It is a belief that when materials are made of the same compounds, they are exactly similar. Seashells and chalk are perfect examples because they are both made of calcium carbonate crystals, but they are completely different in terms of strength.
A new study reveals the secret behind why seashells and lobster claws are hard to break, but chalk can break easily with just a little force. Though all of these are made of the same material, the harder ones are made of clusters of soft biological matter that contributes to their strength to withstand pressure, damage and force.
In the study published in the journal Nature Communications, researchers from the Pacific Northwest National Laboratory (PNNL) found that such clusters combine through chemical reactions with atoms inside the crystals, which was an unforeseen mechanism based on past knowledge. By using the new findings, scientists may someday improve new supplies and materials for ecological energy.
"This work helps us to sort out how rather weak crystals can form composite materials with remarkable mechanical properties," said Jim De Yoreo , one the study's author and a materials scientist at PNNL's Department of Energy.
He added that their finding may provide insight for trapping carbon dioxide in useful materials. This may help deal with excess greenhouse gases in the atmosphere. It may also be used in solar energy applications.
Calcium Carbonate And Its Strength
Considered as one of the most essential materials in the world, calcium carbonate helps in crystallization of chalk, shells and rock. Many animals use this compound to create biominerals like seashells, exoskeletons and pearls.
In humans, biominerals can also be produced inside the body – like the small bones in the ears that help in balance and equilibrium. Containing organic matter and proteins, biominerals convert weak calcium into hard, robust and durable materials.
Many studies had focused on how organisms were able to produce these biominerals. And scientist have been trying to shed light on the basic geochemical principles that form and in turn, construct synthetic materials that have unique properties.
In the experiment, the scientists created spheres out of organic molecules dubbed micelles. Using atomic force microscopy, they were able to observe how calcium carbonate combines proteins and other strength-inducing materials into the structure.
When they added the micelles into the water mixture, and the speheres started growing as calcite envelops it layer by layer. During the formation, calcite generates uneven surfaces, which researchers described as "an array of steps and terraces."
They found that micelles do not casually land on the flat terraces, but rather, they only attach themselves to the edges of the steps. The micelles become compressed like springs that create the strain in the lattice between them.
The material's strength relies on how easy it is to interrupt the underlying crystal matrix. If the material is compressed, it will become very strong and harder to break. If it is less dense, it can be broken apart easily.
The proteins trapped inside crystals of calcium carbonate produce a strain within the structure. This is helpful in making the materials harder to disrupt the crystal structure making it more durable and stronger.
"These results give new insight into the formation of occlusions in natural and synthetic crystals, and will facilitate the synthesis of multifunctional nanocomposite crystals," the study said.
Photo: Phu Thinh Co | Flickr
