ANALYTICAL CHEMISTRY
1424
Hill, U. T., unpublished work. (7) Hummel, R. A., Sandell, E. B., A n a l . C'hitn. Bcta 7 , 308 (1952). ( 8 ) Hutchinson, G. E., J%'ollack, 4.,Trans. Conn. Acad. Arts Sci. 35, 73 (1943). (9) Ikenberry, L. C., Thomas, A , , ASAL. CHEM.23, 1806 (1951). ( l O j Kassner, J. L., Ozier, 11.A, Ibid., 23, 1453 (1951). (11) Luke, C. L., Braun, K . C., Ibid., 24, 1120 (1952). (12) L'Iayr, C., Gebauer, A . , 2 . anal. Chetn. 113, 189 (1938). (13) Milher, T., Ibid., 113, 83 (1938). (14) Millner, T., Kunos, F., Ibid., 113, 102 (1938). (15) Pellowe, E. F., Hardy, F. R . F., Analyst 79, 225 (1954). (16) Richter, F.. 2. anal. Chem. 126,426 (1943). (6)
(17) Ibid., 127, 113 (1944). (18) Saxer, E. T., Jones, E. W., Blast Furnace atid Steel Plant 39, 445, 549 (1951). (19) Schulta, G., "Farbstofftabellen," Akedemixhe Verlagsgesellschaft, Leipzig, 1931.
(20) Sherman, M.,Division of Analytical Chemistry, 118th Meeting. ACS, Chicago, Ill., 1950. (21) Thrun, W. E., ~ ~ N A LCHEM. . 20, 1117 (1948).
RECEIVED for review March 17, 1955. Accepted M a y 23. 1956. Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., March 1 , 1955.
X-Ray Diffraction Powder Patterns of the Calcium Phosphates A. 0 . MclNTOSH and W. L. JABLONSKI Central Research Laboratory, Canadian Industries, Ltd., McMastervilIe, Que., Canada
'The x-raj diffraction powder patterns of 15 calcium phosphates are reported. The monocalcium and dicalcium orthophosphates used as starting materials )t ere of commercial origin. The tricalcium orthophosphate was obtained by precipitation from solution.
T
HE calcium phosphates are important commercially as fer-
tilizers and mineral supplements. T h e common naturally occurring form is phosphate rock, but numerous other calcium phosphates are kno1v-n. The literature on these is voluminous (I, 2, 5, 9, 10) and sometimes contradictory. X-ray diffraction has proved a convenient method for identifying the cryst,alline calcium phosphates. Because the different polymorphs of the same compound can vary greatly in degree of availability to animals and plants, the distinction may be of considerable economic importance (11, 1 4 ) . Crystal structure studies have been reported on only a small number of the calcium phosphates, probably because of the difficulty of obtaining single crystals. Apatite (3), a-tricalcium orthophosphate (13): p-tricalcium orthophosphate (7, l a ) , and dicalcium orthophosphate dihydrate ( 4 ) have been investigated by single-cryst,al methods. I n most, cases, however, only the powder diffraction data are available. The x-ray method requires a file of reference standards, and xra>- data on 15 calcium phosphates have been prepared (Tables I :mtl 11). The American Society for Testing Materials Index of 1 - R a y Diffraction D s t a lists 24 calcium phosphate patterns, but as there are tmo or more sets of data for several of the phosphutej, only 11 different compounds are represented. D a t a on these compounds are included here. Of the additional four, t x o (&calcium metaphosphate and 7-calcium pyrophosphate) appear to have no published x-ray poxvder data. X-RAY APPARATUS AND TECHNIQUE
A photographic technique was employed, the cameras being 14.32 cm. in diameter. The finely ground sample was mounted either in collodion capillaries or in wedge form. TJ7hen the material was formed by heating, the x-ray pattern was obtained after quenching to room temperature. Copper radiation (A = 1.5418 A . ) filtered through nickel foil was employed throughout. T h e intensities were estimated visually by comparison with a standard intensity scale, vhich was prepared by exposing film to the x-ray beam for accurately timed periods. A slit collimating system, approximately 0.5 X 1.0 mm. in aperture, was used.
The tricalcium phosphates were obtained from tricalcium orthophosphate, which was prepared from ammonium phosphate and calcium chloride. The calcium oxide-phosphorus pentoxide ratios of some samples of these st,arting mat,erials were as follows: CaO/PzOh Measured Theoreticar Monocalcium orthophosphate monohydrate (Mallinckrodt) Monocalcium orthophosphate monohydrate (Monsanto) Dicalcium orthophosphate (Allied Chemical) Tricalcium orthophosphate hydrate
0.84
1.0
1.10
1.0
2.id 3 01;
2.0 3.0
These ratios illustrate the variations from theoretical composition that occur even in reagent grade calcium phosphates. Except in the instance described below, no evidence was found t h a t the structures of the ignition products were changed by the presence of impurities. MONOCALCIUM PHOSPH.ATES
Monocalcium orthophosphate hydrate, when heated a t 130" C. changes to the anhydrous form. When heated in air a t 250" C., the anhydrous monocalcium phosphate becomes noncrystalline. Further heating to 500' C. forms p-calcium metaphosphate. Some samples of monocalcium orthophosphate \Then heated at 400" C. form &calcium metaphosphate. It is believed that the formation of this compound is due to the presence of dicalcium phosphate as impurity. \Then a portion of the sample of monocalcium orthophosphate that formed &calcium metaphosphat,e was heated at, 300' C., the x-ray pattern of dicalcium orthophosphate was obtained. At t'his temperature, the monocalcium phosphate is noncrystalline. When some of t'he same sample of monocalcium orthophosphate was recrystallized, the pattern of 8-calcium metaphosphate could not be obtained. When &calcium metaphosphate is heated to 700" C., p-calcium metaphosphate is obtained. If monocalcium orthophosphate is heated at 270" to 280' C. in the presence of steam, calcium acid pyrophosphate is formed. If this is heated in steam a t 325' C., a compound described by Hill and coworkers (10) as tetracalcium dihydrogen hexaphosphate forms. When the acid pyrophosphate is heated in air a t 340" to 360" C., 7-calcium metaphosphate results. Heating this in air a t 450" to 500" C. gives p-calcium metaphosphate. The a-calcium metaphosphate is reported (11) to form at above 963" C., b u t this compound, which melts at 984" C., was not obt ained.
PREPARATION O F MATERIALS
DICALCIUM PHOSPHATES
The starting materials for the preparation of the mono- and dicalcium phosphates n-ere obtained from commercial sources.
Dicalcium phosphate dihydrate was obtained as a commercial sample (Monsanto) and also by crystallization from a 25% acetic
V O L U M E 2 8 , NO. 9, S E P T E M B E R 1 9 5 6
1425
acid solution of dicalcium phosphate (Allied Chemical). The dihydrate occurs naturally as the mineral brushite. When dicalcium phosphate dihydrate is heated a t 180' C., the anhydrous form is obtained. Heating a t 320" to 340" C. gives ycalcium pyrophosphate. At 700' C. the @ form is obtained. Heating this at 1200" C gives a-calcium pyrophosphate, A hydrated calcium pyrophosphate can be prepared from calcium chloride and sodium pyrophosphate. This is noncrystalline and is described by Hill and coworkers ( I f ) as the tetrahydrate. Khen heated at 600" C., it forms @-calcium pyrophosphate. The reaction betu een excess sodium pyrophosphate and calcium chloride gives a ci~stallineproduct, but when heated at 600" C. this doe5 not form anhydrous calcium pyrophosphate. The chemical aualj-sis indicates that this compound is a calcium sodium pyrophosphate.
Tricalcium orthophosphate hydrate has the apatite structure which is possessed also by fluorapatite, chlorapatite, and hydroxyapatite. The isomorphism of these compounds makes it difficult to distinguish them by x-ray methods. However, there are minor differences in the unit cell parameters, so that a precise technique is capable of discriminating between the isomorphs (6, 15).
Table I.
Three Strongest and Innermost Lines of the Calcium Phosphates (Intensities given in parentheses)
Compound Nonocalcium orthophosphate monohydrate Monocalcium orthophosphate Calcium acid pyrophosphate Tetracalcium dihydrogen hexaphosphate &Calcium metaphosphate ?-Calcium metaphosphate 8-Calcium metaphosphate Dicalcium orthophosphate dihydrate Dicalcium orthophosphate ?-Calcium pyrophosphate @-Calciumpyrophosphate a-Calcium pyrophosphate Tricalcium orthophosphate hvdrate p-Tiicalcium orthophosphate a-Tricalcium orthophosphate
TRICA LCIUM PHOSPHATES
The starting material for the tricalcium phosphates was tricalcium orthophoPphate hydrate. This n-as prepared by precipitation from a solution of diammonium hydrogen phosphate and calcium chloride, the p H being controlled with aqueous ammonia so that at, the end of the reaction the preparation was a t p H 9. The analysis of the solid shows a calcium oxide-phosphorus pentoxide ratio of approximately 3.0, corresponding t'o that of tricalcium orthophosphate. The existence of tricalcium orthophosphate hydrate as n distinct compound has been questioned (8). It has been suggested that it is hydroxyapatite n-ith adsorbed or occluded calcium phosphate of one of the acid forms.
3rd
Innermost
1st
2nd
3.90 (100)
11.75 ( 81)
3.71 (81)
11.75 (81)
3.63 (100)
3.50 ( 64)
3.06 (51)
7.23 (11)
3.35 (100)
3.19 ( 58)
3.74 (47)
3.14 3.54 3.49 3.74
(100) (100) (100)
3.58 2.83 2.76 3.52
( 58) ( 30) ( 65)
2.79 3.15 4.76 4.58
(24) (17) (46) (69)
11.8 5.54 5.77 7.06
4.23 3.38 2.94 3.04 2.00
(100) (100) (100) (100) (100)
3.04 2.99 3.11 3.23 3.33
( ( ( ( (
91) 88) 65) 62)
7.62 1.74 3.35 2.76 2.11
(75) (57) (42) (57) (63)
7.62 (75) 6.83 (24) 4.55 ( 7 ) 6.02 ( 9) 11.5 ( 3)
2.80 1100)
3.44
(
57)
1.94 143)
8.19 1. 9),
2.88 (100)
2.61 ( 71)
3.21 (53)
8.13 (11)
2.90 (100)
3.89 ( 43)
3.67 (43)
7.28 ( 7)
(100)
(100)
80)
5,42 ( 4) ( 3) ( 2) ( 8)
(19)
Monocalcium orthophosphate monohydrate
130' C. Monocalcium orthophosphate
+.
calcium metaphosphate (amorphous) 250" C.
270-280' C. (steam) Tetracalcium dihydrogen hexaphosphate
+
300-330" C. (steam)
Calcium acid pyrophosphate
340-360' C. 7-Calcium metaphosphate 450-500O C.
1
p-Calcium metaphosphate
J
450-500" C
970'C.
a-Calcium metaphosphate Monocalcium Phosphates and Derivatives Dicalcium orthophosphate dihydrate
I 150-180" C. 4 Dicalcium orthophosphate
1
1 -
320-340' C.
yCalcium pyrophosphate
/ .1
Tricalcium orthophosphate hydrate
700-750" C.
Calcium pyrophosphate tet rahydrate @-Calciumpyrophosphate (amorphous ) 600' C. I
1140" C. a-Calcium ppophosphate Dicalcium Phosphates and Derivatives
680" C.
p-Tricalcium orthophosphate 1150° c.
a-Tricalcium orthophosphate Tricalcium Phosphates
ANALYTICAL CHEMISTRY
1426
Table 11. X-Ray Powder Diffraction Data d , A. 1/11 Monocalcium Orthophosphate Monohydrate
d , A.
11.75 5.70 1.93 4.45 4.34 4.17 3.90 3.71 3.60 3 38 3 20 3.01 2.96 2.86 2.80 2.74 2.69 2.58 2 46 2.42 2.16 2.09 2.03 2.00 1.96 1 .93 1.86 1.84 1.80 1 77 1.75 1.73 1.71
5 42 4 78 4.44 4.07 3.74 3.33 3.19 2 Y5 2.85 2 81 2.78 2.70 2.61 2 32 2 42 2 34 2.31 2.25 2 23 2 18 2 14 2 07 2 04 1.94 1 93 1.88 1 84 1 77 1 72 1 68 1 65 1.60 1.59 1.53
4 9 27 9 47 100 58 4 4 4 4 20 4 6 3 8 8 8 10 24 3 9 4 16 13 14 24 33
1.44 1.40 1.35 1.84
4
1.67
1.60 1.58 1.55 1.53 1.48
81 9 50 9 9 12
100 81 7 12 35 17 50 8 8 8 31 17 13 13 13 13 13 35 13 17 9 9 35 13 13 13 17 13 I? 9 5 7
I/Ii
Calcium Acid Pyrophosphate
1 50
5 10
13 16 13 4 22
a, A.
I I,
8-Calcium Metaphosphate 5 51 4.72 4.30 3.93
3.54
3.33 3 15 3.05 2.92 2.83 2.69 2 60 2 50 2 31 2.22 2 15 2 08 2 01 1.87 1 81 1.77 1 69 1 66 1.64 1.61 1.58 1.57 1.50 1 47 1 30 1.27 1 . 13
2 2 2 2 100 2 17 4
4 30 4 17
: 9
9
4 6 6 7
Ij
2 7
2 > 4
3 7
9 7
1
1
d , -1.
1/11
@-Calcium Metaphosphate 3.01 2.90 2.85 2.76 2.66 2.62 2 54 2.49 2.40 2 32 2 25
;,:; 2 03 1.97 1.92 1.81 1.78 1.72 1.69 1.68 1.65 1,62 1 6O 1.57 1.56 1.52 1.48 1 39 1 37 1.30 1 28
,
