Fabrication and calibration of ultrafine capillaries having diameters between 0.5 and 60 μ

Abstract

Micro-openings having diameters from 0.5 to 60 μ, lengths from 100 to 4000 times the diameter, and regular cylindrical geometry were needed for studies of flows of gases and liquids. Comparison of predicted flow rates with those measured through these openings would serve as a basis for the prediction of leakage rates of toxic materials through small holes in container walls. A literature search uncovered numerous methods for making small holes in materials, but none of these seemed to be capable of covering the entire dimensional range of interest or especially for producing the smaller-diameter micro-openings. Two new methods of producing micro-openings having diameters spanning the required range and meeting requirements for regular cylindrical geometry were therefore developed. The first, called the cylindrical mount method, involved drawing quartz tubing to the desired diameter, filling the tubing with a low-melting metal alloy, casting the microtubing in epoxy resin, slicing the specimens of the cast material with a cutoff wheel, polishing the ends, and removing the metal alloy. The second, called the disk mount method, consisted of drawing quartz tubing to the desired diameter, drilling a hole in a thin metal disk, inserting the microtubing in the hole, cementing it in place, and then breaking off the ends of the microtubing to the approximate desired length. The cylindrical mount method successfully produced micro-openings with regular cylindrical geometry from 5 to 60 μ in diameter. The disk mount method produced micro-openings of the same quality in the diameter range from 0.5 to 5 μ.