What are the ingredients of zirconium mullite bricks?

When choosing bricks for kiln lining, first look at the ingredients. The ingredients determine the heat resistance, corrosion resistance and lifespan. This article will show you the “formula” of zirconium mullite bricks. At the same time, it will also compare common high-alumina bricks, corundum bricks and other refractory bricks, so that you can identify the right one at a glance.

1. Zirconium mullite bricks: main crystal phase and binding phase

The core of zirconium mullite bricks is “two-phase partnership”. Mullite is the main skeleton, and zircon is the anti-corrosion “shield”. The industrial ingredients usually include the following.

(1) Aluminum source

Calcined alumina powder 55%-65%. Two levels of particle size, coarse powder supports the skeleton, and fine powder fills the gaps.

(2) Zirconium source

Zircon sand or desiliconized zirconium 15%-25%, ZrO₂ content ≥60%. The finer the particles, the better the thermal shock.

(3) Silicon source

Suzhou soil or andalusite 5%–10%, only a small amount of SiO₂ is added to make the mullite formation more complete.

(4) Binder

Pulp waste liquid + dextrin 2%–3%. It provides strength to the green body during molding and leaves micropores after carbonization to buffer thermal expansion.

(5) Trace additives

Adding 0.5%–1% TiO₂ or MgO can reduce the liquid phase appearance temperature by 30–50 ℃, making the sintering denser without affecting the high-temperature performance. The crystal phase composition after firing is roughly: mullite 45%–55%, baddeleyite 20%–30%, glass phase <5%, and the rest is corundum and a small amount of pores. The “phase transformation toughening” of ZrO₂ lowers the thermal expansion coefficient, so the 1100 ℃ water cooling can be cycled ≥30 times, which is better than the 8–10 times of ordinary high-alumina bricks.

2. Comparison of several brick types on the same platform

Place zirconium-mullite bricks side by side with common bricks, and the difference in composition is immediately converted into performance differences.

(1) High-alumina bricks (Al₂O₃≥75%)

No zirconium, the glass phase increases sharply above 1400℃, and the resistance to alkali vapor is only “medium”.

(2) Corundum bricks (Al₂O₃≥90%)

Single crystal phase, refractoriness 1800℃. However, its thermal expansion coefficient is high, and it is easy to crack when the kiln is started and stopped.

(3) Magnesia-alumina bricks (MgO≥80%)

Invincible in alkaline environments, but “melts” in seconds when encountering acidic slag. Moreover, its thermal conductivity is high, and the kiln shell temperature is high.

Zirconium-mullite bricks are in the middle. They are heat-resistant up to 1700℃, are “double-resistant” to acids and alkalis, and “resistant” to thermal shock. The price is only 60%-70% of corundum bricks. Therefore, it is commonly used as a “transition layer” in the upper tank walls of glass kilns and the burner areas of chemical shuttle kilns.

3. Avoid pitfalls when selecting bricks: Pay close attention to the composition list and supply line.

When reviewing the composition list, first check the two hard lines: ZrO₂ ≥ 15% and Al₂O₃ ≥ 55%. Then, add up the three elements: Fe₂O₃ + TiO₂ + R₂O (K₂O + Na₂O); the lower the better.

For the supply line, it is best to choose a tunnel kiln capable of single-shot firing above 1650°C, with a density ≥ 3.2 g/cm³ and a room-temperature pressure resistance ≥ 100 MPa. This will avoid dimensional drift caused by “secondary sintering.”

In short, consistent composition ensures stable performance; stable supply reduces kiln downtime. Submitting both the composition list and kiln operating conditions to a reliable refractory brick supplier is more cost-effective than repeatedly testing bricks.

Henan Ruitai Lianxin Refractory Co., Ltd. has specialized in refractory materials for 20 years. We are dedicated to providing customers with high-quality, high-quality refractory bricks and the most suitable kiln operating solutions. Choosing Ruitai Lianxin means choosing strength.