high-temperature phases of zeolites of the … · anerican mi*eralogist vol. 57, pp. 499-510 (1972)...
Embed Size (px)
Anerican Mi*eralogistVol. 57, pp. 499-510 (1972)
HIGH-TEMPERATURE PHASES OF ZEOLITES OF THENATROLITE GROUP
L. P. veN Renuwr.rx, Department o,f Soil Scian"ae, State Agri,aultwalUruiuersitg , W agening,en, The N etherlands
The thermal changes occurring in zeolites of the natrolite group have beeninvestigated by DTA, TGA, and continuous-heating X-ray photography. Thiscombination of techniques facilitated a better description of the dehydrationphenomena. Several as yet unknown metaphases have been recorded, and sta-bility ranges have been reassessed. Structurally, upon heating natrolite behavesentirely differently from its isotypes mesolite and scolecite which are mutuallysimilar in behavior. Thomsonite and gonnardite also show similar X-ray diffrac-tion powder patterns, with aspects of both natrolite and mesolite,/scolecite.Edingtonite shows an individual pattern and is the only member of the groupwhere heating does not result in a phase amorphous to X-rays (X-amorphous).
The only feature common to all members of the group is that the roomtemperature phase reacts upon heating by a considerable contraction along theo and b axeg and a slight expansion along the c axis, in accordance with thegeneral structure of tlre group.
The thermal properties of few natural zeolites have been studiedas extensiyely as those of the members of the natrolite group. Thisapplies particularly to the species natrolite, mesolite, and scoleciteand to a lesser extent thomsonite, whereas gonnardite and edingtonitehave received very little attention.
As has been pointed out in an earlier communication (van Reeuwijk,1971), previous studies could not possibly give accurate informationabout the physical changes zeolites undergo upon thermal dehydration,due to the employment of inadequate methods and techniques.
The purpose of this reporb is to give an account of the thermal be-havior of all members of the natrolite group as obtained by a com-bination of dynamic thermal analysis methods, aiz., d\ff.eren|ial thermalanalysis (DTA) , thermogravimetric analysis (TGA), differential scan-ning calorimetry (DSC), and continuous heating X-ray diffractiontechniques.
Mernirrer,sA representative specimen of each species was selected from our collection
under study to illustrate the characteristic properties. The Guinier De WolfrX-ra5r photographs (Co-Ko radiation) are given in Figure 1, the chemical analy-ses in Table 1.
. ' - ' . - - YG
L. P, VAN REEUWIJI