Aluminate solutions, aging

The present study deals with the application of RDF to the sodium aluminosilicate hydrogels, which were formed by mixing, aging and heating of sodium silicate solution with sodium aluminate solution under stirring, in order to produce NaA-zeolite crystal. 

Bayerite (P-Aluminum Trihydroxide). Bayeiite is rarely fovmd in nature. It has been synthesized by several methods A pure product is prepared by the Schm, b method (3) in wliich amalgamated aluminum reacts with water at room temperature. Other methods include rapid precipitation from sodium aluminate solution by CO2 gassing, aging of gels produced by neutralization of aluminum salts with NH OH, and rehydration of transition rho alumina. 

The Raman bands of very concentrated A1(N03)3 solutions are consistent with [Al(OH2)6] and NOj in the form of solvent-separated ion pairs.Hydration-shell and bulk-water protons can be distinguished by NMR. Al NMR signals distinguish [Al(OH2)s] from other species, such as [A1(0H2)5(S04)] in sulfate solutions, or [Al2(OH)2(OH2)8] and the more highly polymerized complexes which are produced on the ageing of aqueous aluminate solutions. According to Raman and NMR data, - the cation... 

Gibbsite of high purity is needed to prepare aluminas for catalytic appfi-cations. A number of synthesis protocols are reported, aU characterized by very long aging times for the crystallization to avoid high sodium concentrations, and with the final steps sometimes at acidic pH (44). Nanometersized crystals of gibbsite samples can be prepared by neutralization of sodium aluminate solutions (45) or at acidic pH (46). 

Ageing of Aluminate Solution. The aluminate solutions were allowed to age for 48 hours at room temperature or for 4 hours at 70°C in the absence of any seed crystals or the addition of acid or CO2. 

Figure 2 Bayerite from ageing potassium aluminate solutions...

Figure 6 Gibbsite from ageing potassium aluminate solution...

In a typical aluminosilicate zeolite synthesis, sodium aluminate is dissolved in water along with some fraction of the additional sodium hydroxide that is needed in the reactant mixture. Separately, sodium siHcate is mixed with the remainder of the sodium hydroxide. The two solutions are combined using the required mix order and agitation level, resulting in the initial zeolite gel. In some cases this initial gel is aged at an intermediate temperature for a time to allow evolution of... 

Figure 6.1.10 shows the mean diameter of the spherical aluminum phosphate particles prepared by aging a solution containing 3.98 X l ) 2 mol/dm3 A1(N02)2, 3.98 X I0-2 mol/dm3 Na2HP04, 0.1 mol/dm3 HNOj, and varied amounts of urea at 100°C for 19 h (12). The mean particle size steeply decreases from 560 to 100 nm at urea concentration below 0.2 mol/dm3 and then decreases monotonously to 36 nm as the urea concentration is increased to 1 mol/dm3. Morales et al. (13) proposed a mechanism of alumin um phosphate precipitation by the reaction of aluminum salts with H,P04, which follows steps (a) (d) ...

The phosphors obtained by solid-state reactions are not sufficiently resistant to aging for use in fluorescent lamps. In a pseudo-sol-gel process an aqueous solution of (Y, Tb) (N03)3 is treated with Si02 and heated to 1200°C. After subsequent reductive firing under N2/H2 at 1700-1800 °C, a phosphor is obtained with a resistance to aging comparable to that of the aluminates [5.366],... 

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