![mining-and-refining:-tungsten-[hackaday]](https://i0.wp.com/upmytech.com/wp-content/uploads/2024/04/176604-mining-and-refining-tungsten-hackaday-scaled.jpg?resize=800%2C445&ssl=1)
Mining and Refining: Tungsten [Hackaday]
Our metallurgical history is a little bit like a game of Rock, Paper, Scissors, only without the paper; we’re always looking for something hard enough to cut whatever the current hardest metal is. We started with copper, the first metal to be mined and refined. But then we needed something to cut copper, so we ended up with alloys like bronze, which demanded harder metals like iron, and eventually this arms race of cutting led us to steel, the king of metals.
But even a king needs someone to keep him in check, and while steel can be used to make tools hard enough to cut itself, there’s something even better for the job: tungsten, or more specifically tungsten carbide. We produced almost 120,000 tonnes of tungsten in 2022, much of which was directed to the manufacture of tungsten carbide tooling. Tungsten has the highest melting point known, 3,422 °C, and is an extremely dense, hard, and tough metal. Its properties make it an indispensible industrial metal, and it’s next up in our “Mining and Refining” series.
Build a Mountain, Make Some Tungsten
Tungsten is a rare metal, making up only a fraction of a percent of the Earth’s crust, about 1.25 parts per million. It has never been found in its elemental form in nature; instead, it appears as several mineral-bearing ores. The physical and chemical properties of tungsten, which make it such a useful metal, also ensure that the formation of these ores is limited to geologies where tremendous heat and pressure are exerted, such as where sections of continental crust collide to build mountain ranges. These orogenic belts, located mainly around the Pacific basin but also across the Alpine-Himalayan belt that stretches from southern Spain to Indonesia, are the main source of tungsten ore.
It’s right in the name. TIG welding uses sintered tungsten electrodes; rare earth oxides reduce the work factor to make striking arcs easier. Source: Adobe Stock.Another important industrial use for tungsten is welding electrodes. The high melting point of tungsten makes it perfect for TIG welding — the “T” is for tungsten, after all — which uses a high electric current to create a super hot plasma that melts the base metal and filler. Tungsten electrodes may look like pieces of thick wire, but they’re actually formed in much the same way as tungsten ingots are. Powdered tungsten is mixed with various additives, especially rare earth oxides like lanthanum and thorium, before being pressed and sintered into solid rods. The rare earth oxides serve to reduce the energy needed to remove electrons from the electrode, which makes it easier to strike an arc and makes the electrode last longer.
The toughness and high melting point of tungsten also make it suitable for cutting tools, especially in the form of tungsten carbide (WC). Tungsten carbide is made either by reacting powdered tungsten metal with graphite at high temperatures, or by blowing a mixture of hot carbon monoxide and carbon dioxide through a bed of tungsten trioxide. Either way, the tungsten and carbon bind to each other, creating a material that’s twice as stiff and twice as dense as steel, with a melting point of about 2,800 °C. Tungsten carbide can be mixed with various binders and additives and pressed into complex shapes that can be sintered into solid cutting tools tough enough to withstand the punishing requirements of CNC cutting.