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排序方式: 共有564条查询结果,搜索用时 15 毫秒
121.
122.
Elena Tervoort Theo A. Tervoort Ludwig J. Gauckler 《Journal of the American Ceramic Society》2004,87(8):1530-1535
123.
Peter den Exter Louis Winnubst Theo H. P. Leuwerink Anthonie J. Burggraaf 《Journal of the American Ceramic Society》1994,77(9):2376-2380
The densification behavior of ZrO2 (+ 3 mol% Y2 O3 )/85 wt% Al2 O3 powder compacts, prepared by the hydrolysis of metal chlorides, can be characterized by a transition- and an α-alumina densification stage. The sintering behavior is strongly determined by the densification of the transition alumina aggregates. Intra-aggregate porosity, resulting from calcination at 800°C, partly persists during sintering and alumina phase transformation and negatively influences further macroscopic densification. Calcination at 1200°C, however, densifies the transition alumina aggregates prior to sintering and enables densification to almost full density (96%) within 2 h at 1450°C, thus obtaining a microstructure with an alumina and a zirconia grain size of 1 μm and 0.3–0.4 μm, respectively. 相似文献
124.
Rawley B. Greene Stefan Fünfschilling Theo Fett Michael J. Hoffmann Jamie J. Kruzic 《Journal of the American Ceramic Society》2013,96(1):259-265
The role of microstructure in affecting the fatigue crack growth resistance of grain bridging silicon nitride ceramics doped with rare earth (RE = Y, La, Lu) oxide sintering additives was investigated. Three silicon nitride ceramics were prepared using MgO‐RE2O3 and results were compared with a commercial Al2O3‐Y2O3‐doped material. Decreasing stress intensity range (ΔK) fatigue tests were conducted using compact‐tension specimens to measure steady‐state fatigue crack growth rates. Specimens doped with MgO‐RE2O3 additives showed a significantly higher resistance to crack growth than those with Al2O3‐Y2O3 additives and this difference was attributed to the much higher grain aspect ratio for the MgO‐RE2O3‐doped ceramics. When the crack growth data were normalized with respect to the total contribution of toughening by bridging determined from the monotonically loaded R‐curves, the differences in fatigue resistance were greatly reduced with the data overlapping considerably. Finally, all of the MgO‐RE2O3‐doped silicon nitrides displayed similar steady‐state fatigue crack growth behavior suggesting that they are relatively insensitive to the intergranular film. 相似文献
125.
We have studied dilute and semidilute solutions of poly(γ-benzyl-l-glutamate) in 1,2-dichloroethane by static and dynamic light scattering. The aggregational behaviour of the semiflexible polymer is evidenced in both static and dynamic scattering, and is sensitive to the temperature and the polypeptide molecular weight. In particular, both the reciprocal specific scattering intensity and the effective decay rate of the dynamic correlations exhibit a minimum as a function of the concentration. The slope of effective diffusion coefficient versus the square of the scattering vector displays an anomalous maximum as a function of the concentration which can also be attributed to aggregation. The experimental evidence is compatible with head-to-tail dimerization of the polymer as the concentration increases. 相似文献
126.
Alain B. Kounga Njiwa Theo Fett Jürgen Rödel George D. Quinn 《Journal of the American Ceramic Society》2004,87(8):1502-1508
An evaluation of measurements of crack opening displacements (CODs) on a commercial sintered reaction-bonded silicon nitride (SRBSN) was performed. To determine the intrinsic fracture toughness of this material, a new evaluation method is presented, which takes into account not only the near tip CODs, but the CODs of the complete crack profile. The method is applied on through-thickness cracks in bend bars and contrasted to CODs of Vickers radial cracks. A crack-tip toughness of ∼1.7 MPa·m1/2 is obtained. 相似文献
127.
CARBON-BASED MONOLITHIC STRUCTURES 总被引:9,自引:0,他引:9
Theo Vergunst Marco J. G. Linders Freek Kapteijn Jacob A. Moulijn 《Catalysis Reviews》2001,43(3):291-314
The interest in using monolithic structures for chemical conversion and adsorption processes is increasing. A relatively new type of monolith is based on carbon. The combined favorable properties of carbon and monolithic structures create a support with great potential in catalytic and adsorption processes. This review describes the current state of the art of carbon-based monolithic structures with respect to preparation, obtained support properties, and application in catalytic and adsorption processes, and it evaluates upcoming application areas. 相似文献
128.
Preparation of monolithic catalysts 总被引:10,自引:0,他引:10
T. Alexander Nijhuis Annemarie E. W. Beers Theo Vergunst Ingrid Hoek Freek Kapteijn Jacob A. Moulijn 《Catalysis Reviews》2001,43(4):345-380
Monolithic catalysts can be attractive replacements for conventional catalysts in randomly packed beds or slurry reactors. The conventional procedures for preparing catalysts, however, cannot simply be applied to monolithic catalysts. Different procedures are discussed on how to put a coat layer of a catalyst support material like alumina, silica, or carbon on a monolith body by either filling the pores in that support or by putting a layer on that support. Different methods to apply an active phase to the support are discussed as well. Finally, methods to convert ready-made catalysts into monolithic catalysts are presented. 相似文献
129.
The industrial implementation of enzymes in flow biocatalysis microreactors is expected to be essential for the emergence of a bio‐based circular economy. Major challenges concern the efficient immobilization of delicate enzymes inside miniaturized reactors without compromising their catalytic activity. We describe the exploitation of the widely used His‐tag system in a microfluidic packed‐bed reactor that contains ketoreductase‐functionalized magnetic beads. In a continuous process, these reactors produced highly stereoselective (R)‐configured alcohols (d.r. 99:1) with an average conversion of > 90 % for more than 4 days. We believe that such miniaturized flow reactors can be of great utility for future sustainable production processes. 相似文献
130.
Fabrizio Valenza Sofia Gambaro Maria Luigia Muolo Gabriele Cacciamani Peter Tatarko Theo Graves Saunders Mike J. Reece Andreas Schmidt Thomas Schubert Thomas Weißgärber Alberto Passerone 《International Journal of Applied Ceramic Technology》2017,14(3):295-304
When designing high‐temperature brazing processes for ceramic materials, the interfacial phenomena between the liquid media and the adjoining surfaces must be known to design reliable joints. In order to assess the feasibility of using Ta‐containing alloys for high‐temperature brazing of SiC‐based composites, the wetting of molten Ni‐Ta alloys on ultra‐pure chemical vapor deposited (CVD) SiC substrates has been investigated using the sessile drop technique. For all of the compositions and experimental conditions, good wetting was observed with fast spreading. The interfacial behavior is determined by the competition between the typical interfacial phenomena of the pure elements; specifically, either the dissolution of the ceramic phase by Ni or the formation of a new interfacial layer, TaC, by reaction between Ta and CVD‐SiC, which prevails depends on the relative amount of the single element in the alloy. 相似文献