The System Ammonia-Pyrophosphoric Acid-Water at 0' and 25OC. THAD D. FARR a n d JULIUS D. FLEMING Division of Chemical Development, Tennessee Valley Authority, Wilson Dam, Ala.
Phase relationships in the system NH~-H~PzO~-HZO over the pH range 4 to 8 were determined at 0' and 25OC. At OOC., the saturating phases are (NHd)zHzPz07, ( NH4)3HP&.H20, and ( NHI)~PzO~.HD. These three compounds and (NH4)4Pz07 are the saturating phases at 25' C.
AMMONIUM
polyphosphate fertilizers, which are mixturesof salts of ortho-, pyro-, and more highly condensed phosphoric acids, are prepared by ammoniation of superphosphoric acid (6, 7), and they are finding increasing acceptance. As a part of a study of these materials, measurements were made a t 0" and 25" C. of solubility in the system NH3-H4P2O7-Hz0 over the pH range 4 to 8. The ammonium pyrophosphates and their solutions were prepared by ammoniation and vacuum evaporation of 0.3N pyrophosphoric acid, that was prepared by ion exchange from solutions of recrystallized tetrasodium pyrophosphate. T o minimize hydrolysis of the pyrophosphate, all operations were carried out a t temperatures below 10" C.
Table I. The System N H ~ - H ~ P Z O ~ - H Z O
Liauid Phase Composition, % PzO5 pH N 4.83 7.66 8.23 8.96 9.05 9.24 10.04 10.33 9.26 7.75 6.11 8.33 9.52 11.05 10.69 10.49 10.42 10.61 10.61
11.29 11.55 11.14 11.13 11.12 11.05 10.86 10.52 9.79 9.00 8.53 8.26
20
22.59 30.74 32.24 34.18 31.02 30.88 31.42 32.03 27.36 20.65 28.85 35.34 38.89 42.39 40.27 38.52 37.21 36.22 35.81 35.99 36.60 34.93 35.10 35.12 34.62 33.45 31.82 28.63 24.86 22.67 21.27
... 4.80 4.97 5.09 5.81
. .. .. .
6.50 6.88 7.80 3.51 4.40 4.66 4.84 5.05 5.30 5.75 5.91 6.05
...
6.26 6.40 6.43 6.42 6.42
... 6.79 7.02 7.35 7.95 8.20
Solid Phase Results at 0" C. (NH4)zHzPzOi (NH,)zHzPzO, (NH,)zHzPzO, ( N H ~ ) ~ H P Z O ~ .+H(NH4)zHzP~oi ZO (NHa)3HPz07*HzO (NH,)~HPZO~.HZO (NH~)~HPZO~*HZO (NHI),P>O:.HzO + (NH,)~HPZO~.HZO (NH4)4Pz07*HzO (NHa)rPzO.i.HzO Results at 25" C. (NHdzHzPz07 (NH,)zHzPz07 (NH4)zHzPzOi (NH4)3HPzO,*HzO (NH,)3HPzO:.HzO (NH,)3HPzOi*HzO (NH,)~HPzO~.HZO (NH,)~HPzO~*HZO (NH~)SHPZO~.HZO (NH~)~HPZO~.HZO (NH,)jHPzOj*HzO+ (NH,),PzO, (NH4)dPzO; (NH4)IPzO; (NH,)dPz07 (NHJdPz07 (NH,),PZ07.Hz0 + (NH,)rPzOi (NHI),PzOi.HzO (NH,),Pz07.HzO (NH,)
