Fused Zirconium Corundum Bricks, commonly referred to as AZS refractory bricks, are among the most critical materials used in modern glass kiln construction. As glass furnaces continue to operate at higher temperatures, longer campaigns, and under increasingly aggressive chemical environments, traditional refractory materials often fail to meet durability and performance expectations.
Glass manufacturers face persistent challenges such as molten glass corrosion, alkali vapor attack, thermal cycling, and mechanical erosion. In this context, fused zirconium corundum bricks have become the industry standard for zones exposed to severe corrosion, including melting tanks, throats, sidewalls, and critical contact areas with molten glass.
This article provides a comprehensive, technical, and application-oriented analysis of fused zirconium corundum bricks. We explore their composition, crystal structure, corrosion mechanisms in glass kilns, performance advantages over alternative refractories, and practical guidance for selecting the right AZS grade. The goal is not only to explain what AZS bricks are, but also how to maximize their service life and operational value in real industrial conditions.
Fused zirconium corundum bricks are electrofused refractory products manufactured by melting high-purity alumina (Al₂O₃) and zirconia (ZrO₂) at extremely high temperatures, typically above 1900°C, followed by controlled casting and annealing.
Unlike sintered refractory bricks, fused AZS bricks possess a dense, interlocked crystal structure formed during solidification from the molten state. This unique microstructure gives them exceptional resistance to glass corrosion and penetration.
Depending on zirconia content, fused zirconium corundum bricks are commonly classified as:
AZS-33 (≈33% ZrO₂)
AZS-36 (≈36% ZrO₂)
AZS-41 (≈40–41% ZrO₂)
The balance is primarily alumina, with controlled silica content as a glass-forming phase.
Bulk Density: ≥3.4 g/cm³, Apparent Porosity: ≤1.0%, Cold Crushing Strength: ≥350 MPa, Refractoriness: >1790°C,
Extremely low porosity Dense microstructure Superior resistance to glass penetration Stable performance at temperatures up to 1550–1600°C
The superior performance of fused zirconium corundum bricks is directly linked to their multi-phase crystal structure, which typically includes:
α-Al₂O₃ (corundum phase) – provides mechanical strength and thermal stability
Baddeleyite (monoclinic ZrO₂) – offers excellent corrosion resistance
Glass phase (silicate matrix) – fills micro-gaps and affects corrosion behavior
The distribution, size, and continuity of these phases determine how the brick reacts under molten glass exposure.
In glass kilns, molten glass preferentially attacks weaker glassy phases in refractories. The high zirconia content in AZS bricks significantly reduces glass phase solubility, slowing corrosion rates and limiting penetration depth.
Higher ZrO₂ grades generally exhibit:
Lower corrosion rates
Reduced blistering and spalling
Improved resistance to alkali-rich glass compositions
Fused zirconium corundum bricks are produced via electric arc furnace melting, followed by casting into molds and slow annealing.
Precise batching of high-purity raw materials
Full melting in an electric arc furnace
Controlled casting into molds
Extended annealing to relieve internal stresses
This process yields bricks with:
Extremely low apparent porosity (often ≤1.0%)
High bulk density
Minimal open pores accessible to molten glass
Compared to sintered refractories, fused cast AZS bricks offer superior chemical stability and consistency, which is essential for long furnace campaigns.
Glass kilns represent one of the harshest environments for refractory materials due to the combined effects of:
Continuous contact with molten glass
High operating temperatures (up to 1600°C or more)
Chemical attack from alkalis and boron compounds
Thermal gradients and mechanical stresses
Fused zirconium corundum bricks are specifically designed to handle these challenges.
Melting tank sidewalls
Tank bottoms and corners
Throat and working end
Weirs and dam blocks
Hot face areas exposed to aggressive melts
Understanding how fused zirconium corundum bricks degrade over time is essential for optimizing their use.
Molten glass selectively dissolves the silicate glass phase within AZS bricks. Once depleted, corrosion slows significantly, leaving behind a more resistant zirconia-rich skeleton.
At high temperatures, low-viscosity glass may penetrate micro-channels within the brick. Low porosity and dense casting greatly reduce this effect.
ZrO₂ undergoes phase transformation during heating and cooling. Proper annealing during manufacturing minimizes internal stresses and prevents cracking.
Volatilized alkali compounds attack exposed surfaces above the glass line, especially in superstructure zones.
| Refractory Type | Corrosion Resistance | Thermal Stability | Service Life in Glass Kiln |
|---|---|---|---|
| fire clay brick | Low | Moderate | Short |
| High Alumina Bricks | Moderate | Good | Medium |
| Mullite Bricks | Moderate | Good | Medium |
| Fused Zirconium Corundum Bricks | Excellent | Excellent | Long |
Fused zirconium corundum bricks outperform most alternatives when corrosion resistance is the dominant requirement.
Bulk Density: ≥3.4 g/cm³, Apparent Porosity: ≤1.0%, Cold Crushing Strength: ≥350 MPa, Refractoriness: >1790°C,
Choosing the correct AZS brick grade depends on furnace design, glass composition, and operating conditions.
AZS-33: Suitable for less aggressive zones, cost-effective
AZS-36: Balanced choice for most glass contact areas
AZS-41: Recommended for extremely corrosive zones and long campaigns
Glass chemistry (alkali content, boron presence)
Operating temperature
Expected furnace life
Maintenance strategy
| Property | AZS-33 | AZS-36 | AZS-41 |
|---|---|---|---|
| ZrO₂ (%) | ≥33 | ≥36 | ≥40 |
| Al₂O₃ (%) | Balance | Balance | Balance |
| Bulk Density (g/cm³) | ≥3.75 | ≥3.85 | ≥4.00 |
| Apparent Porosity (%) | ≤1.2 | ≤1.0 | ≤1.0 |
| Cold Crushing Strength (MPa) | ≥350 | ≥400 | ≥450 |
(Values may vary slightly depending on manufacturing process and supplier.)
Even the highest-quality fused zirconium corundum bricks can fail prematurely if improperly installed.
Use compatible mortars or dry joints as specified
Ensure proper expansion allowances
Avoid rapid heating during initial startup
Maintain uniform temperature gradients
Maintain stable furnace temperature
Minimize glass composition fluctuations
Inspect critical zones regularly
Replace worn blocks before catastrophic failure
While glass kilns are the primary application, fused zirconium corundum bricks are also used in:
High-temperature metallurgical furnaces
Special ceramic melting units
Waste vitrification systems
When sourcing AZS bricks, buyers should evaluate more than just price.
Raw material purity
Melting and casting technology
Quality control systems
Export experience and certifications
Reliable suppliers provide consistent chemistry, stable performance, and technical support, which directly influence furnace longevity.
Q1: Are AZS bricks suitable for all glass types?
They are ideal for most soda-lime, borosilicate, and specialty glasses, though grade selection matters.
Q2: Is higher ZrO₂ always better?
Not necessarily. Higher zirconia improves corrosion resistance but increases cost and density.
Q3: Can AZS bricks be repaired?
Minor surface damage can sometimes be repaired, but heavily corroded blocks should be replaced.
Fused zirconium corundum bricks represent the highest level of corrosion-resistant refractories available for glass kiln applications. Their fused cast structure, dense microstructure, and zirconia-rich composition enable long furnace campaigns, reduced maintenance, and improved operational stability.
For glass manufacturers aiming to increase furnace life, reduce downtime, and maintain consistent glass quality, AZS refractory bricks remain an indispensable solution.
Fused AZS bricks are produced through a high-temperature fusion casting process, where precisely controlled proportions of Al₂O₃ (alumina), ZrO₂ (zirconia), and SiO₂ (silica) are melted and cast into dense refractory blocks. Unlike sintered refractory bricks, fused AZS bricks feature: Extremely low porosity Dense microstructure Superior resistance to glass penetration Stable performance at temperatures up to 1550–1600°C
Fused Zirconium Corundum Brick, also known as fused cast zirconia–corundum refractory brick, is a premium refractory material specifically engineered for glass melting furnaces and other high-temperature, high-corrosion industrial environments. Manufactured through an electric arc melting process, this brick combines zirconia (ZrO₂) and alumina (Al₂O₃) in a dense, fully fused microstructure. Compared with sintered refractories, fused zirconium corundum bricks exhibit exceptional resistance to molten glass corrosion, alkali vapor attack, and thermal shock, making them a critical lining material in modern glass production.
Highland Refractory, a trusted supplier of premium AZS Refractory Brick, offers high-performance AZS Brick—engineered from zirconia-alumina-silica (ZrO₂-Al₂O₃-SiO₂) composites for extreme high-temperature and corrosive environments. Our product line includes AZS 33 brick (33% ZrO₂ content), AZS 36 brick (36% ZrO₂), and AZS 41 brick (41% ZrO₂), each designed to withstand continuous operating temperatures up to 1800℃ with exceptional thermal shock resistance and corrosion resistance against molten glass, slags, and acids.
