What you need to know about zircon fire bricks?

Want to choose refractory materials for high temperature kiln lining but feel overwhelmed? First focus on zircon fire bricks, and you will understand after reading this for three minutes.

1.What does zircon fire brick contain?

First look at the ingredients. The main component of zircon fire brick is zircon sand (ZrSiO₄). Its chemical composition is mainly zirconium oxide (ZrO₂) and silicon dioxide (SiO₂), which account for more than 90%.

Among them, ZrO₂ is the core component of the brick that has high temperature resistance and corrosion resistance. Its content is usually between 60%-65%.

In addition, some products will add a small amount of aluminum oxide (Al₂O₃) or yttrium oxide (Y₂O₃) as a stabilizer. This can inhibit the crystal transformation of ZrO₂ at high temperatures and reduce volume changes.

Specifically, these additives can significantly improve the thermal shock stability of bricks and prevent cracking caused by sudden temperature changes.

2.Two red lines: temperature and erosion

(1)Temperature requirements

The best continuous working temperature of zircon fire bricks is ≤1550℃, and the short-term hot spot can reach 1600℃. Once it is crossed, the glass phase softens faster and the brick creeps prematurely under its own weight.

(2)Medium erosion

Acidic slag, borides, and lead vapor are all considered “friendly areas.”

If the process is switched to an alkaline method or contains K₂O or Na₂O vapor, the zircon fire bricks need to be replaced with magnesia-alumina spinel bricks or chrome corundum bricks, otherwise the interface reaction layer will peel off layer by layer.

In addition, the heating rate should not exceed 50℃·h⁻¹, and the speed should be reduced simultaneously during cooling. In this way, thermal stress is released evenly, which is also beneficial to prolonging life.

3.Check four sets of numbers before purchasing

Before purchasing zircon fire bricks, we should pay special attention to four sets of numbers. In general, it can be summed up in eight words: “Check first, measure second, look third, and ask fourth.”

(1)Check the ZrO₂ content. When it is ≥60%, the high temperature range is more stable.

(2)Measure the bulk density. It is best to have a density of ≥3.9 g·cm⁻³. The higher the density, the faster the heat conduction. Therefore, the thickness of the insulation layer should be increased in advance.

(3)Check the apparent porosity. Ordinary grade ≤18%, dense grade ≤12%.

(4)Ask about the cold and hot compressive strength. Normal temperature ≥80 MPa can withstand mechanical slag cleaning.

Arrange the four groups of numbers alongside the furnace curve. In addition, compare the indicators of high alumina bricks and mullite bricks. In this way, you can pick out the levels at a glance and avoid “high configuration and low usage” or “low configuration and high usage”.

Of course, after the indicators are matched, don’t forget to choose the right refractory brick supplier. Suppliers of high-quality refractory bricks can provide chemical reports and dimensional tolerance tables for the same batch. Please note that long-term supply stability is more important than unit price.