Erosion Mechanisms of Electrofused AZS Bricks in Glass Furnaces and How to Select the Right Type

Electrically fused AZS (aluminum-zirconium-silicon) bricks have been the cornerstone of glass furnace linings for decades. Their unique microstructure—in which corundum and zircon crystals interlock and are bound together by a glassy matrix—gives them outstanding resistance to glass melt erosion and thermal shock. However, even the highest-quality AZS materials will eventually deteriorate. For glass manufacturers seeking to extend furnace lifespans from 8 years to 15 years or more, a deep understanding of erosion mechanisms and grade selection is no longer optional.

How Glass Melt Erodes AZS: A Multi-Front Battle

Erosion in the glass contact zone is rarely a simple melting process; rather, it is a complex physicochemical process:

Matrix Dissolution

Glass melt rich in sodium or calcium first attacks the glass-phase matrix between the crystals, which is the weakest link. As the matrix dissolves, the corundum and zirconia crystals lose their anchorage and flake off into the melt. High alkali content and operating temperatures exceeding 1580°C significantly accelerate this process.

Upward Creep Erosion

At the metal liquid meniscus, where the glass melt, atmosphere, and refractory material meet, capillary action draws a thin film of glass melt to creep up the brick surface. Alternating oxidizing and reducing atmospheres cause rapid, localized erosion, resulting in the familiar “grooved” damage. AZS bricks in this zone must possess extremely low open porosity and a highly corrosion-resistant matrix.

Thermal Spalling

Periodic temperature fluctuations near burners and feed ports generate thermal stress. If the rate of glass phase exudation from the brick cannot match the thermal expansion differential, cracks will form, leading to surface spalling. This exposes fresh surfaces, accelerating erosion.

Downward Drilling Erosion at the Pool Bottom

Pool bottom lining bricks must withstand both downward penetration by molten glass and upward erosion microzones. AZS bricks with a stable glass phase, dense structure, and low porosity effectively prevent deep penetration.

Grade Classification: AZS-33, 36, and 41

The numbers in the grade designation roughly correspond to the percentage of ZrO₂ content. Generally, higher zirconia content results in greater erosion resistance, but also higher costs and slight variations in thermal expansion behavior.

AZS-33 (approx. 32–34% ZrO₂)

Ideal for upper structures (rear walls, burner bricks, small furnace openings) and upper grate sections. Offers a balance of moderate erosion resistance and cost-effectiveness. In float glass furnaces, it is commonly used in areas with lighter erosion, such as the large hearth and breast walls in the melting section.

AZS-36 (approx. 35–37% ZrO₂)

The preferred choice for tank and float glass furnace wall bricks, flow channels, and furnace hearths. The higher zirconia content in the matrix slows the penetration of alkali erosion. Its excellent thermal shock resistance makes it more tolerant during furnace heating and cooling cycles.

AZS-41 (approx. 40–42% ZrO₂)

Offers the highest level of protection and is suitable for the most demanding areas: side wall bricks of the flow channel, bubble barriers, areas surrounding electric fusing electrodes, and borosilicate glass melting sections. In high-sodium glass melts, the extremely low glass-phase content and more developed zircon network significantly slow upward drilling erosion. AZS-41 is frequently specified for borosilicate glass furnaces due to its exceptional resistance to low-alkali, high-boron melts.

Practical Selection Framework

When collaborating with glass manufacturers, SuperYu engineers evaluate three core parameters:

Glass type and alkali/alkali-earth metal ratio.

Hot-face operating temperature.

Target furnace lifespan and acceptable overhaul intervals.

Typically, the solution is not a single grade but a zoned lining scheme. For example, in a 400-ton-per-day bottle and jar glass furnace, AZS-41 may be specified for the flow holes and the liquid level line, AZS-36 for the remaining tank walls, and AZS-33 for the upper structure. This effectively balances performance and budget.

Beyond Composition: Manufacturing Quality Is Critical

Even with identical nominal chemical compositions, performance can vary dramatically depending on manufacturing quality. Key variables include:

Oxidation conditions during melting: Precisely controlled arc melting minimizes carbon contamination and porosity.

Casting and annealing: Precise cooling curves reduce residual stress and prevent latent cracks that could later develop into premature spalling.

Cold working and finishing: Diamond-ground joint surfaces ensure expansion joints perform as designed.

If you are evaluating AZS suppliers, request third-party reports on glass erosion rates (mm/year) and ultrasonic testing scans, rather than relying solely on a chemical composition sheet.

Looking Ahead

As the industry moves toward all-electric furnaces and higher cullet utilization rates, the thermal landscape is shifting. The refractory industry is responding with low-glass-phase AZS and improved zirconia distributions. For glass manufacturers, partnering with refractory suppliers who understand these dynamics can directly translate into an additional 2 to 4 years of valuable production time between cold repairs.