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Fine Grain Size (fine + grain_size)
Selected AbstractsHot Isostatic Pressing of Transparent Nd:YAG CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2009Sang-Ho Lee This paper demonstrates that fine-grained (2,3 ,m), transparent Nd:YAG can be achieved at SiO2 doping levels as low as 0.02 wt% by the sinter plus hot isostatic pressing (HIP) approach. Fine grain size is assured by sintering to 98% density, in order to limit grain growth, followed by HIP. Unlike dry-pressed samples, tape-cast samples were free of large, agglomerate-related pores after sintering, and thus high transparency (i.e., >80% transmission at 1064 nm) could be achieved by HIP at <1750°C along with lower silica levels, thereby avoiding conditions shown to cause exaggerated grain growth. Grain growth was substantially limited at lower SiO2 levels because silica is soluble in the YAG lattice up to ,0.02,0.1 wt% at 1750°C, thus allowing sintering and grain growth to occur by solid-state diffusional processes. In contrast, liquid phase enhanced densification and grain growth occur at ,0.08,0.14 wt% SiO2, especially at higher temperatures, because the SiO2 solubility limit is exceeded. [source] Microstructural analysis of iron aluminide formed by self-propagating high-temperature synthesis mechanism in aluminium matrix compositeJOURNAL OF MICROSCOPY, Issue 1 2006ANITA OLSZÓWKA-MYALSKA Summary An aluminium matrix composite with iron aluminide formed in situ as a result of self-propagated high-temperature synthesis was examined. The structural characteristics of the reinforcement investigated by scanning electron microscopy and transmission electron microscopy methods are presented. Iron aluminide particles with a very fine grain size and of two shapes, cubic and needle-like, were observed. No differences in their phase composition were found by the selective electron diffraction pattern method. The composite reinforcement formed in the early stage of self-propagating high-temperature synthesis consisted only of the Al3Fe phase. [source] Electrical Conductivity of Submicrometer Gadolinia-Doped Ceria Sintered at 1000°C Using Precipitation-Synthesized Nanocrystalline PowdersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2008Pandurangan Muralidharan A simple synthetic strategy has been implemented to obtain low-temperature sintered fine grain size gadolinia-doped ceria, Ce0.9Gd0.1O1.95, (CGO) electrolyte pellets with a high density using weakly agglomerated particles of calcined nanopowders synthesized by a homogeneous precipitation process. The precipitants used were diethylamine (DEA process) and ammonium hydroxide in neutral precipitation (NP process). X-ray diffraction patterns revealed the single-phase crystalline CGO of a fluorite-type structure. The crystalline powder was directly synthesized from solution by the DEA process at room temperature, whereas the NP process powder was crystallized upon hydrothermal treatment at an elevated temperature. Transmission electron microscopy images showed homogeneously dispersed spherical-shaped particles of ,5 nm size for nanopowders calcined at 300°C for 4 h. A high densification range from ,96% to 99% of the theoretical was achieved for the nonconventionally low-temperature sintered pellets at 1000°C from weakly bonded particles of CGO nanopowders calcined at 300°C for 4 h without any sintering aid. The dense CGO pellets sintered at 1000°C for 4 h with an average grain size of ,150,300 nm exhibited a promising high electrical conductivity of 2.03 × 10,2 S/cm (DEA process) and 2.17 × 10,2 S/cm (NP process), measured at 650°C, and low activation energy Ea. The electrical conductivities of fine grain size low-temperature sintered CGO pellets are comparable with the literature reports of sintered pellets using sintering aids, and high-temperature sintered CGO pellets above 1300°C with a larger grain size. [source] Deformation Mechanism of Fine-Grained Magnesium Aluminate Spinel Prepared Using an Alkoxide PrecursorJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2000Takeshi Shiono Polycrystalline MgAl2O4 spinel with high purity and stoichiometric composition was prepared using alkoxide precursors. The average grain size of the polycrystal was fine (1.7 ,m). The deformation mechanism of the polycrystal was investigated in air at temperatures of 1300°,1400°C. At 1300°C, oxygen lattice diffusion controlled the deformation, despite the fine grain size; however, increases in the temperature and applied stress caused cavities to nucleate and grow. Spinel possessed better creep resistance than alumina of comparative grain size. The effective diffusion coefficient was determined as follows: [formula omitted] [source] Diagenesis and Their Succession of Gas-bearing and Non-gas-bearing Reservoirs in the Sulige Gas Field of Ordos Basin, ChinaACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 6 2009ZHU Xiaomin Abstract: Comparisons have been made among lithology, diagenesis, and reservoir characteristics of gas-bearing and non-gas-bearing ones in the Sulige gas field of the Ordos Basin based on the laboratory analysis of thin sections, scanning electron microscope, and liquid inclusion of the reservoirs. The reservoirs of the Sulige gas field are now in the middle stage of diagenesis and have undergone compaction, cementation and dissolution. The secondary pore of the reservoir originated from the dissolution of the feldspar and tuff because of the organic acid action from the source rocks during the diagenetic middle stage. Gas-bearing reservoirs are common in soluble pore diagenetic facies of coarse detritus quartzose sandstone, whereas non-gas-bearing ones are common in tense compaction diagenetic facies of mud-bearing medium-fine detritus quartzose sandstone and residual intergranular pore diagenetic facies of mud-bearing medium-coarse detritus quartzose sandstone. The secondary pore is developed in gas-bearing reservoirs of the Sulige gas-field as the medium-coarse grain reservoirs formed in a powerful sedimentary environment and experienced strong dissolution. However, the sediments of fine grain size form the non-gas-bearing reservoirs because of less residual primary pore and secondary pore. [source] Suppression of Ni4Ti3 Precipitation by Grain Size Refinement in Ni-Rich NiTi Shape Memory Alloys,ADVANCED ENGINEERING MATERIALS, Issue 8 2010Egor A. Prokofiev Severe plastic deformation (SPD) processes, such as equal channel angular pressing (ECAP) and high pressure torsion (HPT), are successfully employed to produce ultra fine grain (UFG) and nanocrystalline (NC) microstructures in a Ti,50.7,at% Ni shape memory alloy. The effect of grain size on subsequent Ni-rich particle precipitation during annealing is investigated by transmission electron microscopy (TEM), selected area electron diffraction (SAD, SAED), and X-ray diffraction (XRD). It is observed that Ni4Ti3 precipitation is suppressed in grains of cross-sectional equivalent diameter below approximately 150,nm, and that particle coarsening is inhibited by very fine grain sizes. The results suggest that fine grain sizes impede precipitation processes by disrupting the formation of self-accommodating particle arrays and that the arrays locally compensate for coherency strains during nucleation and growth. [source] Alkoxide Sol-Gel-Processed Cordierite FiberJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2002Mu-Tsun Tsai An alkoxide sol-gel route was developed to prepare stoichometric cordierite fibers. The influences of the aging treatment and heating rate on the sinterability of the gel fibers were also examined. X-ray diffraction analysis revealed that the unaged and aged fibrous gels all remained amorphous <800&, but began crystallization into ,-cordierite and ,-cordierite at ,900°C and 1050°C, respectively; single-phase ,-cordierite fibers were obtained at 1300°C. Heating the unaged fibers yielded denser microstructures, with fine grain sizes of ,0.2,0.4 ,m, whereas the aged fibers exhibited porous microstructures following heating at 1300°C. A higher heating rate and aging treatment resulted in a higher open porosity of the fired fiber. [source] | ||||||||||