ANS:B - Solid state diffusion processes.

During solid-state sintering of powders, the primary mechanism that is active is solid-state diffusion processes. This process involves the movement of atoms across the grain boundaries and within the grains themselves, leading to the rearrangement and bonding of particles. However, the other mechanisms mentioned can also play a role depending on the specific conditions of the sintering process:

1. Evaporation and Condensation: At elevated temperatures, especially in vacuum or controlled atmospheres, there can be some degree of evaporation of volatile species from the powder particles. These species may then condense on nearby surfaces, contributing to particle bonding.
2. Liquid Formation in Grain Boundaries: In some cases, particularly at higher temperatures, localized melting or partial melting can occur at grain boundaries. This can result in the formation of liquid phases that facilitate particle rearrangement and densification.
3. Creation of More Dislocations: Dislocations are linear defects in the crystal lattice structure of materials. During sintering, plastic deformation can occur as a result of the applied stress, leading to the creation of dislocations. These dislocations can aid in the densification process by allowing for the movement of atoms within the grains.

While these mechanisms may be present to varying degrees depending on factors such as temperature, pressure, and composition, solid-state diffusion is generally considered the dominant mechanism responsible for the densification and bonding of powder particles during sintering.