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[en] This study investigates the effect of mixing technique and particle characteristics on the rheology and agglomerate dispersion of tungsten-based powder injection molding (PIM) feedstock. Experiments were conducted with as-received (agglomerated) and rod-milled (deagglomerated) tungsten powder mixed in a paraffin wax-polypropylene binder. Increase in the mixing shear rate decreased the agglomerate size of the agglomerated tungsten powder, decreased the viscosity, and improved the flow stability of the feedstock, interpreted as increased homogeneity of the feedstock. Higher solids volume fraction, lower mixing torques, and improved homogeneity were observed with deagglomerated tungsten powder, emphasizing the importance of particle characteristics and mixing procedures in the PIM process. Hydrodynamic stress due to mixing and the cohesive strength of the tungsten agglomerate were calculated to understand the mechanism of deagglomeration and quantify the effect of mixing. It was concluded that deagglomeration occurs due to a combination of rupture and erosion with the local hydrodynamic stresses exceeding the cohesive strength of the agglomerate
[en] A critical barrier to the routine use of nanomaterials is the tedious, expensive means of their synthesis. Microreaction technology takes advantage of the large surface area-to-volume ratios within microchannel structures to accelerate heat and mass transport. This accelerated transport allows for rapid changes in reaction temperatures and concentrations leading to more uniform heating and mixing which can have dramatic impacts on macromolecular yields and nanoparticle size distributions. Benefits of microreaction technology include higher yield and reactant conversion, better energy efficiency and less by-product generation. Microreactors can help minimize the environmental impact of nanoproduction by enabling solvent free mixing, integrated separation techniques and reagent recycling. The possibility of synthesizing nanomaterials in the required volumes at the point-of-use eliminates the need to store and transport potentially hazardous materials and provides the flexibility for tailoring complex functional nanomaterials. Recognizing these benefits for nanosynthesis, continuous flow microreactors have been used by several research groups to synthesize and characterize nanomaterials. An overview of these efforts and issues related to scale up and other post synthesis processes such as separation and deposition are presented in this paper.
[en] The thermal debinding process is one of the most crucial steps in powder injection molding because it consumes a great deal of the processing time and may introduce defects into the component. To enhance production efficiency and increase defect avoidance, debinding conditions including maximum temperature, heating rate, and holding time should be determined based on the analysis of thermal decomposition behavior. The thermal decomposition behavior of lead magnesium niobate-lead zirconate titanate (PMN-PZT) ceramic feedstock with varying binder compositions was investigated in this paper using experimental analysis and modeling. In this study, the powder volume fraction in the feedstock was fixed at 45 vol% in order to isolate the effects of binder composition on thermal decomposition behavior. Each feedstock was divided into three groups depending on the variation in the filler binder (first), the backbone binder (second), and the entire binder system (third), respectively. Thermal decomposition behaviors for the feedstocks were analyzed by thermogravimetric analysis experiments at heating rates of 2, 5, and 10 °C min−1. All of the TGA graphs showed two sigmoidal curves due to the difference in the molecular weights of the binders. The apparent activation energy for binder decomposition was calculated based on the Kissinger approach. A remarkable change in activation energy was derived from the variation in the entire binder system. Based on the acquired decomposition parameters, master decomposition curve was constructed and verified experimentally in order to provide a predictive design tool for identifying optimal debinding conditions based on the intrinsic kinetics of binder pyrolysis. (paper)