Stability Of Superfine Alumina In Organic Solvent

Alumina ceramic is widely used in electronic industry as the most important material for fabricating sheets because of its superior properties, such as high hardness, isolating performance and strength etc.. Among various processing, tape casting is favored for fabricating laminated ceramic sheets. For tape casting, dispersion is a key factor to the quality of sheets. The quality and sintering behavior of green bodies and the final properties of sintered films are influenced by the homogengity and stability of powder in slurry. At present, organic solvents are widely used in tape casting processing. Thus the stability of the system with organic solvent is very important. Usually, the addition of dispersants is needed in order to assure the stability of the slurry.The rheological behaviors of superfineα－Alumina slurries in an azeotropic mixture of methylehyketone (MEK,66%) and ethanol (EtOH,34%) were determined and used to evaluate the stabilities. The effect of dispersants on stabilities of slurries was studied. Influences of dispersants on the stabilities of the slurries were studied by observing the rheological behaviors of the slurries at various dispersant concentrations. The experiments showed that stabilities of slurries could be achieved by adding glyceryl trioleate (GTO), castor oil (CTO) and S80. However, there were distinctions between the effects of these three dispersants on stabilities of slurries. Effect of GTO and CTO on flow properties of slurries had an advantage over that of S80.In the shear rate range of 0~300s-1, flow curves of slurries dispersed with GTO, CTO and their mixtures followed Casson model very well. At a given shear rate, the shear stress, viscosity and Casson yieldstress of slurries dispersed with GTO and CTO decreased with the increase of dispersant concentration. These showed that stabilities of the slurries increased with the increase of dispersant concentration. In the system of this experiment, the slurries were fully stabilized as concentration of GTO was greater than 2.5%. For the system with CTO, the slurries had lower viscosity at a concentration of 3%. As dispersant concentration was lower 2.7%, viscosities of slurries dispersed with GTO were lower than that of the slurry dispersed by CTO. But when dispersant concentration exceeded 2.7%, the results were on thecontrary.The combining effects of GTO and CTO on stabilities of slurries were studied based on the results of mono-dispersant obtained above. Mixtures of GTO and CTO at various ratios were added to the slurries, and the stabilities of the slurries were compared. The experiments showed that when the proportion of GTO in the mixture is between 2/3 and 5/6, the rheological behavior of slurries dispersed with mixture of GTO and CTO, was obviously superior to that of slurries dispersed with GTO and CTO separately.Slurries with various dispersants for tape casting were prepared, and they were cast on a surface through the action of a blade that levels the slurries. The results showed that quality of green bodies would be influenced by dispersants even if other conditions were all the same. Green bodies that manufactured from slurries with mixture of GTO(1.25%) and CTO(0.25%) were even, sleek and flexible. But, those fabricated from slurry with CTO(1.5%) badly cracked after drying.