Surface behaviour and stability of strontium and cobalt doped-lanthanum chromite powders in water

In this paper, the surface behaviour and stability in water of a powder with the composition La0.8Sr0.2Cr0.92Co0.08O3 prepared by combustion synthesis were studied. The isoelectric point of as-prepared suspensions occurs at pH near 8, while the maximum zeta potentials of 40 to 50 mV are reached at pH 3, but suspensions are not stable as the pH tends to move towards the isoelectric point. Solubility of ions occurs at acidic pH, although chromium and strontium are detected at basic pH, also. If the pH of the suspensions is periodically readjusted, the highest solubility is reached at very acidic conditions and only chromium is detected at basic pH. The effect of 1 wt.% of an anionic polyelectrolyte (ammonium polyacrylate, PAA) on suspension stability shifted down the isoelectric point to pH 6 and very high zeta potentials (> |− 50| mV) were attained at pH 9–10, where the moderate pH assures that the solubility is low.