Márcio Dias Lima

Thin, conductive, carbon nanotube networks over transparent substrates by electrophoretic deposition

A new method was developed for deposition of carbon nanotube networks (CNTNs) over transparent and electrically non-conductive substrates. This method allows the deposition of functionalized or surfactant-stabilized carbon nanotubes dispersed in water. The nanotube films can be applied over complex geometries, on non-conductive rigid or flexible substrates and over large areas in a continuous manner. The carbon nanotube films are deposited by electrophoretic deposition (EPD) using a thin film layer of conductive metal, such as aluminium or titanium. The metal layer oxidizes during the EPD, becoming transparent. The carbon nanotube films can be easily patterned using this technique.

Dynamic percolation of carbon nanotubes in liquid medium

In this article we have measured the electrical behaviour of carbon nanotubes (CNTs) suspended in electrically insulating liquid. The concentration dependence of conductivity shows a percolation behaviour similar to that observed in electrical composites with an insulating matrix. The value of the critical percolation concentration is strongly determined by the aspect ratio of the fillers forming the network through dynamic percolation. We characterized several single- and multi-wall carbon nanotube materials by the newly proposed method and received a good correlation with the results obtained by methods commonly used for CNT characterization (Raman spectroscopy, transmission electron microscopy and electrical conductivity of free standing papers). As a comparison, fine graphite material has also been evaluated. The electrical properties of the suspensions can be used as a method for CNT characterization. This method can yield important information for CNT producers and for the selection of electrically conducting structures for composites applications.

Multiwalled carbon nanotubes catalytically grown from amorphous silica films deposited by combustion CVD

Homogeneous mixtures containing iron oxide and amorphous SiO2 were obtained through the co-deposition of these oxides via combustion chemical vapor deposition technique (CCVD). This technique allows the deposition of thin films with low-cost precursors and equipments. After deposition, the deposited samples were submitted to a heat treatment in an atmosphere composed of natural gas and H2 at 1000°C, in order to promote the growth of carbon nanotubes. Multiwalled carbon nanotubes, with diameters smaller than 15 nm, were obtained.

Chemical resistance of silicate glass-ceramics

ABSTRACT This work is concerned about the chemical characterization of monolithic diopside-based glass ceramics (GCs). Variations from this composition were carried out through the addition of P2O5 to increase crystal density and Al2O3 to optimize the chemical properties of the GCs. The addition of MgO was sufficient for the crystallization of diopside, but additions of P2O5 made the formation of this crystalline phase difficult. The highest volume of diopside crystals was about 76% for the formulation with 5% weight of alumina. As expected, chemical resistance is directly influenced by the composition of the glass ceramic, but not so much by the fraction of crystals volume.

Amorphous Nanowires and Crystalline Thin Films of SiO 2 -Li 2 O Compounds obtained by Combustion Chemical Vapor Deposition

Amorphous silica films deposited by Combustion Chemical Vapor Deposition (CCVD) were modified by lithium addition in the precursor solution. The modified films were characterized by X-ray diffraction and scanning and transmission electron microscopy. The addition of lithium promoted the crystallization of Li 2 O-SiO 2 compounds, mainly crystalline phases like Li 2 SiO 3 , Li 2 Si 2 O 5 , quartz and cristobalite. Besides that, the morphology of the film was modified, leading to the formation of acicular structures and nanowires. The acicular structures were identified through TEM associated with SAED as crystalline phases, mainly constituted by Li 2 SiO 3 and Li 2 SiO 5 . TEM and SEM analysis indicated that the nanowire diameter is between 20 and 80nm. In addition to this, SAED and microprobe EDS analysis indicated that these nanowires are constituted by amorphous silica. The probable growth mechanism of these nanowires is the vapor-liquid-solid (VLS) catalyzed by a liquid particulate composed by Li 2 O-SiO 2 .