US3089848A - Oil compositions containing sodium nitrite - Google Patents

Description

United States Patent 3,089,848 on. coMPosrrroNs CONTAINING soorUM Nlli E This invention relates to lubricating compositions contaming sodium nitrite as a rust preventive. Particularly, the invention relates to compositions wherein the efiectiveness of sodium nitrite is enhanced by certain auxiliary additives and to methods whereby sodium nitrite is dispersed in stable, finely divided form, in lubricating greases.

The use of sodium nitrite as a rust preventive has long been recognized and it has been proposed to add sodium nitrite to lubricating greases in order to inhibit rusting of metal surfaces. This rusting can be caused by water or moisture which may become absorbed or entrained in the .grease during use or actually rejected by water repellant greases, thus directly contacting metal surfaces.

It has now been found that the use of certain auxiliary additive materials, specifically, metal naphthenates and fatty acid partial esters of aliphatic polyhydric alcohols (e.-g. sorbitan monooleate), will increase the effectiveness of the sodium nitrite in preventing rust much more than would be expected.

In addition, a new method of dispersing sodium nitrite in grease has also been found, which overcomes many of the disadvantages of prior methods. One such prior method involved mixing an aqueous solution of sodium nitrite into the lubricating grease and then heating to evaporate the water to thereby obtain a homogeneous dispersion of the nitrite in the grease. However, if the grease contains a soap or salt of a metal other than sodium, particularly divalent metals, then metathesis occurs at the high temperature necessary for the evaporation of water. The result is that metal of the soap or salt thickener is exchanged by sodium, thereby changing the characteristics of the original grease. This has been found particularly objectionable in the manufacture of alkaline earth metal greases, e.g. calcium soap grease, since the structural stability of the grease is down-graded by metathesis with the sodium nitrite. Another disadvantage of this method is that sodium nitrite crystallizes out of the aqueous solution in the form of rather large particles or crystals. These particles give the grease a grainy texture, as well as increasing its wearing tendency due to the abrasive nature of the sodium nitrite particles. Even when increased wear is not too great, the large size crystals give noisy and objectionable anti-friction bearing operation.

Another prior method of dispersing sodium nitrite in grease is disclosed in US. Patent No. 2,738,329. Here, the grease with sodium nitrite present, is heated to form a hot, fluid composition, i.e. heated to a temperature above the melting point of the grease. Upon cooling of the composition, the dropping point of the grease was very materially increased and other changes effected, even by the addition of small amounts of sodium nitrite. Apparently, some form of complex was formed between the grease thickener and the sodium nitrite. Thus, this method is not applicable Where the aim is only to increase the rust resistance of the grease, but not to alter any of its other properties.

3,08%,843 Patented May 14, 1963 ice Another prior method involves the simple addition of powdered sodium nitrite into a finished grease composition with stirring. This method, even though the resulting composition is homogenized, results in a grainy grease, increases its wearing tendency and frequently causes noisy bearing operation.

In the method of the present invention, sodium nitrite can be added to a grease without affecting any of the other properties of the grease except inhibiting rusting caused by entrained Water. Furthermore, a smooth, homogeneous, non-grainy product is obtained.

In the preferred form of the present method, commercial granular sodium nitrite is first dissolved in water, preferably boiling water, to form a super-saturated solution. Then a Water gelling agent is added to gel the solution which will thereby inhibit growth of any crystals that may form. Next, this water gel is mixed with an oil solution containing a low molecular weight polymer and the entire mixture is then heated to drive oif the water. As the water evaporates, the sodium nitrite crystals which are forming are coated by the low molecular weight polymer and their crystal growth is inhibited. The result is an oil dispersion of very finely divided sodium nitrite. This oil dispersion may then be conveniently mixed into the final grease composition, since the sodium nitrite concentrate dispersion is readily dispersed in cold or Warm grease compositions with a minimum of mixing.

The sodium nitrite is used in the final grease composition in amounts of 0.1 to 3.0 wt. percent, preferably 0.3 to 1.0 wt. percent, based on the weight of the total composition. The auxiliary additives which increased the effectiveness of the sodium nitrite are used in amounts of 0.05 to 1.0 part by weight, per part by weight of sodium nitrite.

The naphthenates are preferably the zinc or sodium salts of naphthenic acids, preferably having molecular weights of 250 to 350 and neutralization numbers of 225 to 175.

The fatty acid partial ester materials include the C to C fatty acid partial esters of aliphatic polyhydric alcohols having about 3 to 12, e.g., 3 to 8 carbon atoms, and about 2 to 8, e.g., 3 to 6 hydroxy groups per molecule. Preferred materials are the monoand diesters of C to C alcohols having about 3 to 6 hydroxyl groups and prepared from C to C fatty acids. The above type of partial esters includes the partial esters of the monohydrated aliphatic polyhydric alcohols, which are well known in the art, for example, see US. Patent 2,434,490, as well as partial esters of non-dehydrated aliphatic polyhydric alcohols, e.g. pentaerythritol monooleate.

Specific examples of the above types of partial esters will therefore include: glyceryl monooleate, pentaerythritol monooleate, sorbitan monooleate, the dioleates of sorbitan, mannitan, pentaerythritol and related polyhydric alcohols, the corresponding partial stearic and palmitic acid esters of these alcohols, and partial esters of these alcohols made from mixtures of these fatty acids.

The rust inhibiting combination may be added to any type of grease composition. Included are greases thickened with salts, soaps, soap-salt or mixed salt complexes, polymeric thickeners (e.g. polymers of C to C monoolefins of 10,000 to 200,000 molecular weight such as polyethylene), and inorganic thickeners (e.g. clay, carbon black, silica gel, etc).

Generally, the greases will comprise either a synthetic or mineral lubricating oil thickened with about 3 to 35 wt. percent, usually 3 to 20 wt. percent, of a thickener. In the case of soap-salt and mixed-salt thickeners, the thickener is usually formed by co-neutralization in oil, by metal base, of various mixtures of high molecular weight fatty acids and/or intermediate molecular weight fatty acids with low molecular weight fatty acids.

The high molecular weight fatty acids useful for forming soap-salt, soap and mixed-salt thickeners include naturally-occurring or synthetic, substituted and unsubstituted, saturated and unsaturated, mixed or unmixed fatty acids having about 14 to 30, e.g. 16 to 22, carbon atoms per molecule. Examples of such acids include stearic, hydroxy stearic, such as 12-hydroxy stearic, di-hydroxy stearic, poly-hydroxy stearic and other saturated hydroxy fatty acids, arachidic, oleic, ricinoleic, hydrogenated fish oil, tallow acids, etc.

Intermediate molecular weight fatty acids include those aliphatic, saturated, unsubstituted, mono-carboxylic acids containing 7 to 12 carbon atoms per molecule, e.g., capric, lauric, caprylic, nonanoic acid, etc.

Suitable low molecular weight acids include C to C fatty acids. Acetic acid or its anhydride is preferred.

Metal bases which are frequently used to neutralize the above acids are the hydroxides, oxides or carbonates of alkali metals (e.g. lithium and sodium) or of alkaline earth metals (e.g. calcium, magnesium, strontium and barium).

Various other additives may also be added to the lubricating composition (e.g. 0.1 to 10.0 weight percent based on the total weight of the composition), for example, oxidation inhibitors such as phenyl-alpha-naphthylamine; tackiness agents such as polyisobutylene; stabilizers such as aluminum hydroxy stearate; and the like.

As previously mentioned, the sodium nitrite and the other additives are preferably added to the grease in such a way so as to obtain an extremely small particle size. This is best accomplished by dissolving about 40 to 60 wt. percent based on total weight of water solution, of the combined sodium nitrite and auxiliary enhancing agent in water. Preferably as little water as possible is used to minimize the amount to be later removed by evaporation. This can be accomplished by using hot water, e.g. 150- 212 F., preferably boiling Water. Into this hot water solution, and preferably as quickly as it is formed and before any crystallization can occur, about 0.1 to 1.0 wt. percent, based on total weight of water solution, of a water gelling agent is added. The water gelling agent thickens or gells the solution upon cooling to substantially immobilize the solution. Thus, any sodium nitrite which crystallizes out from the solution is inhibited from growing into larger crystal sizes. Any water gelling or water thickening agent may be used. Preferred are the various ether celluloses such as methyl cellulose, ethyl cellulose or a group of materials sold under the tradename of Jaguar resins. Jaguar is Stein-Halls registered trademark for guar gum, a natural vegetable colloid. Guar gum is a polysaccharide (chemically classified as a galactomannan) consisting of a complex carbohydrate polymer of galactose and mannose. It is non-ionic and therefore will not degel in the presence of ionic salt solutions. Another particularly useful material to prevent the growth of crystals is a carboxy vinyl polymer neutralized with sodium hydroxide. A material of this type which was used in several of the examples is Carbopol 934 which has been neutralized with sodium hydroxide by simple mixing without removing the water of neutralization.

The above described water dispersion, either hot or cold, is next mixed with about .25 to 2.0 parts by weight, per part of water solution, of an oil solution of a polymeric material. Preferably polymers having molecular Weights of about 5,000 to 100,000 and which are oil dispersible can be used. Preferred polymers of this type are polypropylene and polyethylene, i.e. C to C monoolefin polymers. Such polymers are used in amounts of .05 to .15 part by weight, per part by weight of oil.

Next, the combination of the water solution and oil solution is heated sufficiently to drive off substantially all the Water. The result is a stable oil dispersion of the sodium nitrite in a very finely divided form dispersed in the oil. This oil solution in turn can be added to any grease composition.

While the above technique represents a preferred method of preparing the compositions of the invention, it is to be understood that the naphthenates and/ or partial esters may be used with the sodium nitrite employing other methods to disperse the nitrite in oil. For example, just simple mixing of finely divided sodium nitrite and the naphthenate and/or partial ester into the grease will give better rust protection than a like amount of either material alone. This simple mixing will result in a grainy grease giving noisy bearing operation as previously mentioned. However, while less preferred, this method may be used when graininess or noisy bearing operation are not important considerations.

The invention will be further understood by the following examples:

EXAMPLE I (All parts by weight) Inhibitor concentrate 1.-50 parts of sodium nitrite was dissolved in 50 parts of hot water while maintaining a temperature of 210 F. 0.5 part of Carbopol 934 (carboxy vinyl polymer) neutralized with sodium hydroxide in 0.2 part of water was next added, while boiling the sodium nitrite aqueous solution. After all the neutralized Carbopol 934 had been added and while still boiling the solution, there was next added 50 parts of an oil dispersion consisting of 10 wt. percent of atactic polypropylene having an average molecular weight of about 50,000, 1 wt. percent Span (sorbitan monooleate) and 89 wt. percent of a mineral lubricating oil having a viscosity of 55 SUS at 210 F. Boiling of the entire mixture was continued until all the water had been removed. The resulting dispersion had the following composition:

Percent Sodium nitrite 49.5 Neutralized Carbopol 934 0.5 Atactic polypropylene 5.0 Span 80 (sorbitan monooleate) 0.5 Mineral oil 44.5

Inhibitor concentrate 2.-The above preparation was repeated to form a second inhibitor concentrate but which contained no Span 80 whatsoever and instead contained 50.0 wt. percent sodium nitrite.

Inhibitor concentrate 3.A third inhibitor concentrate was prepared by dispersing 50 wt. percent of sodium nitrite in 50 wt. percent of a mineral oil having a viscosity of 55 SUS at 210 F. The sodium nitrite used was one of the most finely divided sodium nitrites available having an average particle size of about 35 microns.

Portions of each of the above inhibitor concentrates 1 to 3 were added by simple mixing at room temperature, in the amounts of 1, 2, 3 and 4 wt. percent, respectively, based on the weight of the total composition, to a calcium salt grease.

The calcium salt grease was prepared by neutralizing with lime, a mixture of acetic acid and Wecoline AAC acids (a mixture of C C and C fatty acids having an average molecular weight of about The neutralized mixture of acids was heated to a temperature of about 440 F. and dehydrated. About 6 moles of acetic acid were used per mole of Wecoline AAC acid. The total amount of thicknener constituted about 22 wt. percent of the grease, while its oil base was a mineral lubricating oil of 55 SUS viscosity at 210 F. After cooking at a temperature of 440 F. the grease was cooled to about mill.

These grease compositions containing the various inhibitor concentrates were tested by the CRC L-41 procedure which is an ASTM Tentative Method of Test for: Rust Preventive Properties of Lubricating Greases. Briefly stated this procedure involves taking a clean small Timken roller bearing, coating and packing the bearing with grease, rotating the hearing at 1750 rpm. under a load of 6 lbs. for one minute, then dipping the bearing in freshly boiled distilled water, followed by storing the bearing over water in a sealed jar for 14 days so as to provide a humid atmosphere. At the end of 14 days' the bearing is cleaned and examined for rust. The bearing is then rated on a scale, wherein R-l represents no rust whatsoever, R-Z represents no more than 2 faint rust spots, and R-3 represents more than 2 faint rust spots. R-3 is considered a complete failure, while R-1 and R-Z are considered as passing. Bearings having large rust spots were considered as failing badly.

The compositions prepared above, including the base grease without any rust preventive whatsoever, were tested by the above procedure. The results obtained are summarized in the following table:

Table 1 RESULTS or ORG L-41 RUST TEST The grease without inhibitor failed badly.

1. Contains oil, sodium nitrite, neutralized Carbopol 934, polypropylene Ilbibfiiis oil, sodium nitrite, neutralized Carbopol 934, polypropylene, (no Span 80).

3. Simple oil concentrate of sodium nitrite.

As seen by the above table, the compositions containing both the sodium nitrite and Span 80 (inhibitor concentrate 1) were very successful in the corrosion test even when used in an amount as low as 1 weight percent of inhibitor concentrate. On the other hand, by leaving out the extremely small amount of Span 80 involved, it required 4% of the inhibitor concentrate in order to effectively inhibit the rusting as shown by the results obtained when using inhibitor concentrates 2 and 3.

A second grease was prepared and all of the above tests repeated. The second grease was formed by nontralizing 13 parts of hydrated lime with 15.1 parts of acetic anhydride and 9.4 parts of Emery 32865 acid (a treated vegetable fatty acid consisting mainly of iso-oleic acid) in 61.5 parts of mineral lubricating oil having a viscosity of 55 SUS at 210 F., to which was added one part of phenyl-alpha-naphthylamine, (all parts are by weight). The neutralized mixture was dehydrated at a temperature of about 300 F. Exactly the same results were obtained with the second grease as were reported in Table 1.

EXAMPLE -II A base grease was prepared (wherein all parts are by weight), by dispersing 9.4 parts of tallow fatty acids and 13 parts of hydrated lime in 61.5 parts of mineral lubricating oil having a viscosity of 55 SUS at 210 F. These materials were mixed together at room temperature, and while stirring, 15.1 parts of acetic anhydride was slowly added, the temperature rising to a maximum of 180 F. After all the anhydride was added, external heating was initiated and the temperature of the composition increased to 320 F. in order to dehydrate the grease. At this point, 1 part of phenyl-alpha-naphthylamine was added as an oxidation inhibitor and the grease was allowed to cool to 90 F. The grease was then passed through a Morehouse mill having an 0.003" clearance. The resulting product had a dropping point above 500 F. and an ASTM unworked penetration at 77 F. of 323 mm./ 10, which upon working 10,000 strokes decreased only to 319 mm./ 10. The grease was also insoluble in both hot and cold water.

To the above base grease, was added sodium nitrite having an average particle size of 35 microns and zinc naphthenate in varying amounts. The zinc naphthenate was the zinc salt of a 250 molecular weight naphthenic acid obtained from a petroleum diesel oil fraction. These two materials were incorporated by mixing directly into the grease and then twice homogenizing in a Morehouse mill in order to thoroughly disperse the additive in the grease. Other samples were made up using the sodium nitrite and naphthenate alone. These various samples were then subjected to CRC L-41 test procedure described above. The results obtained are summarized in the following table:

Table II RUST TESTSCRC L-4l PROCEDURE Amount of Additive 1 Results of Rust Test None Fail (R-3), Badly rusted. 1% Zinc Naph. Fail (R-3).

2% Zinc Naph 2% NaNOz (35p) 1.0% NaNOa (3511).- 0.5% NaNOz (35 4)-. 0.25% Zine Naph...

Badly rusted. Pass (R 1), Unaffected, no rust spots or stains. Fail (It-3), Badly rusted. }Pass (R-l), Excellent protection.

1 Wt. percent based on the weight of the total composition.

EXAMPLE III A colloidal sodium nitrite concentrate base was prepared in the same general manner described above in Example I. The finished concentrate had the following composition:

Composition of concentrate: Percent wt. Water 2.00 Sodium nitrite 49.0 Carbopol 934 (neutralized) 0.13 Span 80 0.05 Atactic polypropylene 5.00

Mineral oil of 55 SUS. viscosity at 210 F 43.82

This concentrate was prepared as follows:

The sodium nitrite was added to an equal amount by weight of water and the mixture heated to boiling to completely dissolve all the nitrite. To this hot saturated aqueous solution was added a dispersion of Carbopol 934 dispersed in an amount of water equal to /2 the amount of water used in dissolving the sodium nitrite. After all the dispersion of Carbopol 934 had been added to the boiling water solution of sodium nitrite, and while still boiling, an oil solution of polypropylene was added. This polypropylene had a molecular weight of about 50,000. Evaporation of water was continued until about only 2 wt. percent of the total composition was water, after which the material was cooled and homogenized in a Morehouse mill at 0.003" clearance. This small amount of water present is desirable since it allows easier handling, results in smaller particle sizes and later gives 7 greater dispersion of the inhibitor concentrate in the oil. However, if desired, the inhibitor concentrate could be evaporated to complete dryness.

Four grease compositions were prepared in the same substantially all of said Water to thereby form a dispersion in said oil of polymer-coated sodium nitrite having an average particle size less than about 15 microns.

3. A method according to claim 2, wherein said olefin general manner as in Example II, but using the inhibitor .5 polymer is polypropylene. concentrate described immediately above. The composi- 4. A method of dispersing sodium nitrite in an oil tions of these greases are summarized in the following which comprises forming a solution of about 40 to 60 table along with their properties: wt. percent, based on the weight of said solution, of so- Table III Formulation (Percent Weight) Grease A Grease B Grease O Grease D Acetic Acid 10.0.. 12.9 12.9. Acetic Anhydride.- 14.0.- Wccoline AAO Acid 5.0.. 3 9-. 3 9 Tallow fatty acid 8.7.. l2rhydroxy stearic acid... 0 2.0 2.0. Hydrated lime 8.3.. 12.0 8.6.. 8.6. PhenyM-naphthylamine. 1.0... 1.0.. 0.3.. 0.3. Mineral oil 71.7.. 60.3... 71.0 67.9. NaNOz Concentrate 4.0.. 4.0-. 0.0... 4.0. Appearance F' ut Excellent Fxcellent Excellent, Dropping Point, F 500 500+ 500+. Penetrations, 77 F., mm./10:

Unworked 320 310 271 269.

Worked 60 strokes 330-... 315 291 208.

Worked 10,000 strokes Semi-Flui 317 304 377.

Rust Tests: ORG L-41 Method, Rating...- R-l (No rusting).. R-l (N0 rusting) R-3 (Fails) R-l (N o rusting). Microscopic examination determination of p size of the sodium nitrite in microns About 10 About 10 About 10.

As seen by the above table, grease C which contained diurn nitrite in boiling water; adding about 0.1 to 1.0 no sodium nitrite failed in the rust test, While greases A, wt. percent, based on the weight of said solution, of a B and D gave no rusting and had good all around propwater gelling agent to the boiling water solution of soerties. Furthermore, the preferred method of the invendium nitrite to thereby inhibit crystal growth of said sotion resulted in sodium nitrite particles of about 10 dium nitrite; adding to the resulting water solution, about micron size, while other common methods of forming 0.25 to 2.0 parts by weight, per part by Weight of Water sodium nitrite crystals result in larger particle size. Thus, solution, of an oil solution comprising 5 to 15 wt. percent the method can give particle sizes of 15 microns or less, of a C to C olefin polymer of 5,000 to 100,000 molecuwhile commercial sodium nitrite is of about 35 micron lar weight, heating the resulting mixture to evaporate size. Simple evaporation of aqueous solutions of sodium substantially all of said water to thereby form a dispernitrite in oil will also give a micron size of 35 or higher. sion in said oil of sodium nitrite having an average parti- As mentioned above, such larger particles (i.e. about 35 cle size less than about 15 microns. microns) give a gritty texture to the grease and causes 5. A method according to claim 4, wherein there is noisy bearing operation which is avoided by the method added to said boiling water, about 0.05 to 1.0 part by of the invention. Weight, per part by weight of sodium nitrite, of a ma- In summary, the present invention primarily relates terial selected from the group consisting of zinc and soto additive combinations of sodium nitrite with zinc or diurn salts of naphthenic acid of 250 to 350 molecular sodium naphthenate and/ or certain partial esters. The weight and C to C fatty acid partial esters of C to invention further relates to a new method of forming C aliphatic polyhydric alcohols having 3 to 6 hydroxy finely divided sodium nitrite in oil. The additive combigroups. nations are best used in the form of oil concentrates com- 6. A method according to claim 5, wherein said maprising about 20 to 60 wt. percent additive and 80 to 40 terial is sorbitan monooleate. wt. percent oil, preferably mineral oil, although of course 7. A method according to claim 5, wherein said oil any less amount of additive in oil can be used. is a mineral lubricating oil.

What is claimed is: 8. A rust inhibitor composition comprising sodium ni- 1. A method of forming a stable dispersion of finely trite dispersed in oil, which is prepared by forming a soludivided sodium nitrite in oil, said dispersion being useful tion of sodium nitrite in water, adding to said solution a as a rust preventive additive, which comprises forming a water gelling agent to gel said solution to thereby inhibit solution of sodium nitrite in water, adding to said solucrystal growth of said sodium nitrite, adding to said solution a water gelling agent to gel said solution to thereby tion an oil solution of an oil-soluble hydrocarbon polymer inhibit crystal growth of said sodium nitrite, adding to having a molecular weight of from 5,000 to 100,000 to said solution an oil solution of an oil-soluble hydrocarcoat said sodium nitrite, heating the resulting mixture bon polymer having a molecular weight of from about to evaporate substantially all of said water to thereby 5,000 to 100,000 to coat said sodium nitrite, heating the form a dispersion in said oil of polymer-coated sodium resulting mixture to evaporate substantially all of said nitrite having an average particle size less than about water to thereby form a dispersion in said oil of poly- 15 microns. mar-coated sodium nitrite having an average particle 5 9. A rust inhibitor composition prepared by forming size less than about 15 microns. a solution of 40 to 60 wt. percent, based on the Weight of 2. A method of forming a stable dispersion of finely said solution of sodium nitrite in boiling water; adding divided sodium nitrite in oil, said dispersion being useful about 0.1 to 1.0 wt. percent, based on the weight of said as a rust preventive additive, which comprises forming a solution, of a water gelling agent to the boiling water solution of sodium nitrite in water, adding to said solu 7 solution of sodium nitrite; adding to the resulting water tion a water gelling agent to gel said solution to thereby solution, about 0.25 to 2.0 parts by weight per part by inhibit crystal growth of said sodium nitrite, adding to weight of water solution, of an oil solution comprising said solution an oil solution of a C to C olefin polymer 5 to 15 wt. percent of a C to C olefin polymer of 5,000 of 5,000 to 100,000 molecular weight to coat said soto 100,000 molecular weight; adding about 0.05 to 1.0 dium nitrite, heating the resulting mixture to evaporate 7 part by Weight, per part by Weight of sodium nitrite, 0f

a material selected from the group consisting of zinc and sodium salts of naphthenic acid of 200 to 350 molecular weight and C to C fatty acid partial esters of C to C aliphatic polyhydric alcohols having 3 to 6 carboxy groups and heating the resulting mixture to evaporate substantially all of said water to thereby form a dispersion in said oil of sodium nitrite having an average particle size less than about 15 microns.

References Cited in the file of this patent UNITED STATES PATENTS Hollabaugh et al.:

10 Kroenig et a1. Jan. 24, 1956 Parry et al. Mar. 13, 1956 Cooke et a1 Aug. 14, 1956 Blake Dec. 19, 1961 FOREIGN PATENTS Great Britain July 10, 1957 Canada Nov. 11, 1958 OTHER REFERENCES Carboxymethylcellulose Uses and Applications, in Industrial and Engineering Chemistry, vol. 37, No. 10, October 1945, p. 946 relied

Claims (1)

1. A METHOD OF FORMING A STABLE DISPERSION OF FINELY DIVIDED SODIUM NITRITE IN OIL, SAID DISPERSION BEING USEFUL AS A RUST PREVENTIVE ADDITIVE, WHICH COMPRISES FORMING A SOLUTION OF SODIUM NITRITE IN WATER, ADDING TO SAID SOLUTION A WATER GELLING AGENT TO GEL SAID SOLUTION TO THEREBY INHIBIT CRYSTAL GROWTH OF SAID SODIUM NITRITE, ADDING TO SAID SOLUTION AN OIL SOLUTION OF AN OIL-SOLUBLE HYDROCARBON POLYMER HAVING A MOLECULAR WEIGHT OF FROM ABOUT 5,000 TO 100,000 TO COAT SAID SODIUM NITRITE, HEATING THE RESULTING MIXTURE TO EVAPORATE SUBSTANTIALLY ALL OF SAID WATER TO THEREBY FORM A DISPERSION IN SAID OIL OF POLYMER-COATED SODIUM NITRITE HAVING AN AVERAGE PARTICLE SIZE LESS THAN ABOUT 15 MICRONS.