Surface Modification and Planar Defects of Calcium Carbonates by Magnetic Water Treatment

Powdery calcium carbonates, predominantly calcite and aragonite, with planar defects and cation–anion mixed surfaces as deposited on low-carbon steel by magnetic water treatment (MWT) were characterized by X-ray diffraction, electron microscopy, and vibration spectroscopy. Calcite were found to form faceted nanoparticles having 3x () commensurate superstructure and with well-developed {} and {} surfaces to exhibit preferred orientations. Aragonite occurred as laths having 3x () commensurate superstructure and with well-developed () surface extending along [100] direction up to micrometers in length. The (hkil)-specific coalescence of calcite and rapid lath growth of aragonite under the combined effects of Lorentz force and a precondensation event account for a beneficial larger particulate/colony size for the removal of the carbonate scale from the steel substrate. The coexisting magnetite particles have well-developed {011} surfaces regardless of MWT

Conductivity Degradation Study of polypyrrole and polypyrrole/5% w/w TiO2 nanocomposite under Heat Treatment in Helium and Atmospheric Air

The thermal aging of the d.c. electrical conductivity sigma in pure polypyrrole (PPy) and in the nanocomposite PPy/5%w/w TiO2 was investigated for thermal treatment times from 0 to 50 hours at different temperatures Tau = 100, 300 and 380 K under atmospheric air and inert He gas. In both materials the fluctuation induced tunneling of charge carriers was followed revealing a granular metal structure. The isothermal variation of sigma with time under atmospheric air and inert He indicates the coexistence of two antagonistic mechanisms, the one increasing and the other decreasing sigma. In XRD patterns from PPy and PPy/5%w/w TiO2 the sharp peaks of rutile and anatase crystallographic types of TiO2 coexist with the broad peak of amorphous PPy. The latter shifts to smaller angles with the addition of TiO2 indicating a greater separation of pyrrole rings, which turns up to be about equal to the diameter of O2- indicating the diffuse of oxygen from TiO2 into PPy. SEM pictures confirm the removal of Cl- in the form of HCl during thermal aging, a process which decreases the conductive part of the polymer and at the same time rearranges the chains. These represent two antagonistic mechanisms the first decreasing, the second increasing conductivity.nbspnbs

Electrical conductivity and TSDC study of the thermal aging in conductive polypyrrole/polyaniline blends

The thermal aging of conducting polypyrrole/polyaniline (PPy/PA) blends heated at 70°C for up to about 600 hours was studied by d.c. conductivity measurements and by thermally stimulated depolarization current (TSDC) spectroscopy in the temperature range from 80 to 300 K. The composition of the samples varied from pure polypyrrole to pure polyaniline with the PA content increasing in steps of 10%. Although the σ = σ(T) curves seem smooth, the corresponding Δσ/ΔT = f(T) curves exhibit systematically a scattering of points in the temperature ranges from 100 to 140 K and from 225 to 320 K approximately for all the samples before and after the heat treatment. TSDC measurements with the MISIM (metal-insulator-sample-insulator-metal) configuration, show a low temperature peak at 100-120 K and a high temperature peak at 280-300 K. The first disappears when the polypyrrole content exceeds 70% and for all the samples after heat treatment, although the high-temperature peak persists. The explanation given to this correspondence between d.c. conductivity and TSDC signals is based on the destruction of conformons and the mobility change of the polymer chains with rising temperature

Effect of hydrostatic pressure on the d.c. conductivity of fresh and thermally aged polypyrrole-polyaniline conductive blends

In this paper we investigate the effect of hydrostatic pressure on the electrical conductivity of polypyrrole-polyaniline conductive (protonated) blends of various compositions. Results are presented for thermally aged blends as well. The modification of the conductivity due to pressure is more pronounced in the fresh samples than in the aged ones. The phenomenon is discussed within the frame of the granular model. The percentage variation of the conductivity upon pressure change for the polypyrrole rich blends is not influenced by the ageing process. This feature suggests that these blends could possibly be used as pressure sensors, which are insensitive to thermal ageing

Low frequency dielectric relaxation phenomena in conducting polypyrrole and conducting polypyrrole-zeolite composites

The dielectric properties of polypyrrole-zeolite composites up to 50 % w/w zeolite were analyzed. Investigations show that in the formalism of complex permittivity, the dispersive region of the conductivity revealed the presence of a dielectric mechanism. It was found that the direct current (dc) conductivity was as increasing function of the percentage w/w content in zeolite. The results show that the long-range electric charge transport and relaxation corresponded to short-range forward and backward motions exhibited different processes

Hopping charge transport mechanisms in conducting polypyrrole: Studying the thermal degradation of the dielectric relaxation

Isotherms of the imaginary part of the permittivity from 10(-2) to 2x10(6) Hz from liquid nitrogen to room temperature for fresh and thermally aged specimens of conducting polypyrrole reveal a dielectric loss peak, which is affected by the reduction of conducting grains with aging. Charge trapping at the interfaces separating the conductive islands seems invalid. Thermal aging indicates that macroscopic conductivity and short range one have different aging evolution. The first (dc conductivity) is dominated by the tunneling of the carriers between neighboring grains through the intermediate insulating barriers, though the second (ac conductivity) is due to a backward-forward movement of the carriers and is controlled by the intrachain transport of them and their hopping between the chains. (C) 2005 American Institute of Physics