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