Adsorption-Induced Deformation of Microporous Carbons: Pore Size Distribution Effect Piotr Kowalczyk,* ,† Alina Ciach, ‡ and Alexander V. Neimark § Applied Physics, RMIT UniVersity, GPO Box 2476V, Victoria 3001, Australia, Institute of Physical Chemistry, Polish Academy of Science, Kasprzaka Street 44/52, 01-224 Warsaw, Poland, and Department of Chemical and Biochemical Engineering, Rutgers, The State UniVersity of New Jersey, 98 Brett Road, Piscataway, New Jersey 08854-8058 ReceiVed February 5, 2008. ReVised Manuscript ReceiVed April 10, 2008 We present a thermodynamic model of adsorption-induced deformation of microporous carbons. The model represents the carbon structure as a macroscopically isotropic disordered three-dimensional medium composed of stacks of slit-shaped pores of different sizes embedded in an incompressible amorphous matrix. Adsorption stress in pores is calculated by means of Monte Carlo simulations. The proposed model reproduces qualitatively the experimental nonmonotonic dilatometric deformation curve for argon adsorption on carbide-derived activated carbon at 243 K and pressure up to 1.2 MPa. The elastic deformation (contraction at low pressures and swelling at higher pressures) results from the adsorption stress that depends strongly on the pore size. The pore size distribution determines the shape of the deformation curve, whereas the bulk modulus controls the extent of the sample deformation. 1. Introduction Understanding the adsorption-induced deformation of mi- croporous solids, in particular carbons, is one of the long-standing problems in adsorption science. 1–5 The phenomenon of adsorp- tion-induced deformation is well documented in the literature. 6–15 The first studies on charcoal swelling were published by Bangham and co-workers 2,3 in 1930, followed by the precise measurements of carbon contraction and expansion performed by Haines and McIntosh. 4 Although mechanical properties of miroporous carbons are critically important for various technological applications, 16–18 the basic mechanisms of deformation during the adsorption-desorption processes are still not completely understood. 1 Deformation of an adsorbent during adsorption-desorption cycles depends on the internal structure of porous body. It is commonly accepted that the pore structure in activated carbons can be viewed as a disordered array of slit-shaped micropores embedded in an amorphous matrix. 19–26 Due to the presence of micropores, activated carbons possess a large surface area. As a result, the adsorbed molecules produce a significant adsorption stress of the order of GPa. 27–30 This stress may be either positive or negative, depending on the interplay of adsorption and confining effects; it causes either contraction or swelling, respectively. 6,27–31 There were a few attempts to describe adsorption-induced deformation on the basis of phenomenological thermodynam- ics. 1,32,33 The most successful approaches to analyzing the experimental data on microporous solids were based on density functional theory and the thermodynamics of vacancy solu- tion. 6,29,33,34 In particular, density functional theory has been instrumental in describing adsorption deformation in ordered microporous materials such as zeolites. 6 In this paper, we extend the thermodynamic approach suggested in ref 6 to adsorption deformation in disordered microporous carbons. 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