Mixtures vs Compounds vs Alloys

Balinju · 06-01-2003, 01:15 PM

Some time ago we were discussing part of this title in another thread and I found it very interesting. Now someone suggested that alloys are only 2 metals heated together, so this would result some kind of mixture.
The thought on this conclusion was that brass for example has both properties of copper and that of zinc.

Now i have several question on this. If brass is only a mixture of these 2 metals, how the hell is it that brass is much much more difficult to cut that copper when zinc is extreemly soft and copper is not as hard as brass?

Another question, if alloys are only mixtures, how the hell does stainless steel not rust when it is an alloy of 70% iron ??
Some also suggested that brass do not react because zinc forms a layer of zinc oxide just like aluminium does but this time on top of the brass.

can anybody clear this up for me please?? I am

KnightElite · 06-01-2003, 01:41 PM

Alloys are not a mixture, they are a "solid solution". Essentially, this means that the ions from the two metals are distributed fairly evenly throughout the sample, and that because of the interactions between them, the alloy has different properties than the original two metals. Also, the relative quantity of each metal will change the alloy as well.

For example, 100% pure copper is very soft. For electrical plugs, it would be too soft, and the pins you plug into the socket would bend much too easily. So the copper that is used there is in fact a 99% Cu 1% Be (Beryllium), which makes it much stronger, without affecting its conductivity overmuch.

You learn all of this if you take a materials science course. It all has to do with the crystal structure of the material, number of grain boudaries, effects of impurities, etc...

06-01-2003, 01:15 PM	#1
Balinju Cooling Savant Join Date: Dec 2002 Location: Malta Posts: 495	Mixtures vs Compounds vs Alloys Some time ago we were discussing part of this title in another thread and I found it very interesting. Now someone suggested that alloys are only 2 metals heated together, so this would result some kind of mixture. The thought on this conclusion was that brass for example has both properties of copper and that of zinc. Now i have several question on this. If brass is only a mixture of these 2 metals, how the hell is it that brass is much much more difficult to cut that copper when zinc is extreemly soft and copper is not as hard as brass? Another question, if alloys are only mixtures, how the hell does stainless steel not rust when it is an alloy of 70% iron ?? Some also suggested that brass do not react because zinc forms a layer of zinc oxide just like aluminium does but this time on top of the brass. can anybody clear this up for me please?? I am __________________ So the bullet proof vest aint a $hit when d laser is pointed to your head Kid

06-01-2003, 01:41 PM	#2
KnightElite Cooling Savant Join Date: Sep 2002 Location: Saskatoon, Saskatchewan Posts: 294	Alloys are not a mixture, they are a "solid solution". Essentially, this means that the ions from the two metals are distributed fairly evenly throughout the sample, and that because of the interactions between them, the alloy has different properties than the original two metals. Also, the relative quantity of each metal will change the alloy as well. For example, 100% pure copper is very soft. For electrical plugs, it would be too soft, and the pins you plug into the socket would bend much too easily. So the copper that is used there is in fact a 99% Cu 1% Be (Beryllium), which makes it much stronger, without affecting its conductivity overmuch. You learn all of this if you take a materials science course. It all has to do with the crystal structure of the material, number of grain boudaries, effects of impurities, etc... __________________ Can anyone else here say that they have a watercooled monster that's 45" tall?

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