Making Glass.docx

Making Glass.docx

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MakingGlass

MakingGlass

Product

SpecificQualities

MethodofManufacture

TypicalFormula

GlassContainersBottles&Jars

Relativelycheapwhenmassproduced.

Resistanttomechanicalshock,capableofbeingfilledatveryfastrates.

Somebottlingplantsfillinexcessof1000bottlesperminute.

Canbere-usedandrecycled.

Canbesterilizedathightemperatures.

inert,donotimparttasteortoxicsubstances.

Automaticallyblownathighspeeds.

Soda-limesilica

Approximatecomposition:

%

SiO2

74

Na2O

14

CaO

11

Al2O3

1

FlatGlass

1.Relativelycheap.

2.Canbetoughened.

3.Weatherresistant.

4.Canbecoated.

Floatprocess.Castandrolled.

Soda-limesilica

Approximatecomposition:

%

SiO2

71

Na2O

16

CaO

9

Al2O3

1

MgO

3

DomesticGlasswareforeverydayuseinhomeandcatering

1.Pleasantappearance.

2.Abilitytostanduptoconstantuse.

3.Doesnotaffectcontents

Mouthblown,pressedorfullyautomaticmassproduced.

Soda-limesilica

Approximatecomposition:

%

%

SiO2

74

Al2O3

3

Na2O

16

K2O

1

CaO

5

B2O3

1

MgO

3

RadiationShielding

Highdensitytoabsorbradiation.

Extrusionandcastingcanbegroundandpolishedtoopticalprecision.

Soda-limesilica

Approximatecomposition:

%

SiO2

3

PbO

1

K2O

1

ThermometerTubing

Thermalstabilityoverawidetemperaturerange,retainingtransparency.

Automaticorhanddrawing.

Soda-limesilica

Borosilicate

Leadglass

Dependingontemperature

rangerequired

LaboratoryGlassware

Highchemicaldurability.

Lowthermalexpansion.

Lampworking（madefromtubingbyheatingandskilfulmanipulation）.

Mouthandautomaticblowing.

Sintering.

MainlyBorosilicateorfusedsilicaforextralowexpansioncoefficient

FullLeadCrystalDomesticGlassware

1.Extrasuitableforartistichandshapingandmouthblowing.

2.Brilliantfinish,attractivewhenfullorempty.

3.Comparativelysoft-easytocutandpolishorengrave.

Handmadebyskilledcraftsmen.

Leadglass

Approximatecomposition:

%

SiO2

3

PbO

1

K2O

1

HeatResistantOventoTableWare

1.Resistanttothermalshock.

2.Attractive.

3.Easytoclean.

4.Canbeusedinmicrowaveovens.

Automaticallypressedorblown.

Borosilicateglass

Approximatecomposition:

%

%

SiO2

80

Na2O

4.5

B2O3

12

Al2O3

5

OpticalGlass

1.Widerangeofrefractiveindices.

2.Widerangeofdispersioncoefficients.

3.Perfecthomogeneity.

4.Completetransparency.

Extrusionandpressing,thengroundandpolishing.

Whilerangeofcompositions

Dependsonapplication

ElectricalComponents:

cathode-raytubes,capacitorsandresistors,computercomponents,printedcircuits

Gooddielectricproperties.

Lowelectricallossesoverawiderangeoftemperatures.

Highoperatingtemperatures.

Blowing.

Drawing-inrodformandinsheets.

SinteringandPressing-glassisgroundtofinegrainsandthenissubsequentlypressedintorequiredshapeandthenfired.

Widerangeofcompositions

GlassBuildingBlocks

Resistanttonormaltemperaturechanges.Resistanttoatmosphericconditions.

Mechanicalstrength.

Attractive.

Translucent.

Automaticpressing

-pressedinhalvesandthenfusedtogether

Soda-limesilicaglass

Similartoflatglass

Ballotini:

minuteglassspheres（1-60microns）whichreflectlight

Highreflectiveproperties:

mixedwithpaintforroadsignsandcinemascreens.

flamedrawing

-velocityofflamesdrawsparticlesofglassuptowerandasthesoftenedglassfallsontheoutside,spheresareformedbysurfacetensioneffects.

Soda-limesilicaglass

Similartoflatglass

GlassFibre

Highstrength-to-weightratio.

Resistanttoattackbycorrosivesubstances.

Resistanttohightemperature.

Flameresistant.

Highelectricalresistance.

Filamentdrawing.

Continuousfilament.

Whitewool.

Crownprocess.

Canbewovenintotextilesorincorporatedwithplasticstoforminsulatingmaterials,boathulls,carbodies,etc.

Sodalimesilicaandwhereresistancetoweatheringisnecessary,aborosilicateglassisused,e.g.

Soda-limesilicaglass

%

%

SiO2

54.5

B2O3

8.3

Al2O3

14.5

Na2O

0.5

CaO

22.0

LightingGlassware

1.ElectricLightBulbs

Economicaltoproduce.

Easytomanufacturebymassproductionmethods.

Resistanttoshock.

Impermeableandinerttogas,vaporandliquid.

Durable.

Transparentortranslucent.

RibbonMachine

-producesbulbattherateofover1,000perminute.

Blanksusedinthemanufactureofvacuumflasksarealsoproducedbythismachine

Sodalimesilicaglass

%

SiO2

72.5

Al2O3

1.3

CaO

6.5

MgO

3.0

Na2O

15.9

K2O

0.3

2.SpecialGlasses

（a）Highpressuremercuryvaporlamps

Lowelectricalconductivity.

Resistancetointensechemicalactivityofmercuryvapor.

Specialglassescanbeformedbyusingmanufacturing

Widerangeofcompositions

（b）Aircraftfire-warningsensors

Lowmeltingpoint.

processes,or,insomecases,laminatedontoordinaryglasses

（c）Glassforencapsulatingelectriccomponents

Highelectricityconductivity.

i.e.sodiumdischargelamps.

3.Tubingforfluorescentlighting

Lowelectricalconductivity.

Resistancetointensechemicalactivity.

ElectricaldischargegeneratesUVlightwhichthencausesfluorescentpowdertoemitvisiblelight.

Highefficiency.

Longlife:

3,000-5,000hours,i.e.aboutoneyearofcontinuoususe.

AutomaticDrawing

Sodalimesilicaglass

%

SiO2

72.5

Al2O3

2.6

CaO

5.7

MgO

2.9

Na2O

14.6

K2O

1.2

B2O3

0.3

4.Domesticandindustrialshadesandbulkheadlights:

inc.lensesfortrafficlights,carlightsandrailwaysignallights

Resistanttohightemperature.

Resistanttothermalshock.

Resistanttoweathering.Accurateandnonfadingcolor:

subjecttostrictBSspecifications.

Mouthblowing.

Handandautomaticpressing-dependingonquantitiesrequired.

1.Soda-limesilicaglass

2.Laminatedwithopalglass

3.Borosilicateglassesandopalglasses

WHATISGLASS?

Glassisaproductobtainedbythefusionofseveralinorganicsubstances,ofwhichnormallysilica（SiO2）intheformofsandisthemainone.Thefusedmassiscooledtoambienttemperatureataratefastenoughtopreventcrystallization,i.e.,themoleculescannotarrangethemselvesintoacrystallinepattern.Thefastrateofcoolingtopreventcrystallizationappliestotransparentglasses,whereasinthecaseoftranslucentoropalglasses,therateofcoolingissuchastoproduceapre-determinedlevelofCrystalformation.

TYPESOFGLASSES

Alargevarietyofglasswithdifferentchemicalandphysicalpropertiescanbemadebyasuitableadjustmenttochemicalcompositions.Furthersectionsofthisbookletdealwithvariousglasses,includingcrystalandopticalglassesofhighrefractiveindexandhighleadcontent.

CommercialGlasses

Themainconstituentofpracticallyallcommercialglassesissand.Sandbyitselfcanbefusedtoproduceglassbutthetemperatureatwhichthiscanbeachievedisabout1700oC.Addingotherchemicalstosandcanconsiderablyreducethetemperatureoffusion.Theadditionofsodiumcarbonate（Na2CO3）,knownassodaash,inaquantitytoproduceafusedmixtureof75%silica（SiO2）and25%ofsodiumoxide（Na2O）,willreducethetemperatureoffusiontoabout800oC.However,aglassofthiscompositioniswatersolubleandisknownaswaterglass.Inordertogivetheglassstability,otherchemicalslikecalciumoxide（CaO）andmagnesiumoxide（MgO）areneeded.TherawmaterialsusedforintroducingCaOandMgOaretheircarbonatesCaCO3（limestone）andMgCO3（dolomite）,whichwhensubjectedtohightemperaturesgiveoffcarbondioxideleavingtheoxidesintheglass.

Mostcommercialglasseswhetherforcontainers,i.e.bottlesandjars,flatglassforwindowsorfordrinkingglasses,havesomewhatsimilarchemicalcompositionsof:

70%-74%

SiO2

（silica）

12%-16%

Na2O

 （sodiumoxide）

5%-11%

CaO

（calciumoxide）

1%-3%

MgO

（magnesiumoxide）

1%-3%

Al2O3

（aluminumoxide）

Withintheseverywidelimitsthecompositionisvariedtosuitaparticularproductsandproductionmethod.Therawmaterialsarecarefullyweighedandthoroughlymixed,asconsistencyofcompositionisofutmostimportance.Tothemixtureofchemicalsafurtherrawmaterialsadded-brokenglass,calledcullet.Culletcancomefromfactoryrejects,itcanbecollectedbythepublicinBottleBanksorfromthebottlingindustry.Almostanyproportionofculletcanbeaddedtothemix（knownasbatch）,provideditisintherightcondition,andgreenglassmadefrombatchcontaining95%ofculletisbynomeansuncommon.AlthoughtheglasscollectedbyBottleBanksmaycomefromseveralmanufacturer,itcanbeusedbyoneofthem,ascontainerglasscompositionshavebeenharmonizedtomakethispossible.Itis,however,importantthatglasscolorsarenotmixedandthattheculletisfreefromimpurities,especiallymetalsandceramics.

Flatglassissimilarincompositiontocontainerglassexceptthatitcontainsahigherproportionofmagnesiumoxide.

Othertypesofglasses

Glassesvarywidelyintheirchemicalmake-up;indeed,thereareveryfewelementintheperiodictablethathavenotbeenincorporatedinaglassofsomekind.However,mostoftheglassesproducedcommerciallyonalargescalemaybeclassifiedintothreemaingroups:

soda-lime,leadandborosilicate,ofwhichthefirstisbyfarthemostcommon.

Soda-limeglasses

Thesearethemostcommoncommercialglassesandhavebeendescribedinthepreviouschapter.Thechemicalandphysicalpropertiesofsoda-limeglassesmakethemsuitableforavisi