Fiber oxides

There are two mechanisms of PAN-based carbon fiber oxidation dependent on oxidation temperature ((67,68). At temperatures below 400°C, oxygen diffuses into the fiber and attacks at pores resulting in significantly increased fiber surface area. At higher temperatures impurities catalyze the oxidation reaction. 

Most recent studies (69) on elevated temperature performance of carbon fiber-based composites show that the oxidation resistance and elevated temperature mechanical properties of carbon fiber reinforced composites are complex and not always direcdy related to the oxidation resistance of the fiber. To some extent, the matrix acts as a protective barrier limiting the diffusion of oxygen to the encased fibers. It is therefore critical to maintain interfacial bonding between the fiber and the matrix, and limit any microcracking that may serve as a diffusion path for oxygen intmsion. Since interfacial performance typically deteriorates with higher modulus carbon fibers it is important to balance fiber oxidative stabiHty with interfacial performance. 

Keywords Inorganic fiber Oxide fiber Silicon carbide fiber Heat resistance Photocatalyst... 

Gel fiber oxide precursors on self-aesembled Gel liber... 

Figure 14a. Carbon Is spectra from wool fibers oxidized in oxygen plasma. (Reproduced, with permission, from Ref. 44. Copyright 1977, Academic Press.)...

After absorption by the fiber, the leuco dye is converted to the original pigment by oxidation and, in this way, fixed to the fiber. Oxidation can be achieved with atmospheric oxygen or by the addition of oxidants, such as hydrogen peroxide, perborate, or 3-nitrobenzene sulfonic acid, to the liquor. 

Theories and instrumentation of Fourier transform IR spectroscopy and electron spectroscopy for chemical analysis are briefly reviewed. The possibility of using these techniques in detection and analysis of acid impurities distributed at surfaces of paper documents produced during the period from 1790 to 1983 is demonstrated. Results show that all of the papers tested contained carboxylic groups. The carboxylic acids found in the paper of 1790 are the results of oxidation and aging. Acids in other papers are due to fiber oxidation as well as the presence of rosin acids. These techniques show promise as nondestructive methods for elucidating chemical characteristics of surfaces of paper documents. 

Comparison of the cyclovoltammetric curves recorded for carbon fibers (CF) in both aqueous and nonaqueous solutions provided evidence of a considerable decrease in double electric layer capacity with increase in CF carbonization temperature (particularly between 1100 and 1400°C) [21,204]. This observation applies to both unmodified and oxidized carbon fibers. Oxidative modification leads to the appearance of a broad anodic peak with a potential between 0.1 and 0.3 V in neutral aqueous solutions (see Fig. 16a). The ab.sence of any peak on CV curves recorded in acetonitrile solutions (Fig. 16b) suggests that functional... 

Braun, J. Holtman, K. Kadla, J.F. Lignin-based carbon fibers oxidative thermostabilization of kraft lignin. Carbon 2005, 43, 385-394. 

Cloth, original/2128 Cloth, oxidized/1636 Fiber, original/1709 Fiber, oxidized/1315... 

Both mass gain and loss contribute total mass loss of the sample, indicating severe carbon fiber oxidation. 

Figure 3-2. Fiber oxidized with peroxide, reduced with thioglycolate, and then extended to fracture in the dry state. Top At low magnification, note the large number of cracks perpendicular to the fiber axis. Bottom Higher magnification shows that these cracks are very deep and extend through the entire cuticle. SEM kindly provided by Sigrid Ruetsch of Textile Research Institute/Princeton.

A variety of CMC systems have been developed and fabricated in the past. These have included aluminum oxide, aluminum nitride and sihcon nitride matrix composites [3-5]. The reinforcement has predominantly consisted of silicon carbide based fibers. Oxide based fibers have also been evaluated over the years as and when they have become available. This chapter reviews the development effort of silicon carbide reinforced aluminum oxide matrix composites fabricated via directed metal oxidation and compares them with those reinforced with oxide fibers. 

R. W. Goettler, S. Sambasivan, V. Dravid, and S. Kim, Interfaces in Oxide Fiber—Oxide Matrix Ceramic Composites, in Computer Aided Design of High Temperature Materials, A. Pechenik, R. Kalia, and P. Vashishta, Eds., Oxford University Press, (1999). p. 333-349. 

L. C. Lev and A. S. Argon, Development of Oxide Coatings for Matching Oxide Fiber-Oxide Matrix Composites, Cer. Eng. Sci. Proc., 15 [5] 743-752 (1994). 

Long-term damage tolerant ceramic materials being stable at high temperature, high gas pressures and velocities, and severe chemical environments are needed e.g. for efficient future gas turbine engines Recently, an oxide fiber/ oxide matrix material which aims to achieve these requirements has been developed at the German Aerospace Center (DLR). The... 

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