Dan's Data letters #153
Publication date: November 2005.Last modified 03-Dec-2011.
Soooper-LED!
On the off chance that fifty other people haven't already sent it to you, and you haven't seen the story yourself, I thought I'd send you these links.
It seems someone has come up with an LED which is actually white (well, at least very, very, very, very, very, very, very pale yellow).
I'm not sure about all the efficiency bumf that's there... surely LEDs do emit heat, albeit not in the light path...
Byrn
Answer:
This isn't a true white LED; it's just a (maybe) better way to make blue ones into white ones.
As you say, the LiveScience reporter doesn't quite have his act together; he admits that LEDs don't have 100% efficiency, then doesn't keep thinking about where the lost energy might perhaps be going.
The actual big news about this discovery, if you ask me, is that the title of the paper is "White-Light Emission from Magic-Sized Cadmium Selenide Nanocrystals".
There's a better, but still not terribly good, explanation at azonano.com, from which the LiveScience piece would appear to have been, as is normal for "popular" science reporting, badly rewritten.
The azonano.com piece points out that modern white LEDs can produce about twice as much light per watt as incandescent bulbs - which used to only be true for coloured LEDs, but it approaching an acceptable state of trueness for white ones now - and last "up to 50,000 hours, about 50 times as long as a 60 watt bulb". That's not a very good statement at all. LEDs that aren't overdriven "last" an unclear period of time before becoming uselessly dim (and/or funny coloured, in the case of white LEDs; the phosphor coating burns out faster than the LED underneath and starts just blocking some of the blue light and emitting none of its own), and also because there's no standard life span for incandescent bulbs, let alone 60 watt ones.
The LiveScience report says
"Then Bowers and another student got the idea to stir the dots into polyurethane and coat a blue LED light bulb with the mix. The lumpy bulb wasn't pretty, but it produced white light similar to a regular light bulb.
"The new device gives off a warm, yellowish-white light that shines twice as bright and lasts 50 times longer than the standard 60 watt light bulb."
...which suggests that they're somewhere in the same Chinese Whispers chain as the azonano.com report.
There are no "blue LED light bulbs" I know of that draw 60 watts and produce 120-incandescent-watt-equivalent brightness; there are some fairly high powered LED "bulbs" that use clusters of LEDs and cost a fortune, but you'd need a pretty big cluster of pretty big LEDs to do 60 watts. At a guess, such a bulb would be unlikely to sell for less than $US2000 (possibly a great deal more), before you added the new magic coating.
You'd need an LED lamp that powerful to meet the livescience.com report's mangled requirements because, by definition, these nano-phosphor white LEDs won't be any more efficient than the blue LED that forms their base. That's the ceiling for this innovation, since it's a new kind of phosphor rather than a new kind of LED. There can be apparent efficiency miracles when you're using luminous measuring systems that take into account the human eye's efficiency peak in the green portion of the spectrum (normal household fluorescent lamp with standard phosphor emits white-ish light with high visible luminous efficacy; without the phosphor it'd emit ultraviolet with zero visible luminous efficacy...), but when you're starting with something clearly visible and going to something else that's also clearly visible, you shouldn't expect that effect to be very large.
Slashdot chewed this news over the other day. Check out the posts here, here and here.
Also, on This Week In Science
I guess it would have to be the US Air Force that makes transparent aluminum first.
Mark
Answer:
Well, aluminium oxynitride (ALON) is "transparent aluminum" (I suppose I should spell and pronounce it the American
way, with a Scottish accent, out of respect) only in the same
way that common glass is "transparent silicon"; it's a compound with that element in it, but with quite different
properties from the element by itself.
Actually, common glass is silica plus sodium carbonate and lime; clean fused silica is the quartz glass used for high-performance applications, some of which may end up using this ALON stuff in the future. But you get the idea.
Note also that this is not the first non-glass transparent ceramic. Nobody wants aeroplane windows made from cubic zirconia, though.
ALON is also not actually very new - it was patented a year before Star Trek IV hit the theatres.
Initial patents for advanced-material manufacturing processes, of course, are often for a process that can't make much of the stuff, or can't make it in useful physical forms, or can't make it cheaper than antimatter. Presumably there've been some advances since '85.
A super-tough glasslike material could be handy for all sorts of things besides bulletproof windows (though it could make some nifty windows, all right - imagine rollover-safe cars with all-window roofs). It's come a bit late to let us make huge CRTs that don't weigh much (and I don't know whether it could be "leaded" to stop X-ray radiation, like glass, anyway), but it could definitely make LCDs much less breakable, just off the top of my head.
And, of course, there's golf. Every advanced material, developed for the betterment of humanity or for very high energy weapons applications, shows up in either golf clubs or tennis racquets sooner or later.
Click. Warm.
I saw this thing over the weekend and I think it may interest you. It has what seem to be "perpetual motion" like properties, and an oh-so-simple trigger mechanism. It is also fun to see it change state. I have no idea how it works, but it does work and works quite well. I wonder what you'd make of it?
I don't sell these things, and I am in no way associated with them, I just used one and found them to be very cool... or actually, warm. I also wonder how the hell they work, and if they in fact work forever.
Saul
Answer:
Perpetual motion? No, not unless you've found one that doesn't need to be boiled to "reset" it.
But indeed these liquid-to-crystal heat packs are fun to play with - this girl seems to agree.
"Phase change" heat packs were patented back in 1978. They contain a supersaturated solution of sodium acetate, whose exothermic crystallisation process is kicked off by clicking the metal doohickey, which spawns a few seed crystals. Boil the resultant solid mass and it absorbs heat and re-liquefies.
The other common kind of heating pack (not counting simple hot water bottles and their relatives, like microwavable wheat bags) only works for one use - it contains iron powder, and catalytically oxidises it. This process is flameless and gives long-lasting heat, but it also consumes oxygen, so when people use it to keep little beasties warm in shipping containers (or keep their snake tank warm during a power outage, or whatever), they have to remember to provide ventilation.
Here's some info on both kinds of pack.
There's yet another kind of pocket-warmer, that runs on lighter fluid with a glass-fibre wick containing, I think, a bit of platinum plated mesh. You light the wick, then cover it with a perforated lid after a few seconds. The flame goes out but the fluid keeps oxidising, and the gadget stays warm for a long time, once again consuming oxygen as it goes. It'll give you the good old "Zippo rash" on any skin exposed to its vapours, though.
(Here in Australia, you can get the lighter fluid warmers here. They sell the acetate type, too, with a marvellously scientifically inaccurate description. Or, of course, there's always eBay.)
In theory, acetate heat packs can be re-used forever. In practice, they'll spring a leak after a while.
Rust bug killer
I want your opinion on electronic rust prevention - specifically, the RustStop RS2000.
According to this page, it overcomes the weaknesses of electronic rustproofing by using more than one method.
I'm sceptical, but I don't want to get all messy with underseal on my rust-prone car. If this is a simple way out, I'm all for it.
Shuhel
Answer:
I'm sure the RustStop works perfectly, provided you remember to dig a big hole and bury your car in it after installing
the device.
You could also drive the car into a lake. Or the ocean. That might screw up the electrics, though. The RS2000 will probably only keep working (battery charge permitting) if the car's buried.
The reason why this thing won't work on a car that's above ground is that there's no circuit between the sacrificial/impressed current anode and almost all of the rustable parts of the car. The conductive tape that you stick the anode(s) in place with means they'll protect the metal right under them just fine, but, y'know, paint'll do that too.
Passive galvanic cathodic protection (your standard "sacrificial anode" system, like when they bolt chunks of magnesium to ships below the waterline) and active impressed current cathodic protection (as used for underground pipelines and other Big Things where there's a long and lousy current path between the anodes and the metal they're protecting) both rely on the fact that the things they're protecting are lumps of metal surrounded by an electrolyte - water or earth.
Iron and steel rust essentially by forming tiny electrochemical cells anywhere that water and oxygen can get to the metal. Zero humidity air: No rust. Iron in a big box full of humid nitrogen: No rust. Iron submerged in salty water that's got no dissolved oxygen in it (which can almost be the case, deep in the ocean): No rust.
The particular curse of iron is that its rust is flaky, so more metal is continuously exposed to the air. Aluminium is much more reactive than iron and corrodes much faster, but its oxide forms a hard thin layer over the rest of the metal and protects it - if something doesn't cut the oxide layer, almost all of the metal survives indefinitely.
To protect flaky-rusting metal like iron, you attach a more reactive metal to it, applying current if necessary to boost the electrochemical path from the iron through the surrounding electrolyte to the sacrificial anode, which corrodes away instead of the iron.
You can demonstrate this effect yourself at home, quite easily; in a bucket of salty water, immerse one "tin" can (which'll actually be made out of steel these days; "tinfoil" was originally tin as well, before aluminium became cheap) and one otherwise identical can with a chunk of magnesium attached to it. Lightweight metal pencil sharpeners are cheap, and for some reason are made from a magnesium alloy, as everybody who had a cool science teacher in high school should already know.
Any way of attaching the magnesium that gives it metal-to-metal contact to the can will do - not glue, but just tying it on with some steel wire would do.
Can A will rust. Can B should remain pristine, while the sharpener slowly disappears. If you leave it long enough, the magnesium will vanish entirely, and then Can B will rust.
Try the same stunt with the two cans just sitting outdoors exposed to the elements, though, and the piece of Can B right under the sharpener will stay unrusted, while the rest of it rusts as normal, because there's no surrounding electrolyte. Rain will form a current path from the magnesium to the steel for a short distance around the sharpener, but most of the can will be unprotected most of the time, and applying a voltage to it won't help.
Modern steel-bodied cars have high quality galvanised panels as a matter of course anyway, which has largely eliminated the rapid-and-serious rust problems that people used to know and hate. They'll still rust eventually, of course, but if you don't scratch the finish and/or expose it to lots of particularly inclement weather, I wouldn't be surprised if a 2005 Toyota Corolla remained cancer-free 20 years from now. Maybe even longer.
A 1985 Alfa Romeo will, of course, probably fit in a matchbox today.
The only really foolproof rust prevention system, of course, is to use one or another "stainless" metal. We may see more stainless steel used in cars in the future, but seeing as it's historically been more expensive than aluminium - which, in turn, is far more expensive than carbon steel - I wouldn't hold my breath for it to show up in many affordable vehicles, if I were you.
There've been a few cathodic protection gizmos for cars in the past, none of which have worked, but the RustStop people insist their product isn't like all those other Scams Engineered By The Barely Literate.
RustStop is stated on various pages to be "the only system to successfully combine both Impressed Current and Sacrificial Anode technologies"... except that impressed current is just a way of making sacrificial anodes work better, so, uh, every impressed current system, uh, combines the "technologies".
They also say that the RS2000 has been "independently tested by an unrelated company" and shown to work, but they won't say who that "unrelated company" was, or where the results can be found. They mention the "tests" over and over, but keep unaccountably forgetting to fill in those blanks.
Instead, they offer testimonials.
No, wait - those are some other equally reliable testimonials. The RustStop ones are here.
And, in a side point, the ruststoponline.com domain is registered by my fellow Australian, Paul Barrs. As get-rich-quick artists go, he does not appear to be a particularly notorious one. But he's still a get-rich-quick artist. Make of this what you will.
While you're making of it what you will, you might also like to make what you will of the RustStop site's numerous irrelevant-link pages, presumably intended to make it look all hip to search engines.
A concept related to impressed current cathodic protection, by the way, is electrolytic rust removal. It really works, and amazingly well; you can use it to do tricks like cleaning up ancient tools so well that you can read the maker's name stamped on them.
To do it, you need an alkaline bath. Some sodium bicarbonate or carbonate in water will do; professional shops use sodium hydroxide, but bicarb or washing soda won't turn your hands to soap nearly as quickly. I've found a large cat litter tray makes a great cheap bath for various hand-tool-sized objects.
You also need a DC power supply. A car battery charger or surplus PC PSU should be just dandy; some sources recommend quite weedy power supplies, because they are weak and have no honour. If you're de-rusting something really big and want the job done inside a week, you'll need a lot of current capacity and enough voltage to push that current through the solution, so something scary like a DC arc welder could be called for.
The last piece of the recipe is a piece of iron you really don't care about. For small jobs, another "tin" can will do. Any plain iron or steel is suitable, but, as a reader reminded me, you should not use stainless steel for this sacrificial electrode unless you feel you need more chromates in your diet.
Connect the object to be cleaned to the negative terminal of your power supply, the sacrificial iron to the positive terminal (don't dip a positive-terminal alligator clip into the bath unless you want it to get eaten), submerge both pieces of metal in the bath without letting them touch, and turn on the juice.
The result will be bubbles, the rapid destruction of the sacrificial iron with lots of 'orrible red gunk accumulating in the bath, and the mystic disappearance of the rust on the object to be cleaned. Just running some water over the cleaned object should remove the loose gunk sitting on it afterwards.
This process verges on the magical the first time you see it, but all it does is remove iron oxide while preserving iron. Actually, technically, it eats a tiny amount of good metal where rust used to be, converting it into a super-thin layer of black oxide. Shiny steel won't be changed.
This process won't, however, regenerate the maker's name on some amorphous blob of oxide that someone dropped in your garden in 1952. The makers of some RustStop-ish gadgets apparently make regenerative claims (or their testimonials do, anyway...). The continuing health of the Bondo Corporation would appear to contradict them.
But since, to borrow a quack medicine favourite, healthy tissue is not harmed, this is by definition the world's least destructive de-rusting technique.
Electrolytic de-rusting does leave a very, very rustable fresh surface, though; anywhere that used to be rusty will now be black and ready to rust again, so as soon as you pull the item out of the bicarb bath, you should give it a coat of oil.
For in-situ de-rusting of bits of cars, houses, battleships and so on, the best quick solution is phosphoric acid products - phosphoric acid is the active ingredient in various "rust converter" paints. The very thought of "naval jelly", however, induces involuntary twitches in many of the world's military personnel for very good reason. If you're going to have to use much of the stuff, serious thought should be given to just selling the car or ship to a suitably gullible person or nation.
