Graphite-epoxy Composites Research Articles

Indirect determination of free chlorine in seawater by cyclic voltammetry using graphite–epoxy composite electrode: Hydrogen adsorption capacity of graphite–epoxy composite is one–third of that of platinum

A new possibility of indirect determination of free chlorine using a graphite–epoxy composite(GEC) electrode instead of Pt disk electrode was suggested by interpreting the relationship between the peak current of the oxidation peak for hydrogen generated through water electrolysis in CV and the amount of the free chlorine. The linear response range of concentration was 0.06–0.2 mg∙L−1 with correlation coefficient of 0.9951 (n = 5) and the sensitivity of 1225 μA cm−2 mg−1 L. The limit of detection (LOD) calculated from the 3σ IUPAC criteria was 1.2 × 10−2 mg L−1. The relative standard deviation (RSD) to 0.06 mg L−1 was 4.65 %(n = 10). The results show that the amount of free chlorine in the disinfected seawater can be indirectly determined by using a GEC electrode without influence of interferences unlike a Pt disk electrode. On the other hand, in this paper, a new method is proposed to evaluate the relative hydrogen adsorption capacity by the sensitivity of GEC electrode compared with that of Pt disk electrode. During the investigation of the hydrogen adsorption on the surface of the working electrode, we obtained the result that the hydrogen adsorption capacity of GEC is one-third of that of platinum.

Indirect determination of free chlorine in seawater by cyclic voltammetry using graphite–epoxy composite electrode: Hydrogen adsorption capacity of graphite–epoxy composite is one–third of that of platinum

A new possibility of indirect determination of free chlorine using a graphite–epoxy composite(GEC) electrode instead of Pt disk electrode was suggested by interpreting the relationship between the peak current of the oxidation peak for hydrogen generated through water electrolysis in CV and the amount of the free chlorine. The linear response range of concentration was 0.06–0.2 mg∙L−1 with correlation coefficient of 0.9951 (n = 5) and the sensitivity of 1225 μA cm−2 mg−1 L. The limit of detection (LOD) calculated from the 3σ IUPAC criteria was 1.2 × 10−2 mg L−1. The relative standard deviation (RSD) to 0.06 mg L−1 was 4.65%(n = 10). The results show that the amount of free chlorine in the disinfected seawater can be indirectly determined by using a GEC electrode without influence of interferences unlike a Pt disk electrode. On the other hand, in this paper, a new method is proposed to evaluate the relative hydrogen adsorption capacity by the sensitivity of GEC electrode compared with that of Pt disk electrode. During the investigation of the hydrogen adsorption on the surface of the working electrode, we obtained the result that the hydrogen adsorption capacity of GEC is one-third of that of platinum.

Mechanical Properties of Basalt / Chopped E-Glass Fiber and Graphite Powder Reinforced Hybrid Composites

In the current investigation an effort has put to study the effect of E-glass chopped mat and graphite powder in variations of 5g, 10g, and 15g on the tensile and flexural behavior of a basalt fiber-reinforced epoxy composite laminate reinforced with E-Glass fiber and Graphite powder. Hand layup technique has been used for the fabrication of the composites. Tensile, flexural, impact, and hardness tests were done on the Basalt/E-glass/Graphite epoxy composite in accordance with ASTM standards. The results indicate significant improvement in tensile strength, impact strength and hardness when E-glass was incorporated in the basalt/epoxy composite. However, basalt/E-glass/10% graphite epoxy composite was shown to have a greater flexural strength. An excellent dispersion of the reinforcements in the polymeric matrix, which elevated surface area for solid interfacial contact and effective load transmission, could possibly be accountable for the improved performance of the laminates that were successfully developed.

Phase and orientation effects in X-ray attenuation of carbonaceous epoxy composites

Composites made of carbon nanotubes (CNTs) reinforced in an epoxy matrix have already been successfully used as electromagnetic interference shielding materials. Different weight fractions of randomly distributed and vertically aligned multiwall carbon nanotubes (MWCNTs), graphite, and carbon fiber reinforced in the epoxy matrix were used to make these composites. The comparisons of percentage attenuation of different composite materials were studied under both diagnostic or hard (narrow beam geometry) and soft X-rays (monochromatic X-rays beam). It was found that the concentration of CNTs and graphite in epoxy composites affects attenuation. The results also demonstrate that the percentage attenuation for CNTs (as made) epoxy composite is always higher than graphite epoxy and treated CNTs epoxy composite at any concentration at the same thickness and tube voltage. This study also confirmed that the metal catalyst particles present in CNTs contribute to a considerable attenuation of X-rays along with CNTs and also demonstrated that the increase in metal content inside CNTs increases the attenuation. For hard X-rays, the orientation of CNTs in composites affects attenuation, and this effect gradually weakens at higher tube voltages. Vertically aligned carbon nanotubes (VACNT) array epoxy, and the thin composites are not suitable to attenuate diagnostic X-rays coming from high tube potential. For thin samples, VACNT array epoxy composites always perform better on attenuation of soft X-rays than randomly oriented CNTs in composites with any other composition lower than 15 wt %. This study also showed that there is a difference in the attenuation of soft X-rays amongst CNTs, graphite, and carbon fiber epoxy composites, which confirms that the attenuation depends on the geometry of the carbon structures. There is a clear effect of the orientation of CNTs in VACNTs epoxy composite on soft X-ray attenuation, and it shows that the radial direction of CNTs attenuates more X-ray radiation than the tube axis direction.

On the evaluation of failure strain in graphite-epoxy composites

Determination of failure strains is a topic of great interest for the design of composite structures. To evaluate the ultimate strains of a composite, tensile tests have been carried out on specimens with a range of fiber orientations between 0° and 90°. Ultimate tensile strengths obtained present low or moderate dispersion, the average values constituting a good estimation of the failure stress. Values of failure strains obtained present high dispersion for almost all orientations, so it is proposed to take as failure strain threshold the minimum value for each orientation. Finally, the shear behavior of the material has been evaluated.

Extraction-assisted voltammetric determination of homocysteine using magnetic nanoparticles modified with molecularly imprinted polymer

Amagnetic graphite-epoxy composite (m-GEC) electrochemical sensor is presentedbased on magnetic imprinted polymer (mag-MIP) to determine homocysteine (Hcy). Mag-MIP was synthesized via precipitation polymerization, using functionalized magnetic nanoparticles (Fe3O4) together with the template molecule (Hcy), the functional monomer 2-hydroxyethyl methacrylate (HEMA), and the structural monomer trimethylolpropane trimethacrylate (TRIM). For mag-NIP (magnetic non-imprinted polymer), the procedure was the same in the absence of Hcy. Morphological and structural properties of the resultant mag-MIP and mag-NIP were examined usingTEM, FT-IR, and Vibrating Sample Magnetometer. Under optimized conditions, the m-GEC/mag-MIP sensor showed a linear range of 0.1-2µmol L-1, with alimit of detection (LOD) of 0.030µmol L-1. In addition, the proposed sensor responded selectively to Hcy compared to several interferents present in biological samples. The recovery values determined by differential pulse voltammetry (DPV) were close to 100% for natural and synthetic samples, indicating good method accuracy. The developed electrochemical sensor proves to be a suitable device for determining Hcy, with advantages related to magnetic separation and electrochemical analysis.

Amine functionalization on thermal and mechanical behaviors of graphite nanofibers-loaded epoxy composites

With the growing demand for faster and more powerful computing, effective heat dissipation is essential to ensure the longevity, reliability, and high performance of electronic systems. In the field of modern electronic packaging materials, there is a great need for graphitic material-loaded polymeric composites (GPCs) with excellent thermal conductivities. However, the enhancement efficiency of GPCs is hindered by the agglomeration of fillers and the interfacial thermal resistance caused by the lack of continuous thermally conductive pathways between the filler and matrix. Understanding the interfaces between filler and matrix is of great importance in optimizing the performances of GPCs. Here, we fabricated graphite nanofibers (GNF)-loaded nanocomposites using acid-functionalized GNF (AGNF) and acid-tetraethylenepentamine-functionalized (TGNF) as a filler and epoxy resin as a matrix with different GNF loading contents to explore the interfacial properties of the nanocomposites. The optimal GNF loading for AGNF was 0.5 wt.%, while the TGNF showed 0.75 wt.%. The highest thermal conductivity (0.51 W m−1 K−1) and fracture toughness (25.8 MPa m1/2) values were found in the TGNF-loaded nanocomposites with a fraction of 0.75 wt.%, representing enhancements of ∼145% and ∼400%, respectively, compared to those of neat nanocomposites. The experimental data presented herein demonstrate that the interfacial properties play a significant role in enhancing the thermal and mechanical performances of the nanocomposites. The present approach is expected to serve as a valuable tool in the design of conductive polymeric nanocomposites for further practical applications, such as thermal interface materials and packaging of high-power electric devices.

Graphite-epoxy composites for bipolar plates: The gas permeability issue

To sustain Hydrogen Economy, proton exchange membrane (PEM) devices are expected to play a central role in both the generation of clean hydrogen and its efficient employment. Bipolar plates are an essential part of PEM devices, therefore investigations directed to technical improvement and cost reduction of these components deserve considerable attention. This work represents an extension of our previous study on graphite-epoxy composites suitable for manufacturing bipolar plates and based on the use of cheap and commercially available materials. Through appropriate changes in the formulation of the composites and in the processing conditions, we succeeded in obtaining materials with full technical compliance, in terms of electrical conductivity and gas permeability. The processability and productivity of the method were improved as well, through the reduction of molding times. The variation of the properties of the samples with the molding pressure was analyzed.

Influence of Temperature and Moisture on Free Vibration Behavior of Skew Laminated Composite Sandwich Panels with CNTRC Core

This paper presents the influence of temperature and moisture on the free vibration characteristics of skew laminated composite sandwich (SLCS) panels. The face sheets of the panels are made of graphite–epoxy composite, while the core consists of carbon nanotube-reinforced composite. The coupled hygro-elastic and thermo-elastic relations for the SLCS shells/panels are formulated using first-order shear deformation theory. The nonmechanical stiffness matrices are represented by the initial stress stiffness matrix developed using nonlinear strain–displacement relations. The temperature and moisture-dependent material properties are considered to analyze the laminated composite sandwich spherical, hyperbolic, ellipsoid, cylindrical Shells, and flat plates. Several numerical examples are comprehensively studied to establish the influence of temperature, moisture, the volume fraction of carbon nanotubes in the core material, functional gradation types, skew angle, and edge constraints on the vibration responses of SLCS shells. Further exploration is devoted to studying the combined effect of moisture, temperature, and the geometrical parameters such as length to width ratio, length to thickness ratio, radius-to-length ratio, and the core thickness to face sheet thickness ratios on the natural frequency of the skew laminated composite sandwich panels.

Graphite/epoxy composite for building Bipolar Plates

Bipolar plates (BPs) are important components of Proton Exchange Membrane Fuel Cells (PEMFC). Graphite-epoxy composites, having a better corrosion resistance than metal-based BPs and better mechanical properties than graphite BPs, are a promising alternative. In this study, we tried to develop graphite-epoxy composites meeting the technical US DOE targets for 2020, with a proper choice of manufacturing conditions that ensure a good compromise between conductivity, flexural strength, and gas permeability. In particular, we studied the influence of the filler to binder ratio, changed the molding temperature and time, and investigated the effects of increasing pressure both on in-plane conductivity and on helium permeability. We found that both formulation and molding pressure are crucial in determining the permeability of the graphite-epoxy composites, whereas molding temperature and time seem to play a minor role.

Analysis of laminated plain carbon steel leaf spring in maxi truck

The number of parts in motor vehicles can be replaced with composite materials and improvements in composite material mechanical properties. When compared to steel, it has a higher elastic strength and a higher strength-to-weight ratio. As a result, one of an automobile's components, the leaf spring, which bears the vehicle's full weight, is an excellent candidate for replacing steel with composite material. To reduce load of leaf spring, it has same dimensional geometry as the leaf spring. Leaf spring is built of a graphite epoxy composites material that is lower cost than steel and have geometrical as well as mechanical property that are comparable to the steel leaf spring. Leaf springs can be designed and analysed using Autocad, and static analysis can be performed on the springs using ANSYS software. Stresses and deflections can also be calculated.

The Impact of Filler Content on Mechanical and Micro-Structural Characterization of Graphite-Epoxy Composites

The Impact of Filler Content on Mechanical and Micro-Structural Characterization of Graphite-Epoxy Composites

Characterization of graphite-epoxy composite electrodes for free electrochemical detection of adenine and guanine in DNA

Graphite-epoxy composites (GECs) are alternative construction materials for electro­chemical sensors. For these materials, the electron transfer rate constant of some redox reaction depends additionally on the stoichiometric relationship between the insulating and conducting phases of the composite. In this work, the influence of dif­fe­rent ratios of araldite/hardener/graphite on the electrochemical properties of GEC electrodes is evaluated for the simultaneous determination of adenine and guanine in the single chain DNA, using the square wave voltammetry technique. Six GEC electro­des were prepared with different ratios of components, and electrochemically charac­terized by cyclic voltammetry in the presence of ferri/ferrocyanide redox couple as a redox probe. GEC electrodes that showed the best electrochemical responses of redox probe were characterized by thermogravimetric analysis (TGA) and used for the simul­taneous determination of free adenine and guanine in a solution, and DNA oligonu­cle­otides. The best results were obtained for GEC electrodes containing twice higher volu­me of araldite resin with respect to the hardener. TGA analysis revealed presence of 15-26 % of resin for these GEC electrodes. The obtained results revealed potential appl­ication of these GEC electrodes as DNA sensors based on the oxidation signal of guanine.

Dummy Molecularly Imprinted Polymers Using DNP as a Template Molecule for Explosive Sensing and Nitroaromatic Compound Discrimination

This work reports a rapid, simple and low-cost voltammetric sensor based on a dummy molecularly imprinted polymer (MIP) that uses 2,4-dinitrophenol (DNP) as a template for the quantification of 2,4,6-trinitrotoluene (TNT) and DNP, and the identification of related substances. Once the polymer was synthesised by thermal precipitation polymerisation, it was integrated onto a graphite epoxy composite (GEC) electrode via sol–gel immobilisation. Scanning electron microscopy (SEM) was performed in order to characterise the polymer and the sensor surface. Responses towards DNP and TNT were evaluated, displaying a linear response range of 1.5 to 8.0 µmol L−1 for DNP and 1.3 to 6.5 µmol L−1 for TNT; the estimated limits of detection were 0.59 µmol L−1 and 0.29 µmol L−1, for DNP and TNT, respectively. Chemometric tools, in particular principal component analysis (PCA), demonstrated the possibilities of the MIP-modified electrodes in nitroaromatic and potential interfering species discrimination with multiple potential applications in the environmental field.

Development of magnetic nanoparticles modified with new molecularly imprinted polymer (MIPs) for selective analysis of glutathione

The present work aims to develop electroanalytical strategies for separating and quantifying one of the most important biothiols, the reduced glutathione (GSH), based on developing and applying a new and selective magnetic molecular imprinted polymer (mag-MIP). This magnetic-supported polymer was synthesized by precipitation, using GSH as a template, having acrylamide as the functional monomer and trimethylolpropane trimethacrylate as a cross-linking agent. These materials' morphological and physical characteristics were investigated by scanning electron microscope, Fourier transform infrared, and vibrating sample magnetometry. Physicochemical parameters, such as adsorption capacity, were obtained and compared with the respective mag-NIP, which are control polymers without the selective cavity. After all characterizations, mag-MIP and mag-NIP were evaluated on magnetic graphite-epoxy composite (m-GEC) electrodes. The characteristics of the obtained sensors were investigated by cyclic voltammetry and differential pulse voltammetry. After optimizing experimental and operational conditions, a linear response for the concentration of GSH, in the range of 1–1400 μmol/L, with low detection and quantification limits of 7 and 20 nmol/L, respectively, were obtained. The GSH levels in mice liver samples were measured by electrochemical and spectrophotometric techniques to compare the method's effectiveness. A high correlation between them and a low relative error of 1.06 % were obtained, indicating the good functionality of the proposed sensor.

Comparison of the shear behavior in graphite-epoxy composites evaluated by means of biaxial test and off-axis tension test

Abstract Characterization of shear behavior in composite materials remains a not fully solved problem. In the last fifty years, many different approaches have been proposed to solve this problem (rail shear, thin-walled tube torsion, off-axis tensile, ±45° tensile, Arcan, Iosipescu, asymmetric four-point bend, plate twist, v-notched rail shear, off-axis flexural, and shear frame), although none of these approaches have achieved an unquestionable solution. For this reason, proposals of alternative methods and comparison between different experimental techniques are of interest. In the present work, the use of cruciform samples with the fiber oriented at 45° with respect to the load directions, and subjected to tension-compression (creating a pure shear stress state at the central part of the samples), is studied. The experimental results of the cruciform samples have been compared with the off-axis tests (with the fiber at 10°) for the same material (AS4/8552), finding a good agreement between the shear experimental curves, especially at the initial part of the curve, where the shear modulus is calculated. Nevertheless, the shear strength value obtained by means of the cruciform specimen has shown to be significantly lower than that obtained using the off-axis test. A Finite Element numerical model of the cruciform specimen has been developed to analyze the stress field of the samples. Numerical results have shown that there is a central area of the cruciform specimens where a pure and uniform shear stress state is developed, which is suitable for the evaluation of the shear constitutive law of the material. It has been observed that there is a (σ 22) stress concentration in the transition between the straight and curved parts of the boundary geometry of the samples, which explain some premature failures of the samples. This premature failure could be avoided with tabs extended up to the beginning of the central part of the sample.

Synthesis, mechanical, thermal, and electrical characterization of graphite–epoxy composites

AbstractHerein, we present a simple procedure for fabricating epoxy/graphite composites using a simple solution blending method. The addition of graphite filler in the epoxy matrix showed a beneficial effect on mechanical properties by enhancing Young's modulus up to 55.25% of its value. The highest thermal conductivity was obtained to be 1.53 ± 0.07 W· m−1· K−1, which depicts a fourfold increment as compared to the neat matrix. The effective thermal conductivity has been predicted using Nan model, which shows a satisfactory agreement with the experimental data. Besides, the investigated composites display enhanced electrical conductivity; this evolution of electrical conductivity as a function of filler volume fraction is well described using percolation theory. Thermogravimetry and differential scanning calorimetry have been used to determine the thermal properties of the composites as a function of filler volume fraction. These findings indicate that the thermal, electrical, and mechanical properties of epoxy/graphite composites could be ideal for thermal management and control of heat transfer devices.

Determination of Chemical Oxygen Demand (COD) Using Nanoparticle-Modified Voltammetric Sensors and Electronic Tongue Principles

This manuscript reports the use of nanoparticle-modified voltammetric sensors for the rapid and green determination of chemical oxygen demand in river waters and waters from agricultural waste. Four different variants of modified electrodes have been prepared: CuO nanoparticles electrogenerated over Cu and covered with Nafion film (CuO/Cu-Nf), and graphite–epoxy composites modified with Cu, CuO, and Cu–Ni alloy nanoparticles. The response features of these electrodes were assessed by calibrating them vs. glucose, glycine, ethyleneglycol, and hydrogenphtalate in alkaline media, as samples providing different difficulty in their (bio)degradation characteristics. The most sensitive electrode was demonstrated to be the (CuO/Cu-Nf) electrode, with an LOD of 12.3 mg O2·L−1. The joint information provided by the sensor array showed the ability of estimating both the organic load and the type of sample in terms of difficulty of degradation, in what can be named an intelligent sensor assembly.

Graphite-epoxy composites for fuel-cell bipolar plates: Wet vs dry mixing and role of the design of experiment in the optimization of molding parameters

Bipolar plates (BPs) are key components of Proton Exchange Membrane Fuel Cells mainly employed in hydrogen-powered electric vehicles. Here, a reliable and detailed experimental method to prepare graphite-epoxy composites suitable for manufacturing BPs is reported. Dry and wet mixing procedures were compared and a simple composition was optimized, with regard to electrical conductivity. The adoption of wet mixing of the components and the choice of the conductive filler were the main factors that contributed to the achievement of good electrical and mechanical properties. The addition of a small percentage of carbon black as a secondary filler was also advantageous. The effects of molding parameters (pressure, temperature and time) on a fixed-composition graphite-epoxy composite were modeled using a Design Of Experiments approach, which provided valuable information for future improvements. Conductivity values well above the US DOE requirements were obtained.

Electrical Properties of Powders of Thermally Reduced Graphite Oxide and Epoxy Composites Based on Them

The effect of annealing thermally reduced graphite oxide powders on their electrical conductivity and density at pressures up to 7 MPa is considered. The specific surface area of ​​the powders is determined at various temperatures of annealing. The complex permittivity of epoxy composites based on these powders used as fillers is measured at frequencies of 1.7, 2.9, and 9.8 GHz. The obtained average value of the dielectric loss tangent of the investigated composites in the specified frequency range exceeded the corresponding average value for epoxy composites based on natural graphite by 5–6 times.