Characterization of Heavv Metal Soaps by X-Ray Diffraction R. D. VOLD .LYD G. S. HATTIKVGDI Uniaersitg of Southern California, Los Angeles 7 , Culg. X-ray diffraction patterns were obtained on twenty-five heavy metal soaps a t room temperature after air drying, oven drying, and cooling slowly frem elevated temperatures. These data have potential value in elucidating the behavior of greases, surface coatings, and other products made from these soaps by their solution or mechanical incorporation in oils. It is also possible. to a certain extent, to identify which of several metal soaps is present from t h e appearance of the x-ray diffraction pattern. I n all of the soaps examined, t h e metal ions are arranged in parallel planes separated by a distance somewhat less than twice t h a t of the fatty acid radical. Soaps of zinc, magnesiiim, lithium, and aluminum give patterns different from one another and from the remaining soaps. Calcium, strontium, and barium soaps give patterns similar to one another, more so for strontium and barium than for calcium. Cadmium and mercury soaps are similar to one another, and probably lead stearate should be classified with them. Manganese soaps do not
crystallize well enough to classify the patterns. Iron, cobalt, and nickel soaps occur in a noncrystalline state, best described as pseudo-glassy. Differences between palmitates and stearates of the same metal appear to be minor. With t h e possible exception of the magnesium soaps. i t appears t h a t the heavy metal soaps studied do not form hydrates readily a t room temperature even though adsorbing water, since t h e diffraction patterns generally changed little after the soaps were dried a t 55' to 110" C. After heating to 200" C. (150" C. for soaps of manganese, iron, cobalt, nickel, and mercury) and cooling a t a mean rate of 0.5" to 1.5" per minute, aluminum, iron, cobalt, and nickel soaps, which were essentially noncrystalline initially, showed diffraction patterns unchanged from those originally obtained. Zinc palmitate and lithium stearate had recrystallized completely. A11 the others were apparently in varying stages intermediate between their original crystalline state and a pseudoglassy or undercooled liquid crystalline state.
I
mercury, manganese, iron, cobalt, and nickel, and of the stearates of lead, aluminum (mono), and lithium. These data are utilized chiefly to determine whether i t is possible by this means t o identify a given heavy metal soap and distinguish b e b e e n palmitates and stearates of the same metal or between soaps of different, metals or groups of metals, whether chemically similar metals give similar diffraction patterns indicative of the same crystalform for the soaps, and whether any inferences can be made a? to the molecular arrangement and degree of perfection of crystallinity. The oven-dry soaps mere also studied to see whether loss of the small amounts of water initially present caused changes in the x-ray patterns indicative of hydrate decomposition. Finally, x-ray patterns were determined of the dry soaps after slow cooling from 150' or 200" C. to axertain whether undercooling occurred after heating, or transformation to a different crystal form, or reversion to the original form but with a greater or lesser degree of crystal perfection, took place.
S SPITE of their wide application in industry, the funda-
mental charaoteristics of heavy metal soaps and their role in various industrial preparations have not been investigated systematically. X-ray diffraction patterns of the soaps a t room temperature and the extent t o which recrystallization occurs after thermal treatment are of considerable importance in elucidating the structure of greases, flatting agents, coatings, and ot,her products made from these soaps. Soaps commonly used in the manufacture of lubricating greases are those of sodium, calcium, and aluminum and, to a lesser estent, of barium, lead, and lithium. Soaps of manganese, cobalt, and lead are employed as driers in the paint and varnish industry; aluminum, calcium, and magnesium soaps are used as Batting agents to reduce the gloss of paints and varnishes and also to thicken paints. Aluminum soaps (Sapalm) found estensive use during the mar as thickening agents for the production of jellied gasoline. Iron and chromium soaps have found application in color printing and dyeing. Calcium and magnesium soaps (particularly the oleates) are utilized in the dry cleaning industry. Zinc and magnesium soaps are used largely in dusting powders and in the rubber industry. I n all these fields under.standing of the phase state of the soap, and the changes XThich it may undergo as a result of processing steps or of the action of solvents, may lead t o greatly improved products or processes. The available data on heavy metal soaps are somewhat scanty, and little effort has been made to correlate them with the behavior of the soaps in organic liquids. Some x-ray information has been obtained on calcium, hariuni, and magnesium s t e a r a h ( 1 0 ) and on the application of such data to greases (9), aluminum dilaurate and distearate (8),aluminum dilaurate in cyclohesane and benzene ( T ) , thallium stearate and oleate (6), calcium palmitate nionohydrate ( 4 ) , and various preparations of cilcium qtearate ( 2 2 ) and systems of calcium stearate in cetane (13). The present article reports the results of s-ray diffraction analysis a t room temperature of air-dry palmitates and stearates ,>f calcium, strontium, barium, magnesium, zinc, cadmium,
MATERIALS A K D PROCEDURE
The majority of the soaps r e r e prepared in Bombay, India, from Kahlbaum-Scheming pnlmitic acid and Merck's stearic acid. The follon-ing constants, indicative of the quality of these acids, were determined on samples of fattv acid recovered by decomposition of the calcium soaps with hydrochloric acid: Acid Palmitic (Kahlbaum-Soherring) Stearic (Merck) Stearic (recovered from >'letasap soaps) Theoretical for pure stearic
Equivalent Weight 256 289 282 284
Iodine
Number
...
3.0 3.6 0.0
CapillarJ M.P.. a C.
48-49 54-56 56-67 69.6
Neither the stearic nor pdmitic acid approximates the purr chemicals very closely, which may give rise to marked differences in the x-ray patterns of the sosps. However, the patterns obtained are probably reasonably representative of what might be expected of commercially available, heavy metal stearates and palmitates. T o test this hypothesis, patterns were also obtained on stearates of calcium, barium, lead, aluminum (mono), and lithium supplied 2311
INDUSTRIAL AND ENGINEERING CHEMISTRY
2312
as such Through the cou t h e 1Ictasap Cheniic:~]Company. ressed technical stearic :xid and, They were made from consequently, must eo onsiderable nmounts of unsaturated f n t t y acids antl homologous saturated fatty acitis. Colistants of this stearic acid are also given in the preceding t:lhIe. PREPARATIOS OF SOAPS. Sixty grams of the fatty :icitl Tyei'e dissolved in 150 ml. of absolute ethyl alcohol at 60" C. and neutralized to phenolphthalein with a 2 -1-solution of carbonate-free sodium hydroxide. The resulting gel was liquefied by warming, antl the solution added slon.1~-n-ith vigorous stirring to a hot sol~ltion of the desired metal chloride in 50 volume 70alcohol in water. The salt was in slight excess of that required for conipletc reaction. The precipitated soap was washed free of soluble impurities with distilled water, and then of any adherent unreacted fatty acid or alkali soap v i t h alcohol and acetone. ;\fter pressing out solvent, the soaps xere oven-dried a t about 100" C., powdered, and stored in glass-stoppered bottles. The calcium, strontium, and barium soaps were dried at 110" C. The drying temperature is significant, since it has been shon-n ( 1 2 ) that some soaps may form stoichiometric hydrates on precipitation from solution, which are not readily reformed from adsorbed water after they have once been decomposed. Further, there is the possibility of transition to a liquid crystalline form on drying a t elevated temperatures, n.hich may or may not recrystallize on cooling. ANALYSIS.The metal content of the soaps v-as determined by standard quantitative procedure appropriate to the metnl. I n a few cases the fatty acid anion was also determined. I n all cases the metal content agreed closely m t h the theoretical value for the normal soap-Le., M ( F A ) , Ivhere M represents the metal, n its valence, and F A tlie fatty acid radical. However, gross analytical data alone cannot distinguish, among soaps whose metals form weak bases such as iron, between the neutral soap and partially hydrolyzed soaps such as FeO(Str).H(Str) or Fe(OH)(Str),.H(Str). Several months after their preparation, the n-atcr content of the soaps was determined by drying to constant weight in an air oven, or under vacuum, a t various temperatures. Table I gives the results. All of the soaps except those of magnesium and calcium had taken up substantially less water than would be required to form a hydrate. Calcium soaps had taken up approsimately one mole of water per mole of soap, and niagnesium soaps some!\-hat more than this.
RE O F HEAVY ~IETA SOAPS L AFTER TABLE I. ~ I O I S T UCOXTENT STORAGE
C.
found
hydrate
4.05 3.04 0.60 0.20 1.04
3.25 3.16 2.92 2.70 3.03
6.61 3.56 0.30 0.13 1.24
2.95 2.88 2.68 2.49 2.77
90 110 110 110 95
Cd
0.53
2.81 2.47 3.08 2.14 3.07 3.07
0.49 0.27 0.30 0.75 1.13 0.90
2.58 2.29 2.82 1.95 2 80 2.80
95 90
co
0.51 0.91 1.62 1.21
.. .. .. ..
2 83 0.21 1.16 0.10 0.52
2.88 2.49 4.97 2.27 5.84
M g Ca Sr Ba %n
3 Fe Ni
Ca
3 Pb
Li
0.13
..
.. .. ..
..
55
55
g" 35
110 110 110 75 110
Under vacuum. AI(OH)z(Str).
Patterns were obtained with a S o r t h X-RAYDIFFRACTIOK. American Philips Company x-rav spectrometer using CUI& radiation. The procedure and sample preparation have already been described ( l a ) . The instrument yields an automatically recorded curve of the intensity of diffracted x-rays us. diffraction angle ( 2 8 ) . Bragg spacings (din), corresponding to interplanar separations of the reciprocal crystal lattice, weIe calculated from the peaks in this curve using the relation n X = 2d sin e, where X = 1.5418 A ( 1 ) . The positions of the peaks were measured a t the center of the peak a t half maximum height, except for poorlv resolved peaks of low intensity, in which case the positions of the peak maxima vere taken. Data for all the soaps, including the positions and relative intensities of the lines or halos, are given in Tables I1 and 111.
Vol. 41, No. 10
1II.)\\.c.vc~~, sincc the degrcc I J ~crJ-*tdliiiity can be iern h t ill tei'iii,q of the "sliarpiiess" of the pattern, representat ivc fivefold rrductions of the original curve3 of intensity z'.?. swtteriug angle :ire s h o x n for fourteen of tlie air-dry so:ips in Figurcl 1. Figiirr 2 givcs the patterns for the stearates :iiitl 1):tlniitates of calcium :md mngnchiurn in the air-dry state, after oven drying. arid after cooling don-ly from 200" C. They show clearly the drastic clinngc~si n the nxture of the soap n-hicli can he induced by heating. AI'I'F:ARA\CE
A\D O R I G I l - OF DIFFRACTION PATTERNS
I~xaniinatioiiof a typical diffraction pattern such as that for culciuni stearate in Figure 1 shows that it con diarp, fairly intense peaks betJveen 28 = 3" and l o 0 , a second group of shai,p intense peaks between 20" and 30°, and a number of fainter peaks (not very clear on the reduced drawings) ypread over the whole angle range. The peaks a t small angles arise from diffraction of x-rays by planes of atoms whose separation is proportional to the length of the soap molecule. In all the soaps thus far examined the metal ions appear to be arranged in planes between n-hich the fatty acid radicals extend in both directions with their axes inclined somewhat to the plane containing the metal ions. The distance between the planes is equal approximately to twice the length of the fatty acid radical times the sine of the angle of inclination, since the soap molecules either have double layers of cations with acid radicals extending out on either side, or a single layer n-ith the chains (in the case of a divalent metal) a t 180" nith respect to one another, and fully extended (10, 12). Successive orders of this distance ( d / 2 , d / 3 , d / 4 , etc.) appear as peaks in the diffraction pattern ( d / l and d!2 generally occur at such small angles that values obtained viith the present instrument are inaccurate). The relative intensities of the several orders vary from soap to soap, being a function both of the crystal type and the scattering p o w r of the various atoms for x-rays. The peaks in t.he intermediate angle range arise from the diffraction of x-rays from planes of at'oms separated by much smaller distances than those just described and are thus referred to as short spacings. The numerical values give distances beh e e n planes in the reciprocal crystal lattice and can be directly related to real distances betn.een the molecules only by making assumptions about the crystal type. Kevertheless, the distances involved are those between one molecule and the next mther than distances measured along the molecular axis, so that reference to the short spacings as side spacings is justified. Individual peaks vary considerably in their angular width at half maximum intensity. A good example is seen in comparing the peak at 20 = 21" for the magnesium soaps in Figure 2. h wide peak such as that shown after heating is referred to as a halo. Halos occur when the actual spacing of planes is variable over a range of distances averaging out to that given by the peak center, or when individual crystallites in which the spacing occurs have small dimensions. Broadening of a peak as a result of thermal treatment or dehydration is often accompanied by a marked reduction in its height also. The occurrence of halos is thus indicative either of a molecular arrangement less orderly than that of a three-dimensional crystal-i.e., a glassy state or a liquid crystalline state-of a very small size of crystallites, or of small spatial extent of crystallized regions in the solid. Patterns from the various soaps varied considerably in over-all intensity even with the same experimental procedure. Curiously, soaps of heavy metals, such as barium, lead, cadmium, or mercury, gave far weaker patterns than soaps of light metals, such as lithium or magnesium, despite the higher intrinsic scattering power of the heavy metal atoms. Likexise the general background intensity of incoherently scattered x-radiation varied from soap to soap. The effectis extreme for soaps of iron, cobalt, and nickel, probably owing to fluorescence of the metal ions under the influence of CuKa radiation.
October 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
2313
COMPARISOIV OF PATTERNS OF AIR-DRY SOAPS
t
L O N GS P A C I N G . M o s t of t h e stearates showed a long spacing varying between 45.5 and 49.8 A. with little correlation of the values for different soaps with the ionic radii of their cations. I n fact, the spacing decreases in the order magnesium, calcium, strontium, barium, despite the opposite trend in ionic radii. I t therefore seems that the cations affect the angle of inclination of the molecular axes of the chains to the planes containing the cations. If the double molecule is assuomed to have a length of about 52 A. (its value for asodium stearate, d, l l ) , the angles of inclination vary between 61 and 73". Zinc, lithium, and aluminum stearates display a much shorter jong spacing (41.1, 39.9, and 42.2 A,), corresponding to an angle of inclination of Zinc palmitate likewise only 52'. shows a shorter long spacing than other palmitates (lithium and aluminum palmitates were not examined). If the angle of inclination of the molecular axis were the same for palmitates an{ stearates, a difference of a t least 4 A. would be expected between the long spacings of the palmitate andstearate of the same metal. The actual differences vary from pictically zero to a niasinium of 2.0 A. (for barium). This rvould require that the palmitate chains be more nearly perpendicular to the planes of terminal groups than are the stearates, which seems rather implausible. Holyever, this conclusion is not necessarily proved, since the stearic acid from which all the stearates were prepared gave, for calcium and barium stearates, a long spacing significantly shorter thnn tlint of a number of other I0" available stearic acids [49.8 for pure calcium stearate ( l a ) , compared to the present value of 47.3; 49.4 for XIetasap Figure 1. X-Ray barium stearate compared to the present value of 45.51. SIDE SPACISGS. I t seemed worth while to consider tlie side spacings of the heavy metal soaps from the standpoint of their utility as a means of identifying the presence of a given soap from the appearance of the diffraction pattern, particularly in view of the partial success of Ferguson et a l . (3) n-ith this approach in studying the phases present in aqueous alkali soap systems. Pertinent data are presented in Table I V on the positions and intensities of the prominent lines which seem to vary in a characteristic manner f r o m soap to soap. Some confidence in this scheme is engendered by the fact that samples of calcium and barium stearate from different sources (Tables I1 and 111) gave essentially similar results, although there are differences in intensity and resolution which are probably attributable to varying perfection of crystal structure in the different samples because of varying amounts of impurities. Despite its probable applicability to soaps of the various metals made from commercial fatty acids, this identification scheme may fail if applied to highly purified soaps or soaps made
I
1 e L C I U M STEARATE
67.3A.
4s.sA.
49.3 A. 6
I
--
'
47.7A.
CADMIUM STEARATE
J$--
-
MERCURIC STEARATE
A.BC
\
-
48.1 A .
E
D
MANGANESE STEARATE
-
ON (IC)
STEARATE
OBALT
STEARATE
U&
NICKEL STEARATE,
20"
-
30 '
DIFFRACTION ANGLE (20)
-
46.3 A.
. c I
46-5A. 47.2h. 46.8A.
Ir 90
Diffraction Patterns of Air-Dried Heavy .\letal Stearates by a different technique. Thus, the pattern here reported for the dry calciuni stearate resembles closely that for the monohydrate of the pure soap (12) and differs markedly from that of the pure anhydrous soap. Subsequent rrork in this laboratory has shown that traces of stearic acid reniaining i n the soap are sufficient t o cause such a change in diffraction pattern.
For converiience, letters -1 through E are used to describe reasonably intense lines occurring in each of several general positions in the diffraction pattern (Figure l), although riot neceasnrily at esactly tlie same position for each soap. Although sharply defined experimentally, these represent merely the centers of unresolved bands of spacings rather than a single crystal spacing. The multiple values sonietinies shown under n. single letter refer to the separate values iden~ificd011 a partinlly resolved niultiple peak. Prominent peaks occur in about the same positions for tlie palmitates as for t,he stearates, such differences as do occur being relatively minor. I t is fortunately true that the relative intensity of the different h i e s frequently
2314
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 41, No. 10
TABLE11. X-RAYSPACINGS OF HEAVY METALSOAPS CALCIUM STEARATE Before drying
(A,)
d Long sparing No. of orders S v . deviation
17.3 4 0.15
d/n, .I. Short syacings
After drying
1/40° 0.55
d
..
4
..
0.14
1/40
d / n , .&. 4.413 4.14R 3.902
4.409 4.116 3.946 3.888 3.410 3.067 2.926
3.4i.2 3,056 2,915
....
....
2.287
Long spacing No. of ordrra Av. deviation
0.08
~
....
1/33 0.73
..
1/33 1.00 0.48
0.22 11.30 0 nn 0.09
..
..
-
4.511 4 349 4.207 4:077 3.868 3.753 3.622
..
1/32 0 97 0.12 0 19
d / n , A. 4.509 4.345 4.193
1/33 1.00 0.15 0.18
0:20 0.50
4:073 3.872 3.T67 3.003
0121
0
1n
0 37
3.415 3.271
0.09 0.16
3.086
0115
....
....
....
2.843 ;,..
.... ....
2.252 2.226 2.101 2.055
..,. ....
....
....
3.419 3.270
..
.. ....
~
"
;
(K.)
d 45.5
7
0.04
d / n , A.
1/21 1.00
.. ..
. . , .
.... i:i44 (Halo!
..
.... .... ....
....
o1is
0.15
d (h.) 45.6 7 0.11
1/31 1.00
1/31
d/n, A,
2.147 2.118 2.075 2.043
o1ig 0.14 0.09 0.09
2.146 2.115
.. ..
4.582 4.429 4,299 4.137 4,082 3.923 3.790 3.632 3.460 3.367 3.296 3.154 2.989 2.890 2.510 2.294 2,265
....
(A,)
4.49;
4.339 4.181
....
0156
.. ..
4.051 3.8.575 3.725 3.609
....
2.080 2.052
.. .. .. .. .. 0:08 0.06
2:246 2.219 2.098 2.853 2.005 1.983
, .
1/30 1.00 0.50 0.43
4.164 (Hrtlo)
0.34 0.05 0.05 0.05 0.05
3:4n9 3.055
o:40
0.07
....
3.063
0:06
....
.. ..
2:4i3 2.356
0'&3 0.07
....
....
d / n . .$.
....
....
1/36
1:OO
..
..
STROSTIUSI P.ALMIT.ATE---1/38 I .OG
1/38 1.00 q.16 0.16 0:21 0.45 0.36
)).27
.4fter drying-
d
(A.)
43.9 7 0.11
d/n, .&. 4.497 4.339 4.189 .,.. 4.079 3.863 3,749 3.623
....
1/36 1.00 ,.
1/36 0.93 0.17 0.22 0:28 0.45
0.37 0.28
0 08 0 16 0.08 0.08 0 05 n 09 0.12 0.05
Heated (200' C.) and slow-rooled
d
(A,)
47.7 6 0.07
d / n , A.
...
I:3% 1.00
1/34
. . .
..
4:i43
o:kz
.... .._
..
,
3.743
....
.... ....
....
o:i5
.... ..
... .... . . .
.. .. ..
0.08
2.609
0:09
o:i3
2,152
0 : io
0.11 0.18 0.16 0.09 0.09
.... .... .... ....
2.098 2.051 2.015 1.994 1.908
o:i7 0.11 0.16 0.08 0.08
.... ....
.... .... .... 1.960 ....
.
I
..
.. 0:09
..
_ _ - -BARIEM PALMITATE Heated (ZOOo C.) a n d slow-cooled
d 45.6 6 0.17
A.
d/n, 4.585
.... ....
1/20 1.00
..
..
J/20 0.60
.. ..
Halo from 4 . 3 9 - 3 . 7 9 A.
....
..
3.627
o:i5
....
....
3.379
....
21964
.... ....
2.300 o:i3 0.11
3.406 3.257 3.121 3.070 2 99.5 2.916 2 828 2.755 2.544
1/36 0.50
d / n , .&. 4.400 4.152 3.916
6.14
d / n , .I
Ii36 ..
..
After drying
1/21 0.67 0.14 0.14 0.14 0.14 0.33 0.30 0.14 0.14 0.15 0.15 0.09 0.10 0.09 0.09 0.14 0.09
d
(K.)
1'38 1.00 0.58 0.34
- Before ~ _ drying ~ _ _ 45.9
d
45.6 5 0.17
..
~~~
'
....
4.587 4.433 4.309 4.152 4.092 3.931 3.787 3.530 3.461 3.373 3.304 3.154 2.977 2.891 2.507 2.293 2.245
....
din, .&.
....
, .
.. ..
3.057 2.932 2.526 2.293
..
..
....
3:417
0.09
. . .
..
2.098 2.055
4.422 4.127 3.929
o:iz
0.09 0.21
..
0.13 0.09 0.16
d/n, .k.
Heated (ZOOo C.) and slow-cooled
..
4
-- - -~
0.22
0.11
d / n , .i. 1 / 3 3 4.400 0.55 4 163 1 .00 0.30 3.952 3:423 3.079
After drying d (.&.) 1/30 45.2 0.77
4
..
0.20
, .
o:iz o:i7
Before d r y i n g d (A,) 1/38 45.5 0.55
1/33 0.55
0.18 0.27
..
Before drying
Short, spscinge
(a,)
0.40
-B.~RIUMSTEARATE
Long spacing No. of ordera 4v. deviation
d
4i.3 5
STROSTIU\: S T E Y R ~-___-TE Heated (200' C.) Before drying After drying a n d slow-cooled d ib.) 1/33 d (.I.) 1/36 d (A,) 1/32 46.2 1.00 42.3 0.96 47.7 1.OO 7 .. i 6 0.11 .. 0. IO .. 0.13 ..
d/n, K. Short spacings
(A,)
17.3
-C A L C I U M P 4 L h l I T A T E
Heated (200° C.) and slow-cooled
.... .... .... .... .... ....
varies in a sufficiently characteristic manner to permit identification even in cases where two soaps have the same prominent lines. Except in so far as the soaps may form mixed crystals, the different alkaline earth palmitates and stearates can be readily distinguished in a mivture by their diffraction patterns. llagnesium soaps are characterized by the absence of line D, calcium soaps by the shorter spacing of line A, and strontium and barium soaps by the shorter spacings of lines C and D in the former.
0:io
.. o:ii ..
o:i; .. .. .. .. .. .
I
Before drying
(.k.)
d 43.5 7 0.15
1/22 1.00
.. ..
After drying d (A,) 1/26 43.6 1.00 7 .. 0.12 ..
Heated (200' C.) A n d slow-cooled d (A.1 1/14 43.2 1.00 6 .. 0.14 ..
1/22 0.45 0.24
d/n, A.
1/26 0.39 0.15
d/n, .I.
4.582 4.415
..
4.420
1/14 0.71 0.29
0124 0.36 0.36
4:073 3.924 3.775
o:ig 0.27 0.23
4:n& 3.933 3.756
o:ig 0.29 0.29
0:21
3.377
....
o1i9
..
31384
....
o'.is ..
2.939
o:i2
2.931
o:i2
2.933
o:ii
21533 2.299
0',09 0.15
....
2.299
21296
0121
.... .... ...
....
0:i2
2.150
o:i5
2.143
.... ....
0:08
2.162 2.140
0.21
....
..
....
..
d/n. A. 4.589 .4.424
....
....
4.079 3.921 3.764
...
3:3i1
....
....
..
..
.. ..
.. ..
....
.... ....
....
....
...
..
..
..
..
4,585
....
.... ....
.... ....
.... ....
. . . . . . .
..
, .
..
0121
.. ..
.. (Cont&hed on p a g e 2316
These differences are conspicuous on the original curves of intensity us. diffraction angle. Stearates and palmitates of the same alkaline earth metal might be distinguished by the shorter long spacing of calcium and barium stearates but not of magnesium or strontium stearates. Mived crystals of stearate and palmitate of the same metal are to be eypected; however, since their crystal structures appear t o be so similar, it is doubtful whether the percentage of stearate
INDUSTRIAL AND ENGINEERING CHEMISTRY
October 1949
~ s HEAVY >IET\L T ~ B L11. E X-RAYE P a c ~ s OF --~fAGTESlI
\I h E A R 4 T L
i,uny apacing S o . of orders \r. deviation
.I < A , '
I'53
I9.X 2
I .Oil
..
11. 1.5
'
Heated (200' C a n d slow-cooled d (A 1/46 47.0 0.12
Hefore i r. sing ~.
1 II.O
..
.i n, h -1iorr ,pacing5
1'46
iik
-r'j2*
SoiP5 (COnknUed)
-
>lAQ?ESIU\l
Before drying
(b
n
ti,'n, A. & ,564
II
3 0.lb
L:i6u
.3,857 13 430
3.0.X
Lung spacing Yo. of orders \I.. deviation
6 0.15
d/n, i 4,615
-pacings
..,
3.936 3.771
0:24 1.00 0.30
...
3 170 3.001
0.09 0.07
....
4.051"
3 288
3.17: 2,995
0.09 tl.07
2.722 2.562 2 39;
u.09 0.06 0 11
..
l f t e r drying d (1. 1/21 48.0
.,O@
7
0 13
din, ; intensities themselves are taken a s roughly proportional t o the height of t h e peak maximum a 3 o v e t h e base line. The intensits of t h e long spacing shown i s rha.t nf t h e third o r d e r : t h e fir-t a n d qecond ordpr- n c r l i r a t t n n small 3 diffraction a n d ? t n p f i r n i i t a r r ~ r a t dpterrni*~ nation of t h e line spacing. 1 Center of halo from 40--41.3 ' Center of halo f r o m 2 0 - 2 4 Halo. (Concluded uis p o g e 13Zh','
or palmitate in such a mixture could be determined with any uxuracy because of the small differences between the single -oaps and the uncertainty as to what the angle of tip would be in w c h a mixed lattice. It seems likely that the magnesium soaps are in a different mitial crystal form a t room temperature from that of the other alkaline earths, since line D is missing, and, contrary to the behavior of calcium, strontium, and barium soaps, line C is more intense than line A. The latter three are probably in a crystal form which is very similar, even if not identical; the main difference is in the relative intensities of lines B and C, although both barium and strontium koaps show a considerably greater total number of resolved line? than d o the calcium soaps
The soaps of metals oi subgroup I1 of the periodic table (zinc, cadmium, and mercury) can be readily distinguished from those of the alkaline earth group-cadmium and mercury by the absence of line A, and zinc by the markedly different order of intensities of lines A, B, C (C is the most intense of the three). Within the subgroup itself zinc soaps are readily differentiated by the much shorter value of the long spacing (7 A. shorter than for cadmium and mercury) as well as by the presence of line 4, missing with the other two, and a different order of intensities in the prominent peaks B and C. Distinction between mercury and cadmium soaps can be made on the basis of line E which, though not very strong, is fairly well resolved and has a markedly
INDUSTRIAL AND ENGINEERING CHEMISTRY
2316
TABLE 11. X-RAYS P A C I S O B
-
-- .~
~ I L K C U R I CP T E A K . 4 I I . - -
~~
Before drying d
(A,)
48.1 9 0.09
Short spacinga
1/31 1.00 ..
..
4 084 4 013
OF
HEAYY hIET.4L
SOAPS
I(C0nClUded)
--___
Heated (150' C.: and slow-cooled
d 47.9 9 0.16 4.060
(A.)
1/33
d
1,OCI
4E;4
1/11 O.RI1
3
0.16 0.46
Before drging
d (.t.j 47.7 9
I/F7 1.I)ll
0.23
3.840 3.731 3.613 3.466 3,203 3.071
3.012 2.937 2,829 2.684
...
d (b.) 17.7 9 10.21
0 : i3
0.06 0.06 0.OG
%.9O!J
0.06 0.06
-;:gig
0 : 13
2.426
....
2 442
48.0
1).
0.11
0.07
0.07
0.04
0.09 0.09
09 ,.
0.20
0 O! * 0.18
0.11
2.25:) 2,232 2.201
: 0:37
0 ; 07
2 : 0i3
0 :h i
071 0.22
4.187
ci,:3i O.O?t
0.15
, ,
2'03s
0:;;
I1 1 0
4 122 4.04'2
4.110
II 52
4
liB
11.46
4,110
(Ir31i
4.116
0.38
4.057
0.07
3.926
!.031 3 938
(J 2 1
0.21
0.10 O.07
3.985
3,943
0.21
4.049 3 934
3.858
0.1P
9.806
11.21
d.8ii
3 . m
O,Ioaps of these tv-o metals crystallize in CCWLED S L O h L Y FROW 200'c. 45*6h. ihe same structure, but much IPS.perfectly in the case of cadmiuni than in the case of mercury. I00 20 ' 36 40' Lithium stearate which, like ziiic stearate, lias a very short long spacing. , MAGNESIUM STEARATE is very different froiii hoth zinc and the dkalirie earth nietals in side spacings. It is conspicuously different from the 49.3 x. dkaline earths by having no peak in the region of 4.5 (group -1) nut1 froin zinc in the esisterice of a major whereas peaks in the peak a t 4.23 region designated as group C a r e \\-ell resolved into separate peaks for lithiurii and a t the saiiie time relatively 1es.i OOLED SLOWLY FROM zacfc. 47.0A. intense than for zinc. Lead stearate gives ride bpacings resenibling those for cadmium and MAGNESIUM PALNITATE mercury in that none occur 1%-ithhigh AIR-DRIED L&8#. inteitsity at larger values than abour 4.1 A . , arid in the fact that the peah near 4.1 A. is the most intense in *he group. I t differs from cadmium DRIED AT 90.C. L7.6 8. dearate in that it s h o w a larger number of resolved lines, and from COOLED SLOWLY FROM ZOOV. 456A. mercuric stearate chiefly i n the relacive intensity of lines within the C group. IVe can conclude that lead IOM 40' stearate has a crystal form more DIFFRACTION AVGLE ( 2 8 ) nearly like that of the soaps of cadmium Figure 2. X-Ray Diffraction Patterns of Air-Dried, Oven-Dried, and Thermall? and mercury than like those of the Treated Calcium and \Iagnesillm Stearates and Palmitates other metals examined. but probab1)not identical ITith them. Aluminuni nionostearatr givw side jpacings totally different spaciriga indicates some degree of parallel arrangenierii r i f the from any of the metal soaps so f a r discussed, i n that the peaks are niolecules Kith their polar heads in regularly spaced planes, the very wide and overlap in such a way as to make it difficult to actual state is better described as pseudo-glassy (undercooled resolve separate bands. There are two groups of such unresolved liquid crystal rather than undercooled liquid). peaks, the wider cent;ring a t ahoui 4.506 A. (group a) and the 31anganese stearate and palmitate resemble iron, cobalt, arid nickel soaps iii that t,lie principal side spacings occur mostly as sharper about 3.939 A . (group T I . The B group, if present a t ail. is not resolved. pinnacles on a single pezk. Hoirever, a considernble number of Tlie m i p a of iron, c o l d t , : i r ~ i lnickel can he coiisicleretl tosuch distiuct pinnacles c m be seeii; furthzr, the pa1niit:ite 1i:is 3 sharp, separately resolved liiie at 4.635 A. >loreover, the ingether, since their chemic:il similarity is reflected in siniilar hei- iiiuch gre:it'er. It can be conhavior iii crysrallization. T h e short spacings consist esclusively tensity in the long spacing pc of a single Ti-ide lido centering nPar 4.16 .;. (group B) for both cluded that the iiiangaiiese soap5 have crystallized to a greater 3te:irates aiid palmitates. The halo is ) I little sharper for cobalt extent, but not sufficiently to permit comparison with the paliiiitatc Than for the others. The long spacirig peaks itre n-cak patterns of the other crystalline soaps. and hro;itl. This behavior is cliaracteri3tic of many soaps after In summary, the diffraction patterns of t,hesoaps of magnesium, heating and cooling. It correspond.; to 3 glass\- rather than a zinc, lithium, and aluminum are different from one another and truly crystalline stat?, or pwqihly, rincr t h e csistcncr of long Timm thow of the reniainirig soaps. Calcium, strontium. :uid
I
er
A %
K.,
.h
-d Ab-
-
L
*
-
2318
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE111. X-RLY Before Drying
(a.l
d
Long spacing No. of orders Av. deviation Short spacina-
49 .a J
0.30 d/n, -4. 4.411 4.071 3.960 3.408 3.058 2.932 2,286
SPiCIVGS O F
After Drying
.
CALCIUX STEARATE 1/30 d 1/38 1,OO i g,7 1 , 00
(a,)
..
1/30 1.00 0.60
0.43 0.27 0.10 0.10 0.10
J
0.38
H E A T YL f E T A L
d & !
1/34 0.35
I
0.22
d/n,.i. 1/38 4.407 0.68 0.53 4.156 0.32 3.912 0.24 3.415 0.11 3.054
(...
d n,J.
I 34
4.154
1:oo
3.054
!I
....
(k.i
Long suacing No. of orders A v . deviation Sbcirt spacing*
49.1
1/12 0.75
J
0.48
....
4.592 4.453 L 372 3.969 3.789 3.373 2.945 2.280 2.181
2.133 2.079
1:OO 0.33 0.33 0.25 0.50 0.33 0.25 0.25 0.17 0.25
0.17
d (A.) 49.7 5 0.15
4.is5 i.473 4.405 3.959 3.814 3.385 2.981 2.295 .... 2.146 2.088
d [.A/
1/8
19.3
1 00
1
,.
n
0.15 d / n ,A . 4 , 620G 4,506' 4.3340 i.015 3.935 2 .8.50
i:ou
0.42 0.42 0.25 0.50
0.33 0.17 0.25
48.2
9
..
3.215 3.082 2.953 2.831 2,702
11.26
2 ' 495
Halo 01 l o w Intensity from 20-24 5'
2 : 285 2.195
2 ; 062 2,013 Long spacing No. of orders Av. deviation
Short spacings
39.9 3 0.07
din,A. 4.234 4 , ooa
3.969 3.731 3.584 3.380 3.228 3.186 2.985
,...
2.903 2 ,856 2.783 2,589 2.489 2.362 2,284
.... ....
2,104
....
0.55
..
1/85 1.00 0.52 0.45 0.40
0.33 0.09 0.06 0.06 0.04
0:02 0.02
0.03 0.04
0.09 0.09 0.11
..
1.924 O:O4 Band from
28.5-32.50
10.0
0,50
4
0.09
d / n , k. 4 234
1;80 1 00
4.011 3.960 3.734 3.583 3.367
o
3.215
0 08 0 06 0 06
3,169 2 992
58
0 50
0.44 0 32 0 06
40.2 '3 0.20
11.36
'4;?bv .I 4.240
1/83 1.00 0.34 0.07
3.191
O:O6
....
3.009 2.970 2.936 2.890
0.60 0.54 0.45
0.05 0.05
0.05
5.04
1.835
0.0h
2.850
0.04
2.592 2 488 2,369 2.275
0.68
2 385 2.489 2.388 2.279 2.172 2.113 2 - . nfix ... 2.000
0104
....
2,103 .... 1.995 1.919
0.10 0.08 0.13
o:nC,
0.05
Band from
29-32'
...
....
0.12 0.10 0.08
0.04
0.03 n.04 .. .. 0.04
Band f r o p
29-31.5
bariuni give patternb similar to one another, Inore bo io1 strontium and barium than for calcium. Cadmium and mercury soaps are quite similar to each other, and it is possible that lead stearate should be classified with them. Manganese soaps do not crystallize well enough to classify the patterns. Iron, cobalt. and nickel soaps occur in a noncrystalline state, probably best characterized as pseudo-glassy. Palmitates and stearates of the aame metal usually give comparable pattern-. EFFECT OF OVEN DRYING ON DIFFRACTION PATTEKNS
-111 the air-dry soaps were further dried at various elevated temperatures with loss of further water, as Table I shows. With the exception of the soaps of cobalt and magnesium there was little change in pattern, which suggests that hydrates are absent under the conditions of preparation and storage and that no gross change in properties would be expected up to tsmperatures equaI to those at which drying occurred.
2.502O
0.37
4.019
0.87 0.10
3.957
0.70
1 .oo 0.33
4.101 3,971 3 . 870 3,669 3,481 3.346 3 215 3.073 2 045 2 832
1.00 0.48 0.30 0.65 0.26
d / n . A. 4.582" 4.470a
1/32 1.00
0.9i 4.334a 0 . 9 7 4.019 0.69 3.927 0.7s
0.21 0 45 0.21 0.15
0.15 0.09
0.06 0.12 0.09
2.659 2 606
0.22 0.17
0.17 0.13 0.13 0.13 0.09
. .
2.543h
U:k
2.458 2.311
0.05 0.05 0.03
-" .' l j 2 b
o:n3
2.425
Halo f r o y
40-43,s
Ls.rgt L L i d ~ x ~halc ple b
4.037 3.965 3.742 3.583 3.373
1.613n
0.27
, .
U.17 0.17
41-46'
0.71
fi30 1.00 0.33 4,372" 0.50
,/i,~,.i.
0 IJ
3,352
3:QYe
I,31 1.00 0.29
1 , X?
0.2s
(.4.,
Long .pacing
50.of orders
Iv. del-iatior
Heated (20U C a n d Slow-coolen d (.%.) 40.7 1 0
42.2
J n , .i qliorr < p a , ~ r , r i . 4.103 3.981 3.870 3.679 .3.482
3+
1ttt.r U r y i n e
(A,)
5
Long a ~ a u i u g No. of orders 2v. deviatior
5
1/12 n,6i
Band frorr
Rand from 41-430
Hefore Drying _____
05
Band from 38 5-41' BARILWS T h A R A T r
d
SOAPS FROM LfETbSAP C H E \ l I C $1 c O \ f P 4 S Y
Heated (200° C.) and Slow-Cooled _ _-~ .
$9.3
Vol. 41, No. 10
Halo.
(:obab. soaps dried a t 45' C. under \ m i u r n (about 1 nim. UI mercury) lost about half as much water as would correspond t i t decomposition of a nionolydrat,e; simultaneously the long spacing decreased about 0.6 A. although otherwise t,he diffractioil pattern was essentially unaltered. However, cobalt stearate undergoes a, transition ( 5 ) below the temperature a t which it was dried, so t,he apparent effect of drying on the long spacing may be due to undercooling after a transition induced by heating, the loss of adsorbed moisture being inridental. ::DrSillg" of magnesium palInit,ate and stearate a t 90" C'. waults in a iorm in which the long spacing is substantially decreased and the numerous short spacings originally present art replaced by a, single intense peak at, 4.18 A. (Figure 2). Thc originally crysialline soap has, therefore, been converted int,o 21 liquid crystalline or mesomorphic form in which the heads of the molecules are still in regular planes (intenbe, sharp, long spacing, hut the lateral arrangement has been lost, except, for an average. distance of separation of planes corresponding to hexagonal close packing. That this change w a p not due to thermal transition was shown by preparing another sample which was not' heated to high temperatures and was dried a t room temperature but, neverthelcss gave the same diffrarunder vacuum with Pz06, tion pattern as the sample dried a t 90" C. The water loss from t,hese soaps was substantial; so there is considerable likelihood of the existence of a hydrate, although the present data are inwfficient to establish it. llthough calcium stearate and palmitate both form nioiiohydrates which have a markedly different diffraction patterii from that of the anhydrous soap ( I d ) , and although the m-ater loss of the present soaps on drying a t 110' C. (Table I ) corresponds closely to that calculated for decomposition of a hydrate, no substantial change occurred in the diffraction pattern (Figure 2). Hence, unless the soap is completely free from traces of cerhin impurities such as free fatty acid, there is no change irl
October 1949 structural rearrangement which otherwise accompanies dehydration, and the pattern of the hydrate structure persists in the dried soap. EFFECT OF HIGH TEMPERATURE ON DIFFRACTION PATTERNS
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE Iv. CHARACTERIZING SIDE d/n, A.
SPACINGS -4ND INTENSITIESa O F
B-
-4
Band
~ / ~ m a x .d/n,
2314
b. ma mar.
Mg(Str)p
Ca(Str)z
4.554 4.409
0.81 1.00
4.137 4.116
0.87 0.53
Sr(Str)r
4.511
0.97
0.20
Ba(Str)l
4.587
0.67
MgPp
4.564 -1.422 4.497
0.63 1.00 1.00
4.207 4.077 1.152 4.092 4.160 4.127 4.181 4.051
0.14 1.00 0.58
C d/n, A.
mar.
3.839 3.946 3.888 3.868
0.98
33.tizz . E
3.931 3,787 3.857 3.929 3.855 3.726 3.609 3.921 3.764 3.941 3.787 3.794 3.696 3.840 3.734
0.28 0.50
d/n, A.
HEAVYMETAL SOAP?
= -
I/Imsx.
Absent 3.410 0.35 R.271
0.16
0.33
Y.373
0.15
0.73 0.34 0.45
3.430 3.417 3,257
0.10 0.34 0.16
E
d/n. A .
...
IIImax
,.
Cap? Since the ability of metal SrPr 0.21 soaps to swell and to form R.381 0.19 4,079 0.23 0.36 gels in organic solvents de4.589 0.45 EaPe pends in part on their crystalb.11 2.391 1.00 4.095 0.48 Zn(Str), 1.561 0.82 4.435 , linity or lack of crystallinity 0.2' 2,959 0.50 0.35 1.082 Absent Cd(StrJ: (IS), the effect of heating 0 21 2,25*5 4.084 0.74 0.52 Absent Hg(Str)p was investigated. The soaps 4.013 were heated in closed cells Intensities are expressed as the amplitude of the peak above the bhse Line divided by that of the lnovt inLeiise peak in the given pattern (frequently the third order of the long spacing), omitting first and second ordem of the to 2000 C. (1503 C. for soaps long spacing from consideration. Relative intensities from line t o line are directly comparable for a given bioap of mercury, manganese, iron, but are not comparable from soap to soap because of different reference intensities in different cases, a s well as ! x ; ~ ~ ; ? o ~ f .the difficulty of reproducing samule surface sufficiently closely to obtain reproducible values of ahqolutr cobalt, and and alloTved - .. . to cool at approximately 2.5" per minute a t 200", 1.8" per minute, a t 150°, and -of white niiiierd oil (Sujol) in the reference cell. The soaps of c:ilcium, strontium, barium, magnesium, zinc, cadmium.
