| With the development of metallurgy technique,the use of mental materials in Stomotolgy become widespread and the basic materials in Stomotolgy.Because of the superior mechanical properties and excellent biocompatibility,some metal materils have been used in prosthetic,orthognathic,filling and plantation widely.Ni-Cr alloy and Au-Pt alloy are principal alloys which used to make PFM in prosthodontics.Au-Pt alloy is noble alloy.Ni-Cr alloy is inexpensive alloy.The corrosion of metal is everywhere.If the metal material in Stomotolgy were corroded,not only reduce its mechanical properties but also bring harm to body.So it is very important to understand the corrosion of metal.The corrosion which the metal was effected by environment dielectric are chemical corrosion and electrochemical corrosion generally.Electrochemical corrosion is corrosion damage phenomenon that the metal contacts with electrolyte to form primary cell.The corrosion in detal alloys is mainly electrochemical corrosion .Using electrochemical technique to measure the corrosion of metal is sensitive and fast.It is also used to supervise and control at the spot.So it is thought highly of the people in general.The Ecorr shows corrosion tendency,the polarization resistance shows corrosion rate,the potentiodynamic curve shows corrosion resistance.The potentiodynamic polarization technique(polarization curve)can obtain quantitative data(for example:open potential,rupture potential,passive range et al)fastly.It is a reliable method that evaluate the corrosion resistance of dental alloys in vitro.The aim of this study is inquiring the corrosion resistance of Ni-Cr,Ti-6Al-4V and Au-Pt alloys in artificial saliva with electrochemical technique and guiding clinic.First,Ni-Cr alloy,Ti-6Al-4Valloy and Au-Pt alloy were made specimens.Among of them,Ti-6A-4V and Au-Pt alloys are from board plates,Ni-Cr alloy specimens are from invensting and casting of dental,then cut off sprute, throw away investing materials of the surface, also blast sanding. All specimens are fraction of 10mm10mm1mm, 3 specimens in each group.The study surface of each specimen was polished to #1000 by silicon carbide abrasive paper. Before 24 hours of experiment, all specimens were cleaned by pure alcohol and washed by distilled water. They were blown dry to be used. Every specimen was link with a copper wire, the surface of study was 0.25cm2, the rest was sealed by nail oil. First, soak three sorts of alloys into artificial saliva so that the surface become stable. After 24 hours, measuring the Ecorr of the specimen until the potential fluctuates not more than 2mV. Taking it as initial scanning potential. Next, anodic potentiodynamic polarization curves of each group were measured by CHI660A electrochemical work station in artificial saliva (37C). Take saturation calomel electrode as auxiliary electrode. Scanning speed is 1mV/s, the last scanning potential is 2mV. By the control system of computer, taking a polarization curve from every alloy and superimposing to compare their shapes. Using SEM to observe surface changes of three alloys. The product of corrosion was analyzed by X-ray diffractometer. The Ecorr is important index which shows the corrosion tendency of metal. The more negative the Ecorr is the more corrosive the alloy is. The Ecorr of three alloys from positive to negative is Au-Pt, Ti-6Al-4V and Ni-Cr. This showed that the corrosion tendency of Au-Pt alloy is the least and that of Ni-Cr alloy is the most. The corrosion tendency of Ti-6Al-4V alloy is between of them. The potential in oral is not more than 600mV. From the polarization curves, we can see that the electric current density of Ti-6Al-4V and Au-Pt alloys are all close to zero below 600mV, but that of Ni-Cr alloy is 2mA/cm2. It is obvious that the corrosion resistance of Ni-Cr alloy is worse than that of Ti-6Al-4V alloy and Au-Pt alloys. Polarization curves showed that current rose with the potential rising. When potential was 0.4-0.5V the electric current of Ni-Cr alloy rising fastly. This...
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