Here’s a practical, lab-tested playbook to stop pellets from sticking/cracking when uniaxially pressing Pr-doped ceria with a stainless-steel die.

Why this happens (so fixes make sense)

• Die–wall friction & stainless galling → surface adhesion on ejection.
• Density gradients from one-direction compaction → radial/lamination cracks.
• Elastic springback after unloading → tensile stress at the pellet–die interface.
• Powder issues (hard agglomerates, wrong moisture/binder) → weak, flaky green bodies.

Quick wins (often enough on their own)

Full protocol (step-by-step)

A) Powder conditioning (crucial for green strength)

• Deagglomerate: ball-mill Pr₀.₁Ce₀.₉O₂₋δ powder in IPA/EtOH with zirconia media (e.g., 200–400 rpm, 4–12 h). Dry at 80 °C, then sieve 100–200 mesh.
• Binder: add 1.0–2.0 wt% PVA (MW 30–70k) or 0.5–1.0 wt% PEG 6000 (dissolved in minimal water/alcohol), spray-granulate while tumbling to form 100–300 μm granules. Dry 60–80 °C, re-sieve. Why: granulation improves flow/packing; binder gives green strength.
• Internal lubricant (optional): 0.2–0.5 wt% zinc stearate or 0.3 wt% stearic acid blended uniformly. (Skip if you only want BN as the release; avoid graphite/MoS₂ that can contaminate.)
• Moisture: slight residual moisture helps—aim ~0.2–0.5 wt%; avoid “wet” powder that cakes.

B) Die preparation

• Material: stainless is prone to galling. If available, WC-Co (carbide) or nitrided tool steel dies stick far less.
• Finish & geometry: mirror polish; add a small entry radius/chamfer on both ends of the die bore to reduce edge shearing.
• Release coating: light, uniform BN spray on bore and punches; let solvent flash-off completely.
• Temperature: pre-warm die to 40–60 °C to avoid condensation and to improve binder compliance.

C) Filling & compaction

• Layering: fill powder in 2–3 increments. After each fill, light pre-press ~10–20 MPa for 10–20 s to collapse voids.
• Main press: your 150 MPa is reasonable; many ceria powders tolerate 200–300 MPa if binder is present. If you increase pressure, increase dwell (60–120 s) rather than “spiking” pressure.
• Hold: at peak pressure, dwell 60–120 s to relax stress and reduce springback.

D) Unloading & ejection (where sticking/cracks usually occur)

• Decompression: ramp down slowly over 60–120 s (not a sudden release).
• Ejection: slow, steady ejection; support the pellet with a compliant pad (felt/PTFE) to cushion. Avoid sideways forces.
• Double-acting if possible: pressing with top & bottom punches (floating die) reduces density gradients and sticking. If your press is single-action, the other measures become even more important.

E) If problems persist

• Use a liner: ultra-thin PTFE/Kapton sleeve inside the die (change each press).
• Increase binder a touch: move PVA to ~2 wt% (don’t overdo; too much causes lamination).
• Check powder mass vs. die diameter: very thick pellets crack more—target thickness ≈ 1–3× diameter/10 (e.g., for 13 mm dia, keep 1.5–3 mm green thickness if feasible).
• Vacuum de-airing: gently vibrate or vacuum-tap filled die before the main press to remove trapped air.
• Tooling upgrade: consider TiN/DLC coating of stainless surfaces or switch to carbide.

F) Before sintering

• Binder burnout: slow heat-up (e.g., 0.5–1 °C/min to 250–300 °C, hold, then to 500–600 °C, hold) to remove PVA/PEG without cracking.
• Green handling: minimal handling; edge-support during transfer.

A minimal “try this first” recipe (often fixes it in one go)

If you share your die diameter, target pellet thickness, and exact binder/lubricant history, I can tune pressures, dwell times, and binder % precisely for Pr-doped ceria. But the BN-release + slow unload/eject + proper granulation/polish combo solves >90% of sticking/breakage cases.

Here’s a practical, lab-tested playbook to stop pellets from sticking to the die and cracking on ejection when cold-pressing 10 mol% Pr-doped ceria with a stainless-steel die.

Why it’s happening (so the fixes make sense)

• High die–wall friction / stainless galling → adhesion on ejection.
• Density gradients in single-action pressing → radial/lamination cracks.
• Elastic springback after unloading → tensile stress at the interface.
• Powder issues (hard agglomerates, poor granulation/binder) → weak, flaky green bodies.

Quick wins (often enough on their own)

Full protocol (step-by-step)

A) Powder conditioning (most important)

• Deagglomerate: Wet ball-mill Pr0.1Ce0.9O2–δ in EtOH/IPA with zirconia media (e.g., 200–400 rpm, 4–12 h). Dry at ~80 °C, then sieve 100–200 mesh.
• Binder & granulation: Dissolve PVA (1–2 wt% of powder) in warm water; mist onto tumbling powder to form free-flowing granules (100–300 μm); dry 60–80 °C and re-sieve.
• Internal lubricant (optional): 0.2–0.5 wt% zinc stearate or 0.3 wt% stearic acid blended uniformly. (Skip if you rely on BN; avoid MoS₂/graphite for air sintering.)
• Moisture: Slight residual moisture helps—target ~0.2–0.5 wt%. Too dry → poor cohesion; too wet → sticking.

B) Die & punches

• Material: Stainless works, but WC-Co carbide or nitrided/tool-steel dies stick far less.
• Finish & geometry: Mirror-polish; add a small entry radius/chamfer both ends.
• Release coating: Light, even BN coat; let solvent flash off fully.
• Pre-warm die to 40–60 °C to reduce condensation and improve binder compliance.

C) Filling & pressing

• Layering: Fill in 2–3 increments. After each fill, pre-press ~10–20 MPa for 10–20 s (or gentle taps) to collapse voids.
• Main press: Your 150 MPa is fine; with binder you can use 150–250 MPa. More important than pressure is dwell 60–120 s at peak to relax stresses.
• Aspect ratio: Thick pellets are crack-prone. As a rule, keep green thickness ≲ 0.2–0.3 × diameter (e.g., for 13 mm die, ~2–4 mm is friendlier).

D) Unloading & ejection

• Decompress slowly: 60–120 s ramp down—avoid a “pressure snap.”
• Eject slowly & axially: Use the smoothest stroke you can; cushion landing with a soft pad (felt/PTFE) to prevent edge chipping.
• Double-acting if possible: A floating die or two-sided pressing reduces density gradients and die-wall stress.

E) If sticking/cracks persist

• Use the liner (PTFE/Kapton) every press—cheap and very effective.
• Slightly raise binder to ~2 wt% PVA (don’t exceed; too much binder causes lamination).
• Vacuum de-airing/vibration after filling to remove trapped air.
• Coat or upgrade tooling: TiN/DLC coating cuts friction; carbide dies are best-in-class.

F) Before sintering

• Binder burnout: Slow ramp (e.g., 0.5–1 °C/min to 250–300 °C, hold 30–60 min; then to 500–600 °C, hold) to remove organics without cracking.
• Handling: Support edges; minimize mechanical shocks to green pellets.

A minimal “try-this-first” recipe

Troubleshooting cues

• Shiny smears on bore / rough pellet skin → friction/galling → improve finish, BN, liner.
• Radial rings/planes in green pellet → density gradients → layer fill, longer dwell, slower unload, consider two-sided pressing.
• Edges chip on exit → ejection too fast or sharp land → add bore chamfer, soft pad.
• Pellet bows (“dish”) → springback mismatch → slower unload, thinner pellet, better granulation.

As mentioned by Ahmed, polishing and using internal lubricant may be the answer. If you are not interested with internal lubricant, heat the die with the pellet and slowly try to push to take out the pellet..

**** Please check whether the pellet is homogenous or the powder concentration at the edges is lower than that at the middle.