I. Overview of High-Alumina Castables

High-alumina castables are a type of refractory material made primarily from high-alumina bauxite and supplemented with various additives. They belong to a key category of monolithic refractory materials. Compared to traditional refractory bricks, high-alumina castables offer advantages such as ease of construction, superior integrity, and excellent thermal shock resistance, playing an irreplaceable role in modern high-temperature industries.

This material primarily consists of three components: high-alumina aggregate (typically with an Al₂O₃ content between 55% and 80%), a fine powder matrix, and a bonding system. Its performance advantages are primarily reflected in high-temperature strength, slag corrosion resistance, and thermal stability, making it an ideal lining material for high-temperature equipment in industries such as metallurgy, building materials, and chemicals.

II. Key Characteristics of High-Alumina Castables

(I) Physical and Chemical Properties

The most notable characteristic of high-alumina castables is their high alumina content (typically ≥55%), which directly contributes to their excellent high-temperature performance. Key technical specifications include:

- Refractoriness: Typically ≥1750°C

- Bulk density: 2.3-2.8 g/cm³

- Room temperature flexural strength: 5-15 MPa

- High temperature flexural strength (1400°C): 3-10 MPa

- Linear change rate (1600°C): ±0.5%

(II) Thermal Properties

High-alumina castables exhibit excellent thermal stability:

- Coefficient of thermal expansion: 5.0-7.0 × 10⁻⁶/°C (20-1000°C)

- Thermal conductivity: 1.5-2.5 W/(m·K) (1000°C)

- Specific heat capacity: 1.0-1.2 kJ/(kg·K)

(III) Mechanical Properties

After proper heat treatment, high-alumina castables form a strong ceramic bond, exhibiting the following:

- Room-temperature compressive strength: 30-80 MPa

- Low high-temperature creep rate (1400°C, 0.2 MPa, 50 hours): <1.0%

- Excellent thermal shock resistance (1100°C water-cooled): >30 times

III. Production Process and Key Technical Points

(I) Raw Material Selection

The quality of high-alumina castables primarily depends on the selection of raw materials:

- Main raw materials: high-alumina bauxite clinker (Al₂O₃ ≥ 75%), sintered corundum, fused corundum, etc.

- Binders: pure calcium aluminate cement, silica fume, alumina fume, etc.

- Additives: dispersants (such as sodium tripolyphosphate), water reducers, explosion-proof fibers, etc.

(II) Mix Design

A typical high-alumina castable formulation includes:

- Aggregate (5-3 mm): 35-45%

- Intermediate particles (3-1 mm): 15-20%

- Fine Powder (<1mm): 35-40%

- Binder: 4-8%

- Additives: 0.1-1.5%

(III) Production Process

The production of high-alumina castables primarily involves the following steps:

1. Raw Material Pretreatment (Crushing and Screening)

2. Accurate Batching (Weighing according to the Design Formula)

3. Uniform Mixing (Forced Mixer)

4. Packaging (Moisture-Proof Treatment)

5. Quality Inspection (Sampling and Testing of Various Properties)

IV. Application Areas and Construction Key Points

(I) Main Application Areas

High-alumina castables are widely used in:

- Steel Industry: Ladles, Tundishes, Heating Furnaces, Iron Taps, etc.

- Cement Industry: Rotary Kiln Mouths, Preheaters, Tertiary Air Ducts, etc.

- Petrochemical Industry: Catalytic Cracking Units, Gasifiers, etc.

- Nonferrous Metallurgy: Aluminum Electrolytic Cells, Copper Smelting Furnaces, etc.

- Waste Incineration: Incinerator lining, flue, etc.

(II) Key Construction Technologies

To ensure optimal performance of high-alumina castables, the following precautions must be taken during construction:

- Formwork: Ensure accurate dimensions and sufficient strength and rigidity.

- Mixing Process: Strictly control the amount of water added (usually 5-8%), and the mixing time is 3-5 minutes.

- Casting: Layered and vibrated, with each layer thickness not exceeding 300mm.

- Curing System: Wet curing at 20-35°C for 24-48 hours.

- Baking Curve: Developed based on material properties, the temperature is typically gradually increased to 800°C over 5-7 days.

V. Technological Development Trends

With the increasing requirements for material performance in high-temperature industries, high-alumina castables are developing in the following directions:

(I) Low-cement/Ultra-low-cement Technology

By optimizing the micropowder system and dispersant, the cement content can be reduced to below 3%, improving high-temperature performance.

(II) Nanotechnology Applications

Introducing nanomaterials such as nano-alumina to improve the sintering and mechanical properties of the material.

(3) Self-Leveling Technology

Develop high-alumina castables with self-leveling properties to simplify the construction process and improve lining uniformity.

(4) Environmentally Friendly Materials

Develop high-alumina castables that do not contain harmful elements such as chromium to meet environmental protection requirements.

(5) Functional Design

Develop specialized castables with special functions (such as resistance to alkali corrosion and CO2 corrosion) for specific working conditions.

VI. Conclusion

As an indispensable key material in modern high-temperature industries, technological advancements in high-alumina castables are directly related to production efficiency and energy consumption in related industries. With the continuous advancement of materials science, the performance of high-alumina castables will be further enhanced, and their application areas will continue to expand. In the future, intelligent production, precise construction, and full lifecycle management will become key directions for the development of high-alumina castable technology, providing stronger support for the sustainable development of the high-temperature industry.