Characterization of electrolytic ZrO2 coating on Co-Cr-Mo implant alloys of hip prosthesis.

An electrolytic Zr(OH)4 gel has been coated on ASTM F-75 Co-Cr-Mo alloy specimens in 0.0625 M ZrO(NO3)2 solution with pH = 2.2 at a current density of 2 mA/cm2. After annealing at 623-973 K for 120 min in air, the ZrO2-coated specimen was evaluated by electrochemical polarization in Hank's solution, wear tests with UHMWPE (Ultra-high molecular-weight polyethylene) under a load stress of 50 MPa, scratch tests, surface morphology observations, and XRD analysis. The ZrO2-coated specimen annealed at 773 K for 120 min revealed a good adhesion of 610 MPa on Co-Cr-Mo substrate, a lower wear loss of UHMWPE and a higher protection potential than the uncoated specimen in Hank's solution. A monoclinic structure with (1 1 1) preferred orientation parallel to the sheet plane was detected at 623 K < or = T < or = 673 K and a tetragonal structure of ZrO2 was detected at T > or = 773 K. Then a monoclinic structure with random orientation and a tetragonal structure were mixed at T > or = 973 K.

Evaluation of metal ion release and corrosion resistance of ZrO2 thin coatings on the dental Co-Cr alloys.

OBJECTIVES: The aim of this study was to determine if electrolytic ZrO2 thin coatings increased the corrosion resistance and decreased the metal ion release of dental cobalt-chromium alloys. METHODS: Dental Co-Cr alloys were electrolytically deposited with ZrO2 ceramic coatings using a 0.0625 M ZrO(NO3)2 solution, at various potentials, for 500 s. The electrolytic ZrO2 gel-coated specimens were annealed at 723 K for 1 h in air. Scanning electron microscopy (SEM) was used to observe the morphology of the ZrO2 ceramic coatings on Co-Cr alloys. A dynamic polarization test was used to compare the corrosion resistance of the ZrO2 coated and uncoated Co-Cr alloys in artificial saliva. Metal ion concentrations were determined with graphite furnace atomic absorption spectroscopy (AAS). RESULTS: The SEM micrographs showed that the Co-Cr alloy can be coated with zirconia oxide at -0.7 V more homogeneously and more completely than at -1.5 V. The polarization curves indicated that the ZrO2 coating on Co-Cr alloys annealed at 723 K for 1 h in air exhibited better corrosion resistance in artificial saliva. The results of the AASs showed that the ZrO2-coated Co-Cr alloys decreased chromium ion release levels, as compared with the uncoated Co-Cr alloys. The scratch test indicated a good bond strength between the ZrO2 and Co-Cr alloy. SIGNIFICANCE: The electrolytically deposited ZrO2 coatings on Co-Cr alloys may improve the corrosion resistance and decrease the release of metal ions. It is suggested that the electrolytic ZrO2 coating method could have a widespread application in dentistry in the future.

Evaluation of different bonded investments for dental titanium casting.

The properties of several different investments were investigated including phosphate bonded, magnesia bonded, and alumina cement investments. Measurements included the setting expansion, thermal expansion, and compressive strength of investments, as well as the tensile strength, elongation, Vickers hardness (VHN) and surface roughness of titanium castings. For phosphate bonded investment, the setting expansion after being mixed with its own mixing solution was 2.10%, which was larger than the other investments; the thermal expansion was -0.25% at 200 degrees C, the compressive strength 14 and 5 MPa after heating. For titanium cast in phosphate bonded investment, the hardness on its top surface was 655 Hv, the tensile strength was 379 MPa, the elongation was 19.4%, and the surface roughness was 2.29 microm. Athough the thermal expansion of phosphate bonded investment is small, the setting expansion is large enough to compensate for the shrinkage of titanium castings. As its thermal expansion at T >/= 600 degrees C was constant and its heating-cooling cycle was almost reversible, these two properties can reduce the thermal shock and thus avoid cracking of the investment.

Evaluation of different bonded investments for dental titanium casting.

The properties of several different investments were investigated including phosphate bonded, magnesia bonded, and alumina cement investments. Measurements included the setting expansion, thermal expansion, and compressive strength of investments, as well as the tensile strength, elongation, Vickers hardness (VHN) and surface roughness of titanium castings. For phosphate bonded investment, the setting expansion after being mixed with its own mixing solution was 2.10%, which was larger than the other investments; the thermal expansion was -0.25% at 200 degrees C, the compressive strength 14 and 5 MPa after heating. For titanium cast in phosphate bonded investment, the hardness on its top surface was 655 Hv, the tensile strength was 379 MPa, the elongation was 19.4%, and the surface roughness was 2.29 microm. Although the thermal expansion of phosphate bonded investment is small, the setting expansion is large enough to compensate for the shrinkage of titanium castings. As its thermal expansion at T > or = 600 degrees C was constant and its heating-cooling cycle was almost reversible, these two properties can reduce the thermal shock and thus avoid cracking of the investment.

Nano-crystallization and surface analysis of electrolytic ZrO2 coatings on Co-Cr alloy.

Zirconia coatings were formed on Co-Cr substrates by electrolytic deposition. The microstructure of electrolytic zirconia-coated films on Co-Cr substrates was examined. According to the results of ESCA, the bonding energies of ZrO2 coating surface layer which changed with the annealing temperature from 400 degrees C, 500 degrees C to 600 degrees C 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 degrees C revealed the major crystallization from m through t and then to m+t. However, TEM observations clearly showed that the interface layer of the coatings were nanosize crystallites, first the formation of tetragonal and monoclinic ZrO2 structures. These different phase transformations are mainly due to the different surface energy of ZrO2 coating in air, in bulk or on Co-Cr alloy.

Electrolytic A12O3 coating on co-cr-mo implant alloys of hip prosthesis.

The ceramic films over metallic implant surfaces have the potential to improve implant performance with respect to implant fixation, wear, or corrosion. In this study, the electrolytic Al2O3 coatings on F-1537 Co-Cr-Mo alloy were conducted in an aqueous solution of Al(NO3)3. Through the cycle polarization test in Hank's solution, it was found that the corrosion potential and protection potential of the alumina-coated were higher than that of the uncoated, and the corrosion current density was lower. The phase transformation of A12O3 film on Co-Cr-Mo alloy annealed at 800 K revealed todlite (5Al2O3 . H2O) and thetaAl2O3 (113) preferred orientation for 20 min, and thetaAl2O3 (200) preferred orientation with eta phase for 80 min. Scanning electron microscopy/energy dispersive spectroscopy observations after the scratch tests showed that the adhesion of the alumina films on Co-Cr-Mo alloy can load a stress over the yield strength (450 MPa) of Co-Cr-Mo alloy. The wear loss of ultra-high molecular-weight polyethylene to the Al2O3-coated specimen was eight times less than that to the uncoated. It is concluded that such Al2O3-coated films on Co-Cr-Mo implant alloy exhibit excellent quality in corrosion, adhesion, and wear for the application of hip prosthesis.

Environmental and developmental regulation of the wound-induced cell wall protein WI12 in the halophyte ice plant.

A wounded gene WI12 was used as a marker to examine the interaction between biotic stress (wounding) and abiotic stress (high salt) in the facultative halophyte ice plant (Mesembryanthemum crystallinum). The deduced WI12 amino acid sequence has 68% similarity to WUN1, a known potato (Solanum tuberosum) wound-induced protein. Wounding, methyl jasmonate, and pathogen infection induced local WI12 expression. Upon wounding, the expression of WI12 reached a maximum level after 3 h in 4-week-old juvenile leaves, whereas the maximum expression was after 24 h in 8-week-old adult leaves. The temporal expression of WI12 in salt-stressed juvenile leaves was similar to that of adult leaves. The result suggests that a salt-induced switch from C3 to Crassulacean acid metabolism has a great influence on the ice plant's response to wounding. The expression of WI12 and the accumulation of WI12 protein were constitutively found in phloem and in wounded mesophyll cells. At the reproductive stage, WI12 was constitutively found in petals and styles, and developmentally regulated in the placenta and developing seeds. The histochemical analysis showed that the appearance of WI12 is controlled by both environmental and developmental factors. Immunogold labeling showed WI12 preferentially accumulates in the cell wall, suggesting its role in the reinforcement of cell wall composition after wounding and during plant development.