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Structural and magnetic properties of Ni doped titanate nanotubes synthesized by hydrothermal method
여준한,Wolfgang M. Sigmund 한양대학교 세라믹연구소 2015 Journal of Ceramic Processing Research Vol.16 No.1
A new method, hydrothermal method, to synthesize Ni doped rutile TiO2 nanotube (TNT) powders is introduced. This method is more scalable than ones used before. Interestingly, our Ni doped TNTs’ structures show different characteristics and properties than ones fabricated by other methods. We report these resulting structural and magnetic properties here. Ni doped nanotubes contained H2Ti2O5H2O doped with trivalent Ni. The layered structures had six nm inner and ten nm outer diameters, aspect ratios of seven, and exhibited ferromagnetism at room temperature (undoped nanotubes were diamagnetic). Contrary to earlier versions of Ni doped TNTs, we found that trivalent Ni atoms substituted H+ in the nanotubes and thus interacted with titanate’s 3d electrons to produce ferromagnetic activity. This opens the possibility to achieve ferromagnetic activity in TNTs in a new way.
여준한,Wolfgang M. Sigmund 한양대학교 세라믹연구소 2015 Journal of Ceramic Processing Research Vol.16 No.1
Titanate nanotube powders with high specific surface area for hydrogen storage were synthesized by alkaline hydrothermal treatment of a TiO2 powder at 150 o C for 48 hrs. With controlling contents of H2O and Na+ in synthesized titanate powders, via ion-exchanging and drying processes, their hydrogen uptake characteristics were evaluated. The titanate nanotube powders showed an increase in the specific surface area with the decreases in Na+ content by the ion-exchanging process and in H2O content by drying processes, but in reverse an decrease in that with severe ion-exchanging or over-drying at high temperature. Their hydrogen uptake increased with decreasing H2O contents in the powders with appropriate Na+ content only under no changing in the particle shape. Therefore, the powders with controlled H2O and Na+ contents had high hydrogen uptake of 2.21 wt% at 90 atm due to proper support of Na+ for interlayer distance in multi-walled tube typed titanate particle.
Woan, Karran V.,Sigmund, Wolfgang M. American Chemical Society 2011 Langmuir Vol.27 No.9
<P>Force interactions of porous silica particles against mirror-polished stainless steel surfaces were quantified in the presence of various solvents to facilitate processing of ceramics with less reliance on organic aids which subsequently need to be burned off. The results were compared to and found to be in good agreement to idealized models of van der Waals force interactions. Significantly, van der Waals attractive forces between steel surfaces and silica surfaces were minimized through the use of tetrahydrofuran and enhanced using methanol. The solvent selections were further extended to settling behavior and were found to follow the general trends determined by Stokes law. The methods presented herein can be extended to other real-world systems.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/langd5/2011/langd5.2011.27.issue-9/la200157v/production/images/medium/la-2011-00157v_0005.gif'></P>
Electrospun materials for energy harvesting, conversion, and storage: A review
Laudenslager, Michael J.,Scheffler, Raymond H.,Sigmund, Wolfgang M. De Gruyter 2010 Pure and Applied Chemistry Vol.82 No.11
<P>Long-length nanofibers are able to form porous networks with high surface-area-to-volume ratios, and decrease diffusion lengths. While there are numerous techniques to create nanostructures, electrospinning is the only technique that allows fabrication of nanofibers at long-length scales. These uniquely shaped fibers are applied to several energy-related devices. This review is an in-depth summary of the uses of electrospun fibers in dye-sensitized solar cells (DSSCs), batteries, capacitors, fuel cells, and hydrogen storage devices. Developments in electrospinning technologies to create novel fiber morphologies are also discussed.</P>
Cho, Chae-Woong,Kim, Sang-Kyun,Paik, Ungyu,Park, Jea-Gun,Sigmund, Wolfgang M. Published for the Materials Research Society by th 2006 Journal of materials research Vol.21 No.2
<P>The influence of the molecular weight of poly(acrylic acid) (PAA) on chemical mechanical planarization (CMP) for shallow trench isolation (STI) was investigated. The adsorption behaviors of PAA as a function of molecular weight on deposited plasma-enhanced tetraethylorthosilicate and chemical vapor deposition Si3N4 films were analyzed by the force measurement using atomic force microscopy (AFM). The AFM results revealed that the affinity of PAA with the nitride film is higher than the affinity with the oxide film, and thus a denser adsorption layer on the nitride film is formed with higher molecular weight of PAA, which leads to higher selectivity in STI CMP. Additionally, to determine the correlation between the dispersion stability of the CeO2 resulting from the presence of PAA with different molecular weight and CMP performance, the colloidal properties of the slurry as a function of the molecular weight of PAA were examined.</P>
Electrospinning of nanofiber Chevrel phase materials
Woan, Karran V.,Scheffler, Raymond H.,Bell, Nelson S.,Sigmund, Wolfgang M. Royal Society of Chemistry 2011 Journal of materials chemistry Vol.21 No.24
<P>A modified sol–gel synthesis for non-oxide sulfide ceramics is presented. Sols are electrospun into continuous nanofiber precursors and then heat treated to obtain Chevrel-phase sulfide materials. In particular, the Mg-Chevrel fibers formed have average diameters of 230 ± 57 nm with grain sizes of 10 ± 3 nm after heat-treatment.</P> <P>Graphic Abstract</P><P>A modified sol–gel synthesis for non-oxide sulfide ceramics is presented. Sols are electrospun into continuous nanofiber Mg-Chevrel and Cu-Chevrel phase sulfide materials. The fibers formed have diameters of 100–300 nm with grain sizes of 10–30 nm after heat treatment. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c1jm10378d'> </P>