unregistred:

Yepp... Thats true... I thought U talked about big differences.

Question: Would the lapping that would have to be done afterwards cause the copper to go stiffer again??? Not as much as before anywayz...

8-Ball:
Nice, although when looking at the diagram I realised I didn't remeber a shit about those curves... Have to dig my books up after all.. :)

Probably not a huge amount, but it will have a slight effect. Also remeber that this is the crucial area in the block.

BillA,

How much deformation are we talking about here. Do you have pictures?

8-ball

Have you learnt anything about ternary phase diagrams.

They're fun!

8-ball

Yepp... 5 years ago... When I studied for a masters in Mechanics.

We looked at nice laped metall surfaces trough microscpes and compared the grains and other stuff to the TTT diagrams.
The examination of the course was that we got a couple of different metallslabs to look at and then we should write down how they had been treated. I didn't Ace it I tell U but I got through.. :)

nothing I can quantify (before I started spending everything on equip)

bp flatness is terribly sensitive, due also to the presence of 'furniture' on one side only

in any case a probably immeasurable effect from annealing

It was my indication in classes that annealing and quenching were not done to pure metals, as the goal was alteration of solid equilibria. I can't think of pure metals with differing crystallization structures that behave as nearly immiscible structural entities, if that's the proper way to describe it.

My text tells me, as I thought, that electron movement is the main executor of thermal transfer.

Alchemy

For starters, no-one ever really uses pure metals.

It may be 99.99% pure, but it will still have defects and these defectes will have associated free enrgies and strain fields which will have an effect on electron mobility.

Annealing will provide thermal energy to allow for the diffusion of vacancies and dislocation motion.

This in turn will lead to a coarsening of the microstructure, where by, before it will have been packed full of dislocations and vacancies, and after the smaller number of dislocations will be aranged into low angle grain boundaries, with a much higher proportion of the material having a low defect concentration.

This will improve conductivity.

As a side note, annealing can be and is used to homogenise the composition of materials which have undergone dendritic solidification, or any other solidification mechanism which results in microsegragation, though this is not what we are trying to do here.

8-ball

We come from opposite directions then. I just had an exam that covered how to interpret eutatic phase diagrams, but I know very little about actual material science.

Anyway I agree, defects in diamond or metals will cause a big drop in conductivity, though oddly enough its for completely different reasons.

According to a lecture I had, removing C13 from synthetic diamonds yields a 50% increase in conductivity (diamonds with conductivities beyond 3000w/mk have been made this way IIRC). I wonder how much an effect impurites have on copper . . .

One more thing, whats to stop oxygen from being taken into the crystal when you anneal? I think C101 has to be melted under special atmosphere to prevent this, though I'm only half sure of that.

I happened across the answer to this particular problem during some revision I have been doing.

The problem is one of particularly high concentrations of dislocations and point defects (vacancies – lattice sites where an atom is missing) resulting from cold working.

A typical cold worked metal will have a dislocation density of the order of 10^16 per meter squared. This means if you took a plane through a block of copper 1m x 1m, there would be 10^16 dislocations crossing it.

As you can appreciate, this is a stupendously high number. As mentioned before, these defects will affect the electrical conductivity of the material.

So, the solution?

Annealing? Yes, though this is the procedure applied to the material. The actual effects of heating the metal are RECOVERY and RECRYSTALLISATION.

RECRYSTALLISATION is the transformation of a cold worked material (High defect concentrations) to one with essentially no significant concentration of dislocations. The mechanism by which this process works is the passage of high angle grain boundaries.

The driving force for this transformation, (It won’t happen without one), is the reduction of stored energy in the dislocations previously discussed, though this is a very small driving force, relative to the majority of other transformations/reactions.

This transformation needs to be nucleated within the material and then must propagate. Both of these are thermally activated, and provided the sample is heated enough to cause nucleation and propagation, the small driving force of the reduction in stored energy will be sufficient to drive the recrystallisation.

Heating the material to promote recrystallisation will also promote recovery.

RECOVERY is a process which has similar effects, ie the reduction in defect density, though not by the motion of grain boundaries.

There will be mutual annihilation of dislocations above 0.3 of the melting point of the material. This temp is high enough to encourage dislocation glide.

Point defects (vacancies) will also be annihilated by diffusing to edge dislocations. This process results in the climb of dislocations.

The stored energy of dislocations will also be reduced by the arrangement of dislocations into low angle grain boundaries, forming a sub-grain structure.


Ok, that’s the theory of what actually happens. I need not delve further into the processes of nucleation of the recrystallisation, nor the kinetics of the transformation, as for the purpose of this discussion, that which I have described is sufficient.

What does this mean.

I have been able to find experimental data on the recrystallisation of copper samples at various temperatures, shown below, though the exact composition of the Cu is not mentioned. I think it is safe to assume that the lack of any mention of compositions is indicative that this is data for pure copper.

As can be seen, for a recrystallisation temperature of 135.2 degrees C, with 90% recrystallisation being achieved in just under 15 minutes.

This temperature is possible in any oven and can be maintained relatively accurately in a fan oven.

A note on the composition.

The presence of impurities will increase the time required at a given temperature due to solute drag effects slowing down the grain boundary velocity.

So to allow for small quantities of impurities, I would suggest 15 minutes at around 140 degrees C, or 1 hour at 110 degrees C. I don’t know what these temps are in Farrenheit, go find a web converter.

I hope everyone has found this informative and useful.

I apologise for the style of writing. I put this together in word for fear of accidentally hitting the “back” button my mouse, and I only use word for writing essays and pieces of coursework. This is my “please the examiner” style of writing.

8-ball

[EDIT: Image resized]

Excellent writeup.

Thanks 8-Ball.

Great knowlege 8ball, U da man.. :)

About one of my questions before. The answer struck me after some thought.

"Will the lapping destroy the nice soft copper??"

Answer to myself: Nope, I don't think so. Not if one is beeing gentle about it.

How came this conclusion?:
All the pieces we studied in the microscope at the university were lapped to make a good surface to look at. That didn't destroy those samples so I guess there shouldent be a problem with our lapping either.

You wouldn't really be able to tell if the lapping had introduced dislocations as they will not be visible under an optical microscope, unless you have specifically etched for dislocations.

The additional energy at dislocations will cause preferential etching at points where dislocations intersect the surface causing etch pits.

If you prepared the samples in the same why I do, you will start with coarse wet and dry paper, roughly 120/200grit, working down to 2000grit, then 6 micron and 1 micron polishes.

There will be a degree of deformation associated with this, (more with the coarse grit wet and dry paper than the polishing), introducing further dislocations, however, this will not be as significant as the dislocation density due to machining or cold working (namely, cold drawn hard copper)

Essentially, you have two options, recrystallise then lapp, risking reintroducing dislocations, or leave it, risking suffering from a "minute" (almost non-existent) deformation in the base.

Either way these will both be minimal effects.

Hope this helps.

8-ball

Or...

'Coarse' lap to, say 600 grit.

Recrystallize.

Final lap with 600 grit and higher.

Marking the base before final lapping, might allow a person to crudely determine whether meaningful deformation had occurred.

The thread's subject line has been changed at 8-Ball's request.

Edit: Apparently not.

Hasn't changed, but it don't matter.

8-ball

Redleader,

I'm trying to find the diffusion coefficient for oxygen in copper, then combined with the temperatures and times I recommended above, I should be able to put a diffusion profile together. It's an error function diffusion profile for a fixed surface composition so it shouldn't be that tough to calculate. It would be a nice opportunity to put my diffusion revision to a good use.

That said, note the temperatures I have given are significantly lower than those originally considered, and the penetration depth (stop sniggering at the back:p) shouldn't be too significant.

Oh, and I'll also need the starting oxygen composition in the electrolytic Cu we use. Anyone?

8-ball

Another suggestion,

You could stick your block in boiling water for 2 hours for the same effect.

I'll have a look at the notes I made when I get into the library tomorrow, and check the temperature dependence of diffusion and recrystallisation.

Essentially, to see whether 15 minutes at 140 degrees or 2 hours at 100 degrees will result in more indiffusion of oxygen, though I strongly suspect both processes will have the same temperature dependence.

8-ball

I've seen 0.04% oxygen mentioned for C110, but nothing very authoritative. (i.e. worth linking)

the chart

Int'l designations

Possibly some relevancy here:
http://properties.copper.org/
For influence of Oxygen the link to "Metallurgy of Copper Wire" is worth a look - http://innovations.copper.org/metall...etallurgy.html.

I spent all last night reading through copper.org. I don't think oxygen will be a problem.

According to their information, a tiny bit of oxygen (~.01% iirc) is actually helpful. Above that oxygenated material tends to come out of solution forming fairly large gaps (though widely spaced since the material collects). The graphs they show suggust that the effect is pretty minor.

As for the rate of difussion, I didn't think much of anything will enter a metal crystal so far below melting. I assumed that anneling would require 400C+.

Thx 8-ball for digging into this!!! Very informative.

One question, all this talk about 'cold working' copper decreasing thermal conductivity does it really apply to the extent suggested at the start of the thread? What I mean. Most of what we do to a piece of copper is to a surface. We are not bending, skieving, or compressing to an extent that would cause significant deformation. Yes the surfaces will be deformed to some depth depending on the method used. But the bulk of the mass will not have sufficient stress applied to cause crystal deformation. Or am I out in left field?

Since most copper bar stock people buy is of the cold drawn type I think annealing would be good at some point during the making of a WB. I guess my question is do you have to wait until it's complete (except for final lapping) before you anneal and to what extent machining and lapping will actually have on thermal conductivity?

I agree, the deformation introduced by machining is not on the same level as the hard drawn copper. This will have undergone something like a 70% change in area as it is drawn through the dies and so on.

I think the original idea was starting with this as it is a lot harder, making it ieasier to machine, and then performing recovery and recrystallisation to reduce the defect density.

However, that resulting microstructure will be finer than if you had started with soft copper.

8-ball

(off-topic)

This reminds me of one of my team members on our capstone design project. We didn't realize until after our report was nearly complete (that is, too late to make major changes) that she got all her environmental information on a particular heavy metal toxin on the website for the lobby group of producers of that particular metal. They, of course, stated quite seriously that the toxin was of no danger to any living creature and made an excellent seasoning on salads.

Okay, maybe not the last part. But the site had a bias that was obvious, and even if it hadn't, someone 2 months away from a B.S. in chemical engineering should realize that the best way to research a possibly controversial topic is *not* entering www.(controversial topic).com in a web browser.

Alchemy was not pleased.

Anyway, thank God I didn't have to pay for this degree. Hooray for South Carolina public universities, where having a third brain cell to rub against the other two guarantees a four-year free ride.

Alchemy

Sorry, I didn't really read your post thoroughly.

If you are using cold drawn copper, it will have an incredibly high defect density. This is the material compared with soft copper which had only 90% of the conductivity. The machining and lapping will have little effect on the overall defect concentration of cold drawn copper, as it is already high. (The local concentrationaround the milling surfaces may increase)

However, milling a soft copper will raise the defect density several orders of magnitude above the normal. So you will have to recrystallise again.

In summary, machine your cold drawn copper bar stock and then lap the base. Then recrystallise, either 140 degrees C for 15 minutes in the oven or 2 hours in boiling water. Once you've finished the recrystallisation, you could give it another quick lap on 2000 grit wet and dry paper, though I don't think it would be necessary.

8-ball

PS, I'm thinking of writing this up properly when I get the time, along with anything else I can find out relating to materials science in extreme cooling and overclocking. Any suggestions are welcome. (This won't be till the summer)

Great. This has been a good diskusion and I think we have came to the conclusion that annealing the copper will help us get more efficient blocks.

8Ball: Uve really dug deep in this shit and U seem to know Ure metalls... Thanx.

Now I guess the final thing to do is to make some similair looking blocks and anneal some of them and then run some IRL testing...

I'm about to build my first watercoolingsystem and If I get the time I will make two WW-looking blocks. One anneald and one that isnt.
Since this is my first attempt at watercooling I guess a lot of U guys could make these tests alot easier than me though.

I guess some people will soon try this so I'm really looking forward to see the results.

give us details on the test setup to measure this
- gonna be SOME rig

All it would need really is any block machined from cold drawn copper bar stock to be tested then treated for 15 mins at 140 degrees, or 2 hours in boiling water, and then retested.

If there is going to be any noticible change, that's how you'd pick it up.

Though, If you do gain an extra 10% in conductivity, I don't see how much of a difference this would make on performance.

8-ball

hmmm
a 10% gain is about twice the difference between Cu and Ag

what is the basis of the 10% value ?
(I would have guessed FAR lower)
but if the mounting induced variation is ±0.2°C (by an 'expert', more typical is 2 or 3 times this);
I think the difference will be incredibly difficult to pickup