When furnace temperatures exceed 1600°C, traditional heavy bricks become bulky and heat-consuming. Alumina bubble bricks, with their lightweight and durable properties, are quietly replacing some high-alumina bricks and corundum bricks as a new choice for furnace linings.
1. First, let’s get to know them: What are alumina bubble bricks?
Alumina bubble bricks use hollow α-Al₂O₃ spheres as an aggregate, with a small amount of binder added. They are isostatically pressed and fired at high temperatures. Their bulk density is only 1.3-1.6 g/cm³, half that of ordinary high-alumina bricks.
Also, their Al₂O₃ content is ≥98%, and their softening threshold under load is ≥1700°C, making them both lightweight and fire-resistant.
Because the spheres contain a large amount of air, their thermal conductivity is ≤0.9 W·m⁻¹·K⁻¹ (at 800°C), significantly improving their thermal insulation capabilities.
2.Where are alumina bubble bricks used?
(1)The roof and walls of high-temperature shuttle kilns and tunnel kilns
The kiln roof must be light and heat-insulated. This not only reduces the load on the steel frame, but also reduces heat dissipation.
Hollow ball bricks solve both problems at once. They are usually compounded with 1260℃ ceramic fiberboard, which can reduce the surface temperature by 80-120℃.
(2)The radiant section lining of large petrochemical reforming furnaces and hydrogen production furnaces
The furnace temperature of this type of kiln is 1550-1650℃, and heavy bricks are prone to peeling. Hollow ball bricks reduce the heating and cooling time by 30% by low heat capacity, making start-up and shutdown more flexible.
(3)Insulation layer of vacuum consumable furnaces and shell furnaces made of titanium alloys and nickel-based alloys
The vacuum environment requires low volatility, and the Fe₂O₃ content in the bricks is ≤0.2% to avoid metal contamination.
At the same time, low density reduces the total weight of the furnace body, which is conducive to the longevity of the sealing ring.
(4) Clean areas of high-temperature experimental furnaces and crystal growth furnaces
Above 1600℃, with frequent lifting and lowering. Alumina bubble bricks have significantly better thermal shock resistance than corundum-mullite bricks, and do not slag, protecting the purity of the sample.
3. Brick selection and matching: the perfect combination of “light” and “heavy”
The strength of alumina bubble bricks alone is limited. The general practice is to paste 100-150 mm corundum bricks or fused zirconium corundum bricks on the hot surface, with 200-250 mm alumina bubble bricks as the backing, and then use aluminum silicate fiber felt for buffering.
In this way, the hot surface resists erosion and the cold surface keeps the temperature, and the steel shell temperature can be stabilized at ≤80℃.
During construction, leave a 2 mm paper gap between bricks. After heating, the spherical shell expands slightly and seals itself to avoid through cracks.
During the shutdown cooling stage, a cooling rate of ≤50℃ per hour can maximize the life of the lining.
In general, alumina hollow ball bricks are not omnipotent. But they are nearly irreplaceable in applications where energy savings and weight reduction are desired, even at temperatures above 1600°C. Before selecting bricks, first confirm the temperature profile and mechanical load, then choose the right refractory brick supplier to maximize furnace lining life and energy efficiency.