Deposition of Corrosion Products Released from Stainless Steel in Liquid Sodium

Deposition of corrosion products have been studied in a thermally convective sodium, using a sodium pot constructed of Type 304 stainless steel with a temperature range between 833 and 943 K. Deposited particles on the deposition test pieces were analyzed for their shapes and chemical compostions.The deposited particles were classified into the following three types: (a) a polyhedral shape with a large content of iron, (b) a hexagonal plate shape with a large content of chromium, and (c) a shape without particular form having a similar composition to that of Type 304 stainless steel but with lesser chromium. The compositions of (a) and (c) were along precipitation lines of the Fe-Cr-Ni ternary phase diagram at 833 K. Hence, the elements, Fe, Cr and Ni, which were released into the sodium deposited to form particles having the chemical composition along the precipitation lines.The size of the polyhedral particle was 3 μm. It seemed that, when the polyhedral particles grew larger than 3 μm, the crystal growth occurred along (100) and (110) planes to form a chain particle. The size of hexagonal plate particle was 0.3 μm. The particle size distribution of all the three shapes showed an average diameter of 4 μm and a standard deviation of 2 in a logarithmic normal distribution.