Formation of aluminosilicate

A range of aluminosilicate solutions were investigated. The gelation behaviour, the species in solution (as observed by NMR) and the zeolite crystallization products are described. The effect of concentration and type of alkali metal cation present in solution gives information about the formation of aluminosilicate complexes and how they interact, under the influence of the cation, to form an aluminosilicate gel, the precursor to zeolite crystallization. 

Fig. 12. Schematic diagram showing formation of aluminosilicate exchanged with transition metal ions or their ammine complex ions.

In 1966 the formation of aluminosilicates in marine environments was hypothesized by Mackenzie and Garrels (1966) who pointed out the potential significance of this process with respect to the oceanic chemistry and for global elemental cycles. As elements are transferred into solid phase and thus become insoluble this process is referred to reverse weathering . Within the scope of this textbook only a brief overview of the major processes and conditions of formation is intended to be outlined. 

McCormick, AV, Bell, AT. and Radke, C.J. (1989) Multinuclear NMR investigation of the formation of aluminosilicate anions J.Phys. Chenu 93,1741-1744. 

It is common practice to describe silicates in terms of a purely ionic model. However, although we might write Si, the A+ charge is unlikely on ionization energy grounds and is incompatible with the commonly observed Si—O—Si bond angle of 140°. Figure 14.22 compares the ionic radii of ions commonly present in silicates the value for the Si ion is an estimate. Since the Al and Si ions are similar sizes, replacement is common and leads to the formation of aluminosilicates. If Al replaces... 

K.J.D. MacKenzie, D.R.M. Brew, R.A. Fletcher and R. Vagana, Formation of Aluminosilicate Geopolymers from 1 1 Layer-lattice Minerals Pre-treated by Various Methods A Comparative Study. 

Fernandez et al. [31] have demonstrated the role played by the reactive alumina content in alkaline activation of fly ashes. It has been confirmed that the amount of the reactive alumina plays an important role in the formation of aluminosilicate gel in a strong alkaline concentration of 8 M NaOH, at 85 °C, as the curing time varies from 2 h to 7 days. Usually, the fly ash which has reactive Si02 and AI2O3 contents in the ratio below 2 is considered to be most appropriate for alkaline activation. Authors have confirmed that alkaline aluminosilicate gelis formed as a major reaction product, regardless of the composition of the ash. It has also been observed that the gel formed in short reaction time, constitute of alumina rich phase in which a Si tetrahedron is surrounded by four Al tetrahedron. 

Leonard, 2004, A novel and template-free method for the spontaneous formation of aluminosilicate macro-channels with mesoporous walls, Chem. Commun., 1674. 

Ellis and Wilson also examined cement formation from aluminosilicate glasses and concentrated solutions of PVPA (Wilson Ellis, 1989 Ellis, 1989 Ellis Wilson, 1990). These cements, like the glass polyalkenoate cements, are a type of glass-ionomer cement. 

X-Ray irradiation of quartz or silica particles induces an electron-trap lattice defect accompanied by a parallel increase in cytotoxicity (Davies, 1968). Aluminosilicate zeolites and clays (Laszlo, 1987) have been shown by electron spin resonance (e.s.r.) studies to involve free-radical intermediates in their catalytic activity. Generation of free radicals in solids may also occur by physical scission of chemical bonds and the consequent formation of dangling bonds , as exemplified by the freshly fractured theory of silicosis (Wright, 1950 Fubini et al., 1991). The entrapment of long-lived metastable free radicals has been shown to occur in the tar of cigarette smoke (Pryor, 1987). 

In such complex system as aluminosilicate precursor gels, various lifetime components can appear reflecting material structure. The gel structure is a result of direct interaction of cations with silicate, aluminate and aluminosilicate anions, redistribution of charges and electron density over the system of aluminosiloxane bonds with effect on the formation of different structural units [24],... 

The formation of the microporous phase dispersed in porous, amorphous matrices was followed by XRD and TEM. The XRD patterns of the BEA-composite prepared using the Al-poor aluminosilicate (6A187Si) are shown in Figure 1. BEA was the sole... 

Recrystallization procedure applied to the amorphous aluminosilicates of different chemical composition resulted in the formation of the dispersed zeolitic domains of the FAU and BEA structure in porous matrices. The structural transformation into the composite material was proved with TEM, XRD and 27Al and 29Si MAS NMR spectroscopies. The IR data revealed that strong Bronsted acid centers were main active sites generated in the composite materials, irrespectively of the Al content. 

The formation of barium chromate often leads to the physical separation of the sealing glass and the metal alloy due to barium chromate s high thermal expansion. Along interfacial regions where oxygen or air access is blocked, chromium or chromia can react with barium-calcium-aluminosilicate (BCAS) glass-ceramic to form a chromium-rich solid solution and a series of pores. 

The general behaviour of the alkali cations in presence of aluminosilicate gels and their influence on zeolite nucleation and crystallization rates has been discussed in detail elsewhere (26). Their specific role in the formation of the various (M)ZSM-5 zeolites can be depicted on the basis of the above described observations. ... 

Kerr, G.T. (1955) Chemistry of crystalline aluminosilicates 1. Factors affecting the formation of zeolite A. 

Flanigen monitored the changes in the IR spectra that occur during the synthesis of NaX zeolite from a sodium aluminosilicate gel. The appearance of absorption bands due to the formation of structural units in the zeoUte as the crystallization of NaX proceeded were observed [93]. In particular, the growth of a band around 575 cm indicated the formation of double six-rings which is one of the structural sub-units of X zeolite. 

---