AC IMPEDANCE STUDY OF POROUS CARBON COLLECTORS FOR Li/SO2, PRIMARY CELLS

Impedance measurements are used to determine the electrochemically active surface area of Teflon-bonded, porous carbon current collectors which are used in Li/SO₂ primary cells. An effective pore radius, pore length, and pore number also result from these measurements. Results are compared to BET measurements. In 0.1 M LiBr/acetonitrile electrolyte, only a small fraction of the BET surface area is electrochemically active.     

Hardness-Lattice Parameter Correlation for Aged Al-Zn-Mg Alloys

Two ternary Al-2.2Zn-0.95Mg and Al-5.5Zn-2.1Mg(in wt pct) alloys,with Zn:Mg ratios close to 2.5 were produced by conventional ingot casting metallurgy.The ingots were solution heat treated at 500℃ for 0.5 h and aged at 180℃ for times between 0.5 and 80 h.The structural characterization was carried out by X-ray diffraction(XRD),transmission electron microscopy(TEM),selected area electron diffraction(SAED) and Vickers microhardness measurements(HV).The study was focused on the investigation of the precipitate...     

Cardenolides fromErysimum cheiranthoides: Feeding deterrents toPieris rapae larvae

Larvae of the cabbage butterfly,Pieris rapae, refuse to feed on the wild mustard,Erysimum cheiranthoides, due to the presence of alcoholextractable deterrents. The active components were extracted inton-BuOH, and this extract was separated into four fractions (I–IV) by reverse-phase HPLC. Fractions III and IV retained the feeding deterrent activity. The activity of fraction III was found to be due to the cardenolide diglycosides 1 and 2, which were previously reported as oviposition deterrents for gravidP. rapae butterflies. Three active compounds were isolated from fraction IV by column chromatography on silica gel followed by reverse-phase HPLC. These compounds were identified as a monoglycoside, digitoxigenin 3-O--D-glucoside (4), and two diglycosides, glucodigigulomethyloside (5) and glucodigifucoside (6). An additional cardenolide isolated from fraction II was identified as cheirotoxin (7). All compounds were identified by UV, NMR (¹H and¹³C), and mass spectrometry, as well as hydrolysis experiments. The feeding deterrent activity of these compounds was compared with that of related commercially available chemicals and other compounds isolated fromE. cheiranthoides.