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51.
《Materials Research Bulletin》1987,22(5):669-676
For the first time, the results of single crystal determination of the true Nasicon are given. The structure refinement yielded the following composition: Na3.09(8)Zr2.01(1)P0.91Si2.09O12. Evidence of the total occupancy of the Zr octahedron is found, displaying that only the Si/P non-stoechiometry mechanism is present in the Nasicon crystal.For the two temperatures which have been investigated (R.T. and 623K), the structures are very close to that of the Nasicon analog: Na3Sc2P3O12. However the Si/P substitution prevents the sodium long range ordering even in the monoclinic low temperature phase and therefore the cross over to the rhombohedral symmetry only involves very small atomic displacements. For both structures, a new sodium position (mid-Na) is displayed in the conduction channel, intermediate between the usual Na(1) and Na(2) sites. 相似文献
52.
《Materials Research Bulletin》1987,22(10):1341-1345
Stabilization factors of the high and low temperature phases of TaSe3 are investigated. The low temperature phase is stabilized by zirconium or titanium impurity. The high temperature phase is stabilized by oxygen impurity. Without oxygen impurity, the low temperature phase is stable up to decomposition temperature and the phase transition is completely suppressed by zirconium impurity. 相似文献
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《Cement and Concrete Composites》2003,25(6):593-598
Tannins and cashew nut shell liquid (CNSL) are groups of natural resins that are receiving wide attention as substitutes to synthetic binders in the production of biocomposites. In this work, blends of hydrolyzed tannin, CNSL, and urea formaldehyde (UF) have been tested to determine their mechanical and physical properties for particle board applications. The blending of hydrolyzed tannin with UF resin has been found to reduce the formaldehyde emission levels significantly. A blend of hydrolyzed tannin and CNSL has been found to possess better dimensional stability. Tannin-blended resins cure faster, i.e. have shorter pot life, and result in composites with better water and moisture resistance when compared to UF. Thermal analysis by differential scanning calorimetry has shown that tannin blends exhibit better thermal stability and have a higher glass transition temperature than UF resin. Generally, it was found that particle boards made from coffee husks, and bonded using the tannin resin blend that include UF and CNSL, possessed superior properties to those made using UF alone. The mechanical and physical properties of coffee husk-particle boards produced using this new resin blend are presented and discussed. 相似文献
55.
《Composites Part A》2001,32(5):683-699
A study of the healing of delamination damage in woven E-glass/epoxy composites is performed. With the ultimate goal of self-healing in mind, two types of healing processes are studied. In the first a catalyzed monomer is manually injected into the delamination. In the second a self-activated material is created by embedding the catalyst directly into the matrix of the composite, then manually injecting the monomer. Healing efficiencies relative to the virgin fracture toughness of up to 67% are obtained when the catalyzed monomer is injected and about 19% for the self-activated materials. Scanning electron microscopy is used to analyze the fracture surfaces and provide physical evidence of repair. 相似文献
56.
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58.
《Acta Metallurgica Materialia》1992,40(4):663-671
Second-phase particles associated with trace amounts of impurities in binary AlLi alloys were characterized by analytical electron microscopy (AEM) and secondary ion mass spectrometry (SIMS). These particles were analyzed by X-ray microanalysis to be Fe-rich and identified by electron diffraction to be Al3Fe. The Al3Fe precipitates were seen to be faulted along a preferred crystallographic direction. Also, they were surrounded by a δ′ precipitate free zone (PFZ) with coarser δ′ at the edge of the PFZ than in the rest of the matrix. SIMS analysis revealed detectable, but negligible, Li in these Al3Fe particles; based on this observation, the above mentioned PFZs are suggested to be a result of vacancy loss to the incoherent interface. 相似文献
59.
《Acta Metallurgica Materialia》1991,39(11):2553-2563
A detailed study has been made of the localized adiabatic shear band formation in a plain carbon and a low alloy eutectoid rail steel subjected to high strain rate compression at initial deformation temperature of 298, 453 and 623 K. Localized adiabatic shearing due to impact is found to be favored with alloy steels and decreasing temperatures of deformation. It is shown that the deformed and transformed shear bands rather than being two separate phenomena are only an outcome of the extent of adiabatic strain localization occuring during deformation; the deformed bands forming with lesser localized flow and the transformed bands forming with extensive localized flow. This study explains convincingly the formation of the white phase on the surface of the rail heads during wheel-rail contact as due to the coalescence of the numerous adiabatic shear bands. 相似文献
60.
《Water research》1996,30(5):1041-1048
Success of two-phase anaerobic systems for primary and secondary sludge treatment has been reported based on both directly and indirectly measured volatile solids (VS) reduction, total gas and methane generation, COD reduction, etc. The objective of this research was to determine whether phase separation increases directly measured VS reduction compared to conventional anaerobic sludge digestion. Two-phase and conventional digesters were operated with sludge feeds from three sources; both 1:1 sludges (primary:waste activated, solids basis) and 100% waste activated sludges (WAS) were studied. The maximum difference between VS reductions in conventional and two-phase systems was about 8.7% with waste activated sludge. The increase in volatile solids reduction in two-phase systems with the 1:1 sludge ranged from 1.9 to 6.0% as compared to conventional systems. This relatively small increase in VS reduction may not be worth the additional cost of operating two-phase digesters at full scale. 相似文献