6 research outputs found
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The effects of nanoparticle addition on the processing, structure and properties of SiC and AlN
Silicon carbide (SiC) and aluminum nitride (AlN) exhibit a combination of thermal and mechanical properties that are relevant to applications in electronics, aerospace, defense and automotive industries. However, the successful translation of these properties into final applications lies in the net-shaping of these ceramics into fully dense microstructures. Increasing the packing density of the starting powders is one effective route to achieve high sintered density and dimensional precision. The current research presents an in-depth study on the effects of nanoparticle addition on the powder injection molding (PIM) of SiC and AlN powder-polymer mixtures. In particular, bimodal mixtures of nanoscale (n) and sub-micrometer (μ) particles were found to have significantly increased powder packing characteristics (solids loading) in the powder-polymer mixtures.
The influence of nanoparticle addition on the multi-step PIM process was examined by comparing the rheological and thermal properties of the novel bimodal μ-n powder-polymer mixtures to conventional monomodal μ powder-polymer mixtures. Additionally, the effect of nanoparticle addition on the mold filling behavior of the powder-polymer mixtures was examined. Subsequently, the effects of increased powder content and reduced particle size owing to nanoparticle addition were studied in the context of the polymer removal kinetics. Finally, nanoparticle addition was found to expedite the liquid phase formation during the sintering stage. The sintered parts of bimodal μ-n mixtures exhibited higher sintered densities, lower shrinkage and better thermal properties than the corresponding monomodal powder mixtures. The above results provide new perspectives which could impact a wide range of materials, powder processing techniques and applications.Keywords: powder injection molding, aluminum nitride, silicon carbide, sinterin
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Synthesis and characterization of palladium/polycarbonate nanocomposites
Metal/polymer nanocomposites are of increasing importance with their tunable
properties being used in catalysis and sensors. Previous studies have focused on
the effects of metal content, molecular weight of polymer and reaction conditions on the structure- property relationship of the metal/polymer nanocomposites. This thesis focuses on the effect of two synthetic routes, ex situ and in situ, on the structure and properties of palladium/polycarbonate (Pd/PC)
nanocomposites. Discrete and agglomerated nanoclusters were obtained from ex situ and in situ methods, respectively. The effects of the varied morphology on the optical, thermal and electrical properties of the nanocomposites were studied. Dependence of the thermal stability of the nanocomposites on the heating rates, Pd content and synthetic methods was also investigated. The ex situ nanocomposites exhibited better optical transmission and thermal stability,
while the in situ nanocomposites showed higher electrical conductivity. These
observations lay the foundation for developing new synthetic strategies for
designing new materials by varying the size, shape, concentration and distribution of metal nanoclusters in various polymer matrices. Such materials will be investigated for sensor and catalyst applications
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The Effects of Nanoparticle Addition on Binder Removal from Injection Molded Aluminum Nitride
The effects of nanoparticle addition on the multi-step debinding of injection molded
aluminum nitride (AlN) samples were studied. Experiments varying the solvent
debinding conditions (time, temperature and aspect ratio) were performed on monomodal,
microscale (μ) and bimodal, micro-nanoscale (μ-n) AlN samples. Variations in the
solvent debinding kinetics as a result of the reduced particle size and increased powder
content were examined. The bimodal μ-n AlN samples showed a slower solvent
extraction of binder components compared to monomodal μ-AlN samples. The activation
energy for solvent extraction estimated from diffusion coefficients (Arrhenius equation)
was in close agreement with the value estimated by the master debinding curve (MDC)
method. An activation value around 50 kJ/mole was estimated by both the methods for μ
and μ-n AlN samples. The thermal debinding behavior of dewaxed samples was also
studied and the trends correlated with the solvent debinding behavior.Keywords: Master debinding curves, Diffusion coefficients, Solvent debinding, Bimodal, Activation energy, Monomoda
Properties of SiC and AlN feedstocks for the powder injection molding of thermal management devices
Structure and thermal stability of cellulose nanocrystal/polysulfone nanocomposites
The thermal stability of nanocomposites of cellulose nanocrystals (CNC) dispersed in polysulfone (PSf) was studied to understand the influence of heating rate and CNC concentration using thermogravimetric analysis (TGA). While heating rate was found to have a positive influence on the degradation onset temperature and the maximum degradation rate (Tmax) of these nanocomposites. The influence of CNC concentration appeared to be relatively low on these parameters. PSf/CNC nanocomposites with up to 2 wt.% CNC were found to follow first order degradation kinetics and at higher concentrations, better fit was seen with second-order degradation kinetics. The activation energy associated with nanocomposites degradation, determined using Kissinger method, revealed strong stabilizing effect of PSf matrix on CNC filler. FTIR analysis showed signature peak shifts that correlated with PSf/CNC interactions. On the other hand, the CNC filler had marginal influence on the stability of PSf matrix. Master decomposition curve (MDC) and weight-time-temperature plots were constructed from the obtained activation energies to describe the time-temperature dependence of the PSf/CNC nanocomposite pyrolysis