Crystals grown with the help of an electron beam solve a 200-year-old geological mystery

A mystery that has haunted materials science for 200 years has finally been solved. The mineral found in many ancient rock formations has strongly resisted scientists’ efforts to grow it in the laboratory, although they have been able to recreate the conditions that they believe formed it in nature. Now, a team has solved the problem, and discovered how to grow dolomite crystals quickly for the first time.

Dolomite is a very important mineral, there is all of it Mountain chain It was named after him. In addition to these peaks in the Italian Alps, dolomite is abundant in the White Cliffs of Dover, the Hoods of Utah, and other rocks dating back more than 100 million years. It actually accounts for approximately 30% of the minerals of its type – carbonates – in the Earth’s crust, but is noticeably absent in more recently formed rocks.

Despite carefully trying to recreate its natural growth conditions, scientists have failed for two centuries to produce dolomite crystals in the laboratory. To solve the puzzle, they had to go back to basics.

“If we understand how dolomite grows in nature, we may learn new strategies to enhance the crystal growth of modern technological materials,” said corresponding author Wenhao Sun of the University of Michigan in the study. statement.

Dolomite crystals form over geological times through the accumulation of alternating layers of calcium and magnesium. It sounds simple enough, albeit time-consuming, but there’s a catch. When there is water, calcium and magnesium atoms can randomly stick to the edge of the crystal growth, often in the wrong place. These faults prevent alternating layers from forming properly, which is why it takes so long – 10 million years – to create one ordered layer of dolomite rock.

Since Sun and the team didn’t have 10 million years to wait, they turned to powerful software to simulate all the possible interactions that occur between atoms in a growing dolomite crystal.

“Each atomic step typically takes more than 5,000 CPU hours on a supercomputer. Now, we can perform the same calculation in 2 milliseconds on a desktop,” said first author Junsu Kim.

The team landed on a theory. Dolomite may grow faster if it is subjected to cycles where there is a lower concentration of calcium and magnesium on a regular basis. Most crystals grow well in supersaturated solutions, where their atomic components are present at very high levels. As for dolomite, this just leads to more defects and slows everything down.

To test the theory, the team consulted with collaborators at Hokkaido University, and designed an ingenious experiment using transmission electron microscopy.

“Electron microscopes typically only use electron beams to image samples,” explained Yuki Kimura, a professor of materials science at Hokkaido University. “However, the beam can also split water, producing acid that can cause the crystals to dissolve. Normally this is a bad thing for imaging, but in this case, dissolution is exactly what we wanted.”

A small crystal of dolomite in a solution of calcium and magnesium was exposed to an electron beam, which was pulsed 4,000 times over the course of two hours, to begin dissolving the crystal. When the beam is turned off, the surrounding solution quickly corrects itself to a more saturated state.

This works like magic. After this treatment, the team was thrilled to notice that the crystal had grown by approximately 100 nanometers. This may not seem like a lot, but it represents 300 newly formed layers of dolomite. The most that had been achieved in the laboratory before was five.

The results are also consistent with what has been observed in nature. There are only a few locations where dolomite forms today, but they are all places with cycles of flooding followed by drier conditions.

Solving the dolomite problem is a major achievement. “This discovery opens the door to studying the geochemical process that influenced the formation of massive dolomites in the natural world,” Juan Manuel García Ruiz, who was not directly involved in the work, wrote in an article. Point of view accompanying the study.

Not only that, but learning how to grow defect-free crystals quickly could have important applications for manufacturing many vital components of products such as semiconductors, solar panels and batteries.

“In the past, crystal cultivators who wanted to make flawless materials would try to cultivate them very slowly,” Sun said. “Our theory shows that you can grow defect-free materials quickly, if you dissolve the defects periodically during growth.”

The study is published in Sciences.