A New Method Of Presetting Nano-scale Catalyst In The Porous Medium

Solid energy devices, such as SOFCs and SOECs, are high energy conversion efficient and low polluting devices. and has been paid great attention to in the energy field and environmental protection. Electronic conductor―ion conductor mixture materials are important candidate for the solid energy devices materials. Metal, such as Ni and Fe, serve as the catalyst and electronic conductor. Nano-structure has some great advantages, improving the three-phase interface area or length which has larger researching value and becomes an important direction in the metal catalyst field.However, the defects of the traditional method such as dipping, is with low efficiency and poor repeatability. In this paper, based on the mature heat treatment methods such as plasma nitriding, the nano-scale catalyst is preset in the porous medium which is commonly used for solid energy devices. An new method of presetting nano-scale catalyst in the metallic plasma is developed and its mechanism is studied.Metallic plasma which is formed by bombarding the metal deposits and diffuses in the porous medium and the nano-scale metal particles can form. Experiments and theoretical calculations show that in the process of presetting, the plasma of metal catalyst diffuses and deposits in the surface and orifice of the porous medium.Within the larger depth of the pore, surface diffusion is the main way of presetting and formation of the nano-scale particles.In the process, within the depth of the porous medium,nano-scale catalyst whose preparation is high and structure is of high quality can be gotten.This method of presetting nano-scale catalyst in micro holes of the porous medium shows the feasibility、application value and development potential.In this paper, the thoery and mechanism of presetting is discussed, based on the basic theory and experimental observation. And the nano-scale catalyst deposition coefficient and surface diffusion coefficient is the main factors influencing or controlling coating and permeating of the method. By the theory and experiment work,the rationality of the micro mechanism of plasma coating and permeating of the method is proved. In this paper, the main influence factors of the presetting process such as basic skeleton material and structural characteristics, temperature, time and atmosphere composition are related and the consequences are discussed. The kinetics and thermodynamics of the presetting process was studied. The zone of the deposited Metal particles on the inner wall is the surface diffusion source of the micro-scale porous. In the metal plasma deposition process, the concentration and particle size increases and stabilize. And in the surface diffusion, in the diffusion resistance of the diffusion front is high. With time or diffusion distance increases, the overall diffusion driving force of the concentration gradient reduces, and surface diffusion trend reduces. Diffusion depth andthe concentration field is going to be stable. The temperature 800℃~1000℃ is advisable for the presetting method. But too high temperature is not conducive to maintaining nano-scale particles. And the trend of closing microporous increases. H2 and Ar mixed atmosphere is suitable for the atmosphere of the method. The specific crafts 1000℃×4h 0.03L/ min H2+0.03L/min Ar and 800℃×24h 0.03L/min H2+0.03L/min Ar presetting Ni are considered as a better presetting technology of the Ni O-YSZ micro-scale porous medium of 2μm×20μm straight hole.