The Dissolving Process into Water for the Mixture of Powdered Substances with Different Solubilities (SiO<sub>2</sub>-Na<sub>2</sub>CO<sub>3</sub> System)

Abstract

A dissolving phenomenon of the mixed system (SiO2-Na2CO3 system) has been studied in this experiment. Thirty two kinds of mixed system were prepared by mixing the fixed amounts, e.g. Ag (A=2, 4, 6, 8), of Na2CO3 (Anhydrous) of constant meshes (40-80, 120-150 mesh) with (10-A) g of SiO2 of constant meshes (20-30, 35-60, 60-80, 80-120 mesh). Each mixture in the state of complete mixing was put into water in a special vessel. The amounts of Na2CO3 which dissolved into 1l H2O at a constant temperature, 40°C, for fixed times, 1, 2, 3 and 4 minutes, were determined by titrating with 0.01N HCl.As described in the previous paper, the relation between the amounts of dissolved Na2CO3 and the time was expressed by the following experimental formula, log(1-Mt/M∞)=Bt, Mt: Amounts of dissolved Na2CO3 at time t, M∞: Amounts of Na2CO3 which is able to dissolve.An agreement of the experimental results with this formula was examined by the analysis of variance. It was found that the dissolving phenomenon can be considered as a diffusion process with an apparent diffusion constant.As -B in the formula is regarded as a diffusion rate of Na2CO3, it can be used as a measure of the dissolving phenomenon. The relations between -B and the weights of Na2CO3 in the mixed system are shown in Fig. 1 and Fig. 2, which show that the dissolving rate of Na2CO3 decreases with increasing the weights of Na2CO3.Eight experimental formulae showing the relations among -B, the valume percentage of each constituent, and the porosity of the mixture were obtained by the regression analysis, and from these equations it was found that the volume percentage of Na2CO3 gives a negative factor but the porosity a positive factor to the dissolving rate, and the volume percentage of SiO2 gives a negative factor, with the exception of the case of SiO2 20-30 mesh.The value of B calculated by the use of Eq. (4. 3. 4) and the observed value of B were found to be in good agreement (Table 10 and 11). From this results, it was ascertained that -B satisfies the aclitivity relationship in reference to the volume percentage of Na2CO3, the volume percentage of SiO2 and the porosity as follows;-B=L[Na2CO3]volume%+N[SiO2]volume%+L[Porosity]L=0.0648-0.00250x-0.000392y+0.0000138xyN=0.0380-0.00104x-0.000247y+0.0000064xyM=-0.0226+0.00085x+0.000169y-0.0000051xyx: mean SiO2 mesh, y: mean Na2CO3 mesh.