CA1081444A - Metal oxide remover composition and method - Google Patents

Abstract

METAL OXIDE REMOVER COMPOSITION AND METHOD

Abstract of the Disclosure Composition and method for removing metal oxides from ferrous metals. The composition contains an ammonia derivative such as an amine, a strong mineral acid and citric acid in an aqueous solution having an acidic pH of about 0.5-3Ø Metal oxides are removed by applying the solution at elevated temperature.

Description

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~081444 15 Field of the Invention -16 This invention relates to a composition and method for 17 removing metal oxides such as rust and mill scale from ferrous 18 metals such as steel. More particularly, the invention ~-19 relates to metal oxide removal from ferrous metals while avoiding corrosion and discoloration of the metal.
21 Description of the Prior Art .'.
22 It is known to use citric acid and citrates for the

2~ Iremoval of rust from ferrous metals, see for example U.S.

24 ¦Patent No. 3,510,432. The disadvantage of such materials is 2~ ¦that they leave a discoloration or black film on the rust-26 ¦free metal.

27 ¦ Another reference teaching the use of citric acid is 28 ¦~.S. Patent No. 3,492,238 which employs citric acid in combination 29 ~with EDTA (ethylene diamine tetracetic acid). This reference 30 ¦employs the solution at a pH of about 6.0-7Ø

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I iO81~44 1 1 Triethanolamine 'nas been employed in metal cleaning 21 formulations as an inhibitor for acid attack on the metal 31 substrate. It has been employed to avoid the blackening or 41 discoloration of the cleaned metal. In this connection, ~¦ reference is made to U.S. Patent No. 1,723,923 which teaches 6l the combination of triethanolamine in highly corrosive pickling 71 baths such as cold concentrated sulphuric form or a heated 8¦ more dilute form. Such pickling baths are corrosive to the 9¦ plant in which they are used and present an ecologically 10¦ unacceptable disposal problem.
11¦ U.S. Patent No. 3,095,379 describes a metal cleaning 12¦ composition which is the high temperature reaction product 13¦ of citric acid and monoethanolamine. Such a formulation has 14 ¦ been found to also leave an undesirable black coating on the 15¦ cleaned metal surfaces. .
16¦ Other references considered include the following:
17¦ U.S. Patent ~os. 2,006,216; 2,505,785; 2,994,664; 3,056,746;
18~ 3,282,848; 3,510,432; 3,589,859 and 3,779,935.
,,. 201 . .
~' 211 22 ¦ SU~MARY OF THE INVENTION
231 The present invention provides a formulation which 24¦ leaves the ferrous metal surface substantially free of metal 25¦ oxides and substantially free of discoloration such as the 26¦ blackened condition formed by various of the prior art formulationc .
27 ¦ In addition, the present cleaning solution is essentially 28¦ non-corrosive and does not attack either the metal being 29¦ cleaned or the equipment utilized in the cleaning operation.
It is thus highly acceptable from an ecological standpoint.

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, 1081444 1 All of these advantages are accomplished with a composition 21 comprising an aqueous solution containing a basic ammonia 3j derivative selected from ammonium hydroxide and organic 4 ¦ amines, citric acid and a strong mineral acid, all of said 5 ¦ components being present in effective concentrations to 6 remove metal oxides from the metal to be cleaned in the 7 absence of acid corrosion and discoloration thereof, the pH
of said solation being about 0.5-3.0 and the weight ratio of 9¦ said ammonia derivative to said citric acid being about 2:7 10 I to 7:2.
11¦ It will be appreciated that the components used will 12 ¦ form ions in aqueous solution. Accordingly, equivalent 13¦ results can be obtained by addition of the various components 14 ¦ as salts which form the desired ions. For example, an amine 15 ¦ citrate salt could be used to supply part of the citric acid 16 ¦ and organic amine components.
17 ¦ It is essential to the efficient operation of the formulation 18 Ithat the pH and component ratios be maintained within the 19 ¦above limitations. In a preferred embodiment, the formulation 20 ¦PH is about 1.0-2.0, most preferably about 1.5. In all 21 ¦cases an effective amount of strong mineral acid to achieve 22 ¦clean surfaces should be present. ~ typical formulation for 23 ¦removing metal oxides from ferrous metals has the following 24 ¦formula in approximate parts by weight, said formula being 25 ¦adapted for use in a concentrate or for dilution with additional 26 ¦water: 30 water, 2-7 basic ammonia derivative, 7-2 citric 27 ¦acid, and at least about .25-.5 of strong mineral acid, said 28 ¦formula having a pH of about 1-2.

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1 ¦ The basic ammonia derivative employed will either be 2 ¦ ammonium hydroxide or an organic amine. Any water soluble 3 ¦ amine is contemplated including aliphatic and aromatic amines.

4 I Examples are alkyl amines, alkanol amines. The amine may be

5 ¦ primary, secondary, tertiar~ or quaternary in structure.

6 ¦ As an optional additive the formulation may include an

7 ¦ organic cationic corrosion inhibitor of the type designed to

8 inhibit the attack of hydrochloric acid or sulphuric acid on ~1 ferrous metals.
10¦ Examples of some usable formulations in approximate 11¦ parts by weight are next given. These formulas are adapted 12¦ for use in the concentration shown or they ~ay be diluted 13¦ with additional ~ater as desired and as will be illustrated 14¦ in the working examples.
15¦ FO~lULA A
16 ¦ 64.0 Water 17¦ lO.5 Triethanolamine 18¦ lO.5 HCl Acid 20 BAUME
19¦ 15.0 Citric Acid 20¦ FORMUL~ B
21¦ 64.0 Water 22¦ lO.5 Triethanolamine 23 ¦ 10-5 H2S4 - 66 BAUME
241 15.0 Citric Acid Where an optional organic cationic corrosion inhibitor 26 is desired it may be added to the above formulas in the 27 amount of about l ounce per gallon of the formulation. For 28 example, in Formula A a suitable additive is the commerical corrosion inhibitor available from Amchem Products Inc. and .

( ( 1l offered under the tradc name "Rodine~213". With respect to Formula B, an appropriate corrosion inhibitor for sulfur c 3 acid available from the same company is known as "Rodine 92A".
4 The above Formulas A and B are believed to be useful formulations and concentrations for many applications. It 6 will be appreciated that the precise concentration of the 7 components is subject to some variation from that shown in 8 the formulas. It is contemplated that each of the components

9 may vary by as much as +20% from the figure shown, provided that the final formulation is operative to remove metal 11 oxides without corroding and discoloring the metal to be 12 cleaned. The following Table I will illustrate the effectiveness 13¦ of the above type of formulations in ability to remove metal 14 ¦oxides while leaving the metal clean and free from corrosion 15¦ and discoloration. Data was obtained by the following procedure.
16 ¦ 7g of citric acid in 30g of water was neutralized by 17 ¦the following materials: triethanolamine, diethanolamine, 18 ¦monoethanolamine and ammonia. The pH was adjusted to 3.5 19 ¦with concentrated HCl. DEX and the material from U.S. Patent 20 1~. 3,510,432 were purchased, while U.S. Patent No. 3,095,379 21 Iwas followed to produce Example I and Example A. Citric 22 acid was run straight in water (7g in 30g water). All examples 23 were placed in lOOml beakers filled to the 30ml mark and 24 pieces (1/2" x 2") of rusty 18 gauge 1020 cold rolled steel placed in them. The results at room temperature and 210F
26 are shown in Table I.

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1~ The formulations of this invention were tested in a 2 commercial operation in which rusty 55 gallon drums were 31 being cleaned. In this operation the cleaning solution was 4¦ applied to the drums by spraying with a nozzle at a pressure ~¦ of 60 psi. For rapid operations it is desirable to employ 61 the cleaning solution at an elevated temperature, for example 7 ¦at about 120-212F to shorten treatment time. To be acceptable 8 in this test operation it was considered that all rust should 9 be removed with the spray within 3 minutes while the cleaned I0 wet drums should not re-rust within 30 minutes. As will be

11 seen, the present formulations met these conditions.

12¦ In this test 30 gallons each of Formulas A and B listed

13¦ above were used, including the optional applicable Rodine

14 ¦corrosion inhibitors in the amounts of 1 ounce per gallon of

15 ¦solution. The concentrates of Formulas A and B were diluted

16 Ifor use with water in the amount by volume shown in the

17 ¦example below. After spraying with the metal oxide remover

18 Isolution, a rinse was applied as indicated. The results are 14 as follows.

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page -8-. , 1 1 To illustrate the criticality of weight ratio of the 2 ¦ ammonia derivative to the citric acid in the formula, the 3 ¦ following experimental work was performed.

Example 1 6 A series of solutions were prepared in lOOml beakers, 7 ¦each beaker contained the amounts shown in the Table below.
8 In each case the beaXer contained 30g of water and the contents 9¦ were adjusted to a pH of 1.5 with the addition of HCl.
10¦ 1 x 1 square inch pieces of rusty drum steel were placed in 11 ¦the solutions at boiling temperatures of approximately 212F
12 for 3 minutes. The results are shown in Table III. The ~3¦ first number at the head of each column refers to the amount 14 ¦ of amine utilized and the number on the right at the head ~ of each column efers to the amount of citric acid.

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108~444 1 It will be observed that Hyamine 3500 was utilized as 21 an 80~ solution. Accordingly, the amount of active ingredient ~¦ is somewhat different than the ratios indicated at the tops 4' of the columns. The results with this particular and preferred ~ quaternary amine point up the fact that the weight ratio 6l does not have a sharp dividing line at the lower and upper 7 limits. The weight ratios indicated throughout this specification 8l should be taken as being approximate ratios subject to some 9 variation on the order of +20~ as previously discussed in 1~ connection with Formulas A and B.
11 .
121 Example 2 13 This example will illustrate the criticality of the pH
14 in the formulations.
Solutions were made up using the amounts shown in Table I'J:
16 lOOml beakers were used. l x l inch (approximate) pieces of 17 rusty drum steel were placed in boiling solutions at approxi-20 ~mately 212F f(~ 3 minutes. The results are shown :s follo~s.

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101~1444 1 ¦ TABLE IV
2 ¦ _ pH 5 pH 4 pH 3pH 2 3 ¦ 7g triethanolamine 30g HOH - - =
4 Enough citric acid to B1 give p~ shown l 7g triethanolamine +
61 30g HOH - - + +
l 5g citric acid 71 Enough con. HCl for given pH
81 5g monoethanolamine l 30g HOH _ 9l Enough citric acid to 10 1give pH shown ¦5g monoethanolamine 11 17g citric acid - - ++ ++
l30 g HOH .
12 1Enough HCl to give pH shown 13 ¦sg N~aOH con.
l7 g citric acid = - + +
14 1Enough HCl to give pH shown 15 ¦ + indicates Bright I ++ indicates ~right and Shiny 16 I - indicates Gray I = indicates Dark Gray 17 I con. indicates concentrated

19 Example 3 I

20 1 This example will illustrate the requirement of the

21 ¦presence of a minimum amount of strcng mineral acid in order

22 ¦to obtain the desired results. In particular, about .25-.5g

23 lor more of strong mineral acid is required in a concentrate

24 ¦formulation containing 30g of water and the weight ratios of

25 ¦the other components shown in Example l. This point was

26 ¦established as follows.

27 ¦ In a l00ml beaker 7g of citric acid was added followed

28 Iby 30g of HOH. Enough triethanolamine was added to give a 30 ~pH of 3 (3.5g approximately). A piece of l" x l" rusty drum 1 1(~8~444 I
1l steel was added to the boiling material for 3 ~inutes. The 2 result was recorded at "A" below. Water was then added to 3 replace the amount boiled out and .25g of concentrated HCl 4 added followed by enough triethanolamine to adjust the pH to 3. Again a rusty l" x l" piece of drum steel was added to 6~ the boiling solution for 3 minutes. "B" was the result.
7 Finally after adding lost water, .5g of concentrated HCl was 8 ¦added and enough triethanolamine to bring the pH back to 3.
¦~s before a l" x l" rusty piece of drum steel was added to 10 ¦the boiling solution for 3 minutes. The result was recorded 11 at "C".
12 ¦ A_ B _ C
13 1 Dark Gray Gray Bright I Mottled and No Streaks 14 ¦ Streaked 16 ¦Example 4 17 ¦ This example illustrates that any strong mineral acid 18 ¦may be utilized. The procedure followed was similar to ¦Example 3. Thus, four solutions were made up in l00ml beakers.
20 ¦Each beaker contained: 7g citric acid, 3.5g triethanolamine, 21 130g HOH. The pH was 3.
22 ¦ In the first instance no strong mineral was added. In 23 ¦the other three beakers concentrated mineral acids as indicated 24 ¦were added and additional triethanolamine was thereafter 2~ ¦added to bring the pH back to 3. In each case a l" x l"
26 ¦sample of rusty drum steel was treated for 3 minutes at 27 ¦boiling temperature. The results were as follows:
28 ~ 2 3 _ 4

29 ¦ None HCl 37~H2S4 con- H3PO4 85 Streaked BrightBright Bright 31 l .;.
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108~44 ll 1 With respect to the amounts of mineral acid added, 21 reference has been made to the minimum of .25-.5g. This 31 amount refers to the usually encountered concentrated form 4~ of the acid. For example, in the case of HCl the concentrated 5l solution is 37% in strength. .25-.5g of this concentrate is 6 the minimum amount referred to. Similarly, in the case of 71 phosphoric acid the .25-.5g refers to the 85~ concentrate of 81 phosphoric acid and 98~ with respect to sulfuric acid.

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Claims (15)

1. A composition for removing metal oxides from ferrous metals comprising: an aqueous solution containing a basic ammonia derivative selected from ammonium hydroxide and organic amines, citric acid and a strong mineral acid, all of said components being present in effective concentrations to remove metal oxides from the metal to be cleaned in the absence of acid corrosion and discoloration thereof, the pH
of said solution being about 0.5-3.0 and the weight ratio of said ammonia derivative to said citric acid being about 2:7 to 7:2.

2. A composition for removing metal oxides from ferrous metals in accordance with claim 1, wherein the pH of said solution is about 1.0-2Ø

3. A composition for removing metal oxides from ferrous metals in accordance with claim 1, wherein the pH of said solution is about 1.5.

4. A composition for removing metal oxides from ferrous metals in accordance with claim 1, wherein said ammonia derivative is ammonium hydroxide.

5. A composition for removing metal oxides from ferrous metals in accordance with claim 1, wherein said ammonia derivative is an aqueous soluble amine.

6. A composition for removing metal oxides from ferrous metals in accordance with claim 5, wherein said aqueous soluble amine is selected from alkyl amines and alkanol amines.

7. A composition for removing metal oxides from ferrous metals in accordance with claim 5, wherein said aqueous soluble amine is a quaternary amine.

8. A composition for removing metal oxides from ferrous metals in accordance with claim 7, wherein said quaternary amine is an 80% solution in ethanol of n-alkyl dimethyl benzyl ammonium chloride.

9. A composition for removing metal oxides from ferrous metals having the following formula in approximate parts by weight, said formula being adapted for use as a concentrate or for dilution with additional water: 30 water, 2-7 basic ammonia derivative, 7-2 citric acid, and at least about .25-.5 of strong mineral acid, said formula having a pH of about 1-2.

10. A composition for removing metal oxides in accordance with claim 9, wherein the mineral acid is hydrochloric acid.

11. A method for removing metal oxides from ferrous metals comprising: contacting the metal from which rust is to be removed with a composition in accordance with claim 1.

12. A method for removing metal oxides from ferrous metals comprising: contacting the metal from which rust is to be removed with a composition in accordance with claim 3.

13. A method for removing metal oxides from ferrous metals comprising: contacting the metal from which rust is to be removed with a composition in accordance with claim 5.

14. A method for removing metal oxides in accordance with claim 11, wherein said contact is executed at an elevated temperature.

15. A method for removing metal oxides in accordance with claim 13, wherein said contact is executed by spraying said composition on the metal at an elevated temperature of about 120-212°F.