Researchers from North Carolina State University are using powdered eggshells to make high-quality magnesium alloys that could be used in an array of automotive, aerospace and biomedical applications. And while Americans consume roughly 275 million eggs every single day, we certainly have a substantial waste stream to work with.
The researchers believe the eggshells could help create a low-cost, more sustainable alternative to conventional calcium materials made from mined ore in energy-intensive processes. Calcium materials, like calcium carbonate and calcium oxide, are used in a wide variety of applications.. Eggshells are 95% calcium carbonate, and the process the researchers use converts it into calcium oxide and nascent calcium.
The benefits of this proof-of-concept project are many, including fewer steps in the supply chain and a more reliable, sustainable one. Also, eggshells are cheap and plentiful. I just blasted a half dozen down the garbage disposal this morning.
So, how do they do it?
First, they drilled a series of evenly spaced holes into a cylindrical block of magnesium. The holes are filled with finely ground eggshells and the block is placed into a steel cylinder.
A steel mandrel with a hole in the center is then lowered into the cylinder. The mandrel presses down on the magnesium block while spinning it at 300 rotations per minute. This process is called friction stir extrusion.
As the mandrel presses down and spins, the eggshell powder and magnesium mix, creating friction between the particles of eggshell and the metal. The friction converts the calcium carbonate into calcium oxide and produces the high-strength alloy Mg2Ca, magnesium two calcium, which can be used in biodegradable medical implants that are designed to dissolve in the body and lightweight body panels in cars or interior structures in planes.
The downward pressure produces the extruded rod of the finished product. You can see it just above that eggshell in the photo.
If anything the project proves that agricultural waste can be upcycled into advanced lightweight materials with a scalable, relatively inexpensive process.
