A Model of Foam Filters

Filtration with foam filters is reported as a successful method to remove inclusions from top-cut silicon scrap. Inclusions in top-cut silicon scrap are needle-like Si₃N₄ particles and round SiC inclusions. A high filtration efficiency of more than 99 pct for 30-ppi SiC filters is achieved. The inclusions that remain are mainly SiC particles smaller than 10 μm. Possibly these particles are primarily secondary inclusions. The filtration efficiency increases with decreasing filter pore size. The main factor that plays a role in deep-bed filtration seems to be interception. Various models are considered to estimate the removal efficiency of foam filters by this mechanism. Here, we propose a new model called “the branch” model. This model gives a high filtration efficiency and agrees the best with the experimental results.