Platinum, a rare and lustrous precious metal, is celebrated for its beauty, density, and resistance to corrosion. It holds a significant place in both luxury goods and industrial applications due to its unique combination of properties. A common question is: how hard is platinum compared to other commonly known metals?
What “Hardness” Means for Metals
In materials science, “hardness” refers to a material’s resistance to permanent deformation, such as scratching, indentation, or abrasion. Two methods are used to quantify this property: scratch hardness and indentation hardness.
The Mohs scale of mineral hardness, a qualitative scale from 1 to 10, measures scratch resistance. It determines which material can scratch another, with diamond (10) being the hardest and talc (1) the softest. For more precise resistance to indentation, industrial scales like the Vickers or Knoop hardness tests are employed. These methods use a diamond indenter to create an impression, and the indentation size calculates a numerical hardness value.
Platinum’s Hardness and Comparisons
Pure platinum is relatively soft, registering approximately 3.5 to 4.5 on the Mohs scale and 40 to 56 HV on the Vickers scale. However, platinum used in most applications, especially jewelry, is alloyed with metals like iridium or ruthenium for enhanced strength and durability.
These alloys significantly increase its hardness. For instance, common platinum alloys used in jewelry can have Vickers hardness values ranging from 80 HV to 250 HV, depending on the specific composition. In comparison, pure gold is notably softer, with a Mohs hardness of 2.5 to 3 and a Vickers hardness around 15 to 30 HV. Sterling silver also falls in a similar range on the Mohs scale (2.5-3) but can reach 60 to 150 HV when alloyed. Stainless steel, a common industrial metal, is harder than platinum alloys, typically ranging from 4 to 6 on the Mohs scale and around 150 to 200 HV. This means that while pure platinum is softer, its common alloyed forms are much more resistant to wear than pure gold or silver.
Why Platinum’s Hardness Matters for Its Applications
Platinum’s hardness profile, particularly when alloyed, contributes to its suitability for diverse applications. In jewelry, its relative hardness and density are beneficial, allowing it to securely hold gemstones in settings and resist wear. While it can scratch, platinum does not lose material; instead, the metal is displaced, leading to a unique patina over time that can be polished back. This characteristic enhances the longevity of platinum jewelry.
Beyond adornment, platinum’s hardness, combined with its exceptional chemical inertness and resistance to corrosion, makes it invaluable in industrial and medical fields. It is used in catalytic converters, where its stability withstands harsh chemical environments. In medical implants and dental work, its biocompatibility and durability against wear are highly valued. The ability to create alloys with varied hardness levels allows engineers to tailor platinum for demanding uses, ensuring both durability and performance where other metals might fail.