From the golden hoop to the American team's shield, this material is indispensable

In Journey to the West, Sun Wukong's golden hoop that can hold up the sky and sweep away thousands of troops; in the Marvel Universe, Wolverine's cold, silver-shining claws; Captain America's indestructible, sleek and shiny shield; and Iron Man's majestic, handsome and cool armor, these "handy weapons" are the most iconic business cards of superheroes. However, looking at all these ancient and modern magic weapons, both at home and abroad, they actually have a common name - alloy .

Alloy kitchen knife

(Photo source: veer photo gallery)

From the magic weapons of superheroes to the kitchen knives of ordinary people, why are alloys used instead of pure metals without exception? What are the irreplaceable advantages of alloys compared to pure metals? This has to start with the origin of alloys .

Part 1

Alloys that have witnessed the development of history

Alloy refers to a solid product with metallic properties obtained by mixing and melting a metal with another or several metals or non-metals, cooling and solidifying. From this point of view, an alloy is a mixture composed of other metals or non-metal elements added to a pure metal .

Materials often become the symbol of an era. In addition to the ancient Stone Age, the use of metals such as aluminum in the Bronze Age and Iron Age in the past hundred years is inseparable from alloys. Bronze is the earliest alloy in the history of metal smelting . It is an alloy composed of pure copper (red copper) with tin or lead added.

As early as the Xia Dynasty, about 5,000 years ago, there are records of people smelting bronze ware in China . The heyday was during the Shang, Western Zhou, Spring and Autumn, and early Warring States periods, which lasted for about 1,600 years. The bronze ware of this period was mainly divided into ritual instruments, weapons, and miscellaneous items. The Zenghouyi chime bells and the Sword of Goujian, King of Yue, are representative bronze ware of this period and are national treasures handed down from generation to generation. Although they have been dormant for more than 2,000 years, their bells are still soul-stirring and their swords are still as sharp as iron.

Zenghouyi chime bells (left) and the Sword of Goujian, King of Yue (right)

Image source: veer gallery

The transition period generally refers to the period from the end of the Warring States Period to the end of the Qin and Han Dynasties. With the collapse of rituals and music, the ritual system constructed by bronze ware gradually disintegrated. The major national affairs were sacrifices and wars. With the emergence of iron in weapons and sacrificial supplies, people began to usher in the Iron Age.

Ironware is an alloy composed of metallic iron and carbon. According to the proportion of carbon in it, it can be divided into pig iron, wrought iron and steel . In fact, in nature, the reserves of iron are much higher than copper. The reason why bronze came before it in terms of time is that the temperature required for iron smelting is relatively high, reaching 1500℃, and people in the Bronze Age could not reach this temperature and process requirements.

Han Dynasty Ironware

(Photo source: Zhengzhou Guxing Han Dynasty Iron Smelting Site Museum)

Part 2

How are alloys stronger than pure metals?

First of all, strictly speaking, there is no 100% pure metal on earth. All metals we come into contact with belong to the category of alloys. Because from a scientific point of view, metals cannot be 100% pure, and it is impossible to test whether they are 100% pure. Therefore, the so-called "pure gold" and "pure silver" in the gold and silver market are only close to 100% purity. Unless the non-gold and non-silver atoms are picked out one by one, 100% pure gold and silver can be obtained, which is obviously impossible to achieve.

However, current refining technology can already produce metals with a purity of 99.999%, and their application performance is no different from that of 100% pure metals. So in layman's terms, we can call metals with a total impurity content of less than 0.1% pure metals.

Image source: veer gallery

Secondly, alloys have some unique advantages that pure metals do not have . For example, the hardness of alloys is generally greater than that of their matrix, the so-called solid solution strengthening. For example, the hardness of aluminum alloys is much greater than that of pure aluminum. However, there are some exceptions, such as sodium-potassium alloys, which are liquid and used as thermal conductors in atomic reactors).

The electrical conductivity and thermal conductivity of the alloy are lower than that of any of the component metals. This property of the alloy can be used to manufacture high electrical resistance and high thermal resistance materials, as well as materials with special properties; some alloys have stronger corrosion resistance than any of the component metals, such as adding 15% chromium and 9% nickel to iron to obtain corrosion-resistant stainless steel.

Part 3

Alloy weapons of various magical powers

The description of the golden hoop in Journey to the West is "The hoop is made of nine-turn iron, forged in a furnace by Laojun himself. King Yu sought it and called it a divine treasure, and the four seas and eight rivers were used as verification." The nine-turn iron here is actually stainless steel, an iron-carbon alloy native to Iran, India and other places, and introduced to China during the Southern and Northern Dynasties .

Image source: TV series "Journey to the West"

In the Ming Dynasty, high-quality weapons were made of stainless steel. After the surface was polished and treated with a corrosive agent, the pattern was visible, and it was called "Bin Tie" . "Laojun forged in the furnace with his own hands" refers to the forging technology that is indispensable in stainless steel processing, which is the process of gradually hardening steel. And combined with the following sentence "four seas and eight rivers are the test", it proves that the golden hoop can be placed in both fresh water and sea water without corrosion and rust, which once again verifies the speculation that its material is stainless steel.

According to the original novel, Wolf's claws and Captain America's shield are both made of adamantium, although this alloy does not exist on Earth. Among Iron Man's many armors, titanium alloy armor occupies the most important position.

Wolverine's claws (left) and Captain America's shield (right)

Image source: Movies "Wolverine" and "Captain America"

Titanium alloy is an alloy made by adding aluminum, vanadium and other metals to titanium . Compared with alloy steel with sufficient strength, titanium alloy is very light; compared with aluminum alloy with sufficient density and lightness, titanium alloy has high enough strength and heat resistance, so it becomes the first choice in fields that require light weight and high strength, such as aerospace. Moreover, titanium alloy has good affinity with the human body, so artificial bones such as prostheses and dentures are also mostly made of titanium alloy.

At present, there are only 108 metal elements discovered by humans, and through the arrangement and combination of different metals with different contents, thousands of alloys with different properties can be formed . Therefore, alloys have a broader design and processing space and more possibilities, which can continuously meet the development of human civilization.

References:

[1] Wu Chengen. Journey to the West[M].

Produced by: Science Popularization China

Produced by: XY Dalian Institute of Chemical Physics, Chinese Academy of Sciences Supervised by: China Science Expo

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