March 2014
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22 Reads
Objective: Low-temperature-degradation (LTD) in partially stabilized zirconia (PSZ) has been reported which results in property changes. LTD is known to begin at the surface and progress inward, producing possible increased surface roughness. The current study measured transformation of PSZ with differing grain sizes and the corresponding property changes due to artificial accelerated aging. Null hypothesis: the grain size of the PSZ will influence the amount of transformation, and more transformation will result in greater property degradations. Methods: Two groups of PSZ materials were provided from two manufacturers, with differing grain sizes (4 groups n=5). SEM images were used to determine grain sizes using line intercept technique. Artificial accelerated aging was accomplished using a MidMark M11 Ultraclave Automatic Sterilizer for 5 hours. A Siemens D500 XRD device with Cu-K-alpha radiation was used to measure tetragonal to monoclinic transformation (t→m). Surface roughness analysis was performed using Scantron Proscan 2000, a non-contact surface-measuring instrument. Nano-hardness and Modulus of Elasticity were measured using MTS Nano G200. Results: Grain sizes, monoclinic transformations, surface roughness, modulus, and nano-hardness values are indicated below for each group. Grain Size (μm) Aging Transformation(%Tm) Surface roughness (Ra) Modulus (GPa) Hardness (GPa) LK Group 1 0.224 (0.019) Before 0 0.204(0.054) 241.2(3.63) 15.9(0.61) After 0.39(0.46) 0.324(0.142) 267.7(2.82) 16.6(0.32) LK Group 2 0.239 (0.015) Before 0 0.328(0.089) 266.7(5.37) 16.6(0.50) After 2.54(0.61) 0.360(0.161) 270.8(4.61) 15.6(0.33) Lava Plus 0.274 (0.013) Before 0 0.156(0.051) 299.6(5.39) 17.0(0.32) After 4.03(0.54) 0.184(0.047) 269.4(12.9) 16.4(1.05) Lava 0.368 (0.035) Before 0 0.168(0.075) 285.1(5.34) 16.4(0.26) After 6.64(1.01) 0.220(0.082) 276.3(4.81) 16.5(0.42) Conclusions: Within the limits of this study, the monoclinic transformation decreases with smaller grains and the zirconia samples experienced a surface roughening upon aging. Furthermore, the modulus and hardness decreased after aging in all but one group. However, grain size did not appear to influence the amount of roughening.