Excimer Laser Processes Ceramic Spinnerettes
Michael D. Wheeler
MÜNSTER, Germany -- A new procedure that employs an excimer laser emitting at 248 nm shows promise for the fabrication of ceramic spinnerettes.
Spinnerettes are small nozzles typically made of a metal alloy that are used in the production of synthetic fibers. They usually feature small holes through which a viscous solution is extruded to form a filament. The solution, which is prepared by melting or chemically dissolving raw material, emerges from the spinnerette as long fibers that are solidified during cooling.
Increasingly, industries have been drawn to the prospect of fabricating spinnerettes out of ceramic for the intrinsic advantages that the material offers over metal. The problem, however, has been to devise a way to fabricate the microstructures in the brittle ceramic with a high degree of accuracy and repeatability.
To address this shortcoming, researchers at Münster Technical College's laser center have applied a laser-based machining technique similar to semiconductor lithography. A KrF excimer laser illuminates a pattern mask that bears the desired geometry of the spinnerette, and a beam-guidance system ensures that the laser energy stays on target.
Emitting 30- to 50-ns pulses and reaching energy densities of 25 J/cm2, the high-intensity beam efficiently carves a pattern in the ceramic substrate.
"With every laser pulse, a layer of the substrate approximately 100 nm [thick] is removed," explained Clemens Lammers, team leader for the project.
This continues until the laser beam works through all the material and the design is complete. According to the researchers' findings, the processing time for a 200-µm-thick ceramic plate is less than 20 seconds at a repetition rate of 100 Hz.
To date, Lammers' team has used the method to process ceramic spinnerettes of numerous geometries with a high degree of accuracy but minimal thermal damage to the surrounding substrate. The researchers have tested the spinnerettes using a computerized system that analyzes the effects on the fiber of roundness, taper and roughness in the spinnerettes and analyzes the reproducibility of the technique.
The method also may find applications in electronics, sensors and medical instruments where thin ceramic is used.
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