Solid State NMR Characterisation of Zinc
and Bismuth in Borosilicate Glasses
The Structure of Automotive Obscuration
Enamels
Joanna Higgs
Contents
• Background – Automotive Enamels
– Structure of Glasses
– NMR
• Model Glasses – Aim
– NMR results
– Further Work
2
Background
Automotive Obscuration Enamels
Functions
–
–
–
–
shield glue from UV light
hide silver connections
control of crystallisation to aid manufacturing
aesthetic design
New Product
– must pass strict industry acid tests
– low firing temp. < 600 C
– control of thermal expansion
3
Background
Glass Structure
• Amorphous solid without long
range periodic atomic arrangement.
• Structural units
– depend on the composition
– affect the physical properties.
• Formed of oxides
– network formers e.g. SiO2 and B2O3
– network modifiers e.g. Na2O
– Intermediates
Si
O
Sodium silicate
Na
4
Borosilicate Glasses
• Zinc and bismuth added for physical properties
– NMR literature: alkali borosilicates without these additions
• Effects of zinc and bismuth on the structure
• Commercial samples: no compositional trends
• Zinc and bismuth substitute boron in the compositions
– do they also substitute it in the glass network?
5
Solid State NMR
• NMR: local structure
• Magic Angle Spinning: 54.74 → narrow spectra
– Using 4 → 30 kHz
• NMR Isotropic Chemical Shift δ
• NMR on Quadrupolar nuclei: I > 1/2
– Looking at 11B and 23Na: spin 3/2
– Also 29Si: spin 1/2
6
Borosilicate Glasses
Compositions:
NMR Experiments:
• Base Glass
Basic: single pulse
11B, 23Na, 29Si
63% Si, 16% Na, 21% B
• B + Zn or Bi = 21 mol%
To improve resolution:
• Si + Na ~ constant for all
samples
•
11B
•
11B
• Some contain more Zn and
Bi than commercial glasses
Multiple Quantum
Magic Angle Spinning
(MQMAS)
Double Rotation (DOR)
7
11B
NMR
11.7 T
7.1 T
10 kHz
10 kHz
B4
B4
3.2 mol% ZnO
B3
B3
15.2 mol% Bi2O3
8
11B
NMR
Zinc
Bismuth
75
75
11.75 T
7.05 T
B4 Relative Abundance / %
70
65
65
60
60
55
55
50
50
45
45
40
40
35
0
5
10
mol% ZnO
15
11.7 T
7.05 T
70
20
35
0
5
10
15
20
mol% Bi2O3
9
11B
– MQMAS
Multiple Quantum
Magic Angle Spinning
Base glass
14.1 T
13.9 kHz
1D MAS spectrum
ppm
t1
t1
π/2
π/2
t2
*
0
Projection
B4
20
+3
+2
+1
p= 0
-1
-2
-3
40
60
*
B3
80
100
30
20
10
0
ppm
*spinning sideband
10
11B
– DOR
• More quantitive and sensitive
than MQMAS
• Difficult to spin
• Eliminates line broadening
11.7 T
Base glass
3 B4
Sites
9.4% Bi
3 B4
Sites
2 B3
Sites
2 B3
Sites
*
*
* denote spinning sidebands
*
*
*
*
11
23Na
Lines fitted
in black
NMR
3.2 % Zinc
14.1 T
7.1 T
10 kHz
iso
(ppm)
6
20 kHz
Zinc
4
4
2
2
0
0
-2
-2
-4
-4
-6
-6
14.1 T
9.4 T
7.05 T
-8
5
10
15
20
mol% ZnO
25
30
14.1 T
9.4 T
7.05 T
-8
-10
0
Bismuth
6
35
-10
0
5
10
15
20
25
30
35
mol% Bi 2O3
Increase in electron density → network becomes less connected
12
29Si
NMR
(a)
(b)
3.2 mol% ZnO
3.4 mol% Bi2O3
7.1 T
3.5 kHz
-60
-70
-80
-90
-100
-110
-120
-130
-140
ppm
-60
Weighted Average Chemical Shift (ppm)
-84
-86
-70
-80
-90
-100
-110
-120
-130
-140
ppm
-84
-86
Zinc
-88
-88
-90
-90
-92
-92
-94
-94
-96
-96
-98
-98
-100
-100
Bismuth
-102
-102
0
5
10
15
20
mol% ZnO
25
30
35
0
5
10
15
20
25
30
35
mol% Bi 2O3
Nuclei less shielded → less bridging oxygens → less connected
13
Conclusions
• Roles of zinc and bismuth:
– Bi and Zn not replacing B in the network
– Network is less connected with higher Bi / Zn content
– Bi and Zn acting as network modifiers
• Zinc and bismuth not acting identically
• Further work: zinc and bismuth together
14
Zinc-Bismuth Glasses
4.5
Density g/cm3
ZB1
ZB2
ZB3
ZB4
ZB5
Mol%
SiO₂ B₂O₃ Na₂O Bi₂O₃ ZnO
64.1 6.1 14.3 15.2
0
64.6 5.6 14.5 11.4 3.8
64.2 5.7 14.7
7.7
7.7
64.1 5.9 14.5
3.9 11.5
62.8 5.9 15.3
0
15.9
4
3.5
3
2.5
0
5 Mol% ZnO 10
15
66
64
11B
Relative Abundance B4 / %
62
11.7 T
60
58
56
54
52
50
48
46
30
25
20
15
10
5
0
-5
-10 -15 -20
ppm
0
2
4
6
8
Mol% Bi2O3
10
12
14
16
15
Acknowledgments
• Industrial Supervisors
– Peter Bishop, Jon Booth, Hong Zheng
• University of Warwick Supervisors
– Mark E. Smith, John V. Hanna
• Warwick NMR Group
– Nathan Barrow, Andy Howes
• Funding from EPSRC
Thank you for listening
16