Surface hardening of Ti-Al-V superalloy spinal implant by using the boronization method.

BACKGROUND: We compared the raw Ti-Al-V super alloy transpedicular implant screws with boronized and surface-hardened transpedicular implant screws. OBJECTIVE: To improve patients' postoperative prognosis with the production of harder and less fragile screws. METHODS: Surface hardening was achieved by applying green-body encapsulation of the specimen with elemental boron paste which is sintered at elevated temperatures to ensure the boron-metal diffusion. Boron transported into the Ti-Al-V super alloy matrix gradually while suppressing aluminum and a homogeneously boronized surface with a thickness of ∼15 microns was obtained. The uniform external shell was enriched with TiB2, which is one of the hardest ceramics. The Ti-Al-V core material, where boron penetration diminishes, shows cohesive transition and ensures intact core-surface structure. RESULTS: Scanning electron microscope images confirmed a complete homogeneous, uniform and non-laminating surface formation. Energy-dispersive X-ray monitored the elemental structural mapping and proved the replacement of the aluminum sites on the surface with boron ending up the TiB2. The procedure was 8.6 fold improved the hardness and the mechanical resistance of the tools. CONCLUSIONS: Surface-hardened, boronized pedicular screws can positively affect the prognosis. In vivo studies are needed to prove the safety of use.

Defect-induced B4C electrodes for high energy density supercapacitor devices.

Boron carbide powders were synthesized by mechanically activated annealing process using anhydrous boron oxide (B2O3) and varying carbon (C) sources such as graphite and activated carbon: The precursors were mechanically activated for different times in a high energy ball mill and reacted in an induction furnace. According to the Raman analyses of the carbon sources, the I(D)/I(G) ratio increased from ~ 0.25 to ~ 0.99, as the carbon material changed from graphite to active carbon, indicating the highly defected and disordered structure of active carbon. Complementary advanced EPR analysis of defect centers in B4C revealed that the intrinsic defects play a major role in the electrochemical performance of the supercapacitor device once they have an electrode component made of bare B4C. Depending on the starting material and synthesis conditions the conductivity, energy, and power density, as well as capacity, can be controlled hence high-performance supercapacitor devices can be produced.

Defect structure in aliovalently-doped and isovalently-substituted PbTiO3 nano-powders.

The defect structure of Fe(3+)-, Cu(2+)-, Mn(4+)- and Gd(3+)-doped PbTiO(3) nano-powders has been studied by electron paramagnetic resonance (EPR) spectroscopy. Analogous to the situation for 'bulk' ferroelectrics, Fe(3+) and Cu(2+) act as acceptor-type functional centers that form defect complexes with charge-compensating oxygen vacancies. The corresponding defect dipoles are aligned along the direction of spontaneous polarization, P(S), and possess an additional defect polarization, P(D). Upon the transition to the nano-regime, the defect structure is modified such that orientations perpendicular to P(S), [Formula: see text] and [Formula: see text] also become realized. Moreover, the binding energy for the defect complexes is lowered such that instead 'free' Fe'(Ti) and V··(O)-centers are formed. As a consequence, the concentration of mobile V··(O) that enhances the ionic conductivity through drift diffusion is increased for the nano-powders. Finally, in the nano-regime the ferroelectric 'hardening' is expected to be considerably decreased as compared to the 'bulk' compounds. In contrast to the acceptor-type dopants, the donor-type Gd(3+) dopant is incorporated as an 'isolated' functional center, where charge compensation by means of lead vacancies is performed in distant coordination spheres.