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Soluble Aluminum Salts

  • Aluminum Sulphate - Wikipedia
    • Al2(SO4)3
    • Al2(SO4)3 + 6 NaHCO3 → 3 Na2SO4 + 2 Al(OH)3 + 6 CO2
    • Solubility in water 31.2 g/100 mL (0 °C) , 36.4 g/100 mL (20 °C), 89.0 g/100 mL (100 °C)

Aluminum Sulphate, Alum is used as a coagulant in water treatment. It brings together large flocs which then drop out of solution and/or are filtered out. This is not intuitive to clayers. We add flocculants to thicker suspensions to keep them from settling out. In thicker suspensions with clay colloids this creates light flocs full of water. While the don't always completely stay in suspension, if there is enough clay then a large house of cards structure is formed from the clay that seems to physically prevent materials from settling to the bottom as a hard pan. It would be a disaster in a glaze bucket if you don't need it so make sure it is only used after a glaze. It produces a dull white scum that looks like scumming on bisque but holds up to cone ten. I like it, but its use is limited. I do not know how thick it can be used.

I wonder if it would be helpful on top of flashing slips but have seen no highly promising results. I have not done careful testing with it. This chemical is available in garden nurseries. I wonder about its use with Iron Sulphate to form orange surfaces. It likely reacts with other soluble materials. I do not know which ones.

  • Potassium Alum
    • KAl(SO4)2 and it is commonly found in its dodecahydrate form as KAl(SO4)2·12H2O.
    • Solubility in water 14.00 g/100 mL (20 °C), 36.80 g/100 mL (50 °C)
    • It is used in water treatment, I believe like its cousin above, it is a flocculant

It is available in some Asian Grocery stores in small quantities. It maintains color and crispness in canned and maybe cooked vegetables. It is used in very small quantities. I have not used it in food or clay. Like alumina sulfate above I wonder if its use with Copperas (iron sulfate) would result in orange iron aluminates on the surface.

  • Sodium Aluminum Sulfate - Wikipedia
    • NaAl(SO4)2·12H2O (sometimes written Na2SO4·Al2(SO4)3·24H2O)
    • Solubility in water, 208 g/100 ml (15 °C)
  • Aluminum Chloride (becomes insoluble see below) This material seems too hazardous for an art studio.
    • Aluminum chloride is a neurotoxin.[] Anhydrous AlCl3? reacts vigorously with bases, so suitable precautions are required. It can cause irritation to the eyes, skin, and the respiratory system if inhaled or on contact.[19]
    • solubility 45.8g/100 ml (20˚C)
    • (from Wikipedia) Aluminium chloride is hygroscopic, having a very pronounced affinity for water. It fumes in moist air and hisses when mixed with liquid water as the Cl− ions are displaced with H2O molecules in the lattice to form the hexahydrate [Al(H2O)6]Cl3 (also white to yellowish in color). The anhydrous phase cannot be regained on heating as HCl is lost leaving aluminium hydroxide or alumina (aluminium oxide): Al(H2O)6Cl3 → Al(OH)3 + 3 HCl + 3 H2O On strong heating (~400°C), aluminium oxide is formed from the aluminium hydroxide via: 2 Al(OH)3 → Al2O3 + 3 H2O

Aluminium hydroxide is mostly insoluble in water but is soluble in acids such as the one formed when aluminum chloride is mixed with water.

I am not a safety expert, or a chemist. Do not use this site as a primary source for safety, chemistry or disposal information.

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Page last modified on May 10, 2018, at 01:27 PM