posted
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 ]
Posts: 318 | Registered: Apr 2002
| IP: Logged |
posted
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.
Posts: 16059 | Registered: Aug 2000
| IP: Logged |
posted
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.
posted
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?
Posts: 3243 | Registered: Apr 2002
| IP: Logged |
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.
posted
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 Posts: 3243 | Registered: Apr 2002
| IP: Logged |
posted
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.
posted
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.
posted
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.
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
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.
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.)
Posts: 32919 | Registered: Mar 2003
| IP: Logged |
posted
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.
posted
An orgy of engineers is a pretty dry, unexciting sort of orgy, isn't it? We go wild over properties of materials.
Posts: 2843 | Registered: A Long Time Ago!
| IP: Logged |
posted
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.
Posts: 16059 | Registered: Aug 2000
| IP: Logged |
posted
Good man, that Terzaghi. Father of modern soil mechanics. Probably wouldn't have the job I have if it weren't for him.
Posts: 609 | Registered: Apr 2003
| IP: Logged |
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?
Posts: 3735 | Registered: Mar 2002
| IP: Logged |
posted
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.
posted
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.
Posts: 4534 | Registered: Jan 2003
| IP: Logged |
posted
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.
posted
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.
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.
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?
Printer-friendly view of this topic
![[Razz]](tongue.gif)
![[Wink]](wink.gif)
I didn't look it up even though my o-chem book is within arm's reach and should have.![[Smile]](smile.gif)
![[Big Grin]](biggrin.gif)
![[Dont Know]](graemlins/dontknow.gif)
