The effect of Sintering Times on Density of Nano zirconia

Objective to investigate the effect of different final sintering times on density of Nano zirconia
Material s and methods eighty four cubic zirconia samples were fabricated from uniaxial compaction of Nano zirconia by laboratory manual hydraulic press at 120MPa.The sintered specimens were randomly divided into four groups according to final sintering time (N=84,n =21per group),the sintered temperature and rate were 1450℃ and 10℃/min fixed for the four cycles . The Four final holding times of sintering were (90,120, 150, and 180) min. Density and apparent porosity percent were measured by Archimedes method according to ISO18754. The linear shrinkage was calculated by electronic varnia caliper .The microstructure and grain size was investigation by field emission scanning electron microscope. Data were analyzed by one –way ANOVA with (p<0.05).
Results the highest apparent and bulk density observed were (6.0846±0.017 &5.3678± 0.0089)g/cm3 respectively for nan zirconia group sintered at 180 minutes final holding time, while the lowest were (6.0449±0.016 &5.1232± 0.00155) g/cm3 for zirconia group sintered at 90minute . The greatest apparent porosity was (2.2169±0.077) percent for Nano scale zirconia sintered at 90 min ,whereas the lowest was(1.7654±0.0331)percent for zirconia sintered at 180 min .The greatest linear shrinkage was (18.524±0.01265)mm for 180 min sintering ,the lowest was(17.5091)mm for 90min .FESEM micrographs showed the greatest grain size was(0.44)μm for 180min sintering time and (0.33)μm for 90min,
Conclusion the result of this study showed prolonged final sintering time associated with increased density, linear shrinkage, increase grain size and reduced porosity percent manifestoed with homogenous dense microstructure