Carbon, materials strength

For nosetip materials 3-directional-reinforced (3D) carbon preforms are formed using small cell sizes for uniform ablation and small pore size. Figure 5 shows typical unit cell dimensions for two of the most common 3D nosetip materials. Carbon-carbon woven preforms have been made with a variety of cell dimensions for different appHcations (27—33). Fibers common to these composites include rayon, polyacrylonitrile, and pitch precursor carbon fibers. Strength of these fibers ranges from 1 to 5 GPa (145,000—725,000 psi) and modulus ranges from 300 to 800 GPa. 

Potential areas of apphcation for carboranes include adhesives, gaskets, and O-rings (27). Research has been reported on improving the oxidation resistance and strength of carbon materials by coating with a carborane siloxane polymer (36). 

Carbon—graphite materials do not gall or weld even when mbbed under excessive load and speed. Early carbon materials contained metal fillers to provide strength and high thermal conductivity, but these desirable properties can now be obtained ia tme carboa—graphite materials that completely eliminate the galling teadeacy and other disadvantages of metals. 

In atmospheric conditions, hydrogen is a colorless, odorless gas much lighter than air in normal conditions. The low density in conjunction with the small particle size allows the penetration of hydrogen molecules in some metals and alloys such as cast iron and high-carbon steel [46]. The penetration may end in small hydrogen leaks, or, in the presence of cracks within the wall, contribute to cracks spread, material strength decrease, and subsequent fracture. 

The strength of articles based on phenolic compositions and solidified without additional pressure and heat supply is 2-4 times lower than the strength of thermally solidified resins this limits their applications as engineering materials. One of the primary causes of material strength decrease is pore formation due to volatilization of water and formaldehyde during polycondensation. Different water adsorbents (calcium carbonate, clay, silicates, methasilicates, zeolites, etc.) should be... 

The present paper addresses the problems posed in these earlier contributions from a new viewpoint, namely the development of a superior carbon material that realizes more fully the strength, stiffness, and thermal properties inherent in the strong chemical bonds of carbon in the graphitic layer (8). Petroleum products, as the carbon precursors for pitch-based carbon fibers and for the carbon matrix of the composite, have proved advantageous for such superior carbon materials. 

The G-band is an intrinsic feature of carbon nanotubes that is closely related to vibrations in all sp2 carbon materials, and allows distinguishing whether the nanotube is semiconducting or metallic. The profile shown in Figure 10.3 reveals the semiconductor character of these CNTs. The intensity of the G-band can be related to the SWCNT concentration in the sample. Although is not a quantitative measurement it can be used as a relative indicator of the sample purity. The D-band usually creates ambiguities whether to be assigned to disordered carbon forms (purity) or to SWCNT defects (quality). Nevertheless, the relative strength and width of the D-band has been used as qualitative measurement of the fraction of defects present in the sample. The quality/purity of the SWCNTS can be evaluated by the G/D intensity ratio values obtained for the different SWCNTs are listed in Table 10.1. 

The surface chemical properties of the carbon materials were characterized as follows measurement of pH of carbon slurries (in 0.1 M NaCl solution) [89] neutralization with bases of different strength and dilute HCl according to Boehm s method [63,66] determination of total oxygen/nitrogen content by elemental analysis (with an accuracy of 0.2%) [170] mass loss of carbon samples after heat treatment in a vacuum. Additionally, the number of primary adsorption centers (a,)) was determined from water vapor adsorption isotherms according to the Dubinin-Serpinsky method [171], as was the heat of immersion in water for selected samples [111,172]. The results of these operations are pre.sented in Table 3. For all samples transmission Fourier Transform Infrared (FTIR) spectra and X-ray photoelectron spectra (XPS) were recorded. 

In our work, Sibunit, an artificial carbon material, was used as a support. The methods of Sibunit synthesis permit one to vary surface and size of the support pores within a wide range. Because of high thermal stability, mechanical strength, and... 

The monolithic structure, good mechanical strength, high surface area, and electrical conductivity of these carbon materials make them attractive as electrodes for various electrochemical applications. As hydrogen oxidation (or oxygen reduction) catalysts may be incorporated to such porous materials, one specific application to consider is the use of this type of material as alkaline fuel cell electrode. 

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