COMENTARIO/CONCLUSIÓN:

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CHAPTER FOUR

RESULTS AND DISCUSSION

The results obtained for the various tests are presented in Tables 4.1 - 4.10, Plates 4.1- 4.8 and Figures 4.1 – 4.12

84 Oxide CuO ZnO Ga2O3 MoO3 Ag2O Eu2O3 SO3 MnO IrO2

Composition 0.022 0.01 0.001 0.57 0.845 0.17 2.0 0.005 0.12

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From Tables 4.1 and 4.2, it is seen that Amaiyi clay contained 22.9% alumina (Al2O3) while Nguzu clay contained 21.8% alumina (Al2O3). It follows that both have low alumina content and so can be classified as high melting clays according to Nnuka and Agbo (2000). The silica contents were 48.9% and 54.4% for Amaiyi and Nguzu clay respectively. This classifies the clays as siliceous fire clay. (Nnuka and Apeh, 1997).The quantity of silica is moderate since it is within the recommended range of (50 -60) % for good clay brick. Silica is considered as filler in clay. It enabled the brick to retain its shape and imparted durability quality, prevented shrinkage and warping. These were confirmed from shrinkage tests and physical examination of the fired samples. Excess of silica is not good as it could make brick brittle and weak on burning.(Altayework, 2013).

The alumina to silica ratios of Nguzu and Amaiyi clays were 2:3 and approximately 1:2% respectively. These suggest low alumina to silica ratio which implies presence of more free quartz. (Nnuka and Agbo, 2000). However, it was observed that the percentage of uncombined silica is not much. Large percentage of uncombined silica in clay is undesirable as it can cause the problem stated previously.

Both clay samples have high Fe2O3 content which strongly supports the reddish colour of the fired samples. The colour of Nguzu was brown while Amaiyi clay was dark on drying to 110⁰C but became reddish when fired to 1200⁰C. High iron

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oxide content is reported to affect high temperature characteristics. (Nnuka and Agbo, 2000). This suggests the need for reduction of the iron content by any separation method like magnetic separation.

Amaiyi clay has calcium oxide CaO content of 2.79% while that of Nguzu clay is 0.49%. Lime (CaO) is reported to normally constitute less than 10 per cent of clay.

It reduces the shrinkage on drying. (Altayework, 2013). This is the reason why Amaiyi clay had lower shrinkage value of 4.0% compared to Nguzu clay which was 4.44%.The values of potassium oxide K2O is almost of the same quantity.

These low temperatures fusing agents melt at low firing temperature to fuse into the structure of the clay, hence helped to bind and densify the material and also reduced the sintering temperature.

Table 4.3A Chemical Composition of Groundnut Shell

Oxide SiO2 P2O5 SO3 K2O CaO TiO2 MnO Al2O3

Composition 16.0 8.0 5.1 10.6 30.4 1.5 0.95 7.6

Oxide Fe2O3 NiO CuO ZnO BaO Eu2O3 CeO2 Yb203

Composition 13.0 0.2 1.2 0.3 1.5 2.2 0.6 0.9

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Table 4.3B Chemical Composition of Rice Husk

Oxide SiO2 P2O5 SO3 K2O CaO TiO2 MnO

Composition 60.8 21.3 2.76 7.77 3.07 0.35 0.771

Oxide Fe2O3 NiO CuO ZnO BaO Eu2O3 Re2O7

Composition 2.41 0.024 0.059 0.24 0.13 0.09 0.19

Table 4.3C Chemical Composition of Sawdust

Oxide SiO2 P2O5 SO3 K2O CaO TiO2 MnO

Composition 17.2 4.7 3.0 19.2 47.4 1.0 0.65

Oxide Fe2O3 NiO CuO ZnO BaO Eu2O3 Re2O7

Composition 5.73 0.024 0.44 0.2 0.13 0.09 0.4

From Table 4.3(A), it was shown that groundnut shell has its most dominant oxides as 16% SiO, 10.6% K2O, 30.4% CaO, 8% P2O5 and 7.6% Alumina. The percentage alumina content of groundnut shell increased the composition of alumina of the composite clay material. This increase in alumina content enhanced the refractoriness of the refractory material. This led credence to the enhanced refractoriness of the material with groundnut shell additives obtained in the results.

The presence of silicon oxide in all the additives was found to be useful by reducing the drying shrinkage of material. It functioned as a filler which aided the

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inter particle binding when fused together. The increase in silica content reduced excessive shrinkage in the composite material that would have occurred after firing. The presence of calcium oxide and other alkalis were noted to have also reduced shrinkage and lowered fusion point. Also, beyond 0.3% composition Calcium oxide, is reported to enhance mullite formation in fire clay thereby improving the high temperature characteristics like sintering temperature. (Nnuka, Ogo and Elechukwu, 1992).

The analysis of the rice husk in Table 4.3(B) revealed that silica (SiO2) was the most dominant mineral of about 60.8% in the additive. However, it contains phosphorus oxide (P2O5) at the composition of 21.3%. Other oxides like CaO, TiO2, K2O, SO3, MnO, Fe2O3, NiO, CuO, ZnO, BaO, Eu2O3 and ReO7 are present in rice husk but in trace quantity of 1-17.9%.

Hence, the waste agro material (rice husk) can be considered as alternative natural source of silica as its silicon content conform to international standard for refractory clay.

Phosphorus oxide was found in all the additives. However, rice husk has the highest composition of 21.3%. Groundnut shell has 8.0% while saw dust has the least value of the oxide-4.7%. Phosphorus oxide is a useful oxide in refractory brick. Alumina reacts with phosphorus to form aluminum phosphate with considerable strength above 350⁰C. (Decker, 2003). The aluminum phosphate bond

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acts as a binder which enhances the brick’s refractory properties like thermal shock resistance, refractoriness and strength. The bond improves non wetting effect of molten metal on the material and also increases the resistance of the material to carbon II oxide attack. The carbon II oxide is a byproduct of the furnace which causes cracking and destruction of the refractory lining. (Decker, 2003). Hence, the presence of the phosphorus oxide in the additives promoted excellent properties of the composite clay brick.

Rice husk contains calcium oxide and potassium oxide at a small quantity. These low temperature fluxing agents have capacity of melting at low temperature to fuse in the matrix of the material structure to reduce the porosity. (Opoku, 2015).

The gmalina sawdust additive contains little of silica but dominated by calcium oxide and other minerals at low values which effect has been discussed above.