US3096169A

US3096169A - Ammoniacal ammonium nitrate solution of reduced corrosive tendencies

Info

Publication number: US3096169A
Application number: US5637A
Authority: US
Inventors: Shapiro Paul; David B Sheldahl; Lawrence V Collings
Original assignee: Sinclair Research Inc
Current assignee: Sinclair Research Inc
Priority date: 1960-02-01
Filing date: 1960-02-01
Publication date: 1963-07-02
Anticipated expiration: 1980-07-02

Description

United States Patent AMMONIACAL AMMONIUM NITRATE SOLUTION 0F REDUCED CORROSIVE TENDENCIES Paul Shapiro, Chicago, Ill., David B. Sheldahl, Griflith,

Irld., and Lawrence V. Collings, Park Forest, Ill., asslgnors, by mesne assignments, to Sinclair Research,

Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Feb. 1, 1960, Ser. No. 5,637 16 Claims. (Cl. 71-59) The present invention relates to the corrosion of ferous metals. More specifically, the present invention reates to a novel composition having reduced corrosion .endencies toward ferrous metal surfaces.

There is a well recognized corrosion problem in iniustries concerned with the manufacture, storage, trans- )ortation and handling of ammoniacal-ammonium nirate solutions. In the handling of such solutions it is Jften necessary to transport and store them in ferrous :ontainers such as drums, tanks and pipelines. In view )f the corrosive nature of ammoniacal-ammonium nitrate iolutions against ferrous metals, many manufacturers w use storage and transportation facilities constructed )f aluminum. Aluminum is used because its oxide film 'enders the metal inert to attack by the ammoniacal salt l0llltl0l'1. This remedy, however, is a costly one. Corosion inhibitors of one type or another also have been :uggested and attempted with varying degrees of limited BUCCCSS.

One effective method for remedying the problem has new to deactivate the ferrous metal, for instance, by passivating the metal surface. Passivity is a property :xhibited by some metals whereby they become inacive toward certain chemical reagents. When a piece of 'eactive metal is made passive, its position in the electro- :hemical series is changed so that it is cathodic to a iece of the same metal which is in the active condiion. "Passivation of ferrous metals employed in a xxrrosive environment, is generally accomplished by conacting the metal with an oxidizing agent. The oxidizing lgent reacts with the ferrous metal forming a thin adlerent oxide film on its surface. This protective film :hields the ferrous metal from its environment and virtutlly no corrosion occurs.

Passive films produced by contacting ferrous metal with LQUCOUS solutions of oxidizing agents are found to be ery fragile and easily destroyed by mechanical damage, :hemical attack or electrolytic reduction. Hence, the lddlllOIl of a supplementary inhibitor has been necessary 0 provide protection when the passive film is destroyed. We have found, however, that some proprietory inhibiors, i.e. inhibitors containing reduced sulfur, e.g. -IH SCN, that are efiective inhibitors will frequently detroy the passive film.

Moreover, most passivation procedures require a twotep process, i.e. the ferrous metal must be first imnersed in an aqueous solution of the oxidizing agent beore it can be exposed to the ammoniacal solution. This s done for two reasons, (1) corrosion of the ferrous netal in the ammonia-ammonium nitrate solutions is exremely rapid resulting in the formation of a gelatinous leposit on the metals surface preventing access of the oxilizing agent to the surface and (2) the oxidizing agent nay be destroyed by reaction with ammonia present in he solution forming nitrogen and its oxides.

It has now been discovered that contacting a ferrous netal with ammoniacal ammonium nitrate solutions conaining a soluble copper compound, a soluble trivalent lrsenic compound and carbonate ions produces a tough vassive film on the ferrous metal that otters improved :orro'sion resistance to the metal. It has also been found hat ammoniacal ammonium nitrate solutions containing 3,096,169 Patented July 2, 1963 the above components, i.e. copper, trivalent arsenic, and carbonate ions, produce in situ a passive film on ferrous metal that is highly resistant to mechanical damage and electrolytic reduction, as well as chemical attack.

The copper compounds in the present invention are the soluble copper compounds as, for instance, the inorganic compounds such as cupric carbonates, hydroxides, sulfates, nitrates, etc. Of the many carbonate ion-producing compounds, the more particularly suitable are the inorganic compounds, for instance, alkali metal and ammonium carbonates. Preferably, the copper and carbonate components of the present invention are provided by a single compound such as basic copper carbonate.

The quantity of the aforementioned components employed in the present invention can vary considerably but are sufficient to give significant protection against corrosion. Gene-rally, the concentration of the copper component is at least about .01 g. per 100 ml. of ammoniacal solution. The maximum amount of the copper compound is limited only by economic feasibility and is generally not greater than about 0.2 g. per 100 ml. of ammoniacal salt solution. The preferred concentration is about .05 to .15 g. per 100 ml. of ammoniacal solution. The amount of carbonate compound employed is usually that sufiicient to provide a carbonate ion concentration of at least about .005, generally about .02 to .l g. per 100 ml. of ammoniacal solution. When basic cupric carbonate is employed, a concentration of about .01 to 0.2 gram/100 ml. of ammoniacal solution, preferably about .05 to .15, is usually suflicient.

The trivalent arsenic component of the present invention can be provided by a solution of any soluble trivalent arsenic compound, preferably a soluble inorganic trivalent arsenic compound. Inorganic trivalent arsenic compounds that can be employed include, for example, arsenic trioxide, an arsenite such as sodium, potassium or ammonium arsenite and sulfies of trivalent arsenic. Since As O dissolves slowly when added to solutions such as ammoniacal ammonium nitrate, it is desirable to first dissolve the compound in alkaline solution such as an aqueous solution of sodium hydroxide, sodium carbonate, ammonia, etc. Like the copper compounds, the arsenic compound may vary in amount, but is sufiicient to aiford the desired corrosion inhibition. Generally, the concentration of trivalent arsenic compound is at least about 0.01 g./100 ml. of ammoniacal solution, usually less than about 0.5 g./100 ml. and preferably about .05 to .25 g./ 100 ml. It is preferred that the composition of the present invention also contain small effective amounts of alkali metal, eg. sodium, hydroxide which can be conveniently provided in the composition as aforementioned, by employing an aqueous solution of the sodium hydroxide to dissolve the trivalent arsenic component. The amount of alkali metal hydroxide employed will usually be as stated before for the arsenic compound. In providing the ammoniacal ammonium nitrate solutions with the components of the present invention, we prefer the absence of significant amounts of halogen ions, e.g. Cl, which are known to be passive film destroyers.

Ammoniacal ammonium nitrate solutions may vary considerably in composition. Generally representative of such solutions encountered in industry and which give rise to the corrosion problem discussed hereinbefore, are those having approximately about 1 to percent ammonium nitrate, usually at least about 40 percent, preferably about 60 to 70 percent, about 5 to 35 percent free ammonia, preferably about 10 to 35 percent, and the substantial balance being Water, for instance, about 10 to 65 percent water. These percentages are by weight.

It has been noted that the corrosion by ammoniacal solutions is intense in the vapor zone, i.e. the portion of the vessel containing the ammoniacal solution which is in contact with vapors of the solution. Although the combination of components of the present invention provides good corrosion protection to the portion of the vessel in contact with the ammoniacal solution, adequate procharacteristics of a ferrous metal such as steel, i.e. makes the metal more electropositive, the phenomenon can be effectively studied by observing changes in the single electrode potential of the metal. A series of simple electrd tection is not always provided the portion in contact with 5 lytic cells were set up to achieve this end. vapor. This problem can be easily remedied by the addi- A steel rod was first activated (i.e. all surface films tion of vapor phase inhibitors such as urea, NH NO were removed) by exposure to 15% HCl at 150 F. until etc. We have also found that the addition of NO{ hydrogen bubbles were observed. The rod was then producing compounds such as an alkali metal nitrite to washed in deionized water and placed in an electrolytic the ammoniacal solution containing the components of 10 test cell filled with an ammoniacal solution consisting of the present invention very effectively reduces vapor phase 66.8% NH NO 16.6% NH and 16.6% H O. The eleccorrosion and this may be due to the formation of a trolytic test cell was a large mouth 8 ounce glass jar hav- CuNH NO complex. The vapor phase inhibitor is gening a salt bridge comprising a glass tube with agar-agar erally present in an amount sufficient to provide adequate solution saturated with KCI connected to a calomel cell rr si n pr and n ly i ab 5 to 15 immersed in saturated KCi. The calomel electrode probe 0.5 g./1OO ml. of ammoniacal solution. and the activated" rod were connected by leads to a The following examples are included to further illu Sheppard potentiometer by which potential measurements trate the invention. were obtained. Similar tests were conducted on the am- EXAMPLEI mania-ammonium nitrate solution containing small con- As aforementioned when a piece of active metal is made 20 of Various oxidiziflg agents combination passive, its position in the electrochemical series is of oxldlzlng agentsmvalent arsefllc compfmnds changed so that it is more cathodic to a piece of the same Where p y were 10 each case fil'st dlssolved Wlth all metal which is in the active condition. Since the formaequal Weight of Sodium hydroxide in dilute aqeuolls tion of passive films produces a change in the electrical tion. The results are shown in Table I.

Table I PASSIVATION OF STEEL IN NHz-NILNO; SOLUTION USING OXIDIZING AGENTS Concentration T t oxidizing agent 21100 in N NHr-NILNO:

solution Observed single electrode potontini of steel (volts to caiomel) Observations -0.74 0.42 to -0.72 (1 hour.)

0.46 to 0.73 (11 minutes)...

0.76 0.47 to 0.73 (4 minutes) --0.46 to -0.7s (1 minutes) 0.30 to 0.35 -(].35 to 0.45

0.29 to 0.20 0.37 to 0.34

0.36 to 0.74 (15 miuutes).... 0.37 to -0.16

Steel corroded, appearance of a slimy green ppt. on the steel surface. Slow corrosion. Rapid corrosion.

Do. Do.

Rapid corrosion, brown ppt. (due to formation of Mn0;) Rapid corrosion, not too soluble. Slow corrosion.

Rapid corrosion.

Slow corrosion. Passive, metal bright and clean.

Do. Do.

Passive, metal bright and clean, large white ppt. forms,

probably insol. AsiOr.

Passive, metal bright and clean. Passive, metal bright and clean, large white ppt. forms,

probably insol. AS505.

Steel corroded.

asslve.

Rapid corrosion.

. Passive.

Rapid corrosion.

lllS (I HQIOOr -0.50 to 0.71 (2D mlnutes) -0.76

Table IContinued Concentration Pest Oxidiziug agent g./1D0 ml. Observed single electrode po- Observations 10. NHr-NH4NO3 tential of steel (volts to calomel) solution 1--.. CuS 0.1 0.39 to 0.28 Passive.

plus (N H0300:

plus AS103 Cu(NO=J, 0.40 to 0.29 Do.

plus (NH4)1CO:

plus

0.76 0.49 to 0.75 (5 minutes) Rapid corrosion. Slow corrosion.

Rapid corrosion.

Do. Slow corrosion.

Table I above indicates that most oxidizing agents when added to NH NH NO solutions produce untable if any, passive films on exposed steel surfaces, due pparently to their reaction with ammonia. Na Cr O O (NH S O and the basic cupric carbonate-trialent arsenic combination apparently are not too reactive tact through the external circuit was maintained with the steel. If after five minutes the Flade potential was not exceeded, the copper wire was then brought into physical contact with the steel. Ordinarily this procedure was suiiicient to destroy the film. Table II below contains the results of this test.

Table II EFFECT OF CONTACT WITH A 2", #12 Cu WIRE ON THE SINGLE ELECTRODE POTENTIAL OF STEEL (VOLTS TO CALOMEL) Test Cone. g./100 ml. Time Time, Physical contact Time,

No. Oxidizing agent N1-I NH4NO= exposed, Electrical contact min. (wire touches rod) min.

solution hours An (NliqhSzOs .l 0. 15 23.0 0.21 to (].78.. 0. 5

B (NIlImSme 0.1 26.0 0.30 to -0.77. 0. 75

0:1 25.5 -0.35 to 0.56 5. 0 0.56 to 0.75 2.0 0.1 26. 0 0.46 to -0.60 5. 0 0.(i0 to 0.71 9.0

0. 1 0.1 26. 5 -0.44 to -0.59 5.0 0.59 to 0.73 2.0

23. 5 0.28 to D.58l. 5.0 -0.58

g1} 27 -0.2a to o.59, -.59 to 0.436 0: 1

1 More than 9 days.

vith the solution and produce passive films in situ. The ame is true in tests 33 and 34 where copper, carbonate nd arsenic were supplied in another manner.

The decay of passivity can be observed by recording he decrease in potential when a metal cathodic to the assive steel is brought into electrical contact with it. .he potential shift in the more active direction (i.e., nore electronegative) is due to the electrolytic reduction if the film by the current that is created by the galvanic ouple. When passive steel is activated there is first a teep fall of the potential in the active direction; second, y a less step change lasting for a fraction of a minlte to several minutes; and third, by a steep descent o the active value (i.e., complete breakdown of the iassive film; 0.71 to -0.77 volts to calomel for -IH --NH NO The value of the potential immedittely preceding this last descent is called the Fladc otential.

To determine the resistance to electrolytic destruction if the passive films produced by the above reagents, an lctivated steel rod was first exposed for about a day to JH NH NO solution containing the oxidizing agent 0 that it might become passivated. Then a two-inch niece of No. 12 copper wire was placed in the test soluion with the passive steel. Initially only electrical con- 9 More than 6 days.

Table II indicates that the basic cupric carbonatearsenite combination produces a very highly stable and resistant passive film when introduced to ammonia-ammonium nitrate solutions. The combination is also efiective in repairing any breaks in the film. A deep scratch was cut on the face of the coupon. The coupon was then reinserted in the ammonia-ammonium nitrate containing the basic cupric carbonate-arsenite combination. The coupon was kept in the ammoniacal salt solution for over 2 weeks with no visible signs of corrosion. A good result was also obtained with another copper, arsenic and carbonate composition in test H.

In summary, the addition of the inhibitor combination of the present invention to corrosive solutions such as ammoniacal salt solutions will inhibit the corrosion of ferrous metal apparatus in which these solutions are handled, stored, etc. This will result in greater product purity and reduce the destruction of shipping and storage facilities which are used commercially such as in the fertilizer business. This advantage can in turn enable manufacturers of these corrosive solutions to use less costly equipment for handling these solutions. Further in many corrosive solutions like ammoniacal salt solutions, the cupric components of the present invention produces a clear solution with an intense blue color,

which color can be used to show that a controlled and adequate concentration of inhibitor is present. In addition, copper is one of the trace elements required for normal growth of many plants. Hence, incorporation of the cupric compounds of the present invention in ammoniacal fertilizer solutions may enhance their Value as fertilizers.

We claim:

1. A composition consisting essentially of an aqueous ammoniacal ammonium nitrate solution, about 0.01 gram to less than about 0.5 g./100 ml. of said solution of a trivalent arsenic compound, soluble in said solution, about 0.01 to about 0.2 gram/100 ml. of said solution of a copper compound soluble in said solution, and about .005 to .1 gram/100 ml. of said solution of carbonate ions, the amounts of said compounds and ions being sufficient to substantially reduce the rate of corrosion by said solution to ferrous surfaces.

2. The composition of claim 1 in which there is in cluded a small amount of alkali metal hydroxide.

3. The composition of claim 2 in which the hydroxide is sodium hydroxide.

4. The composition of claim 1 wherein the concentration of the trivalent arsenic compound is about 0.05 to 0.25 gram/100 ml. of said solution, the concentration of the copper compound is about .05 to .15 gram/100 ml. of said solution and the concentration of the carbonate ions is about 0.02 to .1 gram/100 ml. of said solution.

5. The composition of claim 1 where the copper and carbonate ions are supplied by basic copper carbonate.

6. The composition of claim 3 where the copper and carbonate ions are supplied by basic copper carbonate.

7. A composition resistant to corrosion of ferrous surfaces consisting essentially of an aqueous ammoniacal ammonium nitrate solution of about 40 to 80% ammonium nitrate and about to 35% ammonia, having added thereto about 0.05 to 0.25 gram/100 ml. of said solution of AS303, about 0.01 to 0.2 gram/100 m1. of said solution of basic copper carbonate, and about 0.05 to 0.25 gram/100 ml. of said solution of sodium hydroxide.

8. The composition of claim 7 wherein the amount of basic copper carbonate is about 0.05 to 0.15 gram/100 ml. of said solution.

9. The composition of claim 7 having added thereto a small, eliective amount of sodium nitrite as a vapor phase corrosion inhibitor.

10. A composition consisting essentially of an aqueous ammoniacal ammonium nitrate solution, about 0.01 to less than about 0.5 gram/100 ml. of said solution of an inorganic tri-valent arsenic compound soluble in said solution, about 0.01 to 0.2 gram/1'00 ml. of said solution of a copper compound soluble in said solution, and about .005 to .1 gram/100 ml. of said solution of carbonate ions, the amounts of said compounds and ions being sufficient to substantially reduce the rate of corrosion by said solution to ferrous surfaces.

11. The composition of claim 10 wherein the copper compound is an inorganic copper compound.

12. The composition of claim 11 wherein the ammoniacal ammonium nitrate solution is of about 1 to ammonium nitrate, about 5 to 35% ammonia with the substantial balance being water and the concentration of the trivalent arsenic compound is about 0.01 to 0.5 gram/ ml. of said solution, the concentration of the inorganic copper compound is about 0.01 to 0.2 gram/ 100 ml. of said solution and the concentration of the carbonate ions is about 0.005 to 0.1 gram/100 ml. of said solution.

13. The composition of claim 12 wherein the copper and carbonate ions are supplied by the addition of about 0.01 to 0.2 gram/100 ml. of said solution of basic copper carbonate.

14. The composition of claim 13 in which the trivalent arsenic compound is arsenic trioxide.

15. The composition of claim 12 in which there is included about 0.01 to 0.5 gram/said solution of alkali metal hydroxide.

16. The composition of claim 15 in which the hydroxide is sodium hydroxide.

References Cited in the file of this patent UNITED STATES PATENTS

Claims

1. A COMPOSITION CONSISTING ESSENTIALLY OF AN AQUEOUS AMMONIACAL AMMONIUM NITRATE SOLUTION, ABOUT 0.01 GRAM TO LESS THAN ABOUT 0.5 G./100 ML. OF SAID SOLUTION OF A TRIVALENT ARSENIC COMPOUND, SOLUBLE IN SAID SOLUTION, ABOUT 0.01 TO ABOUT 0.2 GRAM/100 ML. OF SAID SOLUTION OF A COPPER COMPOUND SOLUBLE IN SAID SOLUTION, AND ABOUT .005 TO .1 GRAM/100 ML. OF SAID SOLUTION OF CARBONAATE IONS, THE AMOUNTS OF SAID COMPOUNDS AND IONS BEING SUFFICIENT TO SUBSTANTIALLY REDUCE THE RATE OF CORROSION BY SAID SOLUTION TO FERROUS SURFACES.