Na+-kenyaite

We synthesized pure and well-crystallized Na-magadiite and Na-kenyaite under the carbonate system in a short reaction time. I report here the effects related to the compositions of reactants, reaction time, and temperature on the preparation of... 

The unit cell composition of Na-kenyaite deduced from TGA and the analyses of sodium and silica is Na2 05Si2o04i 03 IO.42H2O, which compares favorably with the approximate composition Na2Si2o04i IOH2O supported by the early work of Lagaly and Beneke [24],... 

Fletcher et al. [100] and Kwon et al. [101,116] synthesized highly crystalline Na+ magadiite and Na" kenyaite when they reduced the alkalinity by replacing NaOH with sodium salts, e.g., Na2C03. 

TABLE 11-2 Phase components in dependence on the concentration of PDDA-Cl (P40) and on the crystallisation time. The crystallization temperature is 175 C. The composition of the reaction mixture is 4 Na O 1 AljOj 40 SiOj 1200 H2O x PDDA-Cl. The phase component were denoted as a amorphous, MFl zeolite MFI, Mo mordenite, SH-P40 novel layer silicate, Ke kenyaite-like silicate, Cr cristobalite, and Q quartz. 

Figure 3 shows XRD pattens of synthetic samples obtained at 180 C in the higher molar ratio of Si/Na [Si02/(NaOH Na2C03) = 20 and H20/(Na0FI -FNa2C03) = 200] with reaetion time. Kenyaite ean be synthesized direetly from amorphous silica, and magadiite was not observed as an intermediate. 

The higher Si/Na molar ratio aeeelerates the formation of kenyaite. Siliea is first dissolved in alkali solution at elelvated temperature, and then the nucleation of kenyaite occurs gradually. Therefore, the Si/Na ratio in the solution is a very important faetor in the formation of kenyaite. Also, the higher content of silica in the composition of starting materials may cause a large Si/Na ratio in the solution. These conditions could accelerate the nucleation of kenyaite that has a... 

The Na /H exchange of alkali silicates changes the hydration/dehydration behavior. The basal spacing of the hilly hydrated kenyaite (sodium form) and the crystalline silicic acid is 1.97-1.99 nm. Air-drying reduces only the spacing of the H form to 1.76-1.80 nm ahCT dehydration the spacing remains 1.86 nm or less [11]. 

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