The equation for compaction is also known as which?

• A. Hixson Crowell
• B. Henderson Hasselbalch
• C. Young's
• D. Heckel's

Answer: (D)

During tablet formation, how a powder densifies under pressure is described by a specific empirical relation. The Heckel equation captures this densification by relating the natural log of the reciprocal of porosity (equivalently, ln[1/(1−D)], where D is the relative density after compression) to the applied pressure. This yields a straight line under many formulations, with the slope reflecting how easily the powder plastically deforms and rearranges as pressure increases, and the intercept linking to the initial porosity before compression. In short, Heckel’s equation provides a practical way to quantify powder plasticity and compressibility during compaction. The other options describe different phenomena: Hixson-Crowell concerns how dissolution changes as surface area changes, Henderson-Hasselbalch is about buffer pH, and Young’s addresses surface wettability via the contact angle.