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Alumina bauxite supply informs you: What are the main factors that influence bauxite sintering?
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2022-11-11
Alumina bauxite supply informs you: What are the main factors that influence bauxite sintering?
According to alumina supply sources, there are two primary factors that influence bauxite sintering: secondary mullite and the liquid phase. The former is determined by the Al2O3/SiO2 ratio and acts as a barrier to sintering, while the latter serves as a sintering catalyst. In addition, solid-state reactions between Fe2O3 and TiO2 that produce corundum and mullite crystal lattices also help promote sintering. So what are the main factors that affect bauxite sintering? Let our editor provide a detailed introduction!
Alumina bauxite supply information indicates that, under conditions of 1200°C to 1400°C, secondary mullite undergoes expansion, thereby hindering sintering. Above 1400°C, the secondary mullite reaction is essentially complete, and the liquid phase promotes grain dissolution and precipitation, leading to densification. The primary factor facilitating sintering is the promotion of sintering itself. In secondary high-alumina bauxites, the Al₂O₃/SiO₂ molar ratio is close to 2.55, which corresponds precisely to the stoichiometric composition of mullite; consequently, a large amount of secondary mullite is formed, making sintering more difficult. The dispersibility of the bauxite also has a significant impact on the formation of secondary mullite. During the calcination of bauxite, non-uniform mineral distribution and the expansion caused by the displacement of particles after reaction play crucial roles. This effect renders the reaction unsafe, as the resulting pores are often difficult to close, thereby impeding the densification of the bauxite.
Except for bauxite lumps, which exhibit a uniform microstructure and undergo sintering in three distinct stages at 1500°C, other bauxites generally have higher water absorption. When bauxite is first calcined and then re-calcined, its dispersibility improves, secondary mullite forms earlier, the process becomes safer, and expansion occurs at lower temperatures, all of which are conducive to sintering.
Alumina bauxite supply informs us that the liquid phase is another major factor influencing bauxite sintering. The liquid phase formed during bauxite calcination is insufficient to completely fill all intergranular pores. Under these conditions, the liquid phase initially draws the solid particles together, bringing them into contact with one another. However, the expansion induced by secondary mullite then pushes the secondary mullite particles apart, and this expansive effect of secondary mullite occurs simultaneously. When the temperature is below 1400–1500°C, the amount of liquid is small and its fluidity is low; in this regime, secondary mullite plays the dominant role. Above 1400–1500°C, secondary mullite becomes more stable, the quantity and fluidity of the liquid phase increase, and liquid-phase sintering becomes prominent, emerging as the primary sintering mechanism. Once the liquid phase has brought the solid particles into near-complete contact, dissolution–recrystallization processes among the solid particles gradually commence, progressively leading to the densification and packing of the particles until a continuous solid skeletal structure is formed; at this point, the liquid phase fills the remaining porosity, and bauxite sintering is complete. Nevertheless, the liquid phase also has its detrimental aspects.
The foregoing provides a detailed overview of the primary factors influencing bauxite sintering; operations should be conducted in accordance with the specific conditions of bauxite calcination.
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