Researchers are using rare earth metals in alloy powders to create green, flashy sparklers

Sparklers can be a lot of fun – they shimmer, hiss and spit arcs of light onto the floor from handsticks or tubes. But the metals they are typically made of limit what the sparks can look like. Well, researchers in ACS Omega report that rare earth metals in alloy powders can produce flashes that change from gold to green and branch out continuously.

Sparklers are released around the world for holidays and special occasions, providing celebratory accents of light. While their flames can span the colors of the rainbow, the flares they emit are limited to dark red, golden, or bright white light.

Recently, Eike Hübner and colleagues found that burning powdered erbium (Er), a rare earth metal, produces a new color-changing spark, going from golden white to light green. However, the green phase only occurred for a short time and was not really noticeable.

Another fun aspect of sparkler fountains is their branching sparks, which repeatedly burst into multiple smaller particles that flash. Commercially available sparklers usually contain iron-carbon powder for this effect, but metal-metal alloys can also do this. So, Hübner and the team wanted to test whether rare-earth-metal-metal alloys could be used to create entirely new types of color-changing, or branched, sparks.

The researchers individually pressed single metal powders and metal-metal alloy powders containing alkali, transition and rare earth metals into a flame. Rare earth alloys provided more colorful sparks than the single metal powders. For example, ytterbium produced intense green explosive lightning. But when the ytterbium-copper alloy (Yb-Cu) was burned, it continuously released a shower of long sparks that went from golden to deep green.

Then the researchers combined rare earth metal alloys with an ammonium perchlorate and nitrocellulose-based propellant to create smokeless fountains. A pulverized version of neodymium magnets created the most attractive fountain of continuously branching sparks, with each initial “parent spark” firing many more sparks in just a fraction of a second. These tests revealed two promising sparkler materials, although the researchers caution that the formulations will need to undergo further safety testing before they can be used in commercial products.