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Nanostructured apatites grown by laser floating zone
摘要： Apatites (AP) ceramics are important due to their application in the orthopaedics field as bioceramic material. Several processes to produce apatites such as oxyapatite (OAP) and hydroxyapatite (HA) materials are used to apply as a temporary substitute for human bone. In the present work, AP powders were prepared by high-energy ball milling and then by laser floating zone (LFZ) technique to transform into a dense cylinder (fibre). The effect of LFZ processing conditions was assessed by structural and electric characterization. Fibres present strong densification and a uniform polycrystalline microstructure, which could favour the use for natural bone treatments and as bio-sensors. However, further work must be assessed to optimize laser processing conditions.
关键词： Bioceramic,Apatites,Laser floating zone,Bio-sensors,Bone treatment,Hydroxyapatite,Oxyapatite
更新于2025-09-23 15:21:01
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Intense red emission on dilute Mn-doped CaYAlO4-based ceramics obtained by laser floating zone
摘要： The laser floating zone (LFZ) technique was used to produce polycrystalline fibers composed by P21/c monoclinic Y4Al2O9 (YAM) and P?421m tetragonal CaYAl3O7 (CYAM) phases embedded into I4/mmm tetragonal CaYAlO4 matrix. The scanning electron microscopy and X-ray diffraction patterns put in evidence the strong effect of growth rate on the microstructural and phases’ evolution. Besides the microstructural and structural analysis, complementary optical techniques as photoluminescence (PL), PL excitation (PLE), and lifetime measurements were used to characterize the produced fibers. The nonintentionally doped fibers were shown to exhibit an intense deep red emission likely due to Mn4+ trace impurities. From the PLE measurements, average crystal field strength was estimated with Dq/B ~ 2.94. Temperature-dependent PL measurements revealed that the red luminescence is due to the overlap of transitions from the almost electronic degenerate 2E and 4T2 excited states to the 4A2 ground state. The emission from the two excited states arises due to the breakdown of the adiabatic approximation. The overall luminescence intensity of the red emission was found to decrease from 11 K to RT, and the internal quantum efficiency, estimated from the ratio of the integrated luminescence at high and low temperatures, was found to be 60%. Time-resolved spectroscopy indicates a single decay time of ca. 2.0 ms at room temperature, corresponding to the spin and parity forbidden 2E → 4A2 transition.
关键词： Laser floating zone,Crystal field strength,Polycrystalline fibers,Mn4+ trace impurities,Red emission
更新于2025-09-16 10:30:52
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Elusive super-hard B6C accessible through the laser-floating zone method
摘要： Boron carbide is among the most promising ceramic materials nowadays: their mechanical properties are outstanding, and they open potential critical applications in near future. Since sinterability is the most critical drawback to this goal, innovative and competitive sintering procedures are attractive research topics in the science and technology of this carbide. This work reports the pioneer use of the laser-floating zone technique with this carbide. Crystallographic, microstructural and mechanical characterization of the so-prepared samples is carefully analysed. One unexpected output is the fabrication of a B6C composite when critical conditions of growth rate are adopted. Since this is one of the hardest materials in Nature and it is achievable only under extremely high pressures and temperatures in hot-pressing, the use of this technique offers a promising alternative for the fabrication. Hardness and elastic modulus of this material reached to 52 GPa and 600 GPa respectively, which is close to theoretical predictions reported in literature.
关键词： mechanical properties,microstructure,superhard materials,laser-floating zone technique,Boron carbide
更新于2025-09-12 10:27:22