Critical crystallization temperature for the occurrence of epitaxy between high-density polyethylene and isotactic polypropylene

The crystallization behavior of high-density polyethylene (HDPE) on highly oriented isotactic polypropylene (iPP) at elevated temperatures (e.g., from 125 to 128 degrees C), was studied using transmission electron microscopy and electron diffraction. The results show that epitaxial crystallization of HDPE on the highly oriented iPP substrates occurs only in a thin layer which is in direct contact with the iPP substrate, when the HDPE is crystallized from the melt on the oriented iPP substrates at 125 degrees C. The critical layer thickness of the epitaxially crystallized HDPE is not more than 30 nm when the HDPE is isothermally crystallized on the oriented iPP substrates at 125 degrees C. When the crystallization temperature is above 125 degrees C, the HDPE crystallizes in the form of crystalline aggregates and a few individual crystalline lamellae. But both the crystalline aggregates and the individual crystalline lamellae have no epitaxial orientation relationship with the iPP substrate. This means that there exists a critical crystallization temperature for the occurrence of epitaxial crystallization of HDPE on the melt-drawn oriented iPP substrates (i.e., 125 degrees C). (C) 1997 John Wiley & Sons, Inc.

STRUCTURE AND PHYSICAL-PROPERTIES OF NEW PHASE OXIDE LA2MOO5

The compound La2MoO5 has a cubic fluorite symmetry. There is strong interaction between the two molybdenum ions (IV). The cubic-La2MoO5 oxide contains separated Mo2O8 clusters and is a semiconductor. The electrical resistivity measurement shows a semiconductor-metal transition around 250 degrees C. Temperature dependence of magnetic susceptibility represents the Curie-Weiss law. The compound La2MoO5 exhibits a paramagnetic behaviour from 170-250 K.

MISCIBILITY OF POLY(EPICHLOROHYDRIN) WITH POLY(VINYL ACETATE) AND POLY(STYRENE-CO-ACRYLONITRILE)

The phase behaviours of poly(vinyl acetate) (PVAc) and poly(styrene-co-acrylonitrile)s (SAN) with poly(epichlorohydrin) (PECH) were examined using differential scanning calorimetry and an optical method using a hot plate. The PECH/PVAc blends showed LCST behaviour. The observed miscibility is thought to be a result of hydrogen-bonding interactions between the alpha-hydrogen atoms of PECH and the carbonyl groups of PVAc. Two SAN copolymers with an acrylonitrile (AN) content of 18 wt% (SAN18) and 25 wt% (SAN25), respectively, were also found to exhibit miscibility with PECH. No phase separation occurred by heating up to about 280-degrees-C, and the individual blend has a single, composition-dependent glass transition temperature. The formation of miscible PECH/SAN blends can be considered as a result of the intramolecular repulsion between styrene and AN units in SAN.

Influence of mean water depth and a subsurface sandbar on the onset and strength of wave breaking

Wave breaking in the open ocean and coastal zones remains an intriguing yet incompletely understood process, with a strong observed association with wave groups. Recent numerical study of the evolution of fully nonlinear, two-dimensional deep water wave groups identified a robust threshold of a diagnostic growth-rate parameter that separated nonlinear wave groups that evolved to breaking from those that evolved with recurrence. This paper investigates whether these deep water wave-breaking results apply more generally, particularly in finite-water-depth conditions. For unforced nonlinear wave groups in intermediate water depths over a flat bottom, it was found that the upper bound of the diagnostic growth-rate threshold parameter established for deep water wave groups is also applicable in intermediate water depths, given by k(0) h greater than or equal to 2, where k(0) is the mean carrier wavenumber and h is the mean depth. For breaking onset over an idealized circular arc sandbar located on an otherwise flat, intermediate-depth (k(0) h greater than or equal to 2) environment, the deep water breaking diagnostic growth rate was found to be applicable provided that the height of the sandbar is less than one-quarter of the ambient mean water depth. Thus, for this range of intermediate-depth conditions, these two classes of bottom topography modify only marginally the diagnostic growth rate found for deep water waves. However, when intermediate-depth wave groups ( k(0) h greater than or equal to 2) shoal over a sandbar whose height exceeds one-half of the ambient water depth, the waves can steepen significantly without breaking. In such cases, the breaking threshold level and the maximum of the diagnostic growth rate increase systematically with the height of the sandbar. Also, the dimensions and position of the sandbar influenced the evolution and breaking threshold of wave groups. For sufficiently high sandbars, the effects of bottom topography can induce additional nonlinearity into the wave field geometry and associated dynamics that modifies the otherwise robust deep water breaking-threshold results.

On the correlation between microstructural changes of Ag-H-ZSM-5 catalysts and their catalytic performances in the selective catalytic reduction of NOx by methane

The silver catalyzed, selective catalytic reduction (SCR) of nitrogen oxides (NOx) by CH4, is shown to be a structure-sensitive reaction. Pretreatment has a great affect on the catalytic performances. Upon thermal treatment in inert gas stream, thermal induced changes in silver morphology lead to the formation of reduced silver species of clusters and particles. Catalysis over this catalyst indicates an initially higher activity but lower selectivity for the CH4-SCR of NOx Reaction induced restructuring of silver results in the formation of ill-defined silver oxides. This, in turn, impacts the adsorption properties and diffusivity of oxygen over silver catalyst, results in the decrease in activity but increase in selectivity of Ag-H-ZSM-5 catalyst for the CH4-SCR of NO.. (c) 2004 Elsevier B.V. All rights reserved.