Characterization of zeolites A and X grown in low earth orbit

Abstract

Crystallization of zeolites A and X carried out in microgravity (J. Warzywoda et al., J. Crystal Growth 220 (2000) 140) indicated that the microgravity-processed crystals had different nucleation and growth histories than their terrestrial controls. Powder and single-crystal X-ray diffraction showed these samples were highly crystalline. Typically, the flight-grown crystals had the higher Si/Al ratios than their terrestrial counterparts (X-ray photoelectron/Auger electron spectroscopy), and electron probe microanalysis showed that these observations continued throughout the crystals. All samples displayed Type I adsorption isotherms, characteristic of materials with a high level of microporosity (BET analysis). The flight samples had smaller surface areas, which is generally attributed to a higher degree of crystalline perfection. For the microgravity-grown crystals the symmetry of the spots by position and intensity around the center of the crystallographic projection, obtained by single-crystal X-ray diffraction, indicated uniform crystal growth. In contrast, their terrestrial counterparts (controls) were characterized by significant differences between the shapes and intensities of characteristic spots for specified families of planes and by variations of the angles (h₁k₁l₁), (h₂k₂l₂) around their literature values. SEM/AFM analysis indicated that the flight crystals had ideal morphologies, and fewer surface defects than their terrestrial controls.