Technical Characteristics and Kiln Application of Phosphate Refractory Bricks

Technical Characteristics and Kiln Application of Phosphate Refractory Bricks

1. Overview

Phosphate refractory bricks are chemically‑bonded refractory materials manufactured with phosphoric acid solution as the binder and bauxite clinker as the main raw material. The raw materials undergo ageing treatment before high‑pressure forming, followed by low‑temperature firing at 550℃‑600℃.

Although their scope of application is narrower than that of high‑alumina bricks, phosphate bricks offer irreplaceable advantages for linings of specific kilns such as lime kilns and zinc‑smelting kilns, and are particularly suitable for critical zones including high‑temperature zones and transition zones. For rotary lime kilns, they can even be adopted for the entire kiln lining. Products with different bulk densities shall be selected according to temperature distribution: bricks of higher bulk density for high‑temperature zones, and bricks of lower bulk density for transition zones.

2. Production Process

Phosphate bricks fall into the category of low‑temperature chemically‑bonded refractory bricks. Their production process consists of the following key steps.
First, bauxite clinker is thoroughly mixed with phosphoric acid solution. Ageing is carried out to ensure uniform penetration and sufficient reaction of raw materials. Next, high‑pressure pressing is applied by a press to obtain dense and homogeneous green bricks. Finally, low‑temperature firing is completed within 550℃‑600℃. This process forms the distinctive chemical‑bonded structure of phosphate bricks, delivering excellent comprehensive performance under designated service conditions.

3. Performance Characteristics

The most prominent merit of phosphate refractory bricks lies in superior wear resistance. They can be classified into wear‑resistant bricks, composite bricks and other grades depending on bulk density and service requirements.

Conventional phosphate bricks suffer from drawbacks such as lower refractoriness‑under‑load and relatively large re‑burning shrinkage. Nevertheless, product performance has been greatly improved through successive technical upgrades. Adding an appropriate proportion of silicon carbide into raw materials further boosts wear resistance, raises refractoriness‑under‑load and enhances slag erosion resistance.

Moreover, new‑type refractory bricks integrating thermal insulation and service functions can be produced by compounding phosphate bricks with lightweight materials. Such composite structures slow down the cooling rate of kiln linings and reduce shell‑surface temperature. They extend the service life of kiln shells, cut fuel consumption and lower production costs.

4. Product Development and Technical Upgrading

Evolved from conventional chemically‑bonded bricks, phosphate refractory bricks have gradually developed into composite chemically‑bonded bricks. A variety of new‑process composite products have been developed to satisfy practical market demands, including high refractoriness‑under‑load bricks, corundum‑mullite bricks, phosphate‑lightweight composite bricks and silica‑corundum bricks.

By optimizing raw‑material formulation and composite technologies, these upgraded products provide more targeted material solutions for diverse kiln operating conditions, meeting differentiated lining‑material requirements in lime production and zinc smelting industries.

5. Application Fields and Service Advantages

For the lime industry, the chemical properties of phosphate bricks match well with the atmosphere inside kiln linings. Lime produced exhibits high activity, which helps improve product quality. For zinc smelting, outstanding wear resistance and strong slag‑erosion resistance enable the material to withstand harsh operating environments and prolong the service life of kiln linings.

Therefore, despite lower versatility compared with high‑alumina bricks, phosphate bricks remain an ideal lining‑material choice for specific working conditions of lime kilns and zinc‑smelting kilns.