This investigation started as a result of The Wizard's use of alumina hydrate as a separation media between pots and glaze catchers. See EPK/Alumina/Biscuit SmackDown

I have learned that "alumina hydrate is not alumina hydrate is not alumina hydrate." Apparently there are many different names for the same thing and many different things with the same name. It is kind of like the "rutile" thing I choked on some time ago. (Technically rutile is one of the 3 crystalline phases of put\re titanium dioxide, but potters refer to the iron bearing titania ore used as a colorant as rutile.)

We have been using hydrate alumina, by the ton, at ZIRCAR for decades (or at least I believed). This material goes by the trade names of DISPERAL and DISPAL, manufactured by Sasol.

When Jamie mentioned it's use, and I saw it come out from between between pot and catcher as a powder after firing with my own eyes I thought it would be a no brainer. Things just didn't work out that easy. I mixed up a batch of Dispal and glue like I would EPK and glue. The alumina mixture is much more of a gel than a dispersion and took a little more work to apply. After firing I noticed the catcher fell off easily - very much like with EPK and glue. The only problem was the alumina was hard as a rock - harder than EPK would be.

After scratching a hole through my heads and surfing the web I realized alumina hydrate is not alumina hydrate is not alumina hydrate.

The Digitalfire Ceramic Materials Database lists Alumina Hydrate, Formula: Al₂O₃.3H₂O as Alum Hydrate, Alumina Trihydrate, Hydrated Alumina, Alpha Aluminum Trihydroxide, Gibbsite Al(OH)3

Sasol's web site states DISPERAL and DISPAL as  tradenames for the high purity, highly dispersible, boehmite alumina powders and sols/dispersions manufactured by Sasol

http://www.sasoltechdata.com/tds/DISPERAL_DISPAL.pdf

Chemistry %

From Wikipedia

Boehmite or Böhmite is an aluminium oxide hydroxide (γ-AlO(OH)) mineral, a component of the aluminium ore bauxite. It is dimorphous with diaspore. It crystallizes in the orthorhombic dipyramidal system and is typically massive in habit. It is white with tints of yellow, green, brown or red due to impurities. It has a vitreous to pearly luster, a Mohs hardness of 3 to 3.5 and a specific gravity of 3.00 to 3.07. http://en.wikipedia.org/wiki/Boehmite

 I finally believe I see that although "Alumina Hydrate" is "Alpha Aluminum Trihydroxide" and Dispal is boehmite which is an aluminum oxide hydroxide, they are not the same thing. This is pretty evident by the chemistry (~65% alimina vs. 80% alumina), specific gravity (2.42 vs. 3.00 to 3.07) and Moh's hardness (2.5 - 3.5 vs. 3 to 3.5)

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Phil Hamling

376 County Route 1

Warwick, NY, USA 10990