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List of Refractory Bricks Used in Glass Melting Furnaces

Original Paper | Published: 28th March 2018
Author: kakugy Guo
14k Accesses | 84 Citations | 89 Altmetric | Metrics

Abstract

Silica Brick

Silica bricks for glass kilns are refractory products primarily composed of flint clay used in the construction of high-temperature portions of glass tank furnaces. Silica bricks for glass kilns should exhibit the following characteristics:

  1. High-temperature volume stability, preventing furnace deformation due to temperature fluctuations. Silica bricks have a high softening temperature under load and low creep rate, ensuring the stability of the furnace structure at 1600°C.
  2. No contamination of molten glass. Silica bricks, mainly composed of SiO2, do not affect the quality of molten glass even if there is chipping or surface melting during use.
  3. Chemical erosion resistance. The upper structure’s silica bricks are exposed to the gas erosion from glass ingredients containing R2O, forming a smooth transformation layer on the surface, reducing the erosion rate and providing protection.
  4. Low bulk density to reduce the furnace’s weight.
    The physical and chemical properties of silica bricks for glass kilns are listed in Table 1-1.
    Table 1-1: Physical and Chemical Properties of Silica Bricks for Glass Kilns
  5. (JC/T616=1996) High-quality silica bricks for glass kilns are categorized into three grades based on their unit weight: XBG-96 for those with a unit weight not exceeding 15kg, ZBG-96 for those with a unit weight between 15 and 25kg, and DBG-96 for those with a unit weight between 25 and 40kg. Refer to Table 1-1-2 for their physical and chemical properties.
    Table 1-2: Physical and Chemical Properties of High-Quality Silica Bricks for Glass Kilns
Clay Brick

Properties and Usage Guidelines for Clay Bricks.

The physical and chemical properties of large clay refractory bricks for glass kilns are specified in the Chinese standard YB/T5108-1993, as shown in Table 1-3.

Table 1-3: Physical and Chemical Properties of Large Clay Refractory Bricks for Glass Kilns

Kaolin Brick

Kaolin bricks are refractory materials with an Al2O3 content of 40% to 44%, and they are made from kaolin as the raw material. There are three production methods: pressing, ramming, and casting. The production process of the first two methods is similar to general refractory materials. In 1964, China successfully experimented with the casting method and began formal production. This method mainly uses bauxite clinker (75%) mixed with soft clay to form a slurry. Water glass is added as a diluent to give the slurry good fluidity. The addition of NaCl and NH4Cl as thickening agents accelerates the solidification of the slurry. The slurry is poured into gypsum molds, dried with electricity after demolding, and then fired in a kiln. The current products include pool furnace bricks (used for lining the pool bottom or walls), feeder trough bricks, heat exchanger cylindrical bricks, and crucibles, among others. The advantages of the casting method are that the product has a dense and uniform structure, good resistance to glass corrosion, and a relatively high degree of mechanization in production. The drawback is that the product may have larger dimensional tolerances and occasional slight distortions.

High-Alumina Brick

Properties of High-Alumina Brick as a Refractory Material

Chemically bonded high-alumina bricks have excellent thermal shock stability, a high softening temperature under load, and high cold crushing strength. They also possess some resistance to chemical erosion. The relevant physical and chemical performance indicators are shown in Table 1-4.

Table 1-4: Physical and Chemical Properties of Chemically Bonded High-Alumina Brick

Silimanite Brick and Mullite Brick

1 Silimanite Brick

In comparison to clay bricks, silimanite bricks and mullite bricks have a higher softening point at high temperatures. They possess a dense fine-grain structure that minimizes the formation of bubbles in molten glass, making them highly suitable for use in feeder troughs, mud tubes, plungers, and ladle bowls. They are used as pool kiln bricks only in special circumstances. You can find the physical and chemical characteristics of different silimanite bricks in Table 1-5.

Table 1-5: Physical and Chemical Characteristics of Silimanite Bricks

2 Mullite Brick

Mullite electrically fused bricks are a type of alumina-silica refractory product primarily composed of mullite crystals that are formed by high-temperature melting and casting. Since mullite is the primary crystal phase in mullite bricks, their properties are predominantly determined by mullite. Mullite bricks have a refractoriness of around 1850°C, a high softening temperature under load, low high-temperature creep rate, good resistance to thermal shock, and resistance to acidic slag erosion. However, mullite bricks should not come into contact with alkaline substances above 1450°C, as this can cause mullite decomposition. In a reducing atmosphere at temperatures above 1370°C, mullite will also decompose, with some SiO2 becoming gaseous and leaving the brick structure. Even at temperatures above 1650°C, in the absence of a reducing atmosphere and under lower oxygen partial pressure, mullite will still decompose. The physical and chemical properties are shown in Table 1-6.

Table 1-6: Physical and Chemical Properties of Mullite Bricks

Magnesia Brick

Refractory materials primarily composed of magnesium oxide (MgO) and having forsterite as the main crystalline phase are collectively referred to as magnesia refractory materials. Currently, the main types of refractory materials are as follows:

  1. Ordinary Magnesia Brick: Manufactured from sintered magnesite as the raw material, sintered to contain approximately 91% MgO. It is a magnesia refractory product bonded directly by silicates. This is a widely used magnesia product for both production and application.
  2. Directly Bonded Magnesia Brick: Made from high-purity sintered magnesia sand as the raw material, sintered to contain over 95% MgO. It is a magnesia refractory product bonded directly between forsterite crystal grains.
  3. Magnesia Silica Brick: Produced from high-silica sintered magnesite as the raw material, sintered to contain SiO2 at 5% to 11%, with a CaO/SiO2 molar ratio of ≤1. It is a magnesia refractory product bonded by forsterite.
  4. Magnesia Chrome Brick: Primarily made from sintered magnesite with the addition of a suitable amount of chrome ore, sintered to contain 8% to 20% Cr2O3. It is a magnesia refractory product bonded by magnesia-chrome spinel.
  5. Magnesia Olivine Brick: Magnesia olivine refractory materials are primarily composed of olivine as the main crystalline phase. They are often made from dunite or pure dunite. Products formed by shaping are called magnesia olivine bricks.
  6. Magnesia Alumina Brick: Manufactured from sintered magnesia as the primary material, with the addition of a suitable amount of Al2O3-rich materials, and sintered to contain 5% to 10% Al2O3. It is a magnesia refractory product bonded by magnesia-alumina spinel.
  7. Magnesia Calcium Brick: Produced from high-calcium sintered magnesite, sintered to contain 6% to 10% CaO, with a CaO/SiO2 molar ratio greater than 2. It is a magnesia refractory product bonded by dicalcium silicate.

6.1 Magnesia Brick and Magnesia Silica Brick

Table 1-7: Physical and Chemical Properties of Magnesia Brick

Table 1-8: Physical and Chemical Properties of Magnesia Brick and Magnesia Silica Brick

6.2 Magnesia Chrome Brick

Based on the raw materials and process characteristics, magnesia chrome bricks can be classified into fused magnesia chrome brick, directly bonded magnesia chrome brick, silicate-bonded magnesia chrome brick, rebound magnesia chrome brick, semi-rebound magnesia chrome brick, pre-reacted magnesia chrome brick, and non-burned magnesia chrome brick.

6.3 Magnesia Olivine Brick and Magnesia Calcium Brick

(1) Magnesia Olivine Brick

Table 1-9: Composition and Performance of Typical Magnesia Chrome Brick

Table 2-1: Physical and Chemical Properties of Magnesia Calcium Brick

6.4 Magnesia Alumina Brick

Magnesia alumina bricks are alkaline refractory materials with around 85% MgO and 5% to 10% Al2O3. Forsterite is the primary crystal phase in magnesia alumina bricks, with magnesia-alumina spinel serving as the matrix (replacing calcium-magnesia olivine in magnesia bricks).

Electrically Fused Castable Refractories

7.1 Electrically Fused Mullite Brick

Electrically fused mullite bricks are made from high-alumina bauxite as the raw material, forming a composition that closely resembles mullite (3Al2O3·2SiO2 with mass percentages of Al2O3 at 72% and SiO2 at 28%). These bricks are melted at around 2300°C and cast into molds at 1850°C, then annealed to eliminate stress. The primary crystal phases are mullite and corundum, with glass filling the gaps between the crystals. These bricks have better resistance to glass corrosion than sintered refractory materials but are less resistant than other electrically fused refractory materials. By adding a small amount (7%-8.5%) of zirconia, mullite crystals become smaller, the brick structure becomes denser, mullite content increases to 60%-70%, and the glass phase’s content decreases, reducing crack formation. Electrically fused mullite bricks have low thermal expansion coefficients, excellent resistance to thermal shock, and strong resistance to glass erosion.

Table 2-2: Physical and Chemical Properties of Electrically Fused Mullite Brick (LNXB11-89)

7.2 Electrically Fused Zirconia Corundum Brick

Table 2-3: Chemical Composition of Electrically Fused Zirconia Corundum Brick

Table 2-4: Electrically Fused Brick for Glass Furnaces

7.3 Electrically Fused Corundum Brick

(1) Electrically fused corundum bricks are produced from high-purity aluminum oxide as the raw material, with a small amount of pure alkali introduced, melted at temperatures between 2000°C and 2200°C. The production process is similar to that of high-alumina products. Particle size distribution should follow the principle of the densest packing and utilize a multi-level ratio to increase the amount of fine powder, thereby enhancing the bulk density of the product and promoting brick sintering. Aluminum oxide has multiple crystal forms, leading to electrically fused α-Al2O3 bricks, electrically fused α-β-Al2O3 bricks, and electrically fused β-Al2O3 bricks.

(2) The physical and chemical properties of electrically fused corundum bricks produced by a refractory materials factory in China are listed in Table 2-5.

Table 2-5: Physical and Chemical Properties of Electrically Fused Corundum Brick

(3) The physical and chemical properties of electrically fused corundum bricks produced by the German company Didier are shown in Table 2-6.

Table 2-6: Physical and Chemical Properties of Electrically Fused Corundum Brick by Didier (Germany)

7.4 Electrically Fused Chrome Corundum Brick

Electrically fused chrome zircon corundum bricks (abbreviated as AZCS bricks, known as ER2161 in France) are produced by introducing 10% to 30% Cr2O3 (primarily replacing Al2O3) into AZS-33 bricks. They are manufactured using a non-shrinking casting method. The bricks have a dark green color both on the surface and internally, and they contain 4.5% shrinkage without interconnected voids. The formation of a solid solution Al2O3·Cr2O3 (approximately 56%, with the rest being monoclinic zirconia phase and glass phase) increases the viscosity of the glass phase significantly, substantially enhancing resistance to glass corrosion. Its resistance to glass corrosion is 3.4 times that of ER1681 and 2.6 times that of ER1711. However, Cr2O3 imparts a colored hue to the glass melt, making it unsuitable for colorless and transparent glass production. Also, its foaming index is not ideal. Therefore, for pool kilns, it is an ideal material for the upper structure.

7.5 Electrically Fused Quartz Brick

The production process of electrically fused quartz bricks is similar to that of quartz glass. High-purity quartz sand (with a SiO2 content of over 99.5%) is used as the raw material. A small amount of Na2O is added as a mineralizer, and the mixture is melted in a graphite resistance furnace (1750-1800°C). After melting, the fused mass is rapidly removed, rolled into bricks, and mechanically processed after cooling in the air. These bricks have an extremely low coefficient of thermal expansion, excellent resistance to thermal shock, and strong resistance to borosilicate glass corrosion, but they are not resistant to sodium-calcium-silica glass corrosion. When exposed to temperatures above 1150°C for an extended period, these bricks will gradually crystallize into beta quartz, consisting only of crystals without a glass phase. The starting temperature for softening under load can be increased to 1720-1730°C.

Zircon Containing Refractory Bricks

8.1 Zircon Mullite Brick

Table 2-7: Physical and Chemical Properties of Dense Zircon Mullite Brick for Glass Melting Furnaces

8.2 Sintered Zircon Corundum Brick

Sintered zircon corundum bricks are made from zircon mullite and aluminum oxide as raw materials, typically containing less than 20% ZrO2. Zircon mullite and aluminum oxide undergo a solid-phase reaction at 1400-1450°C, resulting in a microstructure composed of two phases, mullite, and zirconia. This irreversible reaction is also referred to as an in-situ reaction. The measured starting temperature of the reaction is 1397°C, occurring at temperatures ranging from 1400-1425°C and 1500°C.

8.3 Zirconia Brick

(1) Zirconia bricks are refractory products primarily made from zirconium oxide as the main raw material. There are two main manufacturing methods: sintering and fusion. Zirconium oxide has three crystal forms: monoclinic, tetragonal, and cubic. When zirconium oxide is heated to around 1100°C, it undergoes a crystallographic phase transformation into the tetragonal phase, accompanied by a 7% volume shrinkage; conversely, it expands in volume. At temperatures above 2300°C, tetragonal zirconia transitions into the cubic phase. The densities of the three crystal forms are 5.68 g/cm³ (monoclinic), 6.10 g/cm³ (tetragonal), and 6.27 g/cm³ (cubic).

(2) Zirconia has a high melting point, excellent high-temperature structural strength, and resistance to acid and alkali corrosion.

8.3 Zircon Mullite Brick

Zircon mullite fused cast brick is a refractory product made from mullite and zirconium oxide as raw materials. Zircon mullite fused cast bricks have a dense crystal structure, high softening temperature under load, excellent thermal stability, high mechanical strength at both room and high temperatures, good abrasion resistance, good thermal conductivity, and outstanding resistance to erosion. The physical and chemical properties can be found in Table 2-9.

Table 2-9: Physical and Chemical Properties of Zircon Mullite Fused Cast Brick

8.4 Electrically Fused Re-Bonded Zircon Corundum Brick

Electrically fused re-bonded zircon corundum bricks are produced by using AZS blocks or electrically fused AZS waste bricks as raw materials, with a small amount of high alumina or aluminum oxide added as a bonding agent. When heated to a certain temperature, the electrically fused AZS aggregate melts, and the glass phase infiltrates, forming mullite with the bonding agent. This process allows the brick to sinter, and the sintering temperature ranges from 1600-1700°C. The chemical-phase composition of sintered blocks is very uniform, with a lower glass phase content. In contrast, the chemical-phase composition of waste bricks is less uniform and contains a higher glass phase content (15%-25%). The chemical composition of re-bonded products may vary within the following ranges: Al2O3 50-60%, ZrO2 20-30%, SiO2 14-20%.

About the Authors . . .

kakugy Guo Senior Engineer

CEO & Author Introduction
Advanced Refractory Materials and Furnace Technology
Leader in Oxygen Combustion Technology
info@agrmeng.com

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