The ratios of the crystalline phases found in each clay layer (2 cm thickness) after precipitation process obtained from X-Ray analysis.
Table 1
Phases found in the burned clay layers after precipitation process and their ratios used to dope ZnO.
Layers
Phases (%)
|
1
|
3
|
5
|
7
|
9
|
11
|
13
|
1- Quartz
|
61.8
|
61.8
|
66.13
|
56.81
|
40.33
|
45.28
|
44.33
|
2- Albite
|
18.7
|
15.39
|
19.35
|
23.66
|
30.25
|
28.3
|
27.35
|
3- Montomorillionite
|
9.7
|
7.7
|
6.45
|
12.42
|
10.08
|
5.66
|
|
4- Dolmite
|
9.7
|
7.7
|
8. 0 7
|
7.1
|
10.08
|
11.32
|
|
5- Illite
|
|
|
|
|
9.24
|
|
5.66
|
6- Kaolinite 1A
|
|
|
|
|
|
9.44
|
|
7- Microcline
|
|
|
|
|
|
|
22.64
|
1- SiO2 2- NaAlSi3O8 3- Na-Mg-Al-Si4O11 4- CaMg(CO3)2
5- K(AlFe)2AlSi3O10(Oh)2H2O 6- (Al2Si2O5(Oh)4 7- (KAlSi3O8 )
From the above ratios of the crystalline phases found in the all layers, we can drew the relation between the abundance of the phases (Quartz, Albite, Montomorillonite and Dolmite) in each clay layer and layer number as in Fig. 1.
As clear from Fig. 1 Quartz phase is the major phase concentrated at layer 3 and decrease to reach plateau at layer 9 and higher layers. Albite phase decreases to layer 3 and increase to make plateau at layer 9 and higher layers. The other phases have the same behavior as Albite. This figure reflects our idea about the possibility of partial separation of the phases present in the natural clay by precipitation in water. At layer 3 quartz phase has its main effect while at layer 9 and higher layers quartz still high, 40%, but has its lowest effect, so it expected to participate with albite and other phases in any appeared phenomena.
After doping the all layers with ZnO, Electrical measurement was done and J-E characteristics for all layers doped with ZnO were obtained. Figure 2 and Fig. 3 declared J-E characteristics of ZnO doped with different ratios (up to 20%) from precipitated layer 5 sintered at 1200 ͦ C for 1 hour.
The all layers (1, 3, 7, 9, 11 and 13) have the same behavior as layer 5 and the values of nonlinearity Coefficients α for all layers are tabulated in table no. 2 and calculated as in [5]. We notice that there is a shift in most of the breakdown electric Field Eo to higher values with increasing the doping ratio especially at the higher doping.
Table 2
values of nonlinearity coefficient α for ZnO Doped clays from the mentioned layers(up to 20%).
Weight%
Layer no.
|
1
|
2
|
4
|
5
|
7
|
10
|
13
|
15
|
18
|
20
|
1
|
2
|
3
|
2
|
2
|
4
|
3
|
6
|
15
|
20
|
10
|
3
|
2
|
2
|
2
|
2
|
3
|
4
|
3
|
3
|
6
|
3
|
5
|
2
|
2
|
3
|
3
|
4
|
5
|
3
|
5
|
4
|
5
|
7
|
3
|
3
|
3
|
3
|
4
|
18
|
3
|
4
|
9
|
18
|
9
|
2
|
2
|
4
|
5
|
7
|
13
|
5
|
6
|
10
|
5
|
11
|
2
|
4
|
2
|
4
|
4
|
27
|
11
|
19
|
27
|
18
|
13
|
2
|
4
|
3
|
3
|
3
|
4
|
6
|
14
|
|
6
|
From the above calculation of α, the relation between α and doping layer is given in Fig. 4 for low doping and Fig. 5 for high doping. As clear, before layer 7 or doping 7% α values are away from technical application while in Fig. 5 from 10% doping α decrease sharply to layer 3 then raised a small peak.
At layer 5, followed by two peaks at layers 7 and 11. Referring to Fig. 1 the small peak at layer 5 might be due to Quartz phase. The other two peaks at layer 7 and 11 can be attributed to mixed phases. This may be the reason of the equal height of the two peaks
The relation between α and the doping ratio from the different layers, some peaks are observed in Fig. 6 at 2%, 5%, 10% and 18%. This points that the proper concentration of Si and Al that stabilizes the interface potential barrier and enhances α achieved by doping ratio 10% and 18% from the layers (7, 9) and (1, 3, 11and 13) respectively. Pure Quartz phase has its maximum value at layer 3, but layer 3 is corresponding to the minimum α value, see Fig. 5. This points that pure quartz phase has little effect on the value of α, while mixed ratios of Albite and Quartz are much effective for α enhancement.
The microstructure of ZnO doped 15% clay from layer number 5 are given in Fig. 7. The photographs were taken in three different positions.
The elemental analysis was taken in three positions center of black grain, grain boundary and white grain as shown in Fig. 7 and tabulated in Table 3. A glance to SEM we can observe the presence of two phases black phase and white phase also there is two types of grains bare like grains and rounded edges grains. Elemental analysis declared that bare like grains are zinc silicates contaminated with Al ion as in Table 4.
Table 3
elemental analysis for 3 positions of ZnO doped clay layer no. 5
Positions
|
O
|
Al
|
Si
|
Fe
|
Ca
|
Zn
|
Center of black grain X5
|
4.6
|
1.5
|
3.6
|
0.8
|
|
85.2
|
Grain boundary X6
|
13.5
|
2.7
|
9.4
|
1.4
|
0.72
|
66.5
|
White grain X7
|
17.7
|
2
|
3.8
|
|
|
69.3
|
Positions
|
O
|
Al
|
Si
|
Fe
|
Ca
|
Zn
|
Center of black grain X5
|
4.6
|
1.5
|
3.6
|
0.8
|
|
85.2
|
Grain boundary X6
|
13.5
|
2.7
|
9.4
|
1.4
|
0.72
|
66.5
|
White grain X7
|
17.7
|
2
|
3.8
|
|
|
69.3
|
We notice from Table 3 that percentages of Si, Al, Fe and Ca at grain boundary are higher than other positions, this because silicon oxide has melting point lower than other oxides so it creates liquid phase during sintering process at low temperature, which promotes other oxides to be distributed evenly in the ZnO grain boundary [3]. Al, Si and Fe ions behave as donors that support the grain boundary barrier and increase nonlinearity coefficient.
Table 4
elemental analysis for bare like grain or rod phase.
Elements
|
O
|
Al
|
Si
|
Zn
|
Rod phase X4
|
13.75
|
1.03
|
11.06
|
64.23
|