36. Hydrothermal chemistry of the silicates. Part VIII. Low-temperature crystal growth of aluminosilicates, and of some gallium and germanium analogues

Abstract

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.

Synthesis of free-standing chabazite-type films

“…In gmelinite, the D6R units are stacked in the sequence of ABAB instead of ABCABC [23]. Chabazitegmelinite intergrowths have been reported by several researchers [22,23,26,27], indicating that these two frameworks may share similarly structured nuclei. Moreover, Daniels et al [22] observed that with increase in the Si/Al ratio of the composition, chabazite is the preferred product.…”

Thermodynamic Modeling of the SRS Evaporators: Part II. The 3H System

“…Part of the aluminosilicate framework in the structure of sodalite. 13 Linde Zeolite-A, Na 12 20 because the alumina:silica ratio of the aluminosilicate cage structure is the same as that found in the sodalites ( Figure 1). Zeolite-A is a double unit cell of sodalite without the NaCl, Na 2 SO 4 , NaOH, or Na 2 CO 3 groups (Table I).…”

“…20 ) at temperatures between 85-110°C at pH values ≥10 in 2 or 3 hours (longer residence times were needed if the silica content of the gel increased and crystallization was more rapid in the presence of excess NaOH). 20,18 † waste form is 69 wt% sodalite, 22 wt% glass, 2.4 wt% NaCl, 6.7 wt% nepheline, and 1wt% actinides 10 Zeolite was found to form preferentially in tanks with high pH (12-12.8) when sufficient Al(OH) 3 was present. Since no zeolite had been used in any M-Area processes, experiments were performed 10 to determine how Zeolite-A got into the tanks.…”

An Overview of Zeolite, Zeotype and Mesoporous Solids Chemistry: Design, Synthesis and Catalytic Properties

“…In contrast to this formation mechanism, other authors have suggested the formation of small, highly organized silicate-SDA clusters, so-called secondary building units, a concept already proposed by one of the founding fathers of zeolite chemistry. [16] According to the research group in Leuven, these building blocks form during the earliest stages of zeolite preparation, i.e. already during the mixing of the silicon precursor, the TPAOH template and water at ambient temperature and pressure.…”

“…For example, the anionic metal carbonyl cluster [Ru 6 C(CO) 16 ] 2À [in the presence of bis(triphenylphosphino)iminium (PPN þ ) counterions] has been immobilized by incorporation into the pores of the host by impregnation. The carbonyl ligands are removed in a subsequent step by gentle thermolysis, yielding nm-sized metal particles grafted onto the walls of the MCM-41 host material.…”