【作者】 杨军胜；

【导师】 贺跃辉； 江垚；

【作者基本信息】 中南大学 ， 材料学， 2014， 博士

【摘要】 摘要：本论文的研究目的是结合工业应用需要,为提高材料的过滤通量和过滤精度,分别制备了大通量和梯度孔径TiAl金属间化合物多孔材料,并采用多种手段对TiAl金属间化合物多孔材料的孔结构性能、力学性能和抗腐蚀性能进行了深入研究。为提高多孔材料的抗腐蚀性能,制备了一种新型的Ti3AlC2金属陶瓷多孔材料,结合热力学计算,推测出Ti.A1.C各元素的反应扩散途径。重点考察了Al含量和烧结温度对制备Ti3AlC2金属陶瓷多孔材料的影响,探讨了Ti3A1C2多孔材料反应合成的孔隙形成机制。最后,将TiAl金属间化合物多孔材料成功地应用于粗TiCl4原料的固液分离过程,建立了TiCl4错流过滤模型。本研究的主要内容和获得的结论如下：分别以碳酸铵和尿素为造孔剂,制备了大通量TiAl金属间化合物多孔材料。研究了造孔剂含量对TiAl金属间化合物多孔材料孔径、透气度、孔隙率及体积膨胀率之间的影响。建立了TiAl金属间化合物多孔材料的孔隙度θs与造孔剂含量w,以及多孔材料的透气度和孔结构参数之间的关系式。定量研究了TiAl金属间化合物多孔材料孔隙率θ与抗拉强度σh的关系,满足巴尔申方程σb=Kσ0(1-θ)m。以不同粒度的Ti.Al元素混合粉为原料制备了不同孔径的TiAl金属间化合物多孔材料基体。随原料颗粒粒度增大,材料孔径和透气度亦增大。然后在基体表面喷涂,制备出梯度孔径TiAl金属间化合物多孔材料,研究了基体孔径与喷膜粒子粒径的匹配性,并建立了多孔基体表面孔内粉末堆积状态模型。以实验模型计算,当覆膜粒径D50≈(√2-1)dm,(dm为基体最大孔径)时,其透气度下降率为64.6%,与实验结果透气度真实下降率63%较为接近。进一步研究了膜层厚度对TiAl膜孔结构参数的影响,测试了膜层与基体的结合强度,结果显示可承受8MPa的冲击力,满足工业应用要求。以TiH2.Al、石墨为原料制备了Ti3AlC2金属陶瓷多孔材料,研究了Al含量对Ti3AlC2多孔材料物相组成及孔结构性能的影响。将TiH2:A1:石墨原料粉末按照原子比为3：n：2进行配比(n=0.7,0.8,0.9……1.4),随Al含量增大,其杂质峰TiC随Al含量呈现先减小后增大趋势,变化趋势与孔径和透气度一致。研究了Ti3AlC2金属陶瓷多孔材料孔隙形成机制。第一阶段为反应生成TiAl金属间化合物(主要物相组成为Ti3Al,TiAl),此时,孔隙率保持增长,而最大孔径和透气度几乎维持不变。第二阶段为TiC与TiAl、Ti3Al反应生成Ti3AlC2。此时,TiC会扩散进入TiAl金属间化合物中,TiC偏离原位,孔隙形成；同时,TiC进入TiAl金属间化合物后,原始TiAl金属间化合物体积会增大,进而挤压原来形成的孔隙,出现孔径和透气度减小而孔隙率增加的现象。当TiC完全扩散入TiAl金属间化合物后,TiC偏移原位起主要作用时,孔径、透气度和孔隙率都增加。研究了烧结温度对Ti3AlC2多孔材料孔隙的影响,发现孔隙增长主要由TiH2分解、Kirkendall偏扩散和最终相Ti3AlC2的转变过程有关。本研究制备的TiAl金属间化合物多孔材料在工业生产中成功地实现了粗TiCl4原料的固液分离。以TiAl金属间化合物多孔材料为过滤介质,结合过滤-反冲及反向过滤技术可以完全实现长期的密封式连续过滤粗TiCl4原料液过程,大幅度减轻或避免原料的损失和严重的环境污染,同时,TiAl金属间化合物多孔滤芯具有长期稳定的高通量和高过滤精度。以Altmann模型为依据,通过对边界层悬浮颗粒进行受力分析,计算出颗粒的临界沉降粒径为4.6-5.2μm,经试验验证,选用平均孔径为3.5μm的TiAl膜过滤材料效果最佳。结合Darcy定律,建立了TiCl4工业错流过滤模型。计算出膜孔堵塞阶段膜面阻力Rm=3.00×1011m-1,滤饼形成阶段膜面阻力Rc＝1.73×1011m-1。对滤饼层固体颗粒进行清洗及再生,研究发现,反向过滤可以明显提高TiAl多孔材料的渗透通量。而采用化学清洗方式,其渗透通量可达到1.202m3/m2·h,效果最好。更多还原

【Abstract】 Abstract:Previous works for fabricating porous TiAl intermetallics by Kirkendall have been reported.For industrial application requirements, high permeate flux porous TiAl and gradient pore size TiAl intermeallics were fabricated.The pore structure properties,mechanical properties and environment corrosion resistivities were further investigated by various advanced testing methods.In order to enhance the corrosion resistance performance of porous material,a novel porous Ti3AlC2ceramic was fabricated.A thermodynamic estimation method was proposed to speculate the reaction diffusion path of Ti,Al and C.The effects of Al content and reactive sintering temperature on porous Ti3AIC2ceramics, and pore forming mechanism were taken into consideration.Finally, the porous TiAl intermetallics were successfully applied in the solid-liquid separation of suspended TiCl4raw liquid in industry production procedure.More details were given as follows.High permeate flux porous TiAl intermetallics were fabricated by space-holder of ammonium carbonate and urea, independently. The effect of space-holder addition amount on pore size,permeability, porosity and volume expansion were investigated systematically. According to the mass conservation law, the relation of porosity θS and space-holder amount w was established,and the relationships between permeability and pore structure parameters were investigated as well.The tensile strength of porous TiAl σb and porosity θ match the БaлъщиH equation σb=Kσ0(1-θ)m.Different pore size TiAl substrates were fabricated by powder metallurgy technique with different particle size of Ti,Al elemental powder. The results indicated that the pore size and permeability were increasing with particle size increase.The gradient porous TiAl intermetallics were prepared through spraying fine Ti/Al powders on porous TiAl substrate surface,and then the samples were sintered in vacuum furnace.The pore size of substrate and the particle size of powders were the main factors for the matching of substrate.The powder piling model was proposed to simulate the spraying membrane process, the result revealed that when the particle size D50≈(√2-1)dm,the decrease rate was64.6%,which was approximate to the experimental data63%.The relations between membrane thickness and pore structure parameters were considered. The porous TiAl membrane with uniformly pores, narrow pore size distribution has a metallurgical bonding with matrix, and can withstand8MPa impact force, which is satisfied the industrial demand.Porous Ti3AlC2was fabricated through reactive synthesis technique with TiH2, Al and graphite. The effect of Al content on the phase constitution and pore structure parameters was discussed. The phase TiC firstly decreased and then increased with increase of Al content, while the variation of pore size and permeability showed contradictory trends to that of TiC alteration. The pore forming mechanism is as follows:(1)At first, TiAl was formed previously by Ti and Al, during this stage, the permeability increased, while the pore size and permeability remained largely unchanged.(2) During the second stage, Ti reacted with C to synthesis TiC, and then TiC will diffuse into TiAl alloy to yield Ti3AlC2.With more and more TiC diffusing into TiAl, TiC will deviate its original position, the porosity will increase. At the same time, with TiC diffusing into TiAl, the volume of original TiAl could expand, that will extrude the pores produced by Kirkendall effect, so, the pore size and permeability decreased. When TiC diffused into TiAl completely, the effect of diffusion is the main factor, then the pore size and permeability increased as well.Finally, the fabricated porous TiAl intrmetallics material was successfully applied to the solid-liquid separation of suspended TiCl4raw liquid in industry procedure. The sealed, continuous and long-term filtration procedure was realized using the filtration-backwash technology and porous TiAl intrmetallics tubes as filtration elements, which can alleviate dramatically or even avoid raw material loss and severe environment pollution. The filtration tubes exhibited long-term,stable and high flux and filtration accuracy. The deposition characteristic can be described by the forces balance of a particle in the immediate vicinity of the membrane or cake layer given by Altmann and Ripperger, and the calculated particle deposition size is4.6-5.2μm.Membrane with average pore size of3.5μm was selected for TiCl4filtration.According to Darcy equation, the process of filtration is divided into two stages:at the initial stage of filtration, the particles which are equal to the pore size rush into pore quickly, causing the porosity of membrane decreases, filtration resistance increases and filtration flux decreases as well.At the second stage, fine particles are deposited at the membrane even for high cross-flow velocity and contribute to cake layer formation. During the pore-blocking stage, the membrane resistance is3.00×1011m-1. Compared with all these physical methods, the adhesive force binds particles together and makes cake layer strong and dense that reverse filtration is an effective method to remove cake layer. However, chemical cleaning method is a better method for the alternative, the flux grew quickly and reached a steady state of1.202m3/m2·h.更多还原