ORCID Profile
0000-0002-7078-1274
Current Organisation
University of North Texas
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Publisher: Springer Science and Business Media LLC
Date: 26-08-2011
DOI: 10.1557/JMR.2011.230
Publisher: American Scientific Publishers
Date: 02-2011
Publisher: AIP Publishing
Date: 15-11-2009
DOI: 10.1063/1.3253747
Abstract: Mechanical and electrical properties of carbon fiber (CF) and vertically aligned carbon nanotubes (CNTs) have been thoroughly investigated in previous studies. Growth of radially aligned CNTs on silicon oxide (SiO2) coated CF has recently been accomplished resulting in multiscale composite fiber (CNT/SiO2/CF). CNT/SiO2/CF offers promise as stress and strain sensors in CF reinforced composite materials. However, to date there have been no investigations of the electromechanical properties of CNT/SiO2/CF that would facilitate their usage as sensors in composite materials, which is the focus of this research. This study investigates fundamental mechanical and electrical properties of CF, SiO2/CF (SiO2 coated CF), and CNT/SiO2/CF during localized transverse compression at low loads (μN to mN) and small displacements (nm to a few μms). Force, strain, stiffness, and electrical resistance were monitored simultaneously during compression experiments. For CF, resistance decreased sharply upon compressive loading with hysteresis in both force and resistance being observed at low strain. For SiO2/CF, high resistance and negligible electrical conduction occurred, and the force-displacement curve was linear. CNT/SiO2/CF stiffness increased as force and strain increased and became comparable to that of CF at high strain (∼30%). Hysteresis in both force-displacement and resistance-displacement curves was observed with CNT/SiO2/CF, but was more evident as maximum strain increased and did not depend on strain rate. Force was higher and resistance was lower during compression as compared to decompression. Hysteretic energy loss is associated with internal friction between entangled CNTs. Van der Waals force between deformed and entangled CNTs hindered disentanglement, which reduced the number of electrical current paths and increased resistance during decompression. The results of this study provide new understanding of the mechanical and electrical behavior of CNT/SiO2/CF that will facilitate usage as stress and strain sensors in both stand-alone and composite materials applications.
Publisher: American Chemical Society (ACS)
Date: 04-10-2012
DOI: 10.1021/JP307225W
Publisher: American Scientific Publishers
Date: 02-2011
Publisher: Springer Science and Business Media LLC
Date: 1997
DOI: 10.1557/PROC-480-49
Abstract: With the advent of the modem analytical electron microscope with its ultrahigh vacuum conditions, extremely high current density in a very small probe, and its light element analysis capability, it is imperative that contamination of the TEM s le, particularly by hydrocarbons, is eliminated. The degree of cleanliness required for analysis using surface sensitive techniques is also much greater than for other forms of analysis. Contamination of s les can occur (a) prior to analysis, due to the way s les are prepared or handled, or (b) during analysis. Ex les of surface contamination prior to analysis and during analysis will be given, in order to illustrate their effect on an analysis.Polished Si, Ni, and Ti bulk s les and pre-thinned TEM Ni and Ti s les were intentionally contaminated by two methods. One set of s les was put on a liquid nitrogen cooled stage for one hour in a diffusion pumped Gatan Duomill in which the liquid nitrogen cold trap above the diffusion pump was intentionally left warm. The other set was contaminated by dipping them into a 100 ml solution of acetone containing 0.04 g of an acetone-soluble low temperature wax. Two commercially available plasma cleaners, specifically designed for eliminating hydrocarbon contamination, were used to clean the s les. The bulk s les were examined with x-ray photoelectron spectroscopy and the TEM s les were examined in a 200 keV analytical TEM. The results from these experiments will be discussed.
No related grants have been discovered for Andrey Voevodin.