PubMed · 3331764
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J Wirz, F Schmidli. 1987. [Prosthesis framework/discoloration].. https://pubmed.ncbi.nlm.nih.gov/3331764/
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OBJECTIVES: Previous investigations in the binary system Au-Ti have shown that a Au based alloy with 1.7 wt% Ti reveals properties, which are appropriate to dental applications. Aim of this investigation was to refine the coarse grained dendritic microstructure of the alloy. Derived from experience with traditional high gold alloys and based on theoretical considerations, Ir was chosen as potential grain refiner and its influence on grain size, hardness, and thermal distortion was investigated. METHOD: Seven different Au-Ti alloys with Ir contents of 0-0.5 wt% were prepared in an arc furnace and test pieces cast by the dental casting technique. Microstructures of the alloys were documented by light microscopy. Grain size was assessed by a comparison procedure, hardness was measured by the indentation test, and thermal distortion by a three point bending test in a modified dilatometer. RESULTS: It revealed that Ir has a grain refining effect on the alloy with smallest grain sizes at a concentration of at least 0.3 wt%. It seems that the alloy with 0.5 wt% Ir shows slight grain growth during firing. Little homogenization was observed after firing. The influence of Ir on hardness was negligible. Thermal distortion is minimized with a concentration of 0.1 wt% Ir. In order to profit by the high thermal distortion resistance, the alloy Au(98.2)Ti(1.7)Ir(0.1) (wt) was chosen as definite composition, although 0.1 wt% Ir does not satisfactorily refine the alloy. SIGNIFICANCE: The alloy Au(98.2)Ti(1.7)Ir(0.1) (wt) revealed properties appropriate for the crown and bridge technique.
The corrosion resistance of commercially pure (CP) titanium in 1% NaCl + 0 approximately 1% NaF solution (pH = 6) under different elastic tensile strains was investigated by using electrochemical impedance spectroscopy (EIS) measurement technique. The polarization resistance (Rp), which is inversely proportional to the corrosion rate, of CP titanium in the test solution was obtained from the EIS data. Different elastic tensile strains, namely 0%, 1%, 2%, and 4%, were applied on the test specimens by using a tensile test machine during the corrosion tests. Corrosion morphology was characterized by using a scanning electron microscope. Surface chemical analyses were performed by using energy dispersive spectroscopy and X-ray photoelectron spectroscopy. The results showed that the NaF concentration and the elastic tensile strain had a statistically significant influence on the Rp (P<0.001). The Rp decreased on increasing the NaF concentration and the elastic tensile strain. When the NaF concentration was lower than 0.10%, the Rp value (> 3.4 x 10(5) omega cm2) was mainly ascribed to the formation of a protective titanium dioxide (TiO2) on the metal surface, regardless of the elastic tensile strain applied. However, when the NaF concentration was higher than 0.1%, the protectiveness of TiO2 was destroyed by fluoride ions, leading to severe corrosion of CP titanium.
Focus of the study is to evaluate the effect of dispersant particle size on the structure and various properties of spherical matrix, irregular dispersant admixed type Pd amalgams. The results indicate that amalgams prepared from smaller dispersant particles have a shorter setting time (faster amalgamation reaction), smaller setting expansion, higher eta' content and lower early stage gamma2 content. Smaller dispersant particles also lead to a slightly higher compressive strength, lower creep value, more cathodic corrosion potential and less early stage mercury vapor release. The particle size effect on corrosion current density and chemical composition of gamma1 phase in aged amalgam is less significant.