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Shell Microstructures (shell + microstructure)
Selected AbstractsPO2 Dependence of the Diffuse-Phase Transition in Base Metal Capacitor DielectricsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2006Daniel E. McCauley The diffuse-phase transition in BaTiO3 -based dielectrics for capacitor applications has been studied with respect to its dependence on oxygen partial pressure during sintering. Understanding the mobility of this transition is critical in developing next generation dielectrics for ultra thin (,1 ,m) applications while maintaining the appropriate temperature stability and insulation resistance. Historically, a heterogeneous core/shell microstructure was developed to maintain temperature stability. However, in fired grains of ,250 nm (required for layers ,1 ,m) a well-defined core/shell structure is very difficult to establish. The results from this study demonstrate that careful control of the diffuse-phase transition addresses some of these problems. [source] Microstructure in Silicon Nitride Containing ,-Phase Seeding: III, Grain Growth and CoalescenceJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2001Horng-Hwa Lu The mechanical properties of Si3N4 materials depend mainly on the microstructure, which originates during the densification process. The microscopic evidence indicates that ,-Si3N4 seeds incorporated in the starting powders play an important role in microstructural development, especially in the heterogeneous grain growth of ,-Si3N4 grains during sintering. The growth of ,-grains is initiated from the ,-seeds, resulting in a core/shell microstructure. The presence of Moiré fringes and dislocations is attributed to misfit strain and compositional differences between the core and the shell. Coalescence can occur at the final stage of sintering. [source] Sintering Characteristics in the BaTiO3,Nb2O5,Co3O4 Ternary System: II, Stability of So-called "Core,Shell" StructureJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2000Hirokazu Chazono The sintering characteristics and the reaction of additives with BaTiO3 (BT) were examined for two materials having Nb-rich composition (Comp.N) and Co-rich composition (Comp.C) to elucidate the relation between the stability of the core,shell microstructure and the Nb/Co ratio in the BT,Nb2O5,Co3O4 system. TEM observation revealed that the concentration gradient of Nb and Co existed in the shell region although Nb and Co macroscopically distributed homogeneously. X-ray diffraction analysis showed that the shell formation preceded the densification and completed at about 1280°C for both Comp.N and Comp.C as determined from differential scanning calorimetry. A diffusion couple experiment disclosed that Co had a larger diffusivity than Nb and that the diffusion of Co was suppressed when the sample was codoped with a sufficient amount of Nb. On the basis of these experimental results, new mechanisms of the formation and collapse of core,shell structure in the BT,Nb2O5,Co3O4 system were proposed. [source] Shell structure, ontogeny and affinities of the Lower Cambrian bivalved problematic fossil Mickwitzia muralensis Walcott, 1913LETHAIA, Issue 4 2004UWE BALTHASAR Exceptionally preserved carbonate- and shale-hosted Mickwitzia muralensis from the Lower Cambrian Mural Formation, southern Canadian Rocky Mountains, complement one another to yield an unusually complete account of its ontogeny, ecology and phylogenetic relationships. The shell of M. muralensis is composed of dense phosphatic layers interspersed with porous organic-rich layers. At the insertion of shell-penetrating tubes, shell layers deflect inwards to produce inwardly pointing cones. The tubes are interpreted as having hosted setae that were secreted by outer-epithelial follicles. Follicular setae also occurred at the mantle margin, where they were oriented within the plane of the shell as in modern brachiopods. During ontogeny, the initial setae oriented in the plane of the shell occurred before the first shell-penetrative setae. In the juvenile and early-mature stages of shell secretion, a posterior opening was present between both valves and was used for the protrusion of an attachment structure. In the late-mature shell, this opening became fixed in the ventral valve. Based on the posterior margin and the shell microstructure, a close relationship between Mickwitzia and the paterinids is proposed with differences interpreted as heterochronic. The shell-penetrative setal apparatus of M. muralensis is distinct from that previously described of Micrina, though both types are conceivably homologous to adult and juvenile setae of modern brachiopods. [source] Self-Assembly of Ordered Patterns: Stressed Triangular Tessellations and Fibonacci Parastichous Spirals on Ag Core/SiO2 Shell Microstructures (Adv. Mater.ADVANCED MATERIALS, Issue 45 200945/2009) Stress engineering offers an effective route for self-assembly of ordered patterns. By stressing Ag core/SiO2 shell microstructures, spontaneous occurrence of triangular tessellations and Fibonacci parastichous spirals can be observed on the spherical and conical cores and shells, respectively. On p. 4652, Ze-Xian Cao and co-workers demonstrate that the stressed patterns are an immediate response to the geometry of the shrinking core/shells. The reproduction of Fibonacci spirals, ubiquitous in the world of plants, on the surface of totally inorganic microstructures provides strong confirmation of the mechanical principle of phyllotaxis. [source] Stressed Triangular Tessellations and Fibonacci Parastichous Spirals on Ag Core/SiO2 Shell MicrostructuresADVANCED MATERIALS, Issue 45 2009Chao-Rong Li Abstract Triangular tessellations and Fibonacci parastichous spirals were assembled via thermal stress engineering of Ag-core/SiO2 -shell microstructures, for which the geometry and topology of the primary core/shells play a pivotal role. Patterns on slightly stressed spherical surfaces are simply triangular tessellations with 12 pentamers, whereas additional pentamer,heptamer chains emerge when more vertices are available (>360) on heavily stressed surfaces, all showing an excellent agreement with numerical solutions to the Thomson's problem. Defect-free triangular lattice can be produced on a pierced spherical cap prepared via the draining effect. Remarkably, Fibonacci spirals of definite chirality, 3 by 5 through 13 by 21, and in both sinister and dexter forms, emerge on the conical supports. These results provide strong confirmation of the mechanical principle for phyllotaxis that the phyllotatic patterns are the least-elastic-energy configuration in a confining receptacle, and meanwhile demonstrate an effective path for the en masse fabrication of patterned structures on curved surfaces. [source] Sequential Polymer Precipitation of Core,Shell Microstructured Composites with Giant PermittivityMACROMOLECULAR RAPID COMMUNICATIONS, Issue 5 2010Tingyang Dai Abstract Polymeric core,shell microstructures have been constructed through a new method, namely sequential precipitation, which is intrinsically a self-assembly and phase separation process. High-quality poly(vinyldene fluoride),polycarbonate,lithium perchlorate composite films with spherical core,shell microstructures have been prepared and determined to consist of conducting cores and insulating shells. Because of the percolation effect, the resulting materials present a dielectric constant as high as 104,107 at the threshold. [source] | ||||||||||