spray pyrolysis
/ spray py-ROL-ih-sis /
Spray pyrolysis makes ceramic powder the way a perfume atomiser makes mist, then bakes each droplet on the fly. You dissolve the metals you need in a liquid, spray that solution into a fine mist of tiny droplets, and blow the mist through a hot furnace. As each droplet flies through the heat, its solvent evaporates and the leftover chemicals decompose, so one droplet becomes one solid particle of ceramic. It is a continuous, one-pass process, solution in at one end, dry powder out at the other, with no filtering, washing, or separate reaction step.
The word pyrolysis just means decomposition by heat. Because each particle is minted from a single droplet, and every droplet started from the same well-mixed solution, every particle carries the same recipe, so the chemical uniformity between particles is excellent, especially for multi-metal compounds. The droplets are round, so the particles usually come out spherical, and they are frequently hollow or shell-like, because the solvent evaporates from the outside in, crusting a skin before the interior has dried. Adjusting droplet size, concentration, and furnace temperature lets you steer particle size and whether they end up solid or hollow. The same idea, run with a flame instead of a furnace, is flame spray pyrolysis, the industrial route to tonnage fine oxides like fumed silica and titania.
Its strengths are that it runs continuously at high throughput, holds composition uniform droplet to droplet, and needs no messy liquid-solid separation. The honest weaknesses: the spherical particles are often hollow, so they can be less dense and pack awkwardly, and the fine dust must be captured cleanly from the gas stream. It shines for fine, uniform, multi-component oxide powders and for spray-coating electrode and sensor films, and it overlaps with plain spray-drying, which dries a droplet to a granule without necessarily decomposing it.
Spray a solution of mixed metal nitrates into a furnace at 700 to 900 degrees C: each droplet dries, the nitrates decompose, and out comes a stream of spherical, often hollow oxide particles, each carrying exactly the metal ratio of the starting solution.
One droplet makes one particle, so composition stays uniform; the particles are round and often hollow.
Because the particle shell forms before the core dries, spray-pyrolysis powders are frequently hollow rather than dense spheres. That can trap gas and lower packing density, so it is not automatically the best feedstock for high-density sintering.