Hydrogen Storage in Titanium-Magnesium-Nickel Mixtures
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Hydrogen Storage in Titanium-Magnesium-Nickel Mixtures Janice K. Lomness1,2, Michael D. Hampton1, and Lucille A. Giannuzzi2 Departments of 1Chemistry and 2Mechanical Materials and Aerospace Engineering, University of Central Florida, Orlando, FL 32816 ABSTRACT The hydrogen interaction properties of mechanically alloyed mixtures of Ti, Mg, and Ni have been shown to be strongly dependent on the time and energy of ball milling. Mixtures ball milled at a ball to powder ratio (by mass) of 20:1 were able to absorb 3-4 wt% hydrogen. Mixtures ball milled at a ball to powder ratio of 70:1 were able to absorb up to 11 wt% hydrogen. The dependence of hydrogen uptake on ball milling time and energy is shown to be related to the microstructural morphology of the ball milled powders. The original Mg powder particles were heavily deformed by the ball milling process and contained nano-sized inclusions of both Ti and Ni at the surface. The higher energy ball milled samples showed a more refined microstructure and a greater hydrogen capacity. In addition, there was an inverse relationship between the amount of hydrogen uptake and the size of inclusions at the surface of the particles. INTRODUCTION Many different elemental metals and intermetallic systems have been considered attractive hydrogen storage media because they react directly and reversibly with hydrogen to form metal hydrides [1-5]. Extensive research has been performed on the hydriding/dehydriding properties, surface properties, and the kinetics of these systems, however, very little work has been done to examine the relationship between the microstructure of these systems and the hydriding/dehydring properties. Earlier work from our laboratory showed hydriding properties [6] and the microstructure of ball milled Ti-Mg-Ni Mixtures [7]. In this paper we present a relationship between the microstructure of the ball milled materials to the hydrogen uptake properties. Differential scanning calorimetry (DSC), focused ion beam (FIB) instrumentation, scanning transmission electron microscopy ((S)TEM), and X-ray energy dispersive spectroscopy (XEDS) were utilized in this study. EXPERIMENTAL DETAILS The starting materials used in these investigations consisted of elemental crystalline powders of titanium (170 mesh, 99+%), magnesium (10+100 mesh, 99.8%), and nickel (100+200 mesh99.9%) purchased from Alfa Aesar. Hydrogen (ultra high purity grade), and argon ( high purity grade), were obtained from Air Products and were used without further purification. Mechanical alloying of the powder samples was performed using a modified Paul O. Abbey Inc. mill operating at 60 rev/min with a ceramic sample compartment and steel balls. The elemental powders were combined in the ratio of 53:47:20, Ti:Mg:Ni. The powders were mixed with the steel balls and sealed under an argon atmosphere to minimize oxygen contamination. Samples of the powdered mixture (~200 mg) were obtained for analysis at approximate 0 hr, 37 hr, 47 hr, 85 hr, and 115 hr intervals during the milling process. Any
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