FreeShip- ATH (Alumina Trihydrate), Fine, Hydrated Alumina - (Prompt rebate on orders with 3 or more FreeShip items!)

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This listing is for a fine particle size pure alumina trihydrate (non-colored) usually referred to as "ATH" by folks who have experience with it. Other names for it are "hydrated alumina", "aluminum hydroxide", and "aluminum trihydrate". The description below was written with both it and another filler (Calcium Carbonate) in mind. The specifics and differences between the two are noted. I do know the mesh size for this particular grade. It's 8 micron, quite fine. It is not free flowing.

Here is what you see in the pictures: The 4th and 5th show cast samples of two main types of fillers lined up side-by-side for comparison. The 4th picture shows the samples with reflected light (front lighting) and the 5th picture shows the same samples with transmitted light (back lighting) so you can get an idea of the relative degrees of opacity and translucency. The 2nd picture shows the cast sample of the material in this listing (fine mesh pure ATH) with front lighting and the 3rd picture shows the same sample with back lighting. The 1st picture shows one size of the actual raw material in a bag (like many raw materials it's a nondescript white powder). The available sizes are 50gr, 100gr, 200gr, 300gr, and 500gr (1+ lb). There's a jump in the price between 300gr and 500gr which is due to the jump in shipping cost from a package that can go first class (300gr) and a package that's over 1 pound that cannot go first class (500gr = more than 1 pound). In the last 2 pictures, the "fine ATH" in this listing is the very last sample on the row of side-by-side samples. It's by far and away the most translucent of the series of samples shown.

This is fine ATH, (distinct from the coarse ATH listing) a filler for liquid resins, specifically epoxy and unsaturated polyester. It's one of two major fillers used in manufacturing cast bathroom fixtures, countertops, and smaller items: calcium carbonate and alumina trihydrate (ATH) (ATH has many synonyms: aluminum hydroxide and hydrated alumina are two). Resin filled with ATH is given the name "cultured onyx" (versus "cultured marble" for calcium carbonate filled castings). This is a marketing ploy, of course, and not even an accurate one. Real onyx is quite opaque and almost always dark. "Black onyx" is a stone you can find set into fine jewelry. This inaccuracy comes about from a misnamed Mexican "onyx" mineral that is not true onyx, but a calcite mineral which can be translucent, banded, and colorful. ATH as a filler it has 2 major purposes: to extend the resin, lowering the overall cost of a casting, and as a matrix material with several benefits: allowing thicker cross sections to be cast because of exothermic heat transfer, added rigidity, and decreased tendency for warping due to resin shrinkage. Both these fillers are "natural", produced from minerals.
I focus on these two fillers because they have a long history of use and there is much information available on how best to use them. There are also many grades available. They are by far the two most commonly used fillers in the thermoset liquid resins industry and mass production helps drive down cost. It should also be mentioned that they are widely used as fillers in thermoplastic (meltable) resins.
The source for calcium carbonate is the mineral limestone which is ground to various particle sizes and purified to varying degrees for whiteness. It has been around the longest, predating ATH by quite some time. It is the least expensive of the two. The major difference in appearance between it and ATH is its opacity when combined with resin. It produces whiter and more opaque castings. It has a great many other uses, from construction to pharmaceuticals. The Wiki article is a good one and is here:
https://en.wikipedia.org/wiki/Calcium_carbonate
The article touches on it's use as a filler and extender for both thermoplastic and thermoset polymers:
"Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks as the minerals calcite and aragonite (most notably as limestone, which contains both of those minerals) and is the main component of pearls and the shells of marine organisms, snails, and eggs. Calcium carbonate is the active ingredient in agricultural lime and is created when calcium ions in hard water react with carbonate ions to create limescale. It is medicinally used as a calcium supplement or as an antacid, but excessive consumption can be hazardous....Calcite, aragonite and vaterite are pure calcium carbonate minerals. Industrially important source rocks which are predominantly calcium carbonate include limestone, chalk, marble and travertine.....The main use of calcium carbonate is in the construction industry, either as a building material or limestone aggregate for road building or as an ingredient of cement or as the starting material for the preparation of builder's lime by burning in a kiln. However, because of weathering mainly caused by acid rain,[17] calcium carbonate (in limestone form) is no longer used for building purposes on its own, but only as a raw/primary substance for building materials...[used] In the oil industry..as a raw material in the refining of sugar from sugar beet...component of blackboard chalk...as a filler in paper...as an extender in paints...a popular filler in plastics...as a white paint, known as whitewashing...in ceramics/glazing applications...as scouring powder...as a food additive...a gastric antacid...agricultural lime."

ATH is sometimes referred to as "translucent" filler. I believe that's not an inherent property but simply due to its refractive index being close to the refractive index of many transparent polymers. Its source is the mineral bauxite. The metal aluminum is produced from bauxite and ATH is an intermediate in that production. The Cameo database says this about ATH: "Alumina trihydrate is used as a base in the preparation of transparent lake pigments. It is also used as an inert filler in paints and tends to increase the transparency of colors when dispersed in oils. Alumina trihydrate is used commercially as a paper coating, flame retardant, water repellant, and as a filler in glass, ceramics, inks, detergents, cosmetics, and plastics." The Wiki article on it is here, although it's quite disapointing, not even mentioning its use as a filler: https://en.wikipedia.org/wiki/Aluminium_hydroxide . They do mention that it's a very effective fire retardant.
I carry 1 grade (mesh size) of pure calcium carbonate and two grades of pure ATH. In addition, I also have 2 kinds of ATH that have added decorative colorants (I don't know the mesh sizes). They've been pre-colored with pigments and different sizes of colored particles, which are supposed to resemble natural stone (granite) combined with polyester or epoxy. You can be the judge of how well they succeed. At the moment I only carry 2 colors, there are others available. I'll see how well these sell before getting more.

To demonstrate what these fillers will look like in a finished piece when combined with a liquid resin, I've mixed each of them with a low viscosity epoxy (Fiberlay brand) and poured them onto a stamped decorative aluminum tray (in the corners of that tray), after putting a release agent on the tray. Please note that the "loading" percentage of filler that I used was relatively low. You would normally use perhaps twice the amount of filler I used. You would vibrate the casting in the mold before it gelled to get rid of air bubbles, tap it, vacuum bag it, or perhaps use a different strategy of 1st pouring a low-loaded thin layer in the mold and when that is gelled, fill up the rest of the mold with a much higher loaded mix. You might also use an initial "gel-coat" (a clear thixotropic resin which forms the outer surface of the casting), and add the filled resin after the gel-coat has gelled.
All samples were mixed with the same proportions by weight (always the best way) into 3 separate cups. The amounts were 10/15/2 of epoxy resin/filler/epoxy hardener (the weight unit was grams). The filler was added to the resin side of the epoxy (usually part "A") and allowed to sit for a time to "wet out" properly. Then the hardener side of the epoxy (usually part "B") was mixed with the resin side and filler, scraping the sides of the cups and pouring the mix back and forth into both cups for complete blending (to include all resin and hardener clinging to the sides of the cups).
Since I no longer posses a vacuum chamber to remove bubbles from the mix that were stirred during mixing (I broke my $200 bell jar), I used 2 other old-timers tricks: a brief tutorial on these tricks follows, skip down past it if you wish:

Trick #1) I placed each cup into my "junk" refrigerator, covered with some plastic (to help reduce condensation). This trick works 99% well with platinum cured silicone rubber (the silicone doesn't "thicken" in the cold), but only works maybe 25% with other resins like epoxy. The idea is to lower the temperature which suspends/slows down the cure of the resin, giving air bubbles a little more time to rise. The reason it doesn't work as well with epoxy is, like most substances, epoxy increases in viscosity as the temperature goes down. This fact works against the rising of air bubbles. On the whole, though, the trick still helps some.
Trick #2) After removing from the refridge, I waited until the blend was just about ready to "gel" (a judgement call), and I got my cheapo propane torch out. More air bubbles had risen and if you can get those to "pop" it allows those below to rise faster. This trick is one of those things I should say "Don't Try This At Home!". Liquid resin can catch fire (although filled epoxy is pretty much self-extinguishing if you remove the heat source). The trick is to aim the propane flame downward over the top of the epoxy, perhaps an average of 6" above it, constantly moving the torch over different areas of the resin. This will instantly pop those surface bubbles. It also very briefly heats the top layer of resin, reducing viscosity and further helping more bubbles to rise. You don't hold the torch in one spot for more that 2 seconds or so. Longer and the resin will start a very rapid cure, wrinkling and possibly burning the top surface. Remember, "Don't Try This At Home!" (If you do I will not be responsible for your house burning down!). At least, PLEASE, do it outside!-

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Reviews

Reviews (6)

Average:

Mar 8, 2022

Nicole Bragg

Feb 11, 2022

SaraJ

Apr 26, 2021

Fast delivery. Good packaging. Thanks!

Kris Kramer

Jun 12, 2020

Perfect. Fast shipping. Good value.

norah downey

Feb 6, 2019

thank you fast shipping

Nancy Boughan