Texture development in Fe-doped alumina ceramics via templated grain growth and their application to carbon nanotube growth

Fe-doped alumina (Fe-Al2O3) materials with a controlled microstructure could be designed for some special uses such as a substrate for carbon nanotube growth. In this study, Fe-doped Al2O3 ceramics with varying degrees of texture were prepared via Templated Grain Growth method and utilized for carbon nanotube synthesis by Catalytic Chemical Vapor Deposition in order to investigate how alpha-Al2O3 crystal orientation affects carbon nanotube growth in polycrystalline ceramics. The degree of texture increased with the Fe content in the presence of liquid phase. Three kinds of carbon filaments (few-wall carbon nanotubes bundles, individual multi-wall nanotubes and carbon nanofibres) were observed over Fe-doped Al2O3 ceramics with varying degrees of texture depending on the surface roughness, crystallographic orientation and the size of the catalyst nanoparticles. While well-textured substrates with a rough surface led to a small amount of randomly oriented carbon nanotube bundles, perpendicularly oriented individual multi-wall nanotubes were obtained over relatively smooth single crystal alpha-Al2O3 platelet surfaces (basal planes) which remained in the matrix without growing

A comparative study on few-layer graphene production by exfoliation of different starting materials in a low boiling point solvent

Three different graphite-based powders (expandable graphite and two different nano-graphite powders) were investigated as starting materials for an effective liquid phase exfoliation process in isopropyl alcohol (IPA). The prepared dispersions were analyzed and compared in terms of their graphene concentration, stability, number of graphene layers and quality, as well as the electrical conductivity of the prepared graphene-based materials. Good quality graphene dispersions (ID/IG < 0.3) with a relatively high concentration (∼1.1 mg/ml) were prepared in IPA within 90 min sonication time by utilizing a high specific surface area (∼175 m2/g) nano-graphite powder derived from natural graphite. Transmission electron microscope analyses of this sample revealed mostly folded and scrolled few layer graphene (FLG) sheets (<5 layers) entangled each other. The electrical conductivity of the thin film prepared from this dispersion was ∼15 and 86 S/m, before and after annealing, respectively. FLG prepared from expanded graphite, obtained by thermal treatment of expandable graphite, exhibited both much higher quality (ID/IG < 0.09) and electrical conductivity (∼2104 and 19,200 S/m before and after annealing, respectively) when dispersed in IPA for 90 min. However, the graphene-based material concentration of the prepared dispersion was relatively low (∼0.06 mg/ml)

Organized growth of carbon nanotubes on Fe-doped alumina ceramic substrates

Polycrystalline Fe-doped alumina (Al2O3) ceramics have been produced and used as a substrate for organized carbon nanotubes (CNTs) growth by catalytic chemical vapor deposition (CCVD). In these substrates, Fe3+ cations, which are the catalyst source, are initially substituted to Al3+ in a-Al2O3, instead of being simply deposited as a thin Fe layer on the surface of the substrate. The selective reduction of these substrates resulted in in situ formation of homogeneously distributed Fe nanoparticles forming patterns at nanometerscale steps and kinks. These nanoparticles then catalyzed the growth of high quality CNTs, with some degree of organization thanks to their interaction with the topography of the substrate

Relationship between heating atmosphere and copper foil impurities during graphene growth via low pressure chemical vapor deposition

Low-pressure chemical vapor deposition synthesis of graphene films on two different Cu foils, with different surface oxygen and carbon contents, was performed by controlling H2 and/or Ar flow rates during heating. The influences of heating atmosphere on the final impurity level, quality of the synthesized graphene films and thickness uniformity were investigated depending on Cu foil impurities. Heating of carbon-rich, but oxygen-poor Cu foil in H2 environment resulted in covering the foil surface by residual carbon which then acted as active sites for multilayer graphene growth. Ar-only flow was required during heating to promote high quality graphene growth on this foil. On carbon-poor, but oxygen-rich Cu foil high quality graphene growth was promoted when the heating was carried out under Ar/H2 environment. Almost no carbon residues were observed on this foil even under H2 only flow during heating. The heating atmosphere affected not only graphene growth, but also the type and amount of impurities formed on the surface. H2 and Ar/H2 heating resulted in the formation of spherical nanometer-sized impurities, while irregular-shaped, large (a few mm) SiO2 impurities were observed when Ar alone was used during heating. Quality of the grown films was tested by Quantum Hall Effect measurements

Anisotropic mechanical and functional properties of graphene-based alumina matrix nanocomposites

Graphene platelets (GPLs) containing Al2O3 nanocomposites, which exhibit anisotropic microstructure,have been prepared by spark plasma sintering (SPS), and effects of this anisotropy on mechanical, elec-trical and thermal properties of the nanocomposites have been investigated. 3 vol.% GPLs addition intomonolithic Al2O3caused fracture toughness (Kıc) to increase by 26.7% in the in-plane direction and todecrease by 17.2% in the through thickness direction. Kıcstarted to decrease in the in-plane direction andto increase in the through-thickness direction with further increase in the GPLs amount. The electricalconductivity of the nanocomposites exhibited a slight anisotropy with a lower resistivity in the in-planedirection. Oriented GPLs also led to a less resistive heat conduction path in the in-plane direction. ∼44%increase in the in-plane thermal conductivity was achieved at 600◦C with 15 vol.% GPLs addition into themonolithic Al2O3and this resulted in ∼52% increase in the kin-plane/kthrough-thicknessratio