Metallurgical pathways of lead leaching from brass

Leaded (Pb) brass components used in water pipeworks are prone to lead leaching following soldering or brazing during installation. Synchrotron radiation X-ray imaging shows that in the initial state of potable-water grade brass samples, Pb exists mainly as isolated or linked-together particles from sub-micron to several microns large. On heating to the usual soldering temperature of similar to 200 degrees C, the Pb contents surface rapidly via diffusion pathways involving an interpenetrating Pb-brass structure with orientation relationship (111(-))(a-brass)//(220)(Pb); [011](a-brass)//[(-)113](Pb). On heating to the usual brazing temperature of 700 degrees C, the Pb particles melt and expand in volume, with the Pb content forced into the brass lattice preferentially along {101}(a-brass) planes, forming Pb phase of low sphericity or even large sheets. On immersion in water, the surfaced Pb particles are oxidized to form PbO needles along the normal direction of {(2) over bar(2) over bar}(PbO) planes, which are then easily washed away to cause Pb leaching.