[time-nuts] OCXO housings - Why copper and not iron/steel?

[Attila Kinali]

Moin,

I have been looking at heat capacities of different materials
lately. One thing that struk me odd is, that the volumetric
heat capacity of copper, which is the thing that most people
use when building something that needs to have high heat capacity
to get stable temperature, has only a volumetric heat capacity
of 3.45 J/(cm^3·K). Meanwhile, the much cheaper iron has
a volumetric heat capacity of 3.53 J/(cm^3·K) and steel 
even 3.75 J/(cm^3·K).

In an OCXO, which is generally size limited, getting the most
heat capacity in the limited volume would be the main goal,
wouldn't it? Also optimizing for price would be a major thing.
I can understand that iron is probably not the right choice
due to its tendency to oxidize. But using a soft (annealed) steel
would be easy to machine, cheaper per piece and give almost 10%
higher heat capacity in the same volume. 

So why do people choose copper instead of steel?


			Attila Kinali

PS: Fun fact: Water has a volumetric heat capacity of 4.18 J/(cm^3·K)
at 25°C. We should fill OCXOs with water! :-D

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