**2. Materials and methods**

Activated carbon powder used in this study was obtained from Ranbaxy Fine Chemicals, New Delhi, India. Epoxy used in this study was obtained from Hindustan Advanced Materials (India) Pvt. Ltd., Chakala (east), Mumbai, India. Activated carbon powder filled epoxy gradient composites have been developed by using centrifugation process. In this process centrifugal force is applied in the X direction. Gradient samples are prepared from the activated carbon powder filled mix having 3 wt.% of activated carbon powder. Activated carbon powder was added to a mix of epoxy resin and hardener (10:8). Total mix was thoroughly stirred with the help of a glass rod. Details of set up and process of making gradient composites are as reported in earlier patent (Chand and Hashmi) [27]. Total mix was thoroughly stirred with the help of a glass rod at 24°C for 2 min. The total mix was kept in a cylindrical mould to make graded sample. The sample with mould was rotated at 800 ± 50 RPM at a radius of 130 mm. Graded sample pin was removed from the mould after post curing at room temperature for 24 h. Composite pin was sliced into four pieces starting from centre to periphery and designated as sample 1, 2, 3 and 4, respectively. Samples were coated on both the sides by air drying type silver paint before the electrical measurements.

Density of activated carbon powder filled epoxy gradient samples was measured by using a Mettler Toledo precision balance.

#### **2.1 Resistivity measurements**

Resistance (R) values of activated carbon powder filled epoxy gradient samples were measured by using a kiethley electrometer model 610°C in the temperature range ranging from 28 to 150°C. Heating rate was kept constant at 1°C/min.

DC conductivity (σDC) values were calculated by using the following relation

$$
\rho = \mathbf{R}^\* \mathbf{A} / \mathbf{l} \tag{1}
$$

where R is the resistance value of the sample; A (cm2 ) is the area of the electrodes; and l (cm) is the thickness of the sample.

Conductivity was calculated by using the following formula.

$$
\sigma \mathbf{D} \mathbf{C} = \mathbf{1}/\mathbf{p} \tag{2}
$$

**55**

up to 150°C.

**Figure 2.**

**Table 1.**

*DC Conductivity of Activated Carbon Filled Epoxy Gradient Composites*

*Lists the density (ρ) values of gradient composite at different distances.*

**Sample no. Density (g/cc)** Sample 1 1.000 Sample 2 1.05317 Sample 3 1.06169 Sample 4 1.0999

observation is that there is a peak shift towards the higher temperature side with

*Variation of DC conductivity with temperature for activated carbon filled epoxy sample 1.*

**Figure 4** shows the variation of DC conductivity with temperature for activated

It has been observed that DC conductivity suddenly increases after 100°C in all the cases. Increase of DC conductivity appeared at 124°C and it goes on increasing

**Figure 5** shows the variation of DC conductivity with temperature for activated carbon powder filled epoxy gradient composites sample 4. DC conductivity increases from 110°C then after 132°C there is an increase in DC conductivity. It was reported that electrical conductivity of reinforced papers with respect to the weight fraction of Ag-plated carbon fiber increased with increasing content of carbon fiber. Due to the three-dimensional contacts between carbon fibers the electrical conductivity of the paper increased irrespective of the increase in thickness. The electrical conductivity of the reinforced paper having the Ag-plated carbon fiber was high because of the large number of pores formed on the activated carbon fiber [30]. When the volume percent of carbon content is increased or decreased, the material exhibits a change in resistivity. Heating can affect the conductivity of the polymer material on increasing the temperature [31]. On increasing

increase in activated carbon powder content.

carbon powder epoxy gradient sample 3.

*DOI: http://dx.doi.org/10.5772/intechopen.85233*

#### **2.2 Density measurements**

Densities of activated carbon filled epoxy resin composites were determined by using a Mettler Toledo precision balance.

## **3. Results and discussion**

**Figure 1** shows the schematic view of the gradient composite sample prepared using a mix of activated carbon powder and epoxy. This schematic diagram shows the distribution of activated carbon powder in the composite.

**Table 1** lists the density of activated carbon powder filled epoxy gradient composites at different distances from periphery. This shows the increase of distance from periphery decreases the density of the composite. This is due to the decrease in activated carbon content. **Figure 2** shows the variation of DC conductivity with temperature for activated carbon powder filled epoxy sample 1. In this plot DC conductivity increased at 108°C then at 112°C it became constant up to 128°C and then there is a sudden increase in DC conductivity after 128°C, and it increases up to 150°C.

**Figure 3** shows the variation of DC conductivity with temperature for activated carbon powder filled epoxy gradient composites sample 2. This plot shows that up to 98°C there is no increase in DC conductivity. After 106°C there is a sudden increase in DC conductivity with increase of temperature and a peak was found at 138°C temperature. This plot shows that there is an increase in DC conductivity with the increase in activated carbon powder content at all temperatures. Another important

**Figure 1.** *Schematic diagram of activated carbon distribution in four sections.*


*DC Conductivity of Activated Carbon Filled Epoxy Gradient Composites DOI: http://dx.doi.org/10.5772/intechopen.85233*

**Table 1.**

*Mechanics of Functionally Graded Materials and Structures*

where R is the resistance value of the sample; A (cm2

the distribution of activated carbon powder in the composite.

*Schematic diagram of activated carbon distribution in four sections.*

Conductivity was calculated by using the following formula.

trodes; and l (cm) is the thickness of the sample.

Resistance (R) values of activated carbon powder filled epoxy gradient samples were measured by using a kiethley electrometer model 610°C in the temperature range ranging from 28 to 150°C. Heating rate was kept constant at 1°C/min.

DC conductivity (σDC) values were calculated by using the following relation

ρ = R<sup>∗</sup>A/l (1)

σDC = 1/ρ (2)

Densities of activated carbon filled epoxy resin composites were determined by

**Figure 1** shows the schematic view of the gradient composite sample prepared using a mix of activated carbon powder and epoxy. This schematic diagram shows

**Table 1** lists the density of activated carbon powder filled epoxy gradient composites at different distances from periphery. This shows the increase of distance from periphery decreases the density of the composite. This is due to the decrease in activated carbon content. **Figure 2** shows the variation of DC conductivity with temperature for activated carbon powder filled epoxy sample 1. In this plot DC conductivity increased at 108°C then at 112°C it became constant up to 128°C and then there is a sudden increase in DC conductivity after 128°C, and it increases up

**Figure 3** shows the variation of DC conductivity with temperature for activated carbon powder filled epoxy gradient composites sample 2. This plot shows that up to 98°C there is no increase in DC conductivity. After 106°C there is a sudden increase in DC conductivity with increase of temperature and a peak was found at 138°C temperature. This plot shows that there is an increase in DC conductivity with the increase in activated carbon powder content at all temperatures. Another important

) is the area of the elec-

**2.1 Resistivity measurements**

**2.2 Density measurements**

**3. Results and discussion**

using a Mettler Toledo precision balance.

**54**

**Figure 1.**

to 150°C.

*Lists the density (ρ) values of gradient composite at different distances.*

**Figure 2.**

*Variation of DC conductivity with temperature for activated carbon filled epoxy sample 1.*

observation is that there is a peak shift towards the higher temperature side with increase in activated carbon powder content.

**Figure 4** shows the variation of DC conductivity with temperature for activated carbon powder epoxy gradient sample 3.

It has been observed that DC conductivity suddenly increases after 100°C in all the cases. Increase of DC conductivity appeared at 124°C and it goes on increasing up to 150°C.

**Figure 5** shows the variation of DC conductivity with temperature for activated carbon powder filled epoxy gradient composites sample 4. DC conductivity increases from 110°C then after 132°C there is an increase in DC conductivity.

It was reported that electrical conductivity of reinforced papers with respect to the weight fraction of Ag-plated carbon fiber increased with increasing content of carbon fiber. Due to the three-dimensional contacts between carbon fibers the electrical conductivity of the paper increased irrespective of the increase in thickness. The electrical conductivity of the reinforced paper having the Ag-plated carbon fiber was high because of the large number of pores formed on the activated carbon fiber [30]. When the volume percent of carbon content is increased or decreased, the material exhibits a change in resistivity. Heating can affect the conductivity of the polymer material on increasing the temperature [31]. On increasing

**Figure 3.** *Variation of DC conductivity with temperature for activated carbon filled epoxy sample 2.*

**Figure 4.** *Variation of DC conductivity with temperature for activated carbon filled epoxy sample 3.*

temperature polymer expands as compared to CB aggregates and the interparticle distance between the aggregates increases, which causes destruction of conductive networks and as a result there is an increase in the resistivity with temperature.

It was reported that the electrical resistivity (ρ) of composite at low temperature is dominated by the electronic properties of the nanotubes, and tunneling nature [32–34].

ln σ vs. T<sup>−</sup><sup>1</sup> plot for activated carbon powder filled epoxy has been analysed by using the following Arrhenius equation.

**57**

*DC Conductivity of Activated Carbon Filled Epoxy Gradient Composites*

*Variation of DC conductivity with temperature for activated carbon filled epoxy sample 4.*

**Sample no. Activation energy (eV)** Sample 1 1.056682 Sample 2 1.224812 Sample 3 1.278476 Sample 4 1.297912

*Lists the activation energy (eV) of sample 1, sample 2, sample 3, and sample 4.*

σ = A exp−WE/KT (3)

where WE is the activation energy of conduction; k is Boltzmann's constant; A is

On increasing filler concentration, conductive paths among the filler particles increase, and the average distance becomes smaller as a result conductivity of the

a.DC conductivity value increases from sample 1 to sample 4. This shows the

c.Different transition points are observed in DC conductivity plots in different samples. Transition temperature shifts to lower side with the increase in

d.Activation energy decrease with increase of activated carbon content in the

b.Increase of activated carbon content increases the DC conductivity.

*DOI: http://dx.doi.org/10.5772/intechopen.85233*

a constant; and T is the temperature in (K).

existence of graded structure (**Table 2**).

activated carbon content.

composite increased.

**4. Conclusions**

**Figure 5.**

**Table 2.**

samples.

## *DC Conductivity of Activated Carbon Filled Epoxy Gradient Composites DOI: http://dx.doi.org/10.5772/intechopen.85233*

**Figure 5.**

*Mechanics of Functionally Graded Materials and Structures*

temperature polymer expands as compared to CB aggregates and the interparticle distance between the aggregates increases, which causes destruction of conductive networks and as a result there is an increase in the resistivity with temperature.

*Variation of DC conductivity with temperature for activated carbon filled epoxy sample 3.*

*Variation of DC conductivity with temperature for activated carbon filled epoxy sample 2.*

It was reported that the electrical resistivity (ρ) of composite at low temperature is dominated by the electronic properties of the nanotubes, and tunneling nature

plot for activated carbon powder filled epoxy has been analysed by

**56**

[32–34].

**Figure 4.**

**Figure 3.**

ln σ vs. T<sup>−</sup><sup>1</sup>

using the following Arrhenius equation.

*Variation of DC conductivity with temperature for activated carbon filled epoxy sample 4.*


#### **Table 2.**

*Lists the activation energy (eV) of sample 1, sample 2, sample 3, and sample 4.*

$$
\sigma = \mathbf{A} \exp^{-\mathbf{W}\_0/\mathbf{KT}} \tag{3}
$$

where WE is the activation energy of conduction; k is Boltzmann's constant; A is a constant; and T is the temperature in (K).

On increasing filler concentration, conductive paths among the filler particles increase, and the average distance becomes smaller as a result conductivity of the composite increased.
