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THE QUOTE ABOVE acknowledges one of the greatest James Bond movie lines. In answer to 007’s “Do you expect me to talk?,” Goldfinger replies, “No, Mr. Bond. I expect you to die.” Today at SimanaitisSays, AAAS Science reports on a significant development in manufacturing: ultrafast laser welding of ceramics. Here are tidbits gleaned from this article and my Internet sleuthing.
Laser Basics. The first laser, i.e., Light Amplification by Stimulated Emission of Radiation, was devised in 1960 at Hughes Research Laboratories in Malibu, California. Thus, the laser in the James Bond movie Goldfinger, 1964, confirmed its villain’s early adopter status.
Compared with other light sources, a laser’s principal benefit is its coherence, its tightly focused beam. Familiar applications include laser pointers and, at higher power, cutting, welding, and lithography. Yesterday’s “Bubblegram Memories” here at SimanaitisSays addressed yet another laser application.
What Makes Ceramics Special? Ceramics, the word related to Ancient Greek κέραμος, kéramos, “potter’s clay,” are a great deal more than artisan materials these days. Porcelain is one ceramic compound. Titanium carbide in space vehicle reentry shields is another. Barium titanate is widely used in electrochemical transducers, ceramic capacitors, and data storage devices.
The Challenge of Ceramic Welding. In “Ultrafast Laser Welding of Ceramics,” Science, August 23, 2019, E.H. Penilla, et al. write, “Modern manufacturing is inconceivable without welding, yet reliable ceramic welding is impossible using standard procedures. The same high-temperature resistance that makes engineered ceramics irreplaceable for many demanding applications poses immense obstacles in joining ceramics…. Instead of convenient in-atmosphere, room-temperature welding procedures available for metals and polymers, state-of-the-art ceramic joining involves high-temperature diffusion bonding.”
This technique, though, takes a long time, exists for only a limited number of ceramics, and is feasible for only high-cost components.
Ultrafast Lasers. Researchers Penilla and colleagues at University of California, San Diego, and University of California, Riverside, employed ultrafast (UF) pulsed lasers to mitigate the macroscopic cracking in ceramic welding attributed to thermal shock. The researchers developed two different techniques suitable for specific applications.
Transparent Ceramic Encapsulation. A typical fabrication has an electronic/optoelectronic device within in a transparent ceramic. Here, the challenge is to weld a ceramic cap achieving a hermetic seal without damaging the device within.
The researchers report, “Because the UF laser deposits energy locally, the temperature in most of the assembly is unchanged, which allows temperature-sensitive materials or components such a polymers, metals, or electronic payloads to be encased without damage…. This is useful for communications as well as wireless electronic charging of optoelectronic devices that can be encapsulated.”
UF Version of Conventional Welding. To weld two opaque ceramic cylinders, the researchers focused the laser on a small gap between them. The idea of the gap was to give the laser a limited but adequate access to both pieces.
The ceramic tubes have outer diameters of 12 and 18 mm, about 0.5 and 0.7 in., respectively.
Subtleties of Operation. The researchers studied various aspects of UF welding, including angular rotation of the ceramics being welded.
Angular rotations of 30 degrees/second, 50 degrees/second, and 80 degrees/second corresponded to laser pulse doses of 100,000, 50,000, and 25,000, respectively. Based on ceramic object size, diameters from 0.5 to 0.75-in., welds at these rotational rates took from around 2 to 20 seconds.
Researchers found that the slowest rotation rate degraded the sample through ablation (erosion by heat); the most rapid one resulted in nonuniform welds.
Applications. Hermetic sealing of encapsulated devices has application in military, space, and bio-implantable electronics. Researchers also note, “Our welding concepts should be helpful for producing ceramic micromechanical systems, lab-on-a-chip devices, and biocompatible or chemical- and temperature-resistant electronic and optoelectronic packaging.”
Their techniques are energy-efficient as well. The researchers say that a high-temperature furnace typically consumes around 1000 W with a 5-hour bonding time. Thus, its energy consumption is around 5000 W∙h. By contrast, the researchers’ UF laser had a maximum power of 50 W, and assuming an optical power conversion of 10 percent, its short welding times allow for an energy consumption on the order of 25 W∙h.
By the way, Bond was neither welded nor carved, neither shaken nor stirred by Auric Goldfinger’s laser. ds
© Dennis Simanaitis, SimanaitisSays.com, 2019