On chlorosulphonation and the electron microscopy of polyethylene

It is shown that chlorosulphonation is a major aid to the electron microscopy of polyethylene for various samples which had mostly been crystallized at high pressures and included at least a proportion of the so-called chain-extended form. It is confirmed that sheets of excess electron density are produced at lamellar surfaces, but also including lateral surfaces. This is due primarily to the incorporation of chlorine and sulphur rather than to added uranium. The time to achieve an overall reaction varies sensitively with morphology, decreasing as the number of diffusion channels increases. Crystallinity is gradually lost, but sufficient crystals remain when a sample has become uniform, and in their initial orientations, for diffraction studies to be possible. The technique has been used to demonstrate that, during melt crystallization, the thickness of one lamella changes in response to altered growth conditions. This is direct confirmation that lamellar thickness is determined by secondary nucleation at the growth front. The tapered profile of a growing lamella previously observed in thick crystals of various polymers has been observed for chain-folded polyethylene lamellae, providing further evidence that this is a general feature of melt growth. © 1977 Chapman and Hall Ltd.

Winding-centre-tapped switched reluctance motor drive for multi-source charging in electric vehicle applications

Switched reluctance motors (SRMs) can provide an attractive traction drive for electric vehicle applications. To lower the investment in the off-board charging station facilities, a multi-functional switched reluctance motor topology is proposed on the basis of the traditional asymmetrical half-bridge converter. The SRM phase windings are employed as input filter inductors and centre-tapped windings are also developed to form symmetrical inductors for three-phase grid supply. Owing to the varying rotor position, phase inductors are unequal between one another. A hysteresis control scheme is therefore developed for grid-connection operation. In addition to AC supplies, the proposed topology can also supports the DC-source charging. A new current sharing strategy is employed to diminish the influence of the unequal winding inductances. The simulation and experimental tests are carried out to verify the proposed topology and control methods. Since this work eliminates the need for building charging station infrastructure, its potential economic impact on the automotive market can be significant.