Gold is a metal that has captivated human interest for thousands of years due to its rarity, beauty, and unique properties. It has been used for various purposes, from ancient jewelry to modern electronics. One of the key attributes of gold is its resistance to corrosion and tarnish. This article delves into whether gold rusts and explores its chemical and physical properties in detail.
Understanding Gold’s Chemical Properties
Gold, with the chemical symbol Au, is a transition metal that belongs to group 11 of the periodic table. It is characterized by its shiny, yellow luster and high density. Gold is chemically inert, meaning it does not react easily with other elements or compounds. This property plays a crucial role in why gold does not rust.
Gold’s Resistance to Oxidation
Rusting is a type of corrosion that occurs when iron reacts with oxygen and moisture in the environment, forming iron oxide. This process is known as oxidation. Gold, however, does not undergo this reaction due to its chemical stability. The metal is highly resistant to oxidation because its atomic structure does not easily lose electrons.
Gold’s inertness stems from its electron configuration. The electrons in gold’s outer shell are tightly bound, making it difficult for gold atoms to lose electrons and participate in oxidation reactions. As a result, gold remains unaffected by environmental conditions that would typically cause other metals to corrode or rust.
The Role of Gold’s Atomic Structure
Gold has a face-centered cubic (FCC) crystal structure, where each gold atom is surrounded by twelve neighboring atoms. This close packing of atoms contributes to gold’s stability and resistance to chemical reactions. The FCC structure ensures that gold atoms are well-shielded from external chemical attacks, further enhancing its resistance to corrosion.
Does Gold Rust?
While gold does not rust, it can tarnish under certain conditions. Tarnishing in gold typically involves the formation of a thin, discolored layer on the surface. This tarnishing is often due to the presence of alloying metals used in gold jewelry, such as copper or silver. These alloys can react with sulfur compounds in the air, leading to tarnish. However, pure gold (24 karat gold) is less prone to tarnishing than gold alloys.
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While gold does not rust, it can still experience some forms of corrosion under extreme conditions:
- Aqua regia
- High-temperature oxidation
- Chemical reactions with chlorides
Rust vs. Tarnish
To understand why gold does not rust, it’s crucial to distinguish between rusting and tarnishing:
| Aspect | Rusting | Tarnishing |
|---|---|---|
| Reaction Type | Oxidation (redox reaction) | Corrosion involving sulfur compounds |
| Chemical Reaction | Iron reacts with oxygen and moisture to form iron oxide (rust). | Metal reacts with sulfur or sulfur-containing substances to form sulfides or other compounds. |
| Appearance | Typically reddish-brown, flaky layer | Usually a dull or discolored film, can be black or gray, depending on the metal |
| Environmental Factors | Moisture, oxygen, and sometimes acidic conditions | Sulfur compounds in air or other environmental elements |
Gold Alloys and Their Properties
Pure gold is 24 karats and is too soft for many practical applications, so it is often alloyed with other metals to improve its durability. Common gold alloys include:
- 18k Gold: Composed of 75% gold and 25% other metals, such as copper or silver. This alloy is more durable than pure gold but can still tarnish over time.
- 14k Gold: Contains 58.3% gold and 41.7% other metals. This alloy is more resistant to scratching and tarnishing but still can show signs of wear.
Why Gold is Less Prone to Corrosion?
Gold’s chemical stability is a key factor in its resistance to corrosion. Unlike other metals, gold does not readily form oxides or sulfides. This is due to the high ionization energy and low reactivity of gold atoms. Additionally, gold does not react with acids, bases, or other common corrosive substances, making it an ideal material for various applications where durability and resistance to environmental factors are crucial.
1. Lack of Reactivity with Acids
Gold is famously unreactive with most acids. It does not dissolve in hydrochloric acid, sulfuric acid, or nitric acid, which are commonly used to test and clean other metals. However, gold can dissolve in a mixture of hydrochloric and nitric acids known as aqua regia, but this is a specialized process not typically encountered in everyday conditions.
2. Stability in Different Environments
Gold maintains its luster and appearance even in harsh environments, including exposure to air, water, and various chemicals. This stability makes gold a popular choice for jewelry and decorative items, as it retains its beauty and does not tarnish over time.
Gold’s Behavior in Various Environments
Gold is celebrated for its remarkable durability and resistance to various environmental factors. Here’s a detailed look at how gold behaves in different environments:
- In Air: Gold does not rust or corrode in air. It remains unchanged even when exposed to oxygen. This is because gold does not react with oxygen at normal temperatures and pressures.
- In Water: Gold is also unaffected by water. Unlike iron, which can oxidize in the presence of moisture, gold maintains its integrity in both fresh and saltwater.
- In Acidic and Alkaline Environments: Gold is resistant to most acids. However, it is dissolved by a mixture of hydrochloric acid and nitric acid known as aqua regia. Aqua regia is capable of dissolving gold because it produces chlorine and other reactive species that interact with the gold.
- Exposure to Other Chemicals: While gold does not rust, it can be affected by certain chemicals. For example, gold can be tarnished by substances containing sulfur, leading to the formation of gold sulfide. This tarnishing does not involve rusting but rather a surface discoloration.
Gold’s Practical Applications
Gold’s resistance to rust and corrosion makes it highly valuable for various applications, including:
- Jewelry: Gold’s aesthetic appeal and durability make it a popular choice for fine jewelry.
- Electronics: Gold’s excellent conductivity and resistance to corrosion make it ideal for use in electronic components and connectors.
- Medical Devices: Gold is used in medical implants and devices due to its biocompatibility and resistance to corrosion.
Does Gold Tarnish?
Pure gold, or 24-carat gold, is virtually immune to tarnish because it does not react with oxygen or moisture. However, the tarnish resistance of gold items can vary based on their alloy composition.
Gold is often alloyed with other metals to enhance its properties. For instance:
- White Gold, alloyed with platinum or palladium, is more resistant to tarnish.
- Rose Gold, which contains copper, may tarnish more easily.
In the UK, gold must be at least 37.5% pure (9 carat or 375 fineness) to be legally called gold. In the US, the legal minimum is 10 carat. Different alloys affect wearability and appearance, with higher carat golds like 18 or 22 being more lustrous but softer and more prone to scratches.
Overall, while pure gold does not tarnish, the addition of other metals in gold alloys can influence tarnishing and corrosion resistance.
How Should You Clean Gold Jewelry?
If your gold jewelry looks a bit tarnished, what’s the best way to restore its shine? Start with a simple cleaning method: wash the gold in warm water with a few drops of mild dish soap. Gently scrub with a soft brush or cloth, then dry thoroughly with a soft cloth. For extra shine, use a polishing cloth to gently rub the surface. A soft cotton swab can help with hard-to-reach areas.
Is it okay to use toothpaste or baking soda? Generally, a simple wash is sufficient for real gold. However, when it comes to valuable or collectible gold coins, it’s best to avoid cleaning them yourself to prevent potential damage. Instead, seek advice from a professional for proper care.
Does Fake Gold Rust?
Fake gold, often referred to as gold-plated or gold-filled items, can rust or tarnish depending on its composition. Unlike solid gold, which is highly resistant to rust and tarnish, fake gold is typically made by applying a thin layer of gold over a base metal, such as brass or copper.
Here’s how different types of fake gold can react:
- Gold-Plated Items: These are coated with a thin layer of gold over a base metal. Over time, the gold plating can wear off, exposing the underlying metal to oxidation and tarnish. This can lead to rust or discoloration, especially if the base metal is prone to rust.
- Gold-Filled Items: These have a thicker layer of gold bonded to a base metal, which makes them more durable than gold-plated items. While gold-filled items are more resistant to tarnishing and rusting compared to gold-plated pieces, they can still develop tarnish over time, particularly if the base metal is exposed.
Does White Gold Rust?
White gold does not rust. White gold is an alloy of gold and other metals, such as nickel, palladium, or platinum, which give it its white color. Gold itself is highly resistant to rust and corrosion. Regular cleaning and proper care can help maintain its appearance and prevent tarnishing.
Conclusion
In summary, gold does not rust because it does not oxidize like iron. Its inherent stability and resistance to corrosion make it a preferred material for jewelry, coins, and various industrial applications. However, gold alloys can tarnish or become discolored over time due to the presence of other metals and environmental factors. Proper care and maintenance can help preserve the appearance and value of gold items.
Understanding these aspects of gold helps in appreciating its unique properties and ensures that gold items remain beautiful and valuable for years to come.
More Resources:
gold melting point – Source: BOYI
is gold magnetic – Source: BOYI
FAQ
To remove red tarnish from gold, clean it with a mixture of mild dish soap and warm water. Gently scrub with a soft cloth, rinse, and dry. For persistent tarnish, use a baking soda paste or a gold jewelry cleaner. Avoid abrasive materials and harsh chemicals.
Gold does not corrode in saltwater. Due to its high resistance to oxidation and corrosion, pure gold remains unaffected by saltwater. However, gold alloys, which mix gold with other metals, might be more susceptible to tarnish or corrosion depending on the alloy’s composition.
No, 24k gold does not tarnish. As pure gold, it is highly resistant to oxidation and corrosion. However, it can still get scratched or show signs of wear over time, but it will not tarnish like other metals.
18k gold, which is composed of 75% pure gold and 25% other metals, does not rust. Gold itself is highly resistant to rust and corrosion. However, the other metals in the alloy can affect its tarnish resistance.
Catalog: Materials Guide
This article was written by engineers from the BOYI team. Fuquan Chen is a professional engineer and technical expert with 20 years of experience in rapid prototyping, mold manufacturing, and plastic injection molding.
