Retention Of Crystallinity Research Articles

Hydrothermal stability of US-Ex

USY samples, which were prepared from sodium Y whose Si/Al atomic ratios were in the range of 2.5 to 3.0, were treated hydrothermally under deep-bed conditions and with steam. The nonframework and framework aluminum was extracted with HCl solutions. The hydrothermal stabilities under 100% steam of US-Ex were examined in relation with the unit cell dimensions, chemical analyses, MAS n.m.r., t.g., and i.r. observations. The hydrothermal stability of US-Ex was affected mainly by the amounts of framework and nonframework aluminum and the retention of crystallinity, but not by the amounts of residual alkali metal oxides and the amount of 4-OH nest. Some of Si (3Al) and Si (2Al) units converted to nonframework Si (4Al), Si (3Al), and Si (2Al) units and left the vacancies larger than four OH nests in zeolite framework. It was confirmed that the population of Si (4Al), Si (3Al), and Si (2Si) in parent sodium Y affects the retention of crystallinity of US-Ex.

Phase homogenization of mixtures of poly( m-xylene adipamide) and nylon 6 by interchange reactions

Melt blends of poly( m-xylene adipamide) and nylon 6 prepared by extrusion at 260°C have two glass transitions and are opaque, whereas similar preparation at 290°C yields transparent melts and materials with a single glass transition. This phase homogenization has been shown by thermal, dynamic mechanical, and nuclear magnetic resonance analyses to be the result of interchange reactions. A single phase develops after as few as five interchange reactions per molecule. This segmented block structure explains the high level of crystallinity that is retained after phase homogenization. Such behaviour is possible when the unreacted components have an unfavourable but small interaction energy density, i.e. near miscibility, as argued using thermodynamic theories. Retention of crystallinity is useful for certain property considerations.

Partial destruction of USY and its effect on the hydrothermal stability

The hydrothermal stabilities of ultrastabilized Y under 100% steam were examined in relation with the results of XRD, chemical analyses, and MAS n.m.r. The hydrothermal stability of USY was affected mainly by the retention of crystallinity, but not by the amounts of residual alkali metal oxides. The populations of Si(3Al) in sodium Y affect the partial destruction of structure during the dealumination. Some of Si(3Al) units were converted to nonframework Si(4Al) units and left the vacants larger than four OH nests in the zeolite framework, which causes the formation of secondary pore systems and amorphous fraction.

A novel method for the preparation of extensively dealuminated faujasites

Open structure faujasites may be dealuminated with retention of crystallinity using phosgene (or similar reactants) provided the sample has been made ultrastable in a previous procedure.

The Microstructure of Xe Implanted GaAs

Previous investigators have shown that the surface regions of GaAs samples implanted at room temperature with 40-100 keV Ne ions become amorphous after a dose of the order of 1x1014ions cm-2. Their study also indicated that implantation above room temperature (35°-200°C) results in the retention of crystallinity even with fluences two to three orders of magnitude higher. Investigators using ion backscattering and optical absorption have shown that ion dose rate is also an important variable in ion implantation. In the present investigation, transmission microscopy has been used to further study the temperature and dose rate effects of ion implantation in GaAs. A number of {111} and {l00} single crystal GaAs samples have been implanted with 275 keV Xe ions to doses of 1015 and 1016 ions cm-2 at dose rates ranging from 2.5x1012 to 8.1xl012ions cm-2 sec-1.Low dose (1015ions cm-2) implantations at room temperature produced amorphous layers at all dose rates.