Twenty‐five years of diesel particulate filter (DPF) developments have shown that high‐volume ceramic materials are well suited for the harsh requirements of exhaust after treatment. Nevertheless, problems regarding filter reliability and durability associated with the regeneration of the filter have limited their serious application until only recently. To extend useful filter life, the present study has examined the growth of silicon carbide (SiC) nanofibers by a simple carbothermal reduction process on cordierite support surfaces using cheap raw materials such as kaolin, talc, and carbon black. Transmission electron microscopy confirms the crystalline (β‐SiC) nature of the nanofibers (10–20 nm diameter). The growth of these nanofibers increases the support‐specific surface area restricting the agglomeration of noble metal catalyst particles that otherwise occurs in wash‐coat sintering. As a result, fewer particles are needed to perform the catalyst role (at reduced cost) and the support structure can host the catalyst for prolonged times at higher temperatures. As the future will see increasing economic competition in filter fabrication routes and materials, this new design of catalytic DPF promises to play a significant role.
ABSTRACT:Syndiotactic polystyrene(sPS) forms clathrates with organic solvent molecules between helical chains of trans-trans-gauche-gauche(TTGG) conformation, so called δ form complex. By annealing or extraction, the δ form transforms to the mesophase which has highly regulated molecular cavities between helical chains. Time resolved FT-IR spectra of the sPS films containing δ form complex with toluene were obtained to clarify the relationship between the release of toluene from the δ form and conformational changes of sPS backbone chain. From the results of FT-IR, content of TTGG conformation decreased with annealing time, and increased with extraction time by acetone, indicative of the formation of γ form from amorphous phase. The mesophase extracted holds high content of TTGG conformation and is stable, compared to annealed sample. The solvent extraction method is thus a better technique to make mesophase membranes containing molecular cavities.KEY WORDS Syndiotactic Polystyrene / Mesophase / Time Resolved Measurement / WAXD / FT-IR / Conformation / Characterization / Molecular Cavity / Syndiotactic Polystyrene (sPS) forms four crystalline polymorphisms, α, β, γ, and δ. α and β forms have backbone chains in trans-trans(TT) planer zigzag conformation with identity period 5.1Å. γ and δ forms show trans-trans-gauche-gauche(TTGG) helical chains of s(2/1)2. Although α and β are crystallizable through molten and amorphous sPS, the δ form is formed from sPS solution and sPS helical chain clathrates regularly with used solvent molecules as guests, so called "δ form complex". γ with no guest molecules is derived from δ by annealing above approximately 150 • C, and the packing of TTGG helical chains of γ becomes dense. Guest molecules of δ can be removed from the clathrate δ complex crystal remaining almost constant structure, resulting in a mesophase with molecular cavities whose crystalline structures have been described. 1-6 The "mesophase" means an intermediate phase between δ and γ and is the same as empty δ. 7 The previous article describes two methods to prepare mesophase. 8 One is thermal annealing of δ form, meaning of the removal of guest solvent, above glass transition temperature of sPS. The other is step wise extraction method. The first step is extraction by acetone, relatively poor solvent to sPS which performs the exchange of guest solvent of δ form. The second step is extraction by methanol: methanol exchanges acetone and methanol is evaporated thoroughly under vacuum without structural change. One can obtain mesophase sPS with molecular cavities.Crystalline structure and conformational change of sPS membrane were examined during the release of guest molecules from δ by annealing and extraction. The release of toluene, guest molecules, in sPS δ was investigated by Fourier Transform Infrared Spectrophotometer (FT-IR) spectroscopic in situ. [9][10][11][12][13] The characterization of δ and in situ observation of conformational and structural change were carried out by time resolved FT-IR and wide angle X...
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