| OCR Text |
Show to 5 wt% Fe203 group, corresponding to the mullite-silica cluster on the ternary diagram. However, the higher iron content particles, which account for only about 10 wt% of the total ash, are the ones responsible for the initial development of deposit on the tube under the conditions investigated. Properties of the Deposits Some interesting insight into the process of deposit formation was obtained by wrapping a strip of platinum foil around the steam cooled tube and placing it across the flow for a short time. A scanning electron micrograph looking down on the surface of a platinum strip which was exposed to the flow for 30 seconds is shown in Figure 6. The central feature in the photograph is the splat of a low viscosity, high iron content slag droplet stuck to the platinum surface. Other similar s truc tures can be seen nearby. The droplets have collided at a low angle, traveling from left to right. Much smaller, white aluminosilicate particles are visible in the background. The importance of the high iron content particles is clear from examination of a much thicker deposit removed from the stainless steel tube, shown in Figure 7. In this figure the view is of a potted and polished cross section of deposit cut perpendicular to the tube axis. The flow was from left to right, in the same orientation as in Figures 1, 2, and 3, with the slightly curved deposit-tube boundary visible on the right. The image was obtained from backscattered electrons, therefore the brightest areas are the material of highest atomic weight, here indicating high iron content. The darkest areas are regions which were void in the original sample and which are now filled with the epoxy binder. Most of the deposit consists of the splats of very high iron 17 |
