the acid resistance of car windscreens · 2010-06-21 · the toyota acid test why is the test so...
TRANSCRIPT
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