1416
D. H. BIRDSALL A N D B. B. FARRINGTOR'
S a m p l e preparation The grease used for the initial phase of the program (grease S o . 1, table 1) was a commercial product prepared as follows: The soap concentrate Ti-as prepared by the saponification in a pressure autoclave of a high-grade tallow with calcium hydroxide in the presence of a small amount of mineral oil. After saponification was complete the soap concentrate was completely dehydrated by heating in an open vessel and was then gradually hydrated by adding water as the soap concentrate was cooled from 235°F. to 210°F. Part of the water was evaporated during this hydration process. but a substantial amount remained in the grease intimately associated with soap. The resultant hydrated soap concentrate was mixed with a mineral oil having characteristics as outlined in the TABLE 1 Composition of g i e n s e s SOAP
so.
I
STABILIZER
I
GREASE
Type
~
Weight
i
Tspe
Keight*
MIKERAL OIL
~
-1
~~
pev ceizi
1 , , , . ICalcium tallow 2 . . , Calcium talloIT 3 . . , Calcium talloIv -1.. , , Calcium stearate 5 . . . C a l c i u m stearat'e 6 . , , Calcium stearate 7 , . , . iCalcium stearate 8...'Calcium stearate 9 . , Calcium stearate IO.,, , Calcium stearate ,
,
17.7 12.9 6.4 15
1
Water Water Water Calcium acetate
,
Calcium acetate
,
,
, ,
;i
20 20 20
Stearic acid Stearic acid Stearic acid
1.3 1.1 0.6 2.0 3.0 4.0 0.2 1.o 2.0 3.0
I
t'iscosity Viscosity' Viscositp .;1; .;2; index Keight
200 2600 4000 460 460 460 460 460 460 460
~
l-
40 120 160 50 50 50 50 50 50 50
15 60 70 0 0 0 0
0 0 0
pev cen!
81 86 93 83 82 81 79.8 79 78 77
Indicates amount of stabilizer i n completed grease.
table. The final grease had a Tyater content of 1.3 per cent and a soap content of 17.7 per cent. The above product was placed in an oren at 230°F. and was stirred frequently to insure even dehydration. Samples were taken from the bulk of the grease a t hourly intervals until essentially all of the water had been removed. The water content of each sample was determined by the conventional "water by distillation" test (A.S.T.M. D95-46). Samples for the second phase of the program were obtained during the commercial manufacture of a grease m-ith a soap component similar t o that of grease No. 1 but prepared with a mineral oil of higher viscosity. Samples were taken of the soap concentrate as it was being hydrated and of the finished grease after the constituent mineral oil had been mixed in. This grease is referred to as grease No. 2 in the table. Grease No. 3 was a semifluid commercial product haT-ing a high-viscosity mineral oil. Samples of this grease were taken at only tm-o stages of manufacture, as indicated, merely as a check on results obtained on the other two greases.
F I B E R S T R U C T U R E O F C h L C I U M SOAP G R E A S E S
1423
radically difierent, effect on the fiber shape and size, in the two cases studied the grease is &able only when a fibrous structure is visible under the electron microscope. It is interesting to note that, in both the calcium acetate-stabilized and the \vater-stabilizecl greases, the minimum concentration for a stable product is in the vicinity of equimolar concentrations of stabilizer and soap. The molecular configuration in the hydrated calcium soaps is probably of a type suggested bjDoscher and Told (1) in their study of sodium soaps; that is, soap anions bound together by molecules of water u-ith the calcium ions distributed in t'he interstices. The molecular orientation in the case of calcium acetate stabilization and stearic acid stabilization is undoubtedly more complex ; however, greases of this type may possibly be studied by x-ray diffraction or electron diffraction techniques. The hydrated calcium stearate fibers have a reasonably uniform width of 400500 .I. If the soap molecules are orient'ed perpendicularly to t'he long axis of the fibers, this fiber width would represent approximately the length of ten stearic acid unit cells or twenty steni,ic acid molecules ( 5 ) . The hydrated calcium stearate fibers evidently have no tendency to split asially into smaller components, as do the fibers of sodium laurate reported by JIarton ct al. (6). The cnlcium acetate-stabilized greases hare a tendency to form fibrous bundles more typical of sodium soap fibers. However, the minimum fiber width noted in these micrographs is of the ordei. of 250 &I., a value tvhich tvould again indicate a fiber width of sei-eid molrciiles. 1-1. S L X X i R Y
Thc micrographs presented indirate that the fihci, 01' carystalline structure in hydrated ctalcium soap greases disintegrates conc~irrentlywith the removal of \\-atel'. The fiber disintegration leads in turn t o the separation of soap and oil. Stearic acid and calcium wetate act as fiber builders i n calcium soap gi'eases re radically diff'erent in size and shape from those in the hydratetl grease. For eff'ective structural stabilization calcium acetate 01' \vatel, must be present in molar concentration.? appi~osiniatelyequal to or greater than that of the soap. The authors \\-ish to express their gratitude to Di.. 11. 1'.3Iacdonald and DI.. H. M-.Hotten of the California Research Corporation, Richmond, California, for their helpful suggestions in the preparation of this paper and to the I-niversity of ('alifornia, I3erkeley, for the use of its elecatron microscope. It 1.: FE: ItE s CE s ( I ) I ~ O + I ~ I I I X , 11.. ' ~ . .\SI> Voi.i>. I t . 11.: ,J.I'li>-s.Colloid C'h(~m.62,14s (IM8). (2j F A R R I S ~ ; T13. ~ SIS.. . .\SD HIRDSII.I.. I). €1.:I n s t . Spokcsiiian ( S a t l . 1,uhricating ( ; w a w Irist.) 11,Su. 1 . 4 (1047);Oil G a s . l . 4 6 , 2 6 6 ( 1 9 i i ) . ( 3 ) FARRINGTOS, 13. H . , .%si> I l a r ~ sIT. , 1.: I n d . E n g . Chein. 28,414 (1036). (4) I€OEPPIJ;R, F . : Fettc: u . Srifrn 49, 700 (1912). ( 5 ) >\1.4RPLEY, I
