I am Tang Di, a history buff. Welcome everyone [attention] I, let's talk about the past and the present, and discuss the general trend of the world. Gentleman I, just to learn and make friends!
First, the definition of bronze
The definition of "bronze" has both a broad and a narrow sense. "Bronze" in a broad sense refers to all alloys dominated by copper. According to this, bronze is undoubtedly the earliest alloy used by humans. Ancient bronze mainly refers to copper-tin alloys. Modern metal materials science refers to copper and tin alloys as tin bronze, copper and lead alloys as lead bronze, copper and aluminum alloys as aluminum bronze, etc., which is also consistent with this broad definition of "bronze". "Bronze" in the narrow sense refers to copper and tin alloys. If lead is added to the bronze under this definition, it can be called lead bronze, and phosphorus is added, which is called phosphor bronze.
Ancient Chinese bronzes mainly include the following three types:
1. Tin bronze. The composition is mainly copper and tin (content higher than 2%), and trace amounts of other elements (both less than 2%). 2. Lead bronze. The composition is mainly copper and lead (content higher than 2%), and trace amounts of other elements (all less than 2%). 3. Copper, tin and lead ternary bronze. The components are mainly copper, tin (content higher than 2%), lead (content higher than 2%), and trace amounts of other elements (all less than 2%).
The copper mentioned above refers to red copper, that is, natural copper, also known as pure copper. Copper with a copper content of up to 98 to 99% has a red metallic luster, hence the name. In nature, there is a natural pure copper, which has a Brinell hardness of only 35, and can be hammered directly into a device.
Field archaeological findings prove that when copper was first used, it was indeed made directly to make utensils. The earliest known copper ware, found in the pre-Pottery Neolithic site of Chayoni in Turkey, is a drill bead made directly from natural copper ore, a square expansion cone pin, etc., which is about 7500 years old.
In Ariksh, Iran, a small copper bead was found, which was made of 0.4 mm thick copper sheet, and its material was natural copper, dating back to 7,000 BC. A copper needle made from natural copper processing in large quantities was also found in the Northern Mountains of Sialk, Iran, which belongs to the middle of the 5th millennium BC.
The red bronze ware in China's early bronze artifacts excavated in the Qi family cultural sites are also directly shaped.
How was copper discovered?
Scholars have speculated as follows about the discovery of natural copper and how to use it:
Late Stone Age human beings in the search for suitable stone to make stone tools, natural copper is not difficult to find, initially they will also be natural copper ore as stone to make, grinding to make utensils, in practice found that natural copper has a kind of stone can not be compared to the superiority, not as easy to break, peeling, but can be hammered thin, even elongated and copper also emits a pleasing metallic luster, used to make decorations to wear, can decorate and beautify their own lives.
This is probably when natural copper was first utilized. After a long period of practice and many experiments, human beings have realized that heating natural copper to a certain temperature can increase the plasticity of copper, so that natural copper can be forged into slightly more complex shapes according to needs. This practice of directly using natural copper to rely on the method of making utensils has given people a preliminary perceptual understanding of the physical properties of copper as a metal.
Later, primitive humans who used natural copper further found that if the copper was "put into the fire and burned, it would be easier to make it, and to burn it to the highest temperature of the pottery at that time or higher, the red copper could melt, and the molten copper water could flow, and after solidification, it could be condensed into a certain shape with the container." This is the germ of casting. Scholars have pointed out that since the melting point of copper is only 1083 ° C, the temperature of pottery firing in the late primitive society has reached this level, and the temperature of pottery kilns at that time can reach 1000 ° C, or a little higher."
Natural copper is, after all, less, and most of the copper is obtained by smelting copper ore. How was the smelting of copper invented?
Scholars have speculated that it is precisely in order to obtain a variety of materials to make tools and containers, people may burn the stone (bake the stone hot, and then splash it with water to cause it to crack) in order to obtain a certain stone, resulting in metal smelting. If the copper-containing mineral is burned, the copper beads are melted and precipitated, which may lead to the invention of copper smelting. In addition, a pottery kiln or stove made of copper-containing ore may, under certain conditions, reduce the oxidized part of the copper ore to copper, which is another way of copper smelting.
Among the copper ores in nature, a mineral called malachite is the most common, generally early emerald green, bright and dazzling, very easy to find. Malachite often appears with natural copper and has a similar color to copper, so it is easy to think of copper in it. Nitrate is decomposed by heat, that is, it becomes an oxide. Copper oxide ore can be reduced by heating it with charcoal. The original malachite used in ancient China is mostly copper-rich (10 to 20%) copper oxide, which can be smelted directly into the furnace, and the melting point of copper is 1083 ° C, so the melting temperature is about 1100 ° C (or slightly higher).
Some scholars speculate that malachite has attracted people's attention very early because of its bright color, and it has been collected as an ornament.
When "malachite is accidentally put into the furnace fire, the temperature reaches 1083 ° C and there is a reducing agent such as charcoal, malachite can be reduced to copper in a simple furnace, so malachite is melted and reduced to red copper." When this happened many times, people finally learned to smelt red copper with malachite and charcoal."
From the history of human use of metals, although arsenic copper has replaced red copper for a long time and in a considerable geographical range, the mechanical properties (strength, hardness, etc.) of its castings are still relatively close to pure copper castings. Therefore, whether it is pure copper (that is, red copper) or copper alloys such as arsenic copper, they are eventually replaced by tin-copper alloy bronze due to insufficient mechanical properties. Only after tin bronze was invented and applied, metal artifacts could replace stone tools (and pottery) on a wider scale.
Third, why does bronze replace red copper?
So this is because bronze has more advantages than red copper and arsenic copper. Compared with red copper, tin bronze has the following advantages:
(1) The melting point is low. In terms of physical and chemical properties, the melting point of the general alloy is lower than the original metal melting point; the hardness is higher than that of the original metal; and the volume is slightly larger than that of the original metal. The same is true of bronze in copper-tin alloys. The melting point of red copper is 1083 °C, if it is added to 15%, the melting point is reduced to 960 °C; if it is added to 25%, the melting point will drop to 800 °C. Therefore, this temperature condition is obviously easier to obtain than smelting red copper.
(ii) High hardness. The hardness of copper is 35 degrees (Brinell hardness meter), if it is added 5 to 7%, it will increase to 50 to 60 degrees; if it is added to 7 to 9%, it will increase to 65 to 70 degrees; if it is added to 9 to 11%, it will increase to 70 to 80 degrees, which is more than double the hardness of red copper. In this way, the softer texture of the above-mentioned red copper can be overcome. At the same time, because the hardness of bronze is proportionally increased with the amount of tinning, people can increase or decrease according to the needs of different types of instruments, choose various different proportions, and cast utensils with different alloy hardness.
(3) Suitable for casting. The casting performance of red copper is poor, it is easy to absorb air, and the products made in the hefan casting are often with gas eyes and rough surfaces. Bronze becomes liquid when melted, the fluidity is very strong, the hole is not human, the volume is slightly enlarged when condensing, it can fill the device fan, the filling is good, and there are few pores.
Due to the above three advantages, that is, it has good casting performance, so that bronze has a wide range of adaptability in applications. After people gradually understood the properties of bronze, they began to use copper-tin symbiotic ore to refine bronze, or consciously extracted from tin ore tin mixed with pure copper, and later developed to mix different specific amounts of tin to cast bronze utensils for different purposes.
Tin bronze is not only significantly superior to red copper in performance, but also has more advantages than arsenic copper:
The strength of tin bronze with a tin content of more than 10% increases significantly, while the solid melt strengthening of arsenic copper is relatively slow; the processing hardening rate of the two is comparable, and the hardness of tin bronze with the same content is higher than that of arsenic copper; the tensile strength of tin bronze with the same alloy content is also greater than that of arsenic copper. Although arsenic copper has better hot forging performance than tin bronze, this advantage is naturally overlooked when using casting rather than forging methods to manufacture bronze. In addition to the above reasons, tin bronze eventually eliminated arsenic copper, arsenic copper in the smelting process will produce a highly toxic gas, endangering human health is also an important factor. Therefore, humans must have consciously replaced arsenic with tin to make copper alloys.
How is bronze discovered?
There seem to be two possible ways of how bronze was invented:
First, it was gradually invented in the long-term practice of smelting red copper, and only by first learning to make red copper can it be possible to further master the bronze alloy technology.
The earliest red copper refined from ore, of course, can not reach the purity of natural copper, which contains some impurities brought from the ore, such as a small amount of lead, tin, iron, etc., but because of the small content of tin and lead, it can not be called later bronze. However, people may have inadvertently recognized this alloy close to bronze, and gradually realized that this alloy has many advantages over pure copper (red copper), so they began to consciously smelt red copper first, and then add tin to prepare bronze.
Second, some scholars have pointed out that bronze and bronze smelting are not all through the way of smelting copper, but there is another way to be discovered.
They point out that when metal ores were first mined, one way was to grill the rock with fire and then water it to crack the ore. When tin bronze contains 25% tin, the melting point is only 800 °C, if the ore is a copper-tin symbiotic ore, it is not difficult to obtain bronze in a charcoal or dry wood flame of about 800 °C. This is probably how the first bronzes were found. This long-term accumulation of experience, combined with the technical conditions provided by the pottery industry, will lead to the conscious refining of bronze.
There is a copper-tin symbiotic ore containing 0.94% tin and 12.3% copper, which can be smelted with a copper and tin ratio of 93:7, that is, 7% tin-containing bronze. In contrast, smelting pure copper is not easy, because the melting point of pure copper is 1083 ° C, and although copper oxide ores such as malachite and azurite can reduce copper at temperatures below the copper melting point, it is also necessary to raise the temperature to melt copper and transform the chalcedony or useless rock orogenic minerals into slag, otherwise the copper is still impregnated and cannot be used.
Obviously, the second route above must be possible if there is a copper-tin (or copper-lead) symbiotic ore near the copper smelting site, so this route is only suitable for some areas with such geological and mineral conditions.
Why was copper discovered and used by humans first and not iron?
There is also a related question, that is, why was copper discovered and used by humans first and not iron?
According to the research of scholars, this is mainly due to:
(a) There is natural copper on Earth and very little natural iron. Natural iron has a kind of so-called "onshore iron", which is the so-called granular iron obtained by reducing the iron oxide in the magma when it comes into contact with the coal seam when it is ejected through basalt. This type of iron is found in only a few isolated areas (e.g. Greenland). Iron is easily oxidized, and most of the iron on earth is present in the form of oxides or other compounds, and only iron containing nickel can last without rust. Meteoric iron that falls on celestial bodies has natural iron. Humans generally use meteoric iron later than copper.
(2) In ancient times, iron ore was not easily distinguished from ordinary stones, unlike malachite, which was easy to attract attention because of its special beautiful color.
(3) The melting point of iron is 1537 ° C, which is much higher than the melting point of copper, although in fact, the reduction temperature of iron ore does not need to be so high, but the low temperature is slow to reduce the speed, so it has no meaning for actual production, and the iron produced at low temperature is easy to oxidize when cooling, resulting in rust (iron oxide).
(4) When iron is extracted from iron ore, it is initially spongy, dark and dull, and must be heated and hammered to remove the dregs, unlike copper, which is shiny as soon as it is refined.
(5) Primitive iron - pig iron is brittle, and wrought iron is soft and not hard, only after the invention of the quenching and forging method (heating that is, rapid cooling in cold water) can increase the hardness, better than bronze.
For the above reasons, human use of metals can only start with copper, not from iron.
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