Home About us Contact
|
Home About us Contact | ||
|
|
||
Grain Growth Behavior (grain + growth_behavior)
Selected AbstractsGrain Growth Control and Solid-State Crystal Growth by Li2O/PbO Addition and Dislocation Introduction in the PMN,35PT SystemJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2006Min-Soo Kim Grain growth behavior and solid-state single crystal growth (SSCG) in the Pb(Mg1/3Nb2/3)O3,35 mol% PbTiO3 (PMN,35PT) system have been investigated with varying Li2O/PbO ratios. The effect of dislocation density on crystal growth has also been studied. For SSCG, a BaTiO3 single-crystal seed was embedded in a polycrystalline PMN,PT matrix. During annealing, a PMN,PT single crystal grew from the seed at the cost of the small matrix grains. Addition of Li2O dopant first enhanced and then reduced abnormal grain growth in the matrix. In the 2 mol% Li2O and 6 mol% PbO excess PMN,PT samples annealed at 1200°C, considerable single-crystal growth occurred without formation of abnormally large grains in the matrix. Increasing the dislocation density in the BaTiO3 seed crystal resulted in enhanced growth of single crystals. These results were explained in terms of interface reaction-controlled nucleation and growth, based on crystal growth theories. [source] Effect of Li2O and PbO Additions on Abnormal Grain Growth in the Pb(Mg1/3Nb2/3)O3,35 mol% PbTiO3 SystemJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2004John Gerard Fisher Abnormal grain growth in Pb(Mg1/3Nb2/3)O3,35 mol% PbTiO3 (PMN-35PT) ceramics doped with Li2O and PbO has been investigated. Replacing the PbO dopant with up to 2 mol% Li2O caused an increase in the number of abnormal grains. For the composition containing 2 mol% Li2O and 6 mol% PbO, the amount of abnormal grain growth decreased with increasing sintering temperature. Single crystals of ,6 mm × 6 mm × 2 mm thickness were grown from the 2 mol% Li2O, 6 mol% PbO-containing composition via the templated grain growth method. Grain growth behavior with temperature is explained in terms of the effect of Li2O on interface-reaction-controlled grain growth and the critical driving force. [source] Nanocomposite Formation Through Thermal Decomposition of Mixed Samarium and Magnesium Citrate-Derived Gels Formed by Spray PyrolysisJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2008Thorsten Enz Metal citrate gels of samarium and magnesium were used as precursors for the generation of hollow sphere particles by spray pyrolysis under mild thermal conditions. Six mixtures with different Sm/Mg ratios as well as pure Sm and Mg samples were prepared. As a result of the low synthesis temperature the particles consist of amorphous metal carboxylate networks. The texture of the shells is governed by microporosity yielding the major part of the total surface area. A detailed investigation of thermal decomposition, crystallization, and grain growth behavior was carried out under constant heating rate conditions. The decomposition products are nanocrystalline Sm2O3 and MgO and corresponding two-phase nanocomposites. The pure samarium carboxylate gel features considerably higher thermal stability compared with the one comprised of only magnesium. Accordingly the decomposition behavior of mixed samples is dependent on the Sm/Mg ratio. Furthermore it is shown that small amounts of MgO are able to slow down the kinetics of grain growth of Sm2O3 whereas high amounts are necessary to significantly reduce the final grain size at 1000°C. [source] Effect of Interface Structure on the Microstructural Evolution of CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2006Wook Jo The interface atomic structure was proposed to have a critical effect on microstructure evolution during sintering of ceramic materials. In liquid-phase sintering, spherical grains show normal grain growth behavior without exception, while angular grains often grow abnormally. The coarsening process of spherical grains with a disordered or rough interface atomic structure is diffusion-controlled, because there is little energy barrier for atomic attachments. On the other hand, kink-generating sources such as screw dislocations or two-dimensional (2-D) nuclei are required for angular grains having an ordered or singular interface structure. Coarsening of angular grains based on a 2-D nucleation mechanism could explain the abnormal grain growth behavior. It was also proposed that a densification process is closely related to the interface atomic structure. Enhanced densification by carefully chosen additives during solid state sintering was explained in terms of the grain-boundary structural transition from an ordered to a disordered open structure. [source] Superplasticity and high temperature deformation behaviour in nano grain Tungsten compactsMATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 4-5 2008K. Ameyama Abstract Nano grain tungsten is fabricated by Mechanical Milling (MM) process, and its grain growth behavior and high temperature deformability is investigated. As a result, a nano grain structure, whose grain size is approximately 20 nm or less, is obtained after MM for 360ks. Those nano grains demonstrate an irregular grain boundary structure, i.e., "non-equilibrium grain boundary", and they change to a smooth grain boundary structure by annealing at 1023 K for 3.6 ks. Compacts with nano grain structure indicate superior sintering property even at 1273 K (0.35 Tm). Rhenium addition prevents grain growth during sintering and thus the compacts indicate a further improvement in deformability. The compact is composed of equiaxed grain, whose grain size is 420 nm, and has low dislocation density even after the large deformation. The strain rate sensitivity, i.e., m-value, of 0.41 is obtained in the W-Re compact at 1473 K. Those results strongly imply that the nano grain W-Re compacts show superplasticity at less than half of the melting temperature, i.e., 1473 K (0.42 of the solidus temperature). [source] | ||||||||||