Characterization of non-graphitized carbon blacks: a model with surface crevices

Area of Science:

• Physical Chemistry
• Materials Science
• Surface Science

Background:

• Henry's Law is not obeyed for argon and nitrogen adsorption on Carbopack B and Cabot BP280 non-graphitized carbons at accessible pressures.
• Isotherms below the bulk triple point temperature exhibit unusual behavior near the bulk coexistence pressure (P0), suggesting incomplete wetting.

Purpose of the Study:

• To investigate the influence of surface structure, specifically crevices, on gas adsorption behavior in non-graphitized carbon materials.
• To compare experimental adsorption isotherms with molecular simulations to understand adsorbate behavior at high pressures.

Main Methods:

• Experimental measurement of gas adsorption isotherms for argon and nitrogen on Carbopack B and Cabot BP280.
• Monte Carlo simulations using a molecular model of surfaces with molecular-scale crevices.
• Analysis of isotherm crossing points at the bulk coexistence pressure (P0) below the bulk triple point temperature.

Main Results:

• The width of surface crevices on the non-graphitized carbons is estimated to be between 0.65-0.9 nm.
• Adsorbed density at P0 for Cabot BP280 is lower than for Carbopack B, indicating a higher concentration of surface crevices.
• The observed high-pressure isotherm behavior is explained by a less dense, more disordered adsorbate structure compared to bulk fcc crystals.

Conclusions:

• Surface crevices significantly impact gas adsorption, leading to lower adsorbate density and suppressed multilayer formation.
• The adsorbed density at the bulk coexistence pressure serves as a valuable indicator for assessing the presence and concentration of surface crevices.
• This finding offers a new method for characterizing the surface heterogeneity of non-graphitized carbon materials.