ORGANIC BINDERS TO ENHANCE EFFICIENCY OF ...

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Department of Physics, University of Nairobi., P.O. Box 30197-00100, nairobi, Kenya ... Porous clay ceramics are used as thermal insulators in high temperature applications such as .... Ceramic charcoal stoves (jiko) and (b) Ceramic water flter.
ORGANIC BINDERS TO ENHANCE EFFICIENCY OF CHARCOAL STOVES (JIKOS) & WATER FILTERS F. W. Nyongesa*, , B.O. Aduda and A. A Ogacho Department of Physics, University of Nairobi., P.O. Box 30197-00100, nairobi, Kenya 8TH INTERNATIONAL CONFERENCE OF THE AFRICA MATERIALS RESEARCH SOCIETY (A-MRS) December 6 -11, 2015, ACCRA, GHANA 1.0 INTRODUCTION Porous clay ceramics are used as thermal insulators in high temperature applications such as in kilns and charcoal stoves (jikos). In such applications, these materials suffer cyclic thermal stresses or severe thermal shocks resulting in strength degradation. Clay ceramics are also widely used in water filters. The challenge however has been how to increase the filtration rate without compromising on the structural reliability of the ceramic material. This study explores the effect of a plant derived bidder Corchorous olitorius (mrenda) on the Physio-mechanical and thermal properties of clay ceramics. ‘Mrenda’ is local vegetable with highly viscous soup that is used by potters to plasticize clay for improved strength.

2.0 EXPERIMENTAL Clay ceramic samples were plasticized with varying amounts of “mrenda” binder and their physio-mechanical properties determined., Thermal properties were investigated by characterizing Damage due to thermal shock, through measurement of the residual strengths (KIc) and Hasselman parameters R, R’, R’’’

R measures resistance of material to initiation of fracture by thermal shock, R’ measure of possibility for crack propagation and R′′′ characterizes ability of a material to resist crack propagation. Tests employed water-quenching technique from 1,100 oC to 20 oC

Unclean water

Clean Water

(b)

Fig 2. Ceramic charcoal stoves (jiko) and (b) Ceramic water flter

1.92

3.0

Bulk Density Mg/m3

% Composition

3.5

2.5 2.0

1.5 1.0 0.5

0.0

1.88 1.84

MOR- Green samples (MPa).

3.0 RESULTS AND DISCUSSIONS

18

400

16

350

14

300

12

250

10

200

8

150

6

100

MOR Green MOR Fired

4 2

50 0

0 0

0.2

0.4

0.6

0.8

1.2

1

Binder concentration

1.80

Fig.5 Effect of “mrenda” on MOR

Samples plasticized with binder Plain water's sample (control)

1.76

Normalized Shock Parameters

Fig 1. (a) Corchorous olitorius (mrenda) plant and (b) ‘Mrenda’ used in pots

Fig 3. shows that ‘mrenda’ has high percentage of polymeric components. This adsorbs cations (Ca2+ etc) forming strong bonds with clay solid phase leading to strong inter-particle bonding. Bulk Density and sintered strength (MOR) improved by about 140% (Figs 4 & 5).

(b)

MOR- Fired samples (MPa).

(a)

(a)

1.0

0.8

R

0.6

R'

R'''

0.4

0.2 0.0

0.0

0.3 0.5 0.8 1.0 Normalized Binder Concentration

Fig.6 Effect of ‘Mrenda” on thermal properties of clay samples

1.72

1.68 0

components

Fig.3 Chemical composition of ‘Mrenda’

0.2

0.4

0.6

0.8

1

Normalized binder concentration

Fig.4. Effect of ‘Mrenda on MOR of clay ceramic samples

The observed increase in Hassman parameters R and R (Fig 5) indicates that ‘mrenda’ progressively impaired damage due to crack initiation . On the other hand, the decrease in R′′′ indicates poor resistance of the material to crack propagation once the crack has started. SEM micrographs (Fig 6) shows that Mrenda’ changes fracture path from intergranular to transgranular making it difficult for crack initiation.

ACKNOWLEDGEMENTS We wish to thank the International science Program (Uppsala University) for sponsorship to attend this conference

(a)

(b)

Fig. 7. SEM of ‘mrenda’ plastized samples (a) 0% binder showing inter-granular cracks and (b) 100% binder showing trans-granular cracks

4.0 IMPLICATIONS 1. ‘Mrenda’ is a promising candidate to enhance thermal shock resistance of ceramic ‘stove’ linnings 2. ‘Mrenda’ can be used in development of strong, more porous and effective ceramic membrane for applications in household-scale, water purification system

REFERENCES 1. Aduda B.O., Nyongesa F.W. and Njogu M. S., (2008)., J. Mater Sci., 43, 4107

2 Ogacho A., Aduda B., Nyongesa F.W., (2006)., J. Mater Sci., 41, 8276 3 B.O ADUDA, F.W. NYONGESA and G. OBADO, J. Mater. Sci. Lett.18 (1999) 1653