Some Physical and Chemical Properties of Synthesized Dawsonite

[摘要] NaAl(OH)2CO3was synthesized using colloidal earth (Allophane) as the starting material and some of its were studied in detail. It was found that Dawsonite was formed in the pH range (pH 12.5~12.0) that the concentration of HCO3- was just begun to increase and the presence of HCO3- in the product was clarified from the infrared absorption spectrum. The chemical formular of Dawsonite was therefore presumed as NaAlO (OH) HCO3. From toahhe results of X-ray powder diffraction, both peaks at 5.7 ¡Ê and 2.8 ¡Ê were observed, and fibrous crystalline structure was observed from electron micrograph and also found from the microscopic electron diffraction at 5.7 ¡Ê. Therefore the fibrous axis was considered as =Al=O2=Al=O2=Al=(*image) direction. True specific gravity of Dawsonite was 2.44 and its porosity was 91.4%. It was practically insoluble in water, but decomposed in the boiling water to form Pseudo Boehmite. Stable pH range of Dawsonite was about 4.5~11.5. From the results of D.T.A. and T.G.A., it was observed that CO2was liberated at 350¡É, and H2O at 650¡É, and converted into strongly hygroscopic NaAlO2, which was easily decomposed in water into ¥â-Al(OH)3(Bayerite) and NaOH.

[学科分类] 化学（综合）