Skip to comments.Glass breakthrough (Alumina Glass)
Posted on 08/26/2004 5:46:49 AM PDT by Brett66
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 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.
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.
LOL, first thing I thought of too. (a keyboard...how quaint)
What about the tensile tests? Austempering, marquenching, oh my! Materials was so much fun... OK, not really.
My wife told me to buy 3M last year. I should have listened.
I would expect the match to be close enough that these glasses would make good "windows" in hermetic ceramic packages for optically erasable E-PROMS and various types of optical sensors and emitters.
There be whales
Acording to Fiona, Scotty doesn't know...
Beer In Aluminum Bottles On The Way ^
140 microns is about as small as many people can see. 1 gigapascal is a h*** of a lot of pressure. Scotty, I don't think we're building whale tanks yet!
Fracture toughness will measure ductility. Glass doesent have to be strong in tension. My guess is that this new glass will be used for optics and all current uses... Hmmm, might be time to look at 3M !
This new technique ELIMINATEs the 1GPa Compression requirement. Did you realize that? And the 140 Microns was the seed material size, before sintering. The granualarity is washed away during the 1000 deg C sintering temp.
This is a wonderful accomplishment!
I guess I should read a little more carefully.
No big deal there, Fudd! I'm just excited about this.
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