Graphite “Hijacks” Diamond Formation: Simulation Shocker

Imagine a world where the carbon atoms destined to form a sparkling diamond are instead diverted, becoming the mundane graphite in a pencil. Researchers at UC Davis and George Washington University have uncovered a surprising mechanism that explains how this “carbon hijacking” can occur.

A new study published in Nature Communications throws into question long-held assumptions about diamond formation, with implications for everything from planetary science to industrial manufacturing. The research, led by Professor Davide Donadio at UC Davis, uses powerful machine learning-enhanced molecular simulations to observe carbon crystallization under extreme conditions, mimicking the pressures and temperatures deep within Earth.

Studying the crystallization process of molten carbon, which occurs rapidly and under intense conditions, has always been a challenge. These conditions are incredibly hard to replicate in a lab setting. But these simulations have now made it possible, and they’ve yielded some rather unexpected results.

Unexpected Crystallization: Graphite Steals the Show

The team’s simulations revealed that graphite can spontaneously crystallize even under conditions where diamond should be the stable form. This contradicts conventional wisdom and offers an explanation for inconsistent results seen in previous experimental studies.

“This was a suprise because normally simulating crystallization is much more complicated than that,” said Donadio. “We were even more amazed to observe graphite crystallizing spontaneously at pressures up to 15 GPa—conditions where diamond should be the stable form.”

The findings point to a phenomenon known as Ostwald’s step rule, where materials don’t always form directly into their most stable state, but rather through intermediate, metastable phases. Graphite, it turns out, acts as a “stepping stone” in diamond formation, as its structure bears a closer resemblance to liquid carbon’s density and bonding patterns. This mean that graphite, when present, can “hijack” the crystallization pathway, preventing diamond from forming directly.

“The liquid carbon essentially finds it easier to become graphite first, even though diamond is ultimately more stable under these conditions,” explains Professor Tianshu Li from George Washington University. “It’s nature taking the path of least resistance.”

For decades, the inconsistent laboratory findings surrounding the conditions under which diamonds formed had stumped researchers. This simulation may have solved that mystery. The team created models at pressures between 5 and 30 gigapascals (GPa), and watched what happened as the molten carbon cooled from 5,000 to 3,500 Kelvin (K). They observed that at high pressures, diamond formation was favored, but at lower pressures, graphite spontaneusly took over.

These findings explain why natural diamonds are so rare. The simulation suggests that graphite formation is much more probable than scientists previously understood. This reality has implications for everything from planetary science to material design, and everything in between.

• Planetary Science: Understand the carbon cycle in Earth and other planets.
• Diamond Synthesis: Improve industrial diamond production.
• Quantum Computing: Achieve greater control over crystal structures.

A local gem cutter, Elias Vance, whose family has worked with diamonds for generations, shared his thoughts on the study’s impact: “I’ve always known there was more to it than just pressure and heat. There’s something else, some little kick that makes a diamond, well, a diamond. This research…it kinda makes sense. Life would never be quite the same,” he said thoughtfully, holding a rough stone up to the light.

The research has implications for understanding Earth’s deep carbon cycle, which affects our planet’s climate and geology over vast stretches of time. Additionally, these insights can be used to refine industrial processes for synthesizing diamonds, particularly for advanced applications like quantum computing where precise crystal structures are required. Controling the crystallization pathways could lead to a new wave of materials with precisely controlled structure.

The team’s simulations not only revealed *why* graphite can form where diamond is expected, but also showed *how* the crystallization processes differ at a molecular level. Graphite forms in elongated, column-like structures, while diamond crystallizes through compact crystallites. The key takeaway: small differences in the intitial conditions can lead to radically different outcomes.

One surprising consequence of the research is how it challenges the notion of complete control in manufacturing. A seemingly simple process , cooling molten carbon , is actually a complex interplay of factors where unexpected phases can emerge. This has led to some discussion on X.com with many people posting about how this could change the jewelry business. One commenter wrote, “So my fiance’s ring could have been a pencil tip? Crazy!”, while another jokingly posted, “Graphite: the ultimate diamond imposter”.

Moving forward, the researchers hope to refine their models and explore the influence of other elements on the carbon crystallization process. This could eventually help to perfect the process by which diamonds are created in the laboratory and make *them* more attainable, while also granting scientists greater insight into planetary science. This new understanding of these fundamental processes has the potential to reshape various aspects of technology and our understanding of the Earth itself.