Porous Of Ni <sub> 3 </ Sub> Al Preparation Process And Catalytic Behavior

In recent years, microchanneled reactors have received much attention as compact and efficient hydrogen production systems utilizing alcohol or hydrocarbon, due to their high surface to volume ratio and high rates of heat and mass transfer compared with conventional reactors.Ni₃Al intermetallic compound is one kind of new materials not only with high heat-resistance but also with good formability and mechanical strength. In this respect, intermetallic compound Ni₃Al, an excellent high-temperature structural material, has considerable promise. In this paper, the investigation focuses on the preparation of porous materials. Reaction Sintering of Powder Metallurgy method is adopted. The kind and the amount of pore forming agent are changed, as well as the sintering temperature and time. Adding different pore forming agents into the Ni, Al element powder, made an optimized choice. The effects of the amount of pore forming agent and the sintering temperature in a definite period on the density and porosity of the materials are studied. A formula that is used to calculate the density of the sintered sample is set up. The phases and microstructure of intermetallic compound porous material are investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and high resolution transmission electron microscopy (HRTEM). The results are listed as follows:1. The form of structure of porous Ni₃Al mainly depend on the volatilization of NaCl from porous Ni₃Al materials at high temperature.NaCl is adopted as pore-from material to prepare porous Ni₃Al materials, the size of pore could be controlled by size of NaCl particle directly, and the shape of pore correspondence with the shape of NaCl particle. Addition amount of NaCl has an important effect on this material porosity and porous structure; this specimen porosity rise as addition amount of NaCl increases but density decline and the relationship of them nearly a line.2.In theory, as preparing porosity Ni₃Al by addition pore-forming material, 1/(1-θ)=1/(ρ₀)·[K·ρ_m1+(e^ε1-1)ρ₀₁/ρ(01)ρ_m1e^ε1 +ρ_m2+(e^ε2-1)ρ₀₂/ρ(02)ρ_m2e^ε2·x/(1-x)]isobtained. In experiment, while the rate of temperature rise is 10℃/min,under the sintering process is 600℃for 3h, 801℃for 1h, 1000℃for lh and the pressing pressure is 600MPa,at this process, the relationship between porosity of Ni₃Al and amount of NaClis1/(1-θ)=1.2608 + 2.9235 x/(1-x) .3. Carbon nanotube is prepared using porous Ni₃Al as catalyst. The result indicates: while reaction temperature is 600℃, the catalytic both have the high activity and more fast catalyst speed than at others temperature. Meanwhile, the production of carbon nanotube is also large. As the catalytic time increase, the production of carbon nanotube increase. While the catalytic time reaches 24 h, the production of carbon nanotube is the most and not increased. HRTEM analyse indicate that carbon nanotube is muti-wall carbon nanotube and the number of wall is about 35.4. The mechanical of muti-wall carbon nanotube growing in the porous Ni₃Al is that: while the catalytic decomposition of methanol happens, due to the election of oxidation on the surface of Ni₃Al, nano Ni particle is formed on the surface Ni₃Al. Carbon atom which from the decomposition of methanol become carbon nanotube. As a result, carbon nanotubes are growing in inward of hole of porous Ni₃Al material; meanwhile, much of carbon nanotubes are growing in the hole of porous Ni₃Al.