Saturday, April 28, 2012
IS GLASS A LIQUID OR A SOLID? post by Colin Lorenz
In many old windows, the panes are thicker at the bottom of
than they are at the top. People often claim this fact as evidence of glass
being a liquid. If the glass is close to the glass-tranistion temperature the
more it shifts but if it is further way the molecules will move slower and
appear more solid. Not all antique glass observes the property of being thicker
at the bottom. This is discussed in more detail in the link below.
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I do believe glass is a solid. Many solids have a crystalline structure on microscopic scales. The molecules are arranged in a regular lattice. As the solid is heated the molecules vibrate about their position in the lattice until, at the melting point, the crystal breaks down and the molecules start to flow. There is a sharp distinction between the solid and the liquid state, that is separated by a first order phase transition, i.e. a discontinuous change in the properties of the material such as density. Freezing is marked by a release of heat known as the heat of fusion.
ReplyDeleteI would say there is no clear answer to the question. It is possible to justify the view that glass is a highly viscous liquid or that the view that it is an amorphous solid, or simply that glass is another state of matter that is neither liquid nor solid. There is no clear definition of the distinction between solids and highly viscous liquids. All such phases or states of matter are idealisations of real material properties. Common sense would say that glass is a solid because it is rigid according to everyday experience and the use of the term "supercooled liquid" to describe glass still persists, but is considered by many to be a misnomer that should be avoided.
ReplyDeleteI grew up being taught that glass is an amorphous solid..
ReplyDeleteAn amorphous (or synonymously, non-crystalline) material can be defined as one which is topologically disordered and which does not exhibit either the long-range translational order (periodicity) characteristic of single crystals, or the long-range orientational order characteristic of quasicrystals. Within this definition, such materials could be either solid or liquid, and this distinction is essentially simply one of timescale. A material is a solid when there is no observable long-range translational diffusive motion during the duration of the experiment; in other words, dynamic disorder is absent.
A glassy (or synonymously, vitreous) material is an amorphous solid that exhibits a glass transition. (Thus, by definition, all glasses are amorphous, but not all amorphous solids are necessarily glassy.) The glass transition is marked (as a function of temperature) either by a change in slope of extensive thermodynamic quantities (e.g., volume or entropy) or, equivalently, as a discontinuity in derivative quantities (e.g., specific heat or thermal expansivity).
http://dwb.unl.edu/Teacher/NSF/C01/C01Links/www.ualberta.ca/~bderksen/florin.html
It is more likely that the reason the panes of glass are thicker at the bottom is that it is simply easier to install them that way. There are several examples of glass installed in cathedrals where it is thinner at the bottom than at the top as a result of careless installation.
ReplyDeleteHere are the differences between glasses, fluids, and crystalline structures:
ReplyDelete"crystalline solids: molecules are ordered in a regular lattice
fluids: molecules are disordered and are not rigidly bound.
glasses: molecules are disordered but are rigidly bound."
-http://math.ucr.edu/home/baez/physics/General/Glass/glass.html
Glasses are amorphous solids. This means that there is no long range order of the position of its atoms. Other examples of amorphous solids are plastic, silica, and rubber. We consider these examples to be solids. Therefore, if I had to decide whether if glass was a solid or liquid, I'd choose solid, but its really neither.