green-body uniformity
Two green bodies can weigh the same and read the same average density yet fire completely differently, and the reason is uniformity. Green-body uniformity is about whether the packing, the density, and the composition are the same everywhere inside the part — no dense spots and loose spots, no clusters of agglomerates, no binder-rich streaks. It is the difference between a wall built of evenly laid bricks and one with random gaps and lumps: same total material, very different soundness.
The enemies of uniformity are specific and worth naming. Density gradients from die-wall friction leave one region packed tighter than another. Hard agglomerates — clumps of particles that never broke up — pack loosely inside and prop open a big void around themselves. Poorly dispersed slips let particles flocculate into an open, patchy network, or let coarse particles settle to the bottom before casting finishes. Binder can migrate during drying and leave organic-rich and organic-poor zones. Each of these is a local region that will want to shrink by a different amount than its neighbours when the kiln heats up.
That last point is the whole reason uniformity matters more than almost any single number. Sintering shrinks everything, but it shrinks a loose region more than a dense one; when adjacent regions fight over how much to shrink, the mismatch generates internal stress that warps the part, cracks it, or leaves a residual pore that never closes. Worse, a large void around an agglomerate can survive as a strength-limiting flaw, and firing hotter to close it just triggers runaway grain growth that traps it forever inside a grain. This is why the real goal of forming is not merely high green density but uniform packing — a defect-free, homogeneous green body is the only reliable path to a dense, strong fired ceramic.
Two alumina compacts both average 58 percent green density, but one was pressed from well-milled powder and one contains hard agglomerates. On firing, the uniform one densifies smoothly to a strong part; the agglomerated one keeps a network of large pores where the clumps sat, and fails at a fraction of the strength — same average density, opposite outcome.
Same average density, different uniformity, different part: uneven packing fires into warping, cracks, and residual pores.
Uniformity beats raw density: a homogeneous body at 58 percent fires better than a patchy one at 62 percent. This is why breaking up hard agglomerates and dispersing the powder well matters more than squeezing a bit harder.