How Is Tungsten So Hard and Heat-Resistant?

Tungsten's boiling point is over 10,000 degrees Fahrenheit, and as tungsten carbide, it's one of the hardest materials we know. Learn how it's used for everything from armor-piercing bullets to electron microscopes to ballpoint pens in today's episode of BrainStuff, based on this article: https://science.howstuffworks.com/tungsten.htm

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Episode Transcript

Speaker 1 (00:01):
Welcome to BrainStuff, a production of iHeartRadio. Hey BrainStuff, Lauren
Vogelbaum here. Armor-piercing bullets, rocket engine nozzles, and drill bits
for cutting through solid rock are just some of the
products made with tungsten, one of the most heat-resistant elements,
and when made into tungsten carbide, one of the hardest

(00:24):
substances in the known universe. Tungsten, like most other metallic elements,
is almost never found on Earth as a shiny hunk
of metal. To get a pure piece of it, it
needs to be chemically isolated from other elements that it
appears with in compounds, usually the naturally occurring mineral, wolframite.
That's why tungsten's symbol on the periodic table isn't a T,

(00:48):
but a W, which is short for wolfram. The name
tungsten is Swedish for heavy stone, a reference to the
element's uncanny density and heft. Its atomic number, the number
of protons in the nucleus of its atom, is 74,
and its standard atomic weight is 138.84. A pair of

(01:08):
Spanish chemists and brothers by the name Juan Jose and
Fausto El Ullar are credited with discovering tungsten back in 1783.
They were the first to isolate this lustrous grayish-white metal
from wolframite, which also contains iron and manganese. One of
tungsten's most impressive and useful properties is its high melting point,

(01:30):
the highest of all metallic elements. Pure tungsten melts at
a whopping 6,192 degrees Fahrenheit, that's 3,422 Celsius. And it
won't boil until it reaches 10,030 degrees Fahrenheit, or 5,555 Celsius,
which is the same temperature as the photosphere of the sun.

(01:55):
Just for comparison, even platinum has a melting point of
just a little over half of tungsten's, a mere 3,215
degrees Fahrenheit or 1,768 Celsius. Technically, carbon is the only
element that can get hotter than tungsten without melting. But
that's sort of cheating because carbon doesn't melt at ambient pressures,

(02:17):
or rather it sublimes straight from a solid to a
gas at a bit above tungsten's melting point. at 6,700
Fahrenheit or 3,700 Celsius. All metals have relatively high melting
points because their atoms are held together in tight metallic bonds.
Metallic bonds are so strong because they share electrons across

(02:39):
an entire three-dimensional array of atoms in a crystal lattice
structure held together by the electrostatic force of the electrons.
Tungsten outlasts other metals because of the unusual strength and
directionality of its metallic bonds. Thomas Edison experimented with lots
of different filament materials for the incandescent light bulb, including platinum, iridium,

(03:02):
and bamboo, but it was another American inventor, William Coolidge,
who's credited with making the tungsten filaments that were used
in most light bulbs throughout the 20th century. Tungsten is
useful here because it will emit light, It won't melt
from the heat, and it's relatively inexpensive. Tungsten's high melting

(03:22):
point has other advantages, like when it's mixed in as
an alloy with materials like steel. Tungsten alloys are plated
onto the sections of rockets and missiles that need to
withstand tremendous heat, including the engine nozzles that eject explosive
streams of rocket fuel. Tungsten is also very dense. In

(03:44):
practical terms, if you held a hunk of tungsten in
one hand and the same volume of silver or iron
in the other, the tungsten would feel a lot heavier. Specifically,
the density of tungsten is 19.3 grams per cubic centimeter. Silver,
in comparison, is about half as dense at 10.5 grams,

(04:04):
and iron almost a third as dense at 7.9 grams.
Tungsten is almost exactly as dense as gold. Counterfeiters figured
that one out long ago, and sometimes try to pass
off gold-plated bars of tungsten as pure gold. Of course,
the density of different elements is a reflection of the

(04:25):
size of that element's atoms, the number of protons and
neutrons in the element's nucleus, and the electrons in their orbit,
meaning that the higher an element's atomic number on the
periodic table, the larger and heavier its atoms will be.
Tungsten's high-density heft can be an advantage in certain applications.

(04:46):
It's often used in armor-piercing bullets, for example, for its
density and hardness. The military also uses tungsten to make
so-called kinetic bombardment weapons that shoot a rod of tungsten
like an airborne battering ram to smash through walls and
even the armor on tanks. During the Cold War, the

(05:07):
United States Air Force allegedly experimented with an idea called
Project Thor that would have dropped a bundle of tungsten
rods 20 feet long, that's 6 meters, from orbit onto
enemy targets. These so-called rods from God would have impacted
with the destructive force of a nuclear weapon, but without
the nuclear fallout. However … it turns that the cost

(05:31):
of actually getting such heavy rods into space in the
first place was prohibitive. Pure tungsten isn't that hard. You
can cut through it with a handsaw. But when tungsten
is combined with small amounts of carbon, it becomes tungsten carbide,
one of the hardest and most wear-resistant substances on Earth.

(05:53):
For the article this episode is based on, HowStuffWorks spoke
with John Newsom, a chemist and material scientist via the
American Chemical Society. He explained, when you put small amounts
of carbon or other metals into tungsten, it fixes the
structure and prevents it from being easily deformed. Tungsten carbide

(06:14):
is so hard, at least a nine on the Mohs
hardness scale, that it can only be cut by things
like diamonds or cubic boron nitride. Tungsten carbide is up
to three times as rigid as steel and can last
up to 100 times longer than steel under highly abrasive
conditions and has the greatest compressive strength of all forged metals,

(06:36):
meaning it won't dent or deform when squeezed under tremendous force.
It can, however, be brittle and may shatter under some
types of force. The most common use for tungsten carbide
and the final destination of most of the mined tungsten
on the planet is specialized tools, and particularly drill bits.

(06:57):
Any kind of drill bit for cutting metal or solid
rock needs to withstand the punishing levels of friction and
heat produced without dulling or breaking. Only diamond drills are
harder than tungsten carbide, but they're also much more expensive.
Tungsten's hardness, density, and heat resistance make it ideal for

(07:17):
a lot of niche applications. Electron microscopes shoot out a
stream of electrons from a special emitter tip made from tungsten.
Most welds between metal and glass are made from tungsten,
because tungsten expands and contracts at the same rate as
the most common kind of glass, called borosilicate glass. The

(07:38):
spikes on snowmobile tracks and the tips of trekking poles
are made from tungsten alloys. Professional-grade darts are made with tungsten.
In ballpoint pens, the actual ball is often made from
tungsten carbide. The jewelry industry also makes rings from tungsten carbide,
especially rings marketed to men. These pieces are very scratch-resistant,

(08:01):
which is nice, but as nifty as tungsten carbide is,
I personally would not recommend wearing something so hard to
cut around something so delicate as a finger. In case
of emergency, you want a medical professional to be able
to cut a ring off easily without causing more harm.
The term degloving gets thrown around. Further, when tungsten carbide

(08:24):
does shatter, the pieces are very sharp. If you're going
for an industrial vibe, both jewelry repair and medical experts
recommend stainless steel instead. Leave the tungsten carbide for the
armor-piercing bullets and electron microscopes. Today's episode is based on

(08:47):
the article, Tungsten's Boiling Point is 10,030 Degrees Fahrenheit and
Other Crazy Facts on HowStuffWorks.com, written by Dave Ruse. BrainStuff
is a production of iHeart Podcasts in partnership with HowStuffWorks.com
and is produced by Tyler Klang. For more shows from
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