December 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
area of the blacks was covered by fatty acid at saturation. Thirdly, a considerable proport,ion of the fatty acid remained in the solvent phase a t room temperature, and this proportion would he expected t o increase at higher temperatures in accordance with the usual behavior of adsorption equilibria. The second and third points are particularly significant. If there is a similarity between adsorption from Butyl rubber and adsorption from fluid hydrocarbons, it would seem that only a small part of the surface area of each black particle is covered with fatty acid a t the high temperatures (approximately 300’ F.) attained in practice when tlhe finer blacks are mixed into rubber. This small amount of adsorbed acid on the surface could hardly he effective in dispersing the particle. The authors believe that the results of this investigation indicate that fatty acid is not effective for dispersing blacks in other rubbers, particularIy those rubbers which are hydrocarbons such as GR-S, Hycar OS-IO, and natural rubber.
BIBLIOGRAPHY (1) Amon, F. ET., Smith, W. I?., and Thornhill. F. S., IND.ENG. CHEM.,ASAI.. ED.,15, 256 (1943). (2) Barron, H., Zndia Rubber J . , 90, 638 (1935). (3) Blake, J. T., IND.ENG.CHEM.,20, 1054 (1928). (4) Boiry, F., Rev. gen. Caoutchoz~c,8 , 108 (1931). (5) Bulgin, D.. Trans. Inst. Rubber Ind., 21, 188 (1945). (6) Colurnbiaii Carbon Co., “Columbian Colloidal Carbons,” p.
180 (1938.
2333
(7) Columbian Carbon Co., “The Surface Area of Colloidal Carbons,” (1942). (8) Drogin, I., India Rubber World, 107, 42, (1942). ENG.CHEM.,ANAL.ED., (9) Emmett, P. H., and DeWitt, T., IND. 13,28(1941). (10) Fielding, J. H., IND.ENG.CHEM.,29, 880 (1937). (11) Gehman, S. D., and Field, J. E., I h i d . , 32, 1401 (1940). (12) Glasstone. S., “Textbook of Physical Chemistry,” p. 1200, New York, D. Van Nostrand Go., 1946. (13) Goodwin, N., and Park, C. R., IND. CHEM.,20, 621, 706 (1928). (14) Karrer, E., Dairies, J. M.,and Dioterich, E. O., Rub6er Chem. Technol.,3, 295 (1930). (15) Langmuir, I., J . A m . Chem. SOC.,39, 1848 (1917). (16) Zbid.,38, 2221 (1916); 40, 1361 (1918). (17) Mooney, M . , Rubber Chem. Techno!., 7, 564 (1934). ENG.CHEM.,24, 584 (1932). (18) Morris, T. C., IND. (19) Office of Rubber Reserve, Specifications for Government Synthetic Rubbers, effective Jan. 1, 1947. (20) Pnrk, C. R., and Morris, V. N., INTI.ENG.CHEM.,27. 582 (1935). (21) Parkinson: D., Trans. Inst. Rubber IntJus., C , 263 (1930). (22) Roheits, K. C., J . Rzhber Research J n p t . MaZaya, 7 , 46 (1936). (23) Smith, W. R., Thornhill, F. S.,and Bray, R. I., IND.ENG. CHEM.,33, 1303 (1941). (24) Stamberger, P., Kazctschu/:, 7, 182 (1931). (25) Sweitzer, C. W., and Goodrich, W. C., Rubber Age (Ar. Y . ) , 55, 469 (1944). (26) Whitby, Dolid, and Yorston, J . Chem. S oc.. 129, 1448 (1926). RECEIVED February 18, 1947. The opinions or assortations in this article are those of the authors a n d are not to be construed as official or reflecting the views of t h e Navy Department or naval service a t large.
DIPHASE METAL CLEANERS Relation of Emulsion Stability to Cleaning Eficiency IRVING REICH . ~ N DFOSTER DEE SNELL Eoster D. SmW, he., 29 W e s t 15th St., New York 11, N. Y.
A
materials preferentially we A compariaon is made between t w o classes of metal SOLUTION of 11% of by water. Steel parts cleaned triethanolamine oleate c l e a n e r e t h e unstable emulsion type cleaner and the in this way tend to rust stable type. Metal cleaning tests and umber dispersion in 89% mineral spirits constirapidly and surfaces are not tests were performed. In both cases diphase cleaners were tutes a diphase cleaner when chemically clean. 2. Vapor degreasing inmore effective than stable emulsion cleaners. This greater mixed with water and propvolves condensation of solvent effectiveness is a result of the heavy film of solvent with erly applied. A stable emulvapors upon the surface of the M-hich this cleaner coats the metal surfaces and the sion can be produced by very metal. The condensed solability of the unstable emulsion cleaner not only to wet vigorous agitation, by the advent drips back into a bath. The objections mentioned the soil and &Each it from the surface to be cleaned but to dition of more soap, or by disabove applyto this method. In disperse and suspend the soil and prevent redeposition. solving the oleic acid in the addition solid soil is often left mineral spirits and the triasaresidue on themetal which ethanolamine in water, then must then he hand wioed. 3. Alkali solution cleaning. The metal parts are generallv mixing the two phases. In any of these cases the efficiency of the allowed to soak in an alkali bath with or without water-solubiet cleaner is lost. Thus, contrary to widespread industrial pracdetergent’s. Spray machines may also be used. For rapid and tice, unstable rather than stable emulsions should be sought. effective cleaning high pH values are used. This leads to hazards for operating personnel and to danger of metal surfaces being Diphase cleaners are capable of great flexibility in solving attacked. Contamination builds up rapidly in the bath, resulting problems raised by special types of soil, special metals, and in redeposition of soil. It is difficult t o remove the last traces of specifications for finished surfaces. They can be used to leave alkali from the metal surface, and these can increase susceptithe metal surface chemically clean and ready for plating or other bility t o corrosion. 4. Emulsion cleaning should be divided into two categories. finishing operations, and also to place a rust-protective film A . The metal is treated with a solution of soap or other emuIon the metal surface. Their use in the latter way had an imsifying agents in an organic solvent. The emulsifying agents may portant bearing on production of metal parts during the war. aid loosening and solution or dispersion of the soil. The metal parts are then rinsed with water and generally a pressure stream is used. The solvent adhering to the metal surface largely emulsiMETHODS OF METAL CLEANING fies and is washed away. The flammability or toxicity hazards Important methods of metal cleaning include the following: of solvent-cleaning processes apply. The metal is subjected to the .simultaneous action of two phases only for an instant during rinsing. 1. Treatment with liquid soIvent can be done by spraying, B. The metal is soaked in or sprayed with a more or less stable dipping, or hand scrubbing. I t removes oil and grease rather emulsion, generally one of kerosene or a similar hydrocarbon fraceffectively hut is subjkct to the drawback of fire hazard or, if chlorinated solvents are used, high cost and toxicity. Liquidtion in water, stabilized by soap. Excess alkali may be present. Subsequently the metal is generally rinsed by water. solvent treatment does not remove water-soluble materials or
2334
INDUSTRIAL AND ENGINEERING CHEMISTRY
5. D i p h a s e cleaning. T h e characteristic feature is the siinultaneous contacting of the metal by asolvent which preferentially xvet,s the metal, and water, the mater being present in much gTeater proportion, and the contact lasting a controlled length of time. Although some of t,he solvent may be emulsified in the water, this is incideptal and is avoided as much as possible. 6. Mechanical a b r a s i o n . R.emoval pf oil and grease is a very desirable preliminary. 7. E l e c t r o cleaning. T h e met,al is made the anode or the cathode in an Figure 1. Two Cleaning Baths electrolytic bath. Prepared by Diphase and Stable 8. P i c k l i n g . Emulsion Techniques Acid treatment to remove surface oxide films is preceded by one of the other processes to remove oil and grease. Often two or more of these processes may be used in series, one to remove most of the grease and heavy soil, the other to remove the final traces. In such cases emulsion cleaners are sometimes used for the former, alkali bath cleaners for the latter. The emulsion cleaner is intended to clean extensively, the alkali bath cleaner int'ensively. A diphase cleaner is characterized by the following propwties :
Vol. 40, No. 12
is dissolved in 50 grains of water and these t.wo solutions arc then brought together, a creamy emulsion forms instantly. This can then be diluted viith water without, any visible oil separation. The principle involved is well known. Interfacial tension betxeen v-ater and the solution of triethaiiolamine and oleic acid in lieroserie was found to bt: 12.8 dynes, 1 minute after the interface had formed. The interfacial tension between the solution of oleic acid in mineral spirits and triethanolamine in water waa iess than 0.3 dyne. With age t'he interfacial tension a t the first interface tends to drop slowly toward zero but very rapid lowering of interfacial tension when a new interface forms is of course requisite for good emulsification. These two inetliods of bringing the solvent and water together niay be called the diphase and the stable cindsion techniques. The type and amount of emulsifier play an important role in determining n-hether a stable emulsion is formed. Agitation is also a factor, and a diphase mixture can be converted into a stable emulsion by agitating and passing through such an efficient mixer as a colloid mill. Tho effect of bringing the ingredients together in the two different imys is shown in Figure 1. ,4 second formulation, tabulated below, has been used extensively in industrial metal cleaning and some of the following experiments were conducted using it. Formulation KO.2 Mineral spirits, g. Pine oil, g. Oleic acid, g. Triethanolamine, g. Ethylene glyool monobutyl ether, g.
67 22.5 5.4 3.6 1.5
Here the triethanolamine is present in stoichiomotric excess as compared with the oleic acid. The pine oil and ethylene glycol ether serve several functions. They prevent tlie formation of two layers in the solvent c,oncentrate by acting as key solvents for the soap and they also improve detergency and rust protection. Hoiyever, t,hey do not, figure in the following discussion which could a,ll he based on the simpler Formuhtion KO,
1. A
R
c
D
1. The metal is simultaneously subjected to the action of an aqueous and a solvent phase. Neither phase must be completely emulsified in the other. 2. The solvent phase is capable of dissolving oils and greases and preferentially wetting metal surfaces. 3. The aqueous phase dissolves waber-soluble soils and preferentially wets various mineral soils. 4. The solvent phase is of low viscosity. 5 . The solvent phase shows some tendency t o emulsify either in water or in a suitable aqueous solution which may be used for rinsing.
Experimental work conducted a t the aut,hors' laboratories has demonstrated t,hat diphase cleaners are much more effective than stable emulsion cleaners in removing grease and soil from metal surfaces.
.
r
..
FACTORS GOVERNING STABILITY OF EAIULSIONS
An example of a forinuiation which can be either emulsion or a diphase cleaner is the following: Formulation N o . 1 Mineral spirits, g. Oleic acid, g. Triethanolamine, g.
tt
stahlr
89 7.2 3.8
If these ingredients are mixed together and the resultant solution is stirred with water, very little emulsification occurs. The water becomes slightly cloudy but most of the solvent remains floating as a free solvent layer. If, bn the other hand, t>heoleic acid is dissolved in the mineral spirits while the triethanolamine
Figure 2.
Comparative Wetting Effects of Diphase and Stable Emulsion Cleaner
A . Formula No. E . Formula No. C. Formula No. D. Formula No.
2, diphase, solvent-water ratio 1 t o 90 2, diphase solvent-water ratio 1 t o 8 1, stable,'%olvent-waterratio 1 to 90 1, stable, solvent-water ratio 1 t o R
December 1948
I N D U S T R I A L A N D E N 3 I N E E R I N G CHEMISTRY
2335
in the ratio of 1 to 8. Obviously the diphase cleaner wets the plates with a continuous film of solvent, while the stable emulsion forms no such film. It merely leaves a few droplets of emulsion attached to the plate. These tests were conducted at room temperature. Steel plates which were immersed in stable emulsion, Formulation No. I, for 2 minutes, at a solvent-water ratio of 1 to 30 a t 80" C. were coated with a very light film of solvent which is insufficient to perform the function of a free solvent layer. Under conditions of use, however, emulsions of this type cannot be considered to be completely stable. The tendency of the solvent phase of a diphase cleaner to wet preferentially greasy soil and metal causes a concentration of the solvent a t the metal surface which results in cleansing action out of all proportion to the amount of solvent present. To demonstrate this experimentally, a strip of steel is suspended in a stirred diphase cleaner bath. The solvent concentrate is Formulation No. 2 except that part of the mineral spirits has been replaced with trichlorobenzene to give the solvent phase a density of 1.00 As the bath is stirred the solvent phase floats suspended in droplets. Large amounts of solvent attach to the metal in a n undulating heavy film, portions of which are constantly being detached to be replaced by fresh solvent. CLEANING EFFICIENCY
PRACTICAL TESTS.I n Figure 3 the relative cleaning effects of stable emulsions and diphase cleaners are demonstrated.
F i g u r e 3. Effect of Free Unemulsified Solvent in P r o m o t i n g Soil Removal from Steel Washers Formula No. 2, diphase, solvent-water ratio 1 t o 8 1 stabilized by colloid milling 90 m l . of 2 plus 10 m l . of mineral spirits Formula No. 1, stable, solvent-water ratio 1 t o 8 5. 90 m l . of 4 nlus 10 m l . of mineral svirits 6. Distilled water 7. Formula No. 2, diphase, solvent-water ratio 1 to 30 8. Formula No. 1, stable, solvent-water ratio 1 to 90 9. 90 m l . of 8 plus 10 m l . of mineral spirits 10. 0.1 % of sodium oleate solution . 1. 2. 3. 4.
In u5e a diphase cleaner is diluted with several times its volume of water and heated to about 60" C. Metal objects may be cleaned by repeated dipping, so that the metal surface Antacts both the solvent phase and the aqueous phase. However a more efficient method is to spray the metal parts. The spray intake must be a t the proper level so that both aqueous and solvent phases are in the spray.
Steel washers were soiled by coating them with a paste of 12 grams of umber plus 11 grams of oil. T h e oil was a mixture of 49.5 parts each of minerd and cottonseed oil and 1 p a r t of oleic acid. Eight washers were placed in a 100-ml. Nessler tube along with 100 ml. of the solution being tested and the tube was rotated end over end through a vertical plane for 2 minutes at the rate of 18 complete r.p.m. The rings were then removed, rinsed with water, and photographed. Tests were conducted at 55 C. The results show that diphase cleaners are much more effective than stable emulsions in removing soil of this sort. When the diphase cleaner is converted to a stable emulsion by colloid milling, or if the identical formulation is prepared using the stable emulsion technique, the effectiveness is lost. On the other hand, stable emulsions to which free mineral spirits have been added show considerable effect. The comparative efficiences of stable emulsion cleaners, diphase cleaners, alkali solution, and plain distilled water in removing various types of soil are further demonstrated in Figure 4. Three panels coated with three different soils were used in each test. The soils were as follows: Petrolatum soil, % ' Napalm soil,
yo
PREFERENTIAL WETTING
The authors have described the preferential wetting characteristics of the two phases ( 1 ) . Interfacial contact angle and other measurements have demonstrated that the aqueous phase preferentially wets many mineral soils while the solvent phase preferentially wets metal. This effect is enhanced by the extensive hydrolysis of the triethanolamine oleate; most of the oleic acid remains in the solvent phase while most of the triethanolamine goes to the aqueous phase. The effect of this is shown in Figure 2. The top tinned plates were dipped in diphase cleaners (Formulation No, 21, the bottom ones in stable emulsions (Formulation No. 1). I n preparing both, 1%of oil red 0 was dissolved in the solvent to make it show up readily in photographs. The plates at the left were dipped in mixtures of solvent concentrate diluted with 90 pavt,s of water, those a t the right with mixtures
Umber soil,
yo
Yellow petrolatum Oil Red 0 Yellow petrolatum Napalm gel Talc ZinE stearate Oil Red 0 Umber Mineral oil, med. visc. Oleic acid
99.570
0.5% 79.670 5% 1070
5% 0.5% 50% 49%
1%
The steel panels coated with these soils were suspended for LO minutes in the liquids a t 80" C. while being agitated gently. The mechanical stirrer used for agitation was always run a t the same speed and inserted in the same position relative to the plates. After treatment with the liquids being tested, panels were dipped 100 times a minute into a 2% solution of sodium metasilicate at 90" C. They were then lined up and photographed. I n another series of tests Formulation No. 2 was used as a diphase cleaner in a small commercial spray washer. T h e solvent-water ratio was 1 to 30. The test panels consisted of
INDUSTRIAL AND EN GfNEERING CHEMISTRY
36 P e t r o l a t u m Soil
N a p a l m Soil
U m b e r Sail
Vol. 40, No. 12
were added t o the cleaning bath. Each such addition caused further emulsification of the solvent in the aqueous layer and reduction in the proport,ion of free solvent. Coincident with this, cleaning action became less effcctive, and greater lengths of time were required for adequate cleaning. Finally, when enough soap had been. added to emulsify substantially all of t,he solvent, it became impossible to clean the plates properly. They came out hazy and with a heavy visible throwback of soil. DISPERSING POWER DEPLETIOX O F S O A P I N STbBLE EXVLSIOXS. Diphase cleaners suitably formulat,cd show a much greater tcndency to deflocculate and suspend soils than stable emulsions. This was investigated by the technique of Snell (2).
One gram of oiled umber soil, 20 glass beads, and 100 ml. of the liquid were rotated through a vertical plane in a Kessler tube for 15 minutes. The soil consisted of umber precoated with -ITo of its weight of a mixture of 49.5% each of cottonseed and mineral oil and 196 of oleic acid. The h-essler tube was left undisturbed for 2 hours, then a 25-ml. sample was pipet,t,ed off, dried, ignit,ed, and analyzed for iron by reduction with zinc in acid so1ut)ion and titration with potassium permanganatc. Some of the results obtained are given in Table I.
Figure 4. CoInparati\ e Cleaning Effects of Stable E m t i l ~ i n nDiphase ~, Cleaner, and Water A . Formula No. 1, stable, solvenCh.wwater r a t i o 1 to 30
C o m m e r c i a l e m u l s i o n cleaner s o l v e n t - w a t e r ratio 1 t o 30 C. F o r m u l a No. 2, d i p h a s e , #al,eLt-water ratio 1 t o 30. S o l v e n t adjusted to d e n s i t y 1.00 w i t h t r i c h l o r o b e n e e n e D. Distilled water
€3.
pieccs cut from sheets of cord rolled steel plate yvhich ha,d bwn obtained directlg- from a rolling mill. The soil on these panel? was a tough adhex.nt film of the luhricarits and coolants used
Several platw c1cane;l i n this ~3-a;; rrynircd an average 01 23 seaonds t o rendel, them clean and bright ii,s dctermined by visual inqxxtion. SCKadditional yuanlitios o f triethanolaminc oleate
TABLE I. DCPLETIOS OF SOAP Liquid Formulation No. 2 , dipha-e Formulation N o . 2 , prepared as diphase, t h e n stabilized h y colloid
Solvent-Wiatei Ratio
N g , of Umber pel 25 hI1.
1to 8 1 to 8
8.7 2.0
1 to 8 i t o 90
1.1 1.3 '2.3 13.8
... ,..
Thus stable emulsions appear to bc no better (indeed somewhat worse) than water in ability to deflocculatc and suspend soils of this type. Further, the suspending po~vor of diphase cleaners can be substantially great'or than indicated in Table I. The figure listed for the diphasc cleaner is for the aqueous phase only. Actually a groat deal of' the soil goes t o the solvent phase. This is readily seen in Figure 6, which shows the tubes of liquid used in cleaning the soiled rings as described earlier. It will be observed that the solvent phases of diphase cleaners carry heavy loads of soil. This ability to disperse soil is an important characteristic of all good detergents in whatevsr field. Although a solution is able to wet soil and detach it from the surface to he cleaned, if it docs not effectively disperse and suspend this soil, redcposition often occurs and then part of the soil is simply redistrihuted over the surfacc. This is linown to occur with metal cleaning by alliali baths and emulsion baths. Freyueiitly an over1io.i.i tank is used to remove most of the loose soil vihich detaches from metal surI'a,ws and floats to the top of the bath. The extent to which the dispersing power of soap in soTution is destroyed by the prescnce of emulsified solvent is shown by Table TI. It is readily seen that enormous amounts of soap are required to achieve quite moderate dispersing power in the presence of ernulsjfied solvent. X further experiment was conducted on a Formulation S o . 2
O F D I B P E R S IP~O CT ~IC O FR SOAP TABLE 11. DESTRLCTION
Liquid F o r m u l a t i o n KO. 1 stable Same eninision with 0.S70 additional triethanolamine oleate Same emulsion v i t h 2 ,4v0additional triethanolamine oleate 0 ,37c triethanolamine oleate in water 0 . 6 % triethanolamine oleate in water 1.0%, tripthanolninine oleate 1 n \ I ~ L t E r
Solvent-Water Ratio 1to 8
Trietiianolamine Oleate i n Liquid, 70 1.2
1 to 8
1.8
1.5
1 to 8
3.6
3.2
LIg. of Vniher per 2R nIl. 1, 3
..
0.3
1.0
...
0 . .5
7.6
.,.
1. o
22G
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1948 1
2
3
4
5
6
7
8
9
1
0
Figure 5 . Emulsions and Diphase Cleaners Immediately after Cleaning Rings Shown in Figure 3
emulsion which had been stabilized by colloid milling. To 90 ml. of this at a solvent-water ratio of 1 to 8, 10 ml. of mineral spirits were added. An umber dispersion test now gave a value of 1.7 mg. Thus the presence of free solvent did not increase the dispersing power of the stable emulsion. The low dispersing powers of the stable emulsions must be attributed to the soap being substantially tied up at the surfaces of the emulsified droplets and through hydrolysis, with the fatty acids going into the oil droplets. Thus the concentration of soap available in aqueous solution must be very small. However, when the diphase technique is used, very little solvent is emulsified and a substantial quantity of soap remains in the aqueous phase. Thus, to obtain the maximum dispersing power for soil, the conditions of making and using the cleaning baths must be such a s to cause minimum emulsification of solvent in the aqueous layer. The same effect cannot be obtained by permitting such emulsification to occur %andthen adding free solvent or soap. Adding free solvent will improve initial cleaning results, as the soiled ring tests have shown, but will not raise the dispersing power of the aqueous solution. Adding more soap will raise dis-
2337
persing power only slightly and will favor emulsification of any remaining free solvent, thus preventing proper clea ling. Such efficiency as stable emulsion cleaners do have can be attributed only to limit’ed instability under conditions of use. Thus some free solvent is liberated to wet the metal surface, dissolve the soil, and eventually be removed by mechanical action. The comparatively poor performance of such emulsions is caused by the small amounts of solvent available for c!eaning. The soap or other emulsifier makes the solvent largely unavailable because it is t,ied up in emulsed droplcts which will not mix either with each other or with grease or soil on the metal. At the same time the soap is not free to do its normal job of dispersing and suspending soil, since it is already largely tied up at the solvent-aqueous interface. And so as T w approach the ideal stable emulsion, we get poorer metal-cleaning performance. Mechanical action is involved in all cleaning processes. 3-0 matter how thoroughly t.he cleaning solution dissolved the soil, it is necessary to separate the metal from the contaminated solution in some vay. Usually some mechanical assistance is needed to aid the solution in dissolving or loosening and removing the soil. This usually takes the form of agitation, spraying, flushing, or hand scrubbing. This last’is more effective but it is slow and costly. To a considerable extent mechanical and physicochemical action are inverse t,o each other. Thus if a metal surface which has been treated with one of the diphase cleaners described is rinsed with water, considerable force will be required if a very thin residual film is desired; if an alkaline rinse is used, very little force is required. If the solution is strongly allraline, complete stripping of residual film results with scarcely any agitation. The diphase cleaning technique is flexible to an extraordinary degree. I t is capable of variation to meet problems raised by peculiarities of soil or metal, limitations in cleaning equipment available, special requirements for the state of the cleaned metal surfaces, and economic limitations. Some of these variations have only been touched upon in the present paper. Future papers will discuss in some detail the application of the physicochemical principles involved to specific types of metal cleaning. The field of metal cleaning is so complex that no single formulation or process will fill all requirements. Methods must be adapted to specific cases. Theory can aid in making such adaptations but is as unlikely to provide a universal detergent as it is to lead t o a universal solvent. ACKNOWLEDGMENT
The work described in this paper was done under a grant from The Solventol Chemical Products Company, Detroit, Mich. The last two paragraphs under “Cleaning Efficiency, Practical Tests” describe work done by A. A. Schwartz of the above company. LITERATURE CITED
(1) Reich, Irving, and Snell, F. D., IND. ENG.CHEM.,40, 1233 (1948). (2) Snell, F. D., Ibid., 25, 162-5 (1933).
RECEIVED October 21, 1947. Presented before t h e Division of Colloid Chemistry at t h e 112th Meeting of t h e AXERICAN CHEXICAL SOCIETY,. New York. N. Y.
