Expandable graphites

Nordmann Rassmann has marketed a graphite product called Nord-Min , available in several grades that differ in the temperature at which they start to expand, ranging from 150 to 300 °C. The expansion onset temperature determines the processing temperature range that can be used. The onset temperature must also be compatible with the one at which decomposition, exothermal reaction and ignition occm spontaneously. In the case of PU foams, this tends to be between 300 and 500 °C. 

The evolution of fiunes from the acid inserted into the graphite layer planes can introduce processing problems, imless an acid neutraliser is present. Apphcations of graphite include insulation foam, foamed sealing tape for windows and doors, roof membranes and coatings. The products are black and must not be heated above 200 C. 

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Table 9 Hsts the quantities and doUar values of natural graphite used in the United States in 1988—1989 by product groups (7,15). Refractories and cmcibles account for about half of the known use. Natural graphite has its next greatest use (ca 15%) in lubricants and packings, including expandable graphite.

For the most rigorous specifications it may be necessary to use expanded graphite as a flame-retarder but its use can pose other difficulties. 

Figure 23. New japanese alkaline cells using expanded graphite and other recent improvement...

FIGURE 4.2 Transmission electron microscopic (TEM) image of ethylene-vinyl acetate (EVA)-expanded graphite (EG) (4 wt%) nanocomposites. (From George, J.J. and Bhowmick, A.K., J. Mater. Sci., 43, 702, 2008. Courtesy of Springer.)... 

Figure 120. Expanded graphite which is the basic heat transfer structure for PCM-graphite composites...

In a first step the expanded graphite is pressed in a continuous process to form about 1 cm thick plates (Figure 121 left). These plates form a graphite... 

Figure 121. Left prepressed expanded graphite forms a graphite matrix with thermal conductivity of about 25 W/m K and porosity of 90 vol.%. Right PCM-graphite matrix after infiltration of PCM with about 85 vol.%...

Figure 123. PCM-graphite compound produced from mixing PCM with expanded graphite...

In this method the PCM is mixed with expanded graphite in a compounding process. The result is a compound in granular form (Figure 123). 

Expanded Graphite (grade ABG1005, Superior Graphite) 1,1 10 3... 

PARAMETERS Expanded Graphite, ABG1005, 8wt% Natural Flake Graphite, 2939APH, 8wt% Boron-Doped Flake Graphite, 2939APH-RG, 8wt% Carbon Black, P-267, 5wt% Ni Powder, 10wt%... 

NEW CONCEPT FOR THE METAL-AIR BATTERIES USING COMPOSITES CONDUCTING POLYMERS / EXPANDED GRAPHITE AS CATALYSTS... 

The mechanisms and reasons of catalytic activity of polyaniline (PANI)-type conducting polymers toward oxygen reduction in acidic and saline solutions are investigated by electrochemical and quantum-chemical methods. The PANI/thermally expanded graphite compositions were developed for realization of fully functional air gas-diffusion electrodes. Principally new concept for creation of rechargeable metal-air batteries with such type of catalysts is proposed. The mockups of primary and rechargeable metal-air batteries with new type of polymer composite catalysts were developed and tested. 

Conducting polymers, polyaniline, catalytic activity, PANI/expanded graphite composites, metal-air batteries, primary rechargeable cells. 

The above phenomenon has found a practical application for development of metal-air battery mockups with low costs PANI/Expanded Graphite composite catalysts. 

We believe that new type of conducting polymer / expanded graphite composite electrodes as gas-diffusion cathodes will find in perspective a practical application for some types of batteries and fuel cells. 

The future remains bright for the use of carbon materials in batteries. In the past several years, several new carbon materials have appeared mesophase pitch fibers, expanded graphite and carbon nanotubes. New electrolyte additives for Li-Ion permit the use of low cost PC based electrolytes with natural graphite anodes. Carbon nanotubes are attractive new materials and it appears that they will be available in quantity in the near future. They have a high ratio of the base plane to edge plain found in HOPG. The ultracapacitor application to deposit an electronically conductive polymer on the surface of a carbon nanotube may be the wave of the future. 

The samples of expanded (thermally expanded) graphite (TEG) were provided by the Central Research Institute of Materials (Russian Federation). TEG is a powder of light grey color with low bulk density and extremely developed true surface it can be easily pressed in a flexible plate ( cardboard ). The anodes made of TEG, had the capacity about 200 mA-h/g (Figure 5). However, in spite of the fact that the anodes were made of pressed powder, they had volumetric capacity in 3-4 times smaller, than other tested materials. The discharge curve is shown on Figure 5. 

The thermally expanded graphite was used without any preliminary treatment the carbon was synthesized by carbonation of the raw material in an argon flow at 500°C with subsequent thermal treatment. Carbon residues strongly differing in the crystallinity degree were obtained as depends on the temperature which ranged from 500°C to 1300°C. The identity of each material was checked by X-ray spectroscopy. 

The source carbon materials show a significant electrochemical activity for lithium intercalation though the reversible capacity is relatively low and tends to reduce with cycling. For the thermally expanded graphite... 

Some theoretical prerequisites for application of modified and expanded graphites, Si- and Sn-based composites and alloys, electroconducting polymers as active materials, catalysts and electro-conductive additives for lithium - ion batteries, metal-air batteries and electrochemical capacitors are considered. The models and the main concepts of battery-related use for such materials are proposed. 

Modified graphite expanded graphite Si- and Sn- composites alloys conducting polymers lithium-ion batteries metal-air batteries electrochemical capacitors. 

One of possible ways of improving the specific characteristics of LIB electrodes is the use of thermally expanded graphites (TEG) as electrically conductive additives of positive active mass. The efficiency of TEG s use may be illustrated by analyzing a simple theoretical model proposed by us AM - electrically conductive additive (Figure 4). 

Particularly, let us make comparison of densities for common and expanded graphite in a free state ... 

Thermally expanded graphite is, in principle, one of the most efficient conductive additives to various battery active materials, first of all... 

V.G. Khomenko, V.Z. Barsukov, A.S. Katashinskii and T.I. Motronyuk. New concept for the metal-air batteries using composites conducting polymers/ expanded graphite. This book. 

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