ceramic fabrication

7/26/2019 Ceramic Fabrication

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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.htm


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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/Sodium


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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

ceramic fabrication

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