Machinable Ti 3 SiC 2 /Hydroxyapatite Bioceramic Composites Prepared by Spark Plasma Sintering
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edge lengths of 150 nm ± 5 nm and nanospheres with diameters of 67 nm ± 9 nm. The researchers said that the ratio of cubes to spheres is close to the theoretical ratio (1:2) of the number of holes with octahedral and tetrahedral symmetry, respectively, in the face-centered cubic colloidal crystal template. Using transmission electron microscopy on a single nanocube, the mesopore symmetry was shown to be cubic, pore diameters were estimated at 2.4 nm, and the average unit cell length was determined to be 18.4 nm ± 0.8 nm. Ordered mesopores could not be observed in the nanospheres. The symmetry axis of the nanocubes coincided with the cubic mesopore arrays, suggesting to the researchers that the confinement by the colloidal crystal template influenced the arrangement of the surfactant micelles. Overall mesostructural ordering was verified with small-angle x-ray scattering but detailed information was obtained from nitrogen sorption measurements, which showed that the entire pore system is accessible to guest molecules, which, the researchers said, “lends itself to a wide range of applications involving host-guest interactions where guests are separated by predefined distances.” They said, “[T]he nanoparticle architecture has an advantage over larger mesostructures in that
guests are confined to a countable number of cages limited by the 3D volume of the nanoparticle.” STEVEN TROHALAKI
Machinable Ti3SiC2/Hydroxyapatite Bioceramic Composites Prepared by Spark Plasma Sintering Hydroxyapatite (HAp) is a well known biomaterial for its excellent biocompatibility and ability to bond chemically with host bones. However, the poor mechanical properties of HAp prevent its wide application for load-bearing implants. Re searchers at Tsinghua University in China have reported a Ti3SiC2/HAp composite with a significant improvement of bending strength and fracture toughness compared with those of monolithic HAp. As described in the October issue of the Journal of the American Ceramic Society (p. 3331; DOI: 10.1111/j.1551-2916.2007. 01882.x), S.L. Shi and W. Pan prepared Ti3SiC2/ (Ca10(PO4)6(OH)2) composites using spark plasma sintering. The mechanical properties of the fabricated Ti3SiC2/HAp were examined using the three-point bending test and the Vickers hardness test. The bending strength and fracture toughness of the composites were improved significantly with adding Ti3SiC2. With 50 vol% Ti3SiC2,
maximum bending strength and fracture toughness values were achieved with 250 MPa ± 10 MPa and 3.9 MPa⋅m1/2 ± 0.1 MPa⋅m1/2, respectively. The bending strength and fracture toughness were two to three times and two to five times higher than that of monolithic HAp. The researchers attribute the increase of bending strength to matrix strengthening. They also attribute the enhancement of fracture toughness to the synergistic effect of matrix strengthening and energyabsorbing mechanisms of individual grains of Ti3SiC2 platelets. To characterize the machinability of the composites, the specimen was tested using cemented carbide drills. No
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