High Alumina Bricks Specification Guide: AL45 to AL90

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

By Priya Sharma, Shanker Agencies

High alumina bricks are the workhorses of the refractory world, used in everything from cement kilns to steel ladles. This guide breaks down every grade from AL45 to AL90 with specifications, properties, and application guidance so you can specify the right brick every time.

high alumina bricksrefractory bricksAL45AL60+4 more

Key Takeaways

1The number in AL45 to AL90 is simply the percentage of alumina in the brick. Higher number means it survives more heat and chemical attack, and costs more.

2Buy the grade the zone actually needs. Over-specifying alumina spends money without adding lining life.

3Ask for the alumina percentage and PCE on the test certificate, not just the trade name, because names differ between manufacturers.

4Check bricks on arrival for size, cracks and even colour before they go into the wall. Problems are far cheaper to catch now.

5The same brick is sold under different names in different markets, so always compare on the numbers.

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 (T_0.5) 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:

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

Frequently Asked Questions

What do the grades AL45, AL60 and AL90 actually mean?

The number is the minimum alumina (Al₂O₃) content by weight: AL45 is 45% alumina, AL70 is 70%, AL90 is 90%. High alumina brick is by definition anything above 45% alumina, pressed and fired from calcined bauxite, alumina and bonding clays at 1,400–1,600°C. Each step up the grade ladder buys higher refractoriness and lower iron, and costs more. The engineering skill is picking the lowest grade that safely covers your duty, not the highest grade you can afford.

What is the load-bearing capacity of high alumina brick at temperature?

Two different numbers matter. Cold crushing strength runs from 30–50 MPa at AL45 up to 80–120 MPa at AL90. But the figure that governs a hot lining is refractoriness under load (RUL, T0.5), which is 1,400°C for AL45, 1,460°C for AL60, 1,510°C for AL70, 1,550°C for AL80 and 1,600°C+ for AL90. A brick can have high cold strength and still deform under load at temperature, so specify against RUL for load-bearing positions, not CCS.

Why does a higher alumina grade have worse thermal shock resistance?

Because the dominant mineral phase changes. AL45 through AL70 are mullite-bonded (3Al₂O₃·2SiO₂), and mullite gives excellent creep and thermal shock resistance. From AL80 upward, corundum (α-Al₂O₃) becomes dominant, which is harder and more refractory but tolerates thermal cycling less well. This is why jumping to the highest grade can shorten lining life on a furnace that cycles: you gain refractoriness and lose shock resistance.

What is PCE and how does it differ from RUL?

PCE (Pyrometric Cone Equivalent) measures the softening point of the material on its own, with no load applied, and runs from cone 33–34 at AL45 to 39–40 at AL90. RUL measures deformation under an applied load, which is closer to what a brick actually experiences in a wall. PCE is useful for classifying the material; RUL is what you design a load-bearing lining against. A high PCE on its own tells you little about how the brick behaves carrying a kiln shell.

Does lower iron content matter in high alumina brick?

Yes, particularly in reducing atmospheres and where iron pickup would contaminate the melt. Fe₂O₃ falls from 2.5% max at AL45 to 0.5% max at AL90. Iron oxide acts as a flux, forming a low-melting glass phase that lowers hot strength and can start creep well below the nominal refractoriness. Where a lining deforms prematurely despite being comfortably rated on paper, flux content is often the reason.