Speaker 1: Welcome to Brainstuff, a production of iHeartRadio. Hey Brainstuff, Lauren Vogelbaum. Here.
Speaker 1: If you were to follow humanity's genetic trail back through
Speaker 1: the millennia, you'd find primitive creatures fumbling for a foothold
Speaker 1: on a primeval earth, lacking the natural physical advantages of
Speaker 1: other animals. It's a marvel that humans were able to
Speaker 1: claw their way out of the Cenozoic era at all.
Speaker 1: Of course, Homo sapiens had an advantage over most of
Speaker 1: the other animals the ability to make and use tools.
Speaker 1: While they lacked a lion's teeth and claws or a
Speaker 1: deer's defensive antlers, they learned to craft their own tools
Speaker 1: from the world around them. The oldest known tools date
Speaker 1: back two point six million years to a time when
Speaker 1: humans used shaped stone to carry out a variety of tasks.
Speaker 1: After all, a sharpened rock can potentially stab and bludget,
Speaker 1: but also slice, scrape, and pound. In time, humans began
Speaker 1: to specialize their tools, creating everything from arrowheads to pestles
Speaker 1: for grinding grain. But stone is a brittle and inflexible medium. Eventually,
Speaker 1: our ancestors were able to pinpoint more durable and malleable
Speaker 1: materials a first copper, than bronze, than iron. Their capability
Speaker 1: with these materials is one of the modern measures of civilization,
Speaker 1: and between the fifteenth and twentieth centuries, some countries had
Speaker 1: an industrial leg up on the competition due to the
Speaker 1: availability of iron ore deposits. For example, China, India, England,
Speaker 1: the US, France, Germany, Spain, and Russia all have substantial
Speaker 1: iron ore deposits. When you think of the historical importance
Speaker 1: of all of these societies, you can see the correlation.
Speaker 1: Even today, iron makes possible a huge array of products,
Speaker 1: especially the carbon rich commercial iron, which we call steel. Cars, tractors, bridges,
Speaker 1: trains and their rails, tools, skyscrapers, guns and ships all
Speaker 1: depend on iron and steel to make them strong. But
Speaker 1: as common as iron is an Earth's crust, and it's
Speaker 1: our fourth most common element there, making up about five
Speaker 1: percent of the crust by weight, it comes bound up
Speaker 1: in ores, which are basically rocks that contain iron and
Speaker 1: other stuff. So how do we turn a slab of
Speaker 1: rock into a set of stainless steel, surgical instruments or
Speaker 1: a locomotive. Today, let's talk about how iron and steel
Speaker 1: built the modern world. Iron is incredibly useful. It's less
Speaker 1: brittle than stone butt compared to wood or copper, extremely
Speaker 1: strong when properly heated. It's relatively easy to shape into
Speaker 1: various forms using simple tools. It can handle high temperatures,
Speaker 1: wowing us to build fire tongs and furnaces out of it.
Speaker 1: You can also magnetize iron, making it useful in the
Speaker 1: creation of electric motors and generators, which we talked a
Speaker 1: bit about in our recent episode on induction cooking, and
Speaker 1: again it is common in some areas. Iron concentrates and
Speaker 1: ores make up seventy percent of the stuff. Its ease
Speaker 1: of manipulation is why iron and steel were so important historically.
Speaker 1: To refine aluminum, for example, you need access to huge
Speaker 1: quantities of electricity, and to shape it you have to
Speaker 1: cast or extrude it. That's why iron has been used
Speaker 1: for thousands of years, while aluminum didn't really exist in
Speaker 1: any meaningful way until the twentieth century. The reason that
Speaker 1: the tip of the Washington Monument is a pyramid made
Speaker 1: of aluminum is that aluminum was more valuable than gold
Speaker 1: in eighteen eighty four. There may come a day when
Speaker 1: humans become so technologically advanced that iron is completely repla
Speaker 1: placed by materials like aluminium or various plastics or fibers
Speaker 1: made of carbon or glass, but as of now, iron
Speaker 1: and steel are less expensive for many purposes. The only
Speaker 1: real issue with iron and steel is rust, although we've
Speaker 1: come up with lots of solutions for controlling that by painting, galvanizing,
Speaker 1: chrome plating, or even just coating the iron with what's
Speaker 1: called a sacrificial anode that will corrode faster, sort of
Speaker 1: like hiring a bodyguard who will take a bullet for you. However,
Speaker 1: before iron can be put to any of these uses,
Speaker 1: it has to be mined and refined right after the ground.
Speaker 1: Raw iron ore is a mix of what's called ore
Speaker 1: proper and gang, which is soil. The ore proper can
Speaker 1: usually be separated by crushing the raw ore and simply
Speaker 1: washing away the lighter gang. Breaking down the ore proper
Speaker 1: is more difficult. It's a compound of carbonates, hydrates, oxides, silicates, sulfides,
Speaker 1: and various impurity all bound up together. To get to
Speaker 1: the bits of iron in the ore, you have to
Speaker 1: smelt it out. Smelting involves heating up or until the
Speaker 1: metal becomes spongy, and the different compounds begin to break
Speaker 1: down or break out. Most importantly, it releases oxygen from
Speaker 1: the iron ore, which usually makes up a high percentage
Speaker 1: of it. The most primitive facility to smelt iron is
Speaker 1: a bloomery. There, a blacksmith burns charcoal with iron ore
Speaker 1: and a good supply of oxygen provided by bellows or
Speaker 1: a blower. Charcoal is essentially pure carbon. The carbon combines
Speaker 1: with oxygen to create carbon dioxide and carbon monoxide, and
Speaker 1: releasing lots of heat in the process. Carbon and carbon
Speaker 1: monoxide combined with the oxygen in the orb and carry
Speaker 1: it away, leaving iron metal. However, in a bloomery, the
Speaker 1: fire doesn't get hot enough to melt the iron completely. Instead,
Speaker 1: the iron heats up into a spongy mass containing iron
Speaker 1: and silicates. Heating and hammering this mass, called the bloom
Speaker 1: forces impurities out and mixes the glassy silicates into the
Speaker 1: iron metal to create wrought iron. A wrought iron is
Speaker 1: hardy and easy to work, making it perfect for creating tools.
Speaker 1: Different ancient civilizations around the world were up to different stuff,
Speaker 1: but in general, toolmakers were learning to smelt copper around
Speaker 1: five thousand BCE, bronze around three thousand BCE. And iron
Speaker 1: around two thousand BCE. However, before many of these civilizations
Speaker 1: began to transition from their bronze age to an iron age,
Speaker 1: some toolmakers were already creating iron implements from meteorites called
Speaker 1: black copper by the ancient Egyptians. Meteoric iron isn't the
Speaker 1: sort of thing one finds in huge, consolidated locations, but
Speaker 1: by collecting bits and pieces of it. This this cosmic
Speaker 1: metal was put to use in jewelry and other ornamentation.
Speaker 1: While blacksmiths occasionally used meteoric iron two craft swords. These
Speaker 1: prized weapons were relegated to people of great power, such
Speaker 1: as the caliphs of these six hundred CE. It would
Speaker 1: take almost one thousand years of iron smelting before iron
Speaker 1: became the dominant metal, because furnace technology had to improve,
Speaker 1: and later by the mid thirteen hundred CE, blast furnaces
Speaker 1: that burn hot enough to not just soften iron but
Speaker 1: actually melt it hit the scene. A blast furnace is
Speaker 1: charged with iron ore, limestone, and charcoal or coke, a
Speaker 1: coke being charcoal made from coal which burns very hot.
Speaker 1: Huge quantities of air blast in at the bottom of
Speaker 1: the furnace, and the calcium in the limestone combines with
Speaker 1: the silicates to form slag. Liquid iron collects at the
Speaker 1: bottom of the blast furnace underneath a layer of slag.
Speaker 1: The bla Broxsmith periodically lets the liquid iron flow out
Speaker 1: and cool, typically in a bed of sand. Once it cools,
Speaker 1: this metal is known as pig iron. Pig iron contains
Speaker 1: four to five percent carbon and is so hard and
Speaker 1: brittle that it's almost useless. It was considered a waste
Speaker 1: product of the advanced bloomeres before people figured out what
Speaker 1: to do with it. Basically, you have three options. First,
Speaker 1: you can melt it, mix it with slag, and hammer
Speaker 1: it out to eliminate most of the carbon and create strong,
Speaker 1: malleable wrought iron. A second, you can melt the pig
Speaker 1: iron and combine it with scrap iron, smelt out impurities,
Speaker 1: and add alloys to form cast iron. This metal contains
Speaker 1: two to four percent carbon, along with quantities of silicon, manganese,
Speaker 1: and trace impurities. Cast iron, as the name implies, is
Speaker 1: typically cast into molds to form a wide variety of
Speaker 1: parts and products. The third option for pig iron is
Speaker 1: to push the refining process even further and create steel.
Speaker 1: Steel is iron that has most of the impurities removed
Speaker 1: and has a consistent small concentration of carbon throughout, generally
Speaker 1: less than two percent, but often less than zero point
Speaker 1: three five percent. Impurities like silica, phosphorus, and sulfur weaken
Speaker 1: steel tremendously, so they must be removed. The advantage of
Speaker 1: steel over iron is greatly improved strength. Throughout the eighteen hundreds,
Speaker 1: engineers developed technologies like the Bessemer process and the modern
Speaker 1: open hearth furnace, which burn hot enough to melt steel
Speaker 1: and use oxidation in limestone, respectively to help separate out
Speaker 1: molten iron and steel from everything else. However, most modern
Speaker 1: steel plants use what's called a basic oxygen furnace to
Speaker 1: create steel. The advantage is speed, as the process is
Speaker 1: about ten times faster than the open hearth furnace. In
Speaker 1: these furnaces high peer the oxygen blows through the molten
Speaker 1: pig iron, lowering carbon, silicon, manganese, and phosphorus levels. The
Speaker 1: addition of chemical cleaning agents called fluxes helped to reduce
Speaker 1: the sulfur and phosphorus levels. A variety of other metals
Speaker 1: can be alloyed with the steel at this point to
Speaker 1: create different properties. For example, the addition of ten to
Speaker 1: thirty percent chromium creates stainless steel, which is very resistant
Speaker 1: to rust. The addition of chromium and molybdenum creates chromemulley steel,
Speaker 1: which is strong enough that less can be used for
Speaker 1: parts where weight matters, like in bicycle and automotive manufacturing
Speaker 1: and aerospace engineering. When you think about it, two accidents
Speaker 1: of nature made it much easier for human technology to
Speaker 1: advance and flourish. One is the prominent availability of iron ore.
Speaker 1: The other is the accessibility of coal and oil to
Speaker 1: power the production of iron. Without both of these working
Speaker 1: for us, our societies would look very different today. Today's
Speaker 1: episode is based on the article how iron and Steel
Speaker 1: Work on HowStuffWorks dot com, written by Marshall Brain and
Speaker 1: Robert Lamb. Brain Stuff is a production of iHeartRadio in
Speaker 1: partnership with how Stuffworks dot Com and is produced by
Speaker 1: Tyler Klang. Four more podcasts my heart Radio, visit the
Speaker 1: iHeartRadio app, Apple Podcasts, or wherever you listen to your
Speaker 1: favorite shows.