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GLASS & CERAMIC
SHAPING & FORMATION
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GLASS
Atomic structure noncrystalline (oramor!ous"
#inetics o$ crystalli%ationOn coolin t!eli'ui $rom a !i! temerature) t*o!enomena may occur at t!e oint o$solii+cation) Tm,
I$ t!e li'ui crystalli%es t!ere is aiscontinuous c!ane in V and a
discontinuity in the rate of cooling (= !eato$ crystalli%ation"-
I$ no crystalli%ation occurs t!e li'ui assesinto a suercoole state an V decreases at
about the same rate as a.o/e
Suercoole, conition in *!ic! a li'ui!as.een coole to a temerature.elo* T$ t!at
at *!ic! crystalli%ation normally *ouloccur
http://chemistry.about.com/od/chemistryglossary/a/liquiddef.htmhttp://chemistry.about.com/cs/glossary/g/bldeftemp.htmhttp://chemistry.about.com/cs/glossary/g/bldeftemp.htmhttp://chemistry.about.com/od/chemistryglossary/a/liquiddef.htm7/26/2019 Ceramic Fabrication
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Glasses o not really solii$y in t!etraitional sense no e+nitetemerature at *!ic! t!e li'ui trans$ormsto a soli
0on coolin) a lass continues to .e more/iscous *it! ecreasin temerature T!e molecules ac1 closer an closertoet!er) .ecomin an increasinly enserli'ui-
/olume ecreases continuously *it!
temerature reuction
T!e sli!t c!ane in sloe occurs *!en t!emolecules are essentially una.le to 2o*-
T!is is t!e Glass TransitionTemperature
T
T!e temerature at *!ic! t!etransition in t!e amor!ous reions.et*een t!e lassy an ru..ery state
3elo* t!is T) t!e material is consiereto .e a lass4 a.o/e) it is +rst asuercoole li'ui) an +nally a li'ui
Crystal
iscountinueecrease in /ol at Tm
Tg: glass transition T
Tm: melting T for
crystalline
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Seci+c oints in lass $a.rication,
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5iscosity /s T
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Glass annealing
6!en a ceramic material is coole $rom an ele/atetemerature) internal stresses) calle t!ermalstresses) may .e introuce as a result o$ t!ei7erence in coolin rate an t!ermal contraction.et*een t!e sur$ace an interior reions-
T!ese t!ermal stresses are imortant in .rittleceramics) esecially lasses) since t!ey may*ea1en t!e material lea to $racture
Attemts are mae to a/oi t!ermal stresses) *!ic!
may .e accomlis!e .y coolin t!e iece at asu$+ciently slo* rate
Once suc! stresses !a/e .een introuce) !o*e/er)elimination) or at least a reuction in t!eir
manitue) is ossi.le .y an annealin !eattreatment in *!ic! t!e lass*are is !eate to t!e
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Generally at a temerature sli!tly a.o/e t!e oint at *!ic!
recrystalli%ation occurs
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Glass temerin
en!ance t!e strent! o$ a lass iece .y intentionally inucincomressi/e resiual sur$ace stresses can .e accomlis!e .y a !eat
treatment roceure calle thermal tempering
the glassware is heated to temperature a.o/e t!e lass transitionreion yet .elo* t!e so$tenin oint) t!en coole to room temerature ina 8et o$ air or) in some cases) an oil .at!-
T!e resiual stresses arise $rom i7erences in coolin rates $or sur$acean interior reions-
Initially) t!e sur$ace cools more raily an) once !a/in roe to atemerature .elo* t!e strain oint) .ecomes rii- At t!is time) t!einterior) !a/in coole less raily) is at a !i!er temerature (a.o/e t!estrain oint" an) t!ere$ore) is still lastic- 6it! continue coolin) t!e
interior attemts to contract to a reater eree t!an t!e no* riie9terior *ill allo*-
As a conse'uence) a$ter t!e lass iece !as coole to Tr) it sustains
comressi/e stresses on t!e sur$ace) *it! tensile stresses at interiorreions-
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Glass:Ceramic $a.rication
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Glass Formin
Heat RM to an ele/ate temerature a.o/e *!ic! meltinoccurs
Most commercial lasses are o$ t!e silica;soa;lime /ariety silica ('uart%";Na
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ressin
relati/ely t!ic1?*alle ieces (lates anis!es-
T!e lass iece is resse in a ra!ite?coatecast iron mol *it! esire s!ae
t!e mol is !eate to ensure an e/en sur$ace-
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BLOWING
some lass .lo*in isone .y !an art o.8ect
RM ress in mol
arison (temorarys!ae"4 lace into+nis!in or .lo* mol &$orce to con$orm to t!e
mol contours .y t!e
ressure create $rom a.last o$ air
Glass .ottle) 8ar) li!t .ul.
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DRAWING
Form lon) *ie lass ieces (*ino* lass)s!eet) tu.in) ro etc"!ot rollin may alieFlatness & sur$ace +nis! may .e imro/e .y 2oatin t!e molten
lass s!eet on a .at! o$ molten tin at !i! T $ollo*e slo*lycoole an su.se'uently !eat treate
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Glass rocessin
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CLA@ PRO0CTS
Comosition Clay, quart) $elsar (#AlSi=OB ; NaAlSi=OB ;
CaAl
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Clay minerals lay < roles,- 6!en ae *ater) $orm !yrolasticity
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0ART (SiO
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3iner
3iner a comonent t!at is ae to !ol t!e o*er
toet!er *!ile s!ain t!e .oy
< $unctions o$ .iner,
" ro/ie lasticity necessary $or $ormin
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lastici%er
Plasticizer is the component of a binder that keeps itsoft or lia.le4 it imro/es t!e r!eoloical roerties
Mi9in ceramic o*er *it! lare /ol o$ li'ui torouce a mass t!at e$orma.le:lastic uner P
T!e .iner, *ater) oranic li'ui) comle9 com toac!ie/e re'uire /iscosity & roerties
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Fa.rication
RM millin & rinin screenin &si%in mi9in all RM s!ain
Clay is mi9e *it! *ater an er!as ot!erinreients to i/e 2o* c!aracteristics t!atare comati.le *it! t!e articular $ormin
tec!ni'ue to $orm a lastic .oy & $ormeto esire s!ae *et .oy
T!e $orme iece must !a/e su$+cientmec!anical strent! to remain intact urintransortin) ryin) an +rin oerations-
S!ain met!os, !yrolastic) castin &o*er ressin
6et .oy is t!en rie an +re
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Hyrolastic
Clay minerals) *!en mi9e *it! *ater).ecome !i!ly lastic an lia.le anmay .e mole *it!out crac1in4!o*e/er) t!ey !a/e e9tremely lo* yielstrent!s-
T!e consistency (*ater;clay ratio" o$ t!e!yrolastic mass must i/e a yielstrent! su$+cient to ermit a $orme*are to maintain its s!ae urin!anlin an ryin-
T!e most common !yrolastic $ormintec!ni'ue is e9trusion
$orcin a e$orma.le mass t!rou! a ieori+ce !a/in t!e esire cross?sectionaleometry
Brick, pipe, ceramic .loc1s) an tiles
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Sli Castin ceramic
In Tr) re'uire slurry ceramic o*er articles to .esusene in a li'ui (sli"
S li castin slurry is oure into orous mol(commonly mae o$ laster o$ aris" t!at !as .een
mae .y castin) roun a moel o$ t!e re'uire s!ae *ater $rom t!e sli is a.sor.e into t!e mol (remo/e
t!e li'ui") lea/e a articulate comact:layer on t!emol *all t!e t!ic1ness o$ *!ic! eens on t!e time
T!e nature o$ t!e sli is e9tremely imortant4 it must!a/e a !i! seci+c ra/ity an yet .e /ery 2ui anoura.le een on t!e soli?to *ater ratio anot!er aents t!at are ae-
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A satis$actory castin rate is an essentialre'uirement-
T!e roerties o$ t!e mol itsel$ in2uence t!e'uality o$ t!e castin t!e mol orosity may .e/arie to control t!e castin rate-
0sually laster o$ aris ecomonical) easy to$a.ricate) reusa.le
In aition) t!e cast iece must .e $ree o$ .u..les)an it must !a/e a lo* ryin s!rin1ae an arelati/ely !i! strent!-
T!e rat!er comle9 ceramic s!aes t!at may .erouce .y means o$ sli castin inclue sanitaryla/atory *are) art o.8ects) an seciali%e scienti+cla.oratory *are suc! as ceramic tu.es
< met!os, rain castin & soli castin
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rain sli castin t!e rocesss terminate *!enesire t!ic1ness reac!e) our out t!e e9cess sli-
A$ter rie) t!e mol is isassem.le C!aracteristic t!e Sli !i! seci+c ra/ity) /ery 2ui &oura.le
One o$ t!e t sins o$ sli castin ceramic is t!at it is!ollo*-
lo* cost *ay to rouce comle9 s!aes
sanitary la/atory *are) art o.8ects
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Soli castin *ater $rom sli is a.sor.e into t!e
mol *!en oure) lea/in soli layer on t!e mol*all (t!ic1ness) $(t""
sli may continually ae until a soli cast ismae- T!ese items *ill not .e !ollo*relati/ely)
t!ey *ill .e !ea/ier-
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Po*er comaction
Pressin o$ $ree 2o*in o*er containin a small amounto$ *ater or ot!er .iner) is comacte into t!e esires!ae .y ressure
Pressure alication eens on +nal rouct
T!e eree o$ comaction is ma9imi%e4 $raction o$ /oisace is minimi%e .y usin coarse an +ne articles mi9ein aroriate roortions-
no lastic e$ormation o$ t!e articles urin comaction
One $unction o$ t!e .iner is to lu.ricate t!e o*er
articles as t!ey mo/e ast one anot!er in t!e comactionrocess-
< tyes, ry resse (i-e- *it!out aition o$ .iner" &resse *it! t!e aition o$ suita.le .iner
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ry ressin t!ree .asic stes, +llin t!e ie) comactin t!e
contents) an e8ectin t!e resse soli
A article si%e
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.ottom unc! is in t!e lo* osition a ca/ity t!e ca/ity is+lle *it! $ree 2o*in o*er 4 t!e o*er is struc1 o7le/el *it! t!e to o$ t!e ie- T!e to unc! escens ancomresses t!e o*er eit!er to a reetermine /olumeor set ressure-
A$ter ressin) .ot! unc!es mo/e u*ar T!e comactis t!en e8ecte
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Hot ressin
Pressin er$orme at !i! temeratures T!e ie assem.ly is containe *it!in a !i! temerature $urnace
urin !ot ressin t!e ceramic o*ers may sinter toet!er to$orm a !i!?ensity comonent-
t!e A5ANTAGES o$ t!is rocess,
T!e o*er oes not !a/e to .e o$ t!e !i!est 'uality-< Lare ores t!at are cause .y non uni$orm mi9in are easily
remo/e-
= ensi$y at temeratures lo*er (tyically !al$ t!e meltintemerature o$ t!e material" t!an t!ose neee $or con/entional
ressure less sinterin-> ensi$y co/alently .one materials suc! as 3>C) SiC) an Si=N>
*it!out aiti/es
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ISA5ANTAGE ,
ie $or !i! T is e9ensi/ean o not enerally lastlon-
< limite simle s!ae, 2at
lates) .loc1) cyliner
Gra!ite is t!e most *iely
use ie material (u to
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ryin & Firin
Ceramic $orme !yrolastically:sli castin retain sini+cant orosity & insucient strent!)still contain some li'ui ae in re/ious oeration
Remo/e .y ryin reen .oy
Proceure continue *it! +rin ensity an strent! are en!ance as a result o$ a
!i!?temerature !eat treatment or +rin
e$ect may .e introuce urin t!e oerationrener t!e *are useless (e--) *arae) istortion)
an crac1s" T!ese e$ects normally result $rom stresses t!at are
set u $rom nonuni$orm s!rin1ae-
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ryin early stae) clay articles surroune & searate .y t!in *ater
+lm ryin, remo/e some li'ui remain interarticle searation
ecrease (s!rin1ae"4
As a clay?.ase ceramic .oy ries) it also e9eriences somes!rin1ae
urin ryin) it is critical to control t!e rate o$ *ater remo/al
ryin at interior is accomlis!e .y i7usion o$ *ater moleculesto sur$ace *!ere e/aoration occurs
T!e rate o$ sur$ace e/aoration t!e rate o$ *ater i7usion4 I$rate o$ e/aQi7usionsur$ace *ill ry $aster t!an interior s!rin1
e/aoration rate may .e controlle .y temerature) !umiity)an t!e rate o$ air2o*-
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Ot!er $actors also in2uence s!rin1ae) suc! as t!ic1ness)*ater content) article si%e
nonuni$orm s!rin1ae an e$ect $ormation are more
ronounce in t!ic1 ieces t!an in t!in ones-
6ater content o$ t!e $orme .oy is also critical, t!ereater t!e *ater content) t!e more e9tensi/e t!es!rin1ae conse'uently) t!e *ater content is orinarily
1et as lo* as ossi.le
Clay article si%e also !as an in2uence4 s!rin1ae is
en!ance as t!e article si%e is ecrease- To minimi%e s!rin1ae) t!e si%e o$ t!e articles may .e
increase) or nonlastic materials !a/in relati/ely lare
articles may .e ae to t!e clay-
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+rin
Firin, !eat treatment rocess t!at sintersceramic materials
er$orme in $urnace calle 1iln
Fire .et*een JJ?>JJ C (RM comosition
& esire roerties" causes structure c!anes an
trans$ormations in t!e silicate itsel$
3on are e/eloe .et*een t!e ceramicrain *!ic! lea to ensi+cation an
reuction o$ orosity
aitional s!rin1aeoccurs4 mec!anical strent! increase
E9ecte no crac1in or istortin t!eceramic comact-
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Comle9 reactions occurre
A lass !ase $orms amon t!e crystals *!ic! act as .iner
5itri+cation raual li'ui lass $ormation t!at 2o*s into& +lls ore /olume 4 $(T) t) comosition"
eree o$ /itri+cation controls ceramic roerties (strent!)
ura.ility & ensity"
O reuce T o$ li'ui !ase
A 2u9in aent (comounsto .on t!e materials") suc! metal o9ies) suc! as soium)
otassiuman calcium as $oun in $elsar
T!is $use !ase 2o*s aroun t!e remainin unmelte
articles an +lls in t!e ores as a result o$ sur$ace tension
$orces (or caillary action"4 s!rin1ae also accomanies t!is
rocess-
Comlete /itrici$ation is a/oie .oy .ecome too so$t)
may collase
http://en.wikipedia.org/wiki/Sodiumhttp://en.wikipedia.org/wiki/Potassiumhttp://en.wikipedia.org/wiki/Calciumhttp://en.wikipedia.org/wiki/Calciumhttp://en.wikipedia.org/wiki/Potassiumhttp://en.wikipedia.org/wiki/Sodium7/26/2019 Ceramic Fabrication
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In commercial ceramic *!ic! o$ten consists o$ se/eral
comonentsc!allenin to .e controlle) i7erent
.oilin oints an ecomosition temeratures-
T!e comonents *it! lo* .oilin oints (e--)
*a9es"may .e remo/e .y e/aoration at $airly lo*
temeratures-
T!e rocess o$ .iner remo/al is 1et slo* to reue
ossi.ility o$ macroe$ects .ein rouce-
0on coolin) t!is $use !ase $orms in a ense)
stron .oy
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Gla%in
Gla%in, alication o$ ceramic sur$ace coatinto ma1e t!e iece more imer/ious to *ateran en!ance its aearance
Colorants) suc! as iron o9ie) coer car.onateor co.alt car.onate) an sometimes oaci+ers
suc! as tin o9ieor %irconium o9ie) are use tomoi$y t!e /isual aearance o$ t!e +re la%e-
T!e usual rocessin se'uence *it! la%e*are is,
- Fire t!e iece once .e$ore la%in to !arent!e .oy o$ iece