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Please use this identifier to cite or link to this item: http://hdl.handle.net/1860/1120

Title: Carbide derived carbon from MAX-phases and their separation applications
Authors: Hoffman, Elizabeth N.
Keywords: Materials science;Porous materials;Carbon
Issue Date: 27-Sep-2006
Abstract: Improved sorbents with increased selectivity and permeability are needed to meet growing energy and environmental needs. New forms of carbon based sorbents have been discovered recently, including carbons produced by etching metals from metal carbides, known as carbide derived carbons (CDCs). A common method for the synthesis of CDC is by chlorination at elevated temperatures. The goal of this work is to synthesize CDC from ternary carbides and to explore the links between the initial carbide chemistry and structure with the resulting CDCs properties, including porosity. CDC was produced from MAX-phase carbides, in particular Ti3SiC2, Ti3AlC2, Ti2AlC, and Ta2AlC. Additionally, CDC was produced from Ta-based binary carbides, TaC and Ta2C, and one carbo-nitride Ti2AlC0.5N0.5. The CDC structure was characterized using XRD, Raman microspectroscopy, and HRTEM. Porosity characterization was performed using sorption analysis with both Ar and N2 as adsorbates. It was determined the microporosity of CDC is related to the density of the initial carbide. The layered structure of the MAX-phase carbides lent toward the formation of larger mesopores within the resulting CDCs, while the amount of mesopores was dependent on the chemistry of the carbide. Furthermore, CDC produced from carbides with extremely high theoretical porosity resulted in small specific surface areas due to a collapse of the carbon structure. To expand the potential applications for CDC beyond powder and bulk forms, CDC membranes were produced from a thin film of TiC deposited by magnetron sputtering onto porous ceramic substrates. The TiC thin film was subsequently chlorinated to produce a bilayer membrane with CDC as the active layer. Both gases and liquids are capable of passing the membrane. The membrane separates based on selective adsorption, rather than a size separation molecular sieving effect. Two applications for CDC produced from MAX-phases were investigated: protein adsorption and gas separation. Sorbents capable of adsorbing large protein molecules efficiently are desirable for many medical applications, including the treatment of sepsis. Primarily mesoporous Ti2AlC-CDC and Ti3AlC2-CDC were proven to adsorb a significant amount of proteins compared to two current carbon adsorbents. When tested for gas separation, CDC was capable of selectively adsorbing gases including SF6, CO2, CH4, and H2. However, the gases were not separated based on their size, but rather on their interaction with the CDC surface.
URI: http://hdl.handle.net/1860/1120
Appears in Collections:Drexel Theses and Dissertations

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