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22 апреля 2009 | Автор: Admin | Рубрика: Скачать журналы бесплатно » Научные журналы | Комментариев: 0
Processing Mesocarbon Microbeads To High-Performance Materials For Friction Applications
By Christopher William Norfolk, Chemical And Biomolecular Engineering, Notre Dame
Published by University of Notre Dame | 2005 | Disertation | Pages: 114 | PDF | 4.42 MB
Honeywell, a leading manufacturer of friction materials for aerospace applications, manufactures brakes by densifying a carbon fiber preform using chemical vapor deposition. This has two major drawbacks, namely, the high cost of the fiber preform, and the time required to densify it via CVD. To address these issues, a novel material, mesocarbon microbeads, are investigated. This relatively inexpensive and rapidly processed material has shown good friction characteristics, but unacceptable fracture toughness. Therefore, major goals are to understand the behavior of MCMB during processing, and to investigate the most effective approach to producing hightoughness materials. Dilatometry, thermogravimetric analysis, x-ray diffraction, scanning electron microscopy, pycnometry, indentation, and compact tension were used study sintering, graphitization, and in-situ reinforcement of MCMB-based materials.
It is shown that low temperature sintering consists of two processes: neck formation via a non-densifying liquid-phase sintering mechanism < 800 K, and significant sample shrinkage due to changes of true density in the region 800 – 1200 K. This results in material densification without decreasing porosity. During high temperature treatment, shrinkage is again accompanied by increases in theoretical density, maintaining porosity. However, observation of pore microstructures indicate that high temperature sintering mechanisms are active, which could result in overall porosity elimination given sufficiently long sintering times.
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