Activation porosity, development

Fig. 9.5 Sequence of activities to develop the conceptualisation of porosity and structure in the unit about unbreakable crockery (Example of expanding the meaning of the concepts by activities that are meaningful for students at every step of the teaching and learning process)...

MODELING POROSITY DEVELOPMENT DURING KOH ACTIVATION OF COAL AND PITCH-DERIVED CARBONS FOR ELECTROCHEMICAL CAPACITORS... 

While keeping in mind all these implications, the primary requirement in an attempt to store a huge charge based on the electrostatic forces seems to be high surface area of an activated carbon used. Among different ways of porosity development in carbons, the treatment with an excess of potassium hydroxide is most efficient in terms of microporous texture generation. Porous materials with BET surface areas in excess of 3000 m2/g could be prepared using various polymeric and carbonaceous type precursors [5,6]. 

The reagents ratio, reaction temperature, reaction time and inert gas flow have been reported as the variables of KOH activation process, which influence effectively the porosity development on the treatment of a given carbonaceous material with potassium hydroxide [6],... 

Varying KOH ratio in the mixture is a very effective way of controlling porosity development in resultant activated carbons. The trend in the pore volume and BET surface area increase seems to be similar for various precursors (Fig. la). It is interesting to note, however, a sharp widening of pores, resulting in clearly mesoporous texture, when a large excess of KOH is used in reaction with coal semi-coke (Fig. lb). Increase in the reaction temperature within 600-900°C results in a strong development... 

Activation with KOH was recognized originally as an efficient way of producing microporous carbons with relatively narrow pore size distribution and extremely high surface area. The results of present study demonstrate a considerable flexibility of the process in terms of porosity development and, to some extent, surface properties. 

Thus, the objective of this section is to make a comparison between the results obtained by SAXS technique and by gas adsorption (nitrogen at 77 K and C02 at 273 K). These results include pore size and porosity development. For this study, ACFs, which have been prepared using C02 and steam as activating agents up to different burn-off degrees, have been used. 

Another example to show the usefulness of this technique is to study the effect of the fiber diameter in the porosity development. In doing that, two activated carbon fibers prepared... 

Time-resolved X-ray scattering data are presented for three different carbons that w ere activated in situ in the beamline at the Advanced Photon Souree at the Argonne National Laboratory in Argonne, IL, USA. The resultant data exhibit vai ied behavior, depending on the carbon type. The data suggest a dynamic porosity development mechanism. A net population balance model of pores within a particular size range may explain these observations. 

The SAXS/TGA approach has been demonstrated to be a useful technique for time-resolution of porosity development in carbons during activation processes. Qualitative interpretation of the data obtained thus far suggests that a population balance approach focusing on the rates of production and consumption of pores as a function of size may be a fruitful approach to the development of quantitative models of activation proces.ses. These then could become useful tools for the optimization of pore size distributions for particular applications by providing descriptions and predictions of how various activating agents and time-temperature histories affect resultant pore size distributions. 

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