Something I found really interesting in the article that I hadn't heard about before was self-reinforcing concrete:
quote:Today's concrete buildings have skeletons of steel, but Moeller said that could become obsolete with the development of a recently invented self-reinforcing concrete, though that may be many years off.
The Lafarge Group, a French firm that says it is the world's largest producer of concrete, sponsored the exhibit and is showing off a recent variety called "Ductal" that does not need steel reinforcement. The exhibit shows how a light rail terminal has been built in Calgary, Alberta, almost entirely of Ductal, with concrete arches spanning 20 feet and the concrete only a quarter-inch thick.
How cool is that?
Could any of our engineers talk more about this stuff? It sounds pretty fantastic.
Posted by Annie (Member # 295) on :
Cool. And here's another question:
A random friend whose dad was an engineer of some sort told me that the Romans didn't build with concrete because it only lasts a hundred years. Is this valid? Is all of our concrete construction a lot less permanent than we thought? Or have they re-formulated to address that?
Posted by BannaOj (Member # 3206) on :
Well I'm not a civil and any of them can jump in to contradict me.
The applications are very cool. But I predict it will be quite a while before they become commonplace simply because the current materials work so well and are so much cheaper. Archietects will likely be the ones specifying it for beauty and the civil engineers will whine because it is more difficult to work with. I doubt it will be going into bridges anytime soon because, no one is willing to risk unproven materials in something that deals with public lives on a daily basis.
If they can actually prove that this new stuff is as good as the 50-100 year concrete that they use in roads, then it might catch on. But civil engineering as a whole is a bit of a fuddy duddy profession when it comes to change. This is because they have to be. Lives are at risk.
AJ
Posted by policyvote (Member # 3044) on :
Good thing the structural steel company I used to work for went bankrupt; otherwise, this stuff might've put 'em out of business!
Peace policy
Posted by BannaOj (Member # 3206) on :
Annie, I'm not sure specifically about your question. The 50-100 year concrete that I am referring to is in use in highways which will wear out due to freeze thaw cycles and simply the heavy amount of traffic the interstates experience.
AJ
Posted by Hobbes (Member # 433) on :
Romon concrete and modern day concrete are two very different things. And AJ is right, we're total stick in the muds, hopeuly that'll comfort you next time you drive over a bridge.
Hobbes Posted by Annie (Member # 295) on :
I think it was one of those small-town self-righteous type of "facts." You know - the things that people say to prove that the experts are idiots and everything's going to pot.
Posted by Hobbes (Member # 433) on :
Well what with the liberal agenda and what-not, it seems like everything is going to pot.
Hobbes Posted by advice for robots (Member # 2544) on :
That translucent concrete is pretty cool. Although it's hard to think of lots of practical uses for it beyond a nice design element.
Posted by Noemon (Member # 1115) on :
Well, I think that the concrete used in Hadrian's wall is holding up just fine, isn't it?
Posted by Happy Camper (Member # 5076) on :
Hmmm, well, that's not really a new concept, it just appears that using glass as the reinforcement fiber is new. I think there are probably even better materials that could be used in this application. Oh, and if steel prices continue to rise like they have been recently, then I think we'll be seeing a lot more research and use of this particular material. And yes, we civil engineers don't like to do anything that hasn't been tried and true for decades. And since I work for the government, it's twice as bad. Posted by Dagonee (Member # 5818) on :
As far as I know, Hadrian's wall didn't use concrete. It was made of stone, and filled with rubble and mortar, which likely contained cement.
No concrete, though.
Dagonee
Posted by Erik Slaine (Member # 5583) on :
Does anyone know of anything you could use to substitute for water when making concrete?
Posted by Erik Slaine (Member # 5583) on :
Oh, maybe not Hadrian's wall, but the capitol dome in Rome is concrete.
Posted by Noemon (Member # 1115) on :
Huh--I was misremembering. I had thought that the mortar in Hadrian's wall was concrete.
quote:Does anyone know of anything you could use to substitute for water when making concrete?
How about spit?
Posted by Erik Slaine (Member # 5583) on :
How about something that has no water in it?
Posted by Hobbes (Member # 433) on :
Name me a liquid that isn't water based. really anything you use would be water with something in it, and then the water would be the part that did the work and the rest would just come out of solution. And no, Mercury would not work for makinf concrete.
Hobbes Posted by Noemon (Member # 1115) on :
dehydrated spit?
Posted by Hobbes (Member # 433) on :
That's a rather solid liquid.
Hobbes Posted by Noemon (Member # 1115) on :
There are all sorts of liquids that aren't water--just not too many of them that exist in a liquid state at room temperature.
What about oil? Does it contain water? I guess it must. I hadn't thought about it before.
Posted by Erik Slaine (Member # 5583) on :
Well, I'm looking for another chemical to act as an oxydizer, for where water may be a rare commodity.
Posted by BannaOj (Member # 3206) on :
There are so many liquids that aren't water I'd really like to smack you hobbes However I don't think ethanol will work for portland cement, though it can work quite well for engineering tests.
That's true, you could try using liquid nitrogen, just cool it down until it's liquid and hope the concrete forms really fast.
Oil is actually liquid on it's own, but I don't think it would work.
I'm not sure anything besides water would, but I'm not an expert... though soon I'll be taking a whole course on concrete.
Hobbes Posted by BannaOj (Member # 3206) on :
Stupid civils that have forgotten 4th grade science.
Solid, Liquid, Gas. Those are your basic choices. There are LOADS of things that are non-water-based liquids at room temperature. Water just happens to be the most abundant one on this planet. There are some interesting other plasma and gel states, but those are your exceptions.
[ July 07, 2004, 06:21 PM: Message edited by: BannaOj ]
Posted by Annie (Member # 295) on :
How about Jello?
Posted by Hobbes (Member # 433) on :
AJ, there's not that many liquids that aren't water based, oil is the most prominant, most others are almost never seen by the average person. And most of those are based on either oil or water...
Hobbes Posted by Annie (Member # 295) on :
What do they do when the concrete in the Hoover Dam wears out?
Posted by Hobbes (Member # 433) on :
Annie concrete gets stronger with time, I'm not sure if the hoover dam has solidified yet and actually reached full strength. And it was designed NOT to wear out, roads are different than dams as far as wear and tear goes.
Hobbes "oil" is a very generic kind of liquid. your corn oil is different from your soybean oil. They are chemically different liquids.
Alcohol (grain) is an extremely common liquid. THere are other alcohols like isopropyl alcohol that are different as well. There are all kinds of interesting solvets used in household cleaning products and paint thinners. They are so ubiquitous you simply don't notice them.
And glass is technically a liquid if we want to get creative.
Iodine is not only a pure element but liquid at room temperature. (Actually I lied. Iodine is a solid at room temperature though it has a low melting point, bromine is a liquid)
AJ
[ July 08, 2004, 09:29 PM: Message edited by: BannaOj ]
Posted by Hobbes (Member # 433) on :
How is gas techincally a liquid?
And yes, alchool is different, and the actual full chemical compounds of oils are different, but the thing that makes them an oil is always a same, and it's the part that makes them liquid. And I would use the actual name and/ chemical forumal for it except I haven't taken chemistry in a really long time. Not to say I wasn't just making a quick, not thought-out joke in my first post, but now I'm having fun. Hope you don't mind...
Hobbes Posted by Hobbes (Member # 433) on :
Ohh, and I'm pretty sure the Hoover Dam is soldified, I think it wouldn't be except that the way they made it was dividing it into lots of small cubic pieces, and that allowed it to set a lot, lot faster.
Hobbes Posted by Annie (Member # 295) on :
This is actually really interesting. You could have never told me that I would find a discussion on concrete interesting. Thanks. Posted by BannaOj (Member # 3206) on :
Hobbes don't talk about what you don't know anything about. It's making you look dumber and dumber.
and I said gLass not "gas"
liquids and gases both subscribe to the same functional fluid mechanics laws though the Reynolds numbers and the Nusselt numbers are drastically different.
AJ
Posted by BannaOj (Member # 3206) on :
Actually something that I'm not sure about, is concrete technically a solid?
I'm not sure it is.
AJ
Posted by Erik Slaine (Member # 5583) on :
Thanks for the ideas.
*scratches head*
Posted by Dagonee (Member # 5818) on :
Well, there's always bromine. I think it might give the engineers ugly burns even if it worked, though...
Posted by BannaOj (Member # 3206) on :
Ok I'm supposed to be finishing work. But, I called Steve. Steve asked me why Happy Camper wasn't laying the smack down.
They make Latex based concrete that doesn't have water in it. And the Hoover Dam while at 98% ish strength is still curing and giving off heat, and will be for like another 150 years.
AJ
Posted by Erik Slaine (Member # 5583) on :
Thanks!
Posted by UofUlawguy (Member # 5492) on :
AJ:"And the Hoover Dam . . . is still . . . giving off heat, and will be for like another 150 years."
Living in Las Vegas in July, I've just got to say --
So THAT'S what's causing it!
Or
The Dam's giving off heat? How on earth could you tell?
Posted by Dagonee (Member # 5818) on :
You can't tell - what happens in Vegas stays in Vegas.
Posted by Happy Camper (Member # 5076) on :
It's because I don't give a rats posterior about concrete. And about concrete being something other than a solid, well, it may technically be a suspension. But I guess it really depends on how much liquid has to be present. I'm not a chemist, darn it, I'm a geotechnical engineer. Ask me about clay mineralogy and I'd be able to tell you more about the chemistry.
Posted by Erik Slaine (Member # 5583) on :
*takes notes*
Posted by Dagonee (Member # 5818) on :
No one else is curious what he's up to that he needs waterless concrete for?
Alright, I'll ask: What are you up to that you need waterless concrete for?
Dagonee
Posted by Erik Slaine (Member # 5583) on :
For fictional extraterrestrial construction, on airless rocks, of course. Posted by BannaOj (Member # 3206) on :
For quick curing on busy highways. I think in some cases it may cure stronger too. Steve says the stuff is set in like 15 minutes and it is a pain to get off shoes.
AJ
Posted by ak (Member # 90) on :
I know about steel and a bit about aluminum, but not much at all about cement or concrete. Only that without reinforcement it's great in compression but not at all good in tension.
And Hobbes, yeah, give it up! Lots of liquids are not water or oil.
I think the Romans used a lot of stone in their roads and walls and aquaducts. Stone lasts a whole lot longer than concrete or cement. Not sure about the mortar used to stick them together. The pyramids are just a good fit, neh? I don't know if they used any mortar in them at all, but rather trimmed the blocks until they matched up perfectly, then let gravity and friction do the rest. Of course, a pyramid is not something that has to have much tensile strength anywhere. There are only a few small chambers inside, I guess.
Posted by rivka (Member # 4859) on :
AJ, do you really do much work with pure ethanol? I've never worked in a commercial laboratory, but both in the classes I took in college and in the high school labs I teach, we always use solutions of ethanol and water. Posted by Kwea (Member # 2199) on :
I just saw the Modern Marvels on the History Channel a few weeks ago, and they had a whole show on the Hoover Dam. It was really fascinating.
Both of you are right about the Dam; it did cool much quicker than it would have otherwise, because of the cooling system that runs through the whole Dam. They compartmentalized the structure and ran pipes carrying water through it. Otherwise they could have never made it from concrete, as it would have never cured.
However, it is still curing, and will be for somewhere between the next 130-160 years. That means it will be gaining in strength.
Also, the Dam is constructed to be under compression the whole time, not in tension, so we don't have to worry about it falling apart anytime soon, barring outside influences (i.e. terrorism).
I LOVE the History Channel...
Kwea
Posted by Primal Curve (Member # 3587) on :
Transparent Aluminum? Posted by peter the bookie (Member # 3270) on :
liquids and gases both fall into the realm of fluids. yeah, that's the word. they're both fluids. they both flow. and follow a bunch of the same laws, though gases tend to be considerably more difficult.
the concrete made with latex (at least the stuff i made) still had water in it, but barely any. i don't imagine a water free version would be that difficult to make, but i don't know how well it would do on impact testing. there was another really nasty liquid we put in one that required gloves and masks and goggles, but i don't recall what it was.
i do know that no matter how many times you tell the judges running the compression tests that it's really, really light, they'll still expect it to weigh a ton and nearly throw it across the room because it's so much lighter than they expected. and it will have a rediculous strength to weight ratio, but the actual strength is quite low.
erik, will this be a gravity free structure? actually, would you mind replying via email?
btw, noem, as a former concrete canoe nut, this is totally cool. i wonder if it meets the requirements for the competition? probably not, they get more and more strict as concrete technology gets better.
rivka, there was a study published last year (and i don't have a reference) saying that an 80% ethanol solution was actually better for sterility than just 100% ethanol. i have no idea why, but we, in general, also use solutions for sterilization, but i've had to use 100% for a few applications. it does happen. at the moment, i mostly use 100% when preparing cover slips. oh, and boy howdy is that stuff flammable!
[ July 08, 2004, 08:45 AM: Message edited by: peter the bookie ]
Posted by Noemon (Member # 1115) on :
You know, I just have to say that I feel incredibly stupid about my "wait, does oil contain water" bit up above near the beginning of this thread. It's quite possibly the stupidest thing I've ever said in a public forum. If I were the type to go back and edit my posts to make myself look smarter, that's one I'd be editing. But I'm not, so I won't.
Posted by BannaOj (Member # 3206) on :
The reason why you rarely see pure (100%) ethanol, is because of a distillation phenomenon known as an azeotrope.
What happens (in layman's terms) is different fluids evaporate off at different temperatures. Sometimes you hit a point where they both are happy coexisting with each other. I believe this is around 93% ethanol. To get past this point can be done but you have to start playing with partial pressures and all kinds of interesting tweaks.
Water on earth is the most common liquid. And as it is the fluid that allows life as we know it to exist, of course we are going to see it far more than other liquids.
However, with modern chemistry there are many many other pure liquids available. Most "oil" in the generic sense it has been referred to here is Not a pure liquid, with a variety of shorter chain hydrocarbons. Solid "oil" with longer chain hydrocarbons is more commonly referred to as "grease" for example, you can melt crisco, margarine and butter quite easily. If you have straight "soybean oil" or straight "corn oil" or some sort of specified solvent like triethanolamine (which you will see in shampoos) then you actually have a 'pure' liquid.
Getting water truly "pure" requires either distillation or deionization which are interesting process as well.
AJ
Posted by Bob the Lawyer (Member # 3278) on :
I'm trying to imagine how I would ever run an organic synthesis if it weren't so easy to separate the aqueous (water) phase from the organic (non-water) phase from a liquid.
I suspect it wouldn't be possible. Not even close to being possible. So impossible the mind boggles and its impossibility.
And if you're saying "oils" don't count you're essentially saying "all carbon based liquids" don't count. And, ummm... that means I'm going to have to beat you up?
Posted by BannaOj (Member # 3206) on :
Bob yes, I've done them too.
I think you misunderstand. I'm simply talking about "pure" liquids vs impure ones. Oil (as in crude that comes out of the ground) is a variety of different hydrocarbons, that then have to be refined to be useful.
And don't tell me you haven't done the azeotrope curves for alcohol and water because building your own was the way most people I've seen learn about them.
I was trying to stay away from the whole "organic solvents" bit other than mentioning paint thinner because I didn't want to deal with explaining it.
AJ
Posted by Bob the Lawyer (Member # 3278) on :
Oh, sorry AJ, I was busy reacting to Hobbes' posts that boggled my mind and hadn't gotten through the rest of the thread.
Keep up the good work. *thumbs up*
Posted by BannaOj (Member # 3206) on :
*whew* Yeah that was so obfuscatory that I about had a hissy fit (as you can see from my further posts)
AJ
Posted by Bob the Lawyer (Member # 3278) on :
Totally. It's the first time I've responded to something without reading the thread.
Oh, and the water-ethanol point is 95%. Just to answer your previous question and make me look smarter and more pretentious Posted by BannaOj (Member # 3206) on :
I was debating between 93, 95 and 98% and notice I said "about" in there I didn't look it up even though my o-chem book is within arm's reach and should have.
AJ
Posted by Dagonee (Member # 5818) on :
Hmmm. Anyone who's made grain punch could have told you it was 95% (190 proof is the highest they sell).
Dagonee
Posted by BannaOj (Member # 3206) on :
See my brain was vascillating between 180 and 190 and I already called Steve once about this thread.
AJ
Posted by Erik Slaine (Member # 5583) on :
Oops, better email....
*goes*
Posted by aspectre (Member # 2222) on :
Your friend's father is correct, Annie, Roman concrete is different from the standard concrete of today. Roman concrete structures already a couple thousand years old will easily outlast nearly all structures made in the twentieth century.
Standard modern concrete continues hardening during the first phase, but then begins decomposing. Exactly how long it lasts depends on how its mixed and packed. Even assuming proper proportions of its other ingredients, a "soupy" mixture will harden then fall apart after less than a decade of exposure to the seasons. A mixture with barely enough water that a "snowball" of concrete will maintain its shape -- which is then pounded and vibration tamped to remove airpockets -- will last for up to a couple of hundred years. Hardening for the first hundred or so -- though nearly all of the hardening to full strength will occur over the first week or so -- then gradually weakening over the next hundred or so years.
However, there are exceptions in either directions. The mortar in some medieval cathedrals is holding up quite well. I've driven on little-used concrete highways in the back country which were falling apart after less than fourty years. (I mention 'little-used' to indicate that the cause isn't traffic load). And I've seen WWII-era buildings exposed to saltwater in the air which has penetrated through to the rebar, causing it to rust, destroying the concrete in the process. I'd suspect that insufficient tamping allowed air bubbles/channels to draw in salt-laden moisture.
[ July 09, 2004, 04:30 PM: Message edited by: aspectre ]
Posted by aspectre (Member # 2222) on :
And, Hobbes, the reason concrete in very large/thick structures is poured in segments is because the chemical reaction which forms concrete is exothermic, ie produces heat. As with most things, concrete expands when heated and contracts as it cools. So if the newly poured concrete isn't allowed sufficient surface area and time to cool, the concrete structure will crack during the heating&cooling process.
The heating&cooling during the curing process doesn't matter for relatively thin pourings like that for patios and driveways. However in larger structures -- especially those as large as dams -- the heat has nowhere to go: the hot concrete is surrounded by more hot concrete except at the very surface; allowing the interior heat to build up to a comparatively high temperature. So care must be taken to allow a slow enough pouring that the previously poured concrete is allowed the time to cool to a reasonable temperature. The ThreeGorgesDam in China has developed several very large cracks during its construction. According to project managers, there was enough overdesign in terms of strength that the completed structure will be safe. However, knowing of the past politics there and the penalties which would be assessed against managers for failure-to-complete on such a large project, I'd be very leery of living in the flood plain down below. A catastrophic failure of ThreeGorges would cause the greatest deathtoll of any modern disaster. Considering that China has had an earthquake which caused a ~million deaths...
BTW -- A vivid example of heating&cooling cracking's dependence on pour thickness&time can be seen by doing acrylic pours. The ingredients can be most easily purchased through surfboard shops and other fiberglassing outfits. Pour it too quickly and too thickly, and the acrylic shatters into small crystals resembling that from a shattered front windshield of a car.
Oh, and wear safety goggles if you decide to watch the process. My experience with cracking acrylic came through accident, not experiment. So I wasn't around when it was actually cracking, and thus have no idea how forceful the process is; ie whether it kicks out pieces. Definitely do NOT do the experiment in a glass or ceramic container: odds are it will shatter with sufficient force to cause eye injuries. Nor do I know what a much larger pour would do: ?explode?spontaneously combust?
So do small&thin pours first: no thicker than a standard plexiglass sheet. Then increasingly larger&thicker ones until you see the cracking process.
Also make sure that you do the experiment outdoors or in a well ventilated room, preferably one with fans blowing air out the open windows, with no open flames or sources of sparks. A chem-filter mask is also recommended. The solvent (at least in what I used) is both an intoxicant and highly toxic; as well as explosively combustable when mixed in a proper concentration with air. So if you don't take reasonable care: you could end up drunk-to-unconciousness from breathing the fumes, poisoned, and burnt to a crisp. Do not spill on your skin
Working with acrylic isn't so dangerous or difficult that any responsible adult or teen would be endangered: I wouldn't leave my suggestion posted if it were. However, as with all uses of organic solvents -- including gasoline, etc -- care MUST be taken to handle it in a safe manner.
[ July 08, 2004, 03:31 PM: Message edited by: aspectre ]
Posted by Teshi (Member # 5024) on :
quote: Transparent Aluminum?
One step on the road... Translucent concrete would be amazingly cool to have in your house- blocks that are very strong but transmit light- it's like those old lego blocks that are translucent. You can use them in walls but still keep the inside light.
Posted by BannaOj (Member # 3206) on :
Btw Happy Camper, Steve is now reading this thread (even if he refuses to post) and is ranting about discussing someone named Terzaghi (sp?) with you.
AJ
Well ranting is the wrong word, but I can't think of a better one.
[ July 08, 2004, 09:33 PM: Message edited by: BannaOj ]
Posted by Glenn Arnold (Member # 3192) on :
quote: Hadrian's wall didn't use concrete. It was made of stone, and filled with rubble and mortar, which likely contained cement.
The definition of concrete is a mixture of cement and small stones, or sand. Sounds like Hadrian's wall is in fact made of concrete.
Mortar is simply a mixture of cement that is sticky enough to "glue" rocks together.
CO2 is sometimes used to make a particularly strong cement/concrete. Basically you mix your cement with seltzer.
Also, you can get cement to set up very quickly if you heat the water you use in your mix.
quote: rivka, there was a study published last year (and i don't have a reference) saying that an 80% ethanol solution was actually better for sterility than just 100% ethanol. i have no idea why, but we, in general, also use solutions for sterilization, but i've had to use 100% for a few applications.
That's interesting! I wonder if the trace amounts of benzene (or other organics) usually found in "100%" alcohol have anything to do with that.
quote: oh, and boy howdy is that stuff flammable!
No kidding! Which would be precisely WHY when I see labs that claim to be for high school students that call for alcohol concentrations higher than 20% or so, I am astounded. My chem students are very good about not messing around, and I would be very hesitant to do a lab like that with them. (Not to mention the storage headaches.)
Posted by Architraz Warden (Member # 4285) on :
I've really tried to stay out of this, but I just had to add a little tidbit.
Heat can hamper or damage concrete while it is curing in even the most basic of applications. In various desert areas of the world (I don't know about Phoenix, but maybe), ice is added into the concrete mixture to keep the internal tempurature from getting too high while it is curing.
I've really gotta read about this self-reinforcing concrete. I've always wondered is strong filaments could be added to help with concrete's dismal (well, very nearly non-existant) tension performance.
Now, I'll flee from this orgy of engineers.
Feyd Baron, DoC
Posted by ak (Member # 90) on :
An orgy of engineers is a pretty dry, unexciting sort of orgy, isn't it? We go wild over properties of materials.
Posted by Dagonee (Member # 5818) on :
quote:Yes, the Romans used concrete.
Yes, but not in Hadrian's Wall. It's a stone wall - there are plenty of pictures.
Dagonee
Posted by Noemon (Member # 1115) on :
It is a stone wall, sure, but the stones are set in fairly thick layers of cement mortar. The first time I saw a picture of it I thought that someone had done a really horrible amaturish restoration job on it sometime in the last 50 years or so, actually.
Posted by Dagonee (Member # 5818) on :
Right, but I said it used cement, just not concrete.
I want to walk the wall some day - apparantly it's a good walking tour.
Dagonee
Posted by Noemon (Member # 1115) on :
Yeah, that's one of the things I'd like to do before I die also.
Posted by Happy Camper (Member # 5076) on :
Good man, that Terzaghi. Father of modern soil mechanics. Probably wouldn't have the job I have if it weren't for him.
Posted by Kwea (Member # 2199) on :
I would LOVE to see the wall, it would be so cool.
Remember, Jenni and I went on the geek honeymoon.....we love history!
Kwea
Posted by Glenn Arnold (Member # 3192) on :
Dagonee:
quote: filled with rubble and mortar, which likely contained cement.
How is this not concrete?
Back to the original article, it looks like they are using glass fibers to "pipe" light through the concrete. It isn't transparent, just translucent. Neat idea, and I suspect that you could make translucent lead or tin quite easily, the same way. Aluminum melts at about 1100 F, so I don't think glass fibers would hold up in the mix. Maybe quartz fibers would. I wonder what would happen to the properties of a metal if it was impregnated with glass fibers?
Posted by BannaOj (Member # 3206) on :
The field of study you are referring to is called composite materials though in a wierd combination with metallurgy.
Adding stuff to metal in less than minute quantities often weakens it. They add traces of some non metals like sulfur to make alloys stronger, but tweaking metal alloys is a delicate business. It has to do with the nature of metalic bonding, which is a giant orgy of electron sharing, in most cases (aluminium is a slight exception but similar) Glass fibers large enough to conduct light to make translucence in a thick sheet, would almost certainly destroy the bonding. There's also the melting points. I forget which is harder to do, molten metal (which varies depending on alloy) or molten glass, but if the glass melting point is lower you are going to have big problems. (Whoops, Glenn already mentioned this)
Pure lead is virtually never used in construction because it is too soft among other things. Pure tin is pretty darn uncommon too. There are thousands if not tens of thousands of metal alloyse that do use trace amounts of both in their make up.
The easiest way to get transparent metals right now is to hammer a sheet thin enough that you can see through it, like gold leaf for example. Of course this won't give you the structural properties necessary to build anything.
Steve and I were talking in sci-fi terms of whether making a sheet window out of diamond would be possible. It would definitely be harder than glass. I don't know how brittle it would be. But an interesting idea for spaceship cockpit windows, even if it would be extremely difficult IRL.
AJ
[ July 09, 2004, 02:40 PM: Message edited by: BannaOj ]
Posted by saxon75 (Member # 4589) on :
Interesting. I've had a couple of watches that used synthetic sapphire for the face, instead of glass, but I've no idea what a diamond window would be like.
Posted by BannaOj (Member # 3206) on :
hmmm corrundum (sapphire) is an interesting idea too. It's much easier to make synthetically I know. I know hardness wise it is a 9 on the Mohs scale while diamond is a 10. Don't really know what the structural properties of either are.
Diamond and aluminum actually both have similar covalent bonding going on even if one is a metal and one is a non-metal.
AJ
Posted by aspectre (Member # 2222) on :
Thin-layer (I think less than a hair-width) sapphire bonded to glass is used to create armored windows so tough that standard rifle armor-piercing slugs won't penetrate. The main part of the bullet's energy is expended shattering the sapphire, which then spreads the load across a much larger cross-section of glass. And a final layer of Spectra/nylon-type plastic stretches to keep the shattered glass from blasting inward.
And small diamond windows are standard on vapor-deposition equipment which use lasers to vaporize the deposited material and/or to monitor the process. Similarly, in other equipment which use lasers to conduct and/or monitor either ultra-low or ultra-high pressure experiments.
[ July 09, 2004, 06:06 PM: Message edited by: aspectre ]
Posted by rivka (Member # 4859) on :
Wouldn't diamond's high refractive index present problems in making windows?
Posted by Dagonee (Member # 5818) on :
I'm blind! I'm blind!
Posted by Dagonee (Member # 5818) on :
quote:How is this not concrete?
From the links I found first, it sounded like the rubble was piled in place and coated with mortar to hold it in place, then the stone walls were put up around it. This is done mainly to help the builders keep the dirt in place, not for long-term strength. Since the aggregate isn't mixed in with the cement, it would technically not be concrete.
Further research reveals it was concrete surrounded by stone. I jumped to the wrong conclusion based on the wording at a tourist site. But there are walls built the way described above.
Dagonee
Posted by aspectre (Member # 2222) on :
quote:ZnSe has a very low coefficient of absorption at 10.6 µm but, as laser powers increase, windows made of it suffer from thermal lensing, gradients in the refractive index that distort the beam.
Although synthetic diamond has a coefficient of absorption 100 times higher than ZnSe at this wavelength, its refractive index is less dependent on temperature. Moreover, diamond conducts heat 120 times better than ZnSe and is seven times as strong.
Diamond is also much harder&stronger, and thus much more resistant to physical damage than alternatives.
Plus diamond undergoes far less faraday rotation, which is an extremely useful feature when making interferometry and/or polarimetry measurements.
But you're right, the reflectance does seem high. Perhaps because the most commonly used refractance-to-reflectance equation is for incoherent light, while laserlight is coherent? And a reduction of reflectance through source distance and window thickness being tuned for coherent light at a specific wavelength to obtain a more efficient coupling?
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And AJ is right, we're total stick in the muds, hopeuly that'll comfort you next time you drive over a bridge. ![[Cool]](cool.gif)
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However I don't think ethanol will work for portland cement, though it can work quite well for engineering tests.![[Evil]](graemlins/evil.gif)
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