Use of impedance spectroscopy in the study of the effect of Cr concentration on the electrical properties of SnO2-based ceramics

This paper reports a study of influence of Cr concentration on the electrical properties and microstructure of SnO2-based powders doped with Mn and Nb, prepared by an organic route (Pechini method). All the samples were compacted into discs and sintered at 1300 degrees C for 3h, resulting in ceramics with relative density varying between 78% and 98%. The powders were characterized by X-ray diffraction analysis. Impedance spectroscopy characterization indicated that the conductivity decreases as Cr concentration increases, probably due to Cr segregation at grain boundaries, which reduces grain size, increasing the number of resistive boundaries.

Study of potassium additive on the phase formation and ferroelectric properties of 0.9PMN-0.1PT ceramics

A recent and innovative method to include Ti into the columbite precursor has permitted to synthesize 0.9PMN-0.1PT powders with high homogeneity. The present work describes this methodology, named modified columbite method, showing that the reaction between MN(T)and PbO at 800 degrees C for 2 h results in perovskite single-phase. The crystal structure alterations in the columbite and perovskite phases obtained by this methodology and the effects of potassium doping were investigated by the Rietveld method. Changes in the powder morphology, density and weight loss during the sintering process were also studied. Conclusively, potassium does not affect significantly the perovskite amount, but reduces the particle and grain sizes. This dopant also changes the relaxor behavior of 0.9PMN-0.1 PT ceramic, reducing the dielectric loss and enhancing the diffuseness of the phase transition. (C) 2005 Published by Elsevier Ltd and Techna Gronp S.r.l.

Microstructural evolution during sintering of CoO doped SnO2 ceramics

Addition of 0.5 mol% of CoO into SnO2 promotes densification of this oxide to 99% of the theoretical density during sintering. TEM in this system reveals that after sintering at 1210 degrees C a secondary phase of Co2SnO4 is precipitated at the SnO2 grain boundaries during cooling. This phase is formed by diffusion of Co ions from the bulk to the grain boundary during sintering leaving needle-like defects at the grain bulk. The high resolution TEM micrograph of this system sintered at 1210 degrees C and 1400 degrees C showed an amorphous grain boundary region low in cobalt, indicating that the Co2SnO4 phase is precipitated from this region. (C) 1999 Elsevier B.V. Limited and Techna S.r.l. All rights reserved.

Influence of age on the behavior of dental pulp of dog teeth after capping with an adhesive system or calcium hydroxide

This study evaluated histomorphologically the influence of chronological age of the dog on the dental pulp-healing process after capping with the All Bond 2 system or with calcium hydroxide paste. The animals were divided according to age into young and adult groups. Class 5-type cavities were prepared, and the pulp was submitted to an exposure of a diameter of 0.5 mm. The pulp of the teeth was then protected with the adhesive system or with a calcium hydroxide paste. Sixty days after treatment, the results obtained with the adhesive system in the young group were significantly better than those in the adult group. With calcium hydroxide, the results were similar for both groups. The pulp treated with calcium hydroxide exhibited a complete hard tissue bridge and a pulp without inflammatory reaction, a fact not observed when the adhesive system was used. In conclusion, the chronological age of the pulp influenced the comparative results only for the adhesive system (P = 0.1), and the total results were better with calcium hydroxide than with the All Bond 2 system (P = 0.01).