Independent nanotechnology information and commentary since 2003
Laine "Space Elevator"
Google news: 18
Google Web: 919
Google Groups: 5
Smalley "quantum wire"
Google News: 3
Google Web: 488
Google Groups: 4 (plus an interesting snapshot from 1997)
An armchair nanotube quarterback
5/03/2005 10:26:00 PM
keep this in perspective, please. :-)if you search for "Smalley Carbon NanoTubes"Google News 73Google Web 38200Google Groups 120
Don't sell yourself short, Michael. You have what Dr. Smalley does not -- a project that has the potential to capture the imagination of the public in a way we haven't seen since Apollo.I'm not diminishing Smalley's achievements or doubting that his quantum wire project will have benefits well beyond this particular NASA grant. Inf act, Smalley's project is a perfect example of what NASA always touts as the benefits here on Earth. So, he'll prove his concept in space, and then very likely could revolutionize the power industry at home.However ...Smalley's project is not about space. This NASA grant is simply how he found funding for the last stretch of his two-decade-old project. It's not something that the general public can rally around. Kids won't dream about being astronauts after taking a look at the shuttle's power cables.Smalley and many others in the scientific policy establishment are clueless as to how to spark imaginations. Then, they're surprised when there's a public backlash against something like nanotech, or more cuts in NASA funding from Congress. It's because they spent all their time telling the public what CANNOT be done, rather than making what they CAN do incredibly exciting.
Howard, please don't rant.Michael, how do you plan to get around the problem of defect nucleation in SWCNTs at ~5% strain which causes tensile strength to drop to the range of 13-52 GPa? (See, e.g. http://mmptdpublic.jsc.nasa.gov/jscnano/pubs/tensile_PRL.pdf) Adding polyimide (tensile strength ~100 MPa) to hold SWCNTs together in a ribbon will result in a structure weaker than the SWCNTs themselves, and I just can't see such a ribbon doing the job it needs to do.Inquiring minds wanna know. I'd really, really like to see a space elevator work.Best regards,Attobuoy
Wow. Scolded on my own blog by one-quintillionth of a pseudonymous floating object. It's been that kind of day.But it's my blog and I'll rant if I want to.Actually, Atto, that's a very good question. How do you patch together the hardest substance in the known universe without weakening it?Sounds to me like Michael should put in his order now for about 62,000 miles of Grade A Smalley quantum wire.
truth is, attobouy, i dont even have a guess how to do it... not yet anyway. there are some hints, and a few places have gotten 2,3 or 4% doping of the stuff into simple plastics - and what does that leave you with? stonger plastic. but its no where near strong enough for our plans. and i dont see that changing soon.the production plant we are putting together is for mwcnt and i dont think that we are going to be making SE-rated ribbons for a long long time. i've always had doubts about the composite solution for a strong enough product, and ive said so, several times. my bet is on a lab (maybe smalleys... maybe one in the east coast, north of NY, south of ME...) that will be able to make long-chain, high-quality, consistent, bulk quatities of this stuff. now, thats a tall order, and its not going to be easy, cheap, or soon.i cant wait for the day we get to post a sign that says 'pardon our dust, we are under construction' but i dont think thats gonna be a problem for a while yet.thanks for your interest, and keep the faith, we are working really hard on this thing.sorry for my ramble, its 1250am and its time to go to bed. ;-)mjl
Having seen the preliminary reports from Smalley's research, I don't think spinning the ribbons for the SE will be all that difficult. The problem wil be finding spools large enough to hold that much cable. ;)Seriously, I can envision a system where the cables will be spun much like the way acetate fiber is produced except that the nanotubes will start in a strong acid and injected into a solvent rather than the other way around. You should then be able to braid the smaller fibers into larger bundles and get the size you need to support (suspend?) the tower.
Good morning, Michael.But the real problem seems to be the strength of the nanotubes themselves, whether SWCNT or MWCNT. There's apparently a critical tension, FAR below that needed for a space elevator, at which bonds within the nanotube re-arrange, weakening the nanotube and, if the same tension remains on the tube, causing it to rupture.So it seems not to matter whether you make composites, weave ropes, or make single nanotubes 62,000 miles long, the problem of nanotube strength remains the killer.Or am I missing something?Attobuoy
Attobuoy,My understanding is that while there can be a problem with tension caused by the weight of 62,000 miles of cable it can be greatly reduced by engineering the cable to be thicker at the top and tapering slowly toward the bottom. While it sounds like science fiction (and it once was) it is possible. Also remember that these tensions will never be subjected to a single tube but dispersed across a great many.Think of it this way. A single steel I-beam in the first floor of the Empire State building can only be subjected to so much force before it starts to deform. This force is much less than the weight of all the floors above it and yet it still stands. Distribution of weight among numerous I-beams is the key.
Thank you for your input, Mr. Smith. But you need a certain material strength to make a tapered cable work, and having looked at the available literature, I don't think CNTs have that strength at present nor, because of fundamental problems of stress-inititated defect generation, can they even in theory ever have that strength.I would love to be shown either data or theory to change my opinion.Best regards,Attobuoy
attobouy,i'm not really sure where to start. first, maybe some background on myself. i am not an engineer in any sense of the word. i have a background in business development and finance. those are my strengths, and i am pretty good at it. i had my first million $ before i was 30, and i'm 37, working hard on my 3rd. not trying to brag, here, just setting the stage for what i do, and do not, KNOW. what i know is money, what i dont know is advanced sciences. i work with a lot of really smart people that TELL me, it can be done. can I, personally, prove it? nope. we try to have experts that KNOW thier field, inside and out. my expertise is $. i am learning about: politics, military contracting, law, nanotubes, robotics, telecom, photovoltaics, orbital mechanics, high-altitude atmospherics, faa regulations, social policy, environmental activism, maritime engineering, rocketry and lasers. i think ive learned a lot in 3 years, but i am not an expert in any of these areas. i still have a long ways to go. (and loving every second of it! i really do have the 'coolest' job in the world)now, all that being said, the last thing i want to do, is tackle this problem with 'rose colored glasses'. i am told that some cnt has been tested at 60gpa. i am told that some cnt has been made as long as 4cm (RPI's stuff was a lot longer, but it was full of defects, so i dont rely on it). I am told that if we can make a lot of 4cm tubes, than we can make a ribbon... if smalley or the other east coast lab i was refering to, makes a long 'wire' then it gets easier. i am told all this by people i trust and respect. but i dont KNOW this from my own experiments and brainpower, but ive read the reports and try to follow as best i can... and i am trying very hard to be open to outside data. so, if youve got a reference that you can link or send me, please do. because i want to understand this stuff - thats why i spent 10-14hrs a day on this project, because if it CAN be built, then WE ARE GOING TO BUILD IT. :-)my current understanding is more along the lines of 'mr smith'. the taper matters a lot, and we need something with a total strength of about 90-120gpa.... not easy, but so far as i know, not impossible.by the way, have you read the baseline report on the project? it describes the ribbon in some fair detail. that report is about 2+ years old, and the baseline needs an update soon, so keep that in mind when/if you read it.thanks for your interest, really. i dont mean to go off on a 'rant' but felt that it would help our conversation if you knew where i was coming from.i look forward to hearing from you.take care. mjl
Michael, check out http://www.ce.udel.edu/~baidurya/downloads/Topics%20Applied%20Physics%20vol%2080/yakobson%20and%20avouris%202001%20mechanical%20properties%20of%20CNTs.pdf,"Mechanical Properties of Carbon Nanotubes." In particular, section 4.4, "Yield Strength and Relaxation Mechanisms in Nanotubes" describes the initiation of defects such as that shown in Fig 12, and how such defects lead to failure of the tube under tension, at stress levels below those which would be predicted by looking only at the bond strengths of a perfect nanotube.Best regards,Attobuoy
thanks, i'l check that. meanwhile, this just in, from one of our guys, working on a related issue... i'm posting it, because our regular comment is 'we dont even know all the questions, let alone have all the answers...' but we are working hard, and i have confidence in my team to come up with solutions. anyway, here's an email i got from one of my team, talking about the ribbon 'snapping' under certain conditions, and what those conditions might look like. notice, there are no answers in this email, we just found further questions to explore. and i will pass this link on to him, for his further study. if you'd like, feel free to email me, and i can keep you posted on this issue, i probably wont be responding to this post any further, o.k.?but i wanted to let you know i appreciated your insite, and help. and yes, pointing out a potential problem is help. :-)take care. mjlthe other email follows this......
hmmm, i guess it didnt follow, yesterday, like i thought, well, here it is. take care. mjl_______Hi John,Sorry it has taken me so long to reply to your question. I wanted tofinish reading a preliminary paper on precisely this subject. It iswritten by a friend of mine, Ben (i edited out his contact info, if you want it, email me). If you askhim he may accept to send you a copy. Though my opinion is that itdoesn't do a good job of addressing the issue yet.So far, I don't feel that there is a good answer to this question yet.That's why I have this problem listed on my problems web pagehttp://gassend.com/elevator/problems . There are two aspects of the problem. At the microscopic scale, you canwonder if the energy released by a single nanotube breaking will be able to cause a chain reaction of breaking nanotubes, causing the material tolitterally disintegrate as soon as any nanotube breaks. I would tend tolump this into the "getting the right material" side of things. Is itpossible to have a 100 GPa material that is stable? Or will such amaterial necessarily disintegrate as soon as a single failure occurs init?The problem also occurs at the macro-scale. The space elevator is in ahazardous debris filled environment. It has to be designed to be able totake impacts without failing. This suggests that it should be made outof threads, connected somehow at regular intervals. The question now iswhat happens if one of these threads breaks? With all that energy beingreleased, it could get hot, and/or it could end up going very fast. Whatkind of damage will it cause. I've tried doing some simple modeling tosee if things are really bad, or really good; unfortunately this is oneof those messy cases where you need a lot of detail about the materialand how it is assembled before you can give any intelligent answers.I guess I haven't really helped answer your question. I think that thisis one of the big unknowns in this project. Can the material that canhandle these stresses be made? The material being stable against localfailures being an implicit condition for this material to exist.Best regards,Blaise Gassend
attobouy,Excellent paper. Thank you for posting the link. After reading through it, I find nothing that suggests that nanotubes cannot withstand the types of strains involved in the construction on the SE.Blaise Gassend mentions the need for a 100GPa material. The paper states that a rope of nanotubes should have a breaking stress of 150GPa+.The Stone-Wales dipole inclusion could cause problems, but the paper does not indicate that it would not fall below the 100GPa limit.More study is called for but the current data suggests that it can be done.
Hi, I realize there are naked people a few posts up, so this thread might no longer be read, but I'm just going through all this now.Quick question regarding the Yacobson Avouris paper referenced by attobouy above. The paper concludes: "The ultimate strength of nanotubes and their ensembles is an issue that requires the modeling of inherently mesoscopic phenomena, such as plasticity and fracture, on a microscopic, atomistic level, and constitutes a challenge from the theoretical as well as experimental points of view."Translation: We dunno how strong we can make these tubes, and we don't have the technology or know-how to find out. Has that situation changed since this paper was written? Computer modeling software has become much more sophisticated and powerful just in the last couple of years. Or, is it a question of just not having all the data necessary for CAD to do its job? Vague garbage in, vague garbage out?
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