**1. Introduction**

Activated carbon powder filled epoxy composites having 3 wt.% of activated carbon powder and epoxy resin have been developed. DC conductivity measurements are conducted on the graded composites by using an Electro-meter in the temperature range from 28 to 150°C. DC conductivity increases with the increase of distance in the direction of centrifugal force, which shows the formation of graded structure with the composites. DC conductivity increases on increase in activated carbon powder content. Activation energy was calculated and showed ionic conduction in the composites. Polymers with conductive fillers have many applications in solid state devices, mostly in fabrication of polymer light-emitting diodes, microelectronic components, optical displays as battery and fuel cell electrodes, antistatic media, corrosion-resistant materials, etc. [1–3]. The advantage of using conductive filler is that it is possible to control their electrical conductivity.

Besides good electrical conductivity and optical characteristics, conducting polymers have several other advantages as plasticity, low cost, lightweight and ease of fabrication [4–6].

Functionally graded composites are a novel class of composites which shows unique properties. Their graded property can be used as medical implants, for thermal protection in space vehicles, and they can be used as thermoelectric converter for energy conservation. Due to their versatile nature, they are widely used in nano, optoelectronic and thermoelectric materials also. Future applications of carbon nanotubes (CNT) reinforced functionally graded composite materials (FGCM) is expected to unique material having a wide range of possibilities in various areas such as aerospace, energy, automobile, medicine and structural industry. These materials can be used as gas adsorbents, probes, chemical sensors, nanopipes, nano-reactors, etc.

FGM can be used according the desired applications in biomedical application, as implants in human body to function properly without destroying the surrounding tissues.

Nigrawal and Chand has studied the dielectric properties of activated carbon filled epoxy composites and reported that small values of activation energy obtained at higher frequencies suggested that the conduction in the composite was due to hopping of charge carriers [7].

Epoxy resins are used as a thermosetting polymer matrix for the preparation of the conductive polymer composites [7–9]. Most of the electrically conductive polymer composites consist of carbon fibres or carbon black. A degree of conductivity is achieved when the concentration of the fillers is high enough so as to form a conductive network within the polymer matrix and such critical concentration, is known as percolation threshold. Conductivity of polymers containing conductive fillers, depends on the size and shape of the filler particles, spatial distribution and the contact resistance [10–14] and also determines the conditions of charge transport. Polymers have wide applications as electrical and electronic materials in the field of electro-photography and opto-electronics [15, 16] and can also be used as interfacial barrier layers and protective coatings. However, prior to using these materials in these specialized applications it is essential to know fundamental properties such as the mechanisms of electrical conduction, charge storage, etc.

It is well known that the addition of nano size additives into polymers has paved way for advanced technologies, such as in electrochemical displays, sensors, catalysis and redox capacitors, etc. [7]. For instance graphene based polymer composites possess potential applications in radiation and electromagnetic shielding, antistatic, shrinkage and corrosion-resistant coatings, and other mechanical and functional attributes such as stiffness, barrier, conducting capabilities, light emitting devices, batteries and other functional applications. Other potential applications could be for high temperature conducting adhesive, or for the bipolar plates for polymer electrolyte membrane fuel cells. Several carbon additives have also been utilized to enhance the properties of a polymer, the most popular being carbon blacks, carbon nanotubes [15–19].

During curing of the thermoset matrix, an internal stress comes and increases the pressure between and decreases the contact resistance. Development and modification of carbonaceous materials in necessary to increase the specific energy and power of supercapacitors, by controlling the pore size distribution, introducing electroactive metallic particles or electroconducting polymers [17–19].

It was reported that conductive polymer composite sensor array made from carbon black with polymers [20, 21].

An activated carbon has extended surface area, microporous structure, high adsorption capacity and high degree of surface reactivity. Activated carbon can be used into various structures such as fill-form, felt-form and fabric-form for various applications [22].

**53**

*DC Conductivity of Activated Carbon Filled Epoxy Gradient Composites*

Different types of activated carbon powder and as well as activated carbon fibers

The conductivity of conductive filler polymer systems depends on the filler type, concentration, structure, surface properties, and conductivity properties of the matrix, distribution of particles in the matrix, contacts between particles, and particle orientation. It is well known that carbon black (CB) particles with a larger

In a recent study effects of carbon nanotube on volume fractions, slenderness ratio, and core-to-face sheet thickness ratio on free vibration behavior of sandwich beams with functionally graded carbon nanotube-reinforced composite was reported. Numerical results were also reported to compare the behavior of sandwich beams of carbon nanotube-reinforced composite face sheets to those with

functionally graded carbon nanotube-reinforced composite face sheets [26]. Flexural properties of epoxy nano composites increased on addition of 1 and 5% vol nano-activated carbon as compared to neat epoxy. A noticeable increment in flexural strength and modulus, was observed on addition of 1 and 5% vol nanoactivated carbon as compared to pure epoxy. The effect of potassium hydroxide and phosphoric acid treatment on activated carbon epoxy nano composites were also investigated. The flexural toughness of both the composites were in range between 0.79 and 0.92 J. It was reported that the flexural strength of activated carbon-bamboo stem, activated carbon-oil palm, and activated carbon-coconut shell reinforced epoxy nanocomposites showed almost same value in case of 5% potassium hydrox-

In case of many FGMs components, properties varies in thickness direction [28]. However, in many modern applications these material have variable properties in both thickness and axial directions [28]. In a paper a gradient material in which properties varies in both aspects are developed and studied [28, 29]. Such smart materials are known as bidirectional functionally gradient (BDFGMs) materials. In

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

Density of activated carbon powder filled epoxy gradient samples was measured

which laser metal deposition based AM technique was used [29].

/g were used for electrical double-layer

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

capacitors [23, 24].

ide activated carbon [27].

**2. Materials and methods**

silver paint before the electrical measurements.

by using a Mettler Toledo precision balance.

with surface area in the range of 86–3000 m2

structure may render a relative high conductivity [25].

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

*Mechanics of Functionally Graded Materials and Structures*

of fabrication [4–6].

ing tissues.

due to hopping of charge carriers [7].

carbon black with polymers [20, 21].

Besides good electrical conductivity and optical characteristics, conducting polymers have several other advantages as plasticity, low cost, lightweight and ease

gas adsorbents, probes, chemical sensors, nanopipes, nano-reactors, etc.

Functionally graded composites are a novel class of composites which shows unique properties. Their graded property can be used as medical implants, for thermal protection in space vehicles, and they can be used as thermoelectric converter for energy conservation. Due to their versatile nature, they are widely used in nano, optoelectronic and thermoelectric materials also. Future applications of carbon nanotubes (CNT) reinforced functionally graded composite materials (FGCM) is expected to unique material having a wide range of possibilities in various areas such as aerospace, energy, automobile, medicine and structural industry. These materials can be used as

FGM can be used according the desired applications in biomedical application, as implants in human body to function properly without destroying the surround-

Nigrawal and Chand has studied the dielectric properties of activated carbon

Epoxy resins are used as a thermosetting polymer matrix for the preparation of the conductive polymer composites [7–9]. Most of the electrically conductive polymer composites consist of carbon fibres or carbon black. A degree of conductivity is achieved when the concentration of the fillers is high enough so as to form a conductive network within the polymer matrix and such critical concentration, is known as percolation threshold. Conductivity of polymers containing conductive fillers, depends on the size and shape of the filler particles, spatial distribution and the contact resistance [10–14] and also determines the conditions of charge transport. Polymers have wide applications as electrical and electronic materials in the field of electro-photography and opto-electronics [15, 16] and can also be used as interfacial barrier layers and protective coatings. However, prior to using these materials in these specialized applications it is essential to know fundamental properties such as the mechanisms of electrical conduction, charge storage, etc. It is well known that the addition of nano size additives into polymers has paved way for advanced technologies, such as in electrochemical displays, sensors, catalysis and redox capacitors, etc. [7]. For instance graphene based polymer composites possess potential applications in radiation and electromagnetic shielding, antistatic, shrinkage and corrosion-resistant coatings, and other mechanical and functional attributes such as stiffness, barrier, conducting capabilities, light emitting devices, batteries and other functional applications. Other potential applications could be for high temperature conducting adhesive, or for the bipolar plates for polymer electrolyte membrane fuel cells. Several carbon additives have also been utilized to enhance the properties of a

filled epoxy composites and reported that small values of activation energy obtained at higher frequencies suggested that the conduction in the composite was

polymer, the most popular being carbon blacks, carbon nanotubes [15–19].

electroactive metallic particles or electroconducting polymers [17–19].

the pressure between and decreases the contact resistance. Development and modification of carbonaceous materials in necessary to increase the specific energy and power of supercapacitors, by controlling the pore size distribution, introducing

During curing of the thermoset matrix, an internal stress comes and increases

It was reported that conductive polymer composite sensor array made from

An activated carbon has extended surface area, microporous structure, high adsorption capacity and high degree of surface reactivity. Activated carbon can be used into various structures such as fill-form, felt-form and fabric-form for various

**52**

applications [22].

Different types of activated carbon powder and as well as activated carbon fibers with surface area in the range of 86–3000 m2 /g were used for electrical double-layer capacitors [23, 24].

The conductivity of conductive filler polymer systems depends on the filler type, concentration, structure, surface properties, and conductivity properties of the matrix, distribution of particles in the matrix, contacts between particles, and particle orientation. It is well known that carbon black (CB) particles with a larger structure may render a relative high conductivity [25].

In a recent study effects of carbon nanotube on volume fractions, slenderness ratio, and core-to-face sheet thickness ratio on free vibration behavior of sandwich beams with functionally graded carbon nanotube-reinforced composite was reported. Numerical results were also reported to compare the behavior of sandwich beams of carbon nanotube-reinforced composite face sheets to those with functionally graded carbon nanotube-reinforced composite face sheets [26].

Flexural properties of epoxy nano composites increased on addition of 1 and 5% vol nano-activated carbon as compared to neat epoxy. A noticeable increment in flexural strength and modulus, was observed on addition of 1 and 5% vol nanoactivated carbon as compared to pure epoxy. The effect of potassium hydroxide and phosphoric acid treatment on activated carbon epoxy nano composites were also investigated. The flexural toughness of both the composites were in range between 0.79 and 0.92 J. It was reported that the flexural strength of activated carbon-bamboo stem, activated carbon-oil palm, and activated carbon-coconut shell reinforced epoxy nanocomposites showed almost same value in case of 5% potassium hydroxide activated carbon [27].

In case of many FGMs components, properties varies in thickness direction [28]. However, in many modern applications these material have variable properties in both thickness and axial directions [28]. In a paper a gradient material in which properties varies in both aspects are developed and studied [28, 29]. Such smart materials are known as bidirectional functionally gradient (BDFGMs) materials. In which laser metal deposition based AM technique was used [29].
