The hydrothermal method has been used to study the crystallisation of aluminosilicates from 60" to 250". Hydrous gels of compositions Na,O,Al,O,,rtSiO, (1 < n < 12) in presence of excess of sodium hydroxide yielded analcite, mordenite, zeolites of the harmotome, faujasite and chabazite groups, Linde Molecular Sieve A, a zeolitic phase related to rhodesite, basic sodalite, basic nosean, and a phase related to nepheline hydrate, The species formed have been characterised by optical, X-ray, and chemical methods.The corresponding crystallisation of mixed Na, K-aluminosilicate gels has been compared with that of the homoionic Na-and K-gels. From the mixed gels in the interval 60" to 250" phases in the analcite-leucite, the chabazite, harmotome-phillipsite, felspar, and kalsilite groups were prepared. In addition, boehmite, quartz, and a synthetic zeolite were obtained.When Ga replaced A1 and Ge replaced Si in Na-gels, crystallisation of alkaline gels at 100" yielded, as gallosilicate, a fibrous zeolite resembling thomsonite ; as aluminogermanates, zeolites of faujasite type, and an analogue of Linde Sieve A and of harmotome; and as gallogermanates, zeolites again resembling thomsonite, faujasite, and Linde Sieve A. If Ga or Ge replace A1 or Si, the unit cells of the crystalline phases become slightly larger.Attention has been given to the mechanism of growth of diverse stnictural patterns from alkaline hydrothermal magmas.
An account has been given of the channel system in faujasite and of the occlusion within it of benzene, toluene, cyclopentane and cyclohexane over a range of temperatures and pressures. The numbers of molecules occluded per unit cell range between 32.8 (cyclohexane) and 44-8 (cyclopentane). Near saturation of the crystals the apparent thermal expansivities are a little less than the expansivities of the liquid hydrocarbons. Heats of inclusion have been derived, and also partiai molar entropies 3, of the occluded hydrocarbons. In the region close to saturation (0.93 < 0 < 0.99) the localized sorption model becomes approximately valid. The analysis of Ss in this range of 8 shows that the cyclic hydrocarbons, as well as a number of n-and iso-paraffins previously investigated, have lost a considerable amount of thermal entropy relative to the liquid state. Limitations in the analysis of entropy functions have been indicated.Increasing attention is being given to inclusion complexes from the viewpoints of non-stoichiometry,l-3 structure,4-6 kinetics,6-8 calorimetry 9-11 and statistical thermodynamic interpretation.12-16 The novel uses to which such materials may be put, particularly for separating mixtures 17-19 including the resolution of optical isomers,zO has stimulated a search for new host ~rystals.21-23 The most open and stable of these are found among aluminosilicates, and in particular among the zeolites. In a previous paper 14 we have reported upon the energetics and equilibria of inclusion complexes of paraffin hydrocarbons C1 to c g by the most open known crystal, faujasite. In this paper we record similar measurements for some cyclic hydrocarbons, and consider further the interpretation of these and of some of the previous results. EXPERIMENTAL A N D RESULTS APPARATUS AND MATERIALSThe apparatus and experimental methods have been described elsewhere.14 Cyclopentane and cyclohexane were respectively of 99.95 & 0.02 and 99-99 f 0 0 0 5 % purity as supplied by the Chemical Research Laboratory, Teddington. A.R. benzene and toluene were fractionally distilled in vacuo, and measurements were made of their vapour pressure against temperature curves and their refractive indices. A final purity > 99.5 % was estimated. For the X-ray investigation a Hilger HRX X-ray unit was employed, with 9 cm cameras, and a Guinier camera for powder photography, and a Weissenberg camera for single crystal photographs. SOME STRUCTURAL ASPECTS OF THE HOST CRYSTALIn this section we report on features of the structure of faujasite of importance from the viewpoint of its channel and cage system and so for its inclusion complexes. Work in these laboratories 24 and elsewhere 2% 26, 26a has shown that natural faujasite has a cubic unit cell and space-group 0~7-Fd3m. That from Sasbach in the Kaiserstuhl has a unit cell edge of -24-65 A. The synthetic crystals used in this work have the same space group but a slightly larger unit cell edge of -24.94ii and a somewhat different A1203/Si02 ratio.The nature of the aluminosilicate framework has be...
An account is given of dehydration, sorption, and X-ray diffraction for several closely-related synthetic aluminosilicates belonging to the harmotomephillipsite group of zeolites. A structure is proposed for a cubic variety of the synthetic phases, and the relations between this structure and orthorhombic or monoclinic unit cells of harmotome and phillipsite are indicated. The aluminosilicate framework of the cubic structure is formed by placing cubic structural units a t each comer and a t the centre of each unit cell. These cubic units, which occur also in Linde Sieve A,l are formed by union by oxygen bridges of two rings of four 50, or A10, tetrahedra, giving a cluster of eight such tetrahedra. Each cubic unit is then joined by single oxygen bridges to eight similar units, and thereby a system of intersecting channels with eight-membered rings as " windows " is produced. HARMOTOME, phillipsite, and wellsite are three closely related natural zeolites, harmotome and phillipsite being of fairly widespread occurrence whereas wellsite is rare. Several synthetic minerals have been observed in the calcium, barium, potassium, and sodium aluminosilicate crystallisation fields which bear marked similarities to these natural mineral^.^-^ A structure is now proposed for a synthetic cubic form of the sodium minerals referred to as Species Na-P in an earlier paper.2 This structure, with slight modifications, could also fit the symmetry of tetragonal and orthorhombic sodium forms and, although they differ greatly in symmetry from the cubic mineral, it is shown that the natural minerals may have a closely similar aluminosilicate framework. Dehydration, sorption, and ion exchange were also investigated for the synthetic sodium minerals.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.