ON THE FOAMING KINETICS FOR THE SYNTHESIS
OF POROUS INORGANIC POLYMERS
Jos DENISSEN1, Lubica KRISKOVA1, Yiannis PONTIKES1
1
KU Leuven, Department of Materials Engineering, 3001 Heverlee, Belgium
[email protected], [email protected], [email protected]
Goal: Study the foaming kinetics of IP by heat of reaction (isothermal calorimetry) and kinetics of pore formation (visual
recording), to investigate the influence of the activating solution, addition time of the foaming agent and temperature.
Materials
Fayalite slag, a by-product from secondary copper recycling, is
used as precursor with a D50 of 2.5 μm.
Element wt%
FeO
41
SiO2
39
Al2O3
8
ZnO
6
MgO
3
Heat flow (J/h*g)
Heat of reaction
Activating solution
1.0, 1.2 or 1.4 SiO2/Na2O
Metallic aluminium powder with particle size 1-5 μm was used as foaming agent.
2Al + 6H2O + 2NaOH → 2NaAl(OH)4 + 3H2
Isothermal
Calorimetry
10, 20 or 40 ˚C
100
45
30
15
14-10
14-20
75
14-40
7,5
50
5,0
25
2,5
0,0
0
10
20
30
IP synthesis without aluminium powder showed 3 peaks
namely initial heat, dissolution and polymerisation. This
process finishes between 2 or 40 hours depending mainly
on the temperature and lesser on the activating solution.
The addition of aluminium powder generates additional
heat, finishing the IP synthesis within 1 hour for any
temperature or activating solution. However, the effect of
activating solution and temperature were still visible in
lesser extent.
0
40
Time (h)
200
70
12-20
12-20-Al
150
Heat flow (J/h*g)
Aluminium powder
0.2 wt%
Fayalite slag
S/L = 3.33
Surfactant was added to improve the foam structure and stability.
CML heatflow (J/g)
wt%
19
3
1
<1
76
CML heatflow (J/g)
Mineralogy
Composition
Fayalite
Fe2SiO4
Hercynite
FeAl2O4
Magnetite
Fe3O4
Zincite
ZnO
Amorphous/unidentified
/
Activating solutions were prepared by mixing Na-silicate, demi-water and NaOH
pellets. The SiO2/Na2O molar ratio varied but all solutions contained 75 wt% of
water.
60
100
50
50
40
30
10
20
5
10
0
0
0
1
2
3
4
5
Time (h)
Kinetics of pore formation
Mixing time
The mixing time mainly influences the
speed and duration of the foaming. It also
improves the stability of the foams
Temperature
The process temperature influences the starting time,
duration and speed of foaming at high SiO2/Na2O ratio and
low mixing time.
450
450
400
400
400
400
350
350
350
350
300
250
200
10-40-Al-5
12-40-Al-5
14-40-Al-5
150
100
30
60
90
120 150 180 210 240
Time (s)
300
250
10-40-Al-5
10-40-Al-30
14-40-Al-5
14-40-Al-30
200
150
100
30
60
90
120 150 180 210 240
Time (s)
300
250
200
14-10-Al-5
14-20-Al-5
14-40-Al-5
150
100
30
60
90
120 150 180 210 240
Time (s)
Height (%)
450
Height (%)
450
Height (%)
Height (%)
Activating solution
The SiO2/Na2O ratio influences the starting time
and duration of foaming but not the speed.
300
250
200
12-10-Al-30
12-20-Al-30
12-40-Al-30
150
100
30
60
90
120 150 180 210 240
Time (s)
Conclusion: The temperature and SiO2/Na2O ratio mainly influenced the height (total volume) and speed of the foaming while the
addition time played an important role in the stability of foams. Maximum foaming was obtained at 40 C using an activating solution with a
SiO2/Na2O molar ratio of 1.4 and by adding the Al-powder after 5 minutes of mixing.