chem term paper

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Lovely professionaluniversityTERM PAPER :- chemistry

TOPIC :- glass

10/13/2010

STUDENT NAME :- HARSH TYAGI

REG NO :- 11012423

TEACHER :- ms.SAJEELA AWASTHI

SECTION:- B5004


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Contents 1 Silica glasses

o 1.1 History

o 1.2 Silica

o 1.3 Glass ingredients

o 1.4 Contemporary glass production

o 1.5 Glassmaking in the laboratory

2 Other glasses

o 2.1 Network glasses

o 2.2 Amorphous metals

o 2.3 Electrolytes

o 2.4 Aqueous solutions

o 2.5 Molecular liquids

o 2.6 Polymers

o 2.7 Colloidal glasses

o 2.8 Glass-ceramics

3 Physics of glass

o 3.1 Glass versus a supercooled liquid

o 3.2 Behavior of antique glass

o 3.3 Physical properties

3.3.1 Optical properties

3.3.2 Color

3.3.3 Optical waveguides

4 Glass art

o 4.1 Museums
http://en.wikipedia.org/wiki/Glass#Silica_glasseshttp://en.wikipedia.org/wiki/Glass#Historyhttp://en.wikipedia.org/wiki/Glass#Silicahttp://en.wikipedia.org/wiki/Glass#Glass_ingredientshttp://en.wikipedia.org/wiki/Glass#Contemporary_glass_productionhttp://en.wikipedia.org/wiki/Glass#Glassmaking_in_the_laboratoryhttp://en.wikipedia.org/wiki/Glass#Other_glasseshttp://en.wikipedia.org/wiki/Glass#Network_glasseshttp://en.wikipedia.org/wiki/Glass#Amorphous_metalshttp://en.wikipedia.org/wiki/Glass#Electrolyteshttp://en.wikipedia.org/wiki/Glass#Aqueous_solutionshttp://en.wikipedia.org/wiki/Glass#Molecular_liquidshttp://en.wikipedia.org/wiki/Glass#Polymershttp://en.wikipedia.org/wiki/Glass#Colloidal_glasseshttp://en.wikipedia.org/wiki/Glass#Glass-ceramicshttp://en.wikipedia.org/wiki/Glass#Physics_of_glasshttp://en.wikipedia.org/wiki/Glass#Glass_versus_a_supercooled_liquidhttp://en.wikipedia.org/wiki/Glass#Behavior_of_antique_glasshttp://en.wikipedia.org/wiki/Glass#Physical_propertieshttp://en.wikipedia.org/wiki/Glass#Optical_propertieshttp://en.wikipedia.org/wiki/Glass#Colorhttp://en.wikipedia.org/wiki/Glass#Optical_waveguideshttp://en.wikipedia.org/wiki/Glass#Glass_arthttp://en.wikipedia.org/wiki/Glass#Museumshttp://en.wikipedia.org/wiki/Glass#Historyhttp://en.wikipedia.org/wiki/Glass#Silicahttp://en.wikipedia.org/wiki/Glass#Glass_ingredientshttp://en.wikipedia.org/wiki/Glass#Contemporary_glass_productionhttp://en.wikipedia.org/wiki/Glass#Glassmaking_in_the_laboratoryhttp://en.wikipedia.org/wiki/Glass#Other_glasseshttp://en.wikipedia.org/wiki/Glass#Network_glasseshttp://en.wikipedia.org/wiki/Glass#Amorphous_metalshttp://en.wikipedia.org/wiki/Glass#Electrolyteshttp://en.wikipedia.org/wiki/Glass#Aqueous_solutionshttp://en.wikipedia.org/wiki/Glass#Molecular_liquidshttp://en.wikipedia.org/wiki/Glass#Polymershttp://en.wikipedia.org/wiki/Glass#Colloidal_glasseshttp://en.wikipedia.org/wiki/Glass#Glass-ceramicshttp://en.wikipedia.org/wiki/Glass#Physics_of_glasshttp://en.wikipedia.org/wiki/Glass#Glass_versus_a_supercooled_liquidhttp://en.wikipedia.org/wiki/Glass#Behavior_of_antique_glasshttp://en.wikipedia.org/wiki/Glass#Physical_propertieshttp://en.wikipedia.org/wiki/Glass#Optical_propertieshttp://en.wikipedia.org/wiki/Glass#Colorhttp://en.wikipedia.org/wiki/Glass#Optical_waveguideshttp://en.wikipedia.org/wiki/Glass#Glass_arthttp://en.wikipedia.org/wiki/Glass#Museumshttp://en.wikipedia.org/wiki/Glass#Silica_glasses


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Glass is a non-crystallinesolidmaterial. Glasses are typicallybrittle, andoften opticallytransparent.The most prevalent type of glass, used for centuries inwindowsanddrinkingvessels, issoda-lime glass, made of about 75%silica(SiO2) plusNa2O, andseveral minor additives. Often, the termglassis used in a restricted sense torefer to this specific use.

In science, however, the termglassis usually defined in a much widersense, including every solid that possesses a non-crystalline (i.e.amorphous)structure and that exhibits aglass transitionwhen heated towards the liquidstate. In this wider sense, glasses can be made of quite different classes of

materials: metallic alloys, ionic melts, aqueous solutions, molecular liquids,

and polymers. Of these, polymer glasses (acrylic glass are the mostimportant; for many applications (bottles,eyewear) they are a lighteralternative to traditional silica glasses.

Glasses play an essential role in science and industry. Their chemical,

physical, and in particular optical properties make them suitable for

applications such asflat glass,containerglass,opticsandoptoelectronicsmaterial,laboratory equipment, thermalinsulator (glass wool), reinforcement materials (glass-reinforced

plastic,glass fiber reinforced concrete), andglass art(art glass,studioglass).
http://en.wikipedia.org/wiki/Crystalhttp://en.wikipedia.org/wiki/Solidhttp://en.wikipedia.org/wiki/Brittlehttp://en.wikipedia.org/wiki/Transparenthttp://en.wikipedia.org/wiki/Windowhttp://en.wikipedia.org/wiki/List_of_glasswarehttp://en.wikipedia.org/wiki/List_of_glasswarehttp://en.wikipedia.org/wiki/Soda-lime_glasshttp://en.wikipedia.org/wiki/Silicon_dioxidehttp://en.wikipedia.org/wiki/Sodium_oxidehttp://en.wikipedia.org/wiki/Sodium_oxidehttp://en.wikipedia.org/wiki/Sodium_oxidehttp://en.wikipedia.org/wiki/Amorphous_solidhttp://en.wikipedia.org/wiki/Glass_transitionhttp://en.wikipedia.org/wiki/Acrylic_glasshttp://en.wikipedia.org/wiki/Glass_Bottleshttp://en.wikipedia.org/wiki/Eyewear_(disambiguation)http://en.wikipedia.org/wiki/Flat_glasshttp://en.wikipedia.org/wiki/Container_glasshttp://en.wikipedia.org/wiki/Container_glasshttp://en.wikipedia.org/wiki/Opticshttp://en.wikipedia.org/wiki/Optoelectronicshttp://en.wikipedia.org/wiki/Laboratory_equipmenthttp://en.wikipedia.org/wiki/Glass_woolhttp://en.wikipedia.org/wiki/Glass-reinforced_plastichttp://en.wikipedia.org/wiki/Glass-reinforced_plastichttp://en.wikipedia.org/wiki/Glass_fiber_reinforced_concretehttp://en.wikipedia.org/wiki/Glass_arthttp://en.wikipedia.org/wiki/Art_glasshttp://en.wikipedia.org/wiki/Studio_glasshttp://en.wikipedia.org/wiki/Studio_glasshttp://en.wikipedia.org/wiki/File:Moldavite_Besednice.jpghttp://en.wikipedia.org/wiki/File:Moldavite_Besednice.jpghttp://en.wikipedia.org/wiki/Crystalhttp://en.wikipedia.org/wiki/Solidhttp://en.wikipedia.org/wiki/Brittlehttp://en.wikipedia.org/wiki/Transparenthttp://en.wikipedia.org/wiki/Windowhttp://en.wikipedia.org/wiki/List_of_glasswarehttp://en.wikipedia.org/wiki/List_of_glasswarehttp://en.wikipedia.org/wiki/Soda-lime_glasshttp://en.wikipedia.org/wiki/Silicon_dioxidehttp://en.wikipedia.org/wiki/Sodium_oxidehttp://en.wikipedia.org/wiki/Amorphous_solidhttp://en.wikipedia.org/wiki/Glass_transitionhttp://en.wikipedia.org/wiki/Acrylic_glasshttp://en.wikipedia.org/wiki/Glass_Bottleshttp://en.wikipedia.org/wiki/Eyewear_(disambiguation)http://en.wikipedia.org/wiki/Flat_glasshttp://en.wikipedia.org/wiki/Container_glasshttp://en.wikipedia.org/wiki/Container_glasshttp://en.wikipedia.org/wiki/Opticshttp://en.wikipedia.org/wiki/Optoelectronicshttp://en.wikipedia.org/wiki/Laboratory_equipmenthttp://en.wikipedia.org/wiki/Glass_woolhttp://en.wikipedia.org/wiki/Glass-reinforced_plastichttp://en.wikipedia.org/wiki/Glass-reinforced_plastichttp://en.wikipedia.org/wiki/Glass_fiber_reinforced_concretehttp://en.wikipedia.org/wiki/Glass_arthttp://en.wikipedia.org/wiki/Art_glasshttp://en.wikipedia.org/wiki/Studio_glasshttp://en.wikipedia.org/wiki/Studio_glass


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History

The history of creating glass can be traced back to 3500 BCE inMesopotamia.Thetermglassdeveloped in the lateRoman Empire. It was in theRomanglassmakingcenter atTrier, now in modern Germany, that the late-Latinterm glesum originated, probably from aGermanicword foratransparent,lustroussubstance.Silica

Tetrahedralstructural unit of silica (SiO2), the basic building block of common glasses.

The amorphous structure of glassy Silica (SiO2) in two dimensions. No long range order is present, however there is local

ordering with respect to thetetrahedralarrangement of Oxygen (O) atoms around the Silicon (Si) atoms.
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Silica(the chemical compound SiO2) has a number of distinctcrystallineforms: quartz, tridymite,

cistobalite, and others (including the high pressurepolymorphsStishoviteandCoesite). Nearly all of them

involvetetrahedralSiO4units linked together byshared verticesin different arrangements. Si-O bond

lengths vary between the different crystal forms. For example, in -quartz the bond length is 161 pm,

whereas in -tridymite it ranges from 154171 pm. The Si-O-Si bond angle also varies from 140 in -

tridymite to 144 in -quartz to 180 in -tridymite.

In amorphous silica (fused quartz), the tetrahedra form a network that does not exhibit any long-range

order. However, the tetrahedra themselves represent a high degree of local ordering, i.e. every silicon

atom is coordinated by 4 oxygen atoms and the nearest neighbour Si-O bond length exhbits only a

narrow distribution throughout the structure. The tetrahedra also form a network of ring-like structures

which lead to ordering on intermediate length scales (up to approximately 10 Angstroms or so). Under the

application of high pressure (approximately 40 GPa) silica glass undergoes a

continuouspolyamorphicphase transition into an octahedral form, i.e. the Si atoms are surrounded by 6oxygen atoms instead of four in the ambient pressure tetrahedral glass.[3]

In nature, vitrification of quartz occurs whenlightningstrikessand, forming hollow, branching rootlike

structures calledfulgurite.
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Glass ingredients

Quartz sand(silica) is the main raw material in commercial glass production

While fused quartz is used for some special applications, it is not very common due to its elevated glass

transition temperature of over 2300C. Normally, other substances are added to simplify processing. One

issodium carbonate(Na2CO3), which lowers the glass transition to about 1500 C. However, the soda

makes the glasswater soluble, which is usually undesirable, solime(calcium oxide(CaO), generally

obtained fromlimestone), somemagnesium oxide(MgO) andaluminium oxide(Al2O3) are added to

provide for a better chemical durability. The resulting glass contains about 70 to 74% silica by weight and

is called asoda-lime glass.[4]Soda-lime glasses account for about 90% of manufactured glass.

Most common glass has other ingredients added to change its properties.Lead glassorflint glassis more

'brilliant' because the increasedrefractive indexcauses noticeably more "sparkles". Addingbariumalso

increases the refractive index.Thorium oxidegives glass a high refractive index and low dispersion and

was formerly used in producing high-quality lenses, but due to itsradioactivityhas been replaced

bylanthanum oxidein modern eye glasses. Large amounts ofironare used in glass that

absorbsinfraredenergy, such as heat absorbing filters for movie projectors, whilecerium(IV) oxidecan

be used for glass that absorbsUVwavelengths.

Borosilicate glasses(e.g.Pyrex) have the main constituents silica and boron oxide. They have very low

coefficients of thermal expansion (~5 106 /C at 20C), making them resistant to thermal shock and

therefore less subject to thermal stress. They are commonly used for reagent bottles.

Another common glass ingredient is "cullet" (recycled glass). The recycled glass saves on raw materials

and energy. However, impurities in the cullet can lead to product and equipment failure.
http://en.wikipedia.org/wiki/Sandhttp://en.wikipedia.org/wiki/Sandhttp://en.wikipedia.org/wiki/Celsiushttp://en.wikipedia.org/wiki/Celsiushttp://en.wikipedia.org/wiki/Sodium_carbonatehttp://en.wikipedia.org/wiki/Sodium_carbonatehttp://en.wikipedia.org/wiki/Sodium_silicatehttp://en.wikipedia.org/wiki/Lime_(mineral)http://en.wikipedia.org/wiki/Calcium_oxidehttp://en.wikipedia.org/wiki/Limestonehttp://en.wikipedia.org/wiki/Magnesium_oxidehttp://en.wikipedia.org/wiki/Magnesium_oxidehttp://en.wikipedia.org/wiki/Aluminium_oxidehttp://en.wikipedia.org/wiki/Soda-lime_glasshttp://en.wikipedia.org/wiki/Glass#cite_note-ullmann-3http://en.wikipedia.org/wiki/Glass#cite_note-ullmann-3http://en.wikipedia.org/wiki/Lead_glasshttp://en.wikipedia.org/wiki/Lead_glasshttp://en.wikipedia.org/wiki/Flint_glasshttp://en.wikipedia.org/wiki/Flint_glasshttp://en.wikipedia.org/wiki/Refractive_indexhttp://en.wikipedia.org/wiki/Bariumhttp://en.wikipedia.org/wiki/Thorium_oxidehttp://en.wikipedia.org/wiki/Thorium_oxidehttp://en.wikipedia.org/wiki/Radioactivityhttp://en.wikipedia.org/wiki/Radioactivityhttp://en.wikipedia.org/wiki/Radioactivityhttp://en.wikipedia.org/wiki/Lanthanum_oxidehttp://en.wikipedia.org/wiki/Lanthanum_oxidehttp://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/wiki/Infraredhttp://en.wikipedia.org/wiki/Infraredhttp://en.wikipedia.org/wiki/Infraredhttp://en.wikipedia.org/wiki/Cerium(IV)_oxidehttp://en.wikipedia.org/wiki/UVhttp://en.wikipedia.org/wiki/Borosilicate_glasshttp://en.wikipedia.org/wiki/Borosilicate_glasshttp://en.wikipedia.org/wiki/Pyrexhttp://en.wikipedia.org/wiki/Glass_recyclinghttp://en.wikipedia.org/wiki/File:Piasek_kwarcowy.jpghttp://en.wikipedia.org/wiki/File:Piasek_kwarcowy.jpghttp://en.wikipedia.org/wiki/Sandhttp://en.wikipedia.org/wiki/Celsiushttp://en.wikipedia.org/wiki/Sodium_carbonatehttp://en.wikipedia.org/wiki/Sodium_silicatehttp://en.wikipedia.org/wiki/Lime_(mineral)http://en.wikipedia.org/wiki/Calcium_oxidehttp://en.wikipedia.org/wiki/Limestonehttp://en.wikipedia.org/wiki/Magnesium_oxidehttp://en.wikipedia.org/wiki/Aluminium_oxidehttp://en.wikipedia.org/wiki/Soda-lime_glasshttp://en.wikipedia.org/wiki/Glass#cite_note-ullmann-3http://en.wikipedia.org/wiki/Lead_glasshttp://en.wikipedia.org/wiki/Flint_glasshttp://en.wikipedia.org/wiki/Refractive_indexhttp://en.wikipedia.org/wiki/Bariumhttp://en.wikipedia.org/wiki/Thorium_oxidehttp://en.wikipedia.org/wiki/Radioactivityhttp://en.wikipedia.org/wiki/Lanthanum_oxidehttp://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/wiki/Infraredhttp://en.wikipedia.org/wiki/Cerium(IV)_oxidehttp://en.wikipedia.org/wiki/UVhttp://en.wikipedia.org/wiki/Borosilicate_glasshttp://en.wikipedia.org/wiki/Pyrexhttp://en.wikipedia.org/wiki/Glass_recycling


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Finally, fining agents such assodium sulfate,sodium chloride, orantimony oxideare added to reduce the

bubble content in the glass.[4]Glass batch calculationis the method by which the correct raw material

mixture is determined to achieve the desired glass composition.

[edit]Contemporary glass production

A moderngreenhouseinWisley Garden, England, made fromfloat glass

Main articles:Glass production,Float glass, andGlazierFollowing theglass batchpreparation and mixing, the raw materials are transported to the furnace.Soda-

lime glassformass productionis melted ingas fired units. Smaller scale furnaces for specialty glasses

include electric melters, pot furnaces, and day tanks.[4]

After melting, homogenization and refining (removal of bubbles), the glass isformed. Flat glass for

windows and similar applications is formed by thefloat glassprocess, developed between 1953 and 1957

by SirAlastair Pilkingtonand Kenneth Bickerstaff of the UK's Pilkington Brothers, who created a

continuous ribbon of glass using a molten tin bath on which the molten glass flows unhindered under the

influence of gravity. The top surface of the glass is subjected to nitrogen under pressure to obtain a

polished finish.[5]Container glass for common bottles and jars is formed byblowing and

pressingmethods. Further glass forming techniques are summarized in the tableGlass forming

techniques.

Once the desired form is obtained, glass is usuallyannealedfor the removal of stresses. Surface

treatments, coatings orlaminationmay follow to improve the chemical durability (glass container

coatings,glass container internal treatment), strength (toughened glass,bulletproof glass,windshields),

or optical properties (insulated glazing,anti-reflective coating).
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[edit]Glassmaking in the laboratory

Avitrificationexperiment for the study ofnuclear wastedisposal atPacific Northwest National Laboratory.

New chemical glass compositions or new treatment techniques can be initially investigated in small-

scalelaboratoryexperiments. The raw materials for laboratory-scale glass melts are often different from

those used in mass production because the cost factor has a low priority. In the laboratory mostly

purechemicalsare used. Care must be taken that the raw materials have not reacted with moisture or

other chemicals in the environment (such asalkalioxides and hydroxides,alkaline earthoxides and

hydroxides, orboron oxide), or that the impurities are quantified (loss on ignition).[6]Evaporation losses

during glass melting should be considered during the selection of the raw materials, e.g.,sodium

selenitemay be preferred over easily evaporatingSeO2. Also, more readily reacting raw materials may be

preferred over relativelyinertones, such asAl(OH)3overAl2O3. Usually, the melts are carried out in

platinum crucibles to reduce contamination from the crucible material. Glasshomogeneityis achieved by

homogenizing the raw materials mixture (glass batch), by stirring the melt, and by crushing and re-melting

the first melt. The obtained glass is usuallyannealedto prevent breakage during processing.[6][7]

In order to make glass from materials with poor glass forming tendencies, novel techniques are used to

increase cooling rate, or reduce crystal nucleation triggers. Examples of these techniques

includeaerodynamic levitation(cooling the melt whilst it floats on a gas stream), splat quenching

(pressing the melt between two metal anvils) and roller quenching (pouring the melt through rollers).

See also:Optical lens design,Fabrication and testing of optical components

[edit]Other glasses
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[edit]Network glasses

Acompact disc(CD) utilizingchalcogenide glassesfor solid-state memory technology.

Some glasses that do not include silica as a major constituent may have physico-chemical properties

useful for their application infibre opticsand other specialized technical applications. These

includefluoride glasses,aluminosilicates,phosphate glasses,borate glasses, andchalcogenide glasses.

There are three classes of components for oxide glasses: network formers, intermediates, and modifiers.

The network formers (silicon, boron, germanium) form a highly cross-linked network of chemical bonds.

The intermediates (titanium, aluminium, zirconium, beryllium, magnesium, zinc) can act as both network

formers and modifiers, according to the glass composition. The modifiers (calcium, lead, lithium, sodium,

potassium) alter the network structure; they are usually present as ions, compensated by nearby non-

bridging oxygen atoms, bound by one covalent bond to the glass network and holding one negative

charge to compensate for the positive ion nearby. Some elements can play multiple roles; e.g. lead can

act both as a network former (Pb4+replacing Si4+), or as a modifier.

The presence of non-bridging oxygens lowers the relative number of strong bonds in the material and

disrupts the network, decreasing theviscosityof the melt and lowering the melting temperature.

The alkaline metal ions are small and mobile; their presence in glass allows a degree ofelectrical

conductivity, especially in molten state or at high temperature. Their mobility however decreases the

chemical resistance of the glass, allowing leaching by water and facilitating corrosion. Alkaline earth ions,

with their two positive charges and requirement for two non-bridging oxygen ions to compensate for their

charge, are much less mobile themselves and also hinder diffusion of other ions, especially the alkalis.

The most common commercial glasses contain both alkali and alkaline earth ions (usually sodium and

calcium), for easier processing and satisfying corrosion resistance.[8]Corrosion resistance of glass can be

achieved bydealkalization, removal of the alkali ions from the glass surface by reaction with e.g. sulfur or
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fluorine compounds. Presence of alkaline metal ions has also detrimental effect to theloss tangentof the

glass, and to itselectrical resistance; glasses for electronics (sealing, vacuum tubes, lamps...) have to

take this in account.

Addition oflead(II) oxidelowers melting point, lowersviscosityof the melt, and increasesrefractive index.

Lead oxide also facilitates solubility of other metal oxides and therefore is used in colored glasses. The

viscosity decrease of lead glass melt is very significant (roughly 100 times in comparison with soda

glasses); this allows easier removal of bubbles and working at lower temperatures, hence its frequent use

as an additive invitreous enamelsandglass solders. The highionic radiusof the Pb2+ion renders it

highly immobile in the matrix and hinders the movement of other ions; lead glasses therefore have high

electrical resistance, about two orders of magnitude higher than soda-lime glass (108.5vs

106.5Ohmcm,DCat 250 C). For more details, seelead glass.[9]

Addition offluorinelowers thedielectric constantof glass. Fluorine is highlyelectronegativeand attracts

the electrons in the lattice, lowering the polarizability of the material. Such silicon dioxide-fluoride is used

in manufacture ofintegrated circuitsas an insulator. High levels of fluorine doping lead to formation of

volatile SiF2O and such glass is then thermally unstable. Stable layers were achieved with dielectric

constant down to about 3.53.7.[10]

[edit]Amorphous metals

Samples of amorphous metal

In the past, small batches ofamorphous metalswith high surface area configurations (ribbons, wires,

films, etc.) have been produced through the implementation of extremely rapid rates of cooling. This was

initially termed "splat cooling" by doctoral student W. Klement at Caltech, who showed that cooling rates

on the order of millions of degrees per second is sufficient to impede the formation of crystals, and the

metallic atoms becomes "locked into" a glassy state. Amorphous metal wires have been produced by

sputtering molten metal onto a spinning metal disk. More recently a number of alloys have been produced

in layers with thickness exceeding 1 millimeter. These are known as bulk metallic glasses
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(BMG).Liquidmetal Technologiessell a number of titanium-based BMGs. Batches of amorphous steel

have also been produced that demonstrate mechanical properties far exceeding those found in

conventional steel alloys.[11][12][13]

In 2004,NISTresearchers presented evidence that anisotropicnon-crystalline metallic phase (dubbed

"q-glass") could be grown from the melt. This phase is the first phase, or "primary phase," to form in the

Al-Fe-Si system during rapid cooling. Interestingly, experimental evidence indicates that this phase forms

by afirst-order transition.Transmission electron microscopy(TEM) images show that the q-glass

nucleates from the melt as discrete particles, which grow spherically with a uniform growth rate in all

directions. The diffraction pattern shows it to be an isotropic glassy phase. Yet there is

anucleationbarrier, which implies an interfacial discontinuity (or internal surface) between the glass and

the melt.[14]

[edit]Electrolytes

Electrolytesor moltensaltsare mixtures of differentions. In a mixture of three or more ionic species of

dissimilar size and shape, crystallization can be so difficult that the liquid can easily be supercooled into a

glass. The best studied example is Ca0.4K0.6(NO3)1.4.

[edit]Aqueous solutions

Some aqueous solutions can be supercooled into a glassy state, for instance LiCl:RH2O in the

composition range 4


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[edit]Glass-ceramics

A high strength glass-ceramic cooktop with negligiblethermal expansion.

Glass-ceramicmaterials share many properties with both non-crystalline glass andcrystallineceramics.

They are formed as a glass, and then partially crystallized by heat treatment. For example, the

microstructure of whiteware ceramics frequently contains bothamorphousandcrystallinephases.

Crystalline grains are often embedded within a non-crystalline intergranular phase ofgrain boundaries.

When applied to whiteware ceramics,vitreousmeans the material has an extremely lowpermeabilityto

liquids, often but not always water, when determined by a specified test regime.[18][19]

The term mainly refers to a mix of lithium andaluminosilicateswhich yields an array of materials with

interesting thermomechanical properties. The most commercially important of these have the distinction

of being impervious to thermal shock. Thus, glass-ceramics have become extremely useful for countertop

cooking. The negativethermal expansioncoefficient (TEC) of the crystalline ceramic phase can be

balanced with the positive TEC of the glassy phase. At a certain point (~70% crystalline) the glass-

ceramic has a net TEC near zero. This type ofglass-ceramicexhibits excellent mechanical properties and

can sustain repeated and quick temperature changes up to 1000 C.[18][19]

[edit]Physics of glass

See alsoPhysics of glassUnsolved problems in physics

What is the nature of

thetransitionbetween a fluid orregularsolidand a glassyphase?"The deepest and most interesting

unsolved problem in solid state theory is

probably the theory of the nature of glass

and the glass transition."P.W. Anderson[20]
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In physics, the standard definition of a glass (or vitreous solid) is a solid formed by rapid melt

quenching.[21][22][23][24][25]However, the term glass is often used to describe anyamorphous solidthat

exhibits a glass transition temperature Tg. If the cooling is sufficiently rapid (relative to the

characteristiccrystallizationtime) then crystallization is prevented and instead the disordered atomic

configuration of thesupercooledliquid is frozen into the solid state at Tg. Generally, the structure of

a glass exists in ametastablestate with respect to itscrystallineform, although in certain

circumstances, for example inatacticpolymers, there is no crystalline analogue of the amorphous

phase.[26]As in otheramorphous solids, the atomic structure of a glass lacks any long

rangetranslational periodicity. However, due tochemical bondingcharacteristics glasses do

possess a high degree of short-range order with respect to local atomicpolyhedra.[27]It is deemed

that the bonding structure of glasses, although disordered, has the same symmetry signature

(Hausdorff-Besicovitch dimensionality) as for crystalline materials.[28]

[edit]Glass versus a supercooled liquidGlass is generally classed as an amorphous solid rather than a liquid.[29]Glass displays all the

mechanical properties of a solid. The notion that glass flows to an appreciable extent over extended

periods of time is not supported by empirical research or theoretical analysis (seeviscosity of

amorphous materials). From a more commonsense point of view, glass should be considered a solid

since it is rigid according to everyday experience.[30]

Some people consider glass to be a liquid due to its lack of a first-orderphase transition[29] [31] where

certainthermodynamicvariablessuch asvolume,entropyandenthalpyare discontinuous through

the glass transition range. However, theglass transitionmay be described as analogous to asecond-order phase transition where the intensive thermodynamic variables such as thethermal

expansivityandheat capacityare continuous.[28]Despite this, the equilibrium theory ofphase

transformations in solidsdoes not entirely hold for glass, and hence the glass transition cannot be

classed as one of the classical equilibriumphase transformations in solids.[24][32]

Although theatomicstructure of glass shares characteristics of the structure in asupercooled liquid,

glass tends to behave as a solid below its glass transition temperature.[33]A supercooled liquid

behaves as a liquid, but it is below thefreezing pointof the material, and in some cases will

crystallize almost instantly if a crystal is added as acore. The change in heat capacity at a glasstransition and amelting transitionof comparable materials are typically of the same order of

magnitude, indicating that the change in activedegrees of freedomis comparable as well. Both in a

glass and in a crystal it is mostly only thevibrationaldegrees of freedom that remain active,

whereasrotationalandtranslationalmotion is arrested. This helps to explain why both crystalline

and non-crystalline solids exhibit rigidity on most experimental time scales.
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ipedia.org/wiki/Thermodynamic_variablehttp://en.wikipedia.org/wiki/Volumehttp://en.wikipedia.org/wiki/Entropyhttp://en.wikipedia.org/wiki/Enthalpyhttp://en.wikipedia.org/wiki/Glass_transitionhttp://en.wikipedia.org/wiki/Thermal_expansionhttp://en.wikipedia.org/wiki/Thermal_expansionhttp://en.wikipedia.org/wiki/Heat_capacityhttp://en.wikipedia.org/wiki/Glass#cite_note-autogenerated11507-27http://en.wikipedia.org/wiki/Phase_transformations_in_solidshttp://en.wikipedia.org/wiki/Phase_transformations_in_solidshttp://en.wikipedia.org/wiki/Phase_transformations_in_solidshttp://en.wikipedia.org/wiki/Glass#cite_note-Elliot84-23http://en.wikipedia.org/wiki/Glass#cite_note-31http://en.wikipedia.org/wiki/Atomhttp://en.wikipedia.org/wiki/Supercooled_liquidhttp://en.wikipedia.org/wiki/Glass#cite_note-32http://en.wikipedia.org/wiki/Freezing_pointhttp://en.wikipedia.org/wiki/Corehttp://en.wikipedia.org/wiki/Melting_pointhttp://en.wikipedia.org/wiki/Degrees_of_freedom_(physics_and_chemistry)http://en.wikipedia.org/wiki/Vibrationhttp://en.wikipedia.org/wiki/Rotationalhttp://en.wikipedia.org/wiki/Translation_(physics)


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[edit]Behavior of antique glass

The observation that old windows are often thicker at the bottom than at the top is often offered as

supporting evidence for the view that glass flows over a matter of centuries. It is then assumed that

the glass was once uniform, but has flowed to its new shape, which is a property of liquid.[34]In

actuality, the reason for this is that when panes of glass were commonly made byglassblowers, the

technique used was to spin molten glass so as to create a round, mostly flat and even plate

(thecrown glassprocess, described above). This plate was then cut to fit a window. The pieces

were not, however, absolutely flat; the edges of the disk became thicker as the glass spun. When

actually installed in a window frame, the glass would be placed thicker side down both for the sake

of stability and to prevent water accumulating in the leadcamesat the bottom of the window.

[35]Occasionally such glass has been found thinner side down or thicker on either side of the

window's edge, as would be caused by carelessness at the time of installation.[36]

Mass production of glass window panes in the early twentieth century caused a similar effect. In

glass factories, molten glass was poured onto a large cooling table and allowed to spread. The

resulting glass is thicker at the location of the pour, located at the center of the large sheet. These

sheets were cut into smaller window panes with nonuniform thickness, typically with the location of

the pour centred in one of the panes (known as "bull's-eyes") for decorative effect. Modern glass

intended for windows is produced asfloat glassand is very uniform in thickness.

Several other points exemplify the misconception of the "cathedral glass" theory:

Writing in theAmerican Journal of Physics, physicistEdgar D. Zanottostates "...thepredictedrelaxation timefor GeO2atroom temperatureis1032 years. Hence, the relaxation

period (characteristic flow time) of cathedral glasses would be even longer."[37](1032years is

many times longer than the estimatedage of the Universe.)

If medieval glass has flowed perceptibly, then ancient Roman and Egyptian objects

should have flowed proportionately more but this is not observed. Similarly,

prehistoricobsidianblades should have lost their edge; this is not observed either (although

obsidian may have a different viscosity from window glass).[29]

If glass flows at a rate that allows changes to be seen with the naked eye after centuries,

then the effect should be noticeable in antique telescopes. Any slight deformation in the antique

telescopic lenses would lead to a dramatic decrease in optical performance, a phenomenon that

is not observed.[29]

There are many examples of centuries-old glass shelving which has not bent, even

though it is under much higher stress from gravitational loads than vertical window glass.
http://en.wikipedia.org/w/index.php?title=Glass&action=edit&section=18http://en.wikipedia.org/w/index.php?title=Glass&action=edit&section=18http://en.wikipedia.org/wiki/Glass#cite_note-33http://en.wikipedia.org/wiki/Glassblowinghttp://en.wikipedia.org/wiki/Crown_glass_(window)http://en.wikipedia.org/wiki/Camehttp://en.wikipedia.org/wiki/Camehttp://en.wikipedia.org/wiki/Glass#cite_note-34http://en.wikipedia.org/wiki/Glass#cite_note-35http://en.wikipedia.org/wiki/Float_glasshttp://en.wikipedia.org/wiki/Float_glasshttp://en.wikipedia.org/wiki/Float_glasshttp://en.wikipedia.org/wiki/American_Journal_of_Physicshttp://en.wikipedia.org/wiki/American_Journal_of_Physicshttp://en.wikipedia.org/wiki/Edgar_D._Zanottohttp://en.wikipedia.org/wiki/Relaxation_timehttp://en.wikipedia.org/wiki/Room_temperaturehttp://en.wikipedia.org/wiki/Room_temperaturehttp://en.wikipedia.org/wiki/1_E19_s_and_morehttp://en.wikipedia.org/wiki/1_E19_s_and_morehttp://en.wikipedia.org/wiki/1_E19_s_and_morehttp://en.wikipedia.org/wiki/Glass#cite_note-36http://en.wikipedia.org/wiki/Age_of_the_universehttp://en.wikipedia.org/wiki/Age_of_the_universehttp://en.wikipedia.org/wiki/Age_of_the_universehttp://en.wikipedia.org/wiki/Obsidianhttp://en.wikipedia.org/wiki/Obsidianhttp://en.wikipedia.org/wiki/Glass#cite_note-Gibbs-28http://en.wikipedia.org/wiki/Glass#cite_note-Gibbs-28http://en.wikipedia.org/wiki/Glass#cite_note-Gibbs-28http://en.wikipedia.org/w/index.php?title=Glass&action=edit&section=18http://en.wikipedia.org/wiki/Glass#cite_note-33http://en.wikipedia.org/wiki/Glassblowinghttp://en.wikipedia.org/wiki/Crown_glass_(window)http://en.wikipedia.org/wiki/Camehttp://en.wikipedia.org/wiki/Glass#cite_note-34http://en.wikipedia.org/wiki/Glass#cite_note-35http://en.wikipedia.org/wiki/Float_glasshttp://en.wikipedia.org/wiki/American_Journal_of_Physicshttp://en.wikipedia.org/wiki/Edgar_D._Zanottohttp://en.wikipedia.org/wiki/Relaxation_timehttp://en.wikipedia.org/wiki/Room_temperaturehttp://en.wikipedia.org/wiki/1_E19_s_and_morehttp://en.wikipedia.org/wiki/Glass#cite_note-36http://en.wikipedia.org/wiki/Age_of_the_universehttp://en.wikipedia.org/wiki/Obsidianhttp://en.wikipedia.org/wiki/Glass#cite_note-Gibbs-28http://en.wikipedia.org/wiki/Glass#cite_note-Gibbs-28


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Some glasses have a glass transition temperature close to or below room temperature. The

behavior of a material that has a glass transition close to room temperature depends upon the

timescale during which the material is manipulated. If the material is hit it may break like a solid

glass, but if the material is left on a table for a week it may flow like a liquid. This simply means that

for the fast timescale its transition temperature is above room temperature, but for the slow one it is

below. The shift in temperature with timescale is not very large however, as indicated by the

transition ofpolypropylene glycolof 72 C and 71 C over different timescales.[26]To observe

window glass flowing as liquid at room temperature we would have to wait a much longer time than

any human can exist. Therefore it is safe to consider a glass a solid far enough below its transition

temperature:Cathedral glassdoes not flow because its glass transition temperature is many

hundreds of degrees above room temperature. Close to this temperature there are interesting time-

dependent properties. One of these is known asaging. Many polymers that we use in daily life such

aspolystyreneandpolypropyleneare in a glassy state but they are not too far below their glasstransition temperature as opposed torubberwhich is used above its glass transition temperature.

Their mechanical properties may well change over time and this is serious concern when applying

these materials in construction. In general for polymers there is a relation between the glass

transition temperature and the speed of the deformation.

[edit]Physical properties

See also:List of physical properties of glass[edit]Optical properties

Glass is in widespread use largely due to the production of glass compositions that are transparentto visible wavelengths of light. In contrast,polycrystallinematerials in general do not transmit visible

light.[38]The individual crystallites may be transparent, but their facets (grain boundaries) reflect or

scatter light. Light entering a polycrystal is repeatedly scattered until it re-emerges from the surface

in random directions. Thissubsurface scatteringmechanism,[39][40]together with scattering by surface

irregularities, gives rise todiffuse reflectionand hence, although it does not absorb light, the

polycrystal is not transparent. This mechanism, which causes objects to be opaque, is a crucial

mechanism for vision, because most objects are seen by our eyes through their diffuse reflection.[41]

Glass does not contain the internal subdivisions associated with grain boundaries in polycrystalsand hence does not scatter light in the same manner as a polycrystalline material. The surface of a

glass is often smooth since during glass formation the molecules of the supercooled liquid are not

forced to dispose in rigid crystal geometries and can followsurface tension, which imposes a

microscopically smooth surface. These properties, which give glass its clearness, can be retained

even if glass is partially light-absorbing (colored, see below).[42]
http://en.wikipedia.org/wiki/Polypropylene_glycolhttp://en.wikipedia.org/wiki/Polypropylene_glycolhttp://en.wikipedia.org/wiki/Glass#cite_note-Folmer-25http://en.wikipedia.org/wiki/Cathedral_glasshttp://en.wikipedia.org/wiki/Cathedral_glasshttp://en.wikipedia.org/wiki/Precipitation_hardeninghttp://en.wikipedia.org/wiki/Precipitation_hardeninghttp://en.wikipedia.org/wiki/Polystyrenehttp://en.wikipedia.org/wiki/Polystyrenehttp://en.wikipedia.org/wiki/Polystyrenehttp://en.wikipedia.org/wiki/Polypropylenehttp://en.wikipedia.org/wiki/Polypropylenehttp://en.wikipedia.org/wiki/Rubberhttp://en.wikipedia.org/wiki/Rubberhttp://en.wikipedia.org/wiki/Rubberhttp://en.wikipedia.org/w/index.php?title=Glass&action=edit&section=19http://en.wikipedia.org/w/index.php?title=Glass&action=edit&section=19http://en.wikipedia.org/wiki/List_of_physical_properties_of_glasshttp://en.wikipedia.org/wiki/List_of_physical_properties_of_glasshttp://en.wikipedia.org/w/index.php?title=Glass&action=edit&section=20http://en.wikipedia.org/w/index.php?title=Glass&action=edit&section=20http://en.wikipedia.org/wiki/Polycrystalhttp://en.wikipedia.org/wiki/Glass#cite_note-37http://en.wikipedia.org/wiki/Grain_boundarieshttp://en.wikipedia.org/wiki/Grain_boundarieshttp://en.wikipedia.org/wiki/Subsurface_scatteringhttp://en.wikipedia.org/wiki/Subsurface_scatteringhttp://en.wikipedia.org/wiki/Glass#cite_note-38http://en.wikipedia.org/wiki/Glass#cite_note-39http://en.wikipedia.org/wiki/Glass#cite_note-39http://en.wikipedia.org/wiki/Diffuse_reflectionhttp://en.wikipedia.org/wiki/Glass#cite_note-Kerker1909-40http://en.wikipedia.org/wiki/Glass#cite_note-Kerker1909-40http://en.wikipedia.org/wiki/Surface_tensionhttp://en.wikipedia.org/wiki/Glass#cite_note-O-41http://en.wikipedia.org/wiki/Glass#cite_note-O-41http://en.wikipedia.org/wiki/Polypropylene_glycolhttp://en.wikipedia.org/wiki/Glass#cite_note-Folmer-25http://en.wikipedia.org/wiki/Cathedral_glasshttp://en.wikipedia.org/wiki/Precipitation_hardeninghttp://en.wikipedia.org/wiki/Polystyrenehttp://en.wikipedia.org/wiki/Polypropylenehttp://en.wikipedia.org/wiki/Rubberhttp://en.wikipedia.org/w/index.php?title=Glass&action=edit&section=19http://en.wikipedia.org/wiki/List_of_physical_properties_of_glasshttp://en.wikipedia.org/w/index.php?title=Glass&action=edit&section=20http://en.wikipedia.org/wiki/Polycrystalhttp://en.wikipedia.org/wiki/Glass#cite_note-37http://en.wikipedia.org/wiki/Grain_boundarieshttp://en.wikipedia.org/wiki/Subsurface_scatteringhttp://en.wikipedia.org/wiki/Glass#cite_note-38http://en.wikipedia.org/wiki/Glass#cite_note-39http://en.wikipedia.org/wiki/Diffuse_reflectionhttp://en.wikipedia.org/wiki/Glass#cite_note-Kerker1909-40http://en.wikipedia.org/wiki/Surface_tensionhttp://en.wikipedia.org/wiki/Glass#cite_note-O-41


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Glass has the ability torefract, reflect and transmit light followinggeometrical optics, without

scattering it, and it is used in the manufacture oflensesand windows. Common glass has

arefraction indexaround 1.5. According toFresnel equations, thereflectivityof a sheet of glass is

about 4% per surface (at normal incidence), and itstransmissivityabout 92%.

[edit]Color

Main article:Glass coloring and color markingSee also:Pigment#Pigments_by_chemical_compositionSee also:Transparent_materials#Absorption of light in solids

Common soda-lime float glass appears green in thick sections because of Fe2+impurities.

Many glasses have a chemical composition which includes what are referred to asabsorption

centers. This may cause them to be selective in their absorption ofvisible lightwaves(or white light

frequencies). They absorb certain portions of thevisible spectrum, while reflecting others. The

frequencies of the spectrum which are not absorbed are either reflected back or transmitted for our

physical observation. This is what gives rise tocolor.

Thus,colorin glass may be obtained by addition of electrically charged ions (orcolor centers) that

are homogeneously distributed, and by precipitation of finely dispersed particles (such as

inphotochromic glasses).[43]Ordinarysoda-lime glassappears colorless to the naked eye when it is

thin, althoughiron(II) oxide(FeO) impurities of up to 0.1 wt%[44]produce agreentint which can be

viewed in thick pieces or with the aid of scientific instruments. Further FeO andCr2O3additions may

be used for the production of green bottles.Sulfur, together withcarbonand iron salts, is used to

form iron polysulfides and produce amber glass ranging from yellowish to almost black.

[45]Manganese dioxidecan be added in small amounts to remove the green tint given by iron(II)

oxide.

[edit]Optical waveguides

Main article:Waveguide (optics)
http://en.wikipedia.org/wiki/Refractionhttp://en.wikipedia.org/wiki/Refractionhttp://en.wikipedia.org/wiki/Geometrical_opticshttp://en.wikipedia.org/wiki/Geometrical_opticshttp://en.wikipedia.org/wiki/Lens_(optics)http://en.wikipedia.org/wiki/Refraction_indexhttp://en.wikipedia.org/wiki/Refraction_indexhttp://en.wikipedia.org/wiki/Fresnel_equationshttp://en.wikipedia.org/wiki/Reflectivityhttp://en.wikipedia.org/wiki/Reflectivityhttp://en.wikipedia.org/wiki/Transmissivityhttp://en.wikipedia.org/w/index.php?title=Glass&action=edit&section=21http://en.wikipedia.org/w/index.php?title=Glass&action=edit&section=21http://en.wikipedia.org/wiki/Glass_coloring_and_color_markinghttp://en.wikipedia.org/wiki/Pigment#Pigments_by_chemical_compositionhttp://en.wikipedia.org/wiki/Pigment#Pigments_by_chemical_compositionhttp://en.wikipedia.org/wiki/Transparent_materials#Absorption_of_light_in_solidshttp://en.wikipedia.org/wiki/Transparent_materials#Absorption_of_light_in_solidshttp://en.wikipedia.org/w/index.php?title=Absorption_centers&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Absorption_centers&action=edit&redlink=1http://en.wikipedia.org/wiki/Visible_lighthttp://en.wikipedia.org/wiki/Visible_lighthttp://en.wikipedia.org/wiki/Visible_spectrumhttp://en.wikipedia.org/wiki/Colorhttp://en.wikipedia.org/wiki/Colorhttp://en.wikipedia.org/wiki/Colorhttp://en.wikipedia.org/wiki/Transparent_materials#Absorption_of_light_in_solidshttp://en.wikipedia.org/wiki/Transparent_materials#Absorption_of_light_in_solidshttp://en.wikipedia.org/wiki/Photochromic_lenshttp://en.wikipedia.org/wiki/Photochromic_lenshttp://en.wikipedia.org/wiki/Glass#cite_note-vogel-42http://en.wikipedia.org/wiki/Glass#cite_note-vogel-42http://en.wikipedia.org/wiki/Soda-lime_glasshttp://en.wikipedia.org/wiki/Soda-lime_glasshttp://en.wikipedia.org/wiki/Iron(II)_oxidehttp://en.wikipedia.org/wiki/Iron(II)_oxidehttp://en.wikipedia.org/wiki/Glass#cite_note-seward-43http://en.wikipedia.org/wiki/Greenhttp://en.wikipedia.org/wiki/Greenhttp://en.wikipedia.org/wiki/Chromium(III)_oxidehttp://en.wikipedia.org/wiki/Chromium(III)_oxidehttp://en.wikipedia.org/wiki/Chromium(III)_oxidehttp://en.wikipedia.org/wiki/Chromium(III)_oxidehttp://en.wikipedia.org/wiki/Sulfurhttp://en.wikipedia.org/wiki/Sulfurhttp://en.wikipedia.org/wiki/Sulfurhttp://en.wikipedia.org/wiki/Carbonhttp://en.wikipedia.org/wiki/Glass#cite_note-44http://en.wikipedia.org/wiki/Manganese_dioxidehttp://en.wikipedia.org/wiki/Manganese_dioxidehttp://en.wikipedia.org/wiki/Manganese_dioxidehttp://en.wikipedia.org/w/index.php?title=Glass&action=edit&section=22http://en.wikipedia.org/w/index.php?title=Glass&action=edit&section=22http://en.wikipedia.org/wiki/Waveguide_(optics)http://en.wikipedia.org/wiki/File:Green_color_of_float_glass.jpghttp://en.wikipedia.org/wiki/File:Green_color_of_float_glass.jpghttp://en.wikipedia.org/wiki/Refractionhttp://en.wikipedia.org/wiki/Geometrical_opticshttp://en.wikipedia.org/wiki/Lens_(optics)http://en.wikipedia.org/wiki/Refraction_indexhttp://en.wikipedia.org/wiki/Fresnel_equationshttp://en.wikipedia.org/wiki/Reflectivityhttp://en.wikipedia.org/wiki/Transmissivityhttp://en.wikipedia.org/w/index.php?title=Glass&action=edit&section=21http://en.wikipedia.org/wiki/Glass_coloring_and_color_markinghttp://en.wikipedia.org/wiki/Pigment#Pigments_by_chemical_compositionhttp://en.wikipedia.org/wiki/Transparent_materials#Absorption_of_light_in_solidshttp://en.wikipedia.org/w/index.php?title=Absorption_centers&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Absorption_centers&action=edit&redlink=1http://en.wikipedia.org/wiki/Visible_lighthttp://en.wikipedia.org/wiki/Visible_spectrumhttp://en.wikipedia.org/wiki/Colorhttp://en.wikipedia.org/wiki/Colorhttp://en.wikipedia.org/wiki/Transparent_materials#Absorption_of_light_in_solidshttp://en.wikipedia.org/wiki/Photochromic_lenshttp://en.wikipedia.org/wiki/Glass#cite_note-vogel-42http://en.wikipedia.org/wiki/Soda-lime_glasshttp://en.wikipedia.org/wiki/Iron(II)_oxidehttp://en.wikipedia.org/wiki/Glass#cite_note-seward-43http://en.wikipedia.org/wiki/Greenhttp://en.wikipedia.org/wiki/Chromium(III)_oxidehttp://en.wikipedia.org/wiki/Sulfurhttp://en.wikipedia.org/wiki/Carbonhttp://en.wikipedia.org/wiki/Glass#cite_note-44http://en.wikipedia.org/wiki/Manganese_dioxidehttp://en.wikipedia.org/w/index.php?title=Glass&action=edit&section=22http://en.wikipedia.org/wiki/Waveguide_(optics)


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The propagation of light through a multi-mode optical fiber.

A laser bouncing down anacrylicrod, illustrating the total internal reflection of light in a multimode optical fiber.

Opticallytransparent materialsfocus on the response of a material to incoming light waves of a

range of wavelengths. Frequency selective optical filters can be utilized to alter or enhancethebrightnessandcontrastof adigitalimage. Guided light wave transmission via frequency

selective waveguides involves the emerging field offiber opticsand the ability of certain glassy

compositions as atransmission mediumfor a range of frequencies simultaneously (multimode

optical fiber) with little or nointerferencebetween competing wavelengths or frequencies. This

resonant mode of energy anddata transmissionvia electromagnetic (light)wave propagation, though

low powered, is relatively lossless.

An optical fiber is acylindricaldielectric waveguide that transmits light along its axis by the process

oftotal internal reflection. The fiber consists of acoresurrounded by acladdinglayer. To confine theoptical signal in the core, therefractive indexof the core must be greater than that of the cladding.

Typical values for core and cladding of an optical fiber are 1.48 and 1.46, respectively. When light

traveling in a dense medium hits a boundary at a steep angle, the light will be completely reflected.

This effect is used to confine light in the core. Light travels along the fiber bouncing back and forth

off of the boundary. Because the light must strike the boundary with an angle greater than the critical
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angle, only light that enters the fiber within a certain range of angles will be propagated. This range

of angles is called theacceptance coneof the fiber. The size of this acceptance cone is a function of

the refractive index difference between core and cladding.

Opticalwaveguidesare used as components in integrated optical circuits (e.g.light-emitting diodes,

LEDs) or as the transmission medium in local and long hauloptical communicationsystems. Also of

value tomaterials scienceis the sensitivity of materials tothermal radiationin the infrared (IR)

portion of the EM spectrum. Thisinfrared homing(or "heat-seeking") capability is responsible for

such diverseoptical phenomenaas "night vision" and IR luminescence.

[edit]Glass art

Main article:Studio glassMain article:Art glassMain article:Glass art

Avasebeing created at theReijmyre glassworks,Sweden

Paperweightwith items inside the glass,Corning Museum of Glass
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A glass sculpture byDale Chihuly, The Sun at the Gardens of Glass exhibition in Kew Gardens, London. The piece

is 13 feet (4 metres) high and made from 1000 separate glass objects.

Glass tilesmosaic(detail).

From the 19th century, various types of fancy glass started to become significant branches of

thedecorative arts.Cameo glasswas revived for the first time since the Romans, initially mostly

used for pieces in aneo-classicalstyle. TheArt Nouveaumovement in particular made great use of

glass, withRen Lalique,mile Gall, andDaum of Nancyimportant names in the first French wave

of the movement, producing colored vases and similar pieces, often in cameo glass, and also using
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lustre techniques.Louis Comfort Tiffanyin America specialized in secular stained glass, mostly of

plant subjects, both in panels and his famous lamps. From the 20th century, some glass artists

began to class themselves as in effect sculptors working in glass, and as part of thefine arts.

Several of the most common techniques for producing glass art include:blowing, kiln-casting,

fusing, slumping, pate-de-verre, flame-working, hot-sculpting and cold-working. Cold work includes

traditional stained glass work as well as other methods of shaping glass at room temperature. Glass

can also be cut with adiamondsaw, or copper wheels embedded with abrasives, and polished to

give gleaming facets; the technique used in creatingWaterford crystal.[46]Art is sometimes etched

into glass via the use of acid, caustic, or abrasive substances. Traditionally this was done after the

glass was blown or cast. In the 1920s a new mould-etch process was invented, in which art was

etched directly into the mould, so that each cast piece emerged from the mould with the image

already on the surface of the glass. This reduced manufacturing costs and, combined with a wider

use of colored glass, led to cheap glassware in the 1930s, which later became known as Depressionglass.[47]As the types of acids used in this process are extremely hazardous, abrasive methods have

gained popularity.

Another technique isdevitrification.

Objects made out of glass include not only traditional objects such as vessels (bowls,vases,bottles,

and other containers),paperweights,marbles,beads, but an endless range

ofsculptureandinstallation artas well. Colored glass is often used, though sometimes the glass is

painted, innumerable examples exist of the use of stained glass.

[edit]Museums

Apart from historical collections in general museums, modern works of art in glass can be seen in a

variety of museums, including the Chrysler Museum, theMuseum of Glassin Tacoma, the

Metropolitan Museum of Art, the Toledo Museum of Art, andCorning Museum of Glass, inCorning,

NY, which houses the world's largest collection of glass art and history, with more than 45,000

objects in its collection.[48]

TheHarvard Museum of Natural Historyhas a collection of extremely detailed models of flowers

made of painted glass. These werelampworkedbyLeopold Blaschkaand his son Rudolph, who

never revealed the method he used to make them. The BlaschkaGlass Flowersare still an

inspiration to glassblowers today.[49]
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