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Queen Mary University of LondonQueen Mary University of London
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School of Engineering and Materials Science
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PhD Thesis: Experimental investigation and molecular dynamic simulation of binder removal in powder compacts

Author: JEE, Caroline

Year: 2003

Supervisor(s): Xiao Guo

Binder removal in a key stage in the slurry powder processing of materials, such as tape casting, was developed here as a pre-processing technique for the fabrication of fibre reinforced titanium composites. The process involves: the formulation of suitable slurry consisting of powder and a binder/solvent solution; casting of a powder tape and laying up of the tape-fibre assembly for consolidation into a composite. The organic binder is removed at an intermediate stage without leaving any contaminants in the matrix material. Here, the main objectives are to investigate the debinding mechanisms and conditions of the polymeric binder and the effects of pre-processing conditions on slurry stability and tape uniformity, in order to produce a residue- and void-free composite with uniform fibre distribution. Green tapes were produced from Ti-15V-3Al-3Cr-3Sn, TiF^ and Ti-6A1-4V powders using binder systems of: polyisobutylene (PIB) in cyclohexane and agar in deionised water. Tapes of uniform thickness, high powder loading and uniform powder distribution tapes were successfully achieved. Thermogravimetry, Fourier Transform Infrared Spectrometry, Gas Chromatography and Mass Spectrometry were carried out to examine the thermal decomposition of PIB, and to obtain the optimum burnout conditions. To further understand the decomposition mechanisms of the binders, Reactive Molecular Dynamic (RMD) simulations were performed to determine the molecular activities of the binder at different thermal conditions. A RMD code, MDREACT, was used to simulate chemical reactions such as bond breaking and forming during the simulation. The current models consist of a single chain PIB and PIB on a titanium surface. Simulations were carried out at different temperatures to investigate the degradation behaviour and product distribution. Interactions of degraded products and the kinetics of degradation were also analysed. Likely degradation products from PIB were identified and compared with experimental findings. The results facilitated the optimisation of the debinding conditions. High quality dense monolithic samples were obtained without binder residues in the end.