Wikipedia:Reference desk/Archives/Science/2008 April 18

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April 18

At what temperature does tungsten burn?

Copied from Talk:Tungsten#At_what_temperature_does_tungsten_burn:

"Tungsten metal forms a protective oxide when exposed to air but can be oxidized at high temperature."

From what I read in a research paper a while ago (in which they heat tungsten by induction in still air), the oxide has a lower melting point than the tungsten metal, which allows it to be ablated away by a hot enough flame, and the layers of tungsten underneath oxidized and ablated away and so on. But what temperature, exactly?

• Tungsten(VI) oxide WO₃ is apparently the most common form, melting at 1473 °C
• Tungsten nitride
• Tungsten(IV) oxide WO₂ lists melting point of "1700 °C (decomposes)" - what does that mean?
• Tungsten(III) oxide W₂O₃ ??
• Tungsten pentoxide

Which of these forms under a hot flame? All of them? What's the minimum temperature flame required to turn a piece of tungsten into smoke (rather than just heat it up)? Would a pure oxygen atmosphere make a difference? — Omegatron (talk) 00:11, 18 April 2008 (UTC)

Tungsten is a brittle metal, which makes a great light bulb filament, and can be heated to a higher temperature than carbon, but is difficult to form into a filament. If only it were more ductile! Edison (talk) 05:08, 18 April 2008 (UTC)

Your answer doesn't answer Omegatron's question, but to comment on your answer, I presume you mean "can be heated to a higher temperature than carbon" with respect to oxidation in an oxygen-containing atmosphere, because I know that the melting point of tungsten is lower than the sublimation point of carbon (carbon doesn't melt at atmospheric pressure, it sublimes directly to the gas phase). But in a light bulb the tungsten filament is under a protective argon atmosphere (nitrogen would also react with tungsten at these high temperatures). If you destroy the glass bulb while the light is on, the hot filament will burn instantly as it makes contact with air. Icek (talk) 19:50, 18 April 2008 (UTC)

That doesn't really answer the questions. Let's restate them:

1. Which types of tungsten oxides would form on a piece of tungsten if it were heated in a flame in air?
2. What temperature flame would be required to make the tungsten "disappear" as smoke? — Omegatron (talk) 23:16, 18 April 2008 (UTC)

Icek states that nitrogen is not used in tungsten filament lightbulbs, and implies that carbon filaments could be run at a higher temperature than tungsten,but our article Incandescent light bulb says it nitrogen is used in tungsten bulbs, sometimes with other gases. Rather than burning up "instantly" tungsten filaments sometimes last a few second exposed to the atmosphere. And some smaller lightbulbs still have vacuum around the filament rather than a protective gas. Some early tungsten bulbs used nitrogen alone. An old (1917) source (available online)[1] says carbon filaments were operated at 1600 celsius and tungsten at a higher temperature of 2000 celsius. Carbon filaments were too short-lived (though higher efficiency) if operated near their sublimation temperature. This source also states that nitrogen was used as a fill gas for tungsten filament bulbs. A newer book (1994) says again [2] that carbon filaments are only operated up to 1750 C while tungsten filaments are operated at 2400 to 2750 C with fill gas of argon or nitrogen. Edison (talk) 23:48, 18 April 2008 (UTC)

Thanks for pointing out my error on implying that nitrogen would render a bulb filled with it unworkable - but it does produce some tungsten nitride (see also this patent), it is probably somewhat self-passivating (forming a protective nitride layer on the surface). Icek (talk) 03:08, 19 April 2008 (UTC)

Regarding Omegatron's question, this link does unfortunately not answer it but it says that when light bulbs are broken it's mainly tungsten(VI) oxide. This document which is not freely available should answer the question. Icek (talk) 03:08, 19 April 2008 (UTC)

Watch faces radioactive?

I read that in a previous thread, but didn't want to hijack it. Imagine Reason (talk) 01:12, 18 April 2008 (UTC)

Very old ones made with radium, or newer ones made with tritium (the latter was a fad that I think kind of died out; the former was abandoned for safety reasons, not so much for the consumer as for the workers who made the dials). --Trovatore (talk) 01:14, 18 April 2008 (UTC)

(EC) There's some info at Radium#Historical_uses. And I'm positive that current watches don't use radioactive substances on the face. -- Flyguy649 ^talk 01:16, 18 April 2008 (UTC)

Tritium watches are still an active specialty market item [3], though you probably will find few or none at most watch stores. Dragons flight (talk) 01:28, 18 April 2008 (UTC)

Perhaps not "on the face" exactly, but you can get watches where phosphor paint is "one the face" and the entire face is in a sealed enclosure full of tritium. See this photo from the Tritium article. A quick search of Google or even Amazon for "tritium watch" will show you lots of brand new watches with Tritium in them for purchase.

On a closely related topic I just this week purchased a key fob with tritium in it, though I had to import it from a web-site in Hong Kong. APL (talk) 18:39, 20 April 2008 (UTC)

Actually, I think I'm wrong on that. I think most of them work with the tritium and the phosphor sealed into tiny tubes that are embedded into the face. APL (talk) 19:58, 20 April 2008 (UTC)

The modern material is photo-phosphorescent. You can check this by keeping the watch in the dark for a few days, it will no longer glow. Radioactive materials glow continuously for years. Franamax (talk) 01:23, 18 April 2008 (UTC)

Well, the tritium ones are also sort of "modern". I don't believe they were ever banned. Even though tritium is in some sense much more radioactive than radium (more disintegrations per second in a sample of the same size, either by weight or by moles), the low-energy betas from tritium are usually considered much less dangerous than the high-energy alphas from radium. I don't know if anyone is currently manufacturing them, thouh; they may just not have proved profitable. --Trovatore (talk) 01:31, 18 April 2008 (UTC)

They are certainly still out there. I'd imagine the greater concern might be safety in manufacturing i.e. the possibility of workers breathing in dust. Here is an interesting link on the subject. Franamax (talk) 02:10, 18 April 2008 (UTC)

Franamax, my brand new tritium key chain spent about a week in an opaque airmail envelope as was already glowing when I first peaked into the envelope. APL (talk) 18:39, 20 April 2008 (UTC)

They do still make emergency exit signs with tritium. --69.134.124.30 (talk) 02:27, 18 April 2008 (UTC)

The very sad historical fact is that per United States Radium Corporation women were reportedly employed to paint "glow in the dark" dials and had to lick the brushes to shape them, thereby ingesting radioactive pigment which caused cancer. Edison (talk) 05:05, 18 April 2008 (UTC)

And it's worth just throwing in that this particular case was extremely famous at the time, and became the first real moment in which the public realized that radioactivity was hazardous to one's health, and was also the first time that scientists really began to study the health effects of radioactive materials (Robley D. Evans, in particular—pity we don't have an article on the pioneering health physicist, just on some Civil War rear admiral). --Captain Ref Desk (talk) 12:57, 18 April 2008 (UTC)

Industrial hygene

What are the web sites of the largest professional societies concerning industrial hygiene? 75.61.111.185 (talk) 08:48, 18 April 2008 (UTC)

 Done Occupational hygiene#Professional Societies. 75.61.111.185 (talk) 08:56, 18 April 2008 (UTC)

Aerodynamics of human powered vehicle-land

hi!!!!! I would like to ask a question about human powered vehicles. what is the role of "Aerodynamic lift" in human powered vehicles -land?? and how is it countered for the same vehicles??

          Please reply as soon as possible
                  Thanking you

Hi! and welcome. I decapped the question because all caps is shouting and to indent you need : to format, otherwise ... well, there's a difference. Our linking to Aerodynamic lift gives you mechanical Lift (force), looking at "a mechanical force generated by solid objects as they move through a fluid." Mainly with wings and airfoils with handy links. Any help? Julia Rossi (talk) 09:09, 18 April 2008 (UTC)

Lift is used in aircraft to push them upwards. On land vehicles, however, you don't want them pushed upwards. On the contrary, you sometimes want them pushed downwards so they get better traction. Essentially an upside-down airfoil can be used for this effect, and this is common on some race cars, such as Formula One (see pic of wing at the back of this car: [4]). A human-powered vehicle, however, isn't likely to go fast enough to need this downward force to keep it in contact with the pavement. Thus, any benefit from such a reverse wing is likely to be negated by increased drag and weight. StuRat (talk) 19:33, 18 April 2008 (UTC)

US military and NOTAR

Does the US military currently have any plans to adopt NOTAR technology? --AtTheAbyss (talk) 13:03, 18 April 2008 (UTC)

The newest helicopters being worked on by the Army (the UH-72 Lakota and Bell ARH-70) have standard tail rotor designs. — Lomn 13:25, 18 April 2008 (UTC)

On the other hand, the Coast Guard was apparently evaluating a version of the MD Explorer, known as the MH-90, in the late '90s. It appears one squadron operates out of Florida. — Lomn 13:32, 18 April 2008 (UTC)

According to the article, two of the disadvantages of NOTAR are a loss of efficiency and a loss of maneuverability -- not good things if you're operating in a combat zone. --Carnildo (talk) 21:38, 18 April 2008 (UTC)

Impossible memories

I didn't have any imagineary friends when I was little, but I had some imaginary "experiences". For example, i clearly remember rays of bright colors shooting across the night sky, and two goats singing (in human voice) while grazing. There were other, even sillier, incidents too. I believed in these and remembered them just like actual memories until I was grown up enough to realize they couldn't possibly have happened actually. Is there any name (or an article) for such a phenomenon? Thanks. 125.21.165.158 (talk) 16:01, 18 April 2008 (UTC)

I don't know a name, but I've suspected that such things might be memories of dreams. And, as a little kid, it probably didn't occur to you at the time that they can't be real memories. Friday (talk) 16:38, 18 April 2008 (UTC)

Although the articles only discuss rather serious, negative cases, confabulation and false memory syndrome may be worth a read. Don't scare yourself though; the article only deal with medical and legal nasties, but false memories are rather common. I remember an amusing experiment where people were tricked into remembering meeting non-disney characters during a childhood trip to Disneyland, or remembering balloon rides they never took. I'm guessing confabulation most closely describes what you experienced, but not in a medical way :) 79.66.106.188 (talk) 20:58, 18 April 2008 (UTC)

Hi. I seem to have some false memories too from when I was little, but I have no idea if it was from a dream or if it was true but modified. It goes like this, I see two moons in the sky, yellowish in appearence (and I still remember which room it was in within that building), and they were supposedly Jupiter and Saturn, and I remembered seeing a picture of Saturn on TV at the time. It's possible, but I don't think it was real. It's possible I have memories from before I was one, but they are rather blurry, and I'm not going to tell too much for privacy reasons, and some details may be fake or suggested later in life, such as being fed orange juice while the small clock read 4 pm, and a large banner outside the room and a meeting outside. As time passes, memory can degrade. However, I still have some vivid memories form when I was little, and I do have ones I know are from dreams too, like seeing an emperor in grayish foggy mist approaching. Memories from a very early age, if any at all, can be very blurry, and details can tend to be fake. In fact, as I go back to age 2 or 3, only about a hundred individual memory "moments", and even farther back only about a dozen moments. I can probably recall many thousands of moments as you go to say, 6 or 7 and back. It's also possible that you were remembering a vivid real moment, but over time your brain has added "details" that may not be real as you grow older. Hope this helps. Thanks. ~AH1^(TCU) 23:49, 18 April 2008 (UTC)

Another possibility is that your infant brain may have seen a movie or TV show, not having the awareness to distinguish that memory from a real one. -RunningOnBrains 15:52, 21 April 2008 (UTC)

Stabilised vs non-stabilised swimming pools

I have noticed that many swimming pool chemical products give two sets of different dosage instructions: one for 'stabilsed' pools, the other for 'non-stabilsed' pools. What is the difference, and how do I know which category my own pool fits into ? Thank you--196.207.47.60 (talk) 16:36, 18 April 2008 (UTC)

If I'm not mistaken, non-stablised would describe the water when the pool has just been filled - i.e. nothing has yet been done to get the water to the desired pH level, alkalinity, etc. From my own experience with a hot tub, it can be a bit of a chore to get everything in balance so that on-going maintenance can be accomplished via the doses specified for stabilised water. --LarryMac | Talk 16:48, 18 April 2008 (UTC)

"Stabilized" with respect to pool chemistry usually refers to the presence of cyanuric acid as a stabilizer for the chlorine (or bromine). DMacks (talk) 17:06, 18 April 2008 (UTC)

Right. I went round and round with my brother-in-law last year about this. Here is a page that explains the chemistry in a way that even I can come away believing I kind of understood. To simplify, the cyanuric acid (CYA) bonds with the chlorine, keeping it from being destroyed by sunlight. When you then add chlorine, the CYA gobbles it up until it can't gobble up any more, at which point any additional chlorine goes to "shock" the pool, if that's what you're after. If your pool is "overstabilized", you'll need tons and tons of chlorine to shock it. Any outdoor pool simply must be stabilized and almost certainly is; only indoor pools, as a rule, might not be stabilized. You can buy a CYA test kit cheap. --Milkbreath (talk) 17:53, 18 April 2008 (UTC)

Synthesising oil

There seem to be so many questions about oil recently, and they got me thinking. Will it be possible to chemically syntesise oil? If it will, could it ever be financially viable to do so? Could we improve on oil by making it less polluting or something? If we can't do any of these things, why not? We can make diamonds, right? Michael Clarke, Esq. (talk) 16:52, 18 April 2008 (UTC)

Please reread Steve Summit's response to one of those earlier questions:

Remember that what's "magic" about oil is that it's essentially a free form of energy. In its refined forms it's great for fueling cars and trains and aeroplanes, but what's vastly greater about it is that it taps millions of years of accumulated, concentrated solar energy. It costs a certain amount of money to get it out of the ground and refine it, but the cost is far less than its worth in dollars per joule. (That's precisely why the oil companies are so profitable.)

Instead of oil, let me talk about hydrogen for a moment. Hydrogen is a usable fuel which produces water when it burns. If you want to produce hydrogen from water, it's simple (in principle): just run some electricity through the water (electrolysis). But this doesn't mean we can all start using hydrogen-fueled vehicles and no more oil problems, because the electrolysis consumes more energy that you would get by burning the hydrogen.

Similarly with oil. Organic chemistry is a well studied subject and I'm quite sure it'd be possible to start with combustion products like water and carbon dioxide and produce the hydrocarbons found in oil. But it would take more energy than burning the oil would provide. So this is in no way a practical idea as a fuel source. The reason oil is used so much as fuel i s that it is already there, as Steve said, with "millions of years of accumulated, concentrated solar energy" embodied in it. There's no way to shortcut around that.

--Anonymous, 17:45 UTC, April 18, 2008.

Yes, we can make diamonds (synthetic diamond), and yes, we can synthesize oil. It's actually not terribly difficult at all (see synthetic oil, but keep in mind those methods start with other fossil fuels. There are other synthetic methods that can start with plant matter, see Fischer-Tropsch process). As mentioned repeatedly, the main problem is that it costs energy (which should not be surprising to anyone with a basic understanding of chemistry, since oil is usually used as a source of chemical energy). And so it will never ever be energetically viable to synthesize oil, as you'd need to drive the process with an amount of energy greater than you could retrieve by burning the oil you ended up making. But there are other uses of oil, and very important ones. Virtually the entire petrochemical industry relies on oil and other fossil fuels. As such fuels become scarce, it will become financially viable to synthesize such chemicals from plants, and there are some people already doing just that. And there is certainly the biofuel movement to create renewable fuels, not that it would actually be energetically efficient at all, and the current biofuels compete with land for food crops to create even more issues. Someguy1221 (talk) 17:59, 18 April 2008 (UTC)

There are uses for synthesizing a liquid form of energy, however, if that allows for a greater power-to-weight ratio than the original form. For example, let's say you have electricity from solar, wind, hydro, or nuclear sources. You can create cars that run on electricity, but not planes, as the batteries weigh too much and store too little energy to be useful there. So, using the electricity to synthesize some form of liquid fuel may make sense. Also, since the existing car fleet can't easily be switched to electricity, the synthetic fuel may make sense during the transition period for cars, as well. StuRat (talk) 19:20, 18 April 2008 (UTC)

Yeah, I get that it could never be energetically viable, but that doesn't mean it couldn't make sense financially. If we got all of our fuel from hydrogen, oildstill has many uses. The main one that occurs is plastic. So could it be worthwhile usiing a hydrogen-powered process to synthesise oil which would then be turned into plastics? If therewas no oil left on Earth I can't see any other way to create plastics. Michael Clarke, Esq. (talk) 21:28, 18 April 2008 (UTC)

IMHO the above is an incomplete picture. If there is sun involved in the synthesis then the energetics can work ok and of course biomass does not have to be on land (there is loads of work done since the early 1980s on putting nitrates into shallow sea and harvesting the algae for biomass). Broadly yes you can make oil and the key questions are enviro impact and cash not energy. --BozMo talk 21:41, 18 April 2008 (UTC)

There are other actually many methods to synthesise plastics, such as with bacteria; and other starting materials that can be used to synthesise plastics, such as biomass. Remember the primary reason why nearly all of our plastics use petroleum is probably not because it's easy (it may be a factor but I doubt it's primary) but because petroleum has always been so darn cheap compared to everything else. Many of these methods are not economically feasible at the moment. But as things change (increasing price of petroleum and growing concern over the environmental effects of plastic) and technologies improve (with the additional incentive for these technologies to improve), it may turn out that's more effiecient to use these methods rather then synthesise oil for producing plastics. And so perhaps most of our current plastics may be replaced with alternatives. Or perhaps not, no one knows. You may want to take a look at bioplastic and plastic. I'm sure I came across one example somewhere once of a rather old plastic or potential plastic that didn't or didn't have to use petroleum for it's source material which I felt illustrated that this isn't exactly a completely new field, just one that hasn't attracted much interest until now. (I don't think it was Amylomaize) Nil Einne (talk) 22:06, 18 April 2008 (UTC)

There is much more to automotive fuel than the fact that ancient solar energy is stored in it and that it provides net energy greater than the energy needed to extract refine and transport it to the filling station. Liquid hydrocarbon fuel is presently a far denser form of energy, both by space and by weight, than other forms of portable energy which could be used to power cars such as batteries. There should be a market for synfuel even if it takes more energy to produce than it provides to the car. The input energy used in the synthesis could be something green like a solar array on the roof of a residence or something less green like a breeder reactor. The end result should be a source of energy that will power a car at highway speeds as far as a tank of gas presently does. After over 100 years of electric cars, batteries still suck at energy density compared to liquid fuel. Some process which converts plant material to auto fuel, or which provides hydrogen fuel, even with a greater energy input than the energy the fuel ultimately delivers to the car, would be of interest. We are expected to arrive at the year when the maximum amount of petroleum is extracted from the ground , and worldwide demand is constantly growing, which will steadily drive up the cost of petroleum as old oilfields are re-worked and less promising fields are exploited in more expensive, sometimes more polluting, and sometimes more water-wasting methods. Edison (talk) 23:15, 18 April 2008 (UTC)

Hi. Remember, if it takes energy to make energy, then you're going to need some type of fuel to make the energy so it wouldn't be efficient. For example, if you're using oil or another fossil fuel to provide the energy to synthesize oil, likely the end product that you produce will be less than what you started with. As for diamonds, it doesn't usually take diamonds to make diamonds, but simple "methods" like squeezing pencil lead over a furnace vent just doesn't work at all (which I tried a while ago), and ways to make homemade non-carbon structure diamonds like putting peanut butter with charcoal in the microwave, which I read on the internet, are apparently very VERY dangerous, although it's even possible to make diamonds from deceased pets, but most people prefer natural diamonds, although there are fake diamonds made form glass or plastic because real ones are so expensive. Thanks. ~AH1^(TCU) 23:38, 18 April 2008 (UTC)

Please read the previous posting and notice the argument that PORTABILITY has a value even if there is a net loss of energy. Batteries at their present state of development cannot power a car for a cross country trip. Hydrogen or hydrocarbon fuel can. The prime source of energy need not be fossil fuel: there is nuclear, with breeder reactors making efficient use of available uranium (even conventional reactors function to some extent as breeders). Solar also has some promise as a source of energy which does not rely on fossil fuel. Some net loss of energy is tolerable if the result is automotive fuel. There does not seem to be much political will in the U.S. to provide adequate rail or bus service to most of the residents adequate to their needs. As for diamonds, well they CAN be made to burn in oxygen, but they are not a promising fuel source in general. Edison (talk) 02:27, 19 April 2008 (UTC)

Ok, so it is possible to synthesise oil, and we seem to be at a deadlock on whether it would be worth doing; there are very good points on both sides. But how about the last bit of my question? Would it be possible to improve oil? Michael Clarke, Esq. (talk) 03:58, 19 April 2008 (UTC)

It basically comes down to money, and whether it is economically viable to do. I'm sure its possible to at least filter oil better, but in the quantities its being produced, its not worth it. In regards to synthesising oil and diamonds, oil is all to do with energy, and the point of oil is to obtain natural energy energy without putting in any (eg hydrogen.) Diamonds are made for an entirely different reason. (Incidentally, the diamonds we can synthesise now are made using massive temperatures and pressures, and are almost identical to natural diamonds).

is there any upper limit to (measure) temperature?

is there any upper limit to (measure) temperature? plz answer —Preceding unsigned comment added by Harshkothari (talk • contribs) 19:47, 18 April 2008

No SpinningSpark 21:22, 18 April 2008 (UTC)

No. While a thermometer would melt above a certain temp, a spectrograph can measure temps (from millions of miles away) that are much higher. StuRat (talk) 22:07, 18 April 2008 (UTC)

See Planck temperature. --hydnjo talk 22:13, 18 April 2008 (UTC)

See also negative temperature. Oops, didn't notice Spark's link went here. — Lomn 22:20, 18 April 2008 (UTC)

And if you're confused by the apparently contradictory answers here, this NOVA article might help. --Allen (talk) 03:02, 19 April 2008 (UTC)

I answered whether there's a limit to which temps can be measured, while hydnjo answered if there's a limit to which temps can exist. Two different questions have two different answers. StuRat (talk) 20:07, 19 April 2008 (UTC)

Actually they're quite similar when you are talking about quantum things—that which cannot be measured (or made sense of) cannot be described. --Captain Ref Desk (talk) 13:25, 20 April 2008 (UTC)

What happens when the particles are whizzing around at the speed of light? Aaadddaaammm (talk) 05:21, 22 April 2008 (UTC)