V.M. Sglavo – GlassEng - UNITN 2017

V.M. Sglavo – GlassEng - UNITN 2017

V.M. Sglavo – GlassEng - UNITN 2017

Phaseseparationinglass

Free energy of mixture: ΔGm = ΔHm - T ΔSm

entropy-ΔSm

entalpy-ΔHm

Termodinamica strutturale, J.H. Brophy, R.M. Rose, J. Wulff,, Ambrosiana Ed., 1975

A,Baf3ine idealsituation A,Bnotaf3ine

Halloy

Halloy

Halloy

V.M. Sglavo – GlassEng - UNITN 2017

V.M. Sglavo – GlassEng - UNITN 2017

V.M. Sglavo – GlassEng - UNITN 2017

freeenergy-ΔGm

completemiscibilityinonesinglephase

incompletemiscibilitytwophases

Termodinamica strutturale, J.H. Brophy, R.M. Rose, J. Wulff,, Ambrosiana Ed., 1975

V.M. Sglavo – GlassEng - UNITN 2017

V.M. Sglavo – GlassEng - UNITN 2017

V.M. Sglavo – GlassEng - UNITN 2017

€

G(c)= G(c0)+∂G∂c c0

(c− c0)+12∂2G∂c2

c0

(c − c0)2 + .....

Ifc’=c0-Δc<c0<c”=c0+Δc

€

G = G(c0)+12∂2G∂c2

c0

Δc2

€

ΔG = G −G(c0)=12∂2G∂c2

c0

Δc2

€

∂2G∂c2

c0

> 0

€

∂2G∂c2

c0

< 0

ÚΔG>0

ÚΔG<0

Free energy variation associated to composition fluctuations

c0

Struttura e genesi dello stato vetroso, A. Maddalena, Cleup, 1983

FREEENERGY,G

COMPOSITION(MOLARFRACTIONOFB)

V.M. Sglavo – GlassEng - UNITN 2017

V.M. Sglavo – GlassEng - UNITN 2017

V.M. Sglavo – GlassEng - UNITN 2017

T > TC: complete miscibilityT < TC: immiscibility

spinode

unstablezone

metastablezones

Separationmechanisms:-  nucleationandgrowth(metastablezone)largevariationofG

-  spinodaldecomposition(unstablezone)gradualvariationofcomposition(spontaneous)

Struttura e genesi dello stato vetroso, A. Maddalena, Cleup, 1983

TEMPERATURE

FREEENERGY

COMPOSITION

composition

distance

V.M. Sglavo – GlassEng - UNITN 2017

V.M. Sglavo – GlassEng - UNITN 2017

V.M. Sglavo – GlassEng - UNITN 2017

nucleationandgrowthspinodaldecomposition

interconnectedstructure islesstructure

Introduction to glass science and technology, J. E. Shelby, The Royal Society of Chemistry, 1997

V.M. Sglavo – GlassEng - UNITN 2017

V.M. Sglavo – GlassEng - UNITN 2017

V.M. Sglavo – GlassEng - UNITN 2017

stableimmiscibility metastableimmiscibility

Immiscibility diagrams

Tg

Introduction to glass science and technology, J. E. Shelby, The Royal Society of Chemistry, 1997

V.M. Sglavo – GlassEng - UNITN 2017

V.M. Sglavo – GlassEng - UNITN 2017

V.M. Sglavo – GlassEng - UNITN 2017

Homogenous and biphasic glass

homogenous“isles”separation(SiO2richmatrix)

interconnectedseparation

“isles”separation(SiO2-Na2Omatrix)

SiO2 – Na2O

Introduction to glass science and technology, J. E. Shelby, The Royal Society of Chemistry, 1997

V.M. Sglavo – GlassEng - UNITN 2017

V.M. Sglavo – GlassEng - UNITN 2017

V.M. Sglavo – GlassEng - UNITN 2017

Examples:

sodium-borosilicate glass

Introduction to glass science and technology, J. E. Shelby, The Royal Society of Chemistry, 1997

barium-silicate glass

sodium-silicate glass

V.M. Sglavo – GlassEng - UNITN 2017

V.M. Sglavo – GlassEng - UNITN 2017

V.M. Sglavo – GlassEng - UNITN 2017

lithium-sodium-silicate glass alkali-borosilicate glass

microporousand/orVycor®glass

TC=111°Cwith2mol%Al2O3

Introduction to glass science and technology, J. E. Shelby, The Royal Society of Chemistry, 1997

V.M. Sglavo – GlassEng - UNITN 2017

V.M. Sglavo – GlassEng - UNITN 2017

V.M. Sglavo – GlassEng - UNITN 2017

Technological implications

-  trasparence - opacity (d ≈ visible wavelength = 450-700 nm)

-  heterogeneous nucleation Ò crystallization

- production of high silica glass (Vycor®)

sodium-borosilicateglass

thermaltreatment chemicaletchinginhotacidsolution(HCl)

sinteringspinodaldecomposition:96%SiO2+sodium-borosilicateglass

96%SiO2porousglass(d=2-200nm)

96%SiO2glass