WEBVTT - How Do We Get Iron and Steel Out of Stone? 0:00:01.840 --> 0:00:08.639 Welcome to Brainstuff, a production of iHeartRadio. Hey Brainstuff, Lauren Vogelbaum. Here. 0:00:10.440 --> 0:00:13.320 If you were to follow humanity's genetic trail back through 0:00:13.320 --> 0:00:17.439 the millennia, you'd find primitive creatures fumbling for a foothold 0:00:17.560 --> 0:00:22.200 on a primeval earth, lacking the natural physical advantages of 0:00:22.239 --> 0:00:25.320 other animals. It's a marvel that humans were able to 0:00:25.360 --> 0:00:27.600 claw their way out of the Cenozoic era at all. 0:00:28.920 --> 0:00:32.159 Of course, Homo sapiens had an advantage over most of 0:00:32.200 --> 0:00:35.879 the other animals the ability to make and use tools. 0:00:37.240 --> 0:00:40.080 While they lacked a lion's teeth and claws or a 0:00:40.159 --> 0:00:43.919 deer's defensive antlers, they learned to craft their own tools 0:00:44.000 --> 0:00:48.320 from the world around them. The oldest known tools date 0:00:48.400 --> 0:00:51.559 back two point six million years to a time when 0:00:51.640 --> 0:00:55.680 humans used shaped stone to carry out a variety of tasks. 0:00:56.320 --> 0:00:59.960 After all, a sharpened rock can potentially stab and bludget, 0:01:00.360 --> 0:01:05.440 but also slice, scrape, and pound. In time, humans began 0:01:05.520 --> 0:01:10.119 to specialize their tools, creating everything from arrowheads to pestles 0:01:10.200 --> 0:01:16.759 for grinding grain. But stone is a brittle and inflexible medium. Eventually, 0:01:16.880 --> 0:01:20.720 our ancestors were able to pinpoint more durable and malleable 0:01:20.800 --> 0:01:26.800 materials a first copper, than bronze, than iron. Their capability 0:01:26.840 --> 0:01:29.920 with these materials is one of the modern measures of civilization, 0:01:31.040 --> 0:01:34.800 and between the fifteenth and twentieth centuries, some countries had 0:01:34.840 --> 0:01:37.560 an industrial leg up on the competition due to the 0:01:37.640 --> 0:01:42.920 availability of iron ore deposits. For example, China, India, England, 0:01:43.080 --> 0:01:47.720 the US, France, Germany, Spain, and Russia all have substantial 0:01:47.840 --> 0:01:51.640 iron ore deposits. When you think of the historical importance 0:01:51.680 --> 0:01:54.200 of all of these societies, you can see the correlation. 0:01:55.520 --> 0:01:59.120 Even today, iron makes possible a huge array of products, 0:01:59.520 --> 0:02:06.640 especially the carbon rich commercial iron, which we call steel. Cars, tractors, bridges, 0:02:06.840 --> 0:02:11.639 trains and their rails, tools, skyscrapers, guns and ships all 0:02:11.680 --> 0:02:15.840 depend on iron and steel to make them strong. But 0:02:16.200 --> 0:02:19.160 as common as iron is an Earth's crust, and it's 0:02:19.200 --> 0:02:22.040 our fourth most common element there, making up about five 0:02:22.120 --> 0:02:25.120 percent of the crust by weight, it comes bound up 0:02:25.200 --> 0:02:29.000 in ores, which are basically rocks that contain iron and 0:02:29.240 --> 0:02:33.280 other stuff. So how do we turn a slab of 0:02:33.400 --> 0:02:36.440 rock into a set of stainless steel, surgical instruments or 0:02:36.480 --> 0:02:41.040 a locomotive. Today, let's talk about how iron and steel 0:02:41.320 --> 0:02:47.120 built the modern world. Iron is incredibly useful. It's less 0:02:47.120 --> 0:02:51.000 brittle than stone butt compared to wood or copper, extremely 0:02:51.040 --> 0:02:55.239 strong when properly heated. It's relatively easy to shape into 0:02:55.320 --> 0:03:00.000 various forms using simple tools. It can handle high temperatures, 0:03:00.000 --> 0:03:02.760 wowing us to build fire tongs and furnaces out of it. 0:03:03.600 --> 0:03:06.360 You can also magnetize iron, making it useful in the 0:03:06.400 --> 0:03:09.560 creation of electric motors and generators, which we talked a 0:03:09.560 --> 0:03:13.200 bit about in our recent episode on induction cooking, and 0:03:13.600 --> 0:03:17.760 again it is common in some areas. Iron concentrates and 0:03:17.800 --> 0:03:21.960 ores make up seventy percent of the stuff. Its ease 0:03:22.000 --> 0:03:26.200 of manipulation is why iron and steel were so important historically. 0:03:27.480 --> 0:03:30.920 To refine aluminum, for example, you need access to huge 0:03:31.000 --> 0:03:34.160 quantities of electricity, and to shape it you have to 0:03:34.400 --> 0:03:37.880 cast or extrude it. That's why iron has been used 0:03:37.920 --> 0:03:41.240 for thousands of years, while aluminum didn't really exist in 0:03:41.280 --> 0:03:45.600 any meaningful way until the twentieth century. The reason that 0:03:45.640 --> 0:03:48.320 the tip of the Washington Monument is a pyramid made 0:03:48.360 --> 0:03:51.760 of aluminum is that aluminum was more valuable than gold 0:03:51.920 --> 0:03:56.000 in eighteen eighty four. There may come a day when 0:03:56.080 --> 0:04:00.000 humans become so technologically advanced that iron is completely repla 0:04:00.040 --> 0:04:04.040 placed by materials like aluminium or various plastics or fibers 0:04:04.080 --> 0:04:08.040 made of carbon or glass, but as of now, iron 0:04:08.080 --> 0:04:12.520 and steel are less expensive for many purposes. The only 0:04:12.560 --> 0:04:15.280 real issue with iron and steel is rust, although we've 0:04:15.280 --> 0:04:19.440 come up with lots of solutions for controlling that by painting, galvanizing, 0:04:19.600 --> 0:04:22.279 chrome plating, or even just coating the iron with what's 0:04:22.320 --> 0:04:25.800 called a sacrificial anode that will corrode faster, sort of 0:04:25.800 --> 0:04:30.000 like hiring a bodyguard who will take a bullet for you. However, 0:04:30.400 --> 0:04:32.919 before iron can be put to any of these uses, 0:04:33.160 --> 0:04:36.880 it has to be mined and refined right after the ground. 0:04:37.279 --> 0:04:39.800 Raw iron ore is a mix of what's called ore 0:04:39.839 --> 0:04:44.760 proper and gang, which is soil. The ore proper can 0:04:44.880 --> 0:04:48.000 usually be separated by crushing the raw ore and simply 0:04:48.120 --> 0:04:52.359 washing away the lighter gang. Breaking down the ore proper 0:04:52.600 --> 0:04:58.840 is more difficult. It's a compound of carbonates, hydrates, oxides, silicates, sulfides, 0:04:58.880 --> 0:05:03.080 and various impurity all bound up together. To get to 0:05:03.160 --> 0:05:05.360 the bits of iron in the ore, you have to 0:05:05.480 --> 0:05:09.880 smelt it out. Smelting involves heating up or until the 0:05:09.920 --> 0:05:13.599 metal becomes spongy, and the different compounds begin to break 0:05:13.640 --> 0:05:18.520 down or break out. Most importantly, it releases oxygen from 0:05:18.520 --> 0:05:21.279 the iron ore, which usually makes up a high percentage 0:05:21.320 --> 0:05:25.240 of it. The most primitive facility to smelt iron is 0:05:25.360 --> 0:05:30.320 a bloomery. There, a blacksmith burns charcoal with iron ore 0:05:30.480 --> 0:05:33.359 and a good supply of oxygen provided by bellows or 0:05:33.360 --> 0:05:38.880 a blower. Charcoal is essentially pure carbon. The carbon combines 0:05:38.880 --> 0:05:42.440 with oxygen to create carbon dioxide and carbon monoxide, and 0:05:42.640 --> 0:05:46.560 releasing lots of heat in the process. Carbon and carbon 0:05:46.600 --> 0:05:49.360 monoxide combined with the oxygen in the orb and carry 0:05:49.400 --> 0:05:54.560 it away, leaving iron metal. However, in a bloomery, the 0:05:54.600 --> 0:05:58.799 fire doesn't get hot enough to melt the iron completely. Instead, 0:05:59.080 --> 0:06:02.599 the iron heats up into a spongy mass containing iron 0:06:02.800 --> 0:06:07.679 and silicates. Heating and hammering this mass, called the bloom 0:06:08.080 --> 0:06:12.160 forces impurities out and mixes the glassy silicates into the 0:06:12.200 --> 0:06:16.120 iron metal to create wrought iron. A wrought iron is 0:06:16.240 --> 0:06:20.360 hardy and easy to work, making it perfect for creating tools. 0:06:21.400 --> 0:06:24.880 Different ancient civilizations around the world were up to different stuff, 0:06:25.440 --> 0:06:29.160 but in general, toolmakers were learning to smelt copper around 0:06:29.160 --> 0:06:33.880 five thousand BCE, bronze around three thousand BCE. And iron 0:06:34.000 --> 0:06:39.160 around two thousand BCE. However, before many of these civilizations 0:06:39.279 --> 0:06:42.520 began to transition from their bronze age to an iron age, 0:06:42.839 --> 0:06:49.080 some toolmakers were already creating iron implements from meteorites called 0:06:49.200 --> 0:06:53.000 black copper by the ancient Egyptians. Meteoric iron isn't the 0:06:53.040 --> 0:06:57.400 sort of thing one finds in huge, consolidated locations, but 0:06:57.800 --> 0:07:00.640 by collecting bits and pieces of it. This this cosmic 0:07:00.680 --> 0:07:03.760 metal was put to use in jewelry and other ornamentation. 0:07:05.040 --> 0:07:09.279 While blacksmiths occasionally used meteoric iron two craft swords. These 0:07:09.400 --> 0:07:12.840 prized weapons were relegated to people of great power, such 0:07:12.840 --> 0:07:17.040 as the caliphs of these six hundred CE. It would 0:07:17.040 --> 0:07:20.040 take almost one thousand years of iron smelting before iron 0:07:20.080 --> 0:07:24.000 became the dominant metal, because furnace technology had to improve, 0:07:25.160 --> 0:07:29.320 and later by the mid thirteen hundred CE, blast furnaces 0:07:29.400 --> 0:07:32.280 that burn hot enough to not just soften iron but 0:07:32.360 --> 0:07:36.320 actually melt it hit the scene. A blast furnace is 0:07:36.440 --> 0:07:40.920 charged with iron ore, limestone, and charcoal or coke, a 0:07:41.000 --> 0:07:45.200 coke being charcoal made from coal which burns very hot. 0:07:45.720 --> 0:07:48.240 Huge quantities of air blast in at the bottom of 0:07:48.240 --> 0:07:51.240 the furnace, and the calcium in the limestone combines with 0:07:51.280 --> 0:07:55.840 the silicates to form slag. Liquid iron collects at the 0:07:55.880 --> 0:07:58.880 bottom of the blast furnace underneath a layer of slag. 0:07:59.680 --> 0:08:02.840 The bla Broxsmith periodically lets the liquid iron flow out 0:08:02.840 --> 0:08:07.400 and cool, typically in a bed of sand. Once it cools, 0:08:07.520 --> 0:08:11.440 this metal is known as pig iron. Pig iron contains 0:08:11.560 --> 0:08:14.440 four to five percent carbon and is so hard and 0:08:14.480 --> 0:08:18.000 brittle that it's almost useless. It was considered a waste 0:08:18.080 --> 0:08:21.560 product of the advanced bloomeres before people figured out what 0:08:21.640 --> 0:08:26.440 to do with it. Basically, you have three options. First, 0:08:26.560 --> 0:08:28.960 you can melt it, mix it with slag, and hammer 0:08:29.000 --> 0:08:32.000 it out to eliminate most of the carbon and create strong, 0:08:32.120 --> 0:08:35.920 malleable wrought iron. A second, you can melt the pig 0:08:35.960 --> 0:08:39.280 iron and combine it with scrap iron, smelt out impurities, 0:08:39.360 --> 0:08:43.680 and add alloys to form cast iron. This metal contains 0:08:43.720 --> 0:08:47.640 two to four percent carbon, along with quantities of silicon, manganese, 0:08:47.640 --> 0:08:51.720 and trace impurities. Cast iron, as the name implies, is 0:08:51.760 --> 0:08:55.080 typically cast into molds to form a wide variety of 0:08:55.160 --> 0:08:58.680 parts and products. The third option for pig iron is 0:08:58.760 --> 0:09:02.640 to push the refining process even further and create steel. 0:09:04.000 --> 0:09:06.920 Steel is iron that has most of the impurities removed 0:09:07.400 --> 0:09:11.920 and has a consistent small concentration of carbon throughout, generally 0:09:12.000 --> 0:09:14.880 less than two percent, but often less than zero point 0:09:14.880 --> 0:09:20.080 three five percent. Impurities like silica, phosphorus, and sulfur weaken 0:09:20.200 --> 0:09:24.360 steel tremendously, so they must be removed. The advantage of 0:09:24.360 --> 0:09:29.640 steel over iron is greatly improved strength. Throughout the eighteen hundreds, 0:09:29.720 --> 0:09:33.760 engineers developed technologies like the Bessemer process and the modern 0:09:33.800 --> 0:09:37.440 open hearth furnace, which burn hot enough to melt steel 0:09:37.880 --> 0:09:41.760 and use oxidation in limestone, respectively to help separate out 0:09:41.840 --> 0:09:46.960 molten iron and steel from everything else. However, most modern 0:09:47.000 --> 0:09:50.320 steel plants use what's called a basic oxygen furnace to 0:09:50.360 --> 0:09:54.520 create steel. The advantage is speed, as the process is 0:09:54.559 --> 0:09:58.360 about ten times faster than the open hearth furnace. In 0:09:58.400 --> 0:10:02.000 these furnaces high peer the oxygen blows through the molten 0:10:02.040 --> 0:10:08.240 pig iron, lowering carbon, silicon, manganese, and phosphorus levels. The 0:10:08.280 --> 0:10:12.120 addition of chemical cleaning agents called fluxes helped to reduce 0:10:12.160 --> 0:10:16.360 the sulfur and phosphorus levels. A variety of other metals 0:10:16.360 --> 0:10:18.480 can be alloyed with the steel at this point to 0:10:18.679 --> 0:10:22.920 create different properties. For example, the addition of ten to 0:10:23.120 --> 0:10:27.440 thirty percent chromium creates stainless steel, which is very resistant 0:10:27.440 --> 0:10:32.480 to rust. The addition of chromium and molybdenum creates chromemulley steel, 0:10:32.720 --> 0:10:35.440 which is strong enough that less can be used for 0:10:35.520 --> 0:10:40.080 parts where weight matters, like in bicycle and automotive manufacturing 0:10:40.240 --> 0:10:44.920 and aerospace engineering. When you think about it, two accidents 0:10:44.920 --> 0:10:48.200 of nature made it much easier for human technology to 0:10:48.280 --> 0:10:53.400 advance and flourish. One is the prominent availability of iron ore. 0:10:54.240 --> 0:10:57.600 The other is the accessibility of coal and oil to 0:10:57.679 --> 0:11:01.640 power the production of iron. Without both of these working 0:11:01.720 --> 0:11:10.600 for us, our societies would look very different today. Today's 0:11:10.600 --> 0:11:13.199 episode is based on the article how iron and Steel 0:11:13.280 --> 0:11:16.000 Work on HowStuffWorks dot com, written by Marshall Brain and 0:11:16.120 --> 0:11:19.199 Robert Lamb. Brain Stuff is a production of iHeartRadio in 0:11:19.280 --> 0:11:21.800 partnership with how Stuffworks dot Com and is produced by 0:11:21.800 --> 0:11:25.439 Tyler Klang. Four more podcasts my heart Radio, visit the 0:11:25.480 --> 0:11:28.920 iHeartRadio app, Apple Podcasts, or wherever you listen to your 0:11:28.920 --> 0:11:29.720 favorite shows.