Synthesis of metal oxide aerogels from their salts

Report
Synthesis of metal oxide aerogels from their salts
Helmut Schäfer, Kathleen Heinrich, Barbara Milow, Lorenz Ratke
Institut für Materialphysik im Weltraum, Linder Höhe, D-51147 Köln
Folie 1
Background
Synthesis of aerogels from their metal salts for application as additives in
foundry industry
Desired properties:
- high surface area
- high temperature stability
Simple process route
Synthesis on a large scale
Folie 2
Introduction
Preparation of aerogels
1. Hydrolysis of metal alkoxides
H2O
2. Condensation reaction to hydro- or alcogel
- ROH
3. Ageing
4. Drying
- H2 O
Folie 3
Introduction
Preparation of aerogels
1. Hydrolysis of metal salts
H2O
- HCl
2. Condensation reaction to hydro- or alcogel
3. Ageing
strong exothermic reaction!!
TiCl4, SiCl4, ZrCl4, ZnCl2, SnCl4
Folie 4
Introduction
4. Supercritical Drying with carbon dioxide
Before!!
Removal of residual salts
solvent exchange: water → alcohol or acetone
>Sodium silicate +
KCr(SO4)2
>Al(Cl)3
>FeCl3
>Zr-alkoxide
>Sodium silicate +
FeCl3
Folie 5
Characterization
Adsorption/Desorption measurement with nitrogen
TGA-FTIR
Scanning electron microscopy
Folie 6
Zirconium aerogel:
BET 498 m2/g
Results – BET Surface
0.3
900
Adsorption/Desorption
BJH-Plot
600
dVp /drp
Va /cm3(STP) g-1
0.2
0.1
300
Desorption
Adsorption
0
0
0
0.5
p /p 0
1
1
10
100
r p /nm
Folie 7
Results – BET Surface
Precursor
Catalyst
BET in m2/g
ZrCl4/TiCl4
propylene oxide
577
ZrCl4
propylene oxide
498
SiCl4
-
798
FeCl3 · H2O
propylene oxide
363
AlCl3
propylene oxide
389
Sodium silicate +
SnCl4
-
294
SbCl3
propylene oxide
8
Wide range of different aerogels with high surface areas!!
Folie 8
The right choice
Metal oxide
Fp in °C
Sintering temperature
(calc.) in °C
ZrO2
2680
1695
Al2O3
2050
1275
TiO2
1855
1145
SiO2
1713
1051
Fe2O3
1565
1149
-Toxicity
-Price per kg
-Availability
Folie 9
Results – BET Surface
Metaloxide
Catalyst
BET in m2/g
ZrCl4/TiCl4
propylene oxide
577
ZrCl4
propylene oxide
498
SiCl4
-
798
FeCl3 · H2O
propylene oxide
363
AlCl3
propylene oxide
389
Sodium silicate +
SnCl4
-
294
SbCl3
propylene oxide
8
Sodium silicate +
KCr(SO4)2*H2O
-
400
Zr-, Ti- and Silica-Aerogels showed best results in
preliminary tests for foundry applications!
Folie 10
Results – TGA: Silica-Aerogel
Folie 11
Results – IR (122 °C): (Silica-Aerogel)
Extracted from 3D-IR-Spectra
IR-Library
Folie 12
Results – SEM
Silica-Aerogel (572 m2/g)
Folie 13
Results – Large Scale synthesis
Zirconium-Aerogels
20 cm3 (typical lab scale)
50 cm3 (works fine)
Successful
preparation of
500 cm3 (monolith)
Zirconium aerogel
up to 500 cm3
500 L Pilot plant scale with industrial partners
Folie 14
Conclusion
Aerogels can be easily synthesized from their metal
salts
A wide range of different aerogels with high surface
areas were synthesized
Zirconia aerogel up to 500 cm3 were synthesized
Focus on Zr-, Ti- and Silica-aerogels for foundry
applications
Folie 15

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