Q & A details -What do they use to hold molten steel/tungsten?
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What do they use to hold molten steel/tungsten?

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I'm watching 'Dirty Jobs' and they're recycling steel. I'm curious as to what they can use to hold the liquid metal. Even more curious to me is what they use to hold tungsten in.

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  • 0861788249

    0861788249 2017-01-09 09:45:13

    Ladles and crucibles for holding molten steel are usually made of a shell of heat resistant steel alloy, and are lined with high-temperature ceramics. The ceramics are what actually come in contact with the molten steel. Several different kinds of ceramics can be used. The melting point of Tungsten is second only to that of carbon. (Note: at high temperatures carbon "sublimes", or evaporates like dry ice rather than melting.) There are no known ceramics which have a higher melting point than tungsten. A carbon crucible cannot be used for tungsten because the two would strongly react forming molten tungsten carbide.( which has a lower melting point than either tungsten or carbon.) For this reason, items made of tungsten are usually made by pressing powdered tungsten into a mold using very high pressure. The powder contains a small amount of binder which holds the part in shape after it's been pressed. After that, the parts are "sintered" in an oven. The oven isn't hot enough to melt the tungsten, but the heat causes the solid particles to partially fuse together, forming a slighly porous concrete-like material. Tungsten is somewhat brittle at room temperature. But relatively pure tungsten can be hot- worked and forged like steel. It can also be drawn out into wires while red-hot; for example, for lightbulb filaments. Note that the wire drawing process usually needs to be done in a furnace filled with inert gas like argon, hot tungsten quickly oxidizes in air.

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