A diamond can be set on fire, but the process requires extreme conditions. Although a diamond is recognized as the hardest naturally occurring substance on Earth, this property relates to its resistance to scratching and crushing, not its chemical stability under extreme heat. Understanding the fiery fate of a diamond requires examining its fundamental chemical makeup and the specific environment necessary to initiate a reaction.
The Unique Chemistry of Diamonds
A diamond is composed entirely of carbon atoms, making it a pure form of the element. This structure is known as a giant covalent lattice, where each carbon atom is locked into a tetrahedral arrangement with four neighboring carbon atoms. The resulting structure, formed by incredibly strong covalent bonds, is responsible for the diamond’s hardness and density. This tightly knit crystalline structure gives diamonds an extremely high sublimation point, requiring immense energy to break the bonds. A diamond does not melt like metal; instead, if heated high enough in a vacuum, it converts directly into a gas.
The Combustion Reaction
Burning a diamond is a chemical change known as combustion, or rapid oxidation. This process involves the carbon atoms in the diamond reacting with oxygen from the surrounding air. The chemical equation for this reaction is simple: Carbon (C) plus Oxygen (\(\text{O}_2\)) yields Carbon Dioxide (\(\text{CO}_2\)). The result of this reaction is the complete transformation of the solid diamond into an invisible gas. For a perfectly pure diamond, no ash, soot, or residue remains after the combustion is complete.
The energy barrier to break the strong carbon-carbon bonds is high, which is why diamonds do not ignite easily. Once the reaction begins, it is exothermic, meaning it releases heat that helps sustain the reaction. Unlike the burning of wood or paper, the combustion of a pure diamond does not typically produce a visible flame or smoke, but rather a slow transformation into gas.
Necessary Conditions for Burning
The ignition of a diamond requires a combination of two specific conditions: a high temperature and the presence of oxygen. The temperature threshold for combustion is significantly higher than that of common flammable materials. In a normal air environment (about 21% oxygen), a diamond needs to reach temperatures around \(900^\circ \text{C}\) (\(1,650^\circ \text{F}\)) to begin a sustained reaction.
If the diamond is placed in an atmosphere of pure oxygen, the required ignition temperature drops considerably, falling into a range between \(690^\circ \text{C}\) and \(840^\circ \text{C}\) (\(1,274^\circ \text{F}\) and \(1,540^\circ \text{F}\)). This difference highlights the necessity of a high concentration of oxygen to overcome the diamond’s molecular stability. In contrast, if a diamond is heated to extreme temperatures in a vacuum or an inert environment, such as one filled with nitrogen, it cannot combust because there is no oxygen to react with.
Instead of burning, the diamond will undergo a solid-state transformation, converting into graphite at temperatures between \(1,500^\circ \text{C}\) and \(2,500^\circ \text{C}\). These extreme conditions mean that a typical house fire or exposure to a cigarette lighter’s flame is insufficient to destroy a diamond. Jewelers, however, must take precautions when using high-temperature torches to repair or modify jewelry settings, as the localized heat can easily exceed the diamond’s combustion point.