Hydrated alumino-silicate

Zeolites are hydrated alumino-silicates and are used widely in the chemical and environmental industries. Their activity is influenced by the ratio of silica to aluminum. Amorphous silica-alumina catalysts have a lower activity than zeolitic catalysts and are used in mild hydrocracking reactions where acidic surfaces are required. The acidity is maintained by oxygen atoms attached to the aluminum atoms. 

Another extender occasionally used in epoxide formulations is clay. Clay is a hydrated alumino silicate mineral, also known as kaolin, which is available in a calcined, anhydrous form. The hydrated form is non-abrasive, chemically inert and has a large surface area. It is naturally acidic and this must be taken into account when formulating for applications where corrosion of metallic conductors may be encountered. Hydrated clay disperses readily in most formulations, particularly when dispersants or surfactants are used, and is utilised in epoxide transfer moulding compounds to allow control of flow. 

The fly ash zeolites (FAZ) are available in hydrated alumino-silicate mineral forms and are synthesized from fly ash by its alkali activation. Zeolites can be broadly classified as ion-exchangers, catalysts and molecular filters based on their characteristics and performance. As such, the principal advantage of using the zeolites in industries are their high cation exchange capacity CEC), adsorption and catalytic capacities for various environmental clean-up projects such as adsorbents for removal of heavy metal ions and other wastes. 

Role of alkali and NH cations in the crystallization of ZSM-5 Introduced in an aqueous (alumino) silicate gel (sol), the bare alkali cations will behave in various ways firstly, they will interact with water dipoles and increase the (super) saturation of the sol. Secondly, once hydrated, they will interact with the aluminosilicate anions with, as a result, the precipitation of the so formed gel (salting-out effect). Thirdly, if sufficiently small, they also can order the structural subunits precursors to nucleation species of various zeolites (template function-fulfilled by hydrated Na+ in the case of ZSM-5 (11,48)). ... 

Both humic acids and fulvic acids have a strong affinity for particulate and crystalline substances possessing oxygen atoms at their surfaces and they have been reported to bring about the dissolution of iron phosphate, calcium phosphate (61), uranium dioxide (65), hydrated magnesium alumino-silicates (66) and limonite, a complex mixture of hydrated ferric oxides (67). 

Thus in contact with aluminium and ferric phosphates, the aluminium and ferric ion concentrations are reduced and so the phosphate ion concentration is increased to maintain the solubility product at their constant levels. AIPO4 represents various hydrated and hydroxyl phosphates of aluminium, including any adsorbed or precipitated surface layers on oxides and alumino-silicates. FePO similarly, represents various hydrated and hydroxyl phosphates of iron including adsorbed or precipitated surface layers on iron oxide. 

Clay minerals are a complex group of finely crystalline to amorphous hydrated silicates, mainly alumino-silicates, which were largely formed by alteration, or weathering of silicate minerals. 

Table 10.2 summarizes some examples of zeolites based on their classification by chemical composition. Low-silica zeolites (Si/Al < 5) are synthesized in basic conditions (pH >13) using a silicon source, an aluminum source, and alkali hydroxides at moderate temperatures, typically less than 120°C. The identity of the alkaU species used is a determining factor in which phase is obtained from synthesis, as the relative rates of (alumino)silicate hydrolysis and condensation reactions are dependent on the identity of the alkali cation. It is also believed that hydrated alkali cations effectively direct the assembly of (alumino)silicate precursors into fuUy connected three-dimensional structures. Sodium and potassium hydroxide have been used most frequently in low-silica zeolite syntheses due to their low cost and high solubility in... 

Although aluminium in combinations as alumino-silicate is one of the most abundant constituents of the earth s crust, free alumina is comparatively rare. It is usually found in a hydrated form as bauxite rock, which is actually a mixture of the minerals gibbsite, A1(0H)3, diaspore and boehmite, (both of formula HAIO2). Bauxite is found in Jamaica, British Guiana, Europe and Russia and else-... 

A rather complex mixture is that constituted by the Italian tuffs [8, 53, 54], which contain various hydrated phases, namely three zeolites (phillipsite, chabazite and analcime, Table 1), unreacted glass (pumice, glass fragments, scoriae), hydrated ferric oxides and an X ray amorphous gel-like alumino-silicate, in addition to some non-hydrated phases, such as sanidine and biotite crystals. The most concentrated phases are phillipsite and chabazite, the total content of which usually amounts to 50% or more. Since Italian tuffs, simply because of the elevated contents of the above zeolites, are gaining a pre-eminent position in many industrial, agricultural and environmental applications, it is of great interest to have a rapid and reliable method available for evaluating zeolite content in the rock. 

Liu, J.N., Silsbee, M.R., and Roy, D.M. (1997) Strength and hydration of an activated alumino-silicate material, t Proceedings 10th ICCC, Goteborg, paper... 

Figure 9.5 Displacement of hydrated cations from mica surfaces. Alumino-silicate minerals, including mica, adsorb (blue balls) at aluminate sites. The potassium effectively blocks catechol from forming bidentate H-bonds and coordination complexes with the underlying oxide. Tandem placement of charged amines, such as fysine, next to the catechol moieties effectively repels KT, thus allowing the catechol groups to bond to the surface. (Interpreted from ref. 25.)...

Limestones are rarely pure and often contain alumino-silicate components. When these impure limestones are calcined, dicalcium silicate (2Ca0.Si02) may form as well as lime. This hydrates on contact with water to form CSH gel. Many archaeological lime-based mortars are therefore likely to have originally contained small amounts of gel. 

Myers, R. J., E. L Hopital, J. L. Provis and B. Lothenbach (2015). Effect of temperature and aluminium on calcium (alumino)silicate hydrate chemistry under equilibrium conditions . Cement and Concrete Research 68 83—93. 

Phosphate ions cause a release of silicic acid from aluminosilicates, thus causing their desilication. In this way insoluble alumino- and ferri-phos-phosilicates are formed, with irreversibly-bound phosphate ions. Insoluble forms of phosphorus are also obtained by the reaction of phosphate ions with hydrated A1 and Fe sesquioxides and hydroxylated aluminium ions or with products of the hydrolysis of clay minerals. 

The essentials of modern cement manufacture have been followed for the last 200 years (Lea 1970). A calcium source (usually limestone) and an aluminosilicate source (usually shale or clay) are mixed together and fired at high temperatures (1300 to 1500°C) to produce calcium silicates, aluminates and alumino-ferrites. The calcium silicates hydrate on contact with water to produce CSH gels which are the chief binding agents in the cement. Cements containing CSH gel (including pozzolanic cements) are termed hydraulic because they set and harden on reaction with water and once set, continue to harden if placed underwater (Taylor 1990). 

---