Materials matter.
You wouldn’t want to make a stop sign out
of candle wax or a bench out of chocolate.
Neither would be able to hold up to the weather
outside, and things would get quite sticky 
rather fast.
So if you’re going to create things and
solve problems, you’re going to need the
right supplies.
The right materials.
And two of the three main types of materials
you’ll encounter as an engineer are metals
and ceramics.
[Theme Music]
Engineering, like life, is about choices.
For example: some people decide to get braces
to straighten their teeth.
But choosing to wear braces isn’t as simple
as a yes or a no: there are many different
kinds to pick from.
Two of the most common are braces with traditional
metal brackets, and ceramic ones.
There’s not always an obviously correct
choice: picking the right type of braces is all
about weighing the pros and cons.
That’s true whether you’re the person
wearing them or the engineer designing them.
So to make a good choice, you need to know
more about each material.
As a budding engineer – and, like, a person
in the world – you probably already have a
decent idea of what metals are.
They’re in our cars, our buildings, and
many of the devices we use every day.
And you may have already worked with ceramics,
or at least have had them in your home.
Pottery is usually the first example that comes to mind, but you can also find ceramics in many other things, like
bricks, windows, and even electronics.
So metals and ceramics are definitely common.
But working with them isn’t always easy.
Or simple.
There’s a lot that has to happen before
you get your final product!
For example, imagine what it would actually
take to make a set of brackets for braces.
Before making anything, you have to get the
material that you’re using, which often starts
out as ore that we mine.
Ore is a type of naturally occurring rock
that contains certain elements or minerals.
Once you get ore, you can extract the elements
you want from it.
Then, through processes like casting or
forging, you can make that material into a
more-usable bulk form.
A common example is an ingot, which is usually
a bar of a pure metal, like the bars of gold you see
in old Westerns or in Skyrim.
You can then take those bulk materials and
form them into stock shapes, like sheets,
tubes, or even powders.
That’s what you might find at your local
hardware or home improvement store.
But then, to get your final product, you need
to turn those stock shapes into a preliminary
version of your braces.
Even once you have that, and make any necessary
changes to the design, the braces still need to go
through a cleaning process,
be checked by quality control, and then
packaged up before they can be used or sold.
That’s a lot of steps, and those are just the
basic ones.
In real life, there are even more.
Not to mention the time and effort it took
to pick the right materials, design the brackets,
and make sure they fit well.
You wouldn’t want to get all the way to
the end and then find out they’re just going
to snap in half!
That’s why it’s so important to understand
the properties of the materials you’re using.
Most metals share a few common properties.
They tend to conduct heat and electricity
well.
Many are malleable, or easy to shape
without breaking, and ductile, or easy to
stretch and deform.
Put another way, materials that are made from
metals are relatively strong and stiff, but also
resistant to fracture.
This makes them good for building structures!
Metals also typically reflect light well,
which is what makes them shiny.
That might not be the best if you don’t
want your braces to be so noticeable.
It just depends on what’s most important
to you – brackets that are less noticeable,
or ones that are less likely to break.
If you decide to use metal in a design, for
braces or anything else, there are lots of
different kinds to choose from.
In fact, about three quarters of all known
chemical elements are metals.
Common metals that we find here on Earth are
aluminum – or aluminium as we say back home!
– iron, potassium, and magnesium.
But often, these metals aren’t used by themselves
– they’re added to an alloy,
a metallic material composed of more than one element,
with at least one of those elements being a metal.
Steel is a good example – it’s an iron
alloy.
It’s primarily iron, but it also includes
a bit of carbon mixed in.
Sometimes there are other elements like
chromium or nickel thrown in there too,
depending on the type of steel.
But why not just use the iron itself?
Why go through the trouble of making steel,
or any alloy for that matter?
It’s because alloys have different, and
often better, properties than the individual
elements they’re made from.
For instance, steel tends to have better impact
resistance than iron.
And it’s far more resistant to rust and
corrosion – especially stainless steel.
So you’d want to choose stainless steel over iron
for projects where corrosion would be a problem,
like for the exhaust pipe in a car or a
replacement joint like an artificial hip.
A big reason that metals and alloys are the
way they are is because their chemical structure
is more free-spirited.
The bonds within metals and metallic materials leave a
large number of electrons that aren’t bound to particular
atoms and can move from one atom to another.
That’s known as the free-electron theory
of metals.
It’s like these free electrons can move
as a group though the metal itself.
This explains why some metallic materials
are so good at conducting heat and electricity
– especially simpler metals.
Their electrons can more easily carry that
energy from one place in the metal to the other.
So, metals have a lot of positives.
But they definitely aren’t right for everything,
which is where something like ceramic might
come in.
Ceramics are compounds that aren’t completely
metallic, but they don’t have carbon atoms bonded
in a way that would make them organic, either.
You can define glass materials the same way,
so a lot of people include them in the same 
general category.
The main difference between glass and other
ceramics is in their chemistry.
Ceramics are usually crystalline, which means their
molecules are more ordered, whereas the molecules
in various types of glass are more random.
But no matter how they’re organized, the molecules in
both ceramics and glasses are made up of at least one
metallic element, plus at least one non-metallic element.
They often include oxygen, nitrogen, or carbon.
Common examples include aluminum oxide, better
known as rust,
and silicon carbide, which can form a very hard
material that’s used to make everything from
car brakes to bulletproof vests.
And, of course, there are the more traditional ceramics
that most people think of, like cement, or compounds
made up of of clay materials, like porcelain.
In general, ceramics are relatively stiff
and strong and often very hard.
In this way, they’re similar to metals.
But they’re also extremely brittle and can
fracture very easily.
Which doesn’t sound too good if you’re
gonna have them on your teeth for a few years.
Ceramics are also usually insulators, so
they don’t conduct heat and electricity well –
although there are some that do.
And they tend to be more resistant to
extreme temperatures and harsh environments
than metals and polymers are.
But while most ceramic materials have similar
properties, there are differences.
We could spend hours going through all the
different types of ceramics out there, but
there are a few major ones.
Glass-ceramic materials, or materials whose
chemistry falls between a glass and other ceramics,
are relatively strong and don’t melt easily when heated.
They also tend to be biologically compatible.
And they make good insulators, which is why
they’re commonly used in electronic packaging
applications.
Plus, they can be completely transparent.
Perhaps one of the biggest appeals of glass-ceramic
materials is how easily you can fabricate them.
You can use conventional glass-forming techniques,
and you end up with a product that’s nearly pore-free,
which is great for handling liquids.
So glass-ceramics are really useful!
But sometimes you want something a little
simpler. Like clay.
Clay is inexpensive and commonly found in
nature.
You can often use it as-is after mining it,
meaning that you don’t need to waste time
or resources on refinement.
And it’s super easy to work with.
If you’ve ever taken a pottery class, you know that
clay and water, when mixed in the proper proportions,
forms a material that’s easy to shape.
Put that through a kiln, and you’ve got
something great for mugs and dishes!
For something a little sturdier, you might
try using cement.
It’s mainly used as a binder to help hold
concrete together,
which means you can find it everywhere from
roads, dams, and buildings, to more decorative
applications like patios and staircases.
One big benefit of using cement is that it
can set at room temperature.
Imagine if you had to break out some big flamethrower
every time you wanted to pave a new road!
So yeah, you could say cement’s properties
make it an important part of our lives.
Ceramics and metals also show up in places you might
not expect them, like with microelectromechanical
systems, or MEMS.
These are miniature smart systems that use tiny
sensors to collect information by measuring things like
mechanical, thermal, chemical, or optical properties.
They then use the information to make decisions that
tell devices called microactuators to do something, like
move a fluid or redirect a beam of light.
A major application of MEMS these days
is something you probably know pretty well:
the accelerometer.
For example, there’s one in your phone to
detect its movement.
And cars have accelerometers that trigger
airbags to deploy during a crash.
Compared to older and more conventional airbag
systems, ones that use MEMS are smaller, lighter,
more reliable, and quite a bit cheaper to produce.
And with something as important and life-saving
as an airbag, those are big benefits!
So, there’s a lot to consider when choosing
between materials.
For a set of braces, metal brackets tend to
be more durable and are better at correcting
severely unaligned teeth,
while ceramics tend to irritate the mouth
less and aren’t as visible.
And then there are your personal preferences,
which also matter.
Other factors, like time, resources, and design
limitations, might also influence your designs
in the field.
It’s all about finding materials with the
properties that make them the best fit for
want you want to accomplish.
So today we learned more about two of the
three main types of materials that we use
as engineers: metals and ceramics.
We saw the properties of metals and how we
often use them as alloys in our designs.
Then we went over ceramics and the importance
of clay, cement, and glass-ceramic materials.
Finally, we talked about the applications
of our materials with microelectromechanical
systems and accelerometers.
I’ll see you next time, when we’ll learn
about the third main type of material that we’ll
encounter as engineers: polymers.
Crash Course Engineering is produced in association
with PBS Digital Studios.
If you’d like to keep exploring our world,
check out Eons and go on a journey through
the history of life on Earth.
From the dawn of life, to the “Age of Dinosaurs”,
to the end of the most recent Ice Age.
Crash Course is a Complexly production and this
episode was filmed in the Doctor Cheryl C. Kinney
Studio with the help of these wonderful people.
And our amazing graphics team is Thought Cafe.
