler, the effect being strongly dependent on filler size and independent on filler content This filler/matrix interaction is also responsible for the variations observed in the activation energy of the thermal degradation of the polymer Smaller particles lead to larger relative contact areas and are responsible for the main variations observed in the thermal, mechanical, and electrical properties of the composites

Large piezoelectricity and dielectric permittivity in BaTiO3-xBaSnO3 system: The role of phase coexisting

Abstract: We report ultrahigh dielectric and piezoelectric properties in BaTiO3-xBaSnO3 ceramics at its quasi-quadruple point, a point where four phases (Cubic-Tetragonal-Orthorhombic- Rhombohedral) nearly coexist together in the temperature-composition phase diagram. At this point, dielectric permittivity reaches ∼ 75000, a 6-7-fold increase compared with that of pure BaTiO3 at its Curie point; the piezoelectric coefficient d33 reaches 697 pC/N, 5 times higher than that of pure BaTiO3. Also, a quasi-quadruple point system exhibits double morphotropic phase boundaries, which can be used to reduce the temperature and composition sensitivity of its high piezoelectric properties. A Landau-Devonshire model shows that four-phase coexisting leading to minimizing energy barriers for both polarization rotation and extension might be the origin of giant dielectric and piezoelectric properties around this point. Copyright c � EPLA, 2012

Towards physical properties tailoring of carbon nanotubes-reinforced ceramic matrix composites

Abstract: Carbon nanotubes (CNTs) have been considered as a new promising reinforcement for ceramic matrix composites (CMCs) over the last decade, owing to their exceptional properties. CNT-reinforced CMCs posses a unique microstructure, nanoscale objects dispersed throughout ceramic matrix grain boundaries, which allows tailoring physical properties with an unprecedented combination of remarkable engineered transport properties as well as superior mechanical properties. However, gaining further control over challenging CNTs dispersion is still an important issue with the aim of tailoring multifunctional properties of CNT-reinforced CMCs. This paper reviews the current status of the research and describes all different approaches used to effectively disperse CNTs throughout ceramic matrices, providing an overview of composites microstructure and mechanical, electrical and thermal properties. Besides, all findings reported till date point out a promising approach towards physical properties tailoring of CNT-reinforced ceramic CMCs.

Glass–ceramic glazes for ceramic tiles: a review

Abstract: Glass–ceramics are ceramic materials produced through controlled crystallisation (nucleation and crystal growth) of a parent glass. The great variety of compositions and the possibility of developing special microstructures with specific technological properties have allowed glass–ceramic materials to be used in a wide range of applications. One field for which glass–ceramics have been developed over the past two decades is that of glazes for ceramic tiles. Ceramic tiles are the most common building material for floor and wall coverings in Mediterranean countries. Glazed tiles are produced from frits (glasses quenched in water) applied on the surface of green tiles and subjected to a firing process. In the 1990s, there was growing interest in the development of frits that are able to crystallise on firing because of the need for improvement in the mechanical and chemical properties of glazed tiles. This review offers an extensive evaluation of the research carried out on glass–ceramic glazes used for covering and pavement ceramic tile is accomplished. The main crystalline phases (silicates and oxides) developed in glass–ceramic glazes have been considered. In addition, a section focused on glazes with specific functionality (photocatalytic, antibacterial and antifungal activity, or aesthetic superficial effects) is also included.

Rapid Microwave Preparation of Highly Efficient Ce3+-Substituted Garnet Phosphors for Solid State White Lighting

Abstract: Ce3+-substituted aluminum garnet compounds of yttrium (Y3Al5O12) and lutetium (Lu3Al5O12)—both important compounds in the generation of (In,Ga)N-based solid state white lighting—have been prepared using a simple microwave heating technique involving the use of a microwave susceptor to provide the initial heat source. Carbon used as the susceptor additionally creates a reducing atmosphere around the sample that helps stabilize the desired luminescent compound. High quality, phase-pure materials are prepared within a fraction of the time and using a fraction of the energy required in a conventional ceramic preparation; the microwave technique allows for a reduction of about 95% in preparation time, making it possible to obtain phase pure, Ce3+-substituted garnet compounds in under 20 min of reaction time. It is estimated that the overall reduction in energy compared with ceramic routes as practised in the lab is close to 99%. Conventionally prepared material is compared with material prepared using microwav...

Glass additive in barium titanate ceramics and its influence on electrical breakdown strength in relation with energy storage properties

Abstract: Glass additive was employed to improve the microstructures and energy storage properties of barium titanate ceramics using liquid phase sintering technology. Microstructural observation indicated that the average grain size reduced obviously with increasing glass concentration. Also, the dielectric constant decreased and the dielectric breakdown strength increased as glass concentration increased. The increase in the breakdown strength with decreasing grain size was consistent with the well-known relationship for the mechanical failure. The activation energies of bulk grain and grain boundary as well as their differences were calculated using measured impedance values. Good inverse dependence of the dielectric breakdown strength on the difference between activation energies of bulk grain and grain boundary was obtained for the glass-added BaTiO3 ceramics. It was also found that the energy storage density of the ceramics increased gradually with increasing glass concentration. Possible effect of the interfacial polarization in degrading the energy storage property was discussed.

Ten-year outcome of three-unit fixed dental prostheses made from monolithic lithium disilicate ceramic

Abstract: Background The authors conducted a prospective study to evaluate the long-term outcome of crown-retained fixed dental prostheses (FDPs) made from monolithic lithium disilicate ceramic (IPS e.max Press, Ivoclar Vivadent, Schaan, Liechtenstein). Methods Faculty dentists at the Department of Prosthodontics, Propaedeutics and Dental Materials, School of Dentistry, Christian-Albrechts University at Kiel, Germany, placed 36 three-unit FDPs in 28 patients to replace six anterior and 30 posterior teeth. The proximal connector size (height and width) was 4 × 3 millimeters for anterior FDPs and 4 × 4 mm for posterior FDPs. FDPs were cemented either conventionally with glass ionomer cement (n = 19) or adhesively with resin-based composite (n = 17). Patients made annual recall visits. Results The mean (standard deviation) observation period was 121 (12.8) months. FDPs' survival rate (survival being defined as remaining in place either with or without complications) was 100 percent after five years and 87.9 percent after 10 years, and their success rate (success being defined as remaining unchanged and free of complications) was 91.1 percent after five years and 69.8 percent after 10 years. The cementation method did not affect the outcome. Conclusion Three-unit FDPs made from monolithic lithium disilicate ceramic showed five- and 10-year survival and success rates that were similar to those of conventional metal-ceramic FDPs. Clinical Implications If the manufacturer's recommendations are followed, three-unit FDPs made from monolithic lithium disilicate ceramic may be a safe alternative to metal-ceramic FDPs regardless of the cementation method used.

Multilayer ceramic electronic component

Abstract: A multilayer ceramic electronic component includes: a ceramic body including dielectric layers; an oxide film formed on one surface of the ceramic body; first and second external electrodes formed on both sides of the oxide film on one surface of the ceramic body; a first internal electrode formed on the dielectric layer and including a first electrode lead-out portion exposed to the first external electrode and a first insulating lead-out portion exposed to the oxide film and having a composite-metal-oxide region formed in an exposed edge portion thereof; a second internal electrode facing the first internal electrode, having the dielectric layer interposed therebetween, and including a second electrode lead-out portion exposed to the second external electrode and a second insulating lead-out portion exposed to the oxide film, having a composite-metal-oxide region formed in an exposed edge portion thereof, and overlapped with the first insulating lead-out portion to form additional capacitance.

Lithography-Based Additive Manufacturing of Cellular Ceramic Structures†

Abstract: Lithography-based additive manufacturing technology is a layered manufacturing approach where liquid photopolymerizable resins are solidified with ultraviolet, visible, or infrared light. Using a system based on digital mirror devices, photopolymers can be exposed selectively in order to build parts with defined geometries. By modifying the system with a rotating building platform, suspensions with a high solid loading of ceramic powders can be processed, despite the high viscosity of these resins. Depending on the field of application, various formulations were developed for fabricating customized ceramic parts made of alumina, tricalcium phosphate, or bioactive glasses, respectively. On the one hand the influence of the ceramic filler on the mechanical properties is characterized, on the other hand the good precision and the high surface quality of the process system is discussed. For alumina filled resins a solid loading of 50 vol% was used to obtain fully dense parts (>99% of theoretical density) with high fracture strength (biaxial strength of 516 MPa).

Nanocrystallisation in oxyfluoride systems: mechanisms of crystallisation and photonic properties

Abstract: Rare earth (RE) doped oxyfluoride glass ceramics possess interesting optical properties with applications in telecommunications and optoelectronics, such as solid state lasers, optical amplifiers, etc. These materials combine the transparency and mechanical and chemical resistance of aluminosilicate glasses with the low phonon energy and facile incorporation of RE ions in the fluoride crystals. The incorporation of RE ions in the crystalline phases enhances the laser emission intensity, a major property of these materials. Transparency is achieved when crystal size is in the nanometric scale, usually below 40 nm, which avoids light scattering. A strict control of the nucleation and crystal growth processes is therefore necessary which requires a deep knowledge of the crystallisation mechanisms. The great activity and publications in this field in the last decades merit a review providing a comparative study of the different nanoglass ceramic systems, their structural and optical characterisation and their main properties and applications. This is the objective of this review paper which includes 227 references. A general discussion on glass nucleation and crystallisation theories and more relevant crystallisation parameters and characterisation techniques are put forward in the first section of the review, focused on nanocrystallisation processes in oxyfluoride systems. In the second section, the principal RE doped glass ceramics are presented. After a general introduction about the luminescence processes, including up- and down-conversion, the behaviour of RE elements in glasses and crystals are discussed. Glass ceramic compositions have been divided as follows: glass ceramics with a glass composition following Wang and Ohwaki’s oxyfluoride glass ceramic, and glass ceramics with different matrix compositions, arranged by crystalline phases. Relevant properties, mainly optical and laser, are described in each system along with the most relevant applications of these materials.

Transparent Ce:Y3Al5O12 ceramic phosphors for white light-emitting diodes

Abstract: We present our recent achievement of a transparent ceramic able to produce white light when directly combined with commercially available blue light emitting diodes. The photoluminescence properties of ceramic phosphor (Y1-xCex)(3)Al5O12 are studied as a function of doping fraction (x = 0.0005-0.0020). The emission color is tunable by variations of Ce3+ concentration and ceramic phosphor thickness. A maximum luminous efficacy exceeding 93 lm/W at a low correlated color temperature of similar to 4600 K is obtained, which is superior to samples made from commercial phosphor powders. Hence, the present transparent ceramic phosphor is expected to be an ideal candidate for generating white light. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4742896]

Ceramic Laser Materials

Abstract: Ceramic laser materials have come a long way since the first demonstration of lasing in 1964. Improvements in powder synthesis and ceramic sintering as well as novel ideas have led to notable achievements. These include the first Nd:yttrium aluminum garnet (YAG) ceramic laser in 1995, breaking the 1 KW mark in 2002 and then the remarkable demonstration of more than 100 KW output power from a YAG ceramic laser system in 2009. Additional developments have included highly doped microchip lasers, ultrashort pulse lasers, novel materials such as sesquioxides, fluoride ceramic lasers, selenide ceramic lasers in the 2 to 3 μm region, composite ceramic lasers for better thermal management, and single crystal lasers derived from polycrystalline ceramics. This paper highlights some of these notable achievements.

Anisotropic Oxygen Ion Diffusion in Layered PrBaCo2O5+δ

Abstract: Oxygen diffusion and surface exchange coefficients have been measured on polycrystalline samples of the double perovskite oxide PrBaCo2O5+δ by the isotope exchange depth profile method, using a time-of-flight SIMS instrument. The measured diffusion coefficients show an activation energy of 1.02 eV, as compared to 0.89 eV for the surface exchange coefficients in the temperature range from 300 to 670 °C. Inhomogeneity was observed in the distribution of the oxygen-18 isotopic fraction from grain to grain in the ceramic samples, which was attributed to anisotropy in the diffusion and exchange of oxygen. By the use of a novel combination of electron back scattered diffraction measurements, time-of-flight, and focused ion beam SIMS, this anisotropy was confirmed by in-depth analysis of single grains of known orientation in a ceramic sample exchanged at 300 °C. Diffusion was shown to be faster in a grain oriented with the surface normal close to 100 and 010 (ab-plane oriented) than a grain with a surface normal...

Defect Structure of Flash‐Sintered Strontium Titanate

Abstract: Flash sintering of strontium titanate (SrTiO3) is studied at different applied fields to understand its effect on density and grain growth. In particular, the defect structure is investigated by optical and structural analysis. SrTiO3 exhibited a trend in densification opposite that of ionically or electronically conductive ceramics: as the applied voltage decreased, the density increased. Abnormal grain growth in conventionally sintered SrTiO3 is arrested by flash sintering. Interestingly, undoped SrTiO3 behaved differently than undoped Al2O3, which did not exhibit any signs of flash sintering. Previous attempts at flash sintering could only be achieved in MgO-doped Al2O3. We believe that non-stoichiometric Ruddlesden-Popper phases in SrTiO3, as indicated by ultrafast optical spectroscopy, X-ray diffraction, conductivity measurements, and transmission electron microscopy, assist flash sintering by increasing local conductivity through enhanced defect content.

Polymer derived non-oxide ceramics modified with late transition metals

Abstract: This tutorial review highlights the methods for the preparation of metal modified precursor derived ceramics (PDCs) and concentrates on the rare non-oxide systems enhanced with late transition metals In addition to the main synthetic strategies for modified SiC and SiCN ceramics, an overview of the morphologies, structures and compositions of both, ceramic materials and metal (nano) particles, is presented Potential magnetic and catalytic applications have been discussed for the so manufactured metal containing non-oxide ceramics

Multilayer ceramic electronic component and method of manufacturing the same

Abstract: There is provided a multilayer ceramic electronic component includes a ceramic body including a dielectric layer; and an internal electrode formed in the ceramic body, wherein on a cross-section of the ceramic body in a width-thickness direction, a thickness Te of the internal electrode satisfies 0.1 μm≦Te≦1.0 μm, and when the internal electrode is divided into three regions including a central region and both edge regions in a width direction of the ceramic body and a ratio of an actual total length of the internal electrode corresponding to the sum of lengths of electrode portions to an ideal total length of the internal electrode is defined as connectivity S of the internal electrode, connectivity of the internal electrode in the edge regions satisfies 75%≦S≦98%, and a ratio of connectivity of the internal electrode in the edge regions to connectivity of the internal electrode in the central region is 0.9 to 0.98.

Novel Three-Dimensional Zinc Oxide Superstructures for High Dielectric Constant Polymer Composites Capable of Withstanding High Electric Field

Abstract: High dielectric constant polymer composites capable of withstanding a high electrical field have much application in electronic devices and electrical equipment because of their ease of processing, flexibility, and low cost. Conventional polymer composites with a high dielectric constant, namely ceramic particulate composites and conductive filler based percolative composites, either show low dielectric enhancement or cannot withstand high electric field. Here we report a new strategy for preparing high dielectric constant polymer composites by using novel three-dimensional zinc oxide (3D ZnO) superstructures as fillers. Two kinds of 3D ZnO (flower-like and walnut-like) superstructures were prepared via a template-free solvothermal method. Their poly(vinylidene fluoride) (PVDF) composites as well as commercial ZnO filled PVDF composite were investigated by a broadband dielectric spectroscopy at a wide temperature range (−50 to +150 °C). Our results showed that, compared with the commercial ZnO, the newly ...

Carbide-derived carbon monoliths with hierarchical pore architectures.

Abstract: Porous carbon materials are crucial components in catalysis, gas storage, electronics, and biochemistry. A hierarchical pore architecture in these materials is essential to achieve high surface areas combined with advanced mass transport kinetics. Widely used approaches for the generation of microor mesopores are activation and nanocasting. In contrast, macroporous carbon materials are primarily obtained by carbonization of polymeric precursor gels or replication of larger templates. A relatively new class of microand mesoporous carbon material with tunable porosity are carbide-derived carbon materials (CDCs). High-temperature chlorination of carbides leads to selective removal of metalor semi-metal atoms and allows control over the pore size of the resulting CDCs in a subngstrcm range by changing synthesis conditions or the carbide precursor. These materials have been studied for applications in gas storage and as electrode materials in supercapacitors because of their high specific surface areas. Recently, metal etching from pyrolyzed pre-ceramic components (polysilsesquioxanes or polysilazanes) was found to be a useful route towards carbide-derived carbon materials with enhanced porosity and gas-storage properties. A significant step towards ultrahigh specific surface area combined with a hierarchical mesoporous–microporous system was achieved using nanocasting of silica templates (SBA-15 or KIT-6) with polycarbosilane precursors and subsequent chlorine treatment of the resulting ordered mesoporous silicon carbides. These ordered mesoporous CDCs offer specific surface areas as high as 2800 mg 1 and total pore volumes of up to 2 cmg . Their mesostructure can be easily controlled by changing the silica hard template, resulting in excellent performance in protein adsorption, gas storage, and as electrodes for supercapacitors. However, such carbon materials are available only as nonstructured micrometer-sized powders and cannot be shaped into films without the addition of binders or the use of high mechanical stress, leading to structural deformation. Chlorine treatment of mechanically mixed Si/SiC precursors was found to be a useful route towards monolithic CDC with a hierarchical pore system. The presence of a free metal phase in the precursor system provides the opportunity to introduce a secondary macroporosity of 3 mm sized channels with a volume of 0.23 cmg 1 along with the microporous carbide-derived carbon material system. The introduction of large transport pores in polymerbased CDCs might be an alternative way to form materials that combine high surface areas with efficient fluid transport. The current literature describes a variety of routes for the production of highly macroporous ceramics from precursor polymers with controllable cell and window sizes. In particular, direct blowing of polycarbosilanes was found to be a useful approach for the generation of silicon carbide foams that might be suitable materials for the production of hierarchical CDCs. In the following, we describe a novel synthesis route for monolithic carbide-derived carbon materials, including micro-, meso-, and macroporous structures with extremely high specific surface area. They can be obtained by hightemperature chlorination of macroporous polymer-derived silicon carbide (SiC-PolyHIPE). A soft-templating approach starting from a high internal phase emulsion (HIPE) was used with an external oil phase consisting of liquid polycarbosilane SMP-10 and the cross-linker paradivinylbenzene. Using Span-80 as surfactant to stabilize the internal water phase, the application of oxidic or carbon hard templates and the corresponding template removal under harsh conditions is no longer necessary. After cross-linking the polymer chains, the resulting PolyHIPEs were pyrolyzed to silicon carbides at maximum temperatures of 700, 800, and 1000 8C and subsequently converted into CDCs by chlorine treatment at the maximum pyrolysis temperature (Supporting [*] M. Oschatz, L. Borchardt, Dr. I. Senkovska, N. Klein, Dr. R. Frind, Prof. Dr. S. Kaskel Department of Inorganic Chemistry Dresden University of Technology Bergstrasse 66, 01062 Dresden (Germany) E-mail: stefan.kaskel@chemie.tu-dresden.de

Silicon nitride: the engineering material of the future

Abstract: The purpose of this review is to present the recent developments in silicon nitride (Si3N4) ceramics and to examine the achievements regarding our understanding of the relationship between processing conditions, chemical composition, microstructure and mechanical properties of Si3N4. Si3N4 is one of the most important structural ceramics because it possesses a combination of advanced properties such as good wear and corrosive resistance, high flexural strength, good fracture resistance, good creep resistance and relatively high hardness. These properties are obtained through the processing method involving liquid phase sintering in which a tailored microstructure, with high aspect ratio grains and chemistry of intergranular phase, triggers the toughening and strengthening mechanisms leading to the development of high fracture toughness and fracture strength. However, despite high fracture toughness and strength, Si3N4 ceramic materials still break catastrophically, and the fracture behaviour of this ceramic is considered to be the major obstacle for its wider use as a structural material. In addition to the macrostructure–mechanical properties relationship, this paper also reviews new designs involving laminates possessing no plane of weakness and some theoretical developments involving crack opening displacement. Proposals of how to improve the fracture resistance were also discussed.

Current Application of β-tricalcium Phosphate Composites in Orthopaedics

Abstract: Presently, bioceramic materials have been extensively used in spinal surgery as bone grafts; however, there are some limitations for bioceramic materials. Calcium sulfate is rapidly absorbed in vivo, the degradation of which often occurs prior to the formation of new bones. Hydroxyapatite (HA) is hardly absorbed, which blocks the formation of new bones and remodeling, and results in poor local stability or permanent stress concentration. Only β-tricalcium phosphate (β-TCP) is relatively balanced between scaffold absorption and bone formation. And it is a good biodegradable ceramic material that could supply a large quantity of calcium ion and sulfate ion as well as scaffold structure for bone regeneration. However, the problem of single β-TCP is lack of osteoinductivity and osteogenicity, which restricts its application. Therefore β-TCP composite materials have been used in the field of orthopaedics in recent decades, which fully use excellent properties of other bone repairing materials, such as biodegradability, osteoinductivity, osteogenicity and osteoconductivity. These materials make up for the deficiencies of single β-TCP and endow β-TCP with more biological and physical properties.