A nuclear magnetic resonance investigation of the structure of some alkali silicate glasses

University of Warwick institutional repository:http://go.warwick.ac.uk/wrap

A Thesis Submitted for the Degree of PhD at the University of Warwick

http://go.warwick.ac.uk/wrap/55507

This thesis is made available online and is protected by original copyright. Please scroll down to view the document itself.

A NUCLEAR MAGNETIC RESONANCE

INVESTIGATION OF THE STRUCTURE OF SOME ALKALI SILICATE GLASSES

Muhammad Golam Mortuza

A thesis _submitted to the University

of Warwick, England for the admission to the degree _{of Doctor of Philosophy}

THE

UNIVERSITY

OF

WARWICK

This thesis

is dedicated

_{to my}

supervisors :

CONTENTS

A NUCLEAR MAGNETIC RESONANCE

INVESTIGATION OF THE STRUCTURE OF

SOME ALKALI SILICATE GLASSES

Muhammad Golam Mortuza

A thesis _{submitted to the University}

of Warwick, England for _{the admission} to the degree _{of Doctor of Philosophy}

CONTENTS

Page

CHAPTER 1 INTRODUCTION

1.1 _General 1

1.2 _{Glass and glass ceramics} 1

1.3 _Models for _{glass structure} 5

1.4 Alkali _{silicate glasses : their} formation

and phase diagrams 7

1.5 _{High resolution NMR in silicate glasses}

and glass ceramics 10

1.6 _{Review of the interaction of some pentavalent}

atoms with alkali and alkali silicates 13

1.7 _{Multinuclear studies} 15

1.8 _{Aim of the thesis} 21

References 22

CHAPTER 2 THEORETICAL FRAMEWORK

2.1 _{Nuclear magnetic resonance} (NMR) 28

2.2 _{Nuclear spin interactions} 30

2.2.1 Chemical _{shift interaction} 31

2.2.2 _Magnetic dipole-dipole _interaction 33

2.2.3 _{Nuclear quadrupole interaction} 34

2.3 _{Static powder lineshapes in solids} 38

2.4 _{NMR in rotating solids} 41

2.4.1 _Introduction 41

2.4.2 Generalisation _{of Hamiltonian} for _a

rotating _sample 43

2.4.3 _{Magic angle spinning and line narrowing} 46

2.4.4 _{Extraction of vxx, ayy and aZZ from}

spinning _sidebands 50

2.5 _{Spin-lattice relaxation in rotating solids 53}

2.6 _{Relaxation caused by paramagnetic}

substances 56

References 60

CHAPTER 3: _{INSTRUMENTATION AND TECHNIQUES}

3.1 _{Introduction to pulsed fourier transform}

(PFT) _{spectrometer 62}

Page

3.2 _{The Bruker MSL-360 spectrometer system} 65

3.3 _{The NMR probes and spinners} 67

3.4 _{Operation of the spectrometer} 70

3.4.1 _Introduction 70

3.4.2 _{Magic angle setting} 72

3.4.3 _{Setting up on a nucleus} 73

3.4.4 _{Measurement of spectrum reference} 76

3.4.5 _{Data collection} 77

3.4.6 _{Data processing} 80

3.5 _{Measurement of T1 relaxation time} 81

3.6 _{Materials preparation and characterisation} 85

3.6.1 _Introduction 85

3.6.2 _{Choice of initial materials} 85

3.6.3 _{Preparation of glasses} 86

3.6.4 _{Thermal analysis} 88

3.6.4.1 _{Differential thermal analysis} (DTA) 89

3.6.4.2 _{Differential scanning calorimetry} (DSC) 89

3.6.5 _X-ray diffraction _studies 91

3.6.6 _{Microstructure study of glass ceramics 91}

3.6.6.1 _{Electron microscopy} 91

3.6.6.1.1 _{Sample preparation for SEM 93}

3.6.6.1.2 _{Sample preparation for TEM 93}

3.7 _{Chemical analysis 94}

3.7.1 _{Wet chemical analysis 95}

3.7.2 _{Atomic absorption spectrophotometry 96}

3.7.3 _{UV spectroscopy 96}

3.7.4 _{Infrared spectrophotometry 98}

References 100

CHAPTER 4: _{LITHIUM SILICATE SYSTEM}

4.1 _{Introduction 104}

4.2 _{Conventionally prepared lithium}

silicate _glasses 105

4.2.1 29Si _{NMR 105}

4.2.2

7Li NMR

₁₁₃

4.3 _{Lithium silicate}

glass ceramics 115

4.3.1 29Si _{NMR 115}

Page

4.3.2

7L1 NMR

124

4.3.3 _{DTA and XRD} 124

4.4 _{Discussion of the conventionally}

prepared lithium silicate glass and

glass ceramic res ults 127

4.4.1 29Si _spectra 127

4.4.2 7Li _spectra 132

4.5 Sol-gel _prepared lithium _silicate glasses 133

4.5.1 29Si NMR 133

4.5.2 7Li NMR 135

4.5.3 1H NMR 135

4.6 _{Discussion of the results of sol-gel}

prepared lithium silicate glasses 137

References 139

CHAPTER 5 _: SODIUM SILICATE SYSTEM

5.1 Introduction 142

5.2 _{The effect of paramagnetic} impurity 143

5.2.1 29Si NMR 143

5.2.2 DTA 145

5.3 Effect _{of devitrification} 149

5.4 23Na NMR in sodium disilicate _{glass and}

glass ceramics 155

5.5 Discussion 159

5.5.1 Paramagnetic impurities 159

5.5.2

Devitrification

_{of Na2Si2O5}

161

References 165

CHAPTER 6: EFFECT OF PHOSPHORUS IN ALKALI DISILICATE _SYSTEM

6.1 _Introduction 168

6.2 _{The role of small amounts of P205} 172

6.2.1 _Lithium disilicate 173

6.2.1.1

29Si NMR in base glasses

173

6.2.1.2

29Si NMR in heat treated glasses

173

6.2.1.3 31P NMR

₁₇₅

6.2.1.4 7Li _NMR 178

Page

6.2.2 _{Sodium Disilicate} 178

6.2.2.1 29Si NMR in Na20.2SiO2-P205 _{base glasses} 180

6.2.2.2 29Si NMR in Na20.2SiO2-P2O5 _{glass ceramics} 180

6.2.2.3 31P _{NMR in} base _{and heat treated glasses} 184

6.2.2.4 23Na NMR 186

6.2.3 _Potassium disilicate 190

6.2.3.1 29Si NMR 190

6.2.3.2 31P NMR 190

6.2.4 _Discussion 193

6.3 _{The role of large amounts of phosphorus}

in the sodium disilicate system 203

6.3.1 29Si NMR 204

6.3.2 31P NMR 208

6.3.3 23Na NMR 210

6.3.4 27A1 NMR 213

6.3.5

_Effect

_{of devitrification}

213

6.3.5.1 _NMR 213

6.3.5.2 _XRD 220

6.3.6 _Discussion 223

6.4 _{Analysis of structural properties} 237

6.4.1 _{Differential thermal analysis} 237

6.4.2 _{Infrared spectrophotometry} 239

6.4.3 _{Structural relaxation and fictive}

temperature 241

6.4.4 _{Discussion 242}

6.5 _{General discussion} 247

References 250

CHAPTER 7.29Si _{RELAXATION IN ALKALI SILICATE}

AND ALKALI PHOSPHOSILICATE GLASS AND GLASS CERAMICS

7.1 _{Introduction 255}

7.2 _{Relaxation of} 29Si _{sodium silicate glass}

and glass _ceramics 256

7.2.1 29Si _{relaxation as a function of alkali}

content

256

7.2.2

29Si

_relaxation

_{as a function}

_{of heat}

treatment

259

7.3 _{Relaxation of} 29Si _{in lithium silicate}

system 267

Page

7.4 _{Discussion of sodium and lithium silicates}

29Si T1 relaxation times

7.4.1 29Si _{relaxation in xNa2O. 2SiO2 (x = 28.6,} 25.0,20.0)

7.4.2 29Si _{relaxation in heat treated sodium}

disilicates

7.4.3 29Si _{relaxation in lithium silicates}

7.5 _{Effect of P2O5 additions on the} 29Si

relaxation in alkali disilicates

7.5.1 _{Lithium phosphosilicates}

7.5.2 _{Sodium phosphosilicates}

7.5.3 _{Potassium phosphosilicates}

7.6 _{24scussion of the alkali phosphosilicates}

Si relaxation

7.6.1 _{Low (1-4 moll) P205}

7.6.2 _High ( _{50,60 mol ) P205}

7.7 _General discussion

References

CHAPTER 8: CONCLUSION

8.1 _{Comparison of glass systems}

8.2 _{NMR as a tool for glass ceramists}

8.3 _{Proposal for future work}

References

Appendix _A

267

267

273

274

275 275 275 279

279 279 281 282 287

290 293 293 297

298

LIST OF TABLES

Page

3.1 A list _{of the reference materials used for}

the study of different nuclei 79

3.2 _{Sample composition, preparation and state}

of the glasses and crystalline material

studied

87

3.3 Chemically _{analysed compositions of the}

glasses 97

4.1 29Si _{NMR data for L12O-SiO2 system} 107

4.2 _{Spectral parameters for} 7Li _{in conventionally}

prepared lithium silicate glasses 115

4.3 _{Spectral parameters and composition of}

lithium _{silicate glass ceramics} 119

4.4 7Li _{spectral parameters in lithium silicate 124}

glass ceramics

4.5 _{Data for glass transition temperature, T,}

crystallisation temperature, T _{and liqýidus}

temperature, Tls in lithium _{silicate glasses} 127

4.6 29Si _{NMR spectral parameters of sol-gel}

prepared lithium _{silicate glasses} 133

4.7 _{Data for} 1H _{NMR in sol-gel glasses} 135(a)

5.1 _{Spectral parameters, relaxation times, Tg,}

Tx and Tls of Na20.2SiO2. xMnO

5.2 _{Spectral parameters and Si-O-Si mean bond} angle _of Na2Si2O5 _polymorphs

6.1 29Si _and 31P _{MAS NMR data for lithium}

phosphosilicate _{glasses and glass ceramics}

6.2 29Si _{composition and spectral properties c}

sodium phosphosilicate _{glasses and glass} ceramics

6.3 31P _and 23Na _{MAS NMR spectral parameters}

and compositions _{of the phosphate groups} i sodium phosphosilicate _{glasses and glass}

ceramics

6.4 29Si _and 31P _spectral

characteristics and

compositions _{of the silicate and phosphate} groups in potassium _{phosphosilicate glasse}

-vi-

Tx and Tls of Na20.2SiO2. xMnO

0

₁₄₆

5.2 _{Spectral parameters and Si-O-Si mean bond}

angle _{of Na2Si2O5 polymorphs} 154

6.1 29Si _and 31P _{MAS NMR data for lithium}

phosphosilicate _{glasses and glass ceramics} 177

6.2 29Si _{composition and spectral properties of}

sodium phosphosilicate _{glasses and glass}

ceramics 183

6.3 31P _and 23Na _{MAS NMR spectral parameters}

and compositions _{of the phosphate groups} in sodium phosphosilicate _{glasses and glass}

ceramics

189

6.4

29Si

_and

31P

_spectral

characteristics

and

compositions _{of the silicate and phosphate}

Page

6.5 29Si _{spectral properties of sodium}

disilicate _{base glasses with differing}

phosphorus contents 206

6.6 31P, 23Na _and 27A1 _{spectral properties of}

sodium phosphosilicate glasses 212

6.7 _{Spectral characteristics and crystalline} state of sodium phosphosilicate _glass

ceramics 222

6.8 _{The glass transition, crystallisation and} liquidus _{temperature of sodium phospho-}

silicate glasses 238

6.9 _{Data for fictive temperature and structural} relaxation due to various cooling rate in

sodium _{phosphosilicates} 245

7.1 29Si _{relaxation times and compositions of}

Qm species in sodium silicates 258

7.2 29Si _{relaxation times and compositions in}

sodium disilicate base and heat treated

glasses 261

7.3 _{Data for the} 29Si _{relaxation times and}

compositions _{of Qm species} in lithium

silicates 270

7.4 _{Relaxation times and compositions of alkali}

phosphosilicates 280

LIST OF FIGURES

Page

1.1 Relation between _{the glassy,} liquid _and

solid states (taken from ref. 2). 4

1.2 Effect _{of temperature on rates of}

nucleation and crystal growth (taken

from _ref. 2). 4

1.3 _{A model of vitreous silica, and (inset)}

a tetrahedral unit (taken from ref. 9). 6

1.4 Phase diagrams _{of alkali silicate glasses}

(taken _{from ref. 14). 8}

1.5 Line _{narrowing of} 23Na _{nucleus in sodium}

disilicate _{crystalline material due to} magic angle spinning. (a) Spinning

(b) _{Static. 19}

1.6 29Si _{resonance of 24.6Li2O.} 75.3SiO ₂ (a) Heat _{treated at 525°C/6h and (b) glass}

showing the line narrowing due to the presence of crystalline L12Si2O5.19

2.1 (a) Precession _{of a magnetic moment about a}

fixed _magnetic field _{BO. (b) The effect of}

off-resonance pulse. 37

2.2 _{Splitting of energy} levels _{of I=} 3/2 due

to Zeeman and quadrupolar interactions. 37

2.3 Nuclear _{magnetic resonance powder line shapes} in _solids for different _asymmetry. (a) _to (e) are shown for _{call x w21 and} (f) is for _axially

symmetric ( wl 1= w22

. Solid lines are

drawn with additional Tine broadening. 40

2.4 Powder _pattern for _{proton resonance in gypsum.} The broken line _{is theoretical shape} (equ.

2.41) _{and the solid line is gaussian broadening}

superimposed (ref. 17). 42

2.5 (a) First _{order quadrupolar powder pattern}

for _I= 3/2 _{and q= 0. (b) Second order pattern}

for _{the centre band. v=e qQ/2h and A=}

(a-3/4)

_{vQý/16 vL (ref.}

Q15).

₄₂

2.6

_{Redu2bion of chemical}

_shift

_anisotropy

_from

the Si spectra _{of crystalline Li20.2SiO2.48}

2.7 Reduction _{of dipolar interaction from the} 31p

spectra of L13P04. _{There may be little}

chemical _{shift anisotropy as well. 48}

Page

2.8 Reduction _of first _{orger quadrupolar}

interaction from _{the Li spectra of lithium} disilicate _{glass. There is non-homogeneous}

dipolar _{interaction as well. 51}

2.9 Reduction _{of secggd order quadrupolar} inter-

action from the Na spectra of crystalline Na20.2SiO2.51

2.10 _{Contour plots of p versus µ for the ratio of} first _{pair of sidebands to the isotropic}

line (ref. 32). ₅₄

2.11 Graphical _{analysis of the sidebands of}

Na20.2SiO2.2P2O5 _{glass. 54}

3.1 (a) _{Magnetisation M in laboratory frame} before _{application of the pulse.}

_(b) A n/? pulse rotgtgs the magnetisation M from 0Z

ax}s to 0Y axis when pulse is applied along (X

, 0,0) direction. (c) Dephasing of magnetic moments with time following _a n/2 _pulse

showing decaying _of the _{output signal.} (d)

Input _{pulse applied to} (b). (e) _{Dephasing of} magnetic moments continues _until t» T2 T. (f)

Exponential FID _{corresponding to} (c) _and (e).

(g) _{Fourier transforms of the FID shown in (f). 66}

3.2 _Schematic diagram _{of a PFT NMR spectrometer.} 66

3.3 _{The basic components of the bruker MSL-360}

spectrometer. 68

3.4 _Block diagram _{showing the operation of a}

single coil _probe. 71

3.5 _{Different types of spinners used in (a) DB,}

(b) mushroom, (c) _{home made and (d) Doty probe.}

All _{the scale is in mm. 71}

3.6 _{Setting the magic angle using} 79Br _{resonance in}

KBr. (a) _{At the magic angle, (b) close to the} magic angle _{and (c) on resonance} FID beyond _the

magic angle. 74

3.7 _{Signal corresponding to ( n/2)Xand (n /2)Y}

pulse (ref. 4) ₇₈

3.8

(a) Pulse sequence for saturation

_recovery

method.

(b) Increase

_{of signal}

height

_{due to}

increase _{of relaxation delays (t) in} Li20.2Si0

. O. 1Mn0 (LS3) base glass

(tl

_{< t2}

_{t3 < ---}

_{< t17).}

₈₄

3.9 _{A typical DTA curve}

showing the transformation

temperatures ₉₂

Page

3.10 _{Heat capacity vs. temperature} for

16.67Na 0.33.33Si02

. 50.0P 05 glass determined at a heating rate 773°K/h? The line indicating

the difference between _{two areas of equ.} 3.12

represents the fictive temperature, Tf. 92

4.1 29Si _{spectra of lithium silicate glasses as}

prepared: (a) spinning and (b) static. The

actual compositions are given in the figure. 106

4.2 _{Chemical shifts} (S) _ranges for 29Si _in

lithium _silicate (a) _{glass and (b) crystalline}

Qm species. The data for _{Q0 and Q1 are taken} from _ref. 14.109

4.3 _{Variation in Qm chemical shift as a function of}

Li20 _{content in the lithium silicate glasses.} 110

4.4 _Computer fitting (----) _{of the observed} 29Si

spectrum from glass LS3 () to a combination

of Q3

Q2 (---)

and Q4 (-"-"-).

112

4.5 _{Variation in concentration of Qm species as a}

function _{of Li20 content.} 114

4.6 7Li _{spectra of Li2O-SiO2 base glasses} (a)

spinning (b) static. Analysed compositions are

indicated _{in the diagram.} 116

4.7 29Si _{spectra of lithium silicate glasses} (a)

LS1 (b) LS2 (c) _{LS3 (d) LS4 and (e) LS5 after}

6 hours heat _treatment (1 = as cast, 2= 425°C,

3= 475°C, 4= _{525°C 5= 575°C). 118}

,

4.8 _{Variation in} (a) _{Q4 chemical shift} (b) _{Q h}

alf chemical shift _{and (c)} Q3 full _{width at}

maximum as a function _{of heat} treatment

temperatures for 6 hours _{and in comparison with}

(d) _{the DTA curve for the glass LS3. 120}

4.9 (a) 29Si _{MAS spectrum of crystalline LS3. (b)} Computer fitting _{of the observed a- and}

polymorphs in (a). Dots represent 12 i2

S a

experimental _points.

ex 122

4.10 _Computer fitting _{(---) of the observed} 29Si spectrum (static) from _{crystalline LS3 to a} combination _{of a-} Li2Si2O5 (-"""-) _and

ß-

_{L12Si2O5 (---).}

₁₂₂

4.11

7L1

_spectra

_{of heat treated}

_lithium

_silicate

glasses (a) _spinning (b) _static (c) 1. A

simulation _{of t1e +1/2l-"--1/2 and +3/2. '-+1/2}

transitions _{of Li in crystalline} ES3,2. _with 2500 Hz dipolar _{broadening and 3. the observed}

spectrum. ₁₂₅

Page 4.12 29Si _{MAS spectra of sol-gel prepared} lithium

silicate glasses 134

4.13 7Li _{spectra of sol-gel prepared} lithium

silicate glasses 136

4.14 1H _{spectra of sol-gel prepared} (a)

33.3Li2O. 66.7SiO2 (b) 25. OLi2O. 75. OSiO2 (c)

10.0Li20.90. _{OSiO2 glasses and (d)} LiOH. H20.136

5.1 29Si _{spectra of Na20.2SiO2 glasses with}

varying amounts of MnO. 144

5.2 29Si _relaxation decay of sodium disilicates

with different amounts of MnO. In order to prevent overlapping (MO - MZ) _{of each plot}

is _shifted. 147

5.3 29Si relaxation rate as a function of MnO

content in sodium disilicate base glasses. 148

5.4 Variation _of (a) full _{width at half maximum}

(FWHM) and chemical shift (CS) with MnO content

in sodium disilicate base glasses. 150

5.5 _{DTA traces of sodium} disilicate _{glasses with}

(a) _{no MnO (b) 0.1 mol% MnO and (c) 0.4 mol%}

MnO. Peak heights _{are normalised.} 150

5.6

29Si

_spectra

_{of heat treated}

_{sodium disilicate}

glasses. 152

5.7 29Si _{static spectra of sodium} qýsilicate (a)

base _glass (b) _crystaline (c) _{Si MAS spectra}

of (b) and inset is an extended form _{of centre}

band. 153

5.8 Variation _{of the} 29g _{chemical, shift with} (a)

mean sec and (b) a, _{where a=} Si-O-Si bond

angle. 156

5.9 23Na _{spectra of Na2Si2O5 glass and glass}

ceramics. 157

6.1 29Si _{spectra of lithium phosphosilicate} (a)

base glasses, (b) _{LSP1 and (c) LSP4 (a) heat}

treated _{at various temperatures.} 174

6.2 31P _{spectra of lithium phosphosilicate glass}

and glass ceramics. (a) _{Base glasses} (b) LSP1 and (c) LSP4 (a) heat _{treated at various}

temperatures. ₁₇₆

6.3 7Li _{spectra of lithium}

phosphosilicate glasses (a) _{glass (static) (b)}

crystalline (static)

(c) _{crystalline (spinning). 179}

Page

6.4 29Si _{spectra of sodium phosphosilicate glasses. 181}

6.5 29Si _{spectra of heat treated sodium phospho-}

silicate _glasses. 182

6.6 31P _{spectra of} (a) _{sodium phosphosilicate} base glasses (b) NSP3 heat treated at various

temperatures. The isotropic _{peaks are marked}

at 10 and the rests are spinning sidebands (SS). 185

6.7 _{Formation of orthophosphate and pyrophosphate}

in sodium disilicate _{base glasses with} 1-8 moll P205.187

6.8 23Na _{spectra of sodium phosphosilicate glasses. 188}

6.9 (a) 29Si _{and (b)} 31P _{spectra of potassium}

phosphosilicate _glasses. All the isotropic peaks are assigned according to their

respective environments. The other peaks are

spinning sidebands. 191

6.10 _{A comparison of the crystalline} (a) _{L12O. 2SiO2}

and (b) Li20.2SiO2.1P205 _{static spectra.} 195

6.11 _{A schematic structural model of sodium}

disilicate _{glass with 1- 10 moll P205. The}

amorphous tetrahedral framework is after P. H.

Gaskell, Phil. _Mag., 32,211 (1975). 202

6.12 29Si _{spectra of sodium disilicate base glasses}

with

(a) 8-25 moll P205 and (b) 25-57 mol%

P205" ₂₀₅

6.13 31P _{spectra of sodium disilicate base glasses} with (a) 8-25 _{mol %P 05 and (b)} 25-57 _mol%

P205. _{The Isotropic} U0) _{lines are}

c aracteristics _{of respective environments.}

The other peaks _{are spinning sidebands} (SS). 209

6.14 23Na _{spectra of sodium disilicate base glasses} with varying _{amounts of P205.211}

6.15 27A1 _{spectra of sodium phosphosilicate glasses.}

(a) _{11-25 mol% P205 and (b) 25-70 mold P205.214} 6.16 29Si _{spectra of heat treated high P205}

(< 25 mol%) containing _sodium disilicate

glasses. ₂₁₆

6.17 31P _{spectra of heat treated (a) Na20.2Si02.} 25P20 (NSP9)9 _{(b) Na20.2Si02}

. 38.1P 05 (NSPlä), (c) _Na20.2Si02

. 46.8;

*

; 205 (N P11)

and (d) Na20.2S302.57.3P205 (? SP12) glasses. ₂₁₇

Page 6.18 23Na _{spectra of heat treated} (a) Na20.2SiO2 _.

25P205 (NSP9), (b) Na20.2Si02 _. 38.1P20 (NSP10) (c) _{Na 0.2Si02.46.8P2D5} (NSPi1) _{and (d) Nä20.}

2Si02.57.3P205 _(NSP12)

glasses. 219

6.19 27A1 spectra of heat treated (a) Na20.2SiO2 . 25P205 (NSP9), (b) _Na20.2Si02

. 38.1P2O(NSP10),

(c) _{Na20.2Si02.46.8P205} (NSPI1) _{and (a) Na20.}

2SiO2.57.3P2O5 (NSP12) _glasses. 221

6.20 _X-ray diffraction _{patterns of heat treated}

sodium disilicate glasses with (a) 46.78 mol%

and (b) 57.26 mol% P205 224

6.21 _{Variation of (a) chemicjl shft and ýD) FWHM}

with P205 content for Na, P and Si

resonances in Na20.2SiO2. ZP205 (Z =1 to 57)

glasses. 234

6.22 _{Infrared spectra of Na20.2SiO2. ZP205 (Z =}

0 to 57) glasses. 240

6.23 _{MAS NMR spectra of} 29Si _{in Na20.2SiO2.6OP205} prepared with different fictive temperatures

(a) _{poured into liquid N2}

, other samples

splat cooled at (b) _-10°C, (c) +30°C, (d)

+100°C, (e) +200°C, (f) _+400°C. 243

6.24 _{Variation of six and four coordination of} silicon in Na20.2SiO2.60P2O5 _with fictive

temperature.

244

7.1 29Si _{relaxation in Q3 of varying modifier}

content sodium _silicate base _glasses. The

plots have been shifted _{arbitrarily to prevent}

overlapping.

The difference

between curved

and straight _{portion of the plots are} presented by the broken lines.

(b) _{to (d) are nominal compositions 257}

7.2 29Si _{relaxation time in Q as a function of} Na20 content in _{sodium silicate base glasses.}

Solid line is for long _{component and broken}

line _is for _{short component. 260}

7.3 29Si _{relaxation decay of 32.7Na2O. 67.3SiO2}

(NS1) for _{various heat treatments. Successive} curves have been displaced _{vertically one}

cycle to prevent _overlapping. Broken lines

are obtained as Figure 7.1. 263

7.4

29Si

_relaxation

_{decay of 32.6Na2O. 67.3SiO2}

O. lMnO (NS3) _{for various heat treatments. Each}

of the plots has been shifted _{by two cycles. 264}

Page

7.5

29Si

_relaxation

_{decay of 32.1Na20.67.7Si02}

0.2MnO (NS4) for _{various heat treatments. Each}

of the plots has been shifted by two cycles. 265

7.6 Variation _of long _{and short component}

relaxation times _with heat treatment (a)

temperature _{and (b) time} in Na20.2Sio2.0. lMnO

(NS3) base glass. 266

7.7 29Si _{relaxation in lithium silicates. Each}

plot is shifted by one cycle. The broken lines

are obtained as before (Fig. 7.1). 268

7.8 29Si _{spectra of 24.6Li2O. 75.3SiO2O. lMnO} (LS1) (a) _{base glass and (b) heat treated}

at 475°C/6h (LS1H) for _various delays. 269

7.9 29Si _relaxation decay _{in lithium phos-}

phosilicates. The difference between

curved _{and straight portion} is _{shown by}

inset. ₂₇₆

7.10 29Si _relaxation decay _{in sodium disilicate} with low amounts of P205. The difference

between _{curved and straight line is shown}

by inset. ₂₇₇

7.11 29Si _{relaxation decay in (a) 16.67Na2O. 33.} 33SiO2.50. OP20 _{and (b) 13.33Na O. 26.67SiO2.} 60.0P205. (" _{Q4 -P and (0 Si06}

- P. b. III is _{the difference between the curved} and straight _{portion of the lines.} Error

bars for (b) _{are the same as (a). 278}

7.12 _{Variation of fictive temperature, Tf with}

Na20 in sodium silicate _sysQm (ref. _{48). 283}

7.13

_Transmission

_electron

_micrographs

_{of 24.6}

Li2O. 75.3SiO2 _{sample. (a) Base glass;}

original mag. *66000. (b) Heat _{treated at}

475 C/6h; _{original mag. *50000. (c) Selected} area diffraction _{pattern of} (b) _showing

broad _{intensity maximum. 285}

8.1 _{A comparison of the amounts of observed Qm}

species with the constrained distribution

() _{and unconstrained distribution}

(-.

-. -) models. Experimental data are indicated

as

O (Q4),

"

(Q3) and

_{0 (Q2).}

₂₉₂

ACKNOWLEDGEMENTS

I _would like _{to thank the} Commonwealth Scholarship

Commission in _the United Kingdom for _{providing me with the} financial _{support and the} Department _of Physics _{at the} University _of Warwick for _{providing the research} facilities.

I _{would also} like _to thank _{my fellow countrymen and women,} studying at this University, for their friendship.

The _{technical assistance throughout the course of this} research was invaluable and I am deeply _grateful to Mr. B.

Sheffield, Mr. H. J. Mathers, Mr. R. Lamb _and Mr. D. Goodman. I _wish to _{express my sincere} thanks to Dr. P. F. James, Sheffield University for _{encouraging me to} investigate _the sol-gel prepared lithium silicate glasses and also kindly

providing me with the samples. I am grateful to _all the members of NMR coffee club for providing me with _{a pleasant}

company. I am extremely grateful to Dr. A. T. Boothroyd, Dr. P. R. Dennison, Dr. M. T. _-El-Gemal, Dr. A. P. Kemp, _Mr. A. Boukara _{and Mr.} K. J. Barnfather for _their friendly _cooperation

during _{my work.} I _{particularly thank} Prof. E. F. W. Seymour,

Dr. G. Styles, Dr. D. Mac. Paul, Prof. S. B. Palmer _{and Dr.} H. Mykura for _{encouraging and} inspiring _{me during} the _{period of}

this _study. I _{am deeply grateful} to Miss L. Lucas for her patience and skilful typing of this thesis.

I am particularly indebted _to Dr. M. E. Smith _{and Dr.} I. Farnan _{who were always} happy _to discuss _topics in _{NMR and made} many invaluable suggestions. By far my greatest debts are to my supervisors Dr. Raymond Dupree and Dr. Diane Holland whose

excellent guidance, interest and inspiration made this study possible and made a rewarding experience.

DECLARATION

The _{work presented} here _{was carried out at the}

Department _{of Physics,} University _{of Warwick} from October 1985 to September 1988 under the _{supervision of} Dr. R. Dupree _and Dr. D. Holland. _{The results are outcome of my own independent}

research unless otherwise specified in the text _{and has not}

been submitted for _{any other} degrees. _{A fraction of the work}

of paper numbers 3 and 4 (see below) was carried _out in

collaboration with J. A. Collins _and M. W. G. Lockyer is _not included _{in this thesis.}

Some parts of the thesis have been published, _accepted for _{publication and submitted} for _{publication as follows :}

1) "Six _{Coordinated Silicon in Glasses".}

R. Dupree, D. Holland _{and M. G. Mortuza} Nature, 328,416 (1987).

2) "The _{Role of Small Amounts of P205 in the Structure} of Alkali Disilicate Glasses".

R. Dupree, D. Holland _{and M. G. Mortuza} Phys. Chem. Glasses, 29(1), 18 (1988).

3) "An MAS NMR Study _{of Network-Cation Coordination} in Phosphosilicate _Glasses".

R. Dupree, _{D. Holland, M. G. Mortuza, J. A. Collins} and M. W. G. Lockyer

J. Non-Cryst. _{Solids, 106,403} (1988).

4) _{"Magic Angle Spinning NMR of Alkali Phospho-} alumino-Silicate Glasses".

R. Dupree, D. Holland, _{M. G. Mortuza,} J. A. Collins _{and M. W. G. Lockyer}

J. Non-Cryst. _{Solids, 1989 (in press).}

5) "A MAS NMR Investigation _{of Lithium Silicate} Glasses".

R. Dupree, _{D. Holland and M. G. Mortuza} J. Non-Cryst. _{Solids, 1989 (submitted).}

It is _{anticipated that some more of the experimental} results will be submitted for _publication in _{the future.}

ABSTRACT

The _potential for the _{use of} MAS and _static NMR in the investigation _{of alkali silicate and alkali phosphosilicate} glasses and glass ceramics is the main theme of this thesis. MAS NMR of binary

lithium _{silicate glasses containing} 24-29 _{mol% Li20 shows} that their structure follows the constrained distribution model. However addition

of Li20 in excess of 29 mol% causes deviation from the model and a concentration dependent disproportionation of Q3 to Q4+Q2 occurs. This is observable from MAS NMR in combination with static NMR results. The devitrification _of these _{glasses produces} two _{polymorphs of} lithium

disilicate. The structural _changes during heat treatment _{occur aNve} the _glass transition temperature and are observed from the Si chemical shift and full width at half maximum. The static Li spectra

for _{the crystallised samples exhibit a Pake doublet} indicative _of the presence of Li pairs.

The effect of paramagnetic impurity from 0-0.8 mol% on the 29Si T1 relaxation times in Na20.2SiO2 base glasses is discussed.

The heat treatment _of the _sodium disilicate _{glasses shows a -,} ß-,

Y- _and 6- Na2Si2O5 _as the devitrification _products depending upon

heat treatment. A way of _estimating the _unknown Si-O-Si _mean bond

angle of the polymorphs is presented.

The _{effect of} the _{addition of} 0-70 _moll P205 _{to alkali} disilicate

glasses is described. Small amounts of P205 (1-10 mol%) in the glasses

results in the scavenging of alkali metal ions by phosphate groups. In

sodium and potassium disilicates the phosphate groups resemble

orthophosphate and pyrophosphate but only orthophosphate like units are

formed in lithium disilicate _glasses. As _{a consequence of} the

scavenging, the silicate network partially repolymerises. A structural

model for the disilicates with (1-10) moll P2OS is presented. For

larger _{concentrations of} P205 (>10 _mol%) in _sodium disilicate _glasses

only metaphosphate species are observed and phosphorus occurs as next

nearest neighbour of silicon. However this arrangement gradually

changes to Si-O-Si bond with _{- 25} moll P 05 and the length of

metaphosphate chain increases. On addition oft greater than about 30

mol% P205 some of the network silicon changes radically from its

conventional four coordination to six coordination. Both the

tetrahedral and octahedral environments _{of silicon} at these

concentrations are characteristic of mainly Si-O-P bonds. The six

coordinated silicon occupies a SiPZO7 like environment. The proportion

of "SiP2O7" depends upon the alkali content and the cooling rate. The

cooling rates cause structural relaxation and are used to measure

fictive temperature. This _{gives an estimate of the change of enthalpy}

for the _conversion of one mole of _{six coordinated silicon} from four

coordinated silicon.

The 29Si T1 relaxation _{times in alkali silicate glass, glass} ceramics and alkali phosphosilicates are presented. The T1 in sodium disilicate _{glasses as a function of MnO content is a single exponential}

but _{a two component} T1 is _{observed after} heat _{treatment. The single} component relaxation times for the disilicate composition range becomes

two component as the Na20 content is _reduced. The Tl values in _all the lithium _{silicate glasses, glass ceramics and alkali phosphosilicate}

systems are two component. The conversion _of single component exponential to two component because of heat treatment or Na20 content could be due to either nucleation or _{glass-in-glass phase separation.}

Thus the _{possibilities} for _{obtaining new} information _{about phase} separation in glasses are also briefly discussed _with the help _{of TEM} micrographs.

CHAPTER 1

1.1 GENERAL

Glasses _{are characterised} by the _{absence of} long _range

order in their structure and so consequently determination of structure is difficult. Unlike crystalline materials

determination _{of the position of an atom} is _{not of primary}

interest because the _{whole structure cannot} be expressed _{as a} multiple of a unit cell. The glass structure can be described

as a three dimensional configuration of a variety of species termed _network formers.

Normally in _{silicate glasses the network} former is _the

Si04 tetrahedron. Unlike the _{unit cell} in _{a crystalline}

lattice _{the local order of the network} former, i. e. bond angle and bond length, may vary. Addition of a network modifier,

e. g. Na209 alters the silicon environment and produces

different types _{of species.} Therefore identification _of the

nearest and next nearest neighbour of the network former,

number of species, co-ordination number and a comparison with

the _respective crystal _structure is the _major interest for

spectroscopists or material scientists. With this in mind the simple binary alkali silicate system has primarily been chosen

in this _work to interpret the framework _{structure, mainly} by

means of the nuclear magnetic resonance (NMR) technique.

1.2 GLASS AND GLASS CERAMICS

Glass _can be formed from _{a melt of one or more glass} forming _oxides by cooling _{at a sufficient rate to prevent the}

formation _{of crystalline structure} [1-4]. _{The cooling is}

directly _{related to the volume temperature characteristics} [4]

as shown in Figure (1.1). In the _{region AB the product} is

liquid _{and the viscosity of the melt} is _{comparable to that of}

water. If the melt cools without crystallisation, the

decrease in _volume follows _{the path BE. The product within}

this _region is _{called a supercooled} liquid. The viscosity _of

the _product increases with the decrease _of temperature.

However, _{a sudden change of volume may occur along the path} BC

at a particular temperature T' if the cooling process is

accompanied by crystallisation. Further decrease of

temperature _results either in _glass (EF) _or crystal (CD)

formation depending _{upon the contraction of volume along the}

path BE or BC in the diagram (Figure 1.1). The temperature at

the _point E is _called the _glass transition temperature, Tg.

Thus for _{a melt} to form _{a glass} it has to exhibit _{this glass}

transition _property during _cooling. The contraction _{of volume}

along the extrapolation EG or ABE continues if the material is held _{at the temperature T, a little} below _{Tg. The value of Tg}

is not well defined and depends _{upon the rate of cooling.}

The _glass forming _{oxides are classified into three}

categories : (i) network former, (ii) _{network modifier,} and

(iii) _{intermediate. The principal characteristic of the}

network former is the tetrahedral _{structural arrangement} in

the crystalline state, _{e. g. Si02,} P205, _{B203 and Ge02 [5] etc.}

The _{tetrahedral configuration of the network former is not}

strictly valid because there _{are some oxides, e. g. BeO, which} do not form glass [6]. _{The modifier oxides, e. g. Na20,} Li20, normally break the long chain _{order and weakens the network of}

the _glass. In the case of an intermediate _{oxide, e. g. A1203,} Al occupies the _network former _{position in the glass [1] but}

the _oxide itself does _{not form glass. Geometrical}

considerations, bonding _{criteria, nucleation kinetics of the}

oxides affect the glass forming region. Consequently the amounts of the chemical compositions of glasses varies from one form of oxide to another.

Glass _{ceramics are polycrystalline materials which can}

be produced by controlled crystallisation of glasses [1]. The

process of crystallisation is mainly concerned with nucleation

and the rate of crystal growth. A typical diagram for the

nucleation and the crystal growth is shown in Figure (1.2). The nucleation can be classified _{as (i)} homogeneous nucleation

and (ii) heterogeneous nucleation. Homogeneous nucleation is

generally caused by fluctuation in ion concentration of the

parent liquid phase. This condition is difficult to achieve

because _{glass compositions are not normally} free from foreign

particles. The general equation to express the rate of

homogeneous _{nucleation is given by Becker} [7] _as

I=A _{exp (-} &G/kT) _{exp (-E/kT)}

... ... (1.1)

where A is a constant, AG is the _maximum free energy of

activation for formation of _{a stable nucleus} in the system, E is _{the activation energy required to diffuse molecules across}

the _phase boundary, k is the Boltzmann _{constant and T is} the temperature.

Heterogeneous _{nucleation is a result of the presence of} foreign _{particles and doped materials in the glass melt which}

often behave as nuclei. Epitaxial _{crystal growth may occur}

due _{to presence of these nuclei. The rate of heterogeneous} nucleation is given by [81

I=B

_exp[-(

_{AGf(G) + E)/kT]}

...

_...

_...

(1.2)

where B is a constant _{and the term} f(A) _{is given by}

Liqu$//`4

Supercooled

B liquid

0 a E

Glass

_ýº

C

CL

v

F'

Crystal-1' E

ö _ii

T

_{Tg T}

Temperature ₀

Figure 1.1 Relation between the glassy, liquid

and solid states( taken from ref. 2 ).

Equilibrium _{melting temperature}

Metastable _{zone of supercooling}

Rate of crystal growth

or

0

ä E H

T3

Rate of homogeneous nucleation

Rates of nucleation and growth

Figure 1.2 _{Effect of temperature on rates of} nucleation _{and crystal growth(} taken

from _{ref. 2 ).}

f(9) _{= (2 + cos9)} (1 - cos8)2/4 _{... 000} (1.3)

where 0 is the contact angle at the substrate-melt-precipitate

junction.

A detailed discussion _{of the} formation _{of glass, glass-}

ceramics, nucleation, crystallisation etc. can be found

elsewhere [1-4] and these are not discussed here in detail.

1.3 MODELS FOR GLASS STRUCTURE

The _random distribution _{of atoms prevents material} scientists from determining an absolute structure of glass.

Goldschmidt's _prediction [5] followed by the _work of Zachariasen [6] led _scientists to believe that the framework

of silicate glasses consists of S104 tetrahedra. These S104 tetrahedra _are randomly linked together by _means of Si-O-Si

bonds [9] _{as shown} in Figure (1.3). _{Incorporation of modifier} oxides breaks up Si-O-Si bonding and converts some bridging

oxygens [bo] to non-bridging oxygens [nbo] [6]. The configuration depending upon the _{number of} [nbo] associated

with the network former S14+ is _generally described by the nomenclature Qm [10], where m determines the number of [nbo]

connected to S14+ (Q), i. e. for tetrahedral silicon 0<m<4. Therefore, there _are five _{possible Q species present} in amorphous or crystalline states.

In _order to determine _{the number of species or the}

structure of glasses several _models have been proposed _:

i) Statistical _distribution [11] _{- the distribution}

of

[nbo]

per

silicon

is

determined

from

_probability

_and

composition.

ii)

Constrained

_{random [12] - normally}

_only

_{2Q species}

Figure 1.3 _{A model of vitreous silica, and} (inset)

a tetrahedral unit (taken from ref. 9).

form _where [nbo] _{are homogeneously} distributed. The form _of Qm depends _{upon the composition.}

iii) Mixed Cluster [13] _{- species appear as clusters.}

The _models (i) and (ii) give a means of detecting _and

quantifying the species present in glasses for a particular

composition. These two models give extremes of a continuum of

possibilities. At high enough temperatures, if the

composition forms a glass, a statistical distribution would be

best. However _{at room} temperature _{an intermediate state of}

the two models may be obtained. Experimental evidence for the cluster model to date has not been provided.

1.4 ALKALI SILICATE GLASSES _{: THEIR} FORMATION AND PHASE DIAGRAMS

The building block _of the _{alkali silicate} (R20-SiO2; R= Li, Na, K. Rb, Cs) _system is the Si04 tetrahedron. According

to the _phase diagrams [14] and an assumption considered by Grimmer _{et al.} [15] for the R20-Si02 _systems (Figure 1.4)

there _{exist crystalline} compounds of S104, R2Si2O5, R2SiO3,

R6Si2O7 _and R4Si04 _{corresponding} to Q4, Q3, Q2, Q1 _and Q0 environments. These possible Q species can be shown

structurally as [11]

i

0

i

Q4

0

i

0

Q3 = -O-Si-O-R+;

0

0-R+ Q2 = -0-ii-0-R+

0

0-R+

Q1 = R+--Si-O-R+ _; 0

0-R+ QD = R+O--Si-O-R

0-R+

1500

1300

Li2O+Itquid\,

Liquid

1255 Li4SlO4+liquid

1201 E

1200

ý, 1

Cristobalite + liquid

a äl

1470

Tridymite + liquid

s Li2Si+ liquid

1100

p ₁₀₂₄

[1033

1029

000 LizSi03+

I

Tridymite+LizSi20y Li45iO4+LIZSiO3 Li2Si2O5 ₉₆₀

939

900. _f

40 60 80 II

ý-Li20

Cristobalite + liquid

1500 11470'

Liquid

e 1200 NaZO 2Na2O"SiOZ

+ liquid _{+ liquid}

Naz0 Sioz _Tridymite + liquid _{+ liquid} 1100 a E W I- Si02 Liquid x 1400

1100- Z;

ý 1000

900 N _o

t N

lo

'

800 x_

__ Yl

40 50 60

+K20

Gistobalite +Ilgwid

Tridymite + liquid

_Tridy_mite Quartz PO-4SiO2 : -L I

80 90 ₁₀₀

Sic2

No20.2SiOZ 2Na20"Si02 +liquid

900+ _{NoZO"Si0= 867'} Q8

-Q1 _{Ouortz+liquid} 800 _N N020 2S10z

N+

ä _{in No2O"Si02 N} Noz0 2Si0z+0uortz

CL _N

700 Q{ö 707'

NQ0 II 678'

2M Q3 + Q4

30 40 50 60 70 80 _{90 100}

- --Nazo S'Io2

Figure 1.4 _{Phase diagrams of alkali silicate} glasses( _taken from _ref. 14 ).

The present work deals with the first three _{alkali metal} ions and in the future R will stand for Li, Na and K only.

In _{glasses all these environments} do _{not exist.}

Formation _of [nbo] _within the _{continuous three} dimensional

network of Si04 NO tetrahedra presents _{a discontinuity} in

the _network. Among the Qm species Q0 is _{an isolated} Si04

tetrahedron. Thus formation _{of glass with orthosilicate} (Q0)

environment is difficult because that _{could readily undergo}

crystallisation. The Q1 species is a dimer _{structure and the} structural unit may be shown as

0-R+ _0-R+

R+0- _-

Si

-0-

Si-

0-R+

0

R+

0-R+

Thus there is _{a lack of long chains and the} formation _{of glass}

has also become difficult. Incorporation _of large _{amounts of}

R20(>50 _moll) in the S104 network _{reduces the viscosity} [1],

lowers _{the activation energy for crystallisation} [16] _and

hence lies beyond _{the glass forming region. However, in}

general, long chains exist for Q2, Q3 _{species and} the

formation _{of alkali silicate glasses with Q2, Q3 and Q4 is}

possible. The glass formation _{region also} depends _upon the

type _{of alkali oxide added to the parent network, amount of a} batch _{and the rate of cooling.}

In _{the phase} diagrams (Figure _{1.4) of R20-SiO2 systems} there is _{no common feature about the} formation _{of Qm species.}

The _{regions of} formation _{of Q3 and Q2 species in alkali}

silicates become wider _{with the size of the alkali atom. This} could be the effect _{of steric} hindrances (K>Na>Li) _{which could} broaden _{the glass forming region.}

1.5 HIGH RESOLUTION NMR IN SILICATE GLASSES AND GLASS- CERAMICS

Nuclear _{magnetic resonance} (NMR) is the _{spectroscopy of} magnetic materials that possess nuclear magnetic moments.

Gorter _{and Broer} [14] first tried to establish the _phenomenon

but _{the experiment was unsuccessful.} However the _{effect was}

demonstrated independently by Purcell _{et al.} [18] _{and Bloch et} al. [19]. The NMR signal depends upon the population

difference between two _energy levels. In _{an external magnetic}

field _{the nuclear spins} follow the Boltzmann distribution _and for 31P _{the population} difference is _only 23 in 106 in _{a field}

of 8.45T. In spite of the low sensitivity NMR spectroscopy plays an important role in structural investigation of liquid

and solid state materials through high resolution NMR and

relaxation time measurements.

The _resonance frequencies _{of slightly} different

environments are different [20-22]. However the presence of

broadening _{may prevent} their _observation. In liquids _well

resolved NMR spectral detail can be obtained because of the

random motion of the atoms, ions and molecules which averages

the _various broadening interactions and provides narrow

resonances. In the case of solids such phenomena do not often

occur and very broad lines are obtained. Solid samples may be obtained either as single crystals or as powders. The former

is not always available _{and is not appropriate} to glasses.

In _{the early} days _{of NMR, measurement of relaxation}

times _{as a function} of temperature _{was of primary} interest in

polycrystalline samples. However, static (wide line) NMR has

also been applied to obtain _structural information in borate glasses [23-29], alkali borate _glasses [30-34], borophosphate