Windows made this way usually contain air bubbles and "waves," and aren't always of perfect thickness throughout. But what's actually happening as the glass goes from a liquid to an amorphous solid? In a straightforward phase transition, like when water freezes into ice, the transition is dependent on well-defined temperature and pressure points. The glass transition is different: it also depends on the rate at which the heating or cooling takes place.
Glass is formed by cooling a liquid below its freezing point, then cooling it some more. Cool it fast enough, in a process known as "super-cooling," and the molecules don't have sufficient time to organize themselves into the rigid crystalline lattice structure of a solid. Instead, as the temperature drops the liquid becomes much more "viscous. As this happens, the molecules gradually move more and more slowly, until they are hardly moving at all. This indecisiveness on the part of glass -- choose a state of matter already!
There is an enduring urban legend that the glass windows in medieval cathedrals are thicker at the bottom because over hundreds of years, the glass has "flowed" downward and pooled at the bottom. There is a tiny bit of truth to the legend. At the molecular level, glass does "flow", it just does so very verrry sloooowly.
She emphasizes that this is a conservative estimate; it might take much longer. So there's frankly no way in hell that the irregularities in medieval cathedral windows are due to the flowing properties of glass. Instead, the observed anomalies are probably due to inherent flaws resulting from the manufacturing process.
For more detailed information on the molecular structure of glass, whether or not it can be said to truly "flow," and some fascinating early history, see this excellent discussion. In a article in Discover magazine on the physics of glass, Robert Kunzig discussed the possibility of an "ideal glass": "what you would produce if you could cool a liquid with geologic slowness while somehow preventing it from crystallizing.
Physicists have no idea how to even begin visualizing such a thing. But it could be important. We've heard whispers to the effect that discovering an ideal glass transition phase -- namely, a point during the supercooling process where the molecules have no choice but to move rapidly from the disordered liquid configuration to a highly-ordered solid configuration -- could yield insights into the structure of the early universe, which may have existed in a similar amorphous disordered state.
Alas, the news on that front isn't encouraging. A paper in the June 9 issue of Physical Review Letters , by Princeton University's Salvatore Torquato et al , concluded that such an ideal glass transition phase doesn't exist. Torquato's team performed a bunch of computer simulations and couldn't find any such well-defined transition point.
Torquato told Live Science that "You could have this continuous change from most disordered to most ordered, and there are an infinite number of possible transition phases between these points.
It puts another nail in the coffin for [the ideal transition] theory. Maybe that ideal transition phase is a bit questionable, but the mysterious "Moosino" over at Chi c'e' in Ascolto reports on a very different kind of "transition phase" from amorphous solid into, well, a million little pieces. Apparently she was driving along one day, when one of the side windows of her car spontaneously shattered.
Being such a well-trained scientist, she nosed around until she found some answers. Basically, the side windows of a car are made of tempered glass, a process that causes the exterior surface to compress while the interior is still expanding a bit. The end result is an exterior compression layer and an interior tension layer -- I believe the technical term is an "inclusion. The window goes snap! Or crackle! Or pop! Images : top Rice Krispies cereal box.
Source: Wikipedia, under fair use. But have you ever wondered precisely why Rice Krispies snap, crackle, and pop? What is it about puffed rice that causes it to make such bizarre sounds when you add milk to it? It has to do with the method used to make this breakfast favorite, and what happens to it when liquid is introduced to the equation. Puffed rice has, of course, been around for a long time—much longer than puffed rice breakfast cereals have been.
In India, for example, puffed rice has long been a staple, traditionally made using the hot salt frying or hot sand frying techniques: Salt or sand is first heated in a pan over a fire; then parboiled rice is added to the pan. The high heat and salt or sand cause any remaining water in the rice to evaporate immediately—and as it does so, the rice grains expand due to their starch content and the pressure created by the rapid evaporation.
The grains then dry out quickly and harden , thus creating puffed rice. In China, meanwhile, puffed rice was made in a pressurized iron cauldron, and can be found in records dating back to the Song dynasty to C. Breakfast cereals like Rice Krispies, however, are made a little differently—and the technique used in their creation is much more recent.
The method is usually credited to Minnesota native Alexander P. That extreme heat blast causes each grain to expand and develop air pockets inside the grains called oven-puffing and creates the cereal's delicately crisp texture. So why does it sound like the cereal comes alive when milk is added? What you're hearing is the sound of those toasted bubbles breaking from the pressure of the milk as it pushes air against those fragile baked grain walls that subsequently shatter.
The cereal may have begun as a breakfast food, but about 15 years later Rice Krispie treats, possibly equally as iconic as the cereal itself, got their start. The sweet snack was originally created for a Camp Fire Girls fundraiser by a cook in the Kellogg Cereal Company test kitchen. The recipe was published in and has become an instant classic and beloved treat thanks to the crunchy rice cereal and gooey marshmallow that holds it all together. The original recipe is solid, but variations have kept the treat moving with the times.
Give your next batch a grown-up twist with aromatic coffee and the tart fruity bite of dried cherries. For a simple variation, substitute chopped apricots for the cherries and omit the coffee.
Or combine classic Rice Krispie cereal with colorful Fruity Pebbles for a confetti effect. Skewering each treat on a lollipop adds to the overall whimsy of this sweet.
You can bring smoky-sweet flavor to the marshmallow-rice square with a sprinkle of cooked and crumbled bacon and a drizzle of maple syrup. Or as an alternative, omit the bacon and add a pinch of smoked paprika for a vegetarian variation.
One of the world's most innovative chefs, Ferran Adria , used Rice Krispies for a mock paella that won rave reviews and demonstrated that the oven-puffed cereal's properties have a place in savory dishes just as much as they do in desserts. And another recipe employs crisped rice cereal as a coating for super crunchy, tempura-like shrimp.
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