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Polytetrafluoroethylene (PTFE) films with a void structure are prepared by the sintering process. Such void PTFE films are piezoelectric after proper corona charging. The quasi-static piezoelectric d 33 coefficients up to 250 pC/N are obtained. Pre-ageing treatment is an effective method to further improve the thermal stability. For the samples with pre-ageing treatment, the the d 33 coefficients are very stable when exposed to 120°C. The values of d 33 are slightly applied pressure dependent in the range of 50kPa.

Effects of initial nitrate concentrations and heavy metals on autohydrogenotrophic denitrification were investigated in batch tests to eliminate nitrate from the contaminated drinking water. Nitrate was reduced completely without nitrite accumulation at low initial concentration of nitrate (15 mg N/L), with nitrite accumulation at intermediate initial concentrations (70, and 100 mg N/L), and the denitrification of high initial nitrate concentration (150 mg N/L) was significantly inhibited at the earlier time of the reaction. However, the zero order kinetic model analysis indicated that the rates of nitrate reduction increased with the initial nitrate concentration increasing, and the rate of nitrite reduction in absence of nitrate did not change very much. The denitrification activity was significantly inhibited by Cu and Cr (VI) at the metal concentrations of more than 0.5 mg/L, whereas Zn gave no impact on the nitrate removal efficiency at all levels investigated.

In the present study, an improved process for preparing thermally stable laminated sandwiches of non-porous fluoroethylenepropylene (FEP) and porous polytetrafluoroethylene (PTFE) films is described. Also, the thermal stability of the d33-coefficients for such fluorocarbon films is discussed.

So far, linear polypropylene (PP) foam is the most extensively investigated ferroelectret. In the present studies, cross-linked PP (XPP) foam sheets are modified by a hot-press process, and then corona charged to be piezoelectric. Thereafter their piezoelectric activities are investigated.