Carbon

Vapor‐mediated melt infiltration for synthesizing SiC composite matrices

“…Pore formation is likely a consequence of the molar volume change accompanying the reaction. That is, the molar volume of amorphous C is 8.01 cm 3 /mol (based on a mass density of 1.50 g/cm 3 ) 12 while those of Si and β‐SiC are 12.06 and 12.50 cm 3 /mol, respectively. Therefore, reaction of 1 cm 3 of amorphous C with the equivalent molar amount of Si (1.51 cm 3 ) yields 1.56 cm 3 of SiC, a contraction of 38% relative to the combined volume of the reactants (a similar scenario is expected for graphitic C, where the reaction involves a volume contraction of ~27%.…”

“…Therefore, reaction of 1 cm 3 of amorphous C with the equivalent molar amount of Si (1.51 cm 3 ) yields 1.56 cm 3 of SiC, a contraction of 38% relative to the combined volume of the reactants (a similar scenario is expected for graphitic C, where the reaction involves a volume contraction of ~27%. The difference arises from the difference in density of amorphous C and that of graphite, 12 namely 2.26 g/cm 3 , owing to the highly convoluted turbostratic structure of the former 13 ). The inference is that the volume contraction drives the formation of pores at the surface as C is progressively replaced by SiC.…”

Modulating the porosity of carbons for improved adsorption of hydrogen, carbon dioxide, and methane: a review

“…Molecular sieves are a class of porous materials with very narrow PSDs, which make them useful in gas separation applications wherein species are separated according to their size. [165][166][167][168][169] These materials are derivatives of porous materials such as silicates and zeolites. 166,[170][171] While activated carbons typically have heterogeneous PSDs, if they are synthesised or adapted to change pore entrance dimensions to a single pore size they are known as carbon molecular sieves (CMSs).…”

“…166,[170][171] While activated carbons typically have heterogeneous PSDs, if they are synthesised or adapted to change pore entrance dimensions to a single pore size they are known as carbon molecular sieves (CMSs). 169,172 Prior to the explosion in ZTC research, templated carbons were often referred to as CMSs, 90 however the term is now restricted to non-templated carbons with narrow PSDs. On an industrial scale, CMSs are typically synthesised by depositing pyrolytic carbon at the mouth of the pores in activated carbons, resulting in uniform pore entrances.…”

“…[172][173][174] This results in so-called bottle-neck pores, wherein the pore entrance is narrower than the main pore channel. 169 CMSs can also be synthesised directly by activation of an appropriate precursor(s) under precise conditions. Suitable porogens include nitric acid or oxygen and initial activation is followed by a final heating stage.…”