X‐Ray Tomography Imaging of Porous Polyolefin Particles in an Electron Microscope

Meisterová, Lucie; Zubov, Alexandr; Smolná, Klára; Štěpánek, František; Košek, Juraj

doi:10.1002/mren.201300002

Cited by 11 publications

(6 citation statements)

References 20 publications

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“…The common approach employs the 2D or 3D computer reconstruction of real materials using microscopy or tomography images and its discretization into 2D or 3D mesh, and subsequent simulation of the heat transfer using a suitable method, such as the finite volume method (FVM), finite element method, or lattice Boltzmann method. One of the critical issues with this approach is often, as is the case in our work as well, the quality of the microscopy or tomography images, which often do not capture the morphology in sufficient detail …”

Section: Theorymentioning

confidence: 99%

Determination of heat conductivity of waste glass feed and its applicability for modeling the batch‐to‐glass conversion

et al. 2017

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The effective heat conductivity (k) of reacting melter feed affects the heat transfer and conversion process in the cold cap, a layer of reacting feed floating on molten glass. A heat conductivity meter was used to measure k of samples of a cold cap retrieved from a laboratory-scale melter, loose dry powder feed samples, and samples cut from fast-dried slurry blocks. These blocks were formed to simulate the feed conditions in the cold-cap by rapidly evaporating water from feed slurry poured onto a 200°C surface. Our study indicates that the effective heat conductivity of the feed in the cold cap is significantly higher than that of loose dry powder feed, which is a result of the feed solidification during the water evaporation from the feed slurry. To assess the heat transfer at higher temperatures when feed turns into foam, we developed a theoretical model that predicts the foam heat conductivity based on morphology data from in-situ X-ray computed tomography.The implications for the mathematical modeling of the cold cap are discussed.

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Section: Theorymentioning

confidence: 99%

Determination of heat conductivity of waste glass feed and its applicability for modeling the batch‐to‐glass conversion

et al. 2017

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“…[33][34][35] A variety of samples can be imaged under ambient conditions at 2D and 3D spatial resolutions of up to 150 nm and 170 nm, respectively. [33][34][35] Specifically in the context of supported olefin polymerization catalysts, the technique delivers comprehensive information on the extent and magnitude of large-scale fragmentation phenomena (i. e., crack formation and propagation) and the 3D structure and phase distribution of individual particles [2,4,36,37] more so than other laboratory-based techniques such as SEM, which only yields 2D information. [11,17,19,[38][39][40][41][42] Thus, by using nanoCT in combination with FIB-SEM, we were able to identify three important factors that, in addition to the friability of a given support, are responsible for suboptimal monomer diffusion and stress generation, thus leading to a more frequent occurrence of the sectioning fragmentation mechanism in silica-supported olefin polymerization catalysts.…”

Section: Introductionmentioning

confidence: 99%

Elucidating the Sectioning Fragmentation Mechanism in Silica‐Supported Olefin Polymerization Catalysts with Laboratory‐Based X‐Ray and Electron Microscopy

et al. 2022

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Strict morphological control over growing polymer particles is an indispensable requirement in many catalytic olefin polymerization processes. In catalysts with mechanically stronger supports, e. g., polymerization-grade silicas, the emergence of extensive cracks via the sectioning fragmentation mechanism requires severe stress build-up in the polymerizing catalyst particle. Here, we report on three factors that influence the degree of sectioning in silica-supported olefin polymerization catalysts. Laboratory-based X-ray nano-computed tomography (nanoCT) and focused ion beam-scanning electron microscopy (FIB-SEM) were employed to study catalyst particle morphology and crack propagation in two showcase catalyst systems, i.e., a zirconocene-based catalyst (i.e., Zr/MAO/SiO 2 , with Zr = 2,2'biphenylene-bis-2-indenyl zirconium dichloride and MAO = methylaluminoxane) and a Ziegler-Natta catalyst (i.e., TiCl 4 / MgCl 2 /SiO 2 ), during slurry-phase ethylene polymerization. The absence of extensive macropores in some of the catalysts' larger constituent silica granulates, a sufficient accessibility of the catalyst particle interior at reaction onset, and a high initial polymerization rate were found to favor the occurrence of the sectioning pathway at different length scales. While sectioning is beneficial for reducing diffusion limitations, its appearance in mechanically stronger catalyst supports can indicate a suboptimal support structure or unfavourable reaction conditions.

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“…Pioneering work on the use of synchrotron radiation for the imaging of both polyethylene and polypropylene particles was done with X-ray computed microtomography (CMT). − However, these studies have focused on the polymer phases with 3-D voxel sizes of several microns therefore neglecting the role of the catalyst fragmentation stage occurring at significantly smaller size scales, i.e. on the order of submicron to a few tens of microns.…”

mentioning

confidence: 99%

Correlated X-ray Ptychography and Fluorescence Nano-Tomography on the Fragmentation Behavior of an Individual Catalyst Particle during the Early Stages of Olefin Polymerization

et al. 2020

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A combination of X-ray ptychography and X-ray fluorescence tomography (XRF) has been used to study the fragmentation behavior of an individual Ziegler−Natta catalyst particle, ∼40 μm in diameter, in the early stages of propylene polymerization with submicron spatial resolution. The electron density signal obtained from X-ray ptychography gives the composite phases of the Ziegler−Natta catalyst particle fragments and isotactic polypropylene, while 3-D XRF visualizes multiple isolated clusters, rich in Ti, of several microns in size. The radial distribution of Ti species throughout the polymer−catalyst composite particle shows that the continuous bisection fragmentation model is the main contributor to the fragmentation pathway of the catalyst particle as a whole. Furthermore, within the largest Ti clusters the fragmentation pathway was found to occur through both the continuous bisection and layer-by-layer models. The fragmentation behavior of polyolefin catalysts was for the first time visualized in 3-D by directly imaging and correlating the distribution of the Ti species to the polymer−catalyst composite phase.

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X‐Ray Tomography Imaging of Porous Polyolefin Particles in an Electron Microscope

Cited by 11 publications

References 20 publications

Determination of heat conductivity of waste glass feed and its applicability for modeling the batch‐to‐glass conversion

Determination of heat conductivity of waste glass feed and its applicability for modeling the batch‐to‐glass conversion

Elucidating the Sectioning Fragmentation Mechanism in Silica‐Supported Olefin Polymerization Catalysts with Laboratory‐Based X‐Ray and Electron Microscopy

Correlated X-ray Ptychography and Fluorescence Nano-Tomography on the Fragmentation Behavior of an Individual Catalyst Particle during the Early Stages of Olefin Polymerization

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