Plate Alumina Vs Fused Alumina: Performance Comparison & Refractory Applications

Sintered plate alumina is a type of sintered corundum made from high-purity alumina raw materials. It is highly pure, contains no additives, and undergoes complete firing shrinkage.

With high refractoriness, excellent thermal shock resistance, creep resistance, and wear resistance, plate alumina has become a leading synthetic high-purity alumina aggregate.

It is widely used in high-performance refractory materials for the iron and steel, foundry, petrochemical, ceramic, glass, and other industries.

From an economic perspective, it offers a stable raw material supply, an energy-saving and environmentally friendly production process, and high cost-effectiveness.

Although the overall consumption of refractory materials has declined sharply, especially in steelmaking applications, the consumption of plate alumina has achieved both relative and absolute growth.

The introduction of continuous casting, the steady increase in the proportion of unshaped refractories, and the strong demand for high-quality steel are all driving forces behind the development of plate alumina-based refractory materials.

I.Properties

Plate alumina is a dense, fully sintered α-Al₂O₃ material with an aggregate structure composed of crystal grains ranging from 50 to 400 μm. It is named after the plate-like morphology of its crystal grains.

Plate alumina is produced by rapidly calcining ultrafine α-Al₂O₃ pellets at a temperature slightly below the melting point. After heat treatment, the 18–20 mm pellets are crushed or ground to obtain plate alumina with various particle sizes, as shown in Table 1.

Table 2 summarizes the properties of plate alumina. In terms of chemical composition, high purity is particularly important, with a typical alumina content exceeding 99.4%.

Plate alumina is available in both coarse particles and fine powder down to -325 mesh, corresponding to a particle size of -44 μm. The main impurity in plate alumina is sodium oxide, typically present at a content of 0.2–0.4%.

The main properties of plate alumina are as follows:

High purity (Al2O3>99.4%);

Extremely high crystal hardness;

Low open porosity and closed porosity that is 2–3 times higher;

High particle bulk density: 3.55–3.6 g/cm3;

High melting point: above 2000℃;

Chemical inertness;

Excellent thermal shock resistance;

Superior volume stability;

The presence of microcracks;

High single-crystal grain strength.

II.Production of Sintered Plate Alumina

Sintered plate alumina was first produced in the United States in 1934. It was gradually introduced into production in China in the early 1990s. At present, six domestic manufacturers in China have mass production capacity.

The production processes used by different manufacturers are generally similar. The basic production flow is as follows:

Raw industrial alumina powder receiving → chemical composition and particle size inspection → grinding fineness testing → pelletizing (disc pelletizing or drum pelletizing) → drying → high-temperature shaft kiln firing (1800–1900℃) → physical and chemical property inspection → crushing and grinding → particle size re-inspection → packaging → warehousing

III. Application of Sintered Plate Alumina in Refractory Materials

1. Sliding Nozzle

Good thermal shock resistance and wear resistance are the primary requirements for refractory materials used in sliding nozzles. Sintered plate alumina fully meets these performance requirements.

At present, alumina-carbon sliding nozzles based on sintered plate alumina, with appropriate additions of graphite (or carbon black) and antioxidants, as well as alumina-zirconia-carbon sliding nozzles formulated with sintered plate alumina, zirconia, graphite (or carbon black), and antioxidants, remain the mainstream material systems for sliding nozzles in China.

2. Ladle Castables

With the continuous development of secondary refining technology, the service conditions of refractory materials in steel ladles have become increasingly severe. Molten steel remains in the ladle for longer periods for stirring and heating and is subjected to severe erosion by various types of slag.

Single-component lining materials (such as magnesia- or alumina-based materials) for ladles have been replaced by composite systems. The prevailing refractory configuration for medium and large steel ladles uses alumina-spinel castables (mainly composed of sintered plate alumina and spinel) for the ladle bottom and side walls, with magnesia-carbon bricks applied at the slag line.

3. Precast Refractory Shapes

Precast shapes such as purging plugs, well blocks, injection lances, impact pads, and others are not only part of the ladle refractory lining but also play a vital role in the steelmaking process.

The combined use of sintered plate alumina, spinel, and other refractory raw materials can effectively improve the thermodynamic properties of refractories, significantly enhancing wear resistance and slag corrosion resistance.

IV. Comparison Between Sintered Plate Alumina and Fused Alumina

Fused alumina commonly used in refractory materials includes white fused alumina, sub-white fused alumina and brown fused alumina, which are generally produced by melting alumina or bauxite raw materials. The main differences between sintered plate alumina and fused alumina are summarized as follows:

1.Sintered plate alumina features low impurity content with uniform distribution, while fused alumina has higher impurity content and uneven distribution.

Sintered plate alumina is made of high-purity industrial alumina without any additives during production. Except for a small amount of mechanical iron introduced during crushing - which can be removed by magnetic separation - other impurities such as iron, silicon and sodium exist only in trace amounts.

In the production of fused alumina, iron and carbon are added as auxiliary materials, resulting in much higher contents of iron, carbon, silicon, sodium and other impurities compared with sintered plate alumina.

In addition, during the cooling of fused alumina ingots, the cooling rate varies at different positions, leading to inconsistent impurity distribution. For this reason, fused alumina requires strict manual sorting, whereas sintered plate alumina needs no sorting.

2.Sintered plate alumina exhibits better thermal shock resistance and spalling resistance than fused alumina.

The superior thermal shock and spalling resistance of sintered plate alumina are attributed to its appropriate amount of closed pores. Spherical closed pores can effectively resist thermal shock and inhibit crack propagation.

By contrast, fused alumina contains more open pores and fewer closed pores. It forms large-sized single crystals during slow cooling; microcracks are easily generated in these single crystals after crushing, which further reduce its thermal shock resistance and spalling resistance.

3.The production process of sintered plate alumina is far more energy-saving and environmentally friendly than that of fused alumina.

Fused alumina production is well known for extremely high energy consumption, consuming 2300–3300 kWh per ton. By comparison, the comprehensive energy consumption of sintered plate alumina is only 1/7 to 1/10 of fused alumina.

Fused alumina manufacturing discharges large amounts of waste gas and residue. Sintered plate alumina adopts natural gas as heat source; apart from carbon dioxide from natural gas combustion, there is no other waste gas or solid residue discharge.

In conclusion, from both technical and production perspectives, sintered plate alumina can replace all types of fused alumina.