Jo Higgs

NMR of Automotive Obscuration Enamels –

the acid resistance of car windscreens

Introduction

Funded by

Composition → Physical properties → Atomic structure

Contents

• Project background

• Glass

• NMR and what it can tell us

• Results so far

• Flame spray pyrolysis –side project

• What are they?Low melting temp. glass + Pigment + Printing media

• Windscreen glassAlkali borosilicate glass

Zn, Bi, Ti, F

Pb, Cd, Tl, As, Sb

Automotive Obscuration Enamels

• Functions

– UV screen to protect glue

– Hides electrical connections

– Design element

Automotive Obscuration Enamels

• Melting point

• Acid resistance

• Glass weakening

• Cost

• Colour

• Heavy Metals

Optimisation of Glass Properties

Bismuth

– Substitute for lead

– Commercial factor – cost

– Role in glass structure?

– Bismite Bi2O3

Optimisation of Glass Properties

• Pass the 72 hour sulphuric acid test

• Fire in the range 580oC − 660oC

• Contain as little bismuth as possible

• Good opacity/dark colour

Difficult to achieve in a single glass

Desired Properties for a New Product

• Old test

– 3.7% HCl

– 30 min

• Toyota test

– 1% H2SO4

– 80°C

– 72 h

The Toyota Acid Test

Why is the test so severe?

• Amorphous

• Formed from oxides

– Network formers: SiO2, B2O3

– Network modifiers: Na+, Li+

Glass Structure

Sodium borosilcate glasses

• All contain SiO2, B2O3, Na2O

• Project samples – Commercially used

– Contain all or some of:• Bi, Zn, Li, up to 15%

• Al, F, K, Ti, Ba, Fe < 5%

• Bismuth Model glasses:– Si, B, Na, Bi - simpler system

Sample Compositions

Intended

Actualfrom ICP analysis

Bismuth Sample CompositionsSample Mol%

SiO₂ B₂O₃ Na₂O Bi₂O₃ Al₂O₃

BIS00 63.5 21 15.5 – –

BIS01 63.5 15 15.5 6 –

BIS02 63.5 9 15.5 12 –

BIS03 59.5 20 14.5 6 –

BIS04 56 18.5 13.5 12 –

0.517.5112447BIS04

0.5912.52850BIS03

0.518131355.5BIS02

0.59.5142353BIS01

0.40.1143055.5BIS00

Al₂O₃Bi₂O₃Na₂OB₂O₃SiO₂

Mol%Sample

Probes atomic environment of disordered systems

Provides quantitative information about atomic structure

NMR

11B spectrum

Nuclei studied: 11B, 23Na, 29Si• 11B, 23Na: Quadrupolar - (spin > ½)

• Non-spherical electric charge distributions

– Interact with electric field gradients

• Broad spectral lines

NMR

+++

++ +

+

+

−−Spin > 1/2

• Bismuth model glasses

• Nuclei: 11B, 23Na, 29Si

• Comparison of spectra

• Identify trends

Results so far

11B - Spectra

• 2 resonances

• Chemical shifts correspond to BO3 and BO4

• Spectra show slight differences in chemical shifts

11B - Trends

• Amount of BO4 increases as Si content increases

• Expected trend

70

72

74

76

78

80

82

84

56 57 58 59 60 61 62 63 64

% SiO2 in Sample Composition

Rela

tive

Am

ount

of B

O₄

(%)

11B - Trends

• Amount of BO4 decreases as Bi content increases

• Suggests bismuth is acting as a network modifier

70

72

74

76

78

80

82

84

0 2 4 6 8 10 12 14

% Bi2O3 in Composition

Am

ount

of B

O₄

(%)

23Na - Spectra

• Very similar shape

• Do not have a quadrupolar lineshape

• Change in peak positions

23Na - Trends

• Na peak position decreases with increasing B2O3

• ⇒ Network becomes more connected

-16

-14

-12

-10

-8

8 10 12 14 16 18 20 22

% B₂O₃ in Sample

Sod

ium

pea

k po

sitio

n (p

pm)

23Na - Trends

• Na peak position increases with increasing Bi2O3

• ⇒ Network becomes less condensed ⇒ bismuth is not as good a network former as boron

-16

-14

-12

-10

-8

0 2 4 6 8 10 12 14

% Bi₂O₃ in Sample

Sod

ium

pea

k po

sitio

n (p

pm)

29Si - Spectra

• Change in chemical shifts

• Spectra fitted with 3 peaks

• Peaks assigned to Q2, Q3 and Q4 units

Results so far

Conclusions

• Bismuth is acting as a network modifier

• NMR results are very sensitive to changes in compositions

• Many things changing in compositions

• Makes trends hard to identify

• Need a more systematic sample set

FSP• Produces nanoparticles

• One-step process

• Ceramic materials and glasses

• Effects of production method on structure?

Side Project – Flame Spray Pyrolysis

• Supervisors

Mark E. Smith, John V. Hanna

• Industrial Supervisors

Peter Bishop, Jon Booth

• NMR GroupNathan Barrow, Lindsay Cahill

Acknowledgements