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Selenium colloid was synthesized to quantitative yield from selenous acid using sodium ascorbate as the reducing agent. When pure ascorbate is used, the presence of an added surfactant is required to obtain stable suspensions. Alternatively, exposure of ascorbate solutions to oxygen at elevated temperatures produces surface-active components which can substitute as effective stabilizers. The progress of the reaction with respect to change in particle number, growth, and conversion can be followed spectrophotometrically. A growth phase, in the absence of new particle formation, was observed from approximately 4 to 40 h. The resulting colloid exhibits long-term colloidal stability, and the internal structure of the particles exhibits no tendency to revert from the amorphous to the crystalline state. |
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