Tomaž Kosmač

Short-range repulsive potential developed by the addition of Mg(II) ions to aqueous alumina slurries

Abstract The effect of magnesium acetate additions on the interparticle potential of diluted well-dispersed aqueous alumina suspensions, prepared with the Dolapix CE64 dispersant at inherent pH, and the rheological properties of these suspensions, have been studied. In order to destabilise these suspensions a 0.5 M aqueous magnesium acetate solution was added and the pH and viscosity changes were monitored. The neutralisation of the surface charge on the particles occurs because of the formation of coordinative bonds between magnesium ions and carboxylic groups of the dispersant molecules, which is reflected in the destabilisation of the suspension. A thin and rigid neutral layer on the surface of the particles is formed which prevents the close contact between particles. As a consequence, weak flocculation of the suspension takes place and the resulting short-range repulsive potential was confirmed with force measurements.

The Effect of Dental Grinding and Sandblasting on the Biaxial Flexural Strength and Weibull Modulus of Tetragonal Zirconia

The effects of dental grinding, sandblasting and aging on the biaxial flexural strength of Y-TZP ceramics containing 3 mol % yttria were evaluated. Denta l grinding at a high rotation speed lowers the mean strength and reliability, whereas sandblasting may provide a powerful tool for surface strengthening. The coarse-grained materials were l ess susceptible to grinding induced defects, presumably due to higher fracture toughness. During agi t 140 C for 24 hours, an about 100 μm thick layer has transformed to monoclinic on the surface of the standard-grade Y-TZP ceramics resulting in considerable strength degradation, where as th “corrosion resistant” materials exhibited a much higher resistance toward the low-temperature d egradation. Furthermore, preexisting monoclinic zirconia in the surface of the sandblasted YTZP hinders the propagation of the diffusion-controlled transformation during subsequent exposure to aqueous environments.

Destabilisation of an alkaline aqueous alumina suspension by the addition of magnesium acetate

Abstract Destabilisation of well-dispersed aqueous alumina suspensions prepared with the addition of an anionic dispersant at the inherent pH of alumina particles in water was achieved by the addition of an appropriate amount of magnesium acetate solution. The destabilisation occurred at a pH value higher than that of the IEP of alumina particles in distilled water. This may be due to either the adsorption of magnesium ions or dispersant molecules onto the surface of the alumina particles. To evaluate these two effects on the surface charge of alumina particles in aqueous slurries, the distribution of the different types of surface sites, with respect to the added magnesium acetate, was calculated. For these calculations, the multisite-complexation model for proton adsorption and the charge-distribution model for the adsorption of magnesium ions was used. According to our results, it is the adsorption of magnesium ions onto the surface of the particles that is responsible for the shift in the point of zero zeta-potential towards higher pH values.

Effect of Surface Treatments on Bonding Strength of Zirconia to Dental Cements

The aim of this study was to investigate the effect of surface treatments on bonding strength of two kinds of zirconia to two kinds of dental cements. After thermal cycling, the shear bonding strength of both zirconia with alumina coating increased in both cements. The shear bonding strength of both zirconia with sandblasting decrease in Fuji plus after thermal cycling (p<0.05). There was no significant difference between NANOZR and Y-TZP (p>0.05). The bonding strengths of NANOZR with the alumina coating were higher than those with sandblasting after thermal-cycling (p<0.05).