Do you think metals are all silvery white? Wrong! In fact, they are all black!

Since the late 20th century, society has entered the era of informatization, globalization and knowledge from the industrial age. The development of social productivity has continuously increased the requirements for materials. At the same time, due to the rapid development of science and the maturity of material production technology, other types of materials have also developed rapidly, but the status of metal materials as the most important structural and functional materials has always been difficult to shake.

Among all kinds of materials, metal can be said to play the role of "pillar". Look around you, there must be something made of metal or involved in the making of metal. A most vivid example is the mobile phone that everyone cannot live without. Without metal, it will become a useless brick.

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01

Black is colorful black

When you think of metal, what comes to your mind? Is it a necklace with glittering gold, or pots and pans with shining metallic luster? I don’t know if you have noticed that whenever we think of metal, we never seem to associate it with black, but “ferrous metal” is indeed a large category of metal!

The word "black" can easily lead people to mistakenly believe that ferrous metals must be black, and non-ferrous metals must be colorful. Based on this, many people believe that silvery-white iron, chromium and silver-gray manganese should not be "black" metals. So why are these three and their alloys classified as ferrous metals?

The reason is this: ferrous metal is a general term for iron, chromium and manganese in industry, and also includes alloys of these three metals. In fact, pure iron and chromium are silvery white, while manganese is silvery gray. Since the surface of steel is usually covered with a layer of black ferroferric oxide, and manganese and chromium are mainly used to smelt black alloy steel, they are mistakenly considered to be "ferrous" metals.

Steel and gold represent ferrous metals and non-ferrous metals respectively. Copyrighted images from the gallery. Reproduction is not authorized.

02

The battle between the two major metal schools

The official definition of a metal is "a material that has a lustrous luster, good electrical, thermal and mechanical properties, and a positive temperature coefficient of resistance."

Metals are a big family with 86 members in total. People usually divide them into two "schools" based on their color and properties: ferrous metals and non-ferrous metals. Ferrous metals mainly refer to iron, chromium, manganese and their alloys, such as steel, pig iron, iron alloys, cast iron, etc. Non-ferrous metals refer to metals other than ferrous metals, also known as non-ferrous metals, which are a general term for all metals other than iron, chromium and manganese.

Periodic table of elements, copyrighted image, unauthorized reproduction

Not only do the two have different names, their production is also very different! Due to the large variety of non-ferrous metals, the number of their mineral deposits is much greater than that of ferrous metals. Although there are fewer ferrous metal deposits, the output of each deposit is very high, making the total output of ferrous metals reach 95% of the world's metal production! In addition, iron, chromium, and manganese are the main raw materials for smelting steel, and steel occupies an extremely important position in the national economy and can also be used as an important symbol to measure a country's strength.

03

Interesting origin of the name

“Nonferrous Metals” is translated into “Nonferrous Metals”, which corresponds to the English translation of “Ferrous Metals”. According to an old man who has been working in the nonferrous metal industry for a long time, the process of translating “Ferrous Metals” and “Nonferrous Metals” into “Ferrous Metals” and “Nonferrous Metals” is also an interesting story.

The scholar who first translated "Ferrous Metals" and "Nonferrous Metals" believed that if they were directly translated as "ferrous metals" and "nonferrous metals", or "ferrous metals" and "nonferrous metals", although the accuracy of the translation was taken into consideration, it was not concise enough and was also very difficult to use. So this scholar jumped out of the inertial thinking and started from the optical properties of metals to recreate the translation.

Pure iron is silvery white, but the iron that people often see in their daily work and life is black. This is because the surface of the iron is covered with a layer of black oxide film: ferroferric oxide. It is also because of this oxide film that iron leaves people with a black impression. From this perspective, "Ferrous Metals" is creatively translated as "black metals".

Rusty steel and pure steel Image source: Advanced Steel Materials Research Department, Institute of Metal Research, Chinese Academy of Sciences

With the existence of "ferrous metals", and considering that silver is white, gold is golden, copper is yellow, and lead is gray, "non-ferrous metals" present colorful optical properties, so "Nonferrous Metals" was translated into "non-ferrous metals". From then on, "ferrous metals" and "non-ferrous metals" became "Ferrous Metals" and "Nonferrous Metals" in Chinese and spread in the industry.

04

Metal, the backbone of social development

Metal materials can be said to be the promoter of human social development, because they have played a pivotal role in various transformation periods of human society. In the history of human social development, the Bronze Age and Iron Age that followed the Stone Age were marked by the application of metal materials.

Bronze tripod with animal face pattern Image source: Palace Museum

After World War II, the progress of science and technology promoted the development of new materials. Ductile iron, alloy cast iron, alloy steel, heat-resistant steel, stainless steel, nickel alloy, titanium alloy and cemented carbide were successively developed and applied in actual production.

In modern times, the research and development of metal materials is no longer limited to the traditional pure metal and pure alloy directions. With the improvement of basic theory and process technology, new metal materials have been rapidly developed. These include nanometals, high/medium entropy alloys, high-temperature structural materials such as directional solidified columnar crystals and single crystal alloys, metal matrix composites, and shape memory alloys [1-4].

Various metal materials have become an important material basis for the development of human society. Agricultural modernization, industrial modernization, national defense and scientific and technological modernization all rely on the support of metal materials. From small farm tools, machinery parts, and daily necessities to large advanced weapons such as airplanes, missiles, rockets, satellites, nuclear submarines, as well as components or parts required for cutting-edge technologies such as atomic energy, television, communications, radar, and electronic computers are mostly made of metal.

At present, many countries in the world, especially industrially developed countries, are competing to develop metal and nonferrous metal industries and increase strategic metal reserves. It can be said that metal materials are essential basic materials and important strategic materials for the national economy, people's daily life, national defense industry, and scientific and technological development.

References:

[1] K. Lu, Making strong nanomaterials ductile with gradients, Science 345(6203) (2014) 1455-1456.

[2] W. Xu, B. Zhang, XY Li, K. Lu, Suppressing atomic diffusion with the Schwarz crystal structure in supersaturated Al–Mg alloys, Science 373(6555) (2021) 683-687.

[3] Q. Pan, L. Zhang, R. Feng, Q. Lu, K. An, AC Chuang, JD Poplawsky, PK Liaw, L. Lu, Gradient cell–structured high-entropy alloy with exceptional strength and ductility, Science 374(6570) (2021) 984-989.

[4] P. Shi, R. Li, Y. Li, Y. Wen, Y. Zhong, W. Ren, Z. Shen, T. Zheng, J. Peng, X. Liang, P. Hu, N. Min, Y. Zhang, Y. Ren, PK Liaw, D. Raabe, Y.-D. Wang, Hierarchical crack buffering triples ductility in eutectic herringbone high-entropy alloys, Science 373(6557) (2021) 912-918.

Source: This article is produced by Science Popularization China, produced by Liu Tengyuan (Institute of Metal Research, Chinese Academy of Sciences), and supervised by China Science Popularization Expo

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