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

[Bob kb8tq]

Hi

Simple answer: conductivity. You don’t get much heat capacity either way.

Bob

> On Oct 30, 2020, at 5:49 PM, Attila Kinali <attila at kinali.ch> wrote:
> 
> 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
> 
> -- 
> <JaberWorky>	The bad part of Zurich is where the degenerates
>                throw DARK chocolate at you.
> 
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