| Objective: To study the effect of recasting on electrochemical corrosion properties, ion release, weight loss, surface roughness, surface free energy of a Nickel-Chromium (Ni-Cr) ceramic alloy.Methods: (1) Preparations of casting materials: The Ni-Cr ceramic alloys recast for 1~4 times were available respectively after the Ni-Cr ceramic alloys provided by the manufacturer having been cast 1~4 times. Before being recast again, the Ni-Cr ceramic alloys recast should be dealt with sand blasting, water washing, aqua regia soaking, rinse, cutting, ultrasonic cleaning in distilled water and drying naturally in turn to be the recasting materials in the next time. (2) According to ISO 10271, cylindrical specimens were achieved by casting Ni-Cr ceramic alloys successively for 1~5 times, respectively, under the circumstance of vacuum compressive casting with argon. Then all the specimens were made into electrodes embedded with resin and polished using standard metallurgical procedures, and tested with the electrochemical workstation at the condition of Fusayama artificial saliva at 37 oC and different pH (5.4, 6.4 and 7.4). With scanning electron microscope, the surface characteristics of samples were examined before and after corrosion. (3) According to ISO 10271, rectangular immersing samples were made and polished by the same way. Each sample for immerse test and weight loss test was placed in a tube added corrosive liquid [0.1M NaCl, 1%C3H6O3 (pH=2.35)] and conserved for 7 days and 70 days at 37 oC. After corrosion, the solution of each specimen was tested by inductively coupled plasma atomic emission spectrometer (ICP-AES). And the weight of every specimen was tested before and after immersing. With scanning electron microscope, the surface characteristics of samples were examined before and after immersion test. (4) The samples used in immersion test were reused to produce rectangular samples (10mm×10mm×1.1mm) embedded by resin with one surface exposing. The surfaces tested of specimens were polished to the same roughness tested by surface rough-meter. The surface roughness and the surface free energy of exposing surface of samples, immersed for three months in artificial saliva at 37 oC whose pH is 6.8, were tested.Results: (1) There presented no statistical decrease in the electrochemical corrosion of the porcelain fused to the nickel-chromium ceramic alloys recast from 2 to 5 times comparing to one recast 1 time. Corrosion was obvious for all alloys after polarization test, with forming of corrosion pits most of which appeared at the interdendritic structure. But the differences were difficultly to find. (2) There presented no statistical increase in the ion release and weight loss of the nickel-chromium ceramic alloys recast from 2 to 5 times compare to alloys recast 1 time at the condition of immersing for 7 and 70 days, and the same to weight loss. Corrosion was obvious for all alloys after immerse test, but the differences were difficultly to find. (3) There presented no statistical differences in the surface roughness of the nickel-chromium ceramic alloys recast from 1 to 5 times. Comparatively with alloy recast from 1 time, the surface free energy of the samples of alloys recast 2 times has no statistical difference, but increase significantly for alloys recast 3 to 5 times.Conclusion: Under the circumstance of vacuum compressive casting with argon, there presented no statistical increase in the electrochemical corrosion, ion release immersing for 7 and 70 days, weight loss and the surface roughness and no difference for the surface free energy of alloys recast 2 times. The surface free energy of alloys recast from 3 to 5 times increase statistically. |
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