What is the magical ingredient in U340 to block IR and can we all petition Hoya or Schott to triple it?

[Andrea B.]

I wonder what ever happened to that Copper U?

 

I still have one of mine. But they were a bit impractical long term because the liquid copper sulphate solution would begin to evaporate (or leak) leaving a rather large air bubble in the filter. I've kept mine in a case, but even so the air bubble has grown over time.

[rfcurry]

To expand upon Andrea's remarks regarding the Copper U, the US Navy buys a number of filters from me fairly often. A few years ago, they wanted a Copper U without the UV filter, NIR only. Like Andrea's Copper U, the filter lasted for two years before requiring some new Copper sulphate solution to replace an air bubble. I cannot find the leak in this type of filter. Diminished CuSO4 seems endemic to all the filters of this type, even those costing five times as much as the Copper U. Astronomers wail about the leaks online.

 

I still like CuSO4.

[Andy Perrin]

I take it solid CuSO4 on a substrate isn't an option? Like, could you deposit it by physical or chemical vapor deposition or something?I know it tends to oxidize but maybe a second layer of glass or whatever might stop that.

[Stefano]

That's what I advised, making a sort of sandwich with good UV transmission glass (maybe U glass directly), with a polished slab of CuSO4 in the middle. You can grow crystals of it just by dissolving it in water and letting the water evaporate. You can't melt it and pour it into a mold like you can with common table salt (NaCl), because it decomposes before melting.

[Andy Perrin]

You can grow crystals of it just by dissolving it in water and letting the water evaporate.

I've done that before, but if you want a large single crystal it's not very easy. Optical quality materials are different from grade school science fair projects. But I do think something fancier might work.

[Stefano]

If you want a nice, big crystal you need very pure water and CuSO4 (you want to have the least nucleation centers possible), and... a lot of time. The slower you grow crystals, the better. Is there any faster way to do it?

[Andy Perrin]

Yes, that's what I'm saying — physical or chemical vapor deposition:

https://en.wikipedia.org/wiki/Chemical_vapor_deposition

https://en.wikipedia.org/wiki/Physical_vapor_deposition

 

There are a number of methods within those groupings.

[Stefano]

We have to consider that we actually want to use CuSO4*5H2O, so we must keep those water molecules.

[Andy Perrin]

Hm. I wonder if you can add water vapor in the vapor deposition processes and manage that too.

[Stefano]

Does it change color without them?

Yes, the anidrous form (without water) is white, the heptahydrated form (7 water molecules) is blue-green.

[Stefano]

That's what happens if you put water on the anidrous form: https://it.m.wikipedia.org/wiki/Solfato_rameico#cite_note-copperorg-3.

 

That's the image you see under "Educazione chimica". I couldn't link the image directly for some reason. That's the italian Wikipedia page.

[colinbm]

To expand upon Andrea's remarks regarding the Copper U, the US Navy buys a number of filters from me fairly often. A few years ago, they wanted a Copper U without the UV filter, NIR only. Like Andrea's Copper U, the filter lasted for two years before requiring some new Copper sulphate solution to replace an air bubble. I cannot find the leak in this type of filter. Diminished CuSO4 seems endemic to all the filters of this type, even those costing five times as much as the Copper U. Astronomers wail about the leaks online.

 

I still like CuSO4.

 

Yes I too still like the Copper U, but as expected mine has evaporated to be only 50% solution now.

I have noticed a small approx 1mm hole, am I able to replenish the solution Please ?

Col