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Fare clic per modificare lo stile del sottotitolo23/09/2010

Eur@graduation September14-16 2010, YaoundeCameroon

Lightweight Geopolymer materials forInsulating Applications: Electric and

Thermal Properties.

E l ie K a m se u , C. Leonelli, U. Chinje Melo, P.N. Lemou na D. N o wouo

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23/09/2010Eur@graduation September14-16 2010, YaoundeCameroon

Content

Definition and scope

Interest of the work

Materials and Experimental ProcedureCharacterization

Influence of chemical, mineralogy,

microstructure, phases and pore distribution Applications and Conclusion


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Definition and ScopeThe thermal insulation can refer to materials used to reducethe rate of heat transfer. The term refer also to thermalresistance which is the ratio of the temperature difference

across an insulator and the heat flux: R = T/QAThe thermal insulation represents a considerable stake forthe economy of energy .

It is therefore desirable for specific applications to be able tochoose materials with defined properties in relation to thecost, the efficiency and the environmental impact.


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Interests of the work

Geopolymers are developed using amorphous

aluminosilicates that can come from kaolins,

secondary (recycled) industrial or/and naturalwastes1-3

Amorphous alumina and silica seem their thermalconductivity reduce to minimum (from 18-30 to 1.6

W/mK for Al2O3 or 6-10 to 1.4 W/m.K for SiO2).

Geopolymers have particular microstructureEur@graduation September14-16 2010, YaoundeCameroon

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Geopolymerization of amorphous aluminosilicates,abundantly available and low cost, is projected in this work asenergy-efficient and sustainable process for the production of

insulating materials.

Objective of the Work


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Materials and Preparation

Five compositions of geopolymers were prepared with Si/Al

molar ratio from 1.23 to 2.42.

Series of geopolymers pastes were obtained with variouspercent of foaming agent

The pastes were sealed to avoidthe contact with air during

the first 24 hours of curing and curing progress up to 28

days before characterization.

The compositions studied here have been investigated for theEur@graduation September14-16 2010, YaoundeCameroon
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Characterization: Porosity, humidity

A Mercury-intrusion type MIP, Carlo Erba 2000 equippedwith a macropore unit, Model 120, Fison Instrument wasused to assess the cumulative pore volume (mm3g-1) and the

pore size distribution.The results of Mercury-intrusion Porosimetry Analysispermitted to evaluated the micro, meso and macropores of

various compositions of porous matrices of geopolymersExposition at ambient temperature and weight loss attemperatures between 20C and 100C was used toinvestigate on the capacity of the insulating materials toaccumulate and loss humidity in relation to their mechanical


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Characterization: Electrical

Conductivity Volume resistivity (v ) and Surface resistivity (s ) of geopolymers were measured using an electrometer (model6517A Keithley) connected to a resistivity test chamber

(model 8009 Keithley).The volume resistivity was measured based on alternatepolarity (+500 V, -500 V) and the sample resistance

calculated (Ohms second law) at the end of each constantpotential period.

Surface resistivity was measured applying a polarization(+1000V) between the guarded electrode and the ringelectrode of the test chamber.


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23/09/2010 Eur@graduation

Thermal Conductivity

Eur@graduation September14-16

Thermal Conductivity

Stationary Regime

Fluxmetre

l Keithley SL-1730SB (0-30V, 0-3A)on of thickness and calculation of the thermal conductivityded Hot Plate

Non StationaryRegime

Flash Laseraser Quantel

1053 nm, 100 mJ, 3Wthe sample and calculation of thermal conductivityscope TEKTRONIX TDS3012

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Pore size distribution in Geopolymers and

geopolymer foams


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Electrical Volume Resistivity

Non straightforwardlink between Si/Aland electricalresistivity

Presence of

unreacted alkali ionsand porosity influenced more the

electrical resistivity Eur@graduation September14-16 2010, YaoundeCameroon

Porous

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Electrical: Surface resistivity


0 2 4 6 8 10 120

2

4

6

8

10

12

Si/Al molar ratio

Superficial Resistance ( x 108)olished and washed

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Thermal resistance and

Diffusibility


Na-Matrix

K-Matrix

P =35%

P =45%

P =55%

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Porosity and Thermal Properties

Since pores are small in the geopolymersdeveloped, Knudsen effect is applied as:6

0 the thermal conductivity of the gaswhen the Knudsen effect is noteffective, Kn factor link to the sizes ofpores and parameter linked to gaswhich value is 1.5 for air.

6Jean Cote et Jean-Marie Kon rad, Int. J. Of Heat. And Mass Tran sfer, 52 (2009)79 6-

804Eur@graduation September14-16 2010, Yaounde

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Porosity and Thermal Properties 2

Geopolymers as materials yieldingthe widest bounds.

The parallel flow model (1) and

series flow model (2) is used tocalculate the effective thermalconductivity of upper bound and

lower bound respectively6.s the thermal conductivity of thesolid matrix, g the thermalconductivity of the gas and p thetotal porosity.

(1)

(2)


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Variation of Thermal Conductivity

with Porosity


20 30 40 50 600,15

0,2

0,25

0,3

0,35

0,4

0,45

0,5

Rgression exponentiellepour

Vol% Porosity

Thermal Conductivity W.m-1.K-1

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Lightweight Geopolymers

obtained

Homogeneous small size pores withSi/Al > 1.89

Heterogeneous

large poresWith Si/Al ~ 1


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Conclusion


Mesoporous quasi monomodal matrix of geopolymer can be welldesigned through geopolymerization with enough strength to face

mechanical solicitations.

The Si/Al and the concentration of foaming agent can bemonitored to develop porous geopolymer matrix with desiredinsulating properties.

The porous geopolymer can be used for insulating applications as

well as filters and regulator agents of temperature in regions

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23/09/2010Eur@graduation September14-16 2010, Yaounde

Thank You for your attention

Eur@graduation September14-16 2010, Yaounde

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