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प्रश्न
Explain Bredig’s arc method.
उत्तर
- Colloidal sols can be prepared by electrical disintegration using Bredig’s arc method.
- This process involves vaporization as well as condensation.
- Colloidal sols of metals such as gold, silver, platinum can be prepared by this method.
- In this method, an electric arc is struck between electrodes of metal immersed in the dispersion medium.
- The intense heat produced vapourizes the metal which then condenses to form particles of colloidal sol.
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संबंधित प्रश्न
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Some colloids are stable by their nature, i.e., gels, alloys, and solid foams. Gelatin and jellies are two common examples of a gel. The solid and liquid phases in a gel are interdispersed with both phases being continuous. In most systems, the major factor influencing the stability is the charge on the colloidal particles. If a particular ion is preferentially adsorbed on the surface of the particles, the particles in suspension will repel each other, thereby preventing the formation of aggregates that are larger than colloidal dimensions. The ion can be either positive or negative depending on the particular colloidal system, i.e., air bubbles accumulate negative ions, sulphur particles have a net negative charge in a sulphur sol, and the particles in a metal hydroxide sol are positively charged. Accumulation of charge on a surface is not an unusual phenomenon-dust is attracted to furniture surfaces by electrostatic forces. When salts are added to lyophobic colloidal systems the colloidal particles begin to form larger aggregates and a sediment forms as they settle. This phenomenon is called flocculation, and the suspension can be referred to as flocculated, or colloidally unstable. If the salt is removed, the suspension can usually be restored to its original state; this process is called deflocculation or peptization. The original and restored colloidal systems are called deflocculated, peptized, or stable sols.
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