Temperature dependency of resistivity of the carbon black-polyethylene composites below and above percolation threshold is studied based on the electrical conduction mechanism. Temperature coefficient of resistance of the composites below percolation threshold changed from minus to plus, increasing volume fraction of carbon black; this trend decreased with increasing volume fraction of carbon black. The temperature dependence of resistivity of the composites below percolation threshold can be explained with a tunneling conduction model by incorporating the effect of thermal expansion of the composites into a tunneling gap. Temperature coefficient of resistance of the composites above percolation threshold was positive and its absolute value increased with increasing volume fraction of carbon black. By assuming that the electrical conduction through percolating paths is a thermally activated process and by incorporating the effect of thermal expansion into the volume fraction of carbon black, the temperature dependency of the resistivity above percolation threshold has been well explained without violating the universal law of conductivity. The apparent activation energy is estimated to be 0.14 eV.

We investigated the NO gas sensing characteristics of ZnO-carbon nanotube (ZnO-CNT) layered composites fabricated by coaxial coating of single-walled CNTs with a thin layer of 1 wt% Al-doped ZnO using rf magnetron sputtering deposition. Morphological studies clearly revealed that the ZnO appeared to form beadshaped crystalline nanoparticles with an average diameter as small as 30 nm, attaching to the surface of the nanotubes. It was found that the NO gas sensing properties of the ZnO-CNT layered composites were dramatically improved over Al-doped ZnO thin films. It is reasoned from these observations that an increase in the surface-to-volume ratio associated with the numerous ZnO “nanobeads” on the surface of the CNTs results in the enhancement of the NO gas sensing properties. The ZnO-CNT layered composite sensors exhibited a maximum sensitivity of 13.7 to 2 ppm NO gas at a temperature of 200˚C and a low NO gas detection limit of 0.2 ppm in dry air.

We investigated the effects of Co doping on the NO gas sensing characteristics of ZnO-carbon nanotube (ZnO-CNT) layered composites fabricated by coaxial coating of single-walled CNTs with ZnO using pulsed laser deposition. Structural examinations clearly confirmed a distinct nanostructure of the CNTs coated with ZnO nanoparticles of an average diameter as small as 10 nm and showed little influence of doping 1 at.% Co into ZnO on the morphology of the ZnO-CNT composites. It was found from the gas sensing measurements that 1 at.% Co doping into ZnO gave rise to a significant improvement in the response of the ZnO-CNT composite sensor to NO gas exposure. In particular, the Co-doped ZnO-CNT composite sensor shows a highly sensitive and fast response to NO gas at relatively low temperatures and even at low NO concentrations. The observed significant improvement of the NO gas sensing properties is attributed to an increase in the specific surface area and the role as a catalyst of the doped Co elements. These results suggest that Co-doped ZnOCNT composites are suitable for use as practical high-performance NO gas sensors.

Si-C composite with hollow spherical structure was synthesized using ultrasonic treatment of organosilica powder formed by hydrolysis of phenyltrimethoxysilane. The prepared powder was pyrolyzed at various temperatures ranging from 900 to 1300 ˚C under nitrogen atmosphere to obtain optimum conditions for Li-ion battery anode materials with high capacity and cyclability. The XRD and elemental analysis results show that the pyrolyzed Si/C composite at 1100 ˚C has low oxygen and nitrogen levels, which is desirable for increasing the electrochemical capacity and reducing the irreversible capacity of the first discharge. The solid Si-C composite electrode shows a first charge capacity of ~500 mAhg-1 and a capacity fade within 30 cycles of 0.93% per cycle. On the other hand, the electrochemical performance of the hollow Si-C composite electrode exhibits a reversible charge capacity of ~540 mAhg-1 with an excellent capacity retention of capacity loss 0.43% per cycle up to 30 cycles. The improved electrochemical properties are attributed to facile diffusion of Li ions into the hollow shell with nanoscale thickness. In addition, the empty core space provides a buffer zone to relieve the mechanical stresses incurred during Li insertion.

In this work, the hydrogen storage behaviors of carbon nanotubes (CNTs)/metal-organic frameworks-5 (MOF-5) hybrid composites (CNTs/MOF-5) were studied. Hydrothermal synthesis of MOF-5 was conducted by conventional convection heating using 1-methyl-2-pyrrolidone (NMP) as a solvent. Morphological characteristics and average size of the CNTs/MOF-5 were also obtained using a scanning electron microscopy (SEM). The pore structure and specific surface area of the CNTs/MOF-5 were analyzed by N2/77 K adsorption isotherms. The capacity of hydrogen storage of the CNTs/MOF-5 was investigated at 298 K/100 bar. As a result, the CNTs/MOF-5 had crystalline structures which were formed by hybrid synthesis process. It was noted that the CNTs/MOF-5 can be potentially encouraging materials for hydrogen adsorption and storage applications at room temperature.

The NO gas sensing properties of ZnO-carbon nanotube (ZnO-CNT) composites fabricated by the coaxial coating of single-walled CNTs with ZnO were investigated using pulsed laser deposition. Upon examination, the morphology and crystallinity of the ZnO-CNT composites showed that CNTs were uniformly coated with polycrystalline ZnO with a grain size as small as 5-10 nm. Gas sensing measurements clearly indicated a remarkable enhancement of the sensitivity of ZnO-CNT composites for NO gas compared to that of ZnO films while maintaining the strong sensing stability of the composites, properties that CNT-based sensing materials do not have. The enhanced gas sensing properties of the ZnO-CNT composites are attributed to an increase in the surface adsorption area of the ZnO layer via the coating by CNTs of a high surface-to-volume ratio structure. These results suggest that the ZnO-CNT composite is a promising template for novel solid-state semiconducting gas sensors.

The factors that influence ablation resistance in fiber composites are properties of the reinforced fiber and matrix, plugging quantity of fiber, geometrical arrangement, crack, pore size, and their distributions. To examine ablation resistance according to distribution of crack and pore size that exist in carbon/carbon composites, this study produced various sizes of unit cells of preforms. They were densified using high pressure impregnation and carbonization process. Reinforced fiber is PAN based carbon fiber and composites were heat-treated up to 2800℃. The finally acquired density of carbon/carbon composites reached more than 1.932 g/cm3. The ablation test was performed by a solid propellant rocket engine. The erosion rate of samples is below 0.0286 mm/s. In conclusion, in terms of ablation properties, the higher degree of graphitization is, the more fibers that are arranged vertically to the direction of combustion flame are, and the less interface between reinforced fiber bundle and matrix is, the better ablation resistance is shown.

Rubber reinforcing carbon black N330 was treated by physical activation under CO2 to different degrees of burn-off. The mechanical properties indicating the reinforcement of SBR (Styrene-Butadiene Rubber) vulcanizates filled by activated carbon blacks, such as tensile strength, modulus at 300% strain and elongation at break were determined. During CO2 activation of fresh carbon blacks, the development of microporous structure caused an increase of extremely large specific surface area and the porosity turned out to be an increasing function of the degree of burn-off. The tensile strength and modulus at 300% of activated carbon blacks filled rubber composites were improved at lower loading ratios of 20 and 30 phr, but decreased drastically after 30 phr, which is considered that it might be difficult to get a fully dispersed rubber mixture at higher loading ratios for fillers having very large specific surface areas. However, the Electromagnetic Interference (EMI) shielding effectiveness of SBR rubber composites having activated carbon black at 74% yield were improved at a large extent when compared to those having raw carbon black and increased significantly as a function of increasing loading ratio.

Carbon nanotube (CNT)/ composites were synthesized to enhance the hydrogen storage properties. The emphasis was made on the effect of different shortening methods of CNTs on the open-tip structure and the resulting properties. The use of open CNTs as a starting material resulted in an enhanced hydrogen properties of CNT/ composites. Among the employed methods for the shortening of CNTs, wet milling using ethanol was the most efficient, while ultrasonic acid treatment or thermal decomposition resulted in a less hydrogen storage capacity.

Multidirectional reinforcement is aimed primarily at overcoming interlaminar weakness, hence a major interest lies in the mechanical properties of multidirectional carbon/carbon composites. Mechanical properties depend on the type of carbon fiber, the size of the fiber bundle, the spacing of the bundles, the angles of the bundles relative to the axes of the block, and matrix formation. In the present studies, PAN based carbon fiber preforms manufactured different size of unit cell have been prepared. Densification of these used high pressure infiltration and carbonization technique with coal tar pitch as matrix precursor was carried out. Scanning electron microscopy has been used to study the fracture behavior of composites. The size of unit cell of the preforms has considerably affected on the flexural properties as well as microstructure of the carbon/carbon composites.

Properties of carbon blacks and carbon black/SBR rubber composites filled by surface modified carbon blacks were examined. Although the specific surface area of carbon blacks increased after the surface modifications with heat, acid, and base, there were no obvious changes in resistivity. The composites filled by heat treated carbon blacks showed a higher tensile strength and elongation than those filled by raw blacks. The acid and base treated carbon blacks filled composites also showed higher tensile strength but similar elongation values with those filled by raw blacks. With increasing loading ratio, both tensile strength and elongation increased, and appeared a maximum value at 30-40 phr. Modulus at 300% strain remained increasing with further loading of carbon blacks. At the same loading, the heat treated black filled composites showed similar modulus values with composites filled by raw blacks but for base and acid treated black filled composites much higher values were obtained. After the surface modification, the functional groups which played an important role in reinforcement action were changed.

In this work, activated carbon (AC) after HNO3 modification was used as the support during the production of supported TiO2 to increase the high deposition efficiency and the photocatalytic activity. The results of N2 adsorption showed that the BET surface area of samples decreased with an increasing of the concentration of HNO3 due to the penetration of TiO2. From XRD data, a single crystal structure of anatase peak was observed in diffraction patterns for the AC coated with titanium complexes. From the SEM results, almost all particles were aggregated with each other at the carbon surface and AC was covered with TiO2 particles in all of the samples. The EDX spectra show the presence of C, O, Ti and other elements. It was also observed a decreasing of amount of C content with increasing Ti and O content from the EDX. The results of FT-IR revealed that the modified AC contained more surface oxygen bearing groups than that of the original AC. The effect of surface acidity and basity calculated from Boehm titration method was also evaluated from correlations as a function of NaOH, NaHCO3, and Na2CO3 uptake. The surface modification of AC by HNO3 leads to an increase in the catalytic efficiency of AC/TiO2 catalysts, and the catalytic efficiency increases with increasing of HNO3 concentration.

Electronic packaging involves interconnecting, powering, protecting, and cooling of semiconductor circuits fur the use in a variety of microelectronic applications. For microelectronic circuits, the main type of failure is thermal fatigue, owing to the different thermal expansion coefficients of semiconductor chips and packaging materials. Therefore, the search for matched coefficients of thermal expansion (CTE) of packaging materials in combination with a high thermal conductivity is the main task for developments of heat sink materials electronics, and good mechanical properties are also required. The aim of this work is to develop copper matrix composites reinforced with carbon nanofibers. The advantages of carbon nanofibers, especially the good thermal conductivity, are utlized to obtain a composite material having a thermal conductivity higher than 400 W/mK. The main challenge is to obtain a homogeneous dispersion of carbon nanofibers in copper. In this paper, a technology for obtaining a homogeneous mixture of copper and nanofibers will be presented and the microstructure and properties of consolidated samples will be discussed. In order to improve the bonding strength between copper and nanofibers, different alloying elements were added. The microstructure and the properties will be presented and the influence of interface modification will be discussed.

The preparation of metallic glass composite powders was accomplished by the mechanical alloying of a pure Ti, Cu, Ni, Sn and carbon nanotube (CNT) powder mixture after 8 h milling. In the ball-milled composites, the initial CNT particles were dissolved in the Ti-based alloy glassy matrix. The bulk metallic glass composite was successfully prepared by vacuum hot pressing the as-milled CNT/ metallic glass composite powders. A significant hardness increase with the CNT additions was observed for the consolidated composite compacts.

For microelectronic circuits, the main type of failure is thermal fatigue. Therefore, the search for matched coefficients of thermal expansion (CTE) of packaging materials in combination with a high thermal conductivity is the main task for developments of heat sink materials electronics, and good mechanical properties are also required. The aim of this work is to develop copper matrix composites reinforced with carbon nanofibers to meet these requirements. In this paper, a technology for obtaining a homogeneous mixture of copper and nanofibers will be presented and the microstructure and properties of consolidated samples will be discussed.

Carbon-ceramic composites were fabricated by using fly ash and PANOX fibers as reinforcement. Fly ash, because of its small size particles e.g. submicron to micron level can be effectively dispersed along with fibrous reinforcements. Phenolic resin was used as carbon precursor. Both dry as well as wet methods were used for forming composites. The resulting composites were characterized for their microstructure, thermal and mechanical properties. The microstructure and mechanical properties of composites are found to be dependent on type of the fly ash, fibrous reinforcements as well as processing parameters. The addition of fly ash improves hardness and the fibers, which get co-carbonized on heat treatment, increase the flexural strength of the carbon-ceramic composites. Composites with dual reinforcement exhibit about 30-40% higher strength as compared to the composites made with single reinforcement, either with fly ash as filler or with chopped fibers.

Carbon/Carbon Composites due to their far superior thermo-mechanical properties are used in a number of demanding applications. However, the material still is used only in specific high tech applications with few exceptions in general industrial applications. The material is extremely expensive and the major challenge is to reduce its cost. Various innovative processing routes are outlined to reduce the cost of processing.

In this work, the effects of atmospheric oxygen plasma treatment of carbon fibers on mechanical interfacial properties of carbon fibers-reinforced epoxy matrix composites was studied. The surface properties of the carbon fibers were determined by acid/base values, Fourier-transform infrared spectrometer (FT-IR), and X-ray photoelectron spectroscopy (XPS) analyses. Also, the crack resistance properties of the composites were investigated in critical stress intensity factor (KIC), and critical strain energy release rate mode II (GIIC) measurements. As experimental results, FT-IR of the carbon fibers showed that the carboxyl/ester groups (C=O) at 1632 cm-1 and hydroxyl group (O-H) at 3450 cm-1 were observed for the plasma treated carbon fibers, and the treated carbon fibers had the higher O-H peak intensity than that of the untreated ones. The XPS results also indicated that the O1S/C1S ratio of the carbon fiber surfaces treated by the oxygen plasma led to development of oxygen-containing functional groups. The mechanical interfacial properties of the composites, including KIC (critical stress intensity factor) and GIIC (critical strain energy release rate mode II), were also improved for the oxygen plasma-treated carbon fibersreinforced composites. These results could be explained that the oxygen plasma treatment played an important role to increase interfacial adhesions between carbon fibers and epoxy matrix resins in our composite system.

Anti-oxidation coatings are the key technique for carbon/carbon (C/C) composites used as the thermal structural materials. The microstructure and oxidation behavior of several kinds of high-performance ceramic coatings for C/C composites prepared in Northwestern Polytechnical University were introduced in this paper. It showed that the ceramic coatings such as SiC, Si-MoSi2, SiC-MoSi2, Al2O3-mullite-SiC and SiC/yttrium silicate/glass coatings possessed excellent oxidation resistance at high temperatures, and some of these coatings were characterized with excellent thermal shock resistance. The SiC-MoSi2 coating system has the best oxidation protective property, which can effectively protect C/C composites from oxidation up to 1973 K. In addition, the protection and failure reasons of some coatings at high temperature were also provided.

The study of mechanical properties and fracture behaviour of carbon/carbon composites is significant to its application and development. These are dependent on microstructure and properties of reinforcing fibers and matrix, fiber/matrix interface and porosity/cracks present in the composites. In the present studies high-density carbon/carbon composites have been prepared using PAN and various pitch based carbon fibers as reinforcements and pitch as matrix with repeated densification cycles using high-pressure impregnation and carbonization technique. Scanning electron microscopy has been used to study the fracture behaviour of the highly dense composites and correlated with structure of the composites. The geometry of reinforcement and presence of unfilled voids/cracks was found to influence the path of crack propagation and thereby the strength of composites. The type of stresses (tensile or compressive) accumulated also plays an important role in fracture of composites.