Why Do Diamonds Last Forever?

Introduction

The phrase “diamonds are forever” is often used to emphasize the durability and enduring nature of diamonds, but this statement requires some clarification. In reality, diamonds do not last forever; they can degrade over time into graphite, which is a more stable form of carbon under typical conditions. This process involves complex interactions at the atomic level and is influenced by various factors such as temperature and pressure.

The Structure of Diamonds and Graphite

Diamonds and graphite are both crystalline forms of pure carbon, but they differ significantly in their atomic arrangement and bonding:

• Diamond: Each carbon atom is bonded to four neighboring carbon atoms, forming a tightly packed three-dimensional grid. This structure imparts hardness and stability to diamonds.

• Graphite: In contrast, each carbon atom in graphite is bonded to three neighboring carbon atoms in a planar structure. The planes of atoms in graphite are loosely bonded to each other, allowing them to slide over one another, which is why graphite feels slippery and is used in pencils.

Energy States and Metastability

The concept of energy states is crucial in understanding why diamonds can degrade to graphite. Diamonds are in a metastable state, meaning they are not in the lowest possible energy configuration. The degradation of diamond to graphite can be thought of in terms of a potential energy landscape:

• Imagine standing at the bottom of a small hole (representing the energy state of diamond) next to a deeper hole (representing the energy state of graphite). A wall separates you from the deeper hole, preventing you from falling in.

• To move from the diamond state to the graphite state, energy must be supplied to overcome the barrier (the wall). This energy input can come from heat or other forms of energy, such as ion bombardment.

Kinetic Barriers and Degradation

Although graphite is thermodynamically more stable than diamond, there exists a significant kinetic energy barrier that must be overcome for the conversion to occur. Under normal conditions, the kinetic energy of the carbon atoms in diamond is relatively low, and thus the transition to graphite is extremely slow—often taking millions to billions of years.

As a result, for everyday human uses, diamonds can be considered to last for an extraordinarily long time, making the phrase “diamonds are forever” a good approximation in a human time-scale context.

Conditions Affecting Degradation

1. Temperature: At higher temperatures, the atoms in diamond gain kinetic energy, making it easier for them to overcome the energy barrier and transition to graphite. This degradation will be accelerated when diamonds are subjected to excessive heat.

2. Ion Bombardment: Similarly, when diamonds are bombarded with ions, the energy supplied can facilitate the reconfiguration of the carbon atoms into graphite.

3. Pressure: Deep within the Earth, where the pressure is significantly higher than at the surface, diamonds are the most stable form of carbon. Under these conditions, they do not degrade to graphite.

4. Combustion: It is also important to note that diamonds can combust in the presence of sufficient oxygen at high temperatures, turning into carbon dioxide rather than transforming into graphite.

Conclusion

In summary, while diamonds are incredibly durable and can last for an exceptionally long time under normal conditions, they are not immune to degradation. The stability of diamond is contingent upon the surrounding environment, particularly temperature and pressure. Thus, while they may not last “forever,” they can endure for millions to billions of years, especially in conditions that are typical for human use.