Particles bond together when heated by a sintering process that is a combination of several atomic level events that include diffusion, creep, viscous flow, plastic flow and evaporation. Significant strengthening occurs in powder compacts due to sintering. Sintering consumes surface energy to build bonds between those particles. Small particles have more surface energy and sinter faster than large particles. Since atomic motion increases with temperature, sintering is accelerated by high temperatures. The thermodynamic driving force for sintering then is found in the surface area, interfacial energies and curvature gradients in the particle system. Actual atomic motion is by several transport mechanisms with concomitant microstructure changes.