Kamal K. Kar

Synthesis of Carbon Nanotubes on the Surface of Carbon Fiber/fabric by Catalytic Chemical Vapor Deposition and Their Characterization

Carbon nanotubes (CNTs) were grown radially on the surface of carbon fiber/fabric by catalytic chemical vapor deposition through the decomposition of acetylene gas. Nickel was used as a catalyst. The CNTs were synthesized over a range of temperature from 650°C to 800°C. Scanning electron microscopy and transmission electron microscopy studies reveal the presence of CNTs. The density of CNTs on the carbon fiber is high. Thermal analysis study shows that the CNT coated carbon fiber is more stable in air than in oxygen. Considerable improvement in the remnant and saturation magnetization has been found through a vibrating sample magnetometer study. Current versus voltage measurements show a decrease of ∼47% in onset voltage after the growth of CNTs on the surface of carbon fiber. Measurement of Brunauer Emmett and Teller surface area shows a threefold increase in the surface area of the carbon fibers after the growth of CNTs on their surface. A single‐fiber pull out test indicates that the CNT coated carbon fiber improves the interfacial load transfer with respect to the as‐received fiber. Improvement in storage modulus of a CNT coated carbon fiber composite in a polyester matrix is supported by dynamic mechanical analysis.

Synthesis of polyether ether ketone membrane with pendent phosphonic acid group and determination of proton conductivity and thermal stability

Incorporation of phosphonic acid groups in the polymer backbone by direct phosphonation or by polymerization of prefunctionalized monomers requires harsh reaction conditions. The present research work reported an easy synthesis strategy of phosphonic acid-containing diphosphonated polyether ether ketone (P-PEEK) by polycondensation of difluoro benzophenone and phosphonated bisphenol A (BPA). Phosphonation of BPA was carried out by monophosphoazylation followed by rearrangement in the presence of organolithium compound at −78°C. Nuclear magnetic resonance (NMR) imaging, Fourier transform infrared, and electrospray ionization mass spectrometry were performed to acquire complete structural information about the synthesized monomer and polymer. Degree of phosphonation of the synthesized polymer calculated from proton NMR spectra was as high as 70%. Thermal properties of the P-PEEK were checked using a differential scanning calorimeter (DSC) and a thermogravimetric analyzer. Moderate increase in melting point and glass transition temperature (T g) were observed from the DSC analysis. Solubility of the polymer was improved significantly in the common organic solvents that permitted the polymer to be solution casted. Solid electrolyte membrane exhibited through plane proton conductivity of 7.5 × 10−5 S cm−1 at 25°C under fully hydrated conditions.

Hierarchically structured catalyst layer for the oxygen reduction reaction fabricated by electrodeposition of platinum on carbon nanotube coated carbon fiber

The cost-efficient fabrication of cathode catalyst layers with low Pt-loadings and high oxygen reduction reaction (ORR) performances is of prime importance towards the commercialization of low temperature fuel cells. Here, an attempt has been made to fabricate a hierarchically structured cathode catalyst layer consisting of Pt-nanoparticle clusters supported on defective carbon nanotube (CNT) coated carbon fiber (CNTCF). CNTs were grown on carbon fiber (CF) using chemical vapor deposition (CVD), while electrodeposition was employed to deposit Pt-nanoparticle clusters onto the CNTCF. The effect of Pt-loading on the oxygen reduction reaction (ORR) performance of the Pt-coated CNTCF (Pt-CNTCF) electrocatalysts was studied by varying the electrodeposition time (ted) between 5 and 30 min, which resulted in a variation of the Pt weight fraction in Pt-CNTCF from almost zero to ∼0.3. Linear sweep voltammetry using a Pt-CNTCF modified glassy carbon (GC) rotating disc electrode (RDE) was employed to study the ORR performance of the samples. The CNTCF support, due to the defective structure of the CNTs, itself exhibits significant ORR activity with an electron transfer number (n) of ∼2.6, which leads to a synergistic enhancement of the overall electrocatalytic performance of Pt-CNTCF. For low Pt-loading on the GC (∼5 μg cm−2), the contribution of the CNTCF support dominated, while the Pt-nanoclusters governed the ORR performance at higher Pt-loading (>10 μg cm−2), with n > 3.5. Hence, a very low Pt-loading (∼5 μg cm−2) may not be suitable for polymer electrolyte membrane fuel cells as the production of substantial amounts of H2O2 on the catalyst supports may accelerate membrane degradation.

Surface Finishing of Carbon-Carbon Composites Using Abrasive Flow Machining

Carbon-carbon composites (C/Cs) are widely used in the high-technological applications because of their superior properties compared to the other traditional materials. But the surface finishing of these materials using both conventional and unconventional machining (e.g., abrasive flow machining, AFM) is difficult because of their nonhomogeneity, anisotropy, hardness and intrinsic brittleness. In order to study the feasibility of AFM, 3-D C/Cs were initially ground to a surface roughness value in the range of 0.7 ± 0.1 μm, and then finished using newly reported media containing styrene butadiene rubber as a carrier, silicon carbide (SiC) as abrasives and hydraulic oil as a processing oil. The effects of process parameters, such as abrasive mesh size, extrusion pressure, loading of processing oil and abrasive particles, and the number of cycles on the improvement in surface roughness of the C/C material were studied. The best surface finish was observed at an extrusion pressure of 6 MPa and 150 cycles using a media having 70wt% SiC abrasive particles of 220 mesh size and 12wt% processing oil. Further, the surface texture of the workpieces was studied by scanning electron microscope.

Synthesis of Carbon Nanofibers on Hydroxyapatite by Flame Deposition

Flame deposition was used to grow high quality carbon nanofibers (CNFs) on the hydroxyapatite (HA) using methanol as carbon source. The HA was activated with Fe-compound by a dip coating. These CNFs were purified by acid leaching. The as-produced and purified CNFs were characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscopy (TEM), atomic force microscopy, and Raman spectroscopy. Sizes of the CNFs were found to be 0.05 to 5 μm in diameter and more than 40 μm in length. The agglomeration of Fe-catalyst, which decides the diameter of the CNFs, was controlled by the catalyst coating time as well as sintering temperature of HA. Fibrous structure of CNF was confirmed by TEM. This CNF can be used as reinforcing element for improving the mechanical properties in high strength nanocomposites due to its straight and unidirectional morphology. It can also be an excellent candidate for drug vehicles as indicated by the swelling test.

Numerical Simulation of the Degradation Behavior of the Phenolic Resin Matrix During the Production of Carbon/Carbon Composites

A numerical simulation for the carbonization step during processing of two dimensional (2-D) carbon/carbon (C/C) composites was studied. The composites were made of phenolic resin and carbon fabric. Two-stage decompositions of phenolic resin were used. Subsequently, a 2-D finite difference method (FDM) was used to solve the governing equations for the flow of gases during carbonization in C/C composites. For solving the problem, the combined effects for degradation of phenolic matrix and increasing temperature during carbonization on the material properties were studied. Using material properties, numerical simulation provides pressure, temperature, porosity distribution, specific heat, thermal conductivity, density and viscosity of evolved gas as a function of processing time/temperature and space. The results of 2-D numerical simulation code were compared with the results of a previously published one-dimensional FDM.