1993 Volume 42 Issue 4 Pages 225-233
In order to verify the mechanism of the formation process of hemimorphite (Zn4Si2O7(OH)2·H2O) in galvanized steel pipe for water service, the synthesis of hemimorphite was performed through the application of a co-precipitation reaction, which was named the co-precipitation method. Sodium metasilicate (Na2SiO3·9H2O) solution was mixed with Zn(OH)2 colloidal solution. The precipitate obtained from the mixture was aged in aqueous solution to crystallize it into hemimorphite. The samples which were aged for the prescribed periods were analyzed using X-ray diffraction, infrared spectroscopy and thermal differential analysis. It became clear from the analysis that at the initial stage of hemimorphite formation, dissolved silicate was adsorbed onto the colloidal particles of Zn(OH)2 and precipitated with Zn(OH)2 particles; at the next stage, the adsorbed silicate broke the structure of Zn(OH)2 to form an amorphous compound as a precursor of hemimorphite; and at the final stage, rearrangement of atoms proceeded over a long period to form the framework of the hemimorphite. Furthermore, it was suggested that the OH bond of the Zn-OH-Zn bridge in the hemimorphite crystal was hard to form compared with the other bonds in the crystal.
