Nascent morphology of polyethylene polymerized on flat model catalysts

The morphol. and the thermal behavior of nascent polyethylene (PE) polymd. on flat models for the Phillips CrOx/SiO2 catalyst were investigated using low-voltage SEM (LVSEM) and differential scanning calorimetry (DSC). Ethylene polymns. were performed at 25 Deg and 70 Deg in gas phase. For the applied polymn. conditions, microscopy observations reveal that the formation of the macromols. at the active catalyst sites, and their subsequent crystn. on the catalyst, result in homogeneous polymer layers having a thickness of the order of micrometers. The surface morphol. of the nascent samples consists of spherical entities having a diam. less than one micrometer. Pillar-like objects form the internal structure of the PE films. Because these entities are only loosely connected, high porosity is obsd. within the entire film. Thermal anal. of the samples shows that melting temp. and crystallinity of the nascent PE samples polymd. at 25 DegC are noticeably higher than after melting and recrystn. Samples polymd. at 70 DegC, however, do not show these features. [on SciFinder (R)

Precipitation of primary Fe-rich compounds in secondary AlSi9Cu3(Fe) alloys

The precipitation of primary Fe-bearing compounds in a secondary AlSi9Cu3(Fe) alloy has been investigated over three levels of iron (0.80, 1.00, 1.20 mass%) and manganese (0.25, 0.40, 0.55 mass%), and two levels of chromium (0.06, 0.10 mass%), as well as different cooling rates (2, 10, 20 °C min-1). Differential scanning calorimetry and metallographic techniques have been used in order to quantitatively evaluate the nucleation temperature and the phase fraction of sludge particles. The temperature of sludge formation increases by increasing the initial concentrations of Fe, Mn and Cr, while an increase in the cooling rate shifts the sludge nucleation towards lower temperature. The amount of sludge particles increases progressively with the sludge factor but even more by decreasing the cooling rate. The combination of Fe, Mn and Cr levels, as well as cooling rate, allows to determine a threshold value that prevents the sludge formation. In the analysed range of composition and cooling conditions, functional equations have been developed in order to accurately predict the precipitation temperature and the phase fraction of sludge in AlSi9Cu3(Fe) die-casting alloys