Agglomeration during wet milling of LAST (lead–antimony–silver–tellurium) powders

LAST (lead–antimony–silver–tellurium) compounds comprise a family of semiconducting materials with good thermoelectric properties. However, the as-cast form of LAST exhibits large grain size and hence low mechanical strength. Powder processing can produce a fine powder particle size that enhances fracture strength, however the powders tend to agglomerate if the individual powder diameters are less than a few microns across. Dry milling or wet milling (hexane additions of 0 cm3 and 10 cm3) produced hard agglomerates roughly 40 μm in diameter while wet milling with hexane additions of 25 cm3, 30 cm3 or 50 cm3 resulted in small, porous agglomerates roughly 20 μm in diameter. Thus, by adjusting the amount of milling liquid used while milling LAST powders, one can shift from hard to soft agglomerates, where the literature shows that soft agglomerates are less harmful to the final, sintered product. Also, in agreement with the results from the literature on other materials, wet milling of LAST powders produced smaller particle sizes but required longer times to reach the grindability limit.