Video Transcript
In this video, we will learn about
the metals we commonly use in everyday life and in industry and why they are
suitable for the applications we use them in. The commonly used metals we’re
going to look at are copper, aluminum, iron, steel, tin, lead, silver, and gold. You’ve probably come across all of
these in your daily life. These are all pure metals except
for steel, which is an alloy. However, copper, aluminum, iron,
tin, lead, silver, and gold are usually used in alloys rather than in their pure
form.
The metals and other elements in an
alloy affect the properties of an alloy. For example, aluminum is low in
density, and so aluminum alloys are lightweight and are therefore used in
lightweight applications. So metals and their alloys have
certain properties, and these properties directly determine the applications or uses
of the metals and alloys.
Some of the more important
properties to consider when choosing a metal or an alloy for a certain application
are strength, malleability, corrosion resistance, and density. Besides these physical properties,
cost is also an important factor to consider when choosing a metal or an alloy for a
specific application. Now, let’s have a look at some of
the more noticeable properties of each of the metals listed, as well as their common
applications.
Let’s look at two metals at a time,
and we’ll begin with copper and aluminum. Copper has a lovely pink-orange
color when its surface is clean and aluminum a silver-white color. Silver white is a fairly common
color for a fresh, clean metal surface. But pink orange is a fairly unique
color, quite distinctive to copper. This property would help us
identify copper or an alloy which contains a high amount of copper. Aluminum’s melting point is much
lower than that of copper. It would melt and set much quicker
than copper when molding metal parts.
Now copper is an excellent thermal
and electrical conductor. We use it mostly in its pure form
in electrical wires. Besides its conductivity, copper is
also relatively cheap. Copper is also hard. And though it tarnishes to a green
color over long periods of time, it doesn’t flake away like iron does when iron
corrodes. And so copper is used in plumbing
parts, as well as to strengthen gold and silver alloys. Some coins are made of copper.
For aluminum, we said that one of
its distinguishing properties is its low density. Alloys used to make aircraft and
bicycle bodies contain a high percentage of aluminum, and this makes these
components lightweight. We also use aluminum in beverage
cans, such as soda cans, in food packaging, and foils because this metal is
corrosion resistant and lightweight. Some modern building construction
parts, such as window frames and doors, are fabricated from aluminum. Again this is because of its
corrosion resistance property.
Let’s move on to the next two
metals. Iron is silver gray when its
surfaces are cleaned and fresh with no corrosion, while steel, which contains iron
and carbon, has a gray surface. The melting points of iron and
steel are much higher than the other metals we are investigating in this video. Notice that the melting point for
carbon steel is given in terms of a range. This is because the ratio of iron
to carbon in the carbon steel alloys can be varied. Another video on steels goes into
more depth on this.
Now, iron is used in more
applications than any other metal, but mostly in steels. Pure iron rusts easily and is
relatively soft, so pure iron is not very useful to us. But alloying iron in steel
increases its strength and hardness, perfect for making machine parts. These undergo a lot of friction but
have a long lifespan because of their strength and hardness. Car bodies, tools such as hammers
and drill bits, and reinforcing bars for the construction industry are some of the
common uses of steel alloys.
We said that the proportions of
iron to carbon in carbon steel can be controlled and altered. The relative proportions of these
elements determine the strength-to-brittleness ratio and thus the specific
application of a specific carbon steel. In stainless steel, besides iron
and carbon, there is also chromium and nickel. The presence of chromium and nickel
in the alloy gives it corrosion resistance. We make cutlery and surgical
equipment from stainless steels because of this property of corrosion
resistance.
Let’s move on to tin and lead. A clean surface of tin has a silver
color, while lead has a gray color. Both these metals have relatively
low melting points compared to the other metals we are investigating in this
video. The relatively low melting point of
tin makes it melt quickly and easily but also cool and set quickly. And so we use it in solder. Tin has a low corrosion rate and
doesn’t oxidize very easily. And so a thin layer of tin is
sometimes used to coat steel to prevent the steel from corroding. Think of tin cans. Tin food cans are not made of pure
tin but are only coated in a thin layer of tin. This prevents the steal from
rusting and contaminating the food.
Now lead has a high density and is
also corrosion resistant. For these reasons, it is sometimes
used in the construction industry for roofing and gutters. However, lead is being phased out
in some applications in certain countries because lead is hazardous to the
environment. Lead has another interesting
application in science and medicine. It is used as a shielding medium
from radiation such as X-rays. It is the high density of lead
which gives it this interesting application.
Let’s have a look at the last two
metals, silver and gold. Silver, with its silver color, when
untarnished and gold with its distinctive yellow gold color are both precious
metals. This is because they both have a
high luster, which means they are very shiny. They are rare and costly. Because of their property of a high
luster as well as their desirability because of their cost and rarity, they are both
used in jewelry. Now, gold is highly corrosion
resistant, but silver does tarnish over time. Both these precious metals are
highly malleable and conductive, but they are not commonly used in other
applications because of their high cost.
For the various metals that we have
looked at, we have mostly discussed their physical properties. However, corrosion resistance is a
chemical property. Other chemical properties and
chemical uses of these metals have not been discussed in this video. We have seen that a metal has
specific properties, which determines its usefulness in specific applications. This flowchart can work backwards
or from the middle. For example, if we know the
properties of a specific metal, we can potentially identify the metal. Or if we have a desired application
and we want to make something specific, we’d have to know the properties that suit
that particular application. And from the properties, we could
determine the metal or alloys which are suitable for that application. Let’s practice this a bit.
The table shows the properties of
five different metals. (a) Which metal is most suitable
for use in aircraft bodies? And the answer options are (A)
metal a, (B) metal b, (C) metal c, (D) metal d, or (E) metal e.
The properties of different metals
listed in the table are strength, malleability, corrosion resistance, and
density. Cost is not really a property of a
metal but is a factor that a company will consider when fabricating a specific metal
part. The properties of metals determine
how useful they are in different applications. Note that the pure form of a metal
is often not used for applications. Usually metals are used in
alloys. And the properties of the metals in
the alloy determine the overall properties of the alloy.
The question asks which metal is
most suitable for use in aircraft bodies. When making an aircraft body, a
manufacturer would want to make it lightweight and relatively strong. These two factors of strength and
density are arguably the two most important factors when making an aircraft
body. Of the five given metals — a, b, c,
d, and e — the one with the lowest density also has a moderate strength. These properties or characteristics
would be useful for use in aircraft bodies. Metals a, b, c, and e have high,
very high, or moderate density. They would not be suitable to make
an aircraft body from because the body would not be lightweight. So the metal most suitable for use
in aircraft bodies is metal d. Also, metal d is highly malleable
and corrosion resistant. It can be molded into an aircraft
body shape easily and would have a long lifespan.
(b) Which metal is most suitable
for use in mass-produced gates and railings? And the answer options are the same
as before.
When mass-producing a product, cost
is often an important factor. In most cases but not always, a
company will plan to produce a product at low cost but sell many units and thus make
a good profit overall. When making gates and railings
whose purpose is for security, strength is the most important factor, so strength
and cost are arguably the most important considerations when mass-producing gates
and railings. The most suitable metals from those
in the table with a high strength and a low cost are metals a and b. Both could be suitable to make
gates and railings.
To decide between the two, we’d
need to know the relative cost of each, but we don’t have this information. b has a
high strength, although not as high as a, and also has a high malleability. This means metal b will be easier
to press into shape. This is particularly important if
the gates and railings are made from flat panels pressed and cut into shape, making
metal b cost less overall to make, compared to metal a which is less malleable. So the metal most suitable for
mass-produced gates and railings is metal b.
Part (c) which metal is most
suitable for use in hip replacements? And the answer options are the same
as before.
What properties would an artificial
hip joint need to have? Well, strength would be important
to carry the weight of the body as well as corrosion resistance because the new hip
joint would be constantly surrounded by bodily fluids as well as dissolved
oxygen. Malleability is an undesirable
property for a hip joint replacement. We would not want the weight of the
body to deform or alter the shape of the hip joint replacement. So we’re looking for a metal with a
high strength, a high corrosion resistance, and a low malleability. It would be really great if the
cost of hip replacement were low. However, this type of replacement
only occurs maybe once in the lifetime of a person. And so a high cost is not really an
influencing factor here.
Metals a, b, and e all display high
or very high strength. However, we can rule out metals a
and b because they have a low corrosion resistance, while metal e has a very high
corrosion resistance and a very high strength. Added to that, it has a low
malleability. And although the cost is high, the
part would have a long lifespan. So the metal most suitable for use
in hip replacements is metal e.
Let’s summarize what we’ve learnt
in this video. We compared some commonly used
metals. Specifically, we compared some of
the more noticeable properties of copper, aluminum, iron, steel, tin, lead, silver,
and gold and listed some of the main uses or applications. We noted that these metals are
usually not used in their pure form but mostly in alloys. And we know that steel is an
alloy. We made a general observation that
each metal has its own unique specific properties and that these properties directly
determine and influence the applications of these metals.
We saw that this flowchart can also
work backwards. If we know a specific application
or design brief for a part that needs to be manufactured and understand the
properties that it needs to have, we can then determine which metals are suitable
and which are unsuitable to make that part from. Some of the most important
properties to consider when choosing a metal are its strength, malleability,
corrosion resistance, and density. We also briefly mentioned that
cost, although it is not a property, is an important factor which influences whether
a metal is chosen for use in a specific application or not.
