The main objective of this study was to measure the fracture toughness of the human teeth enamel using the microindentation technique and to compare the results calculated from the equations developed for Palmqvist and radial-median cracks. Vickers microhardness measurements of dental ceramic (alumina) and human teeth were performed using indentation fracture method. The fracture toughness of enamel was calculated using different equations reported in the literature. Vickers microhardness of the sintered alumina specimen (98.8% theoretical density) was measured to be 14.92 GPa under 9.8N indentation load. Three equations based on the radial-median cracks were found to be applicable for the fracture toughness determination of the enamel. Results show that indentation fracture method is adequate to measure microhardness and fracture toughness of dental materials. However the calculation of fracture toughness depended on the nature of the cracks and also on the location of the indentation. Therefore, it is necessary to identify the crack profile and to select the appropriate equation for accurate fracture toughness values.

This paper presents the results concerning the adsorption mechanism of polyacrylic acid (PAA) and polyacrylic acid/polyethylene oxide (PAA/PEO) comb polymer onto lead magnesium niobate (PMN) powders. In the study adsorption behavior of PAA and PAA/PEO onto PMN surface were determined in aqueous solutions and the influence of pH and ionic strength was investigated. Results showed that adsorption of PAA or PAA/PEO increased with decreasing pH of the suspensions. The increase in the ionic strength or the presence of divalent cations caused an increase in the adsorption of both polyelectrolytes. It was observed that the adsorption reaches a maximum when PAA is fully complexed in solution. On the other hand, the increase in the adsorption of PAA/PEO onto PMN in the presence of monovalent or divalent salt was attributed to the decrease in the electrostatic forces rather than complex formation with the divalent metal ions in solution. Turbidity measurements showed that there is no complex formation between the divalent metal ions and PAA/PEO comb polymers due to shielding effect of the PEO teeth.

Lead magnesium niobate (PMN) is an important relaxor ferroelectric material commonly employed in multilayer capacitor and actuator manufacturing owing to its high dielectric constant and superior electrostrictive properties. However, stability of this material in water is not very well known and there is need for a detailed investigation. In this research, solubility of lead magnesium niobate powders in water was determined as a function of solids concentration. The obtained results showed that the amount of cation leaching from the PMN surface depends on the pH value of the suspension and the solids concentration. The Pb 2+ and Mg 2+ ion dissolution was very high especially in the acidic pH range. Nevertheless, neither the dissolution mechanism nor the effects of dissolved ions on the stability were the same for those ions. The study provides new aspects on the solubility of perovskite materials which possess more than one soluble cation in their structure. #

The effect of calcium hydroxide addition on the casting performance of ceramic slips for sanitary ware was studied. Powder composed of feldspar (24 wt.%), quartz (24 wt.%), kaolin (35 wt.%) and ball clay (17 wt.%) was mixed with water to contain 65 wt.% of solids (specific density 1800 g/l). Either Ca(OH) 2 or Na 2 CO 3 was added at concentrations ranging between 0.060 and 0.085 wt.% and the slurries were dispersed by the optimum addition of sodium silicate.Calcium hydroxide in presence of sodium silicate improved the casting behavior of the slips, lowering the viscosity, and water absorption, increasing bending strength and cake thickness, as compared to the addition of sodium carbonate. D

The intermolecular complexation of non‐ionic polymers with weak acids having chemically complementary structures is an important approach to modify the viscosity of polymer solutions. In this study intermolecular complexation of hydroxypropyl methyl cellulose (HPMC) with polyacrylic acid (PAA) in an aqueous medium was studied. The study focuses on the factors affecting the complexation and rheological behavior of the HPMC/PAA system including the stoichiometric ratio of the two polymers, the molecular weight of the PAA, and the pH and ionic strength of the medium. Results showed that interpolymer complexation occurred between HPMC and PAA at low pH. It was attributed to hydrogen bonding between the COOH group of the PAA and the OH group of the HPMC. Under basic conditions (above the critical pH) the viscosity of the interpolymer complex increased accompanied by a transition from a compact interpolymer complexation structure to an extended conformation of interpolymer associates. Introduction of monovalent and multivalent salts (at > pHcritical) decreased the viscosity of the HPMC/PAA interpolymer associates and favored the formation of interpolymer complexes between the two polymers. Copyright © 2012 Society of Chemical Industry