Aluminosilicates formation

Park, H "Thermodynamics of Sodium Aluminosilicate Formation in Aqueous Alkaline Solutions Relevant to Closed-Cycle Kraft Pulp Mills", PhD Thesis, Dept, of Chemical and Bio-Resource Engineering, University of British Columbia, Vancouver, BC, Canada, 1999. 

High resolution Si NMR spectroscopy can provide considerable insights into the structure and distribution of silicate and aluminosilicate anions present in solutions and gels from which zeolites are synthesized. The narrowness of individual lines and the sensitivity of the chemical shift to details of the local chemical environment make it possible in many instances to identify exact chemical structures. Studies using Si NMR have shown that the distribution of anionic structures is sensitive to pH and the nature of the cations in solution. Alkali metal cation NMR has demonstrated the formation of cation-anion pairs the formation of which is postulated to affect the dynamics of silicate and aluminosilicate formation and the equilibium distribution of these species. NMR has proven useful in identifying the connectivity of A1 to Si,... 

As noted above, it is widely adopted that trigonal aluminum is one of the most important chemisorption and catalytic sites in aluminosilicates. Formation of these centers is usually associated with dehydroxylation. In the preceding section this concept was used to discuss different types of BASs formed as a result of water adsorption on the dehydroxylated surface of a model aluminosilicate fragment. The activity of the trigonal aluminum atoms was particularly manifested in the strong activation of the coordinatively bonded water molecules. In the chemical sense, such a site comprises a typical Lewis acid, which is also confirmed by quantum-chemical calculations. 

Both the tropical reverse weathering studies and the recent discovery of the process controlling opal diagenesis in surface sediments demonstrate the importance of rapid authigenic aluminosilicate formation in marine sediments. The focus is now back on determining the importance of these reactions in marine geochemical... 

The Al concentration in the inner cell layers and root cell cytoplasm (symplasm) of plants was lower than in the surrounding medium (Kochian and Jones). Between 30% and 90% of absorbed Al was localized in the apoplast (Mossor-Piettraszewska 2001). Al and silicon appear to be co-localized in root cell walls, perhaps reflecting the primary internal sites of aluminosilicate formation and Al detoxification (Hodson and Sangster 1999). 

Multicomponent sol—gel fibers have been successfuUy developed (1,52). The early stages of sol formation and gelation are cmcial for controlling the fiber microstmcture. Aluminosilicates, zirconates, and aluminates (1,18,52) can be prepared by sol—gel methods. MuUite [55964-99-3] 3AI2 O3 -2Si02, fibers... 

In 1968 Wilson published an account of his early search for alternatives to orthophosphoric acid as a cement-former with aluminosilicate glasses. Aluminosilicate glasses of the type used in dental silicate cements were used in the study and were reacted with concentrated solutions of various organic and inorganic adds. Wilson (1968) made certain general observations on the nature of cement formation which apply to all cements based on aluminosilicate glasses. 

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. ... 

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