US2782100A - Method of improving stability of concentrated hydrogen peroxide in contact with stainless steel and aluminum alloys - Google Patents

Description

Frank P. Greenspan, Buffalo, N. Y., assignor, by mesne assignments, to Food Machinery and Chemical Corporation, San Jose, Calif., a corporation of Delaware No Drawing. Application January 13, 1951, Serial No. 205,968

1 Claim. (Cl. 23-2075) This invention relates to a method of improving the stability of a concentrated solution containing at least 70% hydrogen peroxide when brought in contact with stainless steel and aluminum alloys. 7

This application is a continuation in part of my copending abandoned application Serial No. 734,550 filed March 13, 1947 for Inhibiting the Decomposition Normally Resulting from Contact of Hydrogen Peroxide with Metallic Surfaces.

Highly concentrated hydrogen peroxide is extremely sensitive to minor amounts of contaminants, especially certain metals. When exposed to such metals such hydrogen peroxide decomposes rapidly and the rate of decomposition increases with increases in temperature. Included among such metals are stainless steel and aluminum alloys although the rate of decomposition of highly concentrated hydrogen peroxide will vary with different stainless steel and aluminum alloys. Further such highly concentrated hydrogen peroxide in direct contact with such stainless steel and aluminum alloys attacks and rapidly corrodes the surface of the alloys.

Such stainless steel and aluminum alloys are particularly desirable in handling highly concentrated hydrogen peroxide because most of them possess high Another object is to provide such a method which prevents material decomposition of such concentrated hydrogen peroxide when subjected to elevated temperatures.

Another object is to provide such a method which involves the addition of a minimum amount of the substances necessary to prevent decomposition of such. concentrated hydrogen peroxide and the alloy surfaces contacted thereby, many end uses of hydrogen peroxide having a concentration of 70% or more demanding the minimum use of additives in the concentrated hydrogen peroxide.

It is only recently that highly concentrated hydrogen peroxide, that is, of 70% concentration or higher, has

been produced in sufficient quantity to permit of commercial application of the same. There are available,

- at the present time, aqueous solutions containing hydrogen peroxide of 70% and higher concentration and very little other than hydrogen peroxide and water.

With the practice of the present invention the stability of hydrogen peroxide having a concentration of at least 70% and in contact with stainless steel and aluminum structural strength and other attributes highly desirable in connection with both the handling and also the unusual end uses of concentrated hydrogen peroxide. Thus concentrated hydrogen peroxide find many applications as a chemical propellant wherein the high energy of decomposition combined with the release of large volumes of gases (steam and oxygen) are effectively employed to propel rockets, torpedoes and submarines. For such applications, structural considerations require the use of high strength, high temperature resistant and pressure resistant materials. It is further requisite that the material of construction not result in excessive decomposition of the hydrogen peroxide fuel for most frequently the missile is loaded with hydrogen peroxide and then stored for considerable periods of time prior to use. Since loading calculations are based upon energy requirements at the moment of use and since this energy is a function of the hydrogen peroxide available, it-is important that untoward decomposition of the hydrogen peroxide prior to use would seriously and dangerously affect proper performance of the equipment.

It is therefore the principal object of the present invention to provide a method of improving the stability of a concentrated solution containing at least 70% hydrogen peroxide when brought in contact with the surfacesof stainless steel and aluminum alloys, such alloys being particularly desirable for use in all types of equipment for handling, confining, controlling and conveying such concentrated hydrogen peroxide, such as containers, pipes, pumps and other equipment.

Another object is to provide such a method which reduces deterioration of the surface of such stainless steel and aluminum alloys when contacted with such concentrated hydrogen peroxide.

alloys can be materially improved, in fact to an extent to provide a stability which compares favorably with that achieved with glass ,or substantially pure aluminum which do not accelerate the decomposition of hydrogen peroxide. These alloys are commercially available stainless steel and aluminum alloys which can possess very high structural strength and high temperature and pressure resistance as compared with such glass or substantially pure aluminum.

In accordance with the present invention the stainless steel alloys or aluminum alloys are first passivated by the application of hydrogen peroxide containing a small amount of orthophosphoric acid. Also in so passivating the stainless steel or aluminum alloys, the hydrogen peroxide containing a small amount of orthophosphoric acid must be left in contact with the alloy for at least one hour. After such passivation hydrogen peroxide having a concentration of 70% or higher, and to which a very small amount of orthophcsphoric acid has been added, can be brought into and left in contact with the passivated surfaces of the stainless steel or aluminum alloy for long periods of time with only a slight decomposition of the hydrogen peroxide taking place. The results in regard to stability of such highly concentrated hydrogen peroxide approximate those of hydrogen peroxide of the same concentration in contact with glass or substantially pure aluminum for the same length of time and in some cases the results obtained by the practice of the present invention are superior. The present invention is applicable only to solutions containing hydrogen peroxide of 70% or higher concentration and is not effective in reducing the decomposition of lower concentrations of hydrogen peroxide such as 30% solutions. Accordingly the practice of the present invention is limited only to solutions containing 70% or more hydrogen peroxide.

A number of conditions are essential to the practice of the present invention. It is essential that the passivation of the stainless steel or aluminum alloys be eflfected with a solution containing both hydrogen peroxide and orthophosphoric acid. The alloy surface cannot be effectively passivated by either subjecting it to hydrogen peroxide by itself or by subjecting it to orthophosphoric acid by itself. It is further essential that the concentration of the hydrogen peroxide in this passivating solution be at least 20% and the-orthophosphoric acid present in an amount not less than about 10 parts per million (hereinafter referred to as p. p. m.). It is further essential that this passivating solution must be maintained in contact with the stainless steel or aluminum alloy Patented Feb. 19, 19,57

surface for at least one hour to passivate the alloy. It is also essential that the hydrogen peroxide to be confined by the passivated alloy surface must be highly concentrated, that is, at a concentration of 70%hydrogen peroxide orhigher. It is further essential that this concentrated hydrogen peroxide to be confined must contain orthophosphoric acid, also only a small amount, as little as 5 p. p. m. being required, larger'amounts than p. p..m.--being without further benefit. When these conditions are observed, however, the stainless steel or aluminum alloy :has been found to be substantially as effective as the Pyrex glass orsubstantiallypure aluminum.now used in preventing'decomposition of confined highly concentrated hydrogen peroxide at both low and elevated temperatures. When these conditions are observed, also, the surface of thestainless steel or aluminum al1oy..contacted.b,y the highly concentrated hydrogen peroxide is not corroded, pitted or otherwise adversely affected by .the hydrogen peroxide.

It is known that hydrogen peroxide can be stabilized by the addition thereto of certain materials which tend to retard decomposition of hydrogen peroxide,. but such stabilizers are generally ineffective in the presence of metals. Examples of stabilizers which have been commercially used are sodium stannate, 8-hydroxyquinoline, sodium pyrophosphate, orthophosphoric acid and sodium fluoride. Of these stabilizers, I have found that only orthophosphoric acid is efiective in inhibiting the decomposition of hydrogen peroxide in contact with stainless steel and aluminum alloys andv then only if all of the essential conditions of the present invention and enumerated immediately above have been observed.

I have further found that instead of orthophosphoric acid, orthophosphoric acid forming substances or substances containing orthophosphoric acid or orthophosphoric acid forming substances can be used in both the passivation treatment and also in the highly concentrated hydrogen peroxide to be confined although in the latter it is preferred to use orthophosphoric acid of high purity inasmuch as it is usually desirable to hold the foreign substances in the confined highly concentrated hydrogen peroxide to a minimum.

Table I shows that the concentration of the hydrogen peroxide above the lower operative limit of 20%. and the amount of orthophosphoric acid above the lower operative limit of about 10 p. p. m., used in passivating the alloy, are not critical. This table shows the slight differences in the stability of 90% hydrogenperoxide stabilized with 10 p. p. m. orthophosphoric acid in contact with a stainless steel alloy initially passivated with different solutions containing various concentrations of hydrogen peroxide and various amounts of orthophosphoric acid, the passivation treatments having been carried on at 66 C. and allowed to stand over a period of to hours. The stainless steel alloy used is commercially designated as SS 316 and its composition is as set forth in Table V.

Table I STABILITY OF 90% H202 CONTAINING 10 P. P. M. HsPO4 IN CONTACT WITH SS 316 AFTER VARIOUS PASSIVATING TREATMENTS Percent Active Oxygen Passivatlng'Treatment Loss It has been found that the critical factors in such passivation are that both orthophosphoric acid and hydrogen peroxide must both be present in the passivat ing solution; the concentration of the hydrogen peroxide must be not less than 20%; the orthophosphoric acid must be present in an amount not less than about 10 p. ,p. m.; and the passivating solution must bemaintained in contact with the alloy surface for at leastone hour.

The time required for maximum 'passivation of the stainless steel or aluminum alloy is dependent upon the temperature and concentration of hydrogen peroxide in the passivating solution. Thus with a passivating solution containing 90% hydrogen peroxide and 10 p. p. m. orthophosphoric acid and maintained at 66 C., 12 hours was required fol-maximum passivation, whereas the same solution at C. required 200 hours for maximum passivation. Also with a .passivating' solution.;containing 30% hydrogen peroxide and 10 p. p. m. orthophosphoric acid and maintained at 66 C., 16 hours was required for maximum passivation, whereas the same solution at 30 C., required .200 hours .for maximum passivation. All end uses do not require maximum passivation and under optimum operating conditions a commercially satisfactory passivation of stainless steel or aluminum alloys can be obtained in as little as one hour, although maximum passivating etfect is not achieved at this lower time limit.

In Tables II, III, IV and V, are listed the stabilities of hydrogen peroxide with and without stabilizers, determined in accordance with. the following procedure: 75 ml; of 90% hydrogen peroxide contained in a ml. Erlenmeyer Pyrex glass flask, especially cleaned by successive sodium hydroxide, sulfuric acid and distilled water treatments, was used in all tests. All 90% hy drogen peroxide used was from one source and in an originally unstabilized condition. Flasks containing samples under test were covered by 3 inch squares of aluminum foil. Flasks were weighed at regular intervals and approximately 0.3 gram aliquots were removed for the standard hydrogen peroxide assay. The percentage of active oxygen loss shown in the tables represents a figure corrected for weight change but includes losses due both to decomposition and vaporization of the hydrogen peroxide. All test flasks were allowed to stand in an oven maintained constantly at 66 C.

Table II shows the stabilities of 90% hydrogen peroxide with and without various stabilizers in contact with Pyrex glass and in the absence of any metal.

Table II 90% H202 STABILI'IIES .VVI'IH STABILIZERS IN CONTACT WITH PYREX GLASS (NO METAL) 1 Concentration expressed as p. p. 111. Sn.

' Referring to .Table .II, the 90% hydrogen peroxide stabilities in Pyrex glass show orthophosphoric acid to be uniformly the best stabilizer. good stabilities. Both sodium stannate and sodium pyrophosphate show good stabilities in p. p. m. concentra tion but fall ofi rapidly in 100 and 1000 p. p. m. concentrations, presumably because of the alkalinity increase.

Stabilities of 90% hydrogen peroxide with and without stabilizers in the presence of one type of stainless steel alloy commercially known as SS 347 (Table V) were determined at a temperature of 66 C. by the standard procedure described above and the results are listed in Table III. Strips, /2 inch wide by 3 inches long, of SS 347 were used. These were cleaned by treatment in carbon tetrachloride followed by treatment with a 45% nitric acid solution at 45 C. for 45 minutes. After washing in distilled water, the strips were air dried. When placed in the hydrogen peroxide, the strips were approximately one-half immersed. Under the column headed Non- Passivated, in Table III, are listed the percent active oxygen loss per week of 90% hydrogen peroxide in contact with the SS 347 strips and containing the various kinds and amounts of stabilizers indicated, the strips being immersed only once. Under the column headed Passivated, in Table III, are listed the precent active oxygen loss per week of 90% hydrogen peroxide in contact with SS 347 strips which were given a first immersion corresponding to that indicated in the Non-Passivated column, then removed, washed with distilled water and air dried although these washing and drying steps are not essential. Following this passivation the strips were immersed in samples containing 90% hydrogen peroxide and the same kinds and amounts of stabilizers, the stabilities of these second samples being listed in Table III.

Table III 90% H202 STABILITIES IN CONTACT WITH S9347 WITH AND WITHOUT STABILIZERS Non-Passivated Passivated Amount Stabilizer in Percent Ac- Percent Ac- 1 p. p. m tive Oxygen tive Oxygen Loss Per Loss Per .Week Week None 0 100 10 57.3. Sodium Stannate 100 99.0

1, 000 100 (1 day).

10 69.1.... 8-Hydroxyquinoline 100 72.3. 1,000 100 (1 day 10 .6 Sodium pyrophosphate 100 .3

1,000 100 (1 day).-- 10 13.1 orthophosphor c Acid 100 20.8

1,000 40.8 10 79. 100 (1 day) Sodium Fluoride 100 100.. 90.5.

g 1,000 100 (1 day). 100.

satisfactory, decomposition of 90% hydrogen peroxide being 100% in one day for 1000 p. p.'m. and 72% in one week for 100 p. p. m. Likewise, 10 p. p. m. sodium stannate and sodium pyrophosphate, which are effective stabilizers for 90% hydrogen peroxide in Pyrex glass, show bad stabilities in the presence of stainless steel.

It will be noted that the results with passivated SS 347 show surprising increases in stability for orthophosphoric acid stabilized samples, onlyja 1.2% active oxygen loss per week occurring in the 90% hydrogen peroxide stabilized with 10 p. p. m. orthophosphoric acid. This increase in stability following a passivation treatment with samples containing orthophosphoric acid is pronounced.

8-hydroxyquinoline shows Stabilities of hydrogen peroxide with and without stabilizers in the presence of another type of stainless Table IV 90% H202 STABILITIES IN CONTACT WITH SS 316 WITH VARIOUS STABILIZERS Non-Passivated Passivated Amount Stabilizer in Percent Ac- Percent Acp. p. m. tive Oxygen tive Oxygen Loss Per Loss Per Week Week 49.3. Sodium Stannate j. 77.

(1 day). I 53.1. 8-Hydroxyquinoline 44.7.

100 (1 day). 11 n t 2%? Sodium Pyro 0s a e p p 10g) (1 day). Orthophosphoric Acid 2.14. p 74.. 87.1. Sodium Fluoride... 100 100 100 (1 day).

v 1,000 100 (1 day)... 100 (1 day).

Referring to Table IV, theresults of the tests with SS 316 are similar to those of the tests, Table III, in showing that orthophosphoric acid is the most eitective stabilizer for 90% hydrogen peroxide and thatpassivation with hydrogen peroxidecontaining orthophosphoric acid increases the stability. It will be noted that only a 1.5% active oxygen loss per week occurred in the 90% hydrogen peroxide stabilized with 10 p. p. m. orthophosphoric acid in conjunction with a passivation of SS 316 with hydrogen peroxide containing orthophosphoric acid. This stabilityapproaches that for the best stabilized 90% hydrogen peroxide in Pyrex glass (Table II).

Stabilities of 90% hydrogen peroxide in the presence of other stainless steel alloys were determined. Separate tests were conducted at 30 C. and 66 C. using samples of 90% hydrogen peroxide stabilized with 10 p. p. m. orthophosphoric acid in contact with non-passivated and passivated stainless steel strips. Non-passivated. strips were given the standard carbon tetrachloride and nitric acid treatment. Passivated strips were given the same treatment for non-passivated strips and thereafter Washed with distilled water, air dried and then immersed. in 90% hydrogen peroxide containing 10 p. p. m. orthophosphoric acid and allowed to stand. 15 to 20 hours at the respective temperature. Comparative results on different types of stainless steel alloys are shown in Table V. The compositions of the various stainless steel alloys are shown in Table V, the amounts of alloying elements being.

shown in percentages and the balance of the alloy being iron. Referring to Table V, the figures listed under the columns headed percent active oxygen loss per week have been corrected for weight losses and the figures listed under the columns headed percent absolute concentration loss per week were determined by subtract-- ing the final percent concentration from the original percent concentration.

Curves plotted for the percent active oxygen loss versus time for passivated stainless steel samples in 90% hydrogen peroxide containing 10 p. p. m. orthophosphoric acid represent a proportional relation as indicated by a straight line curve. Accordingly, the slope of the curve, viz, percent active oxygen loss per week, has been used as a stability figure.

.T able V STABILITIES F'90% H2O: CONTAINING P. P. M. Ha'POt IN CONTACT WITH PASSIVATED LAND NON-PASSIVATED STAIN- LESS STEEL ALLOYS V *Passlvated Non-Passlvated 06 0. -Test 30 0. Test 60 C. Test 30 0. Test Stainless Steel Composition 1 Percent Percent Percent Percent Percent Percent, Percent Percent Act. Abso- Act. Abso- Act. Abso- Act. Abso- Oxygen lute Oxygen lute Oxygen lute Oxygen lute Loss/ Cone. Loss/ Conc. Loss/ Cone Loss/ Cone. Wk. Loss/ Wk. Loss/ Wk. Loss/ Wk. Loss/ x Wk. Wk. Wk. Wk.

304 (Dalia-2&0; Ni 8-10; C .08-Cold 1.5 0.9 0.4 0.3 5.0 2.1 1.5 0.7

o e. 309 -Gl2illl-isi; Ni 12-15; C 0.2-Cold 1.5 0.6 0.3 0.3 10.4 4.7 1.5 0.5

U o e 310 '01 24-26; Ni 10-21; C 0.25; Mn 2.1 1.2 0.3 0.3 10.5 3.0 0.0 0.6

' 1.2; Si 2.0-C0ld Rolled. 316 01' 16-18; Ni 10-14; O 0.10; -Mo 1.5 0.7 0.2 0.3 14.0 3.0 1.1 0.5

1.75-2.75-Cold Rolled. Cr 17-19; N18-11; O 0.1; T1 4x0- 1. 0 0. 6 0. 2 0. 2 10. 0 4. 0 0.7 0.5

Cold Rolled. Or 16-18; Ni 6.0-8.0; C 0.12; Mn 1.6 0.6 0.3 0.2 7.1 2.5 1.2 0.2

x11; 0.04; S 0.04; Si 1.5; Ti 1.0; Cr 17-19; Ni 9-12; 0 0.1; Cb 1.2 1.0 0.3 0.3 8.0 3.1 0.7 0.4

Ext); Mn 2.0 Max-Cold Rolled. Cr 18-23; N1 0; C 0.2; Cu 0.9- 7.1 4.0 0.3 0.5 10.3 25.0 11.2 .2

1.25-Cold Rolled. Special UCC 075 Or 18.5; Ni 9.5; Mn 1.25; Sb 0.35; 1.4 0.8 0.5 0.2 7.4 4.2 0.9 03

Si 0.3; C 0.05-Hot Rolled. Special UCCH 981 Cr 18.5; Ni 12.0; Mn 1.5; C 0.04; 1.3 0.8 0.2 0.3 17;0 7.5 0.4 0.3

M0 2.0; Sb 0.3; Si 0.3-Hot Rolled. Wortllite Gr 20.0; N1 24; M0 3.0; S1 3.5; 4.9 2.0 0.3 0.2 25.0 25.0 0.1 0.1

Cu-l-Mn 2.0; C .07, Max.- Hot Rolled. Universal Cyclops 19-9- Or 19.0;VN1 9.0; C .3; Mn 0.75; Si 19.0 25 100 25 DL. 3%.[0' 1.25; W 1.25; Cb 0.40; 'Ilmkcn SS 16-25-6 Gr 10-18; N1 24.99; C .09; Mn 1.7; 1.2 0.3 9.1 4.5

P S .01; Si 0.71; M0 5.0;

Referring to Table V, it will benoted that the stabilities of orthophosphoric acid stabilized 90% hydrogen peroxide in the presence of all stainless steel alloys tested, previously passivated with hydrogen peroxide containing orthophosphoric acid, are good. In-particular itwill-be noted that fpassivated,SSQ304, 309, L316, 321, 347, Special UCC H 975 and H 981, and Timkin SS 16-2S6, show stability results at 66. C. which approximate those of 90% hydrogen peroxide stabilized with-10 p. p-.- m. orth'ophosphoricacid in contact with Pyrex-glassbnly (Table II).

.The percent absolute concentration loss per week at 66 C. is'remarkablylowk, At the elevatedtemperature of 66 C. at whichsuch tests were conducted, water evaporation proceeded with hydrogen peroxide decomposition, its effect on concentration being opposite to that of hydrogen peroxide decomposition. This would be of great importance in those end uses of concentrated hydrogen peroxide at elevated :temperatures "where ithe concentration of hydrogen peroxide at .the .time of .use is of prime importance and outweighsconsiderations ofzpercentageof active oxygen loss.

Table 'V .alsoshows 1the :results of room temperature stability tests on the designated stainless-steel alloys whichwere conductedat a temperature of- C. .Inall other respects the test procedure .was thesame. as that followed at 66 C. Itwillbe. noted ,thatth e .percentac tive oxygen losses per week, are, considerably lower at lower temperatures.

I have found/the same outstanding improvement in stabilities of hydrogen peroxide containing 10 p. p. m. orthophosphoric acid in contact with various types of aluminum alloys which were passivated in accordance with .the present invention. In Table VI are shown the stability results of tests conducted at 30 C. and 66 C. using samples of 90% hydrogenperoxide stabilized with 10 p. p. m. .orthophosphoric acid in contact with nonpassivated and passivated aluminum alloy strips. Non-passivated strips were given the standard aluminum cleaning treatment with N/lS-sodium hydroxide for 15 minutes followed by a 35% sulfuric acid treatment for 45 minutes. Passivated strips were given the same treatment as non-passivated strips and thereafter washed withdistilled water air dried and then immersed .in 90% hydrogenperoxide containing 10 p. p. m..orthophosphoric acid and allowed to stand 15 to 20 hours at the respec tive temperature. The compositions of the various aluminum alloys are shown in Table VI, .the amounts of alloying elements being shown in percentages and the balance of the alloy being aluminum.

As in the case of the stainless steel alloys, a'straight line curve was obtained by plotting the percentactive oxygen lossversus time for passivated aluminum alloy samp'lesin90% hydrogen peroxidecontaining 10 p. p. m. orthophosphoric acid and therefore the slope of the curve, viz, percent active oxygen loss per Week, hasbeen used as a stability figure.

Except as 'otherwise' indicated, the results listed in Table'VI were determinedby the same procedure used in connection with Table V.

Table VI STABILITIES OF 90% H202 GONTAININ G 10 P. P. M. HaPO4 IN CONTACT WITH PASSIVATED AND NON-PASSIVATED ALUMINUM ALLOYS Passivated N on-Passi vated 66 0. Test 30 0. Test 66 0. Test 30 0. Test Aluminum Alloy Composition Percent Percent Percent Percent Percent Percent Percent Percent A Absolute Act. Absolute A Absolute A Absolute Oxygen Gone. Oxygen Cone. Oxygen 0011c. Oxygen Cone. Loss/Wk. Loss/Wk. Loss/Wk. Loss/Wk. Loss/Wk. Loss/Wk. Loss/Wk. Loss/Wk.

High purity; Wrought 1. 6 0. 5 0. 1 0. 3 1. 9 0. 7 0. 35 0. 4 Cr 0.25; Mg 2.5; wrought 1. 6 O. 5 0.25 0. 2 3. 3 1. 7 0.3 0.3 Si 12 die cast 11.0 11.0 0. 3 0. a 28.8 25.0 1. 4 0. 2 Mg 8 0 die east 50. 0 45. 0 1.8 1. 2 56.3 25. 0 4. 0 2. 9 S15.0sand cast 2.8 0.9 0.8 0.4 18.0 17.0 1.6 1.1 Mg 3.8 sand cast 3. 6 2. 0 0. 7 0. 100 90 (1 wk.) 1. 1 0. 8 Si 1.75; Mg 3.8 sand cast 2.6 1.4 0. 4 0.3 11.0 25.0 1. 3 0. 6 Si 7.0; Mg 0.3 sand east 1. 5 0. 5 0.3 0. 1 12. 7 13. 0 0. 5 0. 3 Zn 1.0, Balance Al wrought 2.0 0. 5 2. 2 0. 5 Si 0.5 (appr); Mg 0.8 wrought 0.8 0.5 0 2 0.2 9.1 6.0 0.4 0 2 Referring to Table VI, it will be seen that remarkable loss of 60% per week at a temperature of 66 C. The increases in the stability of 90% hydrogen peroxide conpassivated strips, after having been given the standard taining 10 p. p.'m. orthophosphoric acid in contact with carbon tetrachloride and nitric acid treatment, were aluminum alloys which have been passivated in accordwashed with distilled water, air dried and then immersed ance with the present invention were obtained. More in 90% hydrogen peroxide containing 10 p. p. m. orthoparticularly, it will be noted that passivated aluminum phosphoric acid and allowed to stand 24 hours at 66 C. alloys 528, 356, and 638, show stability results at 66 C. This active oxygen loss of 60% per week at 66 C. comwhich approximate those of 90% hydrogen peroxide pared with an active oxygen loss of 62% per week with containing 10 p. p. m. orthophosphoric acid in contact a non-passivated stainless steel strip of the same'comwith substantially pure aluminum (wrought 99.7% position and similarly immersed in a 30% hydrogen perpurity) and also in contact with Pyrex glass only (Table oxide solution maintained at a temperature of 66 C. II). These aluminum alloys possess high structural Such an active oxygen loss is completely unsatisfactory strength. and the above comparative tests show that the invention Table VI also shows the results of room temperature is not applicable to confining hydrogen peroxide solustability tests on the various aluminum alloys which were tions having a concentration as low as 30%. conducted at a temperature of 30 C. In all other re- Onthe other hand, it has been found that the'invention spects the test procedure was the same as that followed is applicable to confining hydrogen peroxide solutions in connection with the 66 C. tests. It will be noted having a concentration of 70% orhigher with both-stainthat the percent active oxygen losses are considerably less steel and aluminum alloys. Thus a 58-316 stainlower at a reduced temperature. 40 less steel strip was passivated as described in the'preced- Table VII shows the results of stabilities of 90% hying paragraph and immersed in a 70% hydrogen peroxide drogen peroxide, which has not been stabilized with solution containing 10 p. p. m. orthophosphoric acid and orthophosphoric acid or any other stabilizer, in contact maintained at 66 C. The active oxygen loss of the with certain non-passivated aluminum alloys, the tests hydrogen peroxide solution was only 7.5% per week as having been conducted at 66 C. and by the same procompared with a 25% active oxygen loss per week where cedure used in connection with Table VI. By comparing a non-passivated strip of the same alloy was immersed in the figures in Table VII with those in Table VI for passia similar 70% hydrogen peroxide solution containing vated strips, the spectacular increases in stability of the 10 p. p. m. orthophosphoric acid and maintained at the hydrogen peroxide obtained with the present invention will same temperature of 66 C. be readily apparent. In a similar comparative test with aluminum alloy known commercially as 28 the active oxygen loss per Tale VII week of the 70% hydrogen peroxide solution containing STABILITIES 0F 90% E202 UN STABILIZED IN CONTACT 10 p. p. m. orthophosphoric acid and maintained at 66 C. WITH NON'PASSIVATED ALUMINUM ALLOYS was only 1.3% as compared with an active oxygen loss per week of 4.7% with a non-passivated aluminum alloy %%-g strip of the same composition and similarly immersed in a hydrogen peroxide solution containing 10 Aluminum Alloy P p. p. m. orthophosphoric acid and maintained at 66 C.

ercent Percent Act Absolute In both cases the aluminum alloy strip was first given the Oxygen C(mc- 0 standard aluminum cleaning treatment with sodium hy- LOsS/Wk' LOSS/Wk droxide followed by a sulfuric acid treatment. The 99 7 9 0 50 passivated strip was thereafter washed with distilled 3,6; 50 water, air dried and then immersed in 90% hydrogen g 91-8" 50 peroxide containing 10 p. p. m. orthophosphoric acid 43. 981.1111: and allowed to stand for 24 hours. gig- 300M117) Accordingly it will be seen that the invention is dis- 356 100 tinctly applicable to confining 70% solutions of hydrogen In connection with the operative limits of the invention, it has been found that the invention is not applicable to confining low concentration hydrogen peroxide. More specifically, a 30% hydrogen peroxide solution containing 10 p. p. m. orthophosphoric acid in contact with passivated SS-316 stainless steel strips of the composition set forth in Table V showed an active oxygen peroxide.

In a test with an solution of hydrogen peroxide an SS-316 strip of stainless steel passivated as set forth in the fourth last paragragh above was immersed in an 80% hydrogen peroxide solution containing 10 p. p. m. orthophosphoric acid and maintained at 66 C. and the resulting active oxygen loss was only 3.3% per week as compared with a non-passivated SS-316 strip where the active oxygen loss of the 80% hydrogen peroxide solution containing 10 p. p.,m. orthophosphoric acidand similarly maintained at 66 C. was 18.0%.

Further with reference to the operative limits of the invention, it has been found that as low as p. p. m. of orthophosphoric acid can be used in'the highly concen trated hydrogen peroxide to be confined. Thus strips of SS-3l6 (Table V) were passivated in accordance with the invention. Immersed in a 90% hydrogen peroxide solution containingno orthophosphoric acid the active oxygen loss per Week was 50% at 66 C. Immersed in a 90% hydrogen peroxide solution containing p. p. m. orthophosphoric acid at the same temperature the active oxygen loss was 7.8% per week. Immersed in a 90% hydrogen peroxide solutioncontaining 5 p. p. m. orthophosphoric acid at the same-temperature the active oxygen loss was 9.0% loss per week. From a practical standpoint it appears, therefore, that as low as 5 p. p. m. of orthophosphoric acid in the hydrogen peroxide solution to be confined provides the threshold concentration necessary to maintain the passivity of the stainless steel or aluminum alloy surface.

From a study of the foregoing tables, it will be seen that generally the stabilities of highly concentrated hydrogen peroxide of 70% concentration or higher stabilized with orthophosphoric acid in contact with stainless steel alloys and aluminum alloys passivated inaccordance with the present invention, compare favorably with the stabilities of highly concentrated hydrogen peroxide, stabilized with any of the commercially used stabilizers, in contact with Pyrex glass only or substantially pure aluminum. Thus, the present invention can be practiced with stainless steel alloys and aluminum alloys of high structural strength thereby to permit end uses of such alloys which would be unsuitableexcept for the present invention.

As used in the appended claims, orthophosphoric acid is intended to include orthophosphoric acid as such or orthophosphoric acid forming substances 'or'substances containing orthophosphoric acid or orthophosphoric acid forming substances.

It will be apparent that many changes can be made in the process as described above which will, nevertheless, fall within the scope of this invention. Accordingly, it

is my intention that the invention is not restricted to the variousi'details, conditions, amounts and procedures given as typical and illustrative of preferred procedure except as necessitated by the prior art and appended claim.

Iclaim:

The method of storing a concentrated aqueous solution of hydrogen peroxide containing at least hydrogen peroxide in contact with the surface of a metallic alloy selected from the group consisting of stainless steel alloys and aluminum alloys, which comprises contacting the surface of said alloy for at least one hour with an aqueous solution of hydrogen peroxide containing at least 20% hydrogen peroxide and not less than about 10 p. p. m.

orthophosphoric acid, removing said solution from contact with said surface, incorporating at least 5 p. p. m. of orthophosphoric acid with the concentrated solution of hydrogen peroxide to be stored, and bringing said last solution into contact with the so treated metal surface.

References Cited in the fil: of this patent OTHER REFERENCES "Thoipes Dictionary of Applied Chemistry, vol. VI, fourthedition, page 346, Longmans, Green & Co., 1943.

Handling of Hydrogen Peroxide," published by Buffalo Electrochemical Co., Bulfalo, New York, April 1946. Also published by Ofiice of Technical Services as PB; 97,802, October 14, 1949.

"ass-a