Types and Selection Guide of Refractory Materials

As a core foundational material for high-temperature industries, the performance of refractory materials directly determines the service life of kilns and furnaces, energy consumption, and production safety. From iron and steel smelting to photovoltaic manufacturing, and from cement rotary kilns to glass melting furnaces, the selection of refractory materials must balance material properties, process adaptability, and economic efficiency. Based on the classification system, core performance indicators, and typical application scenarios, this paper systematically elaborates on the selection logic of refractory materials.

1. Classification System of Refractory Materials

The classification of refractory materials requires comprehensive judgment based on their chemical composition, manufacturing processes, and service characteristics. Common classification dimensions include the following:

1.1 Chemical and Mineral Composition

Siliceous materials: Mainly composed of silicon dioxide, such as silica bricks (SiO₂ content ≥ 93%). They exhibit strong resistance to acid erosion but poor thermal shock resistance, making them suitable for acidic environments such as coke ovens and glass melting furnaces.

Aluminosilicate materials: Including fireclay bricks (Al₂O₃ content 30%-46%), high-alumina bricks (Al₂O₃ content ≥ 48%), and aluminosilicate fiber boards. High-alumina bricks have a refractoriness of over 1770℃ and are widely used in high-temperature zones of iron and steel metallurgy and cement rotary kilns.

Magnesia materials: With magnesium oxide as the core component, such as magnesia bricks and magnesia-alumina spinel bricks. They possess excellent resistance to alkaline erosion and are commonly used in the burning zone of cement rotary kilns and non-ferrous metal smelting furnaces.

Carbonaceous materials: Including carbon bricks and graphite bricks, which feature high temperature resistance, good thermal shock resistance, and excellent thermal conductivity. However, they must be used in a protective atmosphere, such as electric furnace bottoms and aluminum electrolytic cells.

Zirconia materials: Such as fused zirconia corundum bricks (ZrO₂ content ≥ 33%), which have outstanding resistance to molten glass erosion and are used in the melting section of glass melting furnaces.

1.2 Manufacturing Process and Structural Form

Shaped products: Such as standard bricks and special-shaped bricks, which need to be pre-formed and fired. They are suitable for the masonry of regular furnace chambers, but special-shaped bricks have higher costs.

Monolithic refractories: Including refractory castables, plastic refractories, and gunning materials. They are formed by on-site casting or ramming and can adapt to complex furnace shapes, such as furnace tops and pipe connections.

Fibrous materials: Such as aluminosilicate fiber boards, blankets, and modules. They have a low thermal conductivity (0.12-0.2 W/(m·K)) and excellent thermal shock resistance (≥1000 cycles without cracks), making them suitable for insulation layers or low-temperature working surfaces.

1.3 Classification by Refractoriness

Ordinary refractory materials (1580-1770℃): Such as fireclay bricks, used in areas with small temperature fluctuations.

High-grade refractory materials (1770-2000℃): Such as high-alumina bricks, suitable for high-temperature zones of iron and steel metallurgy.

Super-grade refractory materials (>2000℃): Such as zirconia products, used in ultra-high-temperature laboratory furnaces.

2. Core Performance Indicators and Material Selection Logic

The performance of refractory materials must be quantitatively evaluated through the following key indicators:

Refractoriness: The ability of a material to not melt or soften at high temperatures. For example, magnesia-alumina spinel bricks with a refractoriness of ≥ 1800℃ are required for the burning zone of cement rotary kilns.

Thermal conductivity: A core parameter reflecting thermal insulation performance. At 1000℃, the thermal conductivity of aluminosilicate fiber boards is only 0.16 W/(m·K), which is 40% lower than that of traditional mullite fiber boards, significantly reducing heat loss through the furnace wall.

Thermal shock resistance: Measured by the number of thermal shock cycles (ΔT=1200℃/s). Zirconia-containing aluminosilicate fiber boards used in photovoltaic single crystal furnaces have better thermal shock resistance than graphite felts, with the number of thermal cycles increased by 3 times.

Chemical erosion resistance: Selected according to the medium inside the furnace. Glass melting furnaces require silica bricks to resist erosion by molten glass, while non-ferrous metal smelting furnaces need magnesia bricks or carbon bricks to resist the penetration of alkaline slag.

3. Typical Application Scenarios and Material Selection Cases

Different industrial kilns have significantly different requirements for refractory materials, which must be selected based on working conditions:

3.1 Iron and Steel Metallurgical Kilns

Blast furnace: Fireclay bricks or high-alumina bricks are selected for the upper and middle parts of the furnace shaft; a composite structure of carbon bricks + ceramic cups is adopted for the hearth and furnace bottom to resist the penetration of molten iron and the erosion of alkali metals.

Converter: The furnace lining must withstand chemical erosion and mechanical scouring by high-temperature slag. Magnesia-carbon bricks (MgO content ≥ 75%) have become the mainstream choice due to their strong slag resistance and good thermal shock stability.

Electric furnace: High-alumina castables are used for the furnace cover, and magnesia + asphalt ramming materials are used for the working layer of the furnace bottom to balance temperature resistance and thermal shock resistance.

3.2 Cement Rotary Kiln

Preheating zone: With a temperature of about 800-1000℃, fireclay bricks or low-porosity high-alumina bricks are selected to balance cost and temperature resistance.

Burning zone: With a temperature of 1450-1500℃, magnesia-alumina spinel bricks or directly bonded magnesia-chrome bricks must be adopted to resist the erosion of clinker liquid phase and thermal shock.

Cooling zone: With the temperature dropping below 1200℃, high-alumina bricks or phosphate-bonded high-alumina bricks can be selected.

3.3 Photovoltaic Single Crystal Furnace

Thermal field insulation: Zirconia-containing aluminosilicate fiber boards (ZrO₂ content 15-17%) are used, with a service temperature of up to 1450℃ and low thermal conductivity, which can reduce heat loss through the furnace wall by more than 25%.

Crucible protection: High-purity alumina fiber (Al₂O₃ ≥ 97%) is used for the inner layer, and gradient structure fiber boards are used for the outer layer to balance the requirements of thermal insulation and thermal shock resistance.

4. Selection Principles and Future Trends

Scientific material selection should follow the "four-step method":

Clarify the kiln type and working conditions (temperature, medium, mechanical load);

Prioritize core performance requirements (e.g., refractoriness as the primary indicator for high-temperature kilns);

Balance economy and construction convenience (monolithic materials are used for on-site casting in complex furnace shapes);

Refer to industry standards and cases (in accordance with the *Industrial Furnace Design Manual* and *Technical Specification for the Application of Refractory Materials*).

In the future, with the innovative breakthroughs in refractory fiber materials, nano-modification technology, and other fields, refractory materials will evolve toward higher performance and lower energy consumption. For example, by replacing traditional graphite felts with zirconia-containing aluminosilicate fiber boards in photovoltaic single crystal furnaces, an annual saving of 1500 tons of standard coal can be achieved, and the daily output per furnace can be increased by 12%. This case shows that scientific material selection can not only extend the service life of equipment but also promote the green and efficient development of high-temperature industries. With the continuous upgrading of industrial technology, the demand for refractory materials in emerging fields such as new energy and advanced manufacturing will become more refined, and the research and development of environment-friendly, energy-saving, and long-life refractory materials will become the core direction of the industry's development.