Unusually tight aggregation in detonation nanodiamond: Identification and disintegration

A remarkable observation that detonation of oxygen-deficient explosives in an inert medium produces ultra-fine diamond particles having diameters of 4-5 nm was made four decades ago, but this novel form of diamond has never been isolated in pure form thereafter. The reason for the difficulty was that the core aggregates having a diameter range of 100-200 nm are extremely tight and could not be broken up by any known method of de-aggregation. After a number of futile attempts, we were able to obtain primary particles by using the recently emerging technique of stirred-media milling with micron-sized ceramic beads. The milled aqueous slurry of nanodiamond gave a stable, thick and dark-coloured colloidal solution. After light sonication, dynamic light scattering measurements gave a sharp distribution in the single-digit nano-range, and HRTEM indicated separate particles having diameters of 4-5 nm, which agreed with the X-ray value of 4.4 nm for the primary particles. A model is presented for the core aggregates, which resembles the well-known grape-shaped ‘aggregate structure’ of the hardest type of carbon black.