ISSN:
1551-2916
Quelle:
Blackwell Publishing Journal Backfiles 1879-2005
Thema:
Maschinenbau
,
Physik
Notizen:
The interactions between added boric oxide (B2O3) and organic additives, and their effects on the colloidal stability of aqueous BaTiO3 suspensions have been investigated. The initially Newtonian or pseudoplastic aqueous BaTiO3 suspension with poly(vinyl alcohol) (PVA) becomes dilatant, and its viscosity also increases dramatically when a critical amount of B2O3, 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 BaTiO3 suspension. The dilatancy and viscosity of the aqueous BaTiO3 suspension with PVA and B2O3 increase significantly when a dispersant of ammonium salt of poly(acrylic acid) (PAA-NH4) is present. The ionization of B2O3 is enhanced by the basicity of dissociated PAA−, promoting the formation of PVA-B(OH)4− gel-type structure in the aqueous BaTiO3 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 BaTiO3 suspensions with PVA, B2O3, and PAA-NH4 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 BaTiO3 suspensions. A stability map is constructed to describe the amount of EG required to obtain colloidally stable aqueous BaTiO3 powder suspensions with PVA, PAA-NH4, and B2O3.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1111/j.1151-2916.2002.tb00294.x
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