Mesophase carbonization

Edie, D. D., Robinson, K. E., Fleurot, O., Jones, S. P. and Fain, C. C., High thermal conductivity ribbon fibers from naphthalene-based mesophase. Carbon, 1994, 32(6), 1045 1054. 

Synthetic carbonaceous materials are widely used in these applications. Several types of synthetic materials (e.g. graphitized mesophase carbon microbeads (MCMB), graphitized milled carbon fiber, and even, initially, hard carbons) became the materials of choice at the time of commercialization of first successful lithium-ion batteries in late 1980s. New trends, mainly driven by cost reduction and need for improved performance, currently shift focus towards application of natural graphite. 

Given the complex process to produce mesophase carbon (graphitized microbeads and fibers), natural graphite can be very competitive in terms of its manufacturing costs [18]. The physical characteristics of certain SLC type materials are extremely close to the characteristics of state-of-the-art MCMB grades. 

At the electrochemical performance level, these novel natural graphite-based materials surpass mesophase carbon s characteristics as related to cell/battery safety performance, low irreversible capacity loss, and good rate capability even at high current densities. 

The electrochemical performance of a large number of carbonaceous materials carbonized at temperatures below 1000°C like pitch cokes,173-175 petroleum cokes,115 mesophase carbons,157-173 174... 

For example separate conferences on zeolites, self-assembling mesophases, carbons, sol-gel technology, supported biocatalysts, etc. are held. One can write a list of 20 different scientific basis of preparation .1 The tendency is to enlarge this list, resulting in a distancing between different fields. As a result, a... 

Microstructure Formation in Mesophase Carbon Fibers and Other Graphitic Materials... 

In the previous symposium, we reviewed mesophase mechanisms involved in the formation of petroleum coke ( 2 ). Since 1975, two significant developments have been the use of hot-stage microscopy to observe the dynamic behavior of the carbonaceous mesophase in its fluid state (3-6), and the emergence of carbon fibers spun from mesophase pitch (7-9) as effective competitors in applications in which high elastic modulus or good graphiticity is important. This paper focuses on mesophase carbon fibers as an example of how the plastic mesophase can be manipulated to produce fibers with intense preferred orientations and elastic moduli that approach the theoretical limit for the graphite crystal in the a-direction. 

Figure 1 shows where mesophase carbon fibers fit in the rapidly developing field of structural carbon fibers. At present, fibers produced from polyacrylonitrile (PAN) constitute the bulk of the carbon fiber produced in 1981 all commercial PAN-based fibers fell below and to the left of the "1981 limit" for tensile strength and modulus. Since 1981, there have been major advances in the development of PAN-based fibers to achieve high strengths, particularly at the lower modulus levels (near 40 Mpsi, 276 GPa). 

This paper commences with evidence for lamelliform morphologies in mesophase carbon fiber, summarizes relevant information on disclination structures in the carbonaceous mesophase, and then reviews what we learn of disclination behavior from hot-stage observations and from deformation and carbonization experiments. The results indicate that disclination interactions that occur before the mesophase is fully hardened play an important role in determining the microstructures of mesophase carbon fibers, as well as those of cokes and graphites that form through the carbonaceous mesophase. 

The most common morphology observed in current mesophase carbon fibers of moderate modulus (55 to 75 Mpsi, 379 to 517 GPa) is a cylindrical filament with a random-structured core and a radial rim (12) Given the fracture section of Figure 3, with its scroll-like features, the core appears to be an array of +2ir and -ir disclinations. The radial rim of heavily wrinkled layers usually constitutes half or more of the cross section. 

Figure 2. Mesophase carbon fiber with radial structure and open-wedge shape. Polarized light.

Figure 3. Mesophase carbon fiber with random-core structure and round shape.

Figure 4. Tensile fracture surfaces for three structural types of high-modulus mesophase carbon fibers (E = 100 Mpsi ...

Figure 6. Tensile fracture surfaces for a mesophase carbon filament with tensile modulus of 120 Mpsi (827 GPa).

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