RogueRose
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Highly reflective metal needed - SS, Al or Cu/AgNO3 coatings?
I want to do some research on the best material to use for sun light reflection. The criteria is low maintenance and maintenance must be able to be
done without toxic chemicals or "high tech" machinery (I'm worried about Al oxide layers).
I have considered Stainless steel, aluminum and copper sheeting. I have also thought of using Cu/Ag nitrate which is used in mirror production. IDK
if metal can be coated with a layer of silver or copper with nitrate or if electrolysis would be better.
As far as Al and SS, I figure a polishing process would be a good way to get something to 80-90+% reflective.
Does anyone have any experience with this, either in production or reflective levels of the metals (or alternatives).
The pieces will be used to create a trough or hexagon shapes for a parabolic dish, the trough would be ideal with larger pieces but smaller would work
as well.
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CRUSTY
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Polished stainless steel seems like it would work well enough, although it would be a pain in the ass to cut without the right tools or bits. Aluminum
would be easier to cut, but dealing with potential oxide formation, like you said, might be an issue depending on the external environment and
reflectance criteria. I can't find much on the use of Cu/AgNO3, but if you're willing to spend some money on silver nitrate (AgNO3 is not cheap!), you
can react it with sodium hydroxide, forming silver oxide, which you can then get to coat any glass you want. NurdRage did a video on this method as well. I'm no mirror expert or anything, just spitballing some ideas.
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Sulaiman
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No experience but
Silver is the most reflective metal ... surface corrosion could be problematic
Speculum was a favourite of telescope makers
Aluminium is used on telescope mirrors for cheapness
Stainless steel would give least surface corrosion problems.
For economy I would consider old satellite dishes covered in Al foil
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Muffin Man
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Mylar and Foylon are both used in hydroponic gardens on walls for reflection.
From Google:
Aluminium foil, on the shiny side, has a reflectivity of 88%. You lose 12%. Furthermore aluminum foil tears easily. Mylar film, used in hydroponics,
has a reflectivity of 98%, only 2% loss, is easy to manipulate, and is reasonably priced.
From experience, I know that mylar attracts dust and dirt like nothing mad. It would also provide no structural rigidity if that is a requirement.
You may wish to have a look at FOYLON® by Duracote "Foil Laminated, Reinforced Energy Reflection Fabric"
"designed for tough jobs requiring a reflective surface for heat, radar and light."
Titanium dioxide white paint apparently exists and reflects >90% though I could not find a source.
I also found this:
DuPont™ Ti-Pure® titanium dioxide
TITANIUM DIOXIDE FOR COATINGS
https://www.chemours.com/Titanium_Technologies/de_US/tech_in...
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careysub
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Could you provide more specifics about your application? Length of service? Weight or cost constraints? Is specular reflection OK? Are you
concentrating sunlight? If so, by how much? What kind of environment do you intend to use it in?
Telescope mirrors are SiO2 overcoated (for amateur use) aluminum on glass because that gives very good reflectivity (88-92%) on an easy to prepare
optical surface of high quality. Large professional telescopes skip the SiO2 overcoat, but then they recoat their mirror(s) annually.
Silver has a very short service life as it tarnishes very quickly (even with a benzotriazole protective coat). Ditto copper (though not quite as
fast).
Speculum metal was only used before Liebig discovered how to silver glass. It was not very reflective (68%), it was heavy, expensive (made of copper,
tin and touch of arsenic), a b*tch to figure and polish, and tarnished very quickly. Telescopes that had speculum metal mirrors always two or three
mirrors, because one or two were always being repolished.
Special mutli-layer polymer solar collector mirrors are made commercially now that use a silver layer for reflection, these are probably the
state-of-the-art. Sites selling services (you have to contact them, they are not off-the-shelf items) for these are readily located on-line.
Polished sheet aluminum is the cheapest, lightest, durable material you could try. Simply using detergent spray washing keeps it pretty clean.
[Edited on 15-7-2016 by careysub]
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CRUSTY
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After doing a little more reading, I came across sputtering. Sputtering is a method of depositing a very thin conductive layer onto a given surface,
and if you do it right, it can be used to make mirrors. I found a couple of setups that use the transformer and capacitor from a microwave and a
vacuum pump, which get pretty great results in terms of reflectivity. I'm not sure of their quality in terms of durability or how long they'll last,
but quality aside, this is a pretty cheap way to do it. You could likely manage to do this with only scrapped parts; you could use a reversed fridge
compressor setup for a vacuum pump, and I can say from experience that re-purposing the HV system from a microwave is pretty easy and cheap (I was
able to find one that my local dump was willing to give up, and therefore got all of the working parts for free). Depending on your level of
dedication, sputtering might be worth a try, even though there are quite a few other methods to try.
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NEMO-Chemistry
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I thought 'flat' white paint was supposed to be the most reflective?? I cant remember where i saw it but it was on a gardening site and had something
to do with greenhouses, but my memory is vague on it.
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careysub
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Quote: Originally posted by NEMO-Chemistry  | | I thought 'flat' white paint was supposed to be the most reflective?? I cant remember where i saw it but it was on a gardening site and had something
to do with greenhouses, but my memory is vague on it. |
Flat white paint is the most reflective.
It is of course specular reflection, which diffuses light in all directions - which may or may not be what you want. If you are trying to concentrate
or direct light it is not what you want. For many purposes (nearly all interior illumination uses) it is what you want.
Sir Benjamin Thompson, Count Rumford (an American born Loyalist who spied for the British during the Revolutionary War) greatly improved the interior
lighting of the Royal Society by installing opal glass to diffuse the shafts of direct sunlight.
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NEMO-Chemistry
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Saves me going to google to double check i hadnt gone mad  .
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