High Alumina Bricks: Complete Specification Guide (AL45 to AL90)

What Are High Alumina Bricks?

High alumina bricks are shaped refractory products containing more than 45% alumina (Al₂O₃) by weight. They are manufactured by pressing and firing a mixture of calcined bauxite, alumina, and bonding clays at temperatures between 1,400 and 1,600 degC. The alumina content directly determines the refractoriness, or maximum temperature capability, of the brick.

These bricks are classified by their alumina content into standard grades: AL45 (45% Al₂O₃), AL50, AL60, AL70, AL80, and AL90. Each step up in alumina content brings higher refractoriness but also higher cost. The art of refractory engineering lies in selecting the minimum grade that safely meets your application requirements.

Grade-by-Grade Specification Comparison

Property	AL45	AL50	AL60	AL70	AL80	AL90
Al2O3 (% min)	45	50	60	70	80	90
Fe2O3 (% max)	2.5	2.5	2.0	2.0	1.0	0.5
Bulk density (g/cm3)	2.15–2.25	2.25–2.35	2.35–2.50	2.55–2.65	2.70–2.85	2.90–3.10
Apparent porosity (%)	20–24	18–22	18–22	16–20	16–20	14–18
Cold crushing strength (MPa)	30–50	40–60	50–70	60–80	70–100	80–120
Refractoriness under load (T0.5) degC	1,400	1,420	1,460	1,510	1,550	1,600+
PCE (Pyrometric Cone Equivalent)	33–34	34–35	36–37	37–38	38–39	39–40
Thermal conductivity at 1,000 degC (W/mK)	1.5	1.6	1.8	2.0	2.3	2.8

Understanding the Mineralogy

The performance of a high alumina brick is not determined by chemistry alone. The mineral phases present after firing are equally important:

• Mullite (3Al₂O₃.2SiO₂): The primary crystalline phase in AL45 through AL70 grades. Mullite provides excellent creep resistance and thermal shock resistance. It forms naturally when alumina and silica react at high temperatures.
• Corundum (alpha-Al₂O₃): Becomes the dominant phase in AL80 and AL90 grades. Corundum has the highest hardness and refractoriness but lower thermal shock resistance than mullite.
• Glass phase: The flux content (Fe₂O₃, TiO₂, alkalis) determines the amount of glassy phase. More glass means easier sintering during manufacture but lower hot strength and refractoriness. This is why low Fe₂O₃ is specified for higher grades.

Application Guide by Grade

AL45 — The General-Purpose Workhorse

AL45 bricks are the most economical high alumina option and are suitable for a wide range of applications where temperatures do not exceed 1,400 degC and chemical attack is moderate. Common applications include:

• Cement kiln transition zones
• Back-up lining in steel ladles
• Incinerator linings
• Hot-air ducting in blast furnaces
• Furnace hearths for non-ferrous melting

AL60 — The Step-Up for Demanding Service

AL60 bricks offer a meaningful improvement in refractoriness and slag resistance over AL45. They are specified where the application sees higher temperatures (up to 1,500 degC) or moderate slag attack:

• Cement kiln upper transition zone
• Rotary kiln linings (lime, alumina, lightweight aggregate)
• Blast furnace stove checkerwork
• Torpedo ladle linings

AL70 — The High-Performance Standard

AL70 represents a significant jump in performance and is widely used in steel industry applications:

• Steel ladle working lining (sidewall)
• Electric arc furnace delta and sidewall
• Tundish permanent lining
• Blast furnace bosh and belly

AL80 and AL90 — Premium Performance

These corundum-rich bricks are specified for the most demanding applications where extreme temperature, aggressive slag, or both are present:

• Petrochemical reactor linings
• Carbon black furnaces
• Glass tank regenerator crowns
• Special kiln furniture
• Gasifier linings

How to Specify High Alumina Bricks Correctly

When preparing a purchase specification, include the following minimum parameters:

1. Chemical composition: Minimum Al₂O₃ and maximum Fe₂O₃, alkalis (Na₂O + K₂O)
2. Physical properties: Bulk density (min), apparent porosity (max), cold crushing strength (min)
3. Thermal properties: Refractoriness under load (T_0.5 min), permanent linear change at specified temperature
4. Dimensions: Standard shapes per IS 6 or custom dimensions with tolerances
5. Testing standards: Reference IS, ASTM, or EN standards for testing methods

Common specification mistake: Specifying a higher grade than needed. If your application needs AL60 performance, do not specify AL70 “just to be safe.” You pay 25–40% more with no real benefit and the higher thermal conductivity of the denser brick may actually increase heat losses.

Quality Checks on Delivery

When you receive a shipment of high alumina bricks, perform these checks:

• Visual inspection: Check for cracks, warping, and lamination. Tap bricks together — a clear metallic ring indicates good firing; a dull thud suggests underfiring or internal cracks.
• Dimensional check: Measure a random sample of 20 bricks against the specified dimensions. Tolerances should be within plus or minus 1–2 mm for standard shapes.
• Sample testing: Select random samples for laboratory testing of bulk density, porosity, and CCS. Compare against the data sheet and your specification.

Work with SAPL for Quality-Assured High Alumina Bricks

Shanker Agencies Pvt. Ltd. supplies the complete range of high alumina bricks from AL45 through AL90, sourced from CUMI, Crown Ceramics, and other established manufacturers. Every shipment comes with test certificates, and our engineers can help you select the optimal grade for your application. With over four decades of experience and a track record across hundreds of plants, we help you get the specification right the first time. Reach out to discuss your requirements.