Spray-On Glass

[Aggie]

A German company has reportedly commercialized a spray-on SiO₂ ultra-thin layering product, used to coat surfaces, fabrics etc. for easy cleaning, stain resistance and general protective ability.  Apparently this stuff can even be sprayed on plants to protect against pathogens:

http://www.nanopool.eu/couk/index.htm




Paging Dr. Swato....
Please keep an eye out for this product and an ear out for any public feedback.  As wary as I am about the health consequences of nanotechnology, this seems like an interesting product.

[Opsa]

Looks like there have been some studies on the toxicity of SiO₂.
Here's one.

[Swatopluk]

Ever heard of silicosis?

If it's used on plants, does it not close the pores leading to first suffocation and then dehydration (because the water is drawn up by evaporating through the pores)?
We have an expert on nanoparticles here at the agency. His latest report was not to the industry's liking.

[Pachyderm]

Covering the stoma would not be beneficial to the overall health of the plant...

[Aggie]

Ever heard of silicosis?

If it's used on plants, does it not close the pores leading to first suffocation and then dehydration (because the water is drawn up by evaporating through the pores)?
We have an expert on nanoparticles here at the agency. His latest report was not to the industry's liking.

This appears to be more along the lines of amorphous silica than crystalline, not sure if that'd make a crucial difference.  I am suspicious in general of nanoparticles; many other technological revolutions have not appeared so beneficial in hindsight.

The promoters claim this stuff is breathable enough to allow the plant to respire, so who knows?

[Bob in a quantum-state-of-faith]

Ever heard of silicosis?

If it's used on plants, does it not close the pores leading to first suffocation and then dehydration (because the water is drawn up by evaporating through the pores)?
We have an expert on nanoparticles here at the agency. His latest report was not to the industry's liking.

This appears to be more along the lines of amorphous silica than crystalline, not sure if that'd make a crucial difference.  I am suspicious in general of nanoparticles; many other technological revolutions have not appeared so beneficial in hindsight.

The promoters claim this stuff is breathable enough to allow the plant to respire, so who knows?

Amorphous?  That would mean it's molecular structure is akin to normal window-glass, which is also highly amorphous itself-- more like liquid than solid.

In fact?  100 year old glass can be seen to have sagged in it's frame, due to gravity, and the glass 'flowing' over the years-- it is measurably thicker at the bottom than the top.

Hmmm.   But to be able to pass O2, H2O vapor and CO2, the 'holes' would have to be numerous.

================

Nevermind that, I'd love to see this stuff sprayed over plastic lenses-- NO MORE SCRATCHED UP EYEGLASSES!

[Aggie]

Given the fact that it forms thin flexible layers, I can't imagine that it would be crystallized.

The premise on 'breathability' is that at the thicknesses involved (100 nm), moisture and gases could diffuse through.



I can see a myriad of uses for this type of product, provided it was safe and reasonably cheap. It's the safe part that I wonder about.....

[Sibling Zono (anon1mat0)]

So is this a molecular permeable mesh, and one that doesn't shed nanoparticles which in turn get absorbed by living matter? As with every early discovery it would be nice to know all its properties and downsides.

[Swatopluk]

So is this a molecular permeable mesh, and one that doesn't shed nanoparticles which in turn get absorbed by living matter? As with every early discovery it would be nice to know all its properties and downsides.

Those are surely closely held secrets.

[Bob in a quantum-state-of-faith]

Given the fact that it forms thin flexible layers, I can't imagine that it would be crystallized.

Actually?  No glass is crystal in structure...the name 'glass' has become synonymous with amorphous, non-metallic, non-liquid substances.

[Swatopluk]

I think the non-liquid is not mandatory. The border between liquid and solid is.. eh.. fluent there.

[Griffin NoName]

I think the non-liquid is not mandatory. The border between liquid and solid is.. eh.. fluent there.

A "solvus", in a physical or geochemical system, is a line (binary system) or surface (ternary system) on a phase diagram which separates a homogeneous solid solution from a field of several phases which may form by exsolution or incongruent melting. The line determines a solid solubility limit which changes as a function of temperature.

An example is the formation of perthite when an alkali feldspar is cooled down.

{wikipedia}

Ok. I am just showing off my great knowledge gained when working with paeleontologists and their ilk.

[Lindorm]

Amorphous?  That would mean it's molecular structure is akin to normal window-glass, which is also highly amorphous itself-- more like liquid than solid.

In fact?  100 year old glass can be seen to have sagged in it's frame, due to gravity, and the glass 'flowing' over the years-- it is measurably thicker at the bottom than the top.

Actually, that is a myth. While glass is to some extent viscous, it is not viscous or liquid-like enough to start floating away in any sensible timeframe for a human. If it were so, the 3000-year old persian glass I and Darlica were admiring at an exhibition a few weeks ago would have been a puddle by now, instead of a beautiful vase.

The differences in thickness are actually there, though, and are a result of the manufacturing process. (Coming from a family of glassworkers has it's advantages!). Windowpanes were originally made by taking a piece of flowing glass mass from the oven, attaching it to a pipe, giving it a quick and short blow to puff it up a bit, and then start spinning the pipe like the very blazes. The centrifugal forces would then make a flat glass disc, which would be carefully knocked off from the pipe when it reached sufficient size, and then let off on a cooling bed. The discs were not especially big, and always somewhat thicker at the edge of the disc. Variations in rotating speed and jerking could also lead to uneveness. There would also be a small nub at the centre, where the glass disc had been attached to the blower's pipe. The discs could (if they were small) either be used as they were, or cut to square panes. Since they were expensive and difficult to make, the panes used as much of the disc as possible -including the uneven edges. Normal practice when setting these panes in a window, using lead edging or caulking, would be to try to set them with the thicker side downwards, since that made them easier to fit and join.

Later on, manufacturing processes changed and improved. Machines where introduced that made huge glass cylinders or pipes, which then could be cut and flattened out by craftsmen to form large windowpanes. Again, the process wasn't perfect, and it took a fair amount of skill to cut and flatten the pipe without distorting it. One of the windowpanes in my flat is manufactured by this old process, and has a slight distortion running along one of the edges, a sort of small crease that gives a slight prismatic effect to it. With both these processes, the cutting, grinding and polishing of the panes was a crucial step where an unskilled cutter could ruin large amounts of glass.

From the 1930'ies and onwards, experiments and advances were made in pouring and casting glass, to get large flat sheets. Glass that is poured on a table tends to get slightly where the pour was made, and if there is even a hint of a tilt to the surface, the molten glass inevitably tends to collect in the lower areas. Nowadays, most cast glass is so-called float glass -glass that has been poured on a liquid surface, to ensure it's evenness. Pouring is mostly done by robots with multiple nozzles according to carefully calculated pouring programs.

And certain glass works here in Sweden has now started manufacturing spun disc glass again, for the heritage market...

[Bob in a quantum-state-of-faith]

Actually, that is a myth. While glass is to some extent viscous, it is not viscous or liquid-like enough to start floating away in any sensible timeframe for a human. If it were so, the 3000-year old persian glass I and Darlica were admiring at an exhibition a few weeks ago would have been a puddle by now, instead of a beautiful vase.

I ain't gonna argue-- my memory from that is attached to a "sciency" type show, like Mr Wizard, who did not always fact-check his stuff.

Although I could point out that formulas for glass is as varied as formulas for fertilizers... and that different glass-formulas have different rates of slump, and that some glass is much more elastic than other glass, due to these different formulas.

I seem to recall reading about how ancient glass craftsmen would be constantly experimenting with adding different reagents into the mix, to try to change the glass' properties.

I do remember looking up the difference between common glassware as used in chemistry labs, versus the "corning glass" used in the better chemistry glassware-- aside from the formula, the expansive properties of the two different glass formulas was striking:  'ordinary' glass would expand under heat quite a bit more than corning-glass would.  The simple addition of other chemicals into the mix, reduced corning-glass' expansion properties enough, that by the time one section had expanded enough to break-- the nearby section expanded also, preventing the breakage.

My chemistry teacher and I were curious one slow afternoon, why corning-glass could take direct flames, whereas 'ordinary' glass could not-- it would fracture.

We proved you *could* break corning glass with heat, if you tried hard enough.... the tip of an oxy-acetylene torch, for example.     Or, if you took a beaker you'd heated up well into the 300 degree mark, then plunged it into an ice-bath, it would crack.   

As for the window-glass slump?  As I said, my source for that was not reliable-- in fact?  It may have been in a DIY home show, and not Mr Wizard... I really don't remember where I picked it up.

[Swatopluk]

The old myth is still (to my knowledge) teached in schools, same as the identification of the hemisphere by observing the vortex in the sink.

[Darlica]

Both are indeed common myths...
And the glass one is still told, I have corrected guides who work professionally guiding people in and about historical buildings...

These large glass cylinders L is talking about can still be found on auctions and yard sales here (mostly in the south of Sweden), most of the time they are seen as quite mysterious items as no one usually knows their purpose. Usually the glass in these have air bubbles or some other defect that rendered them useless for windows but of some unknown reason they didn't got smashed and remelted.

IMHO glass is one of the most fascinating materials we have and I would love to try to work with it sometime.