Shulou(Shulou.com)11/24 Report--

Metals occupy 94 of the 118 elements in the periodic table.

Among them, there are gold, silver, copper, iron, tin and other well-known metals, as well as rare elements such as ruthenium, indium, tantalum, and artificial elements such as curium and nobelium. With such a rich variety, metals are destined to make a strong mark in material science.

A slightly surprising phenomenon is that metals that can be widely used are usually not pure metals, but made into substances called alloys. Such substances-alloys-consist of two or more chemical elements (at least one of which is a metal), such as binary alloys, ternary alloys, and multicomponent alloys. They also have some characteristics of metals, but they can change the limitations of pure metal properties and become superior performance materials to meet various needs.

For a long time, metals have influenced the development of human civilization.

Generally speaking, entering the Bronze Age is a sign of entering civilization. For example, bronze is widely used to mint coins. Civilization entering the Iron Age begins to mature. As for the far-reaching industrial revolution, it is supported by steel.

By the late Iron Age, most parts of the world had entered the age of written civilization, the use of iron tools eliminated stone tools, and promoted the rapid development of productivity. The era mentioned here usually refers to an age in archaeology, such as the Bronze Age generally refers to an era after the Copper Age in archaeology. Bronze is an alloy of red copper and tin, so it is also called tin bronze.

China in the Shang Dynasty (16th century BC-11th century BC) is a highly developed Bronze Age, the establishment of a bronze smelting industry. As early as 3000 BC, Mesopotamia and Egypt had entered the Bronze Age. After Qin and Han Dynasties, in addition to bronze, there were some other copper alloys. The earliest copper-zinc alloy, common brass. Brass is the general term for copper-zinc alloy. Later, white copper, that is, copper-nickel alloy, appeared.

Even though modern society no longer labels a metal, that doesn't mean it's no longer important. On the contrary, more new metals have come into use. Aluminum, titanium, magnesium and other elements complement each other and become indispensable metal materials in life. It is difficult to say which metal defines the new era.

In gold shops, we can find gold of high purity, its purity is the fineness, generally expressed in parts per thousand. For example,"full gold" refers to gold with a purity of more than 990‰ and impurities not exceeding 1%,"full gold" has a purity (gold content) of more than 999‰, and so on.

Source: pexels In fact, it is impossible to make it reach 100% in smelting, so it is usually called full gold or full red with purity above 999.6‰. However, these high-purity gold only symbolizes wealth, but it is not an ideal jewelry material. On the one hand, pure gold will only show gold, inevitably a little monotonous; on the other hand, more importantly, pure gold is too soft.

In the hands of skilled goldsmiths, gold jewelry could be made into exquisite hollow shapes, but one had to be very careful when wearing such jewelry. If it was knocked or touched, it might deform, and naturally it would not look so good.

Therefore, gold is often alloyed to make it easier to use. The initial fusion may have been simply to reduce the value of each piece of gold and facilitate trade-after all, a small gold bead the size of a grain of rice can be exchanged for a large bag of rice, which would not have been lost so easily if it had been melted with other ordinary metals to increase its volume.

In fact, we still call pure gold 24-karat gold, a relic of this method. The ancient gold traders weighed the different components of the metal into 24 equal parts, each of which was a Karat (the word was also used in other jewelry transactions, became the unit of mass of gemstones, and evolved into "carats." 1 carat equals 200 milligrams (1 carat equals 205.3 milligrams is the old system before 1913), and its auxiliary unit is minutes, 1 carat equals 100 minutes. To avoid confusion, karat, which stands for gold purity, is written as carat in English, and how many parts of it are gold is how many karats of gold.

24K gold is the general name in life, such as 18K gold decoration is the purity of 18/24, that is, the color of 750‰. If the fineness of gold decoration is expressed as "Cheng," 900‰ gold decoration is called nine Cheng gold.

Apparently, this method divides gold into 24 different purity grades, with the higher the number, the higher the purity. Although this "goldenness" is no longer practical today, 18-carat or 14-carat gold is still common, usually an alloy of gold and silver. Compared to pure gold, they are harder and more varied in color, although the value is reduced, but the jewelry made is still very popular.

Gold was the first precious metal used by humans, and gold artifacts dating back to the birth of local civilizations have been found in many parts of the world. This is not a coincidence, but simply the nature of matter.

In the billions of years since the formation of the solar system, the earth has undergone countless earth-shaking changes. The "earth-shaking" here is not exaggeration-no matter the climate environment or geological structure, there has never been a moment of calm on the earth, and there is also a fierce collision between elements.

The solar system originated from a dead giant star, which released various elements in the form of supernova explosions, some of which made up the main body of the earth. The early Earth was hotter than it is now, and there was flowing lava everywhere, which meant that the denser parts would sink to the bottom because of gravity.

The exploration of the structure of the earth by modern technology has indeed turned out this way: the cooled rocks cover the outer surface and constitute the crust of the earth, which is very thin, less than 1% of the radius of the earth, but where we live; those rocks that remain hot form the mantle, which is more like a layer of heated softened candles, constantly wriggling, and some of them have become flowing magma, which is also part of the main body of the earth; Scientists speculate that heavier metals such as iron and nickel form the core of the earth and penetrate deep into the earth's interior under high pressure.

The Earth onion model figuratively says that the Earth is a giant egg-thin shell, sticky white, and a yolk in the middle. Of course, we can also adopt a more elaborate analytical model, dividing the earth into concentric spheres, peeling off layers like onions, each layer giving a name, which is necessary for geology.

But most of the time, the division of crust, mantle, and core is sufficient. Further, the core can be divided into two parts: the inner core and the outer core. The outer core is about 2900~5100 km deep and is presumed to be liquid. The inner core is about 5100 km below the earth's core.

It is reported that in 1970, Soviet scientists super drilling engineering team drilled holes in the earth, vertical drilling reached 12262 meters deep, becoming the deepest hole on earth. Gold is much denser than iron, and it naturally falls into the core with the movement of the earth's interior-with our current technology, we simply cannot mine the gold sleeping in the core of the earth.

Fortunately, the lava in the mantle is so viscous that it slows down the process of gold sinking. At the same time, sulfur, ranked 16th on the periodic table, combined with gold in time under the action of high temperature and pressure, becoming part of the rock in the form of sulfide. The hot mantle squirmed, searching for weak spots in the crust, pushing against it like a chicken about to hatch.

All of a sudden, somewhere on Earth, there was a landslide, earthquakes and volcanoes, dust rising into the sky, lava pouring out. It is in this process that gold sulfides also follow magma to the surface. As the pressure on the surface plummeted, gold separated from sulfur and became a free metal, clinging to rocks formed when magma cooled and solidified.

After a long geological evolution, the hard stones in the past became loose under the destruction of rain, snow and frost, and all kinds of microorganisms and mosses and weeds came to join in the fun. Eventually, after a long process known as weathering, the rock broke and rolled into the valley, where it continued to be ground into fine sand, and the gold was left on the beach. Most of the main gold producing areas on the earth are located in river valleys. The upper reaches of the Yangtze River are called "Jinsha River" for nothing. The "Jinsha" here is indeed rich.

Most metals are not as lucky as gold.

Copper, for example, although it goes through the same process as gold from lava to the surface, its bond with sulfur is too strong to separate when it reaches the surface. Even after prolonged weathering, copper sulfides remain strong and require some means of conversion to metallic copper. So until today, chalcocite is still an important raw material for smelting copper, and its main component is cuprous sulfide (Cu2S).

Iron and copper have similar experiences, and iron that is lucky enough not to fall into the core remains on the surface in various ways. Chalcopyrite is abundant in nature, and its main component is called copper ferrous sulfide (CuFeS2), which is actually a combination of iron and copper sulfides.

But iron has another good partner besides sulfur-oxygen. During weathering, oxygen in the air combines with iron to form more stable oxides. The soil in southern China is brick-red because it contains a large amount of red iron oxide (Fe2O3).

Compared to gold, copper and iron cannot be directly used by humans, but need to be smelted to obtain free metals. The principle of smelting is not complicated, as long as copper or iron is stripped from their respective ores. However, this requires energy, as well as components that carry impurities such as sulfur or oxygen away from the ore.

As a result, the actual operation became very difficult. Humans have mastered the skill of using fire for hundreds of thousands of years, but the history of copper smelting is only 6,000 or 7,000 years, and the history of iron smelting is only 3000 years.

Generally speaking, iron smelting technology was invented at the end of primitive society, marking a new stage in the history of metallurgy. The history of human forging iron was also around 1400 BC. In China, iron was used in most areas in the late Spring and Autumn Period (5th century BC).

However, like gold, copper and iron are usually alloyed to improve their properties.

There are many kinds of alloys of copper. Bronze and brass were invented by the ancients. They are the results of copper mixed with tin (or lead) and zinc respectively. The ancient Chinese also invented an alloy of copper and nickel that looks like silver and is still used to make coins.

The most famous alloy of iron is steel, which is formed by iron and carbon, and the mass fraction of carbon is between 0.025% and 2.06%. If the carbon content is higher, it is called pig iron. Pig iron does not deform easily, but it cracks easily; if it has a lower carbon content, it will be called wrought iron, which is actually close to pure iron and as soft as belt. Therefore, iron is usually processed into steel for reuse. With the support of modern technology, there are more and more types of steel, such as manganese steel commonly used in machinery, tungsten steel that can be used as bulletproof deck, stainless steel that is not easy to rust, and so on. What about more metals? Their fate is not even as smooth as iron and copper.

Aluminum, for example, is the most abundant metal element in the earth's crust. After a long evolution, most of this element combines with oxygen to form a mineral called bauxite (Al2O3). The bond between aluminum and oxygen is very strong, so it is extremely difficult to extract aluminum from ores. The ancients could not extract aluminum by smelting copper or iron. It was not until electricity was invented and widely used that the process of electrolytic aluminum smelting was invented.

Even so, because of the strong binding force of the ore, its melting point is too high, so it is necessary to add a flux to it-as the name suggests, this is to help the ore melt. This flux is called cryolite because it can play a role in lowering the melting point, and its main component is sodium hexafluoride (Na3AlF6). Aluminum is also not the most difficult metal to smelt.

At the bottom of the periodic table, there are usually two more rows, called lanthanides and actinides. They should have been placed in the third column of the periodic table, but this would have made the table too long, so the usual printed edition truncated them to the bottom.

Most actinides are man-made elements, and Earth stocks are extremely low, with only a few valuable elements, such as thorium and uranium, mainly used in nuclear power plants.

Lanthanide elements can be different, it contains 15 elements, together with scandium and yttrium already in the third column of the periodic table, together known as rare earth metals. These metal elements have unique skills and can be used in many high-tech equipment. For example, there is an element called neodymium, which can be used to make strong magnets. Therefore, rare earth elements are often referred to as "industrial vitamins."

However, smelting rare earth elements is not easy. Not only would they have a high melting point, like aluminum, but the elements were so similar that it was difficult to separate them, like finding one from multiple identical twins. Until now, few countries have mastered the full range of separation technologies.

There is a scientist named Xu Guangxian (1920-2015) in China who has long seen the great value of rare earth elements. It is also under his leadership and appeal that China's rare earth extraction technology is now leading the world. Some people call him China's "father of rare earths."

From gold to rare earths, humans have spent thousands of years, but they have still not been able to thoroughly study the world of metal substances. Most metals have not yet found their most suitable uses, which remains to be developed by us.

Source: "Teaching Material Science to Teenagers"

Author: Sun Yafei

Some of the pictures in this article come from the Internet

copyright belongs to the original author

Editor: Zhang Runxin

This article comes from Weixin Official Accounts: Origin Reading (ID: tupyread), Author: Sun Yafei

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.