| Summary: | 博士 === 國立中興大學 === 材料工程學研究所 === 88 === Three chapters about dental materials were investigated in this study.
1.Properties of investment for precision castings
The aim of this chapter was to investigate the properties of investment for precision castings. The results indicated that the thermal expansion of investment Gilvest Ti is small, but the setting expansion is large enough to compensate the shrinkage of titanium casting. Besides, its thermal expansion at T ³ 600 ℃ was constant and its heating-cooling cycle was almost reversible. These two results can also reduce the thermal shock and then avoid the cracking of investments.
2.Properties and structures of electrolytic ZrO2 coating on dental Co-Cr alloys
This study was conducted to increase the corrosion resistance and to decrease the metal ion release of dental cobalt-chromium alloys by electrolytic ZrO2 thin coatings. The microstructure of electrolytic zirconia coated films on Co-Cr substrates were also examined. The AAS’s results show that the ZrO2 coated Co-Cr alloys decrease the chromium ion level than that of uncoated Co-Cr alloy. According to the results of ESCA, the bonding energies of ZrO2 coating surface layer which changed with the annealing temperature from 400 oC, 500 oC to 600 oC are attributed to amorphous (a), tetragonal (t), and monoclinic (m) structure, respectively. The X-ray diffraction (XRD) of the coatings on the Co-Cr substrates annealed at 400, 500 and 600 oC revealed the major crystallization from m through t and then to m + t. However, the TEM observations clearly showed that the interface layer of the coatings was nanosize crystallites, first the formation of monoclinic and then with tetragonal ZrO2 structures. These different phase transformations are mainly due to different surface energy of ZrO2 coating in air, in bulk or on Co-Cr alloy.
3.Corrosion resistance of ZrO2 coating on cast titanium in fluoride containing solution.
Zirconia coatings were formed on pure titanium by electrolytic deposition. The aim of this chapter was to investigate the effect of electrolytic zirconia coating on the corrosion resistance of cast titanium in fluoride containing solution. The dynamic polarization curves indicated that titanium and ZrO2 coated specimen showed good resistance in artificial saliva and the latter is better. However, the corrosion resistance of uncoated and coated titanium was decreased with increasing the concentration of fluoride in artificial saliva. Also, the corrosion resistance of titanium and ZrO2 coated specimen was decreased seriously in high concentration of NaF and low pH value artificial saliva because HF was formed in acidic NaF solution.
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