Hydrogenation Properties of TiFe Doped with Zirconium
The goal of this study was to optimize the activation behaviour of hydrogen storage alloy TiFe. We found that the addition of a small amount of Zr in TiFe alloy greatly reduces the hydrogenation activation time. Two different procedural synthesis methods were applied: co-melt, where the TiFe was melted and afterward re-melted with the addition of Zr, and single-melt, where Ti, Fe and Zr were melted together in one single operation. The co-melted sample absorbed hydrogen at its maximum capacity in less than three hours without any pre-treatment. The single-melted alloy absorbed its maximum capacity in less than seven hours, also without pre-treatment. The reason for discrepancies between co-melt and single-melt alloys was found to be the different microstructure. The effect of air exposure was also investigated. We found that the air-exposed samples had the same maximum capacity as the argon protected samples but with a slightly longer incubation time, which is probably due to the presence of a dense surface oxide layer. Scanning electron microscopy revealed the presence of a rich Zr intergranular phase in the TiFe matrix, which is responsible for the enhanced hydrogenation properties of these Zr-doped TiFe alloys.
Hydrogen absorption and desorption kinetics of TiFe0.8Ni0.2H
Abstract The determination of kinetic reaction rates data must be carried out under strictly controlled heat and mass transfer conditions and related to a well defined reaction controlling mechanism. A number of functions of the reacted fraction, α, designated R(α), which are characteristic of various reaction mechanisms in the solid state have been presented and successfully applied by Hancock and Sharp [ J. Am. Ceram. Soc. 55 (2), 74 (1972)]. The integrated rate functions R(α) reflect the morphology and the geometry of the transforming phases. The functions R 1 (α) R SC (α) and R D (α) for the first order kinetics, phase boundary migration mechanism known as “shrinking core” and diffusion controlled processes, respectively, were shown to be linear in 1 t 0.5 , where t 0.5 is the time corresponding to α = 0.5. In the present investigation three suitable reaction controlling mechanisms were adapted and modified by introducing a hydrogen pressure dependence function F( P ). Isothermal rate measurement experiments for hydrogen absorption/desorption in the two-phase region TiFe 0.8 Ni 0.2 -TiFe 0.8 Ni 0.2 H in the temperature range 90–150 °C yield temperature-dependent rate constants. Pre-exponential factors and activation energies for the first order and the diffusion controlled reaction mechanisms were derived.
Failure analysis for poor solderability of Au surface of PCB
Nonwetting is one of the common problems and is always rejected in electronic assemblies. ENIG pads of a PCBA exhibited nonwetting after lead-free reflow soldering. With the aid of stereomicroscope, SEM&EDS and XRF, a series of analysis was performed. And after visual inspection, surface and cross section analysis, thickness measurement and solderability test, it can be inferred that oxidation of plating surface was the main reason for nonwetting, and corrosion in Ni plating caused an adverse impact on solderalibity.