Reactive hydrated alumina

AH = -5 3 kJ/mol (written on the basis of one mole of cations). Thus this phase is energetically only marginally more stable than a mixture of end-members. Its entropy of formation is unknown. These data suggest that the formation of the surface precipitate, relative to a mixture of cobalt hydroxides and carbonates adsorbed on a fully hydrated alumina surface, probably does not lower the free energy of the system by more than a small amount. Nevertheless, such a surface precipitate may alter further reactivity. 

Flame Retardant n (1947) A material that reduces the tendency of plastics to burn. Flame retardants are usually incorporated as additives during compounding, but sometimes applied to surfaces of finished articles. Some plasticizers, particularly the phosphate esters and chlorinated paraffins, also serve as flame retardants. Inorganic flame retardants include antimony trioxide, hydrated alumina, monoammonium phosphate, dicyandiamide, zinc borate, boric acid, and ammonium sulfamate. Another group, called reactive-type flame retardants, includes bromine-containing polyols, Chlorendic acid and anhydride, tetrabromo- and tetrachlorophthalic anhydride, tetrabromo bisphenol A, diallyl chlorendate, and unsaturated phosphonated chlorophenols. A few neat resins, such as PVC and the fluoro- and chlorofluo-rocarbons, are flame-retardant (Elias, H (2003) An introduction to plastics. Wiley, New York Modem plastics encyclopedia. McGraw-Hill/Modem Plastics, New York, 1986 1990, 1992, 1993 editions). See Flammability. 

One such bond is a hydratable almnina binder. This binder is referred to as a hydraulically setting, reactive, transitional alumina (y or p AI2O3) and is finely ground for maximmn reactivity and sometimes modified with an organic polymer to provide added low-temperature strength. A reported hydration mechanism is (10)... 

Flame retardants (qv) are incorporated into the formulations in amounts necessary to satisfy existing requirements. Reactive-type diols, such as A/ A/-bis(2-hydroxyethyl)aminomethylphosphonate (Fyrol 6), are preferred, but nonreactive phosphates (Fyrol CEF, Fyrol PCF) are also used. Often, the necessary results are achieved using mineral fillers, such as alumina trihydrate or melamine. Melamine melts away from the flame and forms both a nonflammable gaseous environment and a molten barrier that helps to isolate the combustible polyurethane foam from the flame. Alumina trihydrate releases water of hydration to cool the flame, forming a noncombustible inorganic protective char at the flame front. Flame-resistant upholstery fabric or liners are also used (27). 

In addition to large-scale industrial applications, solid acids, such as amorphous silica-alumina, zeolites, heteropoly acids, and sulfated zirconia, are also versatile catalysts in various hydrocarbon transformations. Zeolites are useful catalysts in fine-chemical production (Friedel-Crafts reactions, heterosubstitution).165-168 Heteropoly compounds have already found industrial application in Japan, for example, in the manufacture of butanols through the hydration of butenes.169 These are water tolerant, versatile solid-phase catalysts and may be used in both acidic and oxidation processes, and operate as bifunctional catalysts in combination with noble metals.158,170-174 Sulfated zirconia and its modified versions are promising candidates for industrial processes if the problem of deactivation/reactivation is solved.175-178... 

Active aluminas (various oxides and hydrated oxides) with high specific areas, good absorption characteristics, catalytic properties and high chemical reactivity are either produced by precipitation processes from aluminum salt solutions e.g. via thermal post-treatment of aluminum hydroxide gels, or by the calcination of a-aluminum hydroxide under specific conditions (low temperatures, very rapid heating). 

During the next 5 years (1935-40), a number of anatase titanium dioxide pigments appeared in which inorganic surface treatments— including, but not limited to, the hydrates of alumina, silica, and antimony—had been used to partially pacify this photochemical reactivity, improving color retention as well as chalk resistance. 

Hydroxylated y-Al203 and hydrated H—Y zeolite surfaces have been found to be reactive toward some iron carbonyls (112,114). Infrared and NMR spectroscopy indicate that reaction of Fe3(CO),2 [or Fe(CO)5] with hydroxylated alumina results in formation of [HFe3(CO)n] (Scheme 3). 

Reaction with silica and alumina. Hydrated lime reacts with pozzolans (materials containing reactive silica and alumina) in the presence of water to produce hydrated calcium silicates and aluminates. The reactions may take months to proceed to completion at ambient temperatures, as in mortars (section 26.6) and lime treated soil (section 26.3), but proceed within hours at elevated temperatures and water vapour pressures (e.g., in steam at 180 °C and a pressure of 10 bar — see sections 26.10,26.11 and 26.12). This pozzolanic reaction is the basis of the strength generated by hydraulic quicklimes (section 26.9). 

The hydrated lime then reacts with the reactive silica and alumina to produce hydrated calcium and magnesium silicates and aluminates. The cement also hydrates completely. 

A scanning electron microscope allows us to observe the evolution of the beta-alumina before and after sulfatatioa The photograph (Figure 7.41) shows at great magnification (x 3,500), the sample surface before the SO2 treatment. We note the presence of needle-shaped peaks or inflorescence whose stmcture is similar to the stmcture of hydrated sodium carbonate. This compound confirms the reactivity of the beta-alumina even at ambient temperature. 

The hydration reaction of other calcium aluminates is similar to that of CA however, the mutual ratio of the individual lydrate phases formed may be altered. In the hydration of C 2 i the fraction of C2AHg formed is increased at the expense of CAHjq, whereas in the hydration of CA2 increased amounts of AH3 are formed. There are, however, distinct differences in the rate of hydration between different calcium aluminates in general, the reactivity increases with increasing C/A ratio. Among the constituents of high-alumina cement, CA2 is the phase with the slowest hydration CA hydrates faster, and Cj2A2 is even more reactive (Das and Daspodda, 1993). 

Alumina. This is a hard, hydrated aluminum oxide which is activated by heating to drive off the moisture. The porous product is available as granules or powders, and it is used chiefly as a desiccant for gases and liquids. It can be reactivated for reuse. 

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