Aluminate based compounds

The product in this case is sodium aluminate, a compound that contains the aluminate ion, [Al(OH)4]. Because aluminum oxide reacts with both acids and bases, it is classified as amphoteric. Other main-group elements that form amphoteric oxides are shown in Fig. J.3. As you can see, these elements lie in a diagonal band across the table from beryllium to polonium. The acidic, amphoteric, or basic character of the oxides of the d-block metals depends on their oxidation state (see Chapter 16). 

Aluminium (Al ) is generally found as the hydroxide, which causes particulate fouling of the RO membrane. Aluminium-based compounds such as sodium aluminate and aluminium sulphate are common coagulants used in potable water treatment. Under proper circumstances, the aluminium precipitate formed in the water treatment plant is completely filtered. Occasional fluctuations in pH can cause excessive amounts of dissolved Al " to pass into the distribution system. 

Mino, L, Sakai, E., and Nishioka, A. (1991) The hydration and calcination mechanism of calcium aluminate-based ultra-high strength cement with calcinm snlfoalnminate compound. Materials Research Society Symposium Proceedings 179, 193-202. 

Another way to prepare calcium aluminate supports and sorbents is based on the interaction of Ca(OH)2 with Al(OH)3 followed by heat treatment of the resulting Ca3[Al(OH)6]2- This last compound can be thermolyzed to yield Cai2Ali4033, in which the zeolite type structure was clearly established. IR spectroscopic investigation provided evidence for the bifunctional nature of the active sites on the surface of calcium aluminate based supports and sorbents. The presence of acidic and basic sites on the surface makes the use of these solids as catalysts for acid-base tranformations of organic substances promising. 

The mechanical behavior of concrete should be viewed from the point of view of a composite material. A composite material is a three dimensional combination of at least two chemically and mechanically distinct materials with a definite interface separating the components. This multiphase material will have different properties from the original components. Concrete qualifies as such a multiphase material. Concrete is composed of hydrated cement paste (C-S-H, CH, aluminate, and ferrite-based compounds) and imhydrated cement, containing a network of a mixture of different materials. In dealing with cement paste behavior, basically it is considered that the paste consists of C-S-H and CH with a capillary system. The model of concrete is simplified by treating it as a matrix containing aggregate embedded in a matrix of cement paste. This model provides information on the mechanical properties of concrete. 

Gel-Based Activated Aluminas. Alumina gels can be formed by wet chemical reaction of soluble aluminum compounds. An example is rapid mixing of aluminum sulfate [17927-65-0], Al2(S0 2 XH20, and sodium aluminate [1302-42-7], NaA102, solutions to form pseudoboehmite and a... 

Portland cement is classified as a hydrauHc cement, ie, it sets or cures in the presence of water. The term Portland comes from its inventor, Joseph Aspdin, who in 1824 obtained a patent for the combination of materials referred to today as Portland cement. He named it after a grayish colored, natural limestone quarried on the Isle of Portland, which his cured mixture resembled. Other types of hydrauHc cements based on calcium materials were known for many centuries before this, going back to Roman times. Portland cement is not an exact composition but rather a range of compositions, which obtain the desired final properties. The compounds that make up Portland cements are calcium siHcates, calcium aluminates, and calcium aluminoferrites (see ). 

Alkaline Aluminate and Silicate-Based Boiler Compounds... 

Materials formed by acid-base reactions between calcium aluminate compounds and phosphate-containing solutions yield high-strength, low-permeability, C02-resistant cements when cured in hydrothermal environments. The addition of hollow aluminosilicate microspheres to the uncured matrix constituents yields slurries with densities as low as approximately 1200 kg/m, which cure to produce materials with properties meeting the criteria for well cementing. These formulations also exhibit low rates of carbona-tion. The cementing formulations are pumpable at temperatures up to 150° C. 

Small amounts of other compounds can be added to Ni-based catalysts to improve the functional characteristics of the final catalyst. Typically, they are calcium aluminate to enhance the mechanical resistance of the catalyst pellets, potassium oxide to improve the resistance to coke formation and silica to form a stable silicate with potassium oxide [34]. Promotion with rare earth oxides such as La2C>3 also results in enhanced resistance to coking. 

Sodium hydroxide dissolves in water to give OH (aq) ions, the strongest base which can exist in an aqueous system. Chloric(VII) acid (perchloric acid) dissociates practically completely in dilute solution to give H30+(aq) ions, which represent the strongest acid which can exist in an aqueous system. The amphoteric behaviour of aluminium is noticed in a series of hydrated salts containing the Al3 + ion and in compounds such as NaA102, which contains the aluminate(III) ion, AIO2-. 

Calcium oxide is the main ingredient in conventional portland cements. Since limestone is the most abundant mineral in nature, it has been easy to produce portland cement at a low cost. The high solubility of calcium oxide makes it difficult to produce phosphate-based cements. However, calcium oxide can be converted to compounds such as silicates, aluminates, or even hydrophosphates, which then can be used in an acid-base reaction with phosphate, forming CBPCs. The cost of phosphates and conversion to the correct mineral forms add to the manufacturing cost, and hence calcium phosphate cements are more expensive than conventional cements. For this reason, their use has been largely limited to dental and other biomedical applications. Calcium phosphate cements have found application as structural materials, but only when wollastonite is used as an admixture in magnesium phosphate cements. Because calcium phosphates are also bone minerals, they are indispensable in biomaterial applications and hence form a class of useful CBPCs that cannot be substituted by any other. 

The methods of mechanochemical synthesis of various aluminates, including double compounds of alkaline, alkaline earth and transition metals, and aluminium, have been developed. The data on their synthesis, based on aluminium hydroxide, are presented according to this sequence. 

Cement binders are based on silicates, aluminates, aluminium silicates, aluminium ferrites of alkaline earth metals (mainly calcium). The hydration of these compounds or their mixtures with the formation of... 

The chromous salts, derived from the oxide CrO, arc analogous to the salts of divalent vanadium, manganese, and iron. This is seen in the isomorphism of the sulphates of the type R" SOj-THgO. The stability of such salts increases in the order of the atomic number of the metal. The chief basic oxide of chromium is the sesquioxidc CraO, which is closely allied to ferric oxide, and, like the latter, resembles aluminium oxide. The hydroxide, Cr(OH)3, with bases yields chromites analogous to, but less stable than, the aluminates. Chromic sulphate enters into the formation of alums. The chromic salts are very stable, but in the trivaJent condition the metal shows a marked tendency to form complex ions, both anions and cations thus it resembles iron in producing complex cyanides, whilst it also yields compounds similar to the cobaltamines. 

The most important compounds apart from aluminum silicate-based ceramics and clay products are aluminum hydroxide and aluminum oxide, since they are raw materials in the manufacture of aluminum. Other industrially important aluminum compounds are aluminum sulfate, aluminum chloride, sodium aluminate, aluminum fluoride and cryolite (see Section 1.7.1). 

In the spectral area with low Si/Al ratio, besides a strong peak for the species of Al(OH), several broadened, weak peaks in the range 72 80ppm could be found in the 27A1-NMR spectra, which is a typical feature of 5-coordinated intermediates. This structure is unstable in solution, but very stable in the solid phase. The aluminate compounds containing 5-coordinated Al species can be found in nature. One example is andalusite. To interpret the polymerization reaction that occurred in aluminosilicate solution, 5-coordinated aluminate was assumed to be existed. Based on the assumption of the presence of 5-coordinated aluminate, Dent Glasser and colleagues proposed another mechanism (described below) for the polymerization of silicate and aluminate ions in the solution,[41] which was named the 5-coordinated intermediate mechanism or base-delayed mechanism. The reactions will follow the steps described in Equation (5.7) ... 

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