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Thermal gravimetric studies of orthophosphates
IHORG.
HUCL.
CHEM.
LETTERS
Yol.
4
PP-
559-562,
1968.
Pergamon Press.
Prineed
In
Great Sdhsln,
THERMAL GRAVIMETRIC STUDIES OF ORTHOPHOSPHATES Lester Steinbrecher and J. Fred Hazel
Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania (R~v~
Disodiumorthophosphate at elevated temperatures
26 Ap~l 19~)
produces tetrasodltun pyrophosphate when calcined
(I).
Monosodlum orthophosphate, NaH2P04, when heated
to a temperature of about 250°C yields Na2H2P207, and this in turn produces insoluble metaphosphates after heating to higher temperatures
(2).
These reac-
tions were investigated by means of water vapor pressure measurements over various phosphate systems (3).
No thermal analysis studies of sodium ortho-
phosphate mixtures have appeared in the literature. The present paper deals with a thermogravimetric analysis of trisodium orthophosphate~
dlsodlum orthophosphate~ monosodium orthophosphate~
phosphorus
pentoxide, orthophosphoric acid, and mixtures of the latter with trisodium phosphate.
Experimental Apparatus.
The thermobalance has been described elsewhere (4~ 5).
Procedure.
The TGA was carried out in a static air atmosphere at a heating
rate of 8°/minute to a temperature of 9OO°C with 100 m E samples. Reagents.
The chemicals were BakerWs analytical grade Na3PO4*I2H20 ~
N a 2 H P 0 4 * ~ O ~ NaH2P04, 85~ phosphoric acid and anhydrous phosphorus pentoxide. Results Trisodium at
60°p b u t t h e
orthophosphatedodecahydrate loss
T h e r e was no w e i g h t to 230 ° with
was n o t c o m p l e t e loss
a b o v e 200 ° .
a sample of this
began to lose
until
a temperature
Dural
(6,
compound.
$59
its
hydration
water
o f 200 ° was r e a c h e d .
7) o b s e r v e d
a weight
loss
up
560
STUDIES OF ORTHOPHOSPHATES
Vol. 4, No. 10
The protonated phosphates displayed stepwise reactions occurring in different temperature ranges. Disodium Orthophos~hate Heptahydrate. and
Water of hydration was lost between ~O°
140°: Na2HPO4.7H20-'~
Condensation occurred at 330 ° to 340o°
Na2HPO 4 + 7H20
i.
Dural (6, 7) reported a condensation
step between 318 ° and 355 ° with dlsodi,-- orthophosphate: 2Na2HP04-'--~ Na4P207 + H20 Monosodium Orthophosphateo
2.
This compound showed two condensation steps, the
first at 200 ° to 240°~ the second at 320 ° to 380°: l. 2000-240 ° 2. 320°-380 °
2NaH2PO4----~ Na2H2P207 Na2H2P207--~2NaPO 3
+
H20
3.
+
H20
4.
No studies with a thermal balance appear to have been made with monosodium orthophosphate, but Boulle and Domlne-Berges (8) found with KH2PO 4 that a reaction analogous to the first stepbeglns at 2200° Phosphorus Pentoxide, Anhydrous.
The compound was thermally stable to 6OO°C.
Sublimation commenced at 6OO°C and was complete at 780°C. Orthophosphorlc Acid.
Eighty-flve percent phosphoric acid was stable up to
IO0 ° . A gradual weight loss was evident from I00 ° to 640 ° which was equlvalent to formation of P205 ° A sharp weight loss was observed from 640° to 780°whlch was analogous to the sublimation temperature seen for phosphorus pentoxide. Sodium Or thophosphate-Orthophosph0r..ic
Acid Mixtures.
A mixture of two moles
of trlsodlum orthophosphate and one mole of orthophosphorlc acid yielded a th~rmogram indicating the formation of disodium orthophosphate in the temperature range 80 ° to 160°~ and its condensation to tetrasodlum pyrophosphate at 330 ° to 340 ° (vide supra). 2Na3PO4*I2H20 + ~ P O 4 ~ 3 N a 2 H P O
4 + 12H20
2Na2HPO4----~ Na4P207 + H20
5. 2.
A mixture of two moles of phosphoric acid and one mole of trisodium orthophosphate produced a synthesis of NaH2PO 4 in the temperature range 60°-170°:
Vol. 4, He. 10
STUDIES OF ORTHOPHOSPHATES
I (.g t&J
--ff m ~
..
.-~D.
._. V ;
~
561
" ' %
4,
No Ht P04('IONo=H=PtOTTONoP03)
Na=HPO4.?HtO(TONo4P=07) H3P04(85%) TOPtOsANHYDROUS Na3 PO4 • 12HzO (TO No3 P04)
& o5 (ANHYDROUS)TO PrOs -..o--o-- 21"~P04: INo=PO4,121"~O(SEENoI-t=P04) •--,o---.o-,- I I'~ P04; 2 No3PO4" 12 H~O(SEE NotH P04) --
0
150
300
450 600 750 TEMPERATURE, °C FIG. I THERMOGRAMS OF PHOSPHATES AND PHOSPHATE MIXTURES
g00
S62
STUDIES OF ORTHOPHOSPHATES
Na3PO4.12H20 + 2H3PO4
Yol. 4, No. 10
~ 2NaH2PO4 + 1 2 ~ 0
Further heating resulted in the two condensation steps noted above:
6. reaction 3
at 2000-2400; reaction 4 at 320° to 340°. Themograms of the individual phosphates and mixtures are shown in Fig. l. References i. VAN WAZER, J. R., Phosphorus and Its Compounds, Vol. I, p. 618. Intersclence Publlshers, Inc., New York, 1958. 2. VAN WAZER, J° R., Phosphorus and Its Compounds, Vol. I, p. 607. Intersclence Publlshers, Inc., New York, 1958. 3. g/EHL, S. J°, WALLACE, G. H., J. Am. Chem. Soc., 49j 376 (1927). 4. MEYER, R. A.p HAZEL, J. F., ML~ht%BBpW. M., Anal. Chlm. Acta, 31, 419 (1964). 5. MEYER, R° A., Dissertation, University of Pennsylvania, Philadelphlap Pa., UoSoAo (1963). 6. DUVAL, C°, Inorganic Thermogravimetrlc Analysis, 2nd Revised Ed., p. 201, E1sevler Publishing Company, New York, 1963. 7. DUVAL, C., Anal. Chim. Acta~ 13, 32 (1955). 8. DUVAL, C°, Inorganic Thermogravlmetric Analysls, 2nd Revised Ed., p. 258. Elsevier Publlshlng Company, New York, 1963.
HUCL.
CHEM.
LETTERS
Yol.
4
PP-
559-562,
1968.
Pergamon Press.
Prineed
In
Great Sdhsln,
THERMAL GRAVIMETRIC STUDIES OF ORTHOPHOSPHATES Lester Steinbrecher and J. Fred Hazel
Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania (R~v~
Disodiumorthophosphate at elevated temperatures
26 Ap~l 19~)
produces tetrasodltun pyrophosphate when calcined
(I).
Monosodlum orthophosphate, NaH2P04, when heated
to a temperature of about 250°C yields Na2H2P207, and this in turn produces insoluble metaphosphates after heating to higher temperatures
(2).
These reac-
tions were investigated by means of water vapor pressure measurements over various phosphate systems (3).
No thermal analysis studies of sodium ortho-
phosphate mixtures have appeared in the literature. The present paper deals with a thermogravimetric analysis of trisodium orthophosphate~
dlsodlum orthophosphate~ monosodium orthophosphate~
phosphorus
pentoxide, orthophosphoric acid, and mixtures of the latter with trisodium phosphate.
Experimental Apparatus.
The thermobalance has been described elsewhere (4~ 5).
Procedure.
The TGA was carried out in a static air atmosphere at a heating
rate of 8°/minute to a temperature of 9OO°C with 100 m E samples. Reagents.
The chemicals were BakerWs analytical grade Na3PO4*I2H20 ~
N a 2 H P 0 4 * ~ O ~ NaH2P04, 85~ phosphoric acid and anhydrous phosphorus pentoxide. Results Trisodium at
60°p b u t t h e
orthophosphatedodecahydrate loss
T h e r e was no w e i g h t to 230 ° with
was n o t c o m p l e t e loss
a b o v e 200 ° .
a sample of this
began to lose
until
a temperature
Dural
(6,
compound.
$59
its
hydration
water
o f 200 ° was r e a c h e d .
7) o b s e r v e d
a weight
loss
up
560
STUDIES OF ORTHOPHOSPHATES
Vol. 4, No. 10
The protonated phosphates displayed stepwise reactions occurring in different temperature ranges. Disodium Orthophos~hate Heptahydrate. and
Water of hydration was lost between ~O°
140°: Na2HPO4.7H20-'~
Condensation occurred at 330 ° to 340o°
Na2HPO 4 + 7H20
i.
Dural (6, 7) reported a condensation
step between 318 ° and 355 ° with dlsodi,-- orthophosphate: 2Na2HP04-'--~ Na4P207 + H20 Monosodium Orthophosphateo
2.
This compound showed two condensation steps, the
first at 200 ° to 240°~ the second at 320 ° to 380°: l. 2000-240 ° 2. 320°-380 °
2NaH2PO4----~ Na2H2P207 Na2H2P207--~2NaPO 3
+
H20
3.
+
H20
4.
No studies with a thermal balance appear to have been made with monosodium orthophosphate, but Boulle and Domlne-Berges (8) found with KH2PO 4 that a reaction analogous to the first stepbeglns at 2200° Phosphorus Pentoxide, Anhydrous.
The compound was thermally stable to 6OO°C.
Sublimation commenced at 6OO°C and was complete at 780°C. Orthophosphorlc Acid.
Eighty-flve percent phosphoric acid was stable up to
IO0 ° . A gradual weight loss was evident from I00 ° to 640 ° which was equlvalent to formation of P205 ° A sharp weight loss was observed from 640° to 780°whlch was analogous to the sublimation temperature seen for phosphorus pentoxide. Sodium Or thophosphate-Orthophosph0r..ic
Acid Mixtures.
A mixture of two moles
of trlsodlum orthophosphate and one mole of orthophosphorlc acid yielded a th~rmogram indicating the formation of disodium orthophosphate in the temperature range 80 ° to 160°~ and its condensation to tetrasodlum pyrophosphate at 330 ° to 340 ° (vide supra). 2Na3PO4*I2H20 + ~ P O 4 ~ 3 N a 2 H P O
4 + 12H20
2Na2HPO4----~ Na4P207 + H20
5. 2.
A mixture of two moles of phosphoric acid and one mole of trisodium orthophosphate produced a synthesis of NaH2PO 4 in the temperature range 60°-170°:
Vol. 4, He. 10
STUDIES OF ORTHOPHOSPHATES
I (.g t&J
--ff m ~
..
.-~D.
._. V ;
~
561
" ' %
4,
No Ht P04('IONo=H=PtOTTONoP03)
Na=HPO4.?HtO(TONo4P=07) H3P04(85%) TOPtOsANHYDROUS Na3 PO4 • 12HzO (TO No3 P04)
& o5 (ANHYDROUS)TO PrOs -..o--o-- 21"~P04: INo=PO4,121"~O(SEENoI-t=P04) •--,o---.o-,- I I'~ P04; 2 No3PO4" 12 H~O(SEE NotH P04) --
0
150
300
450 600 750 TEMPERATURE, °C FIG. I THERMOGRAMS OF PHOSPHATES AND PHOSPHATE MIXTURES
g00
S62
STUDIES OF ORTHOPHOSPHATES
Na3PO4.12H20 + 2H3PO4
Yol. 4, No. 10
~ 2NaH2PO4 + 1 2 ~ 0
Further heating resulted in the two condensation steps noted above:
6. reaction 3
at 2000-2400; reaction 4 at 320° to 340°. Themograms of the individual phosphates and mixtures are shown in Fig. l. References i. VAN WAZER, J. R., Phosphorus and Its Compounds, Vol. I, p. 618. Intersclence Publlshers, Inc., New York, 1958. 2. VAN WAZER, J° R., Phosphorus and Its Compounds, Vol. I, p. 607. Intersclence Publlshers, Inc., New York, 1958. 3. g/EHL, S. J°, WALLACE, G. H., J. Am. Chem. Soc., 49j 376 (1927). 4. MEYER, R. A.p HAZEL, J. F., ML~ht%BBpW. M., Anal. Chlm. Acta, 31, 419 (1964). 5. MEYER, R° A., Dissertation, University of Pennsylvania, Philadelphlap Pa., UoSoAo (1963). 6. DUVAL, C°, Inorganic Thermogravimetrlc Analysis, 2nd Revised Ed., p. 201, E1sevler Publishing Company, New York, 1963. 7. DUVAL, C., Anal. Chim. Acta~ 13, 32 (1955). 8. DUVAL, C°, Inorganic Thermogravlmetric Analysls, 2nd Revised Ed., p. 258. Elsevier Publlshlng Company, New York, 1963.