Analcite dehydration curves

X-ray diffraction of 114 analcite at 25 °C revealed two weak reflections at d = 3.80 (at 23.4° 20) and 3.24 A (at 27.5 26) indexed as (320) and (411), respectively. These forbidden, weak reflections disappear from the pattern on heating the zeolite above 200° C. Their disappearance correlated closely with the pronounced second-order break in the dehydration curve at 200° C and suggests a randomization of the partially ordered distribution of 16Na+ ions over the 24Na+ sites (Vs, 0, x/4) in the unit cell. At the decomposition temperature, 916° C, the apparent cell edge is 13.69 A. 

Caex 114 Analcite. The dehydration curves obtained with Ca2+-containing samples, Caex82114 analcite, and natural wairakite (not shown) were displaced toward higher temperature in accordance with the higher heat of hydration of Ca2+ (Table I). Complete dehydration was obtained only above 500° C. Total H20 contents are similar to or slightly less than the parent analcite. 

Liex, Mgex, and Niex 114 Analcites. TGA curves of samples containing 81, 32, and 11% exchange of Li+, Mg2+, and Ni2+, respectively for Na+ were shifted up in temperature by 50°-100°C. Second-order breaks were observed in the dehydration of Liex 114 and Niex 114. The water content increased by 15-20%, which must be correlated with more efficient accommodation of the H20 molecules in the presence of small ions. Extrapolation to the pure end-member would yield a water content which could not be accommodated in the channels. 

Caex81 116 Analcite. The most persuasive example of a structurally related discontinuity in dehydration behavior was found in the investigation of Caex 116 analcite. Figure 7 shows the TGA data in which the dehydration and rehydration curves describe a nearly closed hysteresis loop. The break at 425°C is correlated with a first-order transformation detected by x-ray at 453°C. The transformation is accompanied by a 10-20% reduction in cell volume as the last water is rejected. 

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