Thursday, September 5, 2013

Part Two of a Pretty Metal Story

by akshiv, This post originally appeared at Neurons and Quarks.


We had just discovered that steel is way better than cast iron, but it is also hard to make. The Chinese solved this problem quite effectively and this knowledge spread to the rest of the world quite quickly. They figured out how to make wrought iron from pig iron. Pig iron is essentially what iron is like once it had been heated and taken out of the ores from which it originated. After this it went through the process of decarbonisation, actually lowering the carbon content so it starts to resemble steel. Steel is an alloy of carbon and iron just like the more widely available cast iron at the time. The difference is that the carbon content of steel is better suited for making stronger tools and weapons. The problem with this is it took an incredibly long time to get to the right temperatures in open-air furnaces. The Chinese developed the blast furnace, which made this process feasible.
The blast furnace has a few steps involved. Essentially, in the top of your furnace you add the fuel, the pig iron, cast iron, and the flux. The flux is used, as a chemical reactant to purify the product most often this was lime. On the bottom you create a draft of oxygen allowing the combustion of the fuel to take place. As the mixture is heated and product forms it starts to settle at the bottom of the molten stew.

This meant that good steel good be made, but it still took a while with the technology available in the Middle Ages. Steel and iron became corner stones in manufacturing and building around the world being used in everything from buildings, to knives, to cannon balls, to pots.

The industrial revolution took this process and accelerated it tenfold. Henry Bessemer is the father of the process by the same name. It allowed for the rapid conversion of pig iron into steel. It starts with a large crucible through which you allow a draft of air to pass through. Either through the heat of the air or a spark provided the dissolved carbon in the coke is ignited. Allow me to explain. Coke is a fuel with carbon content and very few impurities as a result it can produce high temperatures on combustion, it could be manufactured in the industrial revolution due to the excess of coal. This coke was the fuel incorporated into the pig iron. As the carbon from the coke binds to the pig iron the melting point is raised of it is raised, but because of the heat released upon its combustion the mixture stays molten. This means the speed at which it becomes steel is much quicker. Once the carbon concentration drops enough the draft is cut stopping all combustion reactions. This method allowed the conversation of 25 tonnes of pig iron to steel in UNDER HALF AN HOUR!!

That sort of ends the chapter of iron and steel, moving on to the modern day. Today metallurgy has grown to include numerous metals not just iron, gold, copper, and silver. Modern techniques range from the microscopic like using metallography and crystallography to see the microscopic structure of different alloys to macroscopic like using large pressurized chambers to combine specific quantities. Modern applications of metallurgy are vast because of the adverse conditions in which we place building materials. Metallurgy is no longer tied to metalworking instead it has became a portion of material science, where new alloys are made and tested. My favourite example of this science was in the James Webb Telescope, because the telescope has such massive parts and will be subject to enormous amounts of thermal stress new metals had to be created in order to insure that it would work in outer space.
About this Contributor: I just finished my final year of high school. I love playing ultimate frisbee, skiing and playing the clarinet/guitar. I am happiest when learning random trivia or stargazing. Learning for me is its own reward, whether it is about the quantumly tiny or the cosmologically large.

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