MAURINO Valter - Bando LR34/2004 - "Studio preliminare e sviluppo di soluzioni innovative di materiali d’attrito in ambito Automotive”

In this work we demonstrated that BaCO3 and NH3SO3 can be conveniently used as BaSO4 precursors. With BaCO3, BaSO4 is obtained treating the precursor with a sulfate-containing solution, owing to the lower solubility product constant of BaSO4 compared with BaCO3. With this procedure, BaSO4 particles with pseudo-cubic/prismatic morphology are obtained. In this case temperature and reaction time have little influence on morphology, which is mainly controlled by supersaturation, and therefore sulfate concentration. Sulfate counter ion is also affecting morphology, but its effect is less pronounced. The hydrolysis of NH3SO3 in the presence of soluble barium salts produces BaSO4 particles, and different kinds of morphology can be obtained, encompassing rounded and nearly spherical particles, prismatic and pseudo-cubic, irregular shapes with flat and well-developed facets, and even hopper crystals. In this synthesis, temperature and pH are playing a major role in controlling sulfamic acid hydrolysis and, therefore, supersaturation, with remarkable consequences on crystal nucleation and growth. Considering that BaSO4 finds applications in many sectors and for different purposes, the variety of particle size and shape here reported can potentially improve the performance of the materials in which BaSO4 particles are employed