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Transparent Aluminum Is Here
Alien54 writes "Scientists in the US have developed a novel technique to make bulk quantities of glass from alumina for the first time. (link includes a picture of samples) Anatoly Rosenflanz and colleagues at 3M in Minnesota used a "flame-spray" technique to alloy alumina (aluminium oxide) with rare-earth metal oxides to produce strong glass with good optical properties. The method avoids many of the problems encountered in conventional glass forming and could, say the team, be extended to other oxides (see also: A Rosenflanz et al. 2004 Nature 430 761). Scotty would be pleased."
Glass breakthrough
11 August 2004
Scientists in the US have developed a novel technique to make bulk quantities of glass from alumina for the first time. Anatoly Rosenflanz and colleagues at 3M in Minnesota used a "flame-spray" technique to alloy alumina (aluminium oxide) with rare-earth metal oxides to produce strong glass with good optical properties. The method avoids many of the problems encountered in conventional glass forming and could, say the team, be extended to other oxides (A Rosenflanz et al. 2004 Nature 430 761).
Glass is formed when a molten material is cooled so quickly that its constituent atoms do not have time to align themselves into an ordered lattice. However, it is difficult to make glasses from most materials because they need to be cooled -- or quenched -- at rates of up to 10 million degrees per second.
Silica is widely used in glass-making because the quenching rates are much lower, but researchers would like to make glass from alumina as well because of its superior mechanical and optical properties. Alumina can form glass if it is alloyed with calcium or rare-earth oxides, but the required quenching rate can be as high as 1000 degrees per second, which makes it difficult to produce bulk quantities.
Rosenflanz and colleagues started by mixing around 80 mole % of powdered alumina with various rare-earth oxide powders -- including lanthanum, gadolinium and yttrium oxides. Next, they fed the powders into a high-temperature hydrogen-oxygen flame to produce molten particles that were then quenched in water. The resulting glass beads, which were less than 140 microns across, were then heat-treated -- or sintered -- at around 1000C. This produced bulk glass samples in which nanocrystalline alumina-rich phases were dispersed throughout a glassy matrix. The new method avoids the need to apply pressures of 1 gigapascal or more, as is required in existing techniques.
Click to enlarge
Aluminate glasses
The 3M scientists characterised the glasses using optical microscopy, scanning electron microscopy, X-ray diffraction and thermal analysis, and tested the strength of the materials with hardness and fracture toughness tests. They found that their samples were much harder than conventional silica-based glasses and were almost as hard as pure polycrystalline alumina.
Moreover, over 95% of the glasses were transparent (see figure) and had attractive optical properties. For example, fully crystallized alumina-rare earth oxide ceramics showed high refractive indices if the grains were kept below a certain size.
Author
Belle Dumé is Science Writer at PhysicsWeb
Aren't many jewels aluminum compounds?t s/13.html
google search of rubies and aluminum:
http://pearl1.lanl.gov/periodic/elemen
Alumina (aluminium oxide) is not the same as aluminium, that's like saying that water ice(hydrogen oxide) is 'Transparent Hydrogen'.
Alumina or corundum as the natural material is known, is found in nature as a clear mineral - different colour variations give you Ruby and Sapphire.
Jolyon
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If I remember correctly, they did not need the clear aluminum but they did need something to store the whale in. Since they did not have any money they traded the formula for clear aluminum for the whale tank.
Well, alumina has almost none of the same properties as aluminium (since you're from the UK too, I'll spell that word correctly from now on). It's extremely tough (used in drilling bits), non-conductive and non-reactive. One would expect something described as "Transparent Aluminium" to behave a bit like Aluminium. Alumina doesn't.
Athletic Scholarships to universities make as much sense as academic scholarships to sports teams.
Why not link to the article on transparent alumina as well? Though it needs a slight update, mind you.
The World Wide Web is dying. Soon, we shall have only the Internet.
A common misconception caused by the old "spun" method of making glass which makes sheets which are thicker at the bottom than the top. People have often assumed that old glass has "flowed" into that shape. It hasn't: it was made that way. Glass does not in fact flow, not even slowly.
Search on Google for "glass flow" for lots and lots of stuff about this.
TWW
"Encyclopedia" is to "Wikipedia" what "Library" is to "Some people at a bus stop"
Pure aluminum is a metal. Aluminum oxide is not - it's like the difference between hydrogen and water.
As I understand it, pure metals can't be transparent because light is an electromagnetic wave which gets "short-circuited" by conductive materials. Presumably the oxides disrupt this conductivity. And anyway, the alumina is combined with other oxides before being used to form glass.
Karma: Segmentation fault (tried to dereference a null post)
Is nothing new - it's called corundum or as you more probably know it, sapphire (or ruby when it is red).
And hard is only one part of the story. Glass is hard, yet I wouldn't want to make structural elements of an aircraft from large hunks of glass... Aluminum is light and Tough (high energy to break). It is also ductile (deforms before breaking) something that no ceramic is...
So, while this is cool, and will probably be used for super scratch proof layers on spyplane camera transparencies or something like that where they can afford something like this, it isn't what you think it is.
As an aside, translucent alumina is used in something you see everyday - sodium vapor lamps use alumina to encapsulate the sodium metal that they use as their filament.
+++ ATH0 +++
There is some debate, the scientific consensus at the moment is that (ordinary) glass is NOT a liquid. Wikipedia has some interesting background info on this discussion.
In general, the composition of glass makes a huge different in properties such as hardness, inertness, transparancy and color. In ordinary glass, CaO is added to lower solubility in water and various other solvents.
Glass may flow, but it does so very very very slowly. As in "age of the entire universe" slowly.
No, it makes the term "transparent alumina" valid. The term 'Aluminum' refers to an element, whereas alumina refers to a compound of aluminum. If you refer to the properties of aluminum (or aluminium, if it makes this easier for you), you are (or at least will be understood by others to be) referring to the properties of a quantity of essentially pure aluminum, which is transparent under no condition.
Therefore, the term "transparent aluminum" is incorrect. Sorry.
Ce n'est pas un vrai mouvement de robot!
Seems a couple other people beat me to rebuking this, but I figured I'd throw another link in just in case there is any lingering doubt.
Glass is not a liquid. Glass is an amorphous solid.
All editorial writers ever do is come down from the hill after the battle is over and shoot the wounded.
Transparent Aluminum Is Here
NO IT ISN'T! Commercially developed transparent Alumina (think clear ruby/sapphire) is here, HUGE difference. Sorry Trek fans, you will have to wait longer. There will be no clear planes, no clear cases made of Alumina. If cases were transparent Alumina then they would have the same properties as silica glass and you would have a nice greenhouse effect going on slowly (or not so slowly) frying your computer.
Alumina is a mineral/glass/ceramic, Aluminum is a metal!
It's called an Alcubierre Drive. You can finish yourself off now.
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Sure it's been said but bears repeating.
If you have a high quality watch it is likely that the crystal is made from polycrystalline alumina (i.e. corundum...in this case synthetic corundum). The alumina glass is different however in the fact that it is a glass and therefore lacks crystal structure.
Since it doesn't have to be crystallized it is likely that it will be able to be produced in large sizes. However, being a glass it is not going to have the malleable properties of aluminum metal and will probably shatter if hit hard enough.
Sort of....
A better way of explaining it would be that for a photon to be absorbed by an electron, there must be an empty higher energy state for the electron to move to (E = Eo + hv, where Eo is the energy state of the electron and hv is the energy of the photon). In solids with metallic bonding, there are many electrons floating around and many free electronic states for them to move to, so any photon that enters the solid can be absorbed by an electron that will then jump to a higher energy state (which will be free, because there are so many free energy states).
In the case of insulating and semiconducting materials, there is a gap in the energy states, so some transitions are not allowed. For pure, single crystal Al2O3, (aka white sapphire), there are (essentially) no transitions available that correspond to the energy of photons of visible light. If you start substituting in Cr3+ ions for the Al3+ ions, your sapphire will turn red and we call it "ruby". In this case, the Cr impurities provide transitions that can absorb wide ranges of visible light, but not red light. What is more is (if this is fairly pure), the ruby will not only absorb light of other wavelengths, but it will emit red light as well. Try putting a synthetic ruby under a UV light, it will glow red.
However, it should be noted that other defects can scatter and absorb light as well. Grain boundaries, voids, inclusions, etc. will affect your light transmittance. It has been possible for some time now to make polycrystalline alumina that is translucent (Lucalox), but polycrystalline alumina can never be transparant, so there are two ways to make alumina transparant: make it single crystal (only one grain, so no grain boundaries) or amorphous (no grain boundaries, because there is no long range crystal order).
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The internet is the greatest source of biased information in the history of mankind.
This news should not be surprising to anyone, since it's essentially a dupe! http://science.slashdot.org/article.pl?sid=02/02/2 0/0358206&tid=126&tid=14 [slashdot.org]
The amusing thing, is that American scientists are given credit here, but if you look at the original article from 2+1/2 years ago, it was the Germans who discovered it. Hmmm...
You could argue that this article is just a 'refinement' of the previous article. I could believe that only if a link had been provided to the original article. Ah well... Odd that the article itself doesn't mention previous work by the Germans either...
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A more likely reason for the confusion is that Russian has several sounds which English does not.
I think you meant English has several sounds not present in Russian, based upon the example given.
Russian has no consonants to depict the sounds presented by the English letters "j", "qu", "x" and "w". English does in fact have the "zh" sounds. It's just not represented by a single letter. Pronounce "vision".
Russian can approximate all three of these letter using their own alphabet.
x = ks (ax = aks)
j = dzh (jeans = dzheens)
qu = koo + vowel (queer = kooeer)
w = oo + vowel (whale = ooayl)
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