화학공학소재연구정보센터
HWAHAK KONGHAK, Vol.10, No.4, 161-170, August, 1972
Isopolytungstate 음이온의 생성과정에 관한 연구
A Study on the Formation of Isopolytungstate Anions
Much works have been done on isopolytungstate ion formation processes by acidifying sodium tungstate solutions.
Concerning this field of research which are closely related to improving quality of the refined final tungsten products in the metallic form, there have been reports by investigators such as Kepert1), Jander3-7), Souchay8-10), Aveston11), and others.
However these studies were done by potentiometric, conductometric, polarographic and ultracentrifugal methods, and the results were found to be mutually inconsistent.
The cryoscopic method, however, has not been fully investigated in spite of the accuracy of this method at neutral range in contrast to the potentiometric method which have often been tried for the study of isopolytungstates.
Therefore, cryoscopic method was adopted in this work, and the following results were obtained for the condensation of isopolytungstates in various pH ranges, by mean of the pH measurement, U. V. spectrophotometric method, and cryoscopic method.
A. By cryoscopic method ;
1. Initially, HWO4- ions were found in dilute Na2WO4 solutions acidified with HClO4.
2. The W3O114- ions appeared when the mole ratio of H+/WO42- was made to 1.05, and H2W12O406- to 1.55.
3. And, similarly, W2O72- ions appeared at the mole ratios of the following values, 1.15, 1.25, 1.30, and 1.35.
B. By pH measurement :
1. The HWO4- ion appeared in the solutions whose pH values were maintained from 3.7 to 6.5.
2. And W2O72- ions formed at the pH values ranging from 3.8 to 6.3, W3O114- ions at 6.35 and H3W6O213- or H2W12O406- ions at 3.2.
C. By U. V. spectrophotometric method :
The U. V. absorption band due to HWO4- ions observed to range from 335 to 430 mμ in wave length, W2O72- ions from 345 to 435 mμ, W3O114- ions from 350 to 440 mμ, and H2W12O406- ions from 368 to 457 mμ.