Where does granulation collide?

In goldsmithing, granulation is a decorative technique in which minute spheres of gold, each formed by melting small snippets of metal so surface tension draws them into balls, are arranged on a metal ground and joined to it without visible solder. The bond is made by colloidal or diffusion soldering, in which a copper-salt flux reduces to a thin copper film that, on careful heating, fuses the grain to the ground just below the melting point of the gold. Wolters's 1981 The ancient craft of granulation in Gold Bulletin reviews how Etruscan and earlier smiths achieved this. The referent is an ornamental assembly of pre-made grains onto a surface, and it is a different thing from powder being built up into granules or from the mottled face of the Sun.[1]

Unit

The grains fused to a metal surface and the joins that hold them

Recovery means

Not applicable

Measured by

Examined by microscopy and metallography of the grain-to-ground join and the diffusion bond

In pharmaceutical processing, granulation is the opposite build-up: fine drug and excipient powders are agglomerated into larger, free-flowing granules, most often by wetting the powder with a binder liquid so particles stick, grow, and consolidate before drying. Iveson, Litster, Hapgood, and Ennis's 2001 review in Powder Technology frames the mechanics as competing rate processes of wetting and nucleation, consolidation and growth, and breakage. The referent is the enlargement of particles to improve flow, compressibility, and content uniformity for tableting, measured by granule size and density, and it shares only the word with a jeweller fusing grains or with convection on the Sun.[2]

Unit

The granule size distribution, porosity, and strength produced from a powder

Recovery means

Not applicable

Measured by

Tracked by granule size distribution, porosity, flowability, and binder content during the wetting and growth stages

In solar physics, granulation is the ever-shifting pattern of bright cells separated by darker lanes that covers the Sun's visible surface, the tops of convection cells in which hot plasma rises in the bright centres and cooler plasma sinks in the dark intergranular lanes. Nordlund, Stein, and Asplund's 2009 Solar surface convection in Living Reviews in Solar Physics sets out the radiation-hydrodynamic picture of how this convective pattern forms and evolves. The referent is a convective flow pattern, named only for its grain-like appearance, and it has nothing structurally in common with fused gold grains or agglomerated drug powder beyond the shared word.[3]

Unit

The size, lifetime, and flow speed of convective cells on the photosphere

Recovery means

Not applicable

Measured by

Observed by high-resolution imaging and spectroscopy giving cell size, lifetime, and up- and down-flow velocities