Water-Soluble Pastes for Diamond Powder R. S. YOUNG, D. A. BENFIELD, AND G. B. DAUNCEY Diamond Research Laboratory, Industrial Distributors, L t d . , Johannesburg, S o u t h Africa
T
HE use of fine diamond powder to polish gem diamonds has
been in vogue for a very long period, but in recent years its application has been extended t o a variety of polishing operations, such as the preparation of metallographic specimens and the production of a mirror finish on dies and other surfaces of cemented carbide or hardened steel. Diamond powder fulfills the requirement for an abrasive which has a sharp, clean-cutting action with a minimum tendency to burnish, flow, or cold-work the metal surface. It cuts down polishing time and reduces relief between phases differing widely in hardness. I n both industrial applications and in metallography the harder alloys and carbides are met with increasing frequency, and greater use will be made of diamond powder to polish such surfaces. Diamond powder for polishing can be suspended in a liquid medium such as water, kerosene, or olive oil. In recent years, to conserve diamond powder as much as possible, it has been offered for sale in paste form by many suppliers of subsieve powders. Since these powders are usually closely graded into 0 to 2, 1 to 5 , 4 to 8, etc., microns, to facilitate identification the pastes are generally colored to designate a micron size. These pastes are satisfactory media to hold the diamond powder but are not water soluble and must be removed from the work with a solvent for oils or greases. It would be a decided advantage if a satisfactory water-soluble paste were available for this operation. Not only would it enable the polished object to be quickly and easily rinsed free of diamond powder and paste, but the recovery of diamond powder from water is much easier than from an organic solvent. EXPERIMENTAL
A suitable u-ater-soluble paste for suspending diamond polishing powder must fulfill several requirements. It must have the proper consistency so that it will adhere well to the object under polishing operations without being viscous enough to interfere with a free flow under rubbing pressures, Furthermore, this consistency must be maintained a t inside temperatures in industrial plants in all parts of the world, Le., a t approximately 0' to 38" C. The paste should be stable over long periods, with no separation into components on standing. It must not dry out on exposure to air or the slightly elevated temperatures created by polishing for periods up to 30 to 45 minutes. The paste should be capable of acquiring a uniform and stable color from a water-soluble dj-e, t o facilitate identification of the micron size of the diamond powder. These requirements were submitted to many chemical manufacturers throughout the world and a large number of samples were obtained for trial. The pastes were evaluated at this laboratory by carrying out lapping tests for 10 minutes on a hardened steel surface, using a conventional metallographic polishing machine. Fine silicon carbide and aluminum oxide abrasive powders were used in all preliminary tests as a substitute for the more expensive diamond powder. The paste was removed from the work by a stream of water under the tap. If a paste appeared promising under these conditions the lapping time was extended t o 30 to 45 minutes, and diamond powder was employed as the abrasive. Where a sample fulfilled one or more requirements but was lacking in other respects, an attempt was made a t this laboratory to overcome this defect by adding one or more reagents.
I n Table I are listed the pastes obtained for investigation, with their type, trade name, chemical composition if available, and supplier. CELLULOSE DERIVATIVES. From these compounds, pastes were prepared by dispersing suitable quantities in water with the aid of thorough stirring. A fairly low concentration of the cellulose compound, 5 to 20%, yielded the desired consistency. These compounds were found t o be unsuitable for this application. They dry out rapidly during any lapping operation, probably owing t o dehydration under friction, and the dehydrated compound is nearly insoluble in water. In addition, cellulose derivatives do not adhere particularly well to a metal surface and their gel nature is not conducive to uniform dispersion of the diamond powder throughout the mass of the paste. DETERGENTS OF THE SULFATED FATTY A N D AROMATIC HYDROCARBON TYPE. A number of detergents and wetting agents such as Teepol XL, Marlon, sodium lauryl sulfate, and many others were dispersed in glycol or ethylene glycol, but none were found suitable as a polishing paste. FATTY ACIDDERIVATIVES. Two proprietary fatty acid greases, sodium stearate, and a variety of soaps were dispersed in glycol but lapping tests indicated that they rapidly became difficult to work and tended to "roll-up" on the surface being polished. POLYETHYLENE GLYCOLSASD CARBOWAXES.Polyethylene glycols having molecular weights between 200 and 700 are liquids, while those with weights above 1000 are waxlike solids known as Carbowaxes. Carbowax 1500 was found to be the most satisfactory paste for diamond powder. It is an excellent medium in which to incorporate abrasive, does not dry out on lapping, adheres uell to the surface of the material being polished, is completely soluble in water, and is n-hite in color. 9large number of combinations of polyethylene glycols and Carbowaxes were investigated, and the following were also found to be suitable pastes for diamond powder: 1. Equal parts by weight of Carbowax 1540 and polyethylene glycol 200 2. A blend of 407, Carbowax 1540, 40% polyethylene glycol 600, 20Ye polyethylene glycol 200 3. One part of Carbowax 4000 and three parts of polyethylene glycol 600. 4. A blend of 35Ye Carbowax 4000 and 657, polyethylene glycol 200 5. Equal parts of Carbowax 4000 and ethylene glycol 6. Four parts of polyglycol 400 with one part of polyglycol 3500
POLYETHYLEXE GLYCOLS WITH FATTY ACIDS. The terminal hydroxyl groups of polyethylene glycols or Carbowaxes can be esterified by reaction with a saturated fatty acid such as stearic to give esters which are either soluble in water or form colloidal aqueous solutions. Many of these monoesters were dispersed in water or glycerol to form pastes but the latter were not satisfactory, yielding under lapping tests a waxy, unworkable residue. Dispersion of the polyglycol ester in hot ethylene or propylene glycol with thorough stirring, while the resulting mixture is cooled, gave a smooth creamy paste which could be employed as a carrier for diamond powder.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
February 1953
TABLE I. DESC :RIPTION Type Cellulose tives
deriva-
.
Trade Name or Description
Composition
Supplier
Celacol M.2500
Methylcellulose
Cellofas D
Carboxymethylcellulose
Du P o n t Sodium CMG, Grades 2WXH and 12 Ethyl hydroxyethylcellulose 2 600
Sodium carboxymethylcellulose
British Celanese, u. K. Imperial Chemical Industries, U. K. E. I. du Pont de Nemours & Co. U.S.A.
Methocel CP.
4000
Detergents of the Marlon sulfated fattv - .......... and aromatic-hydrocarbon type Teepol X L F a t t y acid derivatives
Soaps of various types Sodium stearate Sodium stearate Water-soluble greases 1930
4192 Polyethylene plycols and Carbowaxes
Carbowax 1000 Carbowax 1500 Carbowax 1540 Carbowax 4000
Polyethylene glycols with lanolin and sorbitol
..
Polyethylene glycol
Polyethylene glycol Polyethylene glycol
Long-chain eationic free base
Norman Evans 85 Rais, U. K. Coalite & Chemical Products, U. K. Jefferson Chemical Co., U.S.A. Whiffen & Sons.
...........
Grinding lubricants Gum arabic Rlonsanto reagents Santomerse
Alkyl phenol condensate
Santocel C
........... ............
Lustrex
............
Sodium naphthenate Triton K-60
Ellis Jones and Co., U. K. *Ellis Jones and Co., U. K.
Monester of poly*ethylene gly001s Monester of polyethylene glycols
U.S.A.
Union Carbide & Carbon Co., U.S.A. Union Carbide & Carbon Co., U.S.A. Union Carbide & Carbon Co., U.S.A. General Metal& lurgical Chemical, Ltd., U. K. Jefferson Chemical Co U.S.A. Jefferson’ Chemical Co., U.S.A. Glyoo Products Co.. U.S.A. Glyco Products Co., U.S.A.
...........
Pol yoxyethylene stearate Polyethylene glycol 400 monostearate Polyethylene glycol monostearate
............
Jefferson Chemical Co., U.S.A.
Nonyl phenol olus 9 moles ethylene oxide Nonyl phenol plus 14 moles ethylene oxide Polyglycol 3500
..........
Jefferson Chemical Co., U.S.A.
...........
Jefferson Chemical Co., U.S.A.
Tween 61
Cataid N F
National 10-130 Starch product
Dinonyl phenol plus 16 moles ethylene oxide
G 1441
Miscellaneous products
..
Union Carbide & Carbon Co., U.S.A. Polyethylene gly- Union Carbide & col Carbon Co., U.S. A. Polyethylene gly- Union Carbide col & Carbon Co.,
Polyglycol 400
G 1431
Kelco Co., U.S.A. Kelco Co U S.A. Kelco,Co:: U:S.A. Hopkin & Williams, U. K.
Sodium naphthenate Stearyl dimethyl benzylammonium chloride
Monsanto Chemical Co., U.S.A. Monsanto Chemical Co U.S.A. Monsantb: Chemical Co., U.S.A. National Starch Products, U.S.A. Hardman & Holden, U. K. Rohm & Haas, U.S.A.
Polyethylene glycol
Polyethylene glycol
Peg 42
Supplier
Sodium alginate Sodium alginate Sodium alginate Sodium alginate
........
Polyethylene glycol 5/30
Noncx 29
Composition
Kelgin LV Kelgin X L Keltex Manucol SS/LH
Sodium stearate
...........
Trade Name or Description
Sodium alginates
General Metallurgical & Chemical, Ltd., U. K. Dow Chemical Co., U.S.A.
Esters of free f a t t y acids Sodium stearate
Polyethylene glycol
Carbowax 4000 monostearate
Type
British Drug Houses, U. K .
Polyethylene glycol 600
Carbowax 1000 monostearate
PASTES
Sodium lauryl sul- British Drug fate Houses, U. K.
Polyethylene glycol
Diglycol stearate S M Y R J 45
Polyethylene gly001s with nonyl and dinonyl phenols and ethylene oxide condensations
Methylcellulose
Polyethylene glycol 200
Polyglycol3500 Polyethylene glycola with fatty acids
Ethyl hydroxyethylcellulose
OF
403
Polyoxyethylene sorbitol lanolin derivative Polyoxyethylene sorbitol lanolin derivative Polyoxyethylene s rbitol monosfearate
The following were found suitable: diglycol stearate S in ethylene glycol, MYRJ 45 in propylene glycol, Peg 42 in ethylene glycol, and polyethylene glycol 400 monostearate in ethylene glycol.
POLYETHYLENE GLYCOLS WITH NONYL AND DINONYL PHENOLS ETHYLENE OXIDE CONDENSATIONS. Various combinations of these substances were tried, and a mixture consisting of 12
AND
parts, by weight, of nonyl phenol and 14 moles of ethylene oxide, with one part of polyglycol 3500, was found t o give a satisfactory paste.
POLYETHYLENE GLYCOLS WITH LANOLIN AND SORBITOL. G 1431 and G 1441, which are polyoxyethylene lanolin sorbitol derivatives, were not suitable, owing t o a lack of proper lubricating qualities under lapping conditions. Tween 61, a polyoxyethylene sorbitol monostearate, when dispersed in ethylene glycol gave a satisfactory paste. SODIUMALGINATES.Sodium alginate dispersions in water in concentrations of 5 t o 10% yield gelatinous pastes similar to those produced b y cellulose derivatives. They dry out far too quickly under lapping conditions t o be of any use for diamond abrasive pastes. MISCELLANEOUS PRODUCTS. A large number of miscellaneous products were tried for this purpose, including sodium naphthenate, cationic free base, stearyl dimethyl benzyl ammonium chloride, starch, grinding lubricants, salts of aromatic sulfonic acids, resins, tar acids and saponified castor oil, gum arabic, alkyl phenols, and various surface active agents. These were tested alone, and mixed with glycerol, ethylene glycol, and other liquids. All of these substances were found to be lacking in one or more of the essential characteristics of a suitable paste. A brief summary of their shortcomings is in the following table:
Jefferson Chemical Co., U.S.A.
Sodium naphthenate
Atlas Powder Co.. U.S.A.
Cationic free base Steayyl. dimethyl benzyl ammonium chloride
Atlas Powder Co., U.S.A. Atlas powder Co., U.S.A.
Grinding lubricants Salts of aromatic sulfonic acids T a r acids and saponified castor oil Gum arabic Alkyl phenol
Dark color: too sticky: presence of free acid corrodes a steel surface Dries too quickly Dries too quickly Poor adhesive qualities; dries too quickly Dries too quickly Dries too quickly: emulsifies with water: dark color Settles into layers; dark color Too sticky Does not hold abrasive well
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INDUSTRIAL AND ENGINEERING CHEMISTRY
MIXIKGTHE DIAMOND POWDER WITH THE PASTE. The diamond abrasive pox-der can be easily dispersed uniformly in those pastes which were found suitable. This may be carried out by any form of efficient mechanical mixing. Alternatively, the paste may be melted, diamond powder added, the liquid thoroughly stirred and allowed to cool to room temperature. COLORING THE PASTE. Since all the pastes recommended above are white, they can readily be dyed various colors to designate the micron size of the diamond powder. The dye may be conveniently introduced into the paste simultaneously with the incorporation of the abrasive powder into the carrier. The addition of a few particles of a dye t o the melted paste, followed by the introduction of the diamond pair-der, with subsequent thorough stirring and cooling, will result in an evenly colored product. Oil-soluble dyes, such as those sold by the British Drug Houses, Ltd., dissolve readily in the recommended pastes, and when the latter are washed off the work with water, the dye likewise is completely water-soluble. OTHERSUSPENDING MEDIA. Although the pastes which were studied in this work comprised quite a variety of types, it should be emphasized t h a t probably many other compounds are available which may be quite satisfactory for this application. A recent reference ( 1 ) gives a table of commercial water-soluble and dispersible flexible synthetic materials of U. S. manufacture, from which a suitable reagent might perhaps be selected. CONCLUSIOh S
From the results of these investigations t h e following substances can be recommended as suitable water-soluble pastes for diamond powder used for abrasive purposes.
Vol. 45, No. 2
The most satisfactory paste is Carbowax 1500, obtainable from Union Carbide and Carbon Co. Various combinations of Carbowaxes and polyethylene glycols, likewise obtainable from Union Carbide, are suitable:
1. Equal parts by %eight of Carbowax 1540 and polyethylene glycol 200 2 . Mixture of 40y0 Carbowax 1540, 40Cj, polyethylene glycol 600, and 20% polyethylene glycol 200 3. One part of Carbowax 4000 and three parts of polyethylene glycol 600 4. Mixture of 3570 Carbowax 4000 and 657, polyethylene glycol 200 5 . Equal parts of Carbowax 4000 and ethylene glycol The polyglycol esters of Glyco Products Co., known as Peg 42 and Diglycol stearate S, when dispersed in ethylene glycol, may be used. Polyethylene glycol 400 monostearate, distributed by General Metallurgical and Chemical, Ltd., likewise dispersed in ethylene glycol, is also suitable. The polyoxyethylene stearates of the Atlas Powder Co., known as MYR.J,45 and Tween 61, when dispersed in propylene and ethylene glycol, respectively, gave good results. Two products of the Jefferson Chemical Co. may also be employed: four parts of polyglycol400 to one part of polyglycol3500 and 12 parts, by weight, of nonj-1 phenol plus 14 moles of ethylene oxide, t o one part of polyglycol 3500. LITERATURE CITED
(1) Zwicker, B. M. G . , IXD.ENG.CHEW.,44, 774 (1952) RECEIVED for review April 17,1952.
ACCEPTED September 23 1 9 6 2 ,
Sodium Dis ersions in Acetoacetic Ester Condensation ORVILLE D. FRAMPTON AND JOHN F. NOBIS Research Division, National Distillers Chemical Co., Cincinnati 37, Ohio
LAISEN ( 4 ) first reported the self-condensation of esters under t h e influence of sodium ethoxide over 80 years ago. Since that time this important reaction has been extended to include the condensation of a wide range of compounds. Not only esters, b u t aldehydes, ketones, nitriles, and certain other classes of compounds may be condensed in a similar manner. A great 18, 16, 81, 2?5)have been aimed at improvmany studies @ , 3 , 6,6, ing yields or elucidating the mechanism of this reaction. The general mechanism for the self-condensation of esters under the influence of sodium alkoxides or other bases has been established largely by Hauser and coworkers (12-16). Severtheless, there still remains some doubt as to the mode of action of metallic sodium when i t is employed directly. Despite the large volume of effort expended over the years, experimental conditions which will result in high yields in a reasonable time are still lacking. Commercial processes for the production of ethyl acetoacetate from ethyl acetate and sodium require nearly 20 hours of reaction time. Even then yields are only 80 to 85% and some unchanged sodium remains which requires special handling. The development of sodium in a highly dispersed form (9, 1 1 , 19) offers a means of overcoming the many difficulties encountered in the use of brick sodium in the acetoacetic ester condensation. T h e objective of this study was t o employ a sodium particle sufficiently small so t h a t complete reaction with ester might be ac-
complished before a crust of insoluble reaction product could cover the sodium surface and, in effect, remove it from the sphere of reaction. I n a finely dispersed form sodium is a much more rapid condensing agent than was formerly supposed. I n fact, in the condensation of ethyl acetate at elevated temperatures dispersed sodium appears to be almost as rapid a condensing agent as triphenylmethglsodium (13-16) is a t room temperature. Dispersed sodium is certainly more rapid than either sodium methoxide or sodium cthoxide, especially where relatively low tcmperatures must be employed. 3iECHANISM
It has been postulated t h a t four steps ( 1 8 ) represent the rracLions involved in the acetoacetic ester condensation when bases such as the sodium alkoxides are involved. (Plate I ) Sodium has long been assumed t o act as a condensing agent through the intermediate formation of a sodium alkoxide from alcohol present in the ester. I n fact, it was thought t h a t a trace of alcohol must be present in the ester t o effect any condensation a t all with sodium as the condensing agent ( 7 , 12, p. 278; 17,WS,86). The data presented in this paper indicate t h a t sodium reacts in a very different manner. When sodium is added directly to excess ester, as is often done in industrial practice, the reducing power of t h e sodium must be taken into account. The acetoacetic ester
