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 1000�C. 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.
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 Dum� is Science Writer at PhysicsWeb
-------------------- Justice inclines her scales so that wisdom comes at the price of suffering. -Aeschylus, Agamemnon
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FUCK the germans: they obviously came from the far future to steal this scientific discovery and incidentally make me looks like I missed some new from over a year ago.
Or somethin'.
-------------------- Justice inclines her scales so that wisdom comes at the price of suffering. -Aeschylus, Agamemnon
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Well, I haven't read very far in either article. For all I know these could be wholly unrelated. I'm honestly curious. And, OK, a little snarky.
Registered: Mar 1999
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....gonna be a Hurricane Francis kinda weekend, so I better get numb whille it's still feasable.
-------------------- Justice inclines her scales so that wisdom comes at the price of suffering. -Aeschylus, Agamemnon
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Cartman
just made by the Presbyterian Church
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OK, so, in the Spiegel article, they say something about baking fine-grained alumina in a furnace in some Special And Probably Patented Way which produces a hard transparent material dubbed "Transparent Aluminum", which is really glass, which is a mixture of silicates formed from a melt by cooling to rigidity without crystallization. And in the PhysicsWeb article, they say something about bonding aluminum oxide powder with rare metal oxide powders in some Other Special And Probably Soon To Be Patented Way which also produces a hard transparent material dubbed "glass", which is also really glass, which is a mixture of silicates formed from a melt by cooling to rigidity without crystallization.
I was done with chemistry long ago.
Registered: Nov 1999
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Forgive me for something whatever, but what is this?
"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."
Um, man has had the ability to form glass for thousands of years, it doesn't need to be heated up to several million degrees, and it certainly doesn't have to cool off at 10 million degrees per second. I've been to a glassworks, they were cooling the stuph off in open air, over like 90 seconds.
-------------------- "I'm nigh-invulnerable when I'm blasting!" Mel Gibson, X-Men
Registered: Aug 1999
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