2.2 Methods
3.1.3 Tomography
The results obtained for the chemical composition and thermal analysis are presented in table 3.1.1 and figure 3.1, 3.2 and 3.3 respectively.
Table 3.1.1 Results of the chemical composition of the clays
Composition % Dabagi Termite hill Fadama
SiO2 64.50 25.00 55.90
Al2O3 16.30 6.30 13.90
Fe2O3 14.26 30.63 24.45
CaO 0.26 1.00 0.76
K2O 0.74 ND 1.13
TiO2 1.71 3.02 1.71
CuO 0.03 0.25 0.03
Cl ND 0.19 ND
V2O 0.08 0.05 0.09
Cr2O3 0.07 0.25 0.06
MnO 0.07 0.26 0.41
NiO 0.02 0.15 0.03
ZnO ND 0.09 0.04
Rb2O ND 16.00 ND
Nb2O ND 0.68 ND
Rh2O3 0.12 3.30 0.28
CdO ND 12.00 ND
BaO ND 0.65 0.15
Re2O7 ND 0.01 0.10
OsO4 ND 0.43 0.18
IrO2 0.18 0.63 ND
Au 0.19 ND ND
PtO2 0.08 ND ND
Ga2O3 0.01 ND 0.05
P2O5 1.1 ND 0.55
SO3 0.12 ND 0.16
Total 99.84 101.19 99.97
53
weight (mg)
Fig. 3.1 Thermogrametric analysis of Dabagi Clay
54
weight (m g)
fig. 3.2 Thermogrametric analysis of Fadama Clay
55
weight (mg)
Fig. 3.3 Thermogrametric analysis of Termite Hill Clay
56
Table 3.1.2: Results of the physical properties of the clays
Desc. Apparent porosity (%)
Bulk density (g/cm3)
Linear shrinkage (%)
Thermal shock resistance (cycles)
Cold crushing strength (MPa)
Softening point (0C)
LOI
Dabagi 38.46 1.81 6.80 7 5.44 1349 4.46
Termite hill
46.15 1.54 5.80 3 4.59 1337 2.98
Fadama 40.29 1.79 6.00 5 5.17 1349 3.69
Table 3.1.3 Physical Properties of Dabagi clay with different percentage of Rice Husk Ash
%Clay & rice husk ash
Apparent porosity (%)
Bulk density (g/cm3)
Linear shrinkage (%)
Thermal shock resistance
(cycles)
Dabagi&1%RHA 43.66 1.62 6.00 4
Dabagi&2%RHA 46.15 1.50 4.80 3
Dabagi&5%RHA 50.76 1.53 3.60 1
Dabagi&10%RHA 53.84 1.54 3.40 1
Dabagi&15%RHA 60.53 1.32 3.60 1
Dabagi&20%RHA 62.03 1.27 3.00 1
Dabagi&25%RHA 63.29 1.26 3.00 1
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Table 3.1.4 Results of the Physical Properties of Dabagi clay with different percentages of Limestone
Dabagi clay+ % limestone
Apparent porosity (%)
Bulk density (g/cm3)
Linear shrinkage (%)
Thermal shock resistance (cycles)
Average strength (MPa)
Softening point (0C)
Dabagi+1%
limestone 37.40 1.54 0.80 12 6.87 1398
Dabagi+2%
limestone 31.38 1.62 1.40 15 7.99 1430
Dabagi+5%
limestone 29.90 1.66 3.40 17 8.77 1491
Dabagi+10%
limestone 26.19 1.81 6.00 18 9.39 1512
Dabagi+15%
limestone 23.95 1.85 8.40 21 10.22 1541
Dabagi+20%
limestone 20.56 1.88 9.00 23 11.27 1564
Dabagi+25%
limestone 15.38 1.92 9.60 26 11.68 1605
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Table 3.1.5 Results of the Physical Properties of Dabagi clay with different percentages of kaolin clay
Dabagi clay+% kaolin
Apparent porosity %
Bulk density g/cm3
Linear shrinkage %
Thermal shock resistance
Average cold crushing
Softening point (0C)
Dabagi+1%
kaolin
34.89 1.59 1.40 8 8.27 1398
Dabagi+2%
kaolin
30.77 1.76 2.00 9 9.03 1430
Dabagi+5%
kaolin
27.04 1.78 4.80 11 9.65 1512
Dabagi+10
%kaolin
24.92 1.88 8.00 14 10.37 1522
Dabagi+15
%kaolin
19.45 1.88 8.80 17 11.37 1541
Dabagi+20
%kaolin
15.38 1.92 9.00 20 12.09 1564
Dabagi+25
%kaolin
4.36 2.35 11.60 23 12.26 1605
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Table 3.1.6 Summary and comparison of the Properties
Parameters dabagi Fadama termite glass Ref.brick ceramics Chester
Chemical composition (%)
SiO2 64.50 55.90 25.00 76-93 51.70 60.50 46.62 Al2O3 16.30 13.90 6.30 12-17 25.44 26.50 25-39 Fe2O3 14.29 24.45 30.63 2-3 0.5-1.2 0.3-0.6 0.4-2.7
MgO ND ND ND 4-5 0.1-.02 0.18-3.0 2-3.0
CaO 0.29 0.75 1.00 4-5 0.1-0.2 0.18-3.0 0.2-1.0 Na2O ND ND ND 2-15 0.10-0.2 0.18-3.0 0.2-1.0
K2O 0.74 1.13 ND 2-9 0.3-3.0
LOI 4.46 3.69 2.93 8-18 8-18 8.18 8-18
Linear shrinkage % 6.80 6 5.6 7-10 7-10 7-10 7-10
Apparent porosity % 38.46 40.29 46.15 10-30 10-30 10-30 10-30 Bulk density g/cm3 1.81 1.79 1.54 2.3 2.3 2.3 2.3 Cold crushing
strength (MPa) 5.44 5.17 5.59 5 5 5 5 Thermal shock
resistance (cycles). 7 5 3
20-32 20-30 20-30 20-30 Pyrometric cone
equivalent (0C) 13 13 12 16-3 16-32 16-32 16-32 Chester, J. H (1973), Grimshow, R.W (1971)
60 3.3 DISCUSSION
The results of the XRF chemical analysis are presented in Table 3.1.1 Dabagi gave the highest alumina content (16.30%), followed by Fadama (13.90%), and termite hill (6.30%), which are below the 25-39% required for fireclay, 25-45% for refractory bricks, 26.50% ceramics, 33.5-36.1% for paper 37.9-38.4% for paint and 38.07% for fertilizer manufacturing industries (Appendix A). However, Dabagi and Fadama clay samples can be used for alumino silicate and fibreglasses because the glasses of such type require12-17% by weight of aluminium oxide. The percentage of Al2O3 obtained in termite hill clay sample can be used for soda lime, borosilicate and colourless glass as the percentage would not have much effect on the formulation of such types of glasses since the excess would add to the chemical durability of the glass and hence would improve the mechanical strength of the glass. (Tooley,1987). The alumina content in clay is a strong indicator for its refractoriness. The higher the amount of alumina in clay, the higher is the refractoriness of the clay. The silica (SiO2) content of Dabagi (64.50%) and Fadama (55.90%) satisfies both the ranges for fireclay, refractory bricks, ceramics, paper, paint and fertilizer. This means it can be used for lining of heat treatment furnaces, melting furnaces for low melting point metals, liquid metal ladles and portion of blast furnaces. While that for termite hill, (25.00%) is short of the standard. Also the silicon oxides for all the three samples are short up the standard for glass formulation.
The percentages iron oxide (Fe2O3) content (14.29%) for Dabagi, (24.45%) for Fadama and (30.63%) for termite hill is higher for all the samples compared to the standard of 0.5-2.4 for refractory bricks and they are neither suitable for coloured and amber glasses, this is because the percentage of iron oxide requirement for this type of glass is
61
between 2-3% by weight of iron oxide nor suitable for the formulation of colourless glass and window glasses whose percentage iron oxide is only 0-1% by weight. Such level of iron oxide usually imparts a reddish colour to clay when fired, making it attractive as a ceramic raw materials according to Nnuka and Agbo (2000). This high iron oxide also affects the high temperature characteristics of the clay. This makes the clay in this category attractive and suitable for structural engineering works. The standard percentage composition requirements of CaO and MgO for soda lime and lead glasses manufacturing were 4-5% (Waudby, 1994), for fireclay and refractory clay bricks were 0.2-1.0%, ceramics o.18-3.0%,Obtainable results of CaO in these clay deposits were 0.29% for Dabagi clay, 1.0% for termite hill clay and 0.754% for Fadama clay these are very low for glass making but suitable for fireclay and refractory bricks, ceramics, paper, paint and fertilizer industries as shown in Appendix A. But MgO was not detected for all the three samples. Higher percentages may be required for fibre and alumina silicate glasses production. The percentages of sodium and potassium oxide obtained in all the samples were considerably small when compared with the standard percentage needed for various glass formulations. Glasses such as borosilicate glasses, lead glasses, fibreglasses and to some extent, aluminosilicate glasses require about 2-9% by weight of Na2O and K2O depending on the type of glass to be manufactured (Manas, 1979). Up to 15% by weight of Na2O is needed for soda lime glasses (Manas, 1979). Also these values are below the standard for fireclay and refractory bricks which is between 0.3-3.0 percentage by weight of sodium and potassium oxide. Loss on ignition (LOI), which is the combustion of volatile matter present in the clay, and is often required, being low. As
62
shown in Table 3.1.2, losses on ignition for all the samples are lower than the 18%
specified upper limit for refractory clays.
The effect of heat on the clay was also studied using TG analysis as shown in figure 3.5-3.7. The TG analysis curves show the changes in the clay when heated. Dabagi, Fadama and termite hills clays started losing water when it was heated up to 2000C and 3000C respectively. The big changes can be seen between 5000C to 7000C for Dabagi and Fadama clays where the dehydration of clays minerals occurred. The effect of fluxes components such as k2O and CaO could be seen when the clays started to have a reaction that began around 9000C. This also marks the beginning of the sintering process for the clay and also as the starting point to select temperature range to determine optimum firing temperature.
In terms of physical property, termite hill clay gave high porosity values of 46.15%, followed by Fadama (40.29%) and then Dabagi clay (38.46%). These values fall above the ranges of 20-30% required for fired brick clay as reported by Chester (1973). The average bulk density of Dabagi and Fadama clay samples as shown in table 3.2 was within the range of 2.06-2.11 g/cm3. This is suitable for siliceous fireclay as reported by Omowumi (2001); and fireclays as reported by Hassan (2001). Bulk density is an important property of a steel work silica brick. The cold crushing strength of Dabagi and Fadama clays are 5.44MPa and 5.17MPa respectively. This is still acceptable, being higher than the recommended minimum of 5MPa. Termite clays have a value short up;
this low value can be traceable to the high silica content and poor vitrification. The average linear shrinkage for all the samples is lower than the recommended range of 7-10% as reported by Chester (1973), this is more desirable. Higher shrinkage values may
63
result in warping and cracking of the brick and this may cause loss of heat in the furnace. The thermal shocks of the three samples are short of the acceptable values of 20-30 cycles as compared (Appendix A). The practical implication of this is that their use is restricted to lining of ladles and slag pots. The highest softening point reached was 13490C for both Dabagi and Fadama while termite hill had 13370C. These are lower than the recommended range of 14300C-17170C (Appendix A) as reported by Chester (1973).
These low values of refractoriness (softening point) are as a result of the high silica content of the clays. This means that their use is restricted to the processing of materials whose melting points do not exceed 17170C.
On the other hand, additions of additives such as the rice husk ash, limestone and kaolin, the physical properties changes.1% addition of rice husk ash, the apparent porosity of Dabagi clay increased as compared to the raw clay from 38.59% to 43.66%.
This increased continuously to 46.15%, 50.76%, 53.84%, 60.53%, 62.03% and 63.29%
at 2%, 5%, 10%, 15%, 20% and 25% addition respectively. From these values it can be observed that, the blends falls within the acceptable value of 45-75% range for both the traditionally manufactured porous ceramic material of 53% as well as the specification for porous insulting refractories as reported by (Chandler, 1967). The bulk density of 100% Dabagi clay is 1.81g/cm3 as shown in Table 3.2. The value decreased to 1.62 on addition of 1% rice husk ash. These values decreased continuously to 1.26g/cm3 at 25%
addition of rice husk ash. The linear shrinkage for 100% raw Dabagi clay was 6.80%. On addition of 1% rice husk ash, there was decreased in linear shrinkage from 6.80% to 3.00% at 25% addition. This decreased continuously to3.00 at 25% addition of rice husk ash. The thermal shock resistance on the other hand, also decreased as compared to
64
the 100% raw clay, as shown in Table 3.3. (Hassan, 2001) adopted the principle below in determining thermal resistance :> 30 Excellent, 25-30, Good, 20-25 Fair, 15-20, Acceptable, 10-15, Poor, < 10, Very poor.The spalling resistance at 9000C for the six blends was poor, since all the blends do not fall within the acceptable range of 15+
cycles.. On addition of limestone to Dabagi clay also as shown in Table 3.1.4.
The apparent porosity at 1% addition of limestone, there was a decreased in the apparent porosity to 37.40%. This decreased continuously to 15.38% at 25% addition of limestone. This means higher percentage of limestone could be tolerated to practically reduce the porosity to zero. The result of bulk density test is also shown in Table 3.4; the value of bulk density was recorded at 1% addition of limestone with the value of 1.54g/cm3. The bulk density at 25% addition of limestone is 1.92%. It is observed that porosity decreased as the bulk density increased. The linear shrinkage for raw Dabagi clay was 6.80%. On addition of 1% limestone, there was an increase in linear shrinkage to 9.60% at 25% addition of limestone. The thermal shock resistance of the specimen made from the seven blends at 9000C shows that at 1% addition of limestone is 12 cycles. This value keep increasing as the percentage of limestone increases up to 26 cycles at 25% addition of limestone. The cold crushing strength value for 100% Dabagi clay was 6.85KN/m2 in the direction of forming. This increased to 15.25KN/m2 (See Appendix A) at 25% addition of limestone in the direction of forming. The cold crushing strength value also increased from 4.03 KN/m2 to 8.10 KN/m2 at 100% clay and 25%
addition of limestonerespectively in the direction normal to forming. From this result, it is clear that addition of limestone to Dabagi clay improved the cold crushing strength characteristics in both directions. The refractoriness (softening point) is shown in Table
65
3.4. The refractoriness for 100% clay was 13490C (PCE 13). This value increased at 25% addition of limestone to 16050C (PCE 23). The result shows a remarkable improvement in the refractoriness as the percentage of limestone increases to an acceptable range of (1500-17000C) for fireclay.
Table 3.5 shows the physical properties of Dabagi clay with various proportion of kaolin clay. The apparent porosity decreased from 38.46% at 100% clay to 34.89% at 1%
addition of kaolin clay. This decreased continuously to 4.36% at 25% addition of kaolin.
It can be said that the higher the percentages of kaolin clay the lower the apparent porosity. The result of bulk density test for 100% Dabagi clay as shown in Table 3.2 is 1.81g/cm3. On addition of 1% kaolin clay, the value decreased to 1.59g/cm3. This value increased eventually to 2.35g/cm3 at 25% addition of kaolin clay. The linear shrinkage for 100% clay is 6.80%. On addition of 1% kaolin clay, there was decreased in linear shrinkage from 6.80% to 11.60% at 25% addition of kaolin clay. The thermal shock resistance as shown in the table above, increased significantly with the increased in the percentages of kaolin clay. The thermal shock resistance of the specimen made at 9000C, at 1% addition of kaolin the thermal shock resistance was 8 cycles. These numbers continuously increased to 23 cycles at 25% addition of kaolin. The cold crushing strength test in both directions of forming is shown in table 3.5. The cold crushing strength value for 1% addition of kaolin was 10.412KN/m2 in the direction of forming, this increase to 13.9 MPa at 25% addition of kaolin. The cold crushing strength value also increased to 6.132MPa at 1% addition of kaolin in the direction normal to forming. This value increased continuously up to 8.769MPa at 25% addition of kaolin.
From this result, it is clear that addition of kaolin clay to Dabagi clay improved the cold
66
crushing strength characteristics in both directions of forming. The softening point (PCE) increased at 1% addition of kaolin to 13980C (PCE 14) as shown in table 3.5. This value increased continuously to 16050C (PCE 23) at 25% addition of kaolin. It can be seen that, at 25% the value lies within the acceptable value of (PCE 16-32) as shown in table 3.6. It is observed in this investigation that porosity decreased as the bulk density increased. This is in agreement with the fact that densification reduces pore spaces and hence volume – upon which density depends. Similarly, the linear shrinkage affects porosity as higher shrinkage resulted to the closure of pores thus leading to reduction in porosity as illustrated in Table 3.6.The cold crushing strength (CCS) was found to depend on the efficiency of firing and degree of vitrification – as given by the linear shrinkage, apparent porosity (Pa) and bulk density (Db). In general, the more vitrified the brick is, the denser it is, and the higher the cold crushing strength. All the three samples recorded the lowest CCS; this may be as a result of poor vitrification, as granular, sand like particles break off from the brick when touched with fingers. The high silica content (64.50%) as against the 16.30% for alumina Dabagi clay, 25.00% silica as against 6.30% alumina for termite clay and 55.90% silica as against 13.90% for alumina for Fadama clay may be responsible. Similar argument could be raised for the thermal shock resistance (TSR)
67
CHAPTER FOUR
CONCLUSIONS AND RECOMMENDATIONS