Preparation of aligned porous niobium scaffold and the optimal control of freeze-drying process

Abstract

In order to prepare aligned porous niobium scaffolds with open interconnected pore channels by a freeze-drying process, the well dispersed aqueous slurries of niobium were directionally frozen and then dried by sublimation of ice crystals at a reduced pressure. Meanwhile, in consideration of the freeze–drying process being a time-consuming process, even a costly process while the manufacture route has been up–scaled to an industrial process, the process of freeze and drying has been analyzed by a numerical method based on an equivalent heat capacity model which is capable of describing freeze–drying process. The results indicated that the microstructure of the sintered samples, which were characterized by SEM, presents well interconnected pore channels. With the niobium volume percentage increasing, the interval of the niobium wall decreases progressively and the layer thickness of the walls increases inversely. The numerical results indicated that the required time for freeze process is strongly affected by the slurry concentration and the temperature of substrate whereas it is relatively affected by the pressure of the chamber and the niobium volume percentage in the frozen body during drying process.