Ask A Scientist Materials Science Archive

name         Heath
status       other
grade        other
location     FL

Question -   What type of metal is used when melting other metals, 
example... when melting iron and other kinds of strong metals they use a 
scoop that go's into a huge oven, why does the scoop not melt too?
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Heath,

The material used in smelting belong to a class of materials called 
ceramics. Ceramics usually have very high melting points (if they show any 
at all). If we were to look at the way the atoms are arranged between a 
metal and a ceramic, we start getting an idea as to why this is so. 
Imagine a row of marbles. On top of this row, place another row of 
marbles. And then on top of that, another row. You can easily imagine that 
each row can slide sideways so that not one particular marble really is 
exclusively always on top of another particular marble. This is the way 
metals are. This is what gives metals their malleability and ductility - 
and which also allows them to melt at achievable temperatures. Ceramics on 
the other hand are built differently. Imagine our set of marbles again, 
but this time, make sure that the marbles in each column are directly on 
top of each other, and then in the gaps formed by every set of four 
marbles (right in the center of a square of marbles), we place a smaller 
marble that just fits exactly within that gap. Such an additional "atom" 
will prevent the slippage from side to side. You can imagine that this 
denser packing will make the material harder and less prone to melting.

Greg (Roberto Gregorius)
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Heath,
The key is to choose a material for the scoop that has
a melting temperature higher than the temperature of
your furnace (which is set to the melting temperature
of the metal you want to melt).  For most high
temperature furnaces it is not another metal that used,
it is a type of ceramic.  A ceramic is a material that
is inorganic, insulating, and an oxide, carbide, or
nitride.  Some examples include:
Al2O3 (aluminum oxide)--has a melting temperature of
2050 degrees Celsius, MgO (Magnesium oxide)--melting
temp is 2800 degrees C, and SiC (silicon
crbide)--melting temp 2500 degrees C.

Compare these melting temperatures to the melting
temperature of iron or steel which is only around 1500
degrees C or 2800 degrees F! No problem. Ceramics are
great!

Ceramics tend to me very hard, very stiff, but very
brittle.

The one drawback of ceramics that comes to mind when
talking about steel is that you have to be very
careful which one you try to use to cut hot steel.
You cannot use anything with carbon in it to cut hot
steel, because it leaves some of the carbon behind,
which makes the steel less strong.  You cannot use
diamond---diamond is made out of carbon, too.  There is
been a lot of work recently in the field of material
science to develop materials for industrial
applications like this.

Michelle Weinberger
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The Crucible, or "scoop" is typicly made of materials with extraordinarily
high melting points, or none at all.  I have heard of crucibles being made of
ceramics and Granite.

Ryan Belscamper
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