At 2:13 PM -0700 9/10/99, David Cretney wrote:
>I am a chemist in training. The tables in front of me show that aluminum
>has about 2.5X's the heat capacity of copper. This means that it will
>require about 2.5X's as much energy to raise its temperature. My
>understanding is that the aluminum will hold more heat and is possibly the
>better conducter of heat.
Copper is by far a better conductor of heat, actually. Sometimes a copper
plate is used in heatsinking to act as a "heat spreader" to distribute heat
coming from a small area (such as a very small chip) to a larger area on an
aluminum heatsink, as otherwise the device would just heat a small spot of
the poorly conducting aluminum.
Keep in mind that, at least in the US, pennies are not really copper. Not
sure when the transition happened (decades ago?), but U.S. pennies are now
made out of zinc with a thin copper cladding. This style of penny was
introduced for a very sensible reason: the cost of producing a solid copper
penny rose above 1 cent, so they reduced the materials cost. Pennies may
not be as ideal a heatsink material as you think.
(In my high school chemistry class we did a cool "experiment" where we took
a shiny new penny, scraped an edge to expose some of the zinc, and then
dropped it in a weak HCl solution. HCl reacts with zinc, but not copper.
In a day or so the HCl had completely eaten the zinc out of the penny,
leaving a copper shell.
Tim Seufert
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