History of Metals
Why and how did man first begin to use metals How did he extract them without the advanced technology and knowledge that we have today, as early as 6000 BC
As human society developed and became more advanced, human needs increased. Human groups began to change from a nomadic lifestyle to a settled lifestyle. They created settlements, began to cultivate the land and kept animals. As these became more complex, human needs expanded and required a wide range of things, such as tools, building supplies, hunting, defense, cooking, worship, storage, etc. A material was needed that could be easily shaped to suit all these needs, and that was hard, strong and did not decay or burn easily. Metals fit all these categories and are ideal for all these basic human needs. The only problem was the difficulty of finding and extracting metals. So at fist humans shaped pieces of stone and wood to suit their needs, but it soon became obvious that metals, due to the above properties, were far superior. This was discovered when small amounts of metals were accidentally discovered and experimented with.
The first metals would have been naturally occurring metals, especially the then-abundant metal gold, and silver and platinum in smaller amounts. As these are relatively unreactive elements (to the right of the Activity Series), they do not easily form compounds with other elements, so they can be found as uncombined, pure metals underground. For example, gold can be found as nuggets or veins in quartz or grains in alluvial sands. The element copper, although more reactive than gold and silver, is occasionally found as an uncombined element, sometimes even as large underground pockets. Natural uncombined iron was also sometimes discovered, but this was not from underground but from space ??“ meteoritic iron. All these metals could be stumbled upon and experimented with by an inquisitive human of the Neolithic Age, and it properties, such as lustre, strength and malleability would be noticed easily. With the discovery and use of fire, shaping these metals into useful objects and tools was made much easier. These metals were the first to be used, but they were not discovered often enough, nor were they plentiful resources, so metalworking did not become an economical process for many thousands of years.The vast majority of metals occur not as uncombined elements, but as ores. An ore is any naturally occurring source of a metal, usually consisting of the metal and a number of minerals and impurities, and from which the metal can be economically extracted. Depending on the ore and the metal it contains, different methods are required to extract the metal. Today we use methods such as electrolysis and reaction with acids and reactive metals, but 6000 years ago, the only method available was heat. Smelting (using heat to extract metals from their ores) is still used for the majority of metals today.
Generally, the less reactive a metal is, the easier it is to extract. The more reactive it is, the more energy and processes are required to extract it. In other words, as you progress along the activity series of metals from right to left, the extraction of those metals gets harder and requires more energy and work and a greater number of processes. The least reactive metals such as gold and silver, as explained above, require almost no work to use, as they do not need to be extracted from ores. But even the one of the least reactive metals that is found in ores, copper, requires relatively high temperatures to extract economically. Small beads of copper can form if the ore is heated in a simple wood fire, which was the only source of heat for a long time, but not enough to make a good tool, container or weapon. These beads have been discovered as ancient jewelry at some archaeological sites in modern day Turkey.Very specific conditions are required for copper to smelt from its ore. The ore needs to be heated to at least 1084?°C (the melting point of pure copper), and it must be heated in an oxygen-starved and carbon-rich atmosphere. A simple wood or charcoal camp fire would burn at only about 600 – 700?°C. Small copper beads could occasionally form, if the fire was heated by fanning it, and since the area just above the coals is relatively oxygen-starved, due to the production of carbon monoxide. This would have worked better with lead, which is just before copper on the activity series. The main ore of lead, galena (lead sulfide, PbS), can be smelted into lead in camp fire conditions, as the melting point of lead is only 327?°C. This could be discovered when people would light camp fires without knowing that there were ores lying around, that they may have used to build the fire. After this discovery, humans might have started experimenting with other rocks to see if they could get anything useful out of them. This of course would not have been very useful as galena is practically the only ore that can be smelted with those primitive conditions. So how did humans discover the secret of copper smelting It most likely happened accidentally. Although we don??™t know for certain how this happened, it can be concluded that the development of pottery and heating in pottery kilns was linked to the discovery of metal smelting. Both the first pottery artifacts and the first smelted copper artifacts have been found from around the same time ??“ about 6000 BC. Also, the only place where the high temperatures of over 1000?°C and the oxygen-starved atmosphere could be found in 6000 BC was in an ancient pottery kiln. So the secret of copper smelting was probably accidentally discovered, and simultaneously in different areas, by inquisitive potters who experimented with different rocks in their kilns. One of the major copper ores, which was most likely the first to be used, is the bright green malachite (a copper carbonate mineral, Cu2(CO3)(OH)2 ). Due to its colour and vivid appearance, a potter might have tried to decorate his pots with its crushed form, using it as paint. This would then turn into metallic copper after a long time of firing in the kiln. After a while, people would have discovered that heating malachite and other minerals in kilns gave them copper, a very useful metal when it was polished, hammered and shaped. But how does simply heating the ore result in the extraction of pure metallic copper It can be explained chemically. When the ore malachite is heated to high temperatures, the carbonates in it break down to release water vapour and carbon dioxide, leaving behind the ionic compound copper oxide:Malachite (copper carbonate) heat copper oxide + carbon dioxide + water (vapour)
Cu2(CO3)(OH)2 (s) heat 2CuO(s) + CO2(g) + H2O(g) When the copper oxide is heated to an even higher temperature (about 1100?°C), it undergoes an oxidation ??“ reduction reaction. Large amounts of carbon monoxide are given off by the burning charcoal, and this attacks the copper oxide, oxidizing the oxygen atoms to form carbon dioxide, and the remaining copper ion is reduced to metallic copper:
O2- O + 2e- Reduction half-reaction:
Cu2+ + 2e- CuNet equation:
Copper oxide + carbon monoxide copper + carbon dioxide
Cu2+O2-(s) + CO(g) Cu(s) + CO2 (g)Soon humans would begin to deliberately smelt copper, and smelting would become a separate activity to pottery firing. This would allow the smelting and metalworking ???industries??™ to develop. Pottery kilns would become specialized smelting furnaces, smiths would learn the art of metalworking, beating, hammering and casting copper moulds to create a wide variety of copper objects. Miners would dig deliberately for copper ores such as malachite and the similar copper carbonate azurite. After sources of these were exhausted, smelting technology would have developed enough to extract copper from its other ores such as copper sulfides, which are more difficult to smelt. Smelters would develop more convenient methods of smelting copper, such as using bellows to heat the furnace even more and mixing the ore with crushed charcoal to ensure an oxygen-starved, carbon (monoxide) rich environment. They also would have learnt to add special minerals called fluxes to the furnace to help the less dense slag (the melted by-products of smelting, which are the unwanted elements and impurities of the ore) to separate from the denser copper, and which could easily be tapped off to leave behind (almost) pure, molten copper. As these technologies advanced, copper began to be produced ???commercially??™ and would replace many tools that were previously made from stone or wood.
So by 3000 BC, the civilized world was truly into the ???Copper Age??™. Copper ores were actively mined, especially on the island of Cyprus, which has extraordinary copper deposits. Cyprus became the centre of many trade routes and also exported copper to many other locations. In fact, the name for copper is derived from the Latin for ???Cypriot copper??™ ??“ ???aes cyprium??™.
However, due to the relative softness and high melting point of copper, many stone tools were still superior to it, but copper would have been used for simple tools and utensils, and especially for decoration and worship, where strength is not an important property, while lustre and colour are.
Another result that the developments in technology had was to prepare the way for the discovery of superior metals and alloys such as bronze, iron and steel, which would be far superior to stone and copper due to their greater strength. Bronze is an alloy of copper and tin (about 85 ??“ 95% copper, 5 ??“ 15% tin), although other metals can give an alloy with very similar properties. It is superior to copper as it is mush harder, and it is easier to work with and to cast into moulds because of its significantly lower melting point (bronze melts at about 950?°C while copper??™s melting point is 1084?°C). Once it was discovered, bronze began to replace copper and was used everywhere for tools and weapons due to its superior properties. Metalworking and extracting technologies continued to develop at a rapid pace, developing into large industries. Trees were cleared at a large scale for furnace fuel and large mines were opened. This also had many environmental impacts, such as large-scale land erosion and land-clearing. These developments also indirectly contributed to the growing cities and economies of the ancient world.But how did humans first learn the art of alloys Bronze was probably first used not as a deliberately made alloy, but as copper with high percentages of impurities in it. Many copper ores contain impurities which are also transferred into the smelted copper. Some of these impurities are actually beneficial and give copper properties similar to bronze. After careful observation and testing, smelters would have realized that certain ores would make the copper stronger, and would learn to deliberately add these ores and even non-copper ores to get the desired product. The first metal that appeared in smelted copper in large enough proportions to show that it was included deliberately was arsenic. This has a very similar effect on copper as tin does, the component we use today for bronze. Arsenic was used as its ore was much more common than cassiterite (tin oxide, the main tin ore), and was found close to copper ore deposits.
The only problem with arsenic is that it gives off toxic fumes when heated and could have poisoned many smiths. It was soon discovered that tin was the ideal metal for alloying with copper. As tin is rarely found as an impurity in copper ores like arsenic, it is necessary to extract it from a separate ore. Tin is relatively easy to extract, as it is after copper and lead on the activity series. Its ore, cassiterite (SnO), is found as veins in rock such as granite. When the rock is eroded away, the cassiterite is exposed as a heavy, black gravel, which can be panned from river beds like gold. It can be smelted in a similar way to copper, then the two molten metals are mixed to form the alloy bronze. The best proportion is about 10% of tin. The first tin bronze, in which the percentage of tin is high enough to suggest that it was deliberately added, appeared in Mesopotamia around 3000 BC. By 2000 BC, Cyprus was fully into its Bronze Age and began to export large amounts of bronze, although it must have imported tin, which did not occur naturally on the island.The Bronze Age lasted for thousands of years, but soon another metal was discovered that surpassed the properties of bronze ??“ iron. Iron had been known for a long time, as it was found, although rarely, as meteoritic iron. This contained a relatively high percentage of nickel, which prevented it from corroding. The dagger of King Tutankhamen, who died in about 1400 BC, was made out of meteoritic iron.
The problem with extracting iron from its various ores, though, is that iron has a melting point of 1537?°C, which no furnace of the time could reach, even with bellows.Although it is not known exactly when iron started to be smelted from ores, but it is suspected that it was also an accidental discovery. There were a number of copper and iron artifacts discovered in the valley of Timna in Israel. The iron ones had an unusually large percentage of copper in them and the copper ones had a large percentage of iron. These proportions did not fit with those of the iron or copper ores of the area. Based on this evidence, it has been suggested that iron was first smelted as a by-product of copper smelting. This could have happened when iron ores were added into the furnace with the copper ores as a flux, to help slag form and leave the pure copper behind. This was quite probable as an iron ore, siderite (FeCO3) was commonly found with the copper ore malachite. So if these ores were smelted together, the copper would have stringy lumps of iron in it, which would be removed to get pure copper. The bits of iron would be experimented with and it would have been discovered that they were very similar to meteoritic iron. Eventually the iron ore would be added deliberately. Siderite is a metal carbonate just like malachite, so it undergoes a very similar reaction. First the carbonate breaks down after being heated and iron oxide is formed:
FeCO3 = FeO + CO2
Then, just as in the copper smelting reaction, the carbon monoxide from the fuel reacts with the oxide to form carbon dioxide, reducing the iron(II) ion to metallic iron:
FeO + CO = Fe + CO2But how does this happen if the melting point of iron (1537?°C) cannot be reached The iron does not melt but is actually reduced as a solid. So the result is a dense spongy mass called a ???bloom??™ which is mixed with slag and other impurities. These impurities are removed by repeated heating (to about 1200?°C) and hammering to squirt the melted slag out. Eventually the smith would end up with a piece of almost pure iron. This is called ???wrought iron??™.
The problem was that wrought iron was still inferior to bronze, as it was softer and corroded easily. But of course there are many ways of improving pure iron. Today we alloy wrought iron with carbon to form steel, a metal that is much harder than bronze.
Even an addition of 0.3% of carbon to iron makes it as hard as bronze, and raising it to 1.2% makes it much harder. If the percentage is raised to above 2%, the hardness increases dramatically, but it also becomes brittle (it shatters rather than bending). Today we call this high-carbon steel cast iron.But what made ancient smiths discover these techniques if bronze was superior to the iron they first used One suggestion is that tin trade routes were blocked as a result of the Philistine invasions of around 1200 BC, or something else caused a decrease in bronze production, so everyone had to turn to iron as a cheap by-product of smelting copper. Obviously the technologies for alloying carbon with iron that we use today were not available so long ago, so how was steel discovered Carbon did not occur naturally in iron ores as an impurity, as arsenic did in copper ores. This discovery was most likely also made accidentally. As a smith hammered the iron at high temperatures to remove impurities, he would unintentionally cause carbon to alloy with the surface of the iron. This is called carburising and results from the contact with hot charcoal and carbon monoxide gas produced by the burning fuel. So the smith would notice that the longer he hammered an iron blade or tool, the harder it would become. The earliest examples of smiths using this technique of carburising are from about 1200 BC.Then another technique was discovered that made steel even harder. This was called quenching and involved heating an iron blade or tool and cooling it quickly by plunging it into water or oil. The only problem with this was that it made the steel brittle, and could leave cracks on the edge of blades. This was fixed by yet another technique, called tempering, which involved heating the quenched steel to about 700?°C and allowing it to cool slowly. The first smelted iron object was a knife found in a Hattic royal tomb from about 2500 BC. The first quenched steel object was a knife from Cyprus from about 1100 BC. By 1000 BC the Iron Age had fully begun. By 1050 BC 80% of metals used in Athens was iron. Steel was far more superior to any other metal and soon replaced bronze tools and weapons. It is still one of the most commonly used metals today.And that is as far as metals go, at least until the late 1800s. Up to iron (and zinc) on the activity series, the metals can be smelted in furnaces, but after that, the metals are too reactive and form compounds that are too stable to decompose with heat. For example, aluminium needs to be reduced by electrolysis, but first it needs to go through a long process of other reactions and it also needs to be in its molten state, which requires very high temperatures. Other metals, like titanium, need to be reacted with more reactive metals such as sodium or magnesium. Mining and extracting technology has advanced a lot since the time of the discovery of metals on which we base our modern methods. All the processes are made much easier and shorter with the use of machinery and other modern techniques. For example, many physical impurities are removed from ores by the froth flotation technique, where the ore is treated with certain chemicals and the desired elements of it float to the top of the solution.Today we have a wide range of metals that suit our different needs. Steel is alloyed with many other metals such as nickel and chromium to rest corrosion, and others which give it many other properties. Metals that are stronger than steel are used where there is a need for strength, such as titanium in airplanes. Tungsten resists heat so it is used in light bulbs. Aluminium is light, strong and rust-resistant, so it is used for window frames and other household objects. There are many more examples of metals and alloys that are used for specific needs in today??™s society because of their properties.
Due to this massive increase in production and use of metals in the modern era, there have been many negative effects as well, especially environmental ones. Mines are opened up everywhere and affect the surrounding ecosystems, and the by-products and fumes that are released during metal extraction and production also have negative effects on the environment.So today things are much easier. There is practically a metal that can be used to suit every one of our needs. With modern technology we have been able to overcome barriers such as high temperatures and strongly-bonded compounds that were impossible to overcome thousands of years ago. The chronology of the discovery of metals reflects and enforces the activity series of metals. The metals furthest to the right of the activity series, the least reactive metals, were found first as they did not need to be extracted from their ores. As we progress to the left of the activity series, the metals become more reactive, form stronger compounds, are harder to extract from their ores, and were discovered in order of their reactivity. The less reactive metals on the right need to be extracted from their ores with heat, and the temperature required increases for the metals that are further left. After a certain point, the metals are too reactive and form such stable compounds that heat alone is not powerful enough to break the bonds, so other techniques, such as electrolysis and complex reactions must be used.
Today all this is possible, but do we take for granted that our ancestors, thousands of years ago, gave us the basis of metalworking and extraction They used their limited knowledge and resources and made great discoveries that we still use today. They had to make these discoveries as their society developed and their needs grew to require a wider range of materials. Today, do we use materials such as metals only to satisfy our needs, or do we waste materials that we don??™t even need It is important to always consider the effects of our actions and usage of different things, and whether it is really worth something that will become a waste of a material or action.
History of Metals