Production of metal microspheres via controlled capillary

Abstract

This thesis presents a novel method to fabricate uniform metal microspheres by a custom-made programmable apparatus via controlled capillary. The programmable apparatus consisted of a programmable module, a robotic mechanical arm and a droplet-formation module comprised of an aluminum cylindrical core that encompassed (1) a material reservoir, (2) a buffer compartment (buffer part) with an embedded heating element, and (3) a cooling compartment (cooling part) with a meter-long glass tube filled with glycerol: DI water solution. The internal heating element could reach a temperature up to 250°C for accommodating a wide range of materials with different melting temperatures, including but not limited to eutectic metal alloys. The size of metal microsphere was determined by a set of programmable parameters executed by the programmable module, to control the air pressure exerted at the orifice of capillary via two independent electronic solenoid valves. The air pressure inside the capillary manipulated the handling time of the molten metal alloy. The molten metal alloy in liquid form was forced out of the capillary under specific air pressure. Molten metal alloy liquid was then segregated to form metal microdroplets when they emerged from the capillary. These microdroplets subsequently entered the meter-long glass tube filled with glycerol and water solution in which microdroplets solidified to form metal microspheres. Bismuth (Bi)-based 117 alloy which forms molten metal at melting temperature of 46.5°C was used to fabricate the metal alloy microspheres. The diameter of the fabricated microspheres ranged from 30 μm to greater than 500 μm. This fabrication technique offers a new prototyping method to produce metal microspheres with good uniformity and yield, with a much lower price tag and reasonable production throughput. Such method offers not only flexibility in production quantity but also versatility in material compatibility and on-demand production. The production module could be, in principal, adopted to a variety of materials for different applications. In this report, the UV-curable polymer microspheres and formation of microdroplet arrays using the custom-made apparatus were also proposed with preliminary experimental results.

Date of Award	2018
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology