Jing Wang

Febrication of MWNTs Composites with In Situ Precipitation Method

In this article stable multi-walled carbon nanotubes (MWNTs) aqueous suspension with a 1.0 wt.% concentration was obtained with a very small quantity of dispersant. Precursor of ceramics were synthesized in the suspension and densely deposited on the surface of MWNTs successfully by a simple and effective in-situ precipitation method. The most important advantage for the in-situ composite method is to make MWNTs homogeneously distributed in the matrix. The fully dense compacts were obtained by spark-plasma-sintering (SPS) the in-situ precipitated composite powders at temperature 200 oC lower than that of composite powders made from the traditional mixing method. Furthermore, the microstructure and the mechanical property of the composites are much better than that of traditional method. The in-situ precipitation could be a promising method to fabricate CNTs composites of ceramics matrix especially those hard to sinter.

Improvement of aramid fiber III reinforced bismaleimide composite interfacial adhesion by oxygen plasma treatment

Abstract Domestic Aramid Fiber III (DAF III) was modified by oxygen plasma treatment. The effects of oxygen plasma treatment power on fiber surface and DAF III reinforced bismaleimides (BMI) composite interfacial properties were investigated, respectively. The fiber surface characteristics were analyzed by X-ray photoelectron spectroscopy, Scanning Electron Microscopy, Atomic Force Microscopy and Dynamic Contact Angles Analysis, respectively. The results showed that oxygen plasma treatment introduced new oxygen containing groups such as C=O and –COO on to the fiber surfaces, changed the fiber surface morphologies and enhanced surface roughness by oxidative reactions and plasma etching. Finally, the fiber surface wettability was effectively improved. The total free energy increased from 49.8 to 71.7 mJ/m2 at maximum with 300 W oxygen plasma treatment. The composite interlaminar shear strength (ILSS) was evaluated by short beam shear measurement. The ILSS value increased from 49.3 to 59.8 MPa (by 21.3%) within 300 W plasma treatment.

Influence of Oxygen Plasma Treatment on Surface Properties of Armos Fiber

Armos fiber (F-12 aramid fiber in paper) was provided with broad application foreground as reinforcement material for advanced composites in aviation and spaceflight field, due to its outstanding properties, such as high modulus, high strength, high temperature resistance, erosion resistance and so on. However, the exertion of property was still limited by slippery surface, low surface energy and weak interfacial adhesion performance. In this study, the effects of oxygen plasma treatment time on polar functional groups introduced onto the fiber surface, surface free energy and surface topographic images were discussed by X-ray photoelectron spectroscopy (XPS) analysis, dynamic contact angle analysis system (DCA) and atomic force microscopy (AFM), respectively. It was found that the content of oxygen element and polar functional groups on fiber surface were all increased obviously after oxygen plasma treatment. The content of oxygen element on surface for untreated F-12 aramid fiber was 11.13%, while it increased to 15.20% after oxygen plasma treatment for 10 min; The content of polar functional groups on surface for untreated F-12 aramid fiber was 28.14%, while it increased to 38.11% after oxygen plasma treatment for 10 min. The polar component (γp) of fiber surface energy increased sharply from 6.82 mN/m to 36.68 mN/m after 10 min plasma treatment, the total surface free energy was increased from 46.26 mN/m to 64.66 mN/m.The results indicated that oxygen plasma treatment had introduced a large amount of reactive functional groups onto the fiber surface, and these groups can form together as covalent bonding to improve the surface wettability and increase the surface energy of fibers. At the same time, oxygen plasma treatment was able to generate a mass of bulges and grooves on F-12 aramid fiber surface, which had an active effect on increasing the chemical bond and mechanical function between fiber and resin and enhancing the interfacial adhesion performance of composite. The fiber surface grooves had been increased with the time prolonging before 10 min while decreased after 10 min, the results maybe relate to partial organic on fiber surface melting. It had an adverse effect on the interfacial adhesion properties of composite. Therefore, the optimum plasma treatment time was between 5 min and 10 min.

Al/Al2O3 Core-Shell Particles Synthesized by Wet-Chemical Based Route

Coating process is attracting more and more attention in the preparation of composite materials mainly due to its predominance in the improvement of the uniformity for different phases. The formation of nanosize alumina shells on the aluminum core particles by a wet-chemical based route was investigated and the composite particles were characterized using TG/DSC, XRD, SEM, TEM, XPS. An enhancement of cermet properties can be expected by using these coated particles as initial powders.

The Microstructure, Mechanical and Dielectric Properties of CNTs/Mullite Ceramics Composites

Carbon nanotube-mullite (Al2O3/SiO2=3/2) composites have been prepared by hot-pressing the corresponding composite powders, in which the multi-walled carbon nanotubes(1~10 vol%) are homogeneously dispersed between the mullite grains. The microstructure of the specimens has been studied and discussed in relation to the properties of the matrix, the bending strength and the fracture toughness, the dielectric constant and the dissipative factor. Carbon nanotube-mullite composites are potential electromagnetic wave absorbers owing to the percolation of the carbon nanotubes.

The effects of thermally reversible agents on PVC stability properties

One kind of thermally reversible cross-linking agents for improving PVC thermally stability was synthesized. The chemical structure and thermally reversible characteristics of cross-linking agents were investigated by FTIR and DSC analysis, respectively. FTIR results confirmed that the cyclopentadienyl barium mercaptides ((CPD-C2H4S)2Ba) were successfully synthesized. DSC results showed it has thermally reversible characteristics and the depolymerization temperature was between 170 ?C and 205 ?C. The effects of cross-linking reaction time on gel content of Poly(vinyl chloride) compounds was evaluated. The gel content value arrived at 42% after being cross-linked for 25 min at 180 C. The static thermally stability measurement proved that the thermally stability of PVC compounds was improved.

Studies of energy and mechanical properties of single-walled carbon nanotubes via higher order cauchy born rule

Based on the higher order Cauchy-Born rule, a nanoscale finite deformation continuum theory, which links interatomic potentials and atomic microstructure of carbon nanotubes to a constitutive model, is presented for analysis of the mechanics of carbon nanotubes. By using of Tersoff-Brenner potential with two sets of parameters, the energy and Young’s modulus of graphite sheet and single-walled carbon nanotubes are studied based on the theory presented. The findings are in good agreement with the existing experimental and theoretical results.