Fragmentation Behavior of Silica-Supported Metallocene/MAO Catalyst in the Early Stages of Olefin Polymerization

2005 ◽  
Vol 38 (11) ◽  
pp. 4673-4678 ◽  
Author(s):  
Xuejing Zheng ◽  
Madri Smit ◽  
John C. Chadwick ◽  
Joachim Loos
Keyword(s):  
Olefin Polymerization ◽  
Fragmentation Behavior ◽  
Early Stages

Influence of Porosity on the Fragmentation of Ziegler-Natta Catalyst in the Early Stages of Propylene Polymerization

e-Polymers ◽  
2006 ◽  
Vol 6 (1) ◽  
Author(s):  
Xuejing Zheng ◽  
Makarand S. Pimplapure ◽  
Günter Weickert ◽  
Joachim Loos
Keyword(s):  
Catalyst Particle ◽  
Particle Growth ◽  
Polymer Particle ◽  
Propylene Polymerization ◽  
Cross Sectional ◽  
Porous Catalyst ◽  
Fragmentation Behavior ◽  
Early Stages ◽  
Natta Catalyst ◽  
Highly Porous

AbstractCatalyst fragmentation and polymer growth in the early stages of propylene polymerization has been investigated using different Ziegler-Natta catalysts. Polymerization was carried out in slurry under mild conditions and stopped at low yield. Scanning electron microscopy (SEM) has been used to characterize the surface and cross sectional morphology of polymer particles at different stages of particle growth. Different fragmentation behavior is observed, and it is found that the way that catalyst fragments in the early stages of polymerization is greatly influenced by the porosity of the catalyst. When a less porous catalyst was used, the resulting mass diffusion limitation causes layer-bylayer fragmentation, starting at the outer surface of the catalyst particle to the center. In contrast, for highly porous catalyst, monomer can easily penetrate into the pores of the catalyst / polymer particle. The polymer growing throughout the particle results in a coarse and instantaneous fragmentation.

Morphology Evolution in the Early Stages of Olefin Polymerization

2006 ◽  
Vol 236 (1) ◽  
pp. 249-258 ◽  
Author(s):  
Xuejing Zheng ◽  
Joachim Loos
Keyword(s):  
Olefin Polymerization ◽  
Morphology Evolution ◽  
Early Stages

Spherulitic crystal growth in the prodissoconch larval of Crassostrea virginica

1983 ◽  
Vol 41 ◽  
pp. 518-519
Author(s):  
George G. Cocks ◽  
Louis Leibovitz ◽  
DoSuk D. Lee
Keyword(s):  
Crystal Structure ◽  
Crassostrea Virginica ◽  
Crystal Orientation ◽  
Developmental Changes ◽  
Gastrula Stage ◽  
Orthorhombic Crystal ◽  
Orthorhombic Crystal Structure ◽  
Stages Of Growth ◽  
Early Stages ◽  
Initial Deposition

Our understanding of the structure and the formation of inorganic minerals in the bivalve shells has been considerably advanced by the use of electron microscope. However, very little is known about the ultrastructure of valves in the larval stage of the oysters. The present study examines the developmental changes which occur between the time of conception to the early stages of Dissoconch in the Crassostrea virginica(Gmelin), focusing on the initial deposition of inorganic crystals by the oysters.The spawning was induced by elevating the temperature of the seawater where the adult oysters were conditioned. The eggs and sperm were collected separately, then immediately mixed for the fertilizations to occur. Fertilized animals were kept in the incubator where various stages of development were stopped and observed. The detailed analysis of the early stages of growth showed that CaCO3 crystals(aragonite), with orthorhombic crystal structure, are deposited as early as gastrula stage(Figuresla-b). The next stage in development, the prodissoconch, revealed that the crystal orientation is in the form of spherulites.

Formation of Dislocation Channels in Neutron Irradiated Molybdenum

1972 ◽  
Vol 30 ◽  
pp. 672-673
Author(s):  
S. Mahajan
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Ambient Temperature ◽  
Room Temperature ◽  
Channel Formation ◽  
Early Stages ◽  
Transmission Electron ◽  
Three Stages ◽  
Two Stages ◽  
Polycrystalline Molybdenum

The evolution of dislocation channels in irradiated metals during deformation can be envisaged to occur in three stages: (i) formation of embryonic cluster free regions, (ii) growth of these regions into microscopically observable channels and (iii) termination of their growth due to the accumulation of dislocation damage. The first two stages are particularly intriguing, and we have attempted to follow the early stages of channel formation in polycrystalline molybdenum, irradiated to 5×1019 n. cm−2 (E > 1 Mev) at the reactor ambient temperature (∼ 60°C), using transmission electron microscopy. The irradiated samples were strained, at room temperature, up to the macroscopic yield point.Figure 1 illustrates the early stages of channel formation. The observations suggest that the cluster free regions, such as A, B and C, form in isolated packets, which could subsequently link-up to evolve a channel.

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