Abstract—minor Problems Arising from Optimizations By
welding of fixed prostheses frameworks can be identified by macroscopic and microscopic visual inspection. The purpose of this study was to highlight the visible discontinuities present in the laser welds of dental Ni-Cr alloys. Ni-Cr base metal alloys designated for fixed prostheses manufacture were selected for the experiments. Using cast plates, preliminary tests were conducted by laser welding. Macroscopic visual inspection was done carefully to assess the defects of the welding rib. Electron microscopy images allowed visualization of small discontinuities, which escapes visual inspection. Making comparison to Ni-Cr alloys taken in the experiment and laser welded, after visual analysis, the best welds appear for Heraenium NA alloy.
Nd:YAG laser penetration into cast titanium and gold alloy with different surface preparations.
This study investigated the effect of surface preparation on the Nd:YAG laser penetration into cast titanium and gold alloy. Cast blocks of each metal were given four different surface preparations: (i) coloured with black marker; (ii) air-abraded with 50 microm Al2O3; (iii) ground with SiC points and (iv) polished with 1 microm Al2O3 (mirror-polished). Two blocks with each of the surface preparations were abutted and laser-welded at their interface using the voltages of 210-260 V in increments of 10 V. After the welded blocks were mechanically separated, the laser penetration was measured using computer graphics. Regardless of the surface preparation, an increase in voltage increased the laser penetration for both metals. The laser penetration into titanium prepared with black marker and air-abrasion was significantly deeper than into the titanium ground with SiC points and mirror-polished. Although there were no statistical differences in penetration among the surface preparations for the gold alloy, the penetration in the mirror-polished specimens was shallower than any of the other preparation methods at higher voltages of 240-260 V. The results obtained in this study suggested that broken metal frameworks with finished surfaces should be painted with black marker or air-abraded before laser welding.
A bifunctional Cr/Yb/Tm:Ca3Ga2Ge3O12 phosphor with near-infrared long-lasting phosphorescence and upconversion luminescence.
Currently, upconversion nanocrystals and long-lasting phosphorescent particles have attracted extensive research interest for their possible applications as bioimaging probes. However, there are few reports concerning the achievement of both upconversion luminescence of lanthanide ions and long-lasting phosphorescence of transition metal ions in a sole host so far. Herein, we demonstrate a novel calcium gallium germanium garnet (Ca3Ga2Ge3O12) host where lanthanide ions such as Tm(3+)/Yb(3+) and transition metal ions such as Cr(3+) can be easily incorporated through substituting the Ca(2+) and Ga(3+) respectively. This Cr/Yb/Tm:Ca3Ga2Ge3O12 phosphor exhibits both broadband near-infrared long-lasting phosphorescence of Cr(3+) with an afterglow time of more than 7000 s and near-infrared to near-infrared upconversion luminescence of Tm(3+). Impressively, it is evidenced that the addition of Yb(3+)/Tm(3+) into Cr:Ca3Ga2Ge3O12 not only results in Tm(3+) upconversion luminescence but also greatly increases Cr(3+) afterglow time. Based on excitation/emission, three-dimensional thermoluminescence, and time-resolved luminescence spectra, the related long-lasting phosphorescence and upconversion luminescent mechanisms are systematically discussed as well.