Is Aluminium Trihydrate Just Another Name for Aluminium Hydroxide?

Confused by all the names for one chemical? This jungle of terms like ATH and Al(OH)₃ can lead to costly mistakes in your orders and waste your valuable time.

Yes, aluminum trihydrate (ATH) is the same chemical compound as aluminum hydroxide, Al(OH)₃. The name ‘trihydrate’ is an older term commonly used in the flame retardant industry, referring to its structure as alumina with three water molecules.

This naming confusion is a constant headache for buyers. In my factory, we use both terms, but they refer to the same white powder. The name ‘aluminum trihydrate¹‘ or ATH is very common with our customers in the plastics and rubber industries. For someone like Mr. Park, who comes from a pharmaceutical background, this term might be new as he is more familiar with ‘aluminum hydroxide²‘. Let’s dig into why these different names exist and what they really mean for you and your business.

Why is it sometimes called trihydrate?

Does the name "trihydrate" make you question the chemical’s identity? This old term might seem confusing or even incorrect, but it actually gives a clue about its main industrial job.

It is called ‘trihydrate’ based on its chemical formula being written as alumina combined with water: Al₂O₃·3H₂O. This highlights the three water molecules that are key to its flame retardant properties, even though Al(OH)₃ is more accurate.

Both formulas represent the same thing, but they tell a different story. "Aluminum hydroxide" or Al(OH)₃ is the chemically correct way to describe the molecule. However, in the flame retardant³ industry, a different perspective is more useful. The decomposition of aluminum hydroxide under heat is 2Al(OH)₃ → Al₂O₃ + 3H₂O. This shows that for every two molecules of aluminum hydroxide, you get one molecule of alumina and three molecules of water. So, industry professionals started thinking of it as a hydrated form of alumina, or aluminum oxide. This Al₂O₃·3H₂O representation directly points to the water content, which is the "active ingredient" for stopping fire. It is a bit of industry shorthand that has stuck around.

In my daily work, I switch between these terms. When I talk to a pharmaceutical buyer like Mr. Park, I use "aluminum hydroxide." When I talk to a wire and cable engineer, I use "ATH." It is just about speaking the right language for the customer.

What is aluminium trihydrate mainly used for?

Now that you know the name, what does it actually do? You might see it listed in very different products, making its primary function unclear and causing you to second-guess its application.

Its main use by far is as a halogen-free flame retardant in plastics, rubber, and composites. It is mixed into materials to improve fire safety in products like cables, building panels, and seating.

While the pharmaceutical use in antacids is well-known, it represents a very small fraction of the total volume produced globally. The industrial flame retardant market⁴ is huge. ATH is a key additive because it is effective, affordable, and safe. When a fire starts, the ATH inside the plastic breaks down. This decomposition absorbs heat from the fire, releases water vapor to cool the material and dilute the oxygen, and leaves behind a protective layer of alumina. This makes it much harder for the product to burn. This is a critical safety feature in public spaces. The seats in a stadium, the insulation around a subway’s electrical cables⁵, and the wall panels in a new building all likely contain ATH to meet fire safety⁶ codes. As a producer, the scale is completely different. We might produce a few tons of high-purity⁷ pharmaceutical grade a month, but we produce thousands of tons of ATH for the flame retardant industry.

What specifications should you check for aluminium trihydrate?

Are you overwhelmed by all the numbers on a technical data sheet? Focusing on the wrong parameters can lead you to buy a product that fails to perform in your specific manufacturing process.

You must check the particle size distribution (PSD), whiteness, purity, and surface treatment. These physical and chemical properties directly impact how the ATH will perform in your final product, from viscosity to mechanical strength.

A good price is meaningless if the product doesn’t work. As a factory manager, these are the four specifications I discuss most often with my industrial customers. Each one is critical for a different reason.

I once worked with a customer whose new batch of solid surface countertops was cracking easily. We investigated and found they had accidentally ordered an ATH with a much coarser particle size than usual. The larger particles were creating weak points in the material. This is a perfect example of why you must confirm these details with your supplier.

How does aluminium trihydrate compare to magnesium hydroxide?

You see another flame retardant called magnesium hydroxide (MDH). Is it a better option? Choosing the wrong one for your polymer system can lead to processing problems and ruined batches.

Magnesium hydroxide (MDH) works just like ATH but decomposes at a much higher temperature (around 330°C vs. 200°C for ATH). This makes MDH necessary for plastics that are processed at high temperatures, like polypropylene.

The choice between ATH and MDH is almost always decided by the processing temperature of your plastic. They are not really direct competitors; they serve different parts of the market. ATH is perfect for polymers that are processed at lower temperatures. However, if you tried to put ATH in polypropylene, which is processed around 220-250°C, the ATH would decompose right inside your equipment. This would release water vapor and ruin your product. For these high-temperature plastics, you must use MDH.

The main takeaway is simple. If your process runs below 200°C, ATH is the most cost-effective flame retardant you can use. If you must go hotter, you need to budget for the more expensive MDH. It is a technical necessity, not a choice based on performance alone.

Conclusion

Aluminum trihydrate is just the industrial name for aluminum hydroxide. Knowing this, and matching the right grade and specifications to your specific application, is the key to successful and cost-effective sourcing.