5 interesting facts about tungsten

What makes tungsten unique, from its name to its melting point

With Metal Cuting's long history of providing pure tungsten and making Metal parts from this extraordinary material, we have a special understanding of the element, its properties and what it can do.

So, just for fun, we thought we'd take a look at some of the more interesting - and sometimes curious - facts about tungsten.

1. What's in a name?

How tungsten got its name -- and why the symbol on the periodic table is W -- is an international conundrum. Back in 1783, two Spanish chemists, brothers Juan Jose and Fausto Elhuyar, discovered the element itself in a sample of a mineral called wolframite.

Today, in many countries around the world, tungsten is known by its Germanic name "Wolfram", after the mineral wolframite. So it's easy to see where the chemical symbol W came from - although if you're like us, you might wonder why the element isn't named "Faustonite", or if there's a Spanish word for wolframite.

However, the name tungsten is used today in the United States as well as in English, French and various other languages. The word comes from the Swedish tung and sten, meaning "heavy stone," an old Swedish name for the mineral scheelite, another source of tungsten ore.

But ironically, tungsten is not used as a name for the element in Sweden or other Nordic countries. There, and in most Germanic and Slavic languages, they use the name Wolfram or Volfram.

Tungsten /Wolfram/Volfram is still mainly extracted from wolframite and scheelite. Of all the pure forms of metals, tungsten has:

Maximum melting point (6192°F or 3422°C)

Minimum vapor pressure (at temperatures above 3000°F or 1650°C)

Highest tensile strength

So whether you call it tungsten or any other name, this set of properties means tungsten is used in many industries and products around the world, from high-speed cutting tools and jet turbine engines, to ammunition, lighting, and even fishing weights.

2. The diameter of the tungsten wire is expressed in milligrams.

You might hear people describe tungsten diameters as 14.7 mg, 3.05 mg, 246.7 mg, and so on.

This is because in the past, due to the lack of tools to accurately measure very thin wires -- for example, from.001" to.020" in diameter -- the practice was to take a 200 mm (about 8 inches) tungsten wire, weigh it, and insert the weight into a mathematical formula to determine the diameter.

To calculate the diameter (D) of the tungsten wire according to the weight per unit length, the formula is:

D = 0.71746 x square root (mg weight /200 mm length)

Standard diameter tolerance ± 3% of the measured weight value, but stricter tolerance may be used depending on the application of the wire product. This method also assumes that the wire has a constant diameter with no significant change at any location on the diameter, neck down or other tapering effect.

3. Most tungsten wires are doped -- whether you need to or not!

Again, this practice dates back to the past -- in particular, the main purpose of tungsten filament is the filament of a light bulb. The problem is, the bulb releases white-hot temperatures that cause the filament to sag early on, causing the tube to malfunction.

Through experiments, the idea evolved to add alumina, silicon dioxide and potassium to alter the mechanical properties of the tungsten filament. Dopant is added in the powder mixing stage.

Interestingly, in the process of hot forging and hot drawing tungsten wire, the alumina and silica excrete gas and the potassium remains. The element gives the wire a non-droop characteristic at white hot temperature.

The addition of these dopants in the powder mixing phase of tungsten filament manufacture dates back to a time when wires had no other important use than light bulb filaments. While there are many other uses for tungsten today -- and while incandescent bulbs are becoming a thing of the past -- the use of dopants in the manufacture of tungsten continues.

4. Tungsten and tungsten carbide are not interchangeable.

Tungsten carbide is known for its wear resistance; In fact, it can only be cut using diamond tools. But while tungsten carbide does contain a lot of tungsten, the common practice of adding cobalt as a binder makes it a hard alloy and gives tungsten carbide very different properties than pure tungsten.

(Carbides, with or without binder, have chemical resistance advantages, but that's the subject of another blog.

Pure tungsten has a number of properties that make it useful; However, it is also known for being difficult to process. Try using a diamond tool, pure tungsten will simply be loaded or "gelled" onto the diamond wheel.

Metal cutting specializes in methods that are very effective for cutting pure tungsten, but interestingly, these same methods don't work when trying to cut tungsten carbide. For example, customers may tell us that they have or want tungsten tubes, but upon further investigation we may discover that they actually have or need tubular tungsten carbide.

Pure tungsten simply cannot be made into tubes except for the final size of the spray gun bore - this assumes that the part has a favorable length-to-diameter ratio. It also assumes that the customer has a lot of money and doesn't want a lot of these carefully produced parts.

Tungsten carbide, on the other hand, can be pressed and burned into tubes, but this is not a cheap or high-volume process. Unlike other metals, tungsten and tungsten carbide cannot be sucked into the tube.

5. Tungsten's high melting point makes obtaining liquid tungsten a challenge.

People sometimes ask if you can have liquid tungsten, and the answer is...... Well, it's complicated. Tungsten, which has the highest melting point of any known metal at 6,192 °F, is obviously difficult to melt.

In theory, if you apply enough heat, anything can melt. However, for commercial purposes, the high tungsten melting point makes liquid tungsten an almost impossible proposition.

The question is simple, what type of container holds a lot of liquid tungsten? Virtually anything you try to use will be melted by the high temperature of tungsten.

That's why tungsten is made in a non-liquid state, using powder metallurgy. Commercially, tungsten products-from pure tungsten to a few possible alloys, such as heavy alloys, copper-tungsten, and silver-tungsten - are made by pressing and sintering into a near-net shape.

For forged products, pressing and sintering are followed by forging and repeated drawing and annealing. This results in a characteristic elongated grain structure that is carried over into the finished product, whether it is a stick or a very fine wire.

The only element known to have a higher melting point than tungsten is carbon, at 6422°F (3550°C). However, even carbon cannot be used to contain liquid tungsten, because at high temperatures the two react to form tungsten carbide.

In the experiment, liquid tungsten was produced using a superconducting electrocopper crucible in which heat was pulled away from the surface, leaving it intact. But again, this is impractical for commercial volumes.

This means that every tungsten product produced is never in liquid state. Metallurgically, this is crucial for everything that follows.

How do facts 1-5 add up?

With all its unique and interesting properties, tungsten is one of the most widely used refractory metals. (No, it's not a rare earth element, although tungsten is lumped in with those elements that make headlines for political reasons - but that's a topic for another time.

As a company offering specialized tungsten wire and rod products since 1967, and as the exclusive North American distributor of Tungsten Corporation of Japan, Metal Cutting Corporation can help you unlock the secrets of tungsten.

Please contact us at zhang@pride-cnc.com