Influence of sintering atmosphere on crystals and performance of slag ceramics

The preparation of ceramic materials is a new way of utilizing steel slag. It is important to investigate the influence of different sintering atmosphere on steel slag ceramics, which is of great significance in promoting the application of steel slag ceramic technology. In this paper, 20% of steel slag and 80% of clay were used as the main raw materials under different atmospheres, namely, air and nitrogen, and were prepared into steel slag ceramic bricks. The ceramic bricks'crystal phase evolvement and performance were analyzed, and the effect of partial oxygen pressure on the oxidation of Fe²⁺ in the steel slag ceramics was investigated quantitatively. The results show that under air conditions, the Fe²⁺ in raw materials is oxidized to form the hematite phase, and the compressive strength and water absorption of sintered samples were 310 MPa and 3.7%, respectively, which is better than those of sintered samples under nitrogen conditions. Under nitrogen condition, the Fe²⁺ in the raw material is kept unchanged to form hercynite and pyroxene, and the size and quantity of pores in the sintered samples are greater than those under air conditions. This contributes to its poor mechanical properties. The critical range of the oxygen's partial pressure for the transformation of Fe²⁺ and its crystals is 0.5% -0.75%. When the partial pressure is less than 0.5%, a black or brown ceramic sample can be obtained and is mainly composed of hercynite and pyroxene. When the partial pressure exceeds 0.75%, Fe²⁺ begins to oxidize to Fe³⁺, hematite begins to form gradually, and its color changes from a brown or brownish red color. Increasing oxygen partial pressure in the sintering environment is an effective way for avoiding black core in the sintered steel slag brick.