Final answer:
In fluidized-bed processing, the atomization of powder is caused by airflow. It is this airflow through the bed of particles that causes them to become fluidized and behave like a fluid, resulting in efficient and uniform processing.
Step-by-step explanation:
The powder is atomized in fluidized-bed processing primarily due to C) Airflow. In this process, air or another gas is pushed through a bed of solid particles, which is often powder, causing the particles to behave like a fluid. This fluid-like behavior is what 'fluidization' refers to, and it allows for efficient contact between the particles and the gas, leading to uniform processing, coating, or chemical reactions. The bed needs to be in a state of fluidization for the powder to be properly dispersed or "atomized", which is indeed implemented by the air or gas flowing through the bed of particles.
In terms of the broader context of the processes that use or result in atomization, the discussion often touches upon various inputs such as pressure, heat, and vibrations. These can influence the behavior of particles in different contexts, such as in the dispersal of aerosols from pressurized vessels where a rapid change in pressure, leading to expansion and cooling, can occur.