Wikipedia:Reference desk/Archives/Science/2014 May 6

= May 6 =

is anything harder than diamonds? if not, why not?
our article Superhard_material says: "Diamond is the hardest known material to date with a Vickers hardness in the range..."

why? Shouldn't we have discovered or synthesized something harder - after all, diamonds have been known about for millennia? Is there any particular reason that with all the advances in chemistry, millions of newly synthesized and discovered compounds, elements, and materials, we still don't have anything harder? Is it hte hardest hting that COULD exist - and if so, why? 212.96.61.236 (talk) 02:41, 6 May 2014 (UTC)


 * The Carbon article makes the smaller claim that diamond is the hardest naturally occurring substance...which leaves open the possibility of artificial substances that are harder.
 * If I had to speculate as to why diamond is so hard, it's because carbon atoms really love to bond together in large groups - and because the 'face-centered-cubic' crystal structure is an incredibly closely packed crystal. I don't believe any other elements bond together as well as carbon does - and I don't think there is a way to pack atoms more tightly than in face-centered-cubic.  So it wouldn't surprise me if diamond couldn't (even theoretically) be beaten for hardness.
 * But I think we're going to have to wait for a chemistry expert to come along to answer this question...I'm only guessing here.
 * SteveBaker (talk) 03:11, 6 May 2014 (UTC)


 * One thing to understand is that there are some materials for which the hardness cannot realistically be measured. To measure the hardness you need a sample with macroscopic size in all 3 dimensions. So the hardness of things like carbon nanotubes, graphene, and linear acetylenic carbon can't be measured. But they have tensile strengths comparable to or better than diamond, which suggests that they would have comparable or better hardness, if it could physically be measured. Mr.Z-man 03:33, 6 May 2014 (UTC)


 * Reading further the articles also says:
 * "The hardness of synthetic diamond (70–150 GPa) is very dependent on the relative purity of the crystal itself. The more perfect the crystal structure, the harder the diamond becomes. It has recently been reported that HPHT single crystals and nanocrystalline diamond aggregates (aggregated diamond nanorods) can be harder than natural diamond."
 * One might also consider the hardness of Neutronium.
 * But as to original question, I would guess that diamond is very low energy state mechanically, and thus when it occurs very stable. Such ultra stable things hang around for many millions for Man to find.
 * As to graphene and nanotubes/rods as they are 1 and 2 dimensional I would net expect them to be hard, but rather to flex and distort under compressive load. One might imagine, though, protecting a diamond cutter with a layer of graphene... All the best: Rich Farmbrough, 08:07, 6 May 2014 (UTC).
 * As to graphene and nanotubes/rods as they are 1 and 2 dimensional I would net expect them to be hard, but rather to flex and distort under compressive load. One might imagine, though, protecting a diamond cutter with a layer of graphene... All the best: Rich Farmbrough, 08:07, 6 May 2014 (UTC).
 * As to graphene and nanotubes/rods as they are 1 and 2 dimensional I would net expect them to be hard, but rather to flex and distort under compressive load. One might imagine, though, protecting a diamond cutter with a layer of graphene... All the best: Rich Farmbrough, 08:07, 6 May 2014 (UTC).


 * (Massive WP:OR ahead!)
 * I'd say the octet rule pretty much proves that carbon is optimal; the maximum of electrons in the outer shell is eight, so the maximum of bonds any atom can have with equal atoms is four. There might be exceptions, but they would be unlikely to beat the total strength of the bonds.
 * The corresponding elements are found in the 4th period group of the periodic table: carbon silicon etc. (The article mentions that there are many exceptions over 20, so we don't need to go past silicon.) These elements have four electrons each, so these are "half a bond" each, ready to bond with neighboring atoms.
 * Only materials with a regular mesh look promising; if different bonds are at different length, they will probably be somewhat above their ground state and thus easier to break. This would not only rule out amorphous materials but also most if not all compounds of more than two different elements. Two-element compounds could be competitive, if all bonds are between different elements.
 * Carbon or silicon is easy to decide; with carbon, you have more bonds per kg; so even if they are slightly weaker than those of silicon, they represent a higher "total bond strength." OTOH, the "bonds per kg" is probably the wrong metric when it does not come to specific strength; a "bonds per m²" metric would be more useful. Carbon is the winner in both, but the margin is much smaller in the latter. - ¡Ouch! (hurt me / more pain) 09:47, 6 May 2014 (UTC)


 * Cubic boron nitride is a strong contender (although it doesn't surpass diamond). According to its Wikipedia article: "Its hardness is inferior only to diamond, but its thermal and chemical stability is superior." Double sharp (talk) 12:19, 6 May 2014 (UTC)


 * My tax man is far  harder then any diamond; he can even squeezes  blood out of a stone.--Aspro (talk) 23:07, 6 May 2014 (UTC)
 * Then I wonder how much he can squeeze out of Microsoft?
 * Good catch Double sharp; two-element combinations which work out to an average of 4 valence electrons can be strong competitors. It certainly doesn't look like coincidence that boron and nitrogen are the closest neighbors of carbon on the periodic table.
 * Periodic table shows that a boron atom and a nitrogen atom combined are slightly larger than two carbon atoms (carbon is right at the "sweet spot" where the atomic radius almost stops decreasing) so the inferior hardness of BN could be due to a lower total of bonds per m².
 * The new group numbering classifies the carbon group as the 14th, too, not the 4th. (It used to be Group IVA/B...) (...and 4th period was a complete brainfart on my part.) - ¡Ouch! (hurt me / more pain) 05:58, 7 May 2014 (UTC)
 * Wow. While I was typing my contributions, Wnt added to the topic not once, but twice and I didn't run into a single edit conflict. As much as I hate the recent change towards serif headlines, I have to admit that the underlying Wiki engine is quite a mother. - ¡Ouch! (hurt me / more pain) 06:06, 7 May 2014 (UTC)
 * Change your skin in preferences. Never see them again. One of them looks just like Wikipedia of the late 2000s (still the same logo, though, but it's not much different from the old one. Sagittarian Milky Way (talk) 22:23, 9 May 2014 (UTC)


 * Remember diamond is actually in a higher energy state than graphite - they eventually break down at STP. Lots of things (like N2) are at a low energy state ... unless they have all the right bonds to resist breaking that won't help. Wnt (talk) 05:41, 7 May 2014 (UTC)
 * What, diamonds ain't forever? —Tamfang (talk) 02:37, 8 May 2014 (UTC)


 * Also, I wonder if a quasicrystalline phase of carbon could be created, and if so whether it would be more or less hard than diamond. Wnt (talk) 05:42, 7 May 2014 (UTC)


 * I thought lonsdaleite occurs naturally and could in principle be harder than diamond (except natural samples are never pure enough for that). 70.36.142.114 (talk) 09:22, 8 May 2014 (UTC)

Superconductor question
I have several question about superconductor:

1. If we have a superconducting power line powering a load at 100 kV, will it arc to another conductor or the electricity will prefer to go to the easy way instead of arcing everywhere?

2. Do anyone have invented the superconducting switch yet?

3. Is superconducting electrical stuff is more compact than normal conducting electrical stuff? 118.137.229.230 (talk) 10:13, 6 May 2014 (UTC)


 * Regarding #1, surely electricity won't just arc to a superconductor just because it's the "easy way", otherwise the first time somebody made a superconductor, all the world's electricity would have arced to it :) 91.120.14.30 (talk) 11:06, 6 May 2014 (UTC)


 * I meant it will arc from the superconductor... but if what you said is true, we have a powerful electricity stealer device :) 118.137.229.230 (talk) 13:59, 6 May 2014 (UTC)


 * While electricity, like water, seeks the path of least resistance, the distance to the superconductor, which presumably has high resistance, is a big factor. So, only nearby electrical charges would be able to overcome this resistance and make the jump. Going back to the water analogue, rivers can't find their way to every low spot, due to intervening mountains, etc., otherwise we wouldn't have any land below sea level.


 * Also, if a big spark does make it to the superconductor, like a lightning strike, it presumably will damage the superconductor, let the coolant escape, etc., so that it's no longer a superconductor. StuRat (talk) 14:53, 6 May 2014 (UTC)


 * For #3, yes, superconductors are much more compact! Justin15w (talk) 14:40, 6 May 2014 (UTC)




 * Yes, but you really need to include the coolant system and thermal insulation in the size of the superconductor. Once you do that, I doubt if it qualifies as more compact. StuRat (talk) 15:02, 6 May 2014 (UTC)


 * 1) Normally, some electricity would go down any available path, with more going down the paths of least resistance. However, when one path has zero resistance, I'd predict it would all go that way, assuming there's no high resistance jump required to get there. StuRat (talk) 15:04, 6 May 2014 (UTC)


 * StuRat, it would be better if you did not post on stuff you obviously have not got a clue about. Power distribution is done with AC, for which current flow is influenced by magnetic induction phenomena.  Even with superconductors, you get things like skin effect, where the current tends concentrate on the surface of a conductor, and stay away from the centre, and you get proximity effect - current in a conductor is influenced by current in nearby conductors.  For a wire near a flat surface sheet or block conductor carrying the return current, the return current tends to follow the path nearest the wire, however it may be routed, and not go through the path of least resistance (ie the direct point to point path). 121.221.131.231 (talk) 17:57, 6 May 2014 (UTC)


 * Well, there's HVDC, a serious contender, and with superconductivity advances I suppose it would become more appealing. Wnt (talk) 18:51, 6 May 2014 (UTC)


 * 121.221.131.231, it you who doesn't know what you're talking about. First, as WNT notes above, there's HVDC, and you seem to be focused on long distance power distribution without superconductivity, while this Q is on power distribution with superconductivity, and nothing in it says it's talking about long distance transmission.  Indeed, the logistics of cooling a wire over a long distance make long distance superconductor use less likely in the near future.  For high energy/short distance applications, like in factories, superconductivity may be practical sooner.  And, even without superconductivity, over short distances, the transformer losses from stepping up and down the voltage outweigh the losses over the length of the wire, making AC less desirable.   StuRat (talk) 19:37, 6 May 2014 (UTC)


 * Superconduction is the disappearance of electrical resistance in certain materials at very low temperatures. This would allow Electric power distribution at much higher currents through smaller conductors than used today, but the cooling requirements have so far prevented wide application of the principle. The reason for using high voltages in conventional power lines is to reduce "I2R" losses in cable resistance: the same power can be transmitted through a transmission line either at low voltage and high current, or with a higher voltage and lower current. However on a superconductor line there is no need to use a high voltage. The Breakdown voltages of adjacent solids, gases or vacuum that might lead to arcing are no different, if for some reason 100kV is really needed. The matter in an arc is in the ionized state of plasma which has low resistance but not the zero resistance of superconduction.


 * DC is sometimes preferred to AC for power distribution because, for the same power, it avoids high peak current, high peak voltage, skin effect loss and power factor loss. The traditional advantage of AC that its voltage level is easily converted up or down in Transformers is being eroded by efficient semiconductor Power inverters that do the same function for DC supplies. Superconductors have limited tolerance to magnetic fields so they will not necessarily always be used for AC power distribution.


 * The Cryotron is a switch that operates using superconductivity quenched by magnetism and its inventor suggested its use in digital logic circuits - U.S. Patent 2,832,897. 84.209.89.214 (talk) 19:18, 6 May 2014 (UTC)

Freeze-thaw damage of molecules
How does repeated freezing and thawing cause damage to certain molecules? Are some covalent bonds more susceptible than others and what makes them susceptible? I'm not talking about freeze-thaw damage of geological structures; I'm interested in what goes on in a microcentrifuge tube. --129.215.47.59 (talk) 17:22, 6 May 2014 (UTC)


 * There are many sources of damage that can occur during freezing and thawing, including changes in pH of the solution, formation of crystals of both solute and solvent, the formation of liquid-solid boundaries, and temperature changes themselves. In the case of liquid-solid boundary formation, for instance, a large molecule that is temporarily half in solid ice and half in liquid water could find itself under unusual stresses. Any of these stresses can cause bonds to break or proteins to irreversibly misfold during either freezing or thawing. As you mention, this does differentially affect different molecules. Precisely why some molecules are resistant to freeze-thaw damage is an area of active research, and you can see a lot of that if you search on Google Scholar for something like "freeze thaw protein damage". Biophysics and Biochemistry and Low Temperature by Franks discusses the various sources of damage, and can be picked up on Amazon rather cheaply used, or perhaps is available in your school library. Unfortunately we don't have an article on this at Wikipedia (we do have articles on freeze-thaw damage to larger structures, but not molecules) - closest we have is cryoprotectant. Someguy1221 (talk) 01:50, 7 May 2014 (UTC)


 * I think that an interesting clue is that some of the good cryoprotectants like trehalose confer great resistance to dehydration as well. Freezing water out of something like eisbock deprives the solutes of their solvent, and I suppose something similar might occur on a microscopic level. Wnt (talk) 05:46, 7 May 2014 (UTC)


 * For all practical purposes: freeze damage happens only to the tertiary structure of macromolecules (i.e. proteins), causing them to denature (by several mechanisms related to concentrating solutes). It is not relevant for small molecules at all and it does not cause chemical bonds to break. Cacycle (talk) 12:45, 10 May 2014 (UTC)

Home-made versus store-bought water for tissue culture
At the institute where I work/study, water is demineralised and UV treated and then past through "MilliQ" filters into Duran bottles before autoclaving. Is there any reason this water couldn't be considered suitable for use in cell culture? Many people seem to avoid the risk by buying in water from Life Technologies but is there really a risk? --129.215.47.59 (talk) 17:50, 6 May 2014 (UTC)
 * The article Autoclave has information on this sterilizing device. However aseptic technique, designed to provide a barrier between the microrganisms in the environment and the sterile cell culture, depends upon several elements: a sterile work area, good personal hygiene, sterile reagents and media, and sterile handling. See Life Technologies' own aseptic techniques checklist and its associated videos that show best-practice sterile procedures. 84.209.89.214 (talk) 18:16, 6 May 2014 (UTC)


 * Think you are confusing risk with an effort to conform to scientific certainty. By buying in analytical water, the lab has a base line that other labs can follow. --Aspro (talk) 18:39, 6 May 2014 (UTC)
 * "Home-made" water is perfectly fine for use in TC, indeed I've never known anyone to actually buy in their water, what a waste of money! The only reason to do that would be if the lab is involved in preparing cells/tissues for clinical trials. Fgf10 (talk) 19:40, 6 May 2014 (UTC)
 * Exactly: If the OP's lab can purify water but still at the same time buy in water, it suggests to me that they require and outside source to provide water that has Type approval for clinical trials. Perhaps the OP can come back on this and provide more background.--Aspro (talk) 19:58, 6 May 2014 (UTC)


 * I don't exactly have my finger on the pulse of my institute but I'm not aware of our involvement in any type of clinical trial. Most (but not all) of our work pertains to animals of agricultural importance. I also haven't done a survey to find out whether my experience can be applied to the majority of my colleagues. I also doubt that the water from Life Technologies is any purer than what our "central services unit" can produce, unless the Duran bottles are contaminated in the autoclave. 78.148.106.196 (talk) 20:32, 6 May 2014 (UTC) (aka 129.215.47.59)


 * Clinical is not a preserve of work done on human studies  alone. Veterinarian R&D follow the exact same protocols.   I used to make my coffee in the lab with distilled water with a little bit of ethanol  as a wetting agent- (well a lot off ethanol actually and big slurp of some dairy cream)  but id don't  think it turn out better that  my great grandmother’s protocol (loads of palm sugar, cream,  moonshine, and some coffee grounds -if you could get them) --Aspro (talk) 22:08, 6 May 2014 (UTC)


 * Definitely it's worth paying attention to the specifics about the autoclave. After all, you have loosely capped bottles with concentrated steam being forced into them.  Depending on the source of the water for the autoclave, I suppose you might have gases from water chlorination, maybe even traces of ions dissolved in the water or iron from the autoclave or vented gasses from other bottles in the autoclave working their way in.  In practice ... like as not you're planning to go by a witch recipe and dump large amounts of fetal bovine serum into the medium, in which case worrying about the purity and consistency of the steam may really be stretching it.  then again, according to  it is possible for bacteria to grow in water used for autoclaving, which ends up depositing endotoxins, which doesn't sound good.  Also, according to  the water quality should be better than 1 megaohm/cm, but it also says water that pure will corrode anything but stainless steel in the autoclave, so it may be that some autoclaves can't even support the recommended level of water quality.  I am surprised though that more effort isn't spent coming up with containers that work for autoclaving material while fully sealed!  Wnt (talk) 05:20, 7 May 2014 (UTC)


 * Why do the bottles need to remain unsealed? If the pressure is such that the water outside the bottles reaches 115 C, won't the pressure inside the bottles rise to balance that? 129.215.47.59 (talk) 10:47, 7 May 2014 (UTC)


 * Certainly. But not until after they break. :)  Remember, the pressure involved in an autoclave is many times the pressure involved if you had a complete vacuum inside the bottle.  That pressure comes to bear quite rapidly, while the heating of the contents through glass takes a long time.  Wnt (talk) 15:39, 7 May 2014 (UTC)

Tissue culture water is tested for cytotoxicity and lipopolysaccharide (LPS) concentrations. Regular MilliQ water may be cytotoxic or cytoinhibitory due to contamination with bacterial products. Especially if autoclaved in regular lab bottles that previously had contact with bacterial cultures! Cacycle (talk) 16:51, 10 May 2014 (UTC)

Aerogel - Compressive strength
I was explaining what Aerogel is to my wife, and she asked a question I could not answer.

As I understand it, the least dense aerogels are actually lighter than air. If you put plastic around an Aerogel and sucked out the air, would it float or collapse? I've seen the picture of a brick resting on aerogel, but I have no idea how to go from that to a sphere of a specific radius. Tdjewell (talk) 21:38, 6 May 2014 (UTC)


 * This is an interesting question. Take a five gallon can and evacuate the air out of it and the atmospheric pressure will crush it. Aerogel is pretty tuff in compression. Consider a sphere, a thousand foot in volume (approximately 10ft by ten by ten, or for the mathematicians  out  there: $$\!V = \frac{4}{3}\pi r^3$$. Rap it in  cling film and pump the air out and it will more than likely float.--Aspro (talk) 22:30, 6 May 2014 (UTC)


 * Off the top of my head, I think you will have about  forty pounds of lift (assuming you cannot achieve a perfect vacuum). Pure hydrogen will give you 74 pounds of lift (me thinks but can't be bothered to look it up).--Aspro (talk) 22:45, 6 May 2014 (UTC)


 * Apparently this is proposed: aerographene as a material in a SpaceShaft. Graphene is quite remarkable: I've never seen anything published as usable for so many purposes... and yet, why do we not see it used for anything? Wnt (talk) 23:34, 6 May 2014 (UTC)
 * It takes about 25 years for anything like this --from discovery, to being availably to the hoi polloi--. Wait a while - Patience is a virtue --Aspro (talk) 00:20, 7 May 2014 (UTC)


 * The helium in a weather balloon expands as the balloon rises and the atmospheric pressure (and density) drops, giving the balloon more or less constant lift up until the altitude where the balloon is fully inflated by the expanded lifting gas, but your aerogel box will not expand so its lift will decrease with altitude right off the bat. -- 190.213.85.228 (talk) 22:54, 9 May 2014 (UTC)