The term “platinum gold” refers to a specific class of metal alloys created by combining the noble metals Platinum (Pt) and Gold (Au). Platinum gold is a composite material engineered to leverage the advantageous properties of both metals. These alloys are not a standardized commodity but rather a family of materials whose characteristics change dramatically based on the precise ratio of Platinum to Gold. This combination results in materials with unique mechanical, chemical, and electrical performance suitable for highly specialized applications.
Defining the Platinum-Gold Alloy System
The fundamental science of platinum-gold alloys is described by their phase diagram, which illustrates how the two elements interact at different temperatures and compositions. At high temperatures, Platinum and Gold form a continuous solid solution, meaning the atoms of one metal can be fully mixed with the atoms of the other in a single crystalline structure. However, at lower temperatures, the Pt-Au system exhibits a “miscibility gap,” where the single solution begins to separate into two distinct solid phases, one rich in gold and one rich in platinum. This limited mutual solubility at room temperature is a defining characteristic of the alloy system.
The physical and chemical characteristics of a specific alloy are largely determined by its composition ratio. An alloy with a 70% Gold and 30% Platinum ratio behaves differently from a platinum-rich alloy, such as the 90% Platinum and 10% Gold formulation. The tendency for these elements to separate at lower temperatures allows for heat treatment processes, known as age-hardening, which can significantly modify the alloy’s strength and other mechanical properties. This ability to tailor the material’s internal structure through thermal processing makes the Pt-Au system versatile for industrial use.
Unique Properties of Platinum-Gold Alloys
Combining these two noble metals yields properties superior to either element alone. The addition of platinum to gold, and vice versa, significantly increases the hardness and mechanical strength of the resulting alloy. A particular platinum-gold alloy, consisting of 90% Platinum and 10% Gold, has been engineered to be up to 100 times more wear-resistant than high-strength steel. This durability is not solely due to hardness but is attributed to a unique mechanism where the alloy manages heat generated during friction.
The alloy’s exceptional wear resistance is partly a result of its ability to form a thin, protective carbon film during sliding, behaving like a self-lubricating material. Furthermore, platinum-gold compositions maintain the high chemical inertness characteristic of both parent metals. They are highly resistant to corrosion and chemical attack, remaining insoluble in most strong acids and alkalis. This stability, coupled with their unique surface chemistry, also gives them superior catalytic properties, making them effective for certain low-temperature selective oxidation reactions in chemical manufacturing.
Commercial and Industrial Applications
The superior mechanical and chemical properties of platinum-gold alloys make them indispensable in several high-performance industrial sectors. One of the primary uses is in high-precision electronic components, specifically for electrical contacts and coatings where reliability and longevity are paramount. The ultra-wear-resistant Pt-Au alloy is engineered to replace traditional gold coatings, offering an extended service life for contacts in devices ranging from satellites to consumer electronics. This enhanced durability reduces maintenance costs and improves the reliability of long-life systems.
In specialized manufacturing, platinum-gold alloys are used for spinnerets, high-precision components used in the production of synthetic fibers like viscose rayon. These alloys withstand the combined corrosive action of alkaline solutions and severe abrasive wear. The material is also valued in the medical and dental fields, where its inertness and biocompatibility make it suitable for dental restorations, such as crowns and bridge work. Researchers also utilize Pt-Au alloys in laboratory equipment, such as crucibles, where they offer high strength and resistance to wetting by molten glass at elevated temperatures.
Clarifying Common Terminology Confusion
The term “platinum gold” is frequently a source of confusion for the general public, largely because of its overlap with jewelry terminology. The most common point of confusion is with “White Gold,” which is a distinct alloy typically made by mixing yellow gold with white metals like nickel or, more commonly, Palladium. White Gold usually requires a final plating of rhodium to achieve its bright white, mirror-like finish, which wears off over time. Scientific platinum-gold alloys, by contrast, are engineered for technical performance and do not rely on rhodium plating.
The actual Pt-Au alloys used in high-end jewelry, such as PlatinGold, are highly specific formulations that contain a very high precious metal content, often 950 parts per thousand platinum and a small percentage of gold and other elements like ruthenium. A separate historical source of confusion comes from the Spanish term “platina,” meaning “little silver,” which was the original name given by conquistadors to the unrefined platinum they found mixed with gold.