These factors can be summarized into three main categories: the properties of the AZS bricks themselves, the characteristics of the molten glass, and the operating environment and conditions.
I. The properties of the AZS bricks themselves (intrinsic factors), which are the cornerstone determining their corrosion resistance.
1.1 Chemical Composition and Phase Composition
- ZrO₂ Content: This is the most critical factor. Generally, the higher the ZrO₂ content (e.g., 33#, 36#, 41# AZS bricks), the better the corrosion resistance. ZrO₂ reacts with molten glass at high temperatures to form a highly viscous liquid phase that can form a protective layer on the brick surface, significantly slowing down further erosion.
- Al₂O₃/SiO₂ ratio: Affects the refractoriness and chemical properties of the brick.
- Impurity content: Impurities such as Fe₂O₃, TiO₂, and Na₂O reduce the high-temperature performance of the brick, forming eutectic deposits and accelerating erosion.
1.2 Microstructure
- Crystalline and glassy phases: AZS bricks consist of corundum (Al₂O₃), zircon (ZrO₂) eutectic crystals, and a small amount of glassy phase. The content and distribution of the glassy phase are crucial. Excessive glassy phase or uneven distribution of the glassy phase will become weak points for erosion.
- Form of ZrO₂: Zircon crystals are best distributed finely and uniformly in the eutectic network, rather than aggregated. This uniformly distributed structure most effectively blocks the penetration and dissolution of molten glass.
- Porosity and Pore Structure:
Apparent Porosity: The lower the apparent porosity, the more difficult it is for molten glass to penetrate into the brick body, resulting in better erosion resistance. This is one of the key indicators for evaluating the quality of AZ bricks.
Pore Size Distribution: Small, closed pores are more advantageous than large, interconnected pores.
1.3 Manufacturing Process
- Sintering Process vs. Electrofusion Process: Generally, electrofused AZS bricks have far superior erosion resistance than sintered AZS bricks because their crystal development is more complete and their structure is denser.
- Melting and Casting Processes: Melting temperature, cooling rate, etc., all affect the final phase composition and crystal structure.
- Casting Method: AZS bricks produced using tilted casting technology have a denser structure, fewer shrinkage cavities, and superior overall performance.
II. Characteristics of Molten Glass (Corrosive Media Factors): Molten glass is the "attacker," and its properties directly determine the severity of erosion.
2.1 Chemical Composition of Molten Glass
Alkali metal oxides (Na₂O, K₂O): These are the most corrosive components. They can disrupt the silicate network structure of AZS bricks, especially dissolving SiO₂ and Al₂O₃. The higher the Na₂O content, the more severe the corrosion.
Alkaline earth metal oxides (CaO, MgO): These are less corrosive than alkali metals, but they also participate in reactions.
Other components: Such as B₂O₃, PbO, F⁻, etc., also significantly alter the viscosity of molten glass and its wettability to refractory materials, thus affecting the corrosion rate.
2.2 Physical Properties of Molten Glass
Viscosity: This is one of the most critical properties. Lower viscosity molten glass has better fluidity, resulting in stronger convection and scouring effects, faster diffusion mass transfer, and more severe corrosion. Increased temperature significantly reduces viscosity.
Surface Tension and Wettability: The better the wettability of molten glass on AZS bricks, the larger the contact area, and the stronger the erosion and penetration.
III. Operating Environment and Conditions (External Operating Factors): Even the same brick can exhibit drastically different performance under different environments.
3.1 Temperature
- Absolute Temperature: This is the most significant external factor. For every 50-100°C increase in temperature, the erosion rate typically doubles. This is because high temperatures drastically reduce the viscosity of the molten glass, increase the chemical reaction rate, and intensify the diffusion between the brick and the molten glass.
- Temperature Fluctuations: Frequent temperature fluctuations can cause thermal shock peeling of the protective layer on the surface of AZS bricks, exposing a fresh surface and leading to "abnormally accelerated erosion."
3.2 Fluid Dynamics Conditions
- Static vs. Dynamic: The "static corrosion test" you mentioned represents the mildest conditions. In actual kilns, the flow and scouring of molten glass are extremely important factors.
- Flow rate: In areas with high glass melt flow (such as near the feeding port, flow hole, and bubbling zone), mechanical erosion continuously removes the protective layer from the brick surface, resulting in an erosion rate much higher than under static conditions.
- Flow state: Laminar or turbulent flow? Turbulent flow has a much stronger erosive effect than laminar flow.
3.3 Kiln atmosphere
- Oxidation-reduction atmosphere: Affects the valence state of variable-valence elements (such as Fe₂O₃/FeO) in the brick, thereby changing the viscosity and quantity of the glass phase and affecting erosion resistance.
- Atmosphere stability: Atmosphere fluctuations are also detrimental.
3.4 Compatibility of adjacent refractory materials
- Chemical reactions between different refractory materials can form low-melting-point substances, becoming the starting point for erosion.
In summary, the glass melt erosion of AZS bricks is a complex process involving the coupling of multiple factors.
Therefore, when selecting and using AZS bricks, it is essential to comprehensively consider the specific glass composition, melting temperature, and kiln location to achieve optimal performance and economy. Static laboratory tests (such as the 1500°C*36h test you mentioned) are an important screening method, but the final evaluation needs to be combined with dynamic simulation or kiln practice data that are closer to reality.
We are manufacturer of AZS refractory for glass furnace, any inquiries, please contact: [email protected], +8613213181902(WhatsApp/MP).
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