Production of β-SiC by pyrolysis of rice husk in gas furnaces

Short fibers and fine particles of β-SiC were obtained by pyrolysis of Colombian rice husk (RH). The synthesis of SiC was carried out in a gas furnace: a mathematical model was developed in order to design and build this equipment and the process was optimized using an experimental design that included variables such as temperature, pyrolysis time, type of catalyst, and process atmosphere. The obtained material was characterized by using FTIR, DRX and SEM for microstructural characterization and EDS technique for chemical analysis.     

Polar and Non-Polar Solvent Permeation Resistance of Blow-Molded Bottles of Polyethylene/Blends of Modified Polyamide and Polyamide 6 Clay Nanocomposite

Investigations on white spirit and acetone permeation resistance of modified polyamide and nylon 6 clay (MPANYC) blends and their corresponding polyethylene/MPANYC bottles were reported in this study. The white spirit and acetone permeation resistance of MPANYC sheets improve consistently with increasing NYC contents present in MPANYC resins after blending nylon 6 clay (NYC) in modified polyamide (MPA) resins. However, the order of barrier improvement of the PE/MPANYC and PE/NYC bottle specimens is not corresponding to the order of barrier improvement of the MPANYC and/or NYC barrier resins added in PE. The blow-molded PE/NYC bottle specimen exhibits similarly worse white spirit and acetone solvent permeation resistance as the PE bottle specimen, wherein no clearly formed NYC laminas but only dispersed NYC droplets or agglomerates were found on the fracture surfaces of the PE/NYC bottles. However, after blending optimum compositions of MPANYC in PE, the PE/MPANYC bottles with demarcated MPANYC laminas exhibit significantly better white spirit and acetone permeation resistance than the PE/MPA bottle, wherein the white spirit and acetone permeation rates of the PE/MPA₈NYC₁ bottle are about 1.3 and 1.4 times slower than those of the PE/MPA bottle, respectively. In order to understand these interesting barrier properties of PE/MPANYC and PE/NYC bottles, rheological, thermal, wide angle X-ray diffraction and morphological properties of the base MPANYC and NYC resins and their corresponding morphology present in the blow-molded bottles were investigated.     

Carbon membranes from cellulose and metal loaded cellulose

The focus of this work was to find a low-cost precursor for carbon molecular sieve (CMS) membranes, and a simple way of producing them. In addition, several ways of modifying a carbon material are described. The modification method used in this study was metal doping of carbon. CMS membranes were formed by vacuum carbonization of cellulose and metal loaded cellulose. Metal additives include oxides of Ca, Mg, Fe(III) and Si, and nitrates of Ag, Cu and Fe(III).The carbon membrane containing Fe-nitrate has promising separation performance for the gas pairs O₂/N₂ and CO₂/CH₄. Carbon containing nitrates of Cu or Ag show high selectivity, but reduced O₂ and CO₂ permeability compared to carbon with Fe-nitrate. Element analysis indicates that Cu migrates to the carbon surface, creating an extra layer resistance to gas transport. A silver mirror is also seen on the surface of Ag-nitrate-containing carbon. However, the Ag- and Cu-containing membranes show a high H₂ permeability. Adding metal oxides makes the carbon membranes retard the transport of easily condensable gases (e.g. CO₂). This can be exploited for enhanced H₂/CO₂ separation efficiency.     

High quality double wall carbon nanotubes with a defined diameter distribution by chemical vapor deposition from alcohol

We have synthesized double wall carbon nanotubes (DWNTs) with few defects and little amorphous carbon by hot wall chemical vapor deposition (CVD) of alcohol. Catalysts for the DWNT growth were made from cobalt and molybdenum acetates. Scanning electron microscopy, transmission electron microscopy, multi frequency resonance Raman spectroscopy and optical absorption spectroscopy were used for characterization of the product with regard to DWNT yield, the nanotube diameter distribution, defect concentration and amorphous carbon content. Base pressures lower than 1 × 10⁻⁵ mbar in the CVD reactor considerably suppress defects in the DWNTs. Optimized growth conditions for DWNT formation are presented.     

In-situ studies of electron field emission of single carbon nanotubes inside the TEM

Electron field emission characteristics of individual multi-walled carbon nanotubes (MWCNTs) were investigated in situ inside the transmission electron microscope (TEM). For a single MWCNT it was found that while field-emission can hardly occur from the side of the nanotube, a curved nanotube may result in finite side emission and the best emission geometry is the top emission geometry. Current-voltage (I-V) measurements made at different vacuum conditions and voltage sweeps emphasize the importance of the adsorbates on the electron field emission of MWCNTs. For a contaminated MWCNT, although the field emission current was reduced, the stability of its emission was improved. A current of up to several tens of μA was observed for a single MWCNT, but it was found that long time emission usually results in drastic structure damage that may lead to sudden emission failure.     

Rubber–clay nanocomposite by solution blending

Ethylene vinyl acetate rubber (45% vinyl acetate content, EVA‐45) and organomodified clay (12Me‐MMT) composites were prepared by solution blending of the rubber and the clay. A combination of X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy studies showed that the composites obtained are on the nanometer scale. The measurements of the dynamic mechanical properties for different compositions over a temperature range (?100 to +100°C) showed that the storage moduli of these rubber–clay nanocomposites are higher above the glass to rubber transition temperature compared to the neat rubber. The tensile strength of the nanocomposites is about 1.6 times higher than that of the EVA‐45. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2216–2220, 2003     

Surface morphology and nodule formation mechanism of cellulose acetate membranes by atomic force microscopy

By the use of atomic force microscopy (AFM), formation mechanism of nodular structure in cellulose acetate membranes was systematically investigated. Elementary factors affecting the nodule formation were delineated on the basis of both kinetic and thermodynamic considerations. It was shown that (1) the exact nature of nodular structure is thermodynamic equilibrium glassy state; nodular structure will vanish in the rubbery state; (2) the thermodynamic factor affecting nodule formation is the membrane formation temperature; with the membrane formation temperature decreasing, more chain segments are able to form nodular structures; (3) nodule formation is dependent on the segment rearrangement; variation of the solvent environment is the major kinetic factor affecting the segment rearrangement and nodule formation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1328–1335, 2003     

Synthesis and characteristics of carbon encapsulated magnetic nanoparticles produced by a hydrothermal reaction

A novel process to synthesize carbon encapsulated magnetic nanoparticles was developed by heating an aqueous glucose solution containing Fe@Au (Au coated Fe nanoparticles) or Ni nanoparticles at 160–180 °C for 2 h. In comparison with traditional methods, such a hydrothermal approach is not only simple but also able to provide functional groups such as –OH on the surface of carbon sphere. Only pure Fe nanoparticles did not favor the formation of carbon encapsulated magnetic nanoparticles due to the oxidation of Fe nanoparticles by H₂O during the reaction and their surfaces had to be coated by an Au shell in advance. The results of TEM, HRTEM, XRD, XPS and vibration sample magnetometer characterization show that uniform carbon spheres containing some embedded Fe@Au nanoparticles with a saturation of 14.6 emu/g are obtained and the size of a typical product is 200 nm. Carbon encapsulated Ni nanoparticles have been successfully prepared in the same way.     

Interfacial shear strength of C/C composites

Fiber-bundle push-out, single-fiber push-in, and single-fiber push-out tests were conducted in order to examine the applicability of these methods for determining the interfacial shear strength of carbon-carbon composites. The fiber-bundle push-out test resulted mostly in fractures along the fiber/matrix interface but created a small amount of fractures in the matrix. Hence, the evaluated strength was regarded as an approximate value. In order to precisely evaluate the interfacial strength, push-in and push-out tests for a single fiber were performed using a micro-Vickers indentation tester. In these tests, the load has to be placed within a target fiber, and the indentation should not extend to the matrix. This condition restricted the load that could be applied to a carbon fiber. Within this limit, a single carbon fiber could not be pushed-in. For the sake of load reduction, single-fiber push-out tests were conducted using thin specimens. The thickness appropriate for a single-fiber push-out specimen was estimated based on the interfacial shear strength obtained by the bundle push-out tests. Below this thickness, single-fiber push-out tests could be successfully performed.     

Synthesis, fabrication and characterization of poly[3-3′(vinylcarbazole)] (PVK) Langmuir-Schaefer films

Poly[3-3′(vinylcarbazole)] (PVK) was synthetized with N-vinylcarbazole as monomer by oxidative polymerization with ferric chloride. The resulting polymer was then deposited on various solid supports by using Langmuir-Schaefer (LS) method. The pressure-area isotherm of PVK revealed the possibility of compact monolayer formation at air-water interface. Different layers of PVK were doped with iodine vapours. Both scanning probe microscopy and optical microscopy images indicated a good uniformity of the films. The morphology and the thickness of PVK films were investigated using atomic force microscopy. The voltammetric investigation of I₂ doped PVK showed a distinctive electrochemical behaviour. The photoinduced charge transfer across a donor/acceptor (D/A) hybrid interface provided an effective method to study the photoelectrochemical properties of the composite LS films.