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How do salts help produce homogeneous precursor powders for advanced ceramics?
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advanced ceramics
Steps in doctor blading, a tape-casting process employed in the production of ceramic films. Ceramic powder and solvent are mixed to form a slurry, which is treated with various additives and binders, homogenized, and then pumped directly to a tape-casting machine. There the slurry is continuously cast onto the surface of a moving carrier film. The edge of a smooth knife, generally called a doctor blade, spreads the slurry onto the carrier film at a specified thickness, thereby generating a flexible tape. Heat lamps gently evaporate the solvent, and the dry tape is peeled away from the carrier film and rolled onto a take-up reel for additional processing.
To produce homogeneous precursor powders for advanced ceramics, ceramists utilize the decomposition of various saltsāsuch as carbonates, nitrates, and sulfatesāto achieve uniform chemical composition at the atomic level.1
These salts facilitate homogeneity through several chemical processing routes:
- Coprecipitation: Salt compounds are dissolved in aqueous solutions and precipitated simultaneously by adjusting the pH. This creates an intimate, reactive mixture of the desired precursors.2
- Freeze-drying: Water-soluble salts (typically sulfates) are dissolved and sprayed into a chilled liquid to freeze them into small droplets. Rapid freezing prevents the segregation of chemical constituents, ensuring a uniform mixture.2
- Pechini Process: Salts or oxides are dissolved in an aqueous solution with an alpha-hydroxycarboxylic acid to form chelates. These are then polymerized into a resin, which is later decomposed to yield a mixed oxide with extremely small particle sizes.3
Following these methods, the resulting powders undergo high-temperature calcination to decompose the salts and form the final, fine-grained ceramic oxides.2