Gold has held its value for millennia, prized for its density, rarity, and remarkable resistance to corrosion, which prevents it from tarnishing in air or water. However, the very properties that make it a desirable choice for coinage and jewelry also reveal a significant structural limitation. Gold’s enduring appeal is not based on its physical robustness; in fact, the metal is notoriously soft. To accurately determine which materials surpass gold, materials science relies on three distinct measures of strength: hardness, tensile strength, and chemical stability.
Understanding Gold’s Structural Weakness
Pure gold is one of the most malleable and ductile metals known, properties stemming from its face-centered cubic (FCC) crystal lattice structure. This specific arrangement of atoms allows planes of atoms to slide past one another with minimal friction when stress is applied, enabling the metal to be easily stretched into thin wires or hammered into translucent sheets without fracturing. This flexibility means that gold offers little resistance to permanent deformation.
The softness of gold is evident on the Mohs scale of mineral hardness, where it scores only 2.5 to 3, meaning it can be easily scratched by a fingernail or a copper coin. Its Vickers hardness value is extremely low, around 25 Hv. For comparison, the tensile strength of pure, annealed gold is only about 120 megapascals (MPa). These low values establish gold as a poor choice for any application requiring structural integrity.
Materials That Are Significantly Harder
Hardness is defined as a material’s resistance to scratching, indentation, or abrasion, and gold is vastly outperformed by several materials used in industrial and cutting applications. Diamond, the hardest known material, sits at the top of the Mohs scale with a perfect score of 10 and a Vickers hardness of approximately 10,000 Hv. This disparity illustrates that diamond is orders of magnitude harder than gold, which is why it is used to shape and polish virtually all other materials.
Synthetic carbon-based materials, such as man-made diamond counterparts, also exhibit superior hardness. Tungsten carbide, a cemented carbide used extensively in cutting tools and armor-piercing ammunition, registers between 8 and 9 on the Mohs scale. With a Vickers hardness around 2,400 Hv, tungsten carbide is nearly 100 times harder than pure gold. Specialized ceramics, including boron carbide and silicon carbide, are also designed for wear resistance. These compounds utilize strong covalent bonds within their crystal structures, granting them hardness scores between 9 and 9.5 Mohs, necessary for industrial abrasives and engine components that must withstand constant friction.
Materials With Superior Tensile Strength
While hardness measures resistance to surface deformation, tensile strength measures the resistance to being pulled apart, a metric where modern nanomaterials achieve results that dwarf gold’s capabilities. Graphene, a single layer of carbon atoms arranged in a two-dimensional hexagonal lattice, is often cited as the strongest material ever tested. Its intrinsic tensile strength is approximately 130 gigapascals (GPa), which translates to about 200 times stronger than the best structural steel alloys.
Carbon nanotubes (CNTs), essentially graphene sheets rolled into cylinders, also exhibit exceptional structural integrity. Multi-walled CNTs have demonstrated tensile strengths of up to 100 GPa, with an elastic modulus—a measure of stiffness—approaching one terapascals (TPa). These nanostructures derive their strength from the robust carbon-carbon covalent bonds. They are prized for their unparalleled strength-to-weight ratio, which is important in advanced composite materials for aerospace and high-performance engineering. Advanced steel and titanium alloys, while not reaching the theoretical limits of carbon nanomaterials, still offer structural tensile strengths far greater than gold, serving as the backbone for modern construction and transportation.
Materials With Extreme Chemical Stability
The term “strength” can also refer to chemical stability, or the material’s ability to resist degradation from heat, corrosion, and chemical agents. Gold is known as a noble metal because of its resistance to most single acids, but it can be dissolved by a mixture of nitric and hydrochloric acids known as aqua regia. Several materials exceed gold’s inertness.
Iridium, a member of the platinum group metals, is widely considered the most corrosion-resistant element. Unlike gold, iridium is insoluble in aqua regia and boasts a high melting point of 2,410 degrees Celsius, compared to gold’s 1,064 degrees Celsius. This chemical resilience makes iridium ideal for high-temperature crucibles and electrical contacts. Rhodium, another platinum group metal, is also significantly harder and more resistant to tarnishing and general corrosion than gold, often used as a protective plating. Refractory metals, such as tantalum and niobium, possess exceptional thermal stability and resist heat-induced chemical breakdown. Tantalum, for example, is highly resistant to chemical attack below 150 degrees Celsius, making it a choice for laboratory equipment and chemical processing plants.