Gas atomization processing of tin and silicon modified lanthum-nickel for nickel-metal hydride battery applications

Numerous researchers have studied the relevant material properties of so-called AB₅ alloys for battery applications using conventional cast and crush alloy techniques. The previous works nearly ignored the potential for alternative direct powder production methods, like high pressure gas atomization (HPGA) that could reduce manufacturing cost of nickel-metal hydride powder.; This work examined the relationship between gas atomization processes, powder particle solidification phases, and hydrogen absorption properties of ultra fine (<25 μm) atomized powders with high surface area for enhanced battery performance. Concurrently, development of a gas atomization nozzle that is more efficient than all current designs is needed to increase the yield of ultrafine AB₅ alloy powder for further processing advantage.; Miniature convergent-divergent jets based on rocket technology were used to design two new atomization nozzles, HPGA-II and HPGA-III. The HPGA-II nozzle was demonstrated to be more efficient in producing fine powders at half the operating pressures of the existing Ames HPGA (HPGA-I) nozzle that operated, at 7.57 MPa. A design concept advanced in this dissertation enabled the design of the HPGA-III that was 16.8% (comparing surface area) more efficient than HPGA-II. HPGA-III operated at 3.13 MPa produced a 40 wt.% yield of <25 μm powders of 316L stainless steel. This nozzle was demonstrated to produce a high yield of ultrafine powders that are essential for development of a direct production process for AB₅ alloys for powders for battery applications.; Rapid solidification by gas atomization of LaNi_4.6Si _0.4 and LaNi_4.85Sn_0.15, LaNi_4.75Sn _0.25 and LaNi_5.5Sn_0.3 alloys was studied. Small atomized particles (<25 μm) were resilient to hydrogen induced fracture in gas-phase hydrogen cycling. Rapid annealing of the gasatomized AB ₅ alloys at 900°C for 5 minutes was sufficient to fully remove quenched-in nonequilibrium substitution-rich phases La-Ni-Si and La-Ni-Sn alloys. During annealing, preferential diffusion paths for Sn were observed on 002 and 202 planes using XRD. The activation enthalpy and interdiffusion coefficient for tin diffusing in La(Ni,Sn)₅ intermetallic were determined to be 152.24 KJ.mole-1 and 1.975 (10-6) cm 2. sec-1, respectively, using a simple isotropic diffusion model.; These ultrafine powders benefited from the rapid solidification process by having refined solute segregation in the microstructure of the gas atomized powders which enabled a rapid anneal treatment of the powders.