Determination of the particle interactions, rheology and the surface roughness relationship for dental restorative ceramics

Abstract

The effect of inter-particle interactions on the slurry properties and the final surface roughness of the dental ceramic restoratives was investigated. A commercial dental ceramic powder, IPS Empress 2 veneer, was used as the raw material.The magnitudes of the particle-particle interactions were computed by the DLVO theory for the ceramic slurries of different electrolyte solutions (0.1 M, 0.25 M, 0.5 M, 0.75 M, 1 M NaCl and CaCl 2 ). As expected, the energies of particle-particle interactions were influenced significantly by the presence of electrolytes. These computations demonstrated that addition of electrolytes leads to a progressive depression of the repulsive double layer forces. The absence of these forces should inevitably lead to agglomeration caused by the ever-present van der Waals forces.The rheological measurements carried out using the slurries with same solution properties supported the findings of the DLVO computations. It was found that dental ceramic slurries showed a Newtonian behavior in the absence of electrolytes, which is indicative of little or no agglomeration in the slurry. On the other hand, the same slurries displayed a non-Newtonian, shear thinning behavior in the presence of electrolytes which can be attributed to agglomeration or gelation.Roughness of the ceramic surfaces produced from these slurries was studied by SEM analysis and profilometer measurements. Contact angle studies were also carried out on the same surfaces. It was observed that the surface became rougher initially with electrolyte addition to a maximum, most probably due to formation of isolated agglomerates due to a reduction of the repulsive double layer forces. After reaching a maximum, surface roughness decreased to a much lower value with further increase in electrolyte concentration. This was most probably caused by the formation of a relatively homogeneous, gel-like structure within the extensively agglomerated slurry due to a complete collapse of the double layer.

Rice-like hollow nano-CaCO 3 synthesis

“…As soon as the CO 2 bubbles were injected in the solution, rice-like CaCO 3 particles formed with an average particle size of about 250 nm. Not much aggregation was seen due to the stability effect of Ca(OH) 2 solution [29], where the zeta potential values were higher than þ30 mV [20]. As the crystallization progress, the particles was shown to grow slightly as their number increased due to newly formed nano-CaCO 3 particles.…”

“…The surface potential of the colloidal system is related to the magnitude of the zeta potential. Particles with zeta potentials more positive than þ30 mV or more negative than À 30 mV are considered stable [20]. The zeta potential values for the CaCO 3 have been reported in the literature sometimes positive, sometimes negative, and sometimes variable zeta potential values [13].…”

Numerical and experimental analysis of the sedimentation of spherical colloidal suspensions under centrifugal force

“…50 are indicated in the literature, for example, 0.7 × 10 20 J and 3.8 × 10 20 J. 30,51 As a result, the Hamaker constant used in this work was chosen instead on the basis of a qualitative analysis of the experimental silica suspensions. When silica was dispersed in 0.1M KCl, aggregation was observed within several minutes of preparing the suspension.…”

Stability of CaCO3 in Ca(OH)2 solution

“…Zeta potential is also the most effective parameter to calculate interaction energy between particles for the colloidal stability. Particles with zeta potentials more positive than + 30 mV or more negative than − 30 mV are considered stable (Kes, 2007). However, a neat consensus could not be arrived by the authors on the zeta potential for the CaCO 3 in the literature because sometimes positive, sometimes negative, and sometimes variable zeta potential values have been reported (Moulin and Roques, 2003).…”