Bifluoride ammonium

White crystalline solid prismatic crystal faint odor of ammonia stable at ambient temperature but decomposes on heating at 60°C melts at 107.5°C on very rapid heating density 1.586 g/cm vapor pressure 435 torr at 25°C readily dissolves in water (21.6g/100g at 20°C, and 36.6g/100g at 40°C). 

Ammonium bicarbonate is made by passing carbon dioxide through an aqueous solution of ammonia in an absorption column or a packed tower  

In this process, ammonia solution flows countercurrent to the ascending stream of CO2. Crystals of ammonium bicarbonate precipitate out when the solution becomes sufficiently saturated. The crystals are filtered or centrifuged out of the mother liquor, washed, and air-dried. Pure product may be obtained by using high purity CO2. Alternatively, high purity ammonium bicarbonate may be obtained by subliming the product formed at relatively low temperatures. 

Ammonium bicarbonate decomposes to CO2, ammonia, and water vapor on heating it liberates CO2 when treated with dilute mineral acids  

It reacts with sulfates of alkabne-earth metals precipitating out their carbonates  

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There are several processes available for the manufacture of cryoHte. The choice is mainly dictated by the cost and quaUty of the available sources of soda, alumina, and fluoriae. Starting materials iaclude sodium aluminate from Bayer s alumina process hydrogen fluoride from kiln gases or aqueous hydrofluoric acid sodium fluoride ammonium bifluoride, fluorosiUcic acid, fluoroboric acid, sodium fluosiUcate, and aluminum fluorosiUcate aluminum oxide, aluminum sulfate, aluminum chloride, alumina hydrate and sodium hydroxide, sodium carbonate, sodium chloride, and sodium aluminate. 

Two well-known salts of ammonia (qv) are the normal ammonium fluoride [12125-01 -8] NH F, and ammonium bifluoride [1341 -49-7] NH4HF2 the latter is sometimes named ammonium acid, or hydrogen difluoride. Much of the commercial interest in the ammonium fluorides stems from their chemical reactivity as less ha2ardous substitutes for hydrofluoric acid. 

Ammonium fluoride is a white, deflquescent, crystalline salt. It tends to lose ammonia gas to revert to the more stable ammonium bifluoride. Its solubiUty in water is 45.3 g/100 g of H2O at 25°C and its heat of formation is —466.9 kJ/mol ( — 116 kcal/mol). Ammonium fluoride is available principally as a laboratory reagent. If it is needed in large quantities, one mole of aqueous ammonia can be mixed with one mole of the more readily available ammonium bifluoride (1). 

Properties. Ammonium bifluoride, NH4HF2, is a colorless, orthorhombic crystal (2). The compound is odorless however, less than 1% excess HF can cause an acid odor. The salt has no tendency to form hydrates yet is hygroscopic if the ambient humidity is over 50%. A number of chemical and physical properties are Hsted in Table 1. 

Corrosion. Ammonium bifluoride dissolves in aqueous solutions to yield the acidic bifluoride ion the pH of a 5% solution is 3.5. In most cases, NH4HF2 solutions react readily with surface oxide coatings on metals thus NH4HF2 is used in pickling solutions (see Metal surface treatments). Many plastics, such as polyethylene, polypropylene, unplasticized PVC, and carbon brick, are resistant to attack by ammonium bifluoride. 

Manufacture. Anhydrous ammonium bifluoride containing 0.1% H2O and 93% NH4HF2 can be made by dehydrating ammonium fluoride solutions and by thermally decomposing the dry crystals (7). Commercial ammonium bifluoride, which usually contains 1% NH F, is made by gas-phase reaction of one mole of anhydrous ammonia and two moles of anhydrous hydrogen fluoride (8) the melt that forms is flaked on a cooled dmm. The cost of the material in 1992 was 1.48/kg. 

Precautions in Handling. Ammonium bifluoride, like all soluble fluorides, is toxic if taken internally. Hydrofluoric acid bums may occur if the material comes in contact with moist skin. Ammonium bifluoride solutions should be thoroughly washed from the skin with mildly alkaline soap as soon as possible however, if contact has been prolonged, the affected areas should be soaked with 0.13% solution of Zephiran chloride, or 0.2% Hyamine 1622 (Lonza, Inc.) or calcium gluconate, the treatment recommended for hydrofluoric acid bums. If any of these solutions come in contact with the eyes, they should be washed with water for at least 10 min and a physician should be consulted. 

Applications. Ammonium bifluoride solubilizes sihca and sihcates by forming ammonium fluorosilicate [16919-19-0] (NH 2 ip6 ... 

Ammonium bifluoride is used as a sour or neutralizer for alkalies in commercial laundries and textile plants. Treatment also removes iron stain by forming colorless ammonium iron fluorides that are readily rinsed from the fabric (17). 

Ammonium and Lithium Fluoroborates. Ammonia reacts with fluoroboric acid to produce ammonium fluoroborate (53). An alternative method is the fusion of ammonium bifluoride and boric acid (54) ... 

PbF2 is readily prepared by the action of hydrogen fluoride on lead hydroxide, lead carbonate, or a-lead oxide. It can also be obtained by precipitation from lead nitrate or lead acetate solutions using potassium fluoride, ammonium fluoride, or ammonium bifluoride. 

Manufacture. Lithium fluoride is manufactured by the reaction of lithium carbonate or lithium hydroxide with dilute hydrofluoric acid. If the lithium carbonate is converted to the soluble bicarbonate, insolubles can be removed by filtration and a purer lithium fluoride can be made on addition of hydrofluoric acid (12). High purity material can also be made from other soluble lithium salts such as the chloride or nitrate with hydrofluoric acid or ammonium bifluoride (13). 

Formation of a gelatinous precipitate that is difficult to filter can be avoided by addition of magnesium oxide to the acid solution. In order to increase particle size it is often necessary to keep the solution hot for several hours however, this problem is avoided by heating an intimate mixture of ammonium bifluoride with magnesium carbonate to 150—400°C (11). Particles of Mgp2 similar in size to those of the magnesium carbonate are obtained. 

The same results are obtained by adding magnesium carbonate to an aqueous solution of ammonium bifluoride and ammonium hydroxide and warming to 60°C (12). The resulting precipitate is ammonium magnesium fluoride [35278-29-6] which settles rapidly. 

A stannic chloride pentahydrate—ammonium bifluoride formulation for fireproofing wool is commercially available and used in New Zealand and AustraHa (20) (see Elal retardants for textiles). 

Reduction of Beryllium Fluoride with Magnesium. The Schwen2feier process (11) is used to prepare a purified, anhydrous beryUium fluoride [7787-49-7], Bep2, for reduction to the metal. BeryUium hydroxide is dissolved in ammonium bifluoride solution to give a concentration of 20 g/L... 

Aluminium bromide and chloride Ammonium bifluoride and other bifluorides... 

AMMO 2.5 EC , cypermetlu-in, 13 Ammonia, 13 Ammonium acetate, 13 Ammonium arsenate, 13 Ammonium benzoate, 13 Ammonium bicarbonate, 13 Ammonium bifluoride, 14 Ammonium bisulfite, 14 Ammonium carbamate, 14 Ammonium carbonate, 14 Ammonium chloride, 14 Ammonium chlorplatmate, 14 Ammonium clu omate, 14 Ammonium citrate, 14 Ammonium diclu omate, 14 Ammonium fluoride, 14 Ammonium fomiate, 15 Ammonium hexafluorosilicate, 15 Ammonium hydroxide, 15 Ammonium metavanadate, 15 Ammonium molybdate, 15 Ammonium nitrate, 15 Ammonium oxalate, 15 Ammonium perfluorooctanoate, 15 Ammonium persulfate, 15 Ammonium phosphate, 15 Ammonium picrate, 16 Ammonium salicylate, 16... 

Tin-nickel alloy coatings are deposited from a bath containing stannous chloride, nickel chloride, ammonium bifluoride and ammonia " . The useful deposit contains 65% tin and the conditions are maintained to obtain... 

C) for cast iron and up to 140 °F for marstenitic SS (60 °C). It is widely used where silicates are present with the iron oxides. Typically, 5 to 7.5% HC1 is employed. The ammonium bifluoride normally is present at 0.5%, but it may be increased to a maximum of 1.5% for a boiler that has not been cleaned for many years. The presence of hydrofluoric acid (HF), which is formed by the reaction of ammonium bifluoride with HC1 (see equation), tends to increase the rate of iron oxide dissolution and reduce the corrosion rate of exposed steel, when compared to using HC1 alone. This is due to the stability of the hexafluoroferric ion (FeFg3 ), which prevents the ferric ion from corroding exposed steel. 

Derivations of the Citrosolve process use the addition of ammonium bifluoride in the first stage and later the addition of sodium bromate as an improvement over air or sodium nitrite. 

Where silicates are present and hydrofluoric acid is required, the most usual means of addition is through the use of ammonium bifluoride. (See Section 13.4.4.1, Solvents for Removing Iron Oxides, Hydrochloric Acid and Ammonium Bifluoride). 

Aluminium sulphate Ammonium bifluoride Ammonium bisulphite Ammonium bromide Ammonium persulphate Antimony trichloride Beryllium chloride Cadmium chloride Calcium hypochlorite Copper nitrate Copper sulphate Cupric chloride Cuprous chloride Ferric chloride Ferric nitrate... 

The actual fluoride-forming reaction in the ammonium bifluoride route is hydro-fluorination. Hydrogen fluoride, which is present in chemical combination in the bifluoride, is readily released on heating. Bifluorides are easier to handle than hydrogen fluoride. The particular advantage of ammonium bifluoride over other alkali hydrogen fluorides is that it is volatile, and thus can be readily distilled out from the reaction mixture. 

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