High-pressure Synthesis Of Ni-Al-Fe And Er-Ni Intermetallics And Their Properties

Intermetallics have special organizational structure which make it heritage theadvantage of alloys and ceramics. As high-temperature structural materials, hydrogenstorage materials, permanent magnet materials and shape memory materials,intermetalics have been widely applied in modern industry. Intermetallics hightemperature structural materials have low density, excellent high temperaturemechanical properties and high performance in temperature corrosion. NiAl and otherintemetallics have been used in the aerospace, chemical engineering and etc.Intermetalics hydrogen storage materials is a latent solid hydrogen storage materialsalso attracted many researcher. Intermetallics hydrides are much safer than traditionalhydrogen storage methods and still maintain the high hydrogen storage density.Intermetallics hydrogen storage materials have broad application in new energydevice in future. Intermetallics fabricated in traditional methods, such as melting,reaction sinter and self-propagating high temperature, have a high porosity ratio dueto the volume shrinkage and the vaporization of low melting point metals. Though wecan obtain a high density product through powder metallurgy method, themanufacturing facilities is an obstacle in molding process. Means forpressure-assisted combustion synthesis has been reported in the past, and the denserintermetallics structural materials can be produced in this method. However, therepressure they used is not high enough to synthesize some function materials withtopology close-packed which allows us to seek the methods at higher pressure. The new instruments in State Key Laboratory of Inorganic Synthesis and PreparativeChemistry, Jilin University provide good conditions for the high pressure synthesisexperiment. In my dissertation, the experiments were finished mainly using theWalker multi-anvil and Quickpress3.0piston-cylinder high pressure high temperatureinstrument. The synthesis experiments were carried out at the range from0.5to5GPawith different reactant, and then characterization and properties were also referred inmy research.In this paper, a piston-cylinder high pressure high temperature instrument is used toprepare a series nickel-aluminum, iron-aluminum intermetallics under the pressure of0.5GPa and the temperature of700℃. The XRD spectra showed that the majorproducts were in B2structure. We also saw non-obvious porus from the SEM image.The density is more than98%theoretical density. We changed the ratio of startmaterials, the samples we synthesized were composed with B2and γ phase products.There is no report in existing literature. We believe that the reason is the applicationof pressure. The high pressure induce the denser γ phase product generated. Thecooling method, quenching treatment, make the γ phase product retain in our sample.Then we did isothermal oxidation experiment at1000℃in air with selected samples.At this condition, all samples showed good high temperature oxidation resistance. Theantioxidant property of these samples derived from the Al₂O₃layer in the surface.Usually the antioxidant property of high iron content sample is decrease due to theferrite which is easy to fall from the matri. However in our sample which compositionis AlNi_0.4Fe（0.6）, the hercynite was formed which is stable in high temperature and hasgood antioxidant ability.Another part of this paper is synthesis of Cubic Laves ErNi₂intermetallics andanalysis its structure. Under atmospheric pressure, Er-Ni at a stoichiometric ratio forma Er_1-xNi₂compound due to the departure of the radii ratio rEr/rNifrome the cubicLaves phase structure theoretical value. Through the high pressure high temperaturereaction, we prepared single phase ErNi₂intermetallics at the condition of4GPa,1300℃. The impact of temperature and pressure on the synthesis process were alsoargued. From the single crystal X-ray diffraction data, the structure was resolved. The ErNi₂belongs to the cubic Fd-3m space group, unit cell parameters a=0.71373（10）nm, Z=8. We also found a new single-crystal at the Er:Ni=1:2named Er₆₄Ni₁₂₈in mydissertation. It belongs to the cubic F-43m space group, unit cell parameters a=14.2325（6） nm, Z=1. The classic ReNi₂（Re=rare earth） intermetallics decrease theirsymmetry with the order Re vacancies in their unit cell, and the absence of the Reatoms extend the Re-Re bond length and release the elastic potential energy. Underhigh pressure, the Re atoms reoccupied the vacancies and form the cubic lavesstructure compound. In the Er₆₄Ni₁₂₈single crystal we found, the symmetry decreasedue to the deviation of the atoms. The nickel and erbium atoms depart from thenormal site, but the relative position of these atoms are maintain. The ErNi₂intermetallics hydrogen absorption performance was studied. After the preactivationtreatment, we use a gravimetric method measured the hydrogen absorbingperformance at room temperature. We draw the pressure–composition isotherms（PCI） curve according to the experimental results. We found in130KPa, the samplereached the saturation point. The ErNi₂intermetallic has a maximum hydrogenstorage capacity of approximately1.05w%. The test sample showed a low plateaupressure, which make a certain application potential in the future.