Talk:Glass/Archive 1

message: I am desperately looking for glass properties and by properties I mean: Young's Modulus, Density, Poisson's Ratio etc.
I am tempted to add space in the article and leave the values empty - could spark someone to edit it, but I supt; if you would like to see a section on the subject included, at least provide seed information that others can build upon. --Cheers, Folajimi (leave a note) 15:37, 27 September 2006 (UTC)
thread_title: Glass Properties

message: The Broad, Cylinder, French or German technique for making window glass is illustrated in Diderot's Encyclopedie (circa 1750-70), and can probably be dated to much earlier than that. I will try to dig up some earlier references. As an earlier author suggests, Blenko started working in West Virginia no earlier than the 1920s(?) Ids135 04:05, 22 July 2005 (UTC)
replies: text: Now corrected in article Parasite 06:37, 4 February 2006 (UTC)
thread_title: Cylinder glass predates Blenko by 150 or more years

message: I'm not convinced by the Egyptian bit. They would not have been able to melt sand on its own (despite its ready availability!) so at the very least they must have added soda. It also seems extraordinary that they appear to have invented the float glass process millennia before Pilkington Glass of St Helens. jimfbleak 15:56 9 Jun 2003 (UTC)
:The ancient Egyptian glass (circa 1500 BC) is a soda-lime-silica glass that is not that different compsitionally from modern container and plate glass manufactured today.  The soda was derived from littoral natron (hydrated sodium carbonate) in which lime and magnesia were impurities.  The first applications were as simulated gems then rudimentary containers. Reference: Kurkjian, Charles R. and Prindle, William R. (1998). Perspectives on the History of Glass Composition. Journal of the American Ceramic Society, 81 (4) 795-813.--tod 05:59, 29 Jul 2004 (UTC)
thread_title: Egyptian priority for glass

message: Three things: 1. Nowhere do I see a broader definition of glass (non-crystalline solid) - this SHOULD be mentioned!  2.  Everything flows at sufficient pressure/force (or decomposes). 3. Comparing glasses of different ages (eg Modern vs Egyptian) is spurious unless the chemical composition and the heat treatment is identical.DEN/3/13/2004
===ASTM definition and comments===
1.  A broader definition would complicate and confuse the article.  All glasses are non-crystalline (syn. amourphous) by definition.  However, not all non-crystalline solids are glasses.  Non-crystalline is a more general term.  A definition would be good though.  One possibility is the ASTM definition:  A glass is an inorganic product of fusion that has been cooled to a rigid condition without crystallization.  Translation:  A glass is material (not based on chains or rings of carbon atoms) that has been produced by melting a liquid that was subsequently cooled to solid form without forming crystals.  Note that in addition to being non-crystalline, a glass is not a polymer (plastic) but can be a metal.  There exist non-crystalline polymers (i.e., polycarbonate, polymethylmethacrylate (plexiglas)), not a glass. And non-crystalline metals (metallic glasses) which are a glass.  Also a glass must be formed from a molten liquid.  Therefor this definition would exclude non-crystalline materials produced by other such as vapor deposition, oxidation, grinding, radiation exposure.  For example, fused quartz is a pure silica glass produced by melting quartz sand and is a glass.  The non-crystalline silica produced by oxidizing a silicon wafer in computer chip manufacturing is not a glass. 3. see comment above.  --tod 05:59, 29 Jul 2004 (UTC)
thread_title: 3 improvements

message: 1.  A broader definition would complicate and confuse the article.  All glasses are non-crystalline (syn. amourphous) by definition.  However, not all non-crystalline solids are glasses.  Non-crystalline is a more general term.  A definition would be good though.  One possibility is the ASTM definition:  A glass is an inorganic product of fusion that has been cooled to a rigid condition without crystallization.  Translation:  A glass is material (not based on chains or rings of carbon atoms) that has been produced by melting a liquid that was subsequently cooled to solid form without forming crystals.  Note that in addition to being non-crystalline, a glass is not a polymer (plastic) but can be a metal.  There exist non-crystalline polymers (i.e., polycarbonate, polymethylmethacrylate (plexiglas)), not a glass. And non-crystalline metals (metallic glasses) which are a glass.  Also a glass must be formed from a molten liquid.  Therefor this definition would exclude non-crystalline materials produced by other such as vapor deposition, oxidation, grinding, radiation exposure.  For example, fused quartz is a pure silica glass produced by melting quartz sand and is a glass.  The non-crystalline silica produced by oxidizing a silicon wafer in computer chip manufacturing is not a glass. 3. see comment above.  --tod 05:59, 29 Jul 2004 (UTC)
thread_title: ASTM definition and comments

message: When a solid "creeps," this refers to a permanent, plastic, time-dependant deformation that usually relies upon some applied force *usually* at high temperatures.  (Think of centrifugal forces on a nickel-base turbine engine blade.)  Creep for crytalline solids is heavily dependant on things like dislocations, difussion constants, Burgers vectors, and others.  Flow, however, is more poorly understood for glasses.  There exists only a very fine line between creep and flow, and sometimes to avoid addressing the issue, the literature will talk of "time-dependant flow" of glass.  Flow depends heavily on viscosity, which is a very non-linear variable related to a exponential function of temperature.  An added level of indirection is the *type* of flow, be it Newtonian or non-Newtonian, which relates to strain-rate effects.  Those are questions better asked to a fluid-mechanics expert instead of a materials scientist, though.
Flow is failry well understood for glasses. Molten glass in general pretty much behaves as a newtonian liquid.  The temperature dependence of viscosity is common to most all liquids.  Near the glass transition temperature it is viscoelastic (which arguable can be complicated, but known), below it is an elastic solid.  There are two additional situations that complicate things further.  One is flow under very high strain rates as may occur during very high speed fiber drawing or very high speed press and blow manufacture (i.e. bottles).  You then can run into shear thinning, a non-linear viscosity effect.  Second, occurs if the particular glass composition is susceptible to phase separation (think oil and water).  --tod 05:59, 29 Jul 2004 (UTC)
thread_title:  more on 'flow=/=creep' 

message: ::I would recommend just adding it, possibly under "architectural glass" - what you have written is fascinating and would make an excellent addition to the article.  Length is not really a problem, certainly not for material this topical (it answers questions like "Why is broken glass dangerous?" "How do they make car windows safer?").  The fibreglass stuff might should go here in summary only and into the fibreglass article in detail, but your comments here certainly seem very apropos. --Andrew 19:08, 23 Jul 2004 (UTC)
replies: text: A, One of the reasons car windows are safer is the multiple layer nature of (windshields in the US, I don't know elsewhere) as the plastic internal layer hangs onto all (most, anyway) of the sharp dangerous pieces and keeps them from flying about cutting this and that important thing. You generally get a drooping layer of plastic with sharp bits stuck to it. Much safer, if not entirely safe, and a better deal all around. Better still, of course, is to stay out of accidents altogether. ww 16:17, 4 Aug 2004 (UTC)
thread_title: not too long, just add it

message: While you are correct that 'toughened glass' could be considered a misnomer (toughness has a specific meaning with regard to the strength of materials), tempering glass is not.  In fact there are two ways to temper glass to increase its strength: thermal and chemical.  Regarding thermal tempering, you are incorrect that the surface of a glass is in tension even at room temperature.  On initial cooling you are correct that the surface is in tension and the interior is in compression. However, below the glass transition temperature the stresses reverse and the surface is in compression and the interior is in tension increasing the strength of the glass.  Prince Rupert's drops are a laboratory curiousity demonstrating this phenomena.  If a drop of molten glass is cast into a container of water, it solidifies into a shape roughly resembling a tadpole.  You can bang on the big end with a hammer and the glass drop will not break.  However if you nip the tail, the drop disintegrates into dust usually with a pop.  Thermal tempering is usually applied to windshields.  Chemical tempering is usually accomplished by ion exchanging a smaller atom for a larger atom at the surface again putting the surface in compression. Although glazing and surface crystallization can also be used.  For example, soda-lime-silica glass can be placed into molten potassium nitrate and exchange potassium for sodium in the surface increasing the strength of the glass.  Thermal tempering can increase the strength of glass from 70 to 200 MPa while chemical tempering can increase it 500 to 700 MPa.  Chemical tempering is commonly used to increase the strength of beverage containers. --tod 05:59, 29 Jul 2004 (UTC)
replies: text: Tod, You know, I've played with that tadpole drop thing, and had completely forgotten it. I stand corrected, ouch. I was inverted. And Prince Rupert's drops are a great WP article. I encourage you to creat it if it doesn't yet exist. ww 16:17, 4 Aug 2004 (UTC)
thread_title: surface in compression in tempered glass, not interior

message: :Most ordinary glass is opaque to ultraviolet light with wavelengths shorter than about 380 nm, though special glasses are made which have less transparency toward the ultraviolet.
This sentence from the article seems to be self-contradictory or confusing. Someone other than me ought to fix it. --Yath 05:49, 26 Jul 2004 (UTC)
replies: text: I am really confused.  A simple experiment will show the reason why greenhouses are built of glass.  1)Put a sheet of ordinary window glass between your face and the sun; you will still feel the solar radiation. 2)Put the same sheet of glass between your face and a barbeque grill; you will be shielded from the heat.  Conclusion?  glass is relatively transparent to ultraviolet compared with infrared.  Will someone with more knowledge than I have please explain the discrepancy?  Too Old 17:04, 17 Sep 2004 (UTC)
replies: text:  Yes you can feel the solar radiation through glass.  But since most of the power is in the visible, that would be true independent of whether or not it passed any ultraviollet at all. The conclusion you have doesn't follow from the given experiment.  The correct conclusion for that experement (if the facts are as reported) is that glass is more transparent in the visible than in the infrared. Nahaj 01:52, 23 April 2006 (UTC)

text:  Heat is transmited by convection/conduction as well as from radiation. In your experiment, the glass sheet shields you from the *hot air* coming from the grill. This is not relevant in experiment 1, where air at both sides of the sheet is at the same temperature. -- T
===due to poor precision in terms used; too common in article===
This confusion probably arises from the undefined term 'ordinary glass.'  I suspect what was meant was the family of glasses based on the 1:1:6  soda-lime-silica composition (roughly 14 Na2O, 12 CaO, 75 SiO2 on a weight percent basis) that is nearly ubiquitous in the manufacture of clear container and window (plate) glass. The UV cutoff wavelength of glass is primarily composition dependent.  Pure silica (100% SiO2) glass can have a UV cutoff below 200 nm, while  glasses containing, for example, ceria (CeO2) or titania (TiO2), will shift the cutoff to wavelengths below 380.  If enough of these oxides are added the cutoff will shift to wavelength below 400 nm which will manifest itself as a coloration  of the glass as the blue end of the visible spectrum is absorbed along with the UV.
Which brings up my main criticism of the article.  There are many instances of vague or undefined terms such as 'common', 'pure', and 'ordinary' that can be confusing without context. --tod 05:59, 29 Jul 2004 (UTC)
thread_title:  Ultraviolet transparency confusion 

message: This confusion probably arises from the undefined term 'ordinary glass.'  I suspect what was meant was the family of glasses based on the 1:1:6  soda-lime-silica composition (roughly 14 Na2O, 12 CaO, 75 SiO2 on a weight percent basis) that is nearly ubiquitous in the manufacture of clear container and window (plate) glass. The UV cutoff wavelength of glass is primarily composition dependent.  Pure silica (100% SiO2) glass can have a UV cutoff below 200 nm, while  glasses containing, for example, ceria (CeO2) or titania (TiO2), will shift the cutoff to wavelengths below 380.  If enough of these oxides are added the cutoff will shift to wavelength below 400 nm which will manifest itself as a coloration  of the glass as the blue end of the visible spectrum is absorbed along with the UV.
Which brings up my main criticism of the article.  There are many instances of vague or undefined terms such as 'common', 'pure', and 'ordinary' that can be confusing without context. --tod 05:59, 29 Jul 2004 (UTC)
thread_title: due to poor precision in terms used; too common in article

message: The heading 'Arguments against glass flow' seems to imply that the question of glass flowing is contraversial.  If this is the case, the article should make that more clear IMHO and have a "for glass flowing section".  If this is not the case, the heading should reead "Evidence against glass flow", not "Arguments" Bletch 12:32, 17 Sep 2004 (UTC)
thread_title:  Is the flowing question contraversial? 

message: Okey, glass is not flowing.
But is it a liquid? I think that, but I am not sure. But it would be important to include that in the article (whether or not it is)
It _is_ a liquid if there is no first order phase transition between room temperature and high temperatures, and the decrementation of viscosity is continual.
So..?
It is my understanding that glass is indeed a liquid. Glass knives are frequently used to process samples for electron microscopy. Only freshly made knives are sharp enough due to the liquid nature of the glass.
:Try using fused quartz instead.  Flint glass undergoes some (highly localized) dissolution in water, because of minute fluctuations in sodium and calcium content: this is probably what causes your knives to dull.--Joel 00:36, 24 Apr 2005 (UTC)
replies: text: Not a physicist or chemist, but I've seen it said glass is "extremely low viscosity liquid". Comment?  Trekphiler 05:27, 9 December 2005 (UTC)
thread_title:  liquid? 

message: The article describes the ability of some glasses to block UV light, which is parenthetically described as "ionizing radiation."  It is my understanding that the term 'ionizing radiation' usually applies to high-energy particles resulting from radioactive decay, or electromagnetic radiation at frequencies higher than UV, such as x-rays or gamma rays. Although the article is correct in saying that UV may be biologically harmful, it may not be accurate to describe the UV blocked by glasses as 'ionizing radiation.'
:No, ionizing radiation is anything with enough energy to ionize an atom/molecule, i.e. to break a bond.  Look at Ultraviolet#Health effects for confirmation that UV does indeed have this property.  You're right, however, that most other forms of ionizing radiation are more energetic, and many can pass through glass quite easily, especially if there's no lead or uranium in the mix.--Joel 01:08, 24 Apr 2005 (UTC)
thread_title:  UV Radiation 

message: Hello.  As a casual reader, I find the following two statements a little confusing.  They do not seem to be consistant:
* From the 3rd paragraph in the introduction:  Pure silica has a melting point of about 2000 °C (3632 °F), so two other substances are always added to the sand in the glass-making process. One is soda (sodium carbonate Na2CO3), or potash, the equivalent potassium compound, which lowers the melting point to about 1000 °C. However, the soda makes the glass water-soluble, which is obviously unhelpful, so lime (calcium oxide, CaO) is the third component, added to restore insolubility.
* From the 3rd paragraph in the Overview:  Sodium is generally used to lower the otherwise impossibly high (when glass was first discovered) temperatures needed. Additional soda or potash is sometimes added to further lower the melting point.
I think this should be cleaned up.  I don't know anything about glass making, so I am not making this change.
--  JamesTeterenko 22:33, 17 Sep 2004 (UTC)
replies: text: I gave it a once over.  See what you think.--Joel 01:24, 24 Apr 2005 (UTC)
thread_title:  Melting point additives