Abstract
The interactions between added boric oxide (B 2 O 3 ) and organic additives, and their effects on the colloidal stability of aqueous BaTiO 3 suspensions have been investigated. The initially Newtonian or pseudoplastic aqueous BaTiO 3 suspension with poly(vinyl alcohol) (PVA) becomes dilatant, and its viscosity also increases dramatically when a critical amount of B 2 O 3 , 0.4 wt%, is added. This has been attributed to a chemical reaction between the dissociated borate ion (B(OH) 4 - ) and PVA, which form a gel-type structure in the aqueous BaTiO 3 suspension. The dilatancy and viscosity of the aqueous BaTiO 3 suspension with PVA and B 2 O 3 increase significantly when a dispersant of ammonium salt of poly(acrylic acid) (PAA-NH 4 ) is present. The ionization of B 2 O 3 is enhanced by the basicity of dissociated PAA - , promoting the formation of PVA-B(OH) 4 - gel-type structure in the aqueous BaTiO 3 suspensions. With added plasticizer of 1,2- (e.g., ethylene glycol (EG)) or 1,3-diol (e.g, 1,3-propanediol (PPDL)) molecular structure, both the dilatancy and viscosity of aqueous BaTiO 3 suspensions with PVA, B 2 O 3 , and PAA-NH 4 decrease dramatically. Stable compounds of diol-B(OH) 4 - are formed before the dissociated B(OH) 4 - reacts with PVA, reducing the degree of gelation of aqueous BaTiO 3 suspensions. A stability map is constructed to describe the amount of EG required to obtain colloidally stable aqueous BaTiO 3 powder suspensions with PVA, PAA-NH 4 , and B 2 O 3 .