Nb-based powder was fabricated via mechanical grinding. The influence of stearic acid on the grinding process was studied. The structural evolution and morphological evolution of the milled powder were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) analysis. It is indicated that an appropriate amount of stearic acid accelerates the particle refinement process and favors the production of superfine Nb-based particles with good dispersivity and high activity. However, an inappropriate amount of stearic acid has an adverse effect on the refinement process.
Si3N4 powders were synthesized by a carbothermal reduction method using a SiO2 + C combustion synthesis precur- sor derived from a mixed solution consisting of silicic acid (Si source), polyacrylamide (additive), nitric acid (oxidizer), urea (fuel), and glucose (C source). Scanning electron microscopy (SEM) micrographs showed that the obtained precursor exhibited a uniform mixture of SiO2 + C composed of porous blocky particles up to ～20 μm. The precursor was subsequently calcined under nitrogen at 1200-1550°C for 2 h. X-ray diffraction (XRD) analysis revealed that the initial reduction reaction started at about 1300°C, and the complete transition of SiO2 into Si3N4 was found at 1550°C. The Si3N4 powders, synthesized at 1550°C, exhibit a mixture phase of α- and β-Si3N4 and consist of mainly agglomerates of fine particles of 100-300 nm, needle-like crystals and whiskers with a diameter of about 100 nm and a length up to several micrometers, and a minor amount of irregular-shaped growths.
Micro powder injection molding (μPIM) was investigated for possible mass production of micro-components at relatively low cost. However, scaling down to such a level produces challenges in injection molding and debinding. Micro gears were fabricated by μPIM from in-house feedstock. The effect of injection speed and injection pressure on the replication of the micro gear cavity was investigated. Solvent debinding and thermal debinding processes were discussed. The results show that micro gears can be successfully fabricated under the injection pressure of 70 MPa and the 60% injection speed. Either too low or too high injection speed can cause incomplete filling of micro gears. The same is the case with too low injection pressure. Too high injection pressure can bring cracks. Solvent debinding of micro gears was performed in a mixture of petroleum ether and ethanol. Subsequently, micro gears were successfully debound by a multistep heating schedule.
