Aqua ammonia, aqueous ammonia and ammonium hydroxide are synonymous terms referring to a solution of ammonia in water.
Ammonia dissolved in water is present principally as the ion NH4+. Non-ionized molecular NH4OH, sometimes referred to as an associated form of ammonium hydroxide, is also present. Hydrated molecules of NH3 may also exist as NH3 · H20 or NH3 · 2H20.
Ammonia dissolved in water is commonly referred to as "aqua ammonia".
Grade/Strength of Solution
The grade or strength of Ammonium Hydroxide usually available commercially is 26-Degree Baumé. However, any strength product can be custom blended to meet the project requirements.
The Baumé reading refers to a specific gravity scale. A 26-Degree Baumé solution is equivalent to 29.4% by weight of ammonia dissolved in water. Since the Baumé reading varies with temperature, the reading is standardized at 60° F.
The density of the material compared to water is 0.8974 pounds per cubic foot.
The freezing point of a 26-Degree Baumé solution is about -112° F.
Aqua ammonia is corrosive to copper, copper alloys, aluminum alloys and galvanized surfaces.
An Aqua solution has a vapor pressure that varies with temperature. At ambient temperatures, the vapor pressure of 26-degree Baumé material just about equals atmospheric pressure.
Aqua ammonia is an excellent acid neutralizer. Its pH varies with concentration. Typical values are 11.7 at 1%, 12.2 at 5%, 12.4 at 10% and 13.5 at 30%.
Aqua ammonia is widely used as a reagent in SCR and SNCR systems that is injected in the combustion air to reduce NOx emissions.
Aqua ammonia is used in many applications instead of anhydrous ammonia to avoid the regulatory threshold limits posed on anhydrous ammonia as an extremely hazardous substance.
Storage & Handling
Aqua ammonia is shipped and stored in "non-pressurized" containers and is the reason why this is the strongest strength material generally available in the marketplace.
Aqua should be stored in a closed container and kept cool, otherwise, the ammonia gas will come out of the solution and the material strength will be reduced.