WO2000070125A1

WO2000070125A1 - Metal cleaning process

Info

Publication number: WO2000070125A1
Application number: PCT/GB2000/001754
Authority: WO
Inventors: Michael John Day; Vincent Brian Croud
Original assignee: Warwick International Group Limited
Priority date: 1999-05-13
Filing date: 2000-05-12
Publication date: 2000-11-23
Also published as: GB9910989D0; AU4768300A; GB2349892A

Abstract

A metal cleaning process in which the metal is contacted with an alkaline cleaning solution comprising at least 0.1 weight percent surfactant, at least 0.05 weight percent hydrogen peroxide, and an effective amount of at least one sequestrant, for example so as to stabilise the solution during use at 18°C in an inert container prior to use so as that the peroxide concentration decreases by less than 2 percent in 7 days. A preferred sequestrant is sodium diethylene triamine pentamethylene phosphonate, used either per se or in combination with 2,2' dipyridylamine or 1,2'-diaminocyclohexal tetrakis methylene phosphonic acid. The metal may be contacted with the solution for between 1 and 120 minutes at a temperature in the range ambient to 70°C. The metal may be rinsed with water after it has been contacted with the solution and air dried after it has been rinsed. The metal may be contacted with the solution in a metal or plastics cleaning bath which is preferably agitated or stirred, or a thickened solution may be sprayed onto the metal. The solution may be formed from a concentrate by dilution with water.

Description

METALCLEANINGPROCESS

This invention relates to a metal cleaning process in which the metal is contacted with an alkaline cleaning solution containing hydrogen peroxide and surfactant. The hydrogen peroxide used for creating such a solution is acid per se and will commonly contain a stabiliser for preventing or reducing auto-decomposition. Typical stabilisers are silicates, and also sequestrants, which are active in an acid environment, as opposed to the alkaline environment of the cleaning solution. Unless specifically stated, the term "solution" used herein refers to the solution as used in the cleaning process of the invention.

Whilst chlorinated solvents have been the most commonly used metal cleaning chemicals, other products, in particular aqueous liquids, have also been used. For example: acidic liquids, typically containing a high level of phosphoric acid and low levels of surfactant and solvent, for cleaning of aluminium and stainless steel; alkaline liquids, containing sodium or potassium hydroxide and low levels of surfactant and solvent, and sometimes also containing phosphate or pyrophosphate, for heavy duty cleaning of stainless steel; similarly, alkaline liquids, containing silicate, phosphate, carbonate or bicarbonate, and perhaps low levels of surfactant, for cleaning aluminium or brass. Examples of aqueous metal cleaners for different applications can be found in "Advanced Cleaning Product Formulations - Household, Industrial, Automotive", by Ernest W Flick, published by Noyes Publications 1989 ISBN0- 8155-1186-8, Chapter 7. Hydrogen peroxide is not normally used to clean metals.

The performance of aqueous products often falls below that of chlorinated solvents, and may leave residues which can cause problems with subsequent application of materials, for example plating and perhaps also with adhesion of paints and other finishes.

Alkalinity is known to impart good performance to cleaning compositions based on surfactants. Such compositions are generally safe for use on most metal surfaces but lack the performance required. Use of hydrogen peroxide for the treatment of metal surfaces is known. Normally the peroxide is stored and used under acidic conditions because it is unstable under alkaline conditions, particularly in the presence of transition metal ions as discussed later. See, for example, Electrochemical Society Proceedings Volume 97-35, pages 23 to 30 ("Minimising Sulfur Contamination and Rinse Water Volume Required following a Sulfuric Acid/Hydrogen Peroxide Clean by Performing a Chemically Basic Rinse", by P J Clews et al, and also pages 113 to 119, ibid, "Fe Removal in SC2 Solutions", by S Dhanda et al.

The instability of alkaline hydrogen peroxide, particularly in the presence of certain metal ions, is also recognised in European Patent Application EP 0690483, which is directed to the cleaning of wafer substrates of metal contamination by other types of cleaning solution. Reference is made to the possibly dangerous nature of such decomposition, and to the need to replenish the solution with additional peroxide.

Cotter and Mahoon in Int. J. Adhesion and Adhesives, Jan 1982 have disclosed the use of hydrogen peroxide for metal etching under alkaline conditions. They treated pre-cleaned titanium with an etching solution consisting of 0.5M sodium hydroxide and 0.2M hydrogen peroxide for 20 minutes at 65 °C. There is no reference to or suggestion of the use of a sequestrant. This treatment produced an oxide surface up to 0.2 micron thick which was temperature stable and could form high strength adhesive bonds. After the etching of a test piece the concentration of hydrogen peroxide was greatly reduced, and the test solution was replenished with hydrogen peroxide prior to use on another test piece. A conventional alkaline degreasing agent was used prior to the etching process.

Laycock et al in short communication 0010-938X(95)00113-1 (Corrosion Science, vol 37 (10) ppl637-42, 1995) reported the treatment of chromium containing stainless steel with an aqueous liquid containing 300 ppm hydrogen peroxide and 120 ppm phosphonate (sodium salt) as stabiliser. The pH was adjusted to 12 with sodium hydroxide and the metal treated for 240 hours at 65°C to investigate the effect of inclusion of the phosphonate on the corrosion potential. A coloured film 80nm thick formed on the surface of the metal. This was thought to be due to re-precipitation of dissolved material. The phosphonate was shown to increase the dissolution rate following the onset of transpassivity in the Cr(III) component of the passive film.

It will be appreciated that in the above prior art uses of hydrogen peroxide the treatment conditions are fairly severe in terms of pH and temperature.

There is also a series of patent specifications, all in the name of Hughes Aircraft Company (EP 0574858; PCT/US92/08150; PCT/US90/06464; US 5244000; US 5196134) relating to the removal of flux from a soldering process using solutions comprising hydrogen peroxide and surfactant(s). None disclose the use of a sequestrant, and with the exception of PCT US90/06464 the hydrogen peroxide is added at the point of use. Since they refer to vigorous gas formation on introduction of a flux contaminated material, it might be surmised that the evolution of a gas, presumably oxygen with concomitant loss of cleaning ability, is viewed not as a disadvantage, but rather as advantageous or even necessary for obtaining the desired cleaning action. In such a case there would be a positive disincentive to add a sequestrant to prevent decomposition of the peroxide. PCT/US90/06464 refers to the need after use to replenish the peroxide, and if necessary other components of the composition (cleaning solution).

Russian Specification No SU 1795412 relates to cleaning a metal mould surface of organic contaminants with a solution which may comprise hydrogen peroxide and a surfactant. The abstract neither refers to nor suggests the provision of a sequestrant in the cleaning solution.

The cleaning and disinfecting composition of US Specification No 5620627 (Kramer) involves a surfactant and a hydrogen peroxide generator, and the latter may be a solid. There is no reference to, neither suggestion of, the use of a sequestrant.

A stable alkaline detergent composition containing hydrogen peroxide and a novel dual sequestrant stabilisation system is disclosed in International Patent Application Serial No. WO96/01311. This composition was not used for metal cleaning. In this disclosure stability during storage and before dilution at the point of use is the problem to be solved and there is no mention of any benefits of the stability imparted by the sequestration system during use of the compositions, or thereafter. In particular a cleaning bath is not disclosed or suggested.

According to the present invention there is provided a metal cleaning process in which the metal is contacted with an alkaline cleaning solution comprising at least 0.1 weight percent surfactant, at least 0.05 weight percent hydrogen peroxide and an effective amount of at least one sequestrant. The solution preferably contains at least 0.5 weight percent surfactant. It preferably contains at least 0.2 weight percent hydrogen peroxide, preferably 1 to 8 percent, and more preferably 1.5 to 5 percent.

As will be readily recognised by the skilled person, the stability of alkaline hydrogen peroxide is greatly affected by transition metal ions, which are regarded as promoting catalytic decomposition, and that such decomposition occurs even at extremely low active concentrations of such transition metals. Transition metal ions are commonly present in components used for making up or diluting alkaline peroxide solutions, and may also be introduced during storage or use of the cleaning solution. For this reason, many alkaline hydrogen peroxide solutions are made up just prior to use, and much of the peroxide is simply decomposed during use.

The presence of the sequestrant(s) in the solutions used in the present invention is intended effectively to prevent (or greatly retard) decomposition of the peroxide due to the presence of metal ions. To this end, it or they need to be of a type and of a concentration which is effective under the conditions of storage and use to significantly hinder or prevent the catalytic action of any transition metal ions likely to be encountered, whether present as a result of impurities in the initial components, including diluents such as water, including tap water (for example when making up from a concentrate), or ions introduced during use, e.g. as a result of the cleaning action of the solution, or different storage conditions.

In other words, the phrase "effective amount of at least one sequestrant" as used herein denotes a material or combination of materials of a type and concentration sufficient to serve a specified function, so that the actual compound(s) selected will need to be functional at the pH of the cleaning solution, and in an amount at least sufficient to deal with levels of the transition metal ions in the existing solution prior to use, and also expected levels arising during at least an initial period of use.

The particular description herein refers in particular to preferred concentrations for sodium diethylene triamine pentamethylene phosphonate (DTPMP), sold by Solutia in a 25% solution as Dequest 2066; 2,2' dipyridylamine (DPA); and 1,2'- diaminocyclohexyl tetrakis methylene phosphonic acid (DACTMP). In general, the preferred total amount of sequestrant is in the range 0.02 to 0.7, more preferably 0.03 to 0.3, and most preferably 0.05 to 0.15 weight percent.

Naturally, with continued use, there will be both progressive exhaustion of the peroxide and other components, including a decrease in effectiveness of the sequestrant if further metal ions are introduced. Relative rates of exhaustion of peroxide and sequestrant will depend largely on the manner of use, including the relative amounts of oxidisable matter and metal ions to be encountered. As rule of thumb, when the latter constitute unknowns, the preferred weight ratio of peroxide to total sequestrant is in the range 8 to 160:1, more preferably 20 to 80:1, and most preferably 30 to 50:1.

It has been found that the action of cleaning solutions prepared according to the present invention is effective and relatively rapid. Gas bubble formation while a soiled metal test piece is inserted into the cleaning solution and cleaned is low, and certainly not "vigorous" as in some of the prior art noted above. After cleaning is visibly complete it is found that further decomposition of the peroxide ceases or reduces to a very low level relatively quickly, so that the solution thereafter retains a high storage stability, to the extent that it may even be used in a stainless steel metal tank. As described more particularly later in Example 16, there has been identified a generally linear decrease in peroxide content with amount of use.

A preferred sequestrant is sodium diethylene triamine pentamethylene phosphonate (DTPMP), used alone or in combination with at least one of DPA and DACTMP. The minimum preferred concentration of DTPMP in weight percent is 0.02, more preferably 0.025 and most preferably 0.03. The maximum prefeπed concentration of DTPMP in weight percent, is 0.6, preferably 0.3, and most preferably 0.2. Where present, the minimum prefeπed concentration of DPA or DACTMP in weight percent is 0.005, more preferably 0.01, and most preferably 0.02. The maximum prefeπed concentration of DPA or DACTMP in weight percent is 0.1, more preferably 0.08 and most preferably 0.07. DPA and DACTMP are sequestrants in their own right, but are not necessarily "effective" as herein defined when used per se.

A combined sequestration system is particularly prefeπed as this gives the maximum stability during storage and use, and such stability is the key to the commercial utility of the invention. Most preferably the cleaning solution comprises a mixture of DTPMP and DPA. However, other sequestering agents for transition metal ions may be used instead of, or in addition to, the prefeπed sequestrant and combinations mentioned above.

Table \

The following series of experiments demonstrates the effect of providing one sequestrant (D2066) alone or in combination with D2066 or DPA. In each case, the test solutions shown in Table 1 above were used, where comparative Formulations TA and TB comprise only a very minor amount of effective sequestrant, due to the caustic having been pre-treated with DTPMP, and Formulations Tl and T2 are solutions for use according to the invention. The use of pre-sequestered caustic prevents or greatly reduces decomposition of the peroxide by transition metal ion impurities in the caustic.

In each of a first series of tests intended to show the stability for storage confeπed by the sequestrant(s), 300ml of the cleaning solution was placed in a clean glass beaker, and maintained at about 18°C. Samples were taken from the solution at set times and analysed for peroxide concentration. Table 2 sets out the series of measurements of peroxide concentrations over time.

Table 2

It will be seen from Table 2 that over the period of the test significant decomposition occurs only in the case of reference solution TA. Accordingly, an amount of sequestrant which gives rise to less than 2 percent reduction of peroxide concentration of a solution for use in the process of the present invention when stored in an inert container at 18°C over a period of 7 days, can be regarded as falling within the foregoing definition of "effective amount" (Test A). It should be understood that contamination form external sources should be avoided.

In a second series of experiments intended to illustrate the stability for storage confeπed by the sequestrant(s) in the presence of a clean metal, a test piece of stainless steel SS316L of dimensions 95mm x 35 mm x 5mm was cleaned to be waterbreak free on each tabulated day by use of a known prior art solution Blue Gold (Registered Trade Mark) which is an aqueous surfactant type system. After rinsing with deionised water, it was suspended for 10 minutes with stiπing in 300 ml of the test solutions TA, Tl and T2 at about 18°C so that the solution came halfway up its 95mm length. After withdrawal of the test piece, available oxygen was measured giving the results shown in Table 3 below as peroxide depletion. The size of the aliquots was sufficiently small as to have no appreciable effect on the volume of the liquid.

Table 3

N = negligible (less than 2%)

It will be seen from Table 3 that significant decomposition over the period of the test occurs only for reference solution TA. Thus an amount of sequestrant which gives rise to less than 10 percent, preferably less than 5 percent, and more preferably less than 2 percent reduction of peroxide concentration of a solution for use in the process of the present invention over a period of 7 days when stored under the conditions of the second series of experiments outlined above, can be regarded as coming within the foregoing definition of "effective amount" (Test B).

A third series of experiments was also performed, similar to the second series, but wherein the stainless steel test pieces were machined parts with a uniform coating of cutting oil residue (used oil containing metal swarf). The cutting oil was "Supercent B" made by Century Oils Limited, a mineral oil based emulsifiable cutting oil. After the initial make up of the cleaning bath, tests were performed on the machined parts at set times. The tests consisted of dipping a fresh test piece into the cleaning bath for 10 minutes with stirring of the cleaning bath. At the end of the time period the test piece was removed and tested for cleanliness, both visually and using a waterbreak test. Furthermore an aliquot of the cleaning bath was removed for pH and available oxygen measurements. The results are shown in Tables 4 to 6 below, where n/a = result not available. Tests on solution TB were discontinued after the end of the first test as degreasing was found not to occur when surfactants are excluded, and no measurement was made on solution T2 on day 4.

Table 4 - pH

Particularly in view of the influence of pH on cleaning action and stability, Table 4 confirms that variation in pH over the period of the tests was negligible, apart from the final day of TA. Table 5 - Waterbreak Test

c-clean; nc - not clean; s - shiny; ns - not shiny; wbf - waterbreak free; * - surface marks; ** - not degreased

Thus in addition to greater stability (see below), solutions Tl and T2 have a superior cleaning action compared to reference solution TA even when the latter is fresh.

Table 6 - Loss of Available Oxygen (%)

N = negligible (less than 2%)

It will be seen from Table 6 that the peroxide of reference solution TA is almost completely destroyed over 7 days, where solutions Tl and T2 used according to the present invention show virtually no decomposition of peroxide, apart presumably from the very minor amount used in the actual cleaning process. Thus, an amount of sequestrant which gives rise to less than 20 percent, preferably less than 10 percent, more preferably less than 5 percent, and most preferably less than 2 percent, reduction of peroxide concentration of a solution for use in the process of the present invention over a period of 7 days when stored under the conditions of the third series of experiments outlined above, can be regarded as lying within the foregoing definition of "effective amount" (Test C).

If the cleaning solution conforms to any one of Tests A to C it is considered to contain an "effective amount" of sequestrant. Preferably it conforms to at least two of the tests, for example tests A and B, and most preferably all three.

In the process of the invention the metal may be contacted with the solution for between 1 and 120 minutes, and preferably between 5 minutes and 60 minutes. The temperature during cleaning may be in the range 15 to 70°C, and is preferably at or close to ambient temperature, for example in the range 15 to 25°C. The use of a temperature near to ambient eliminates the need for heating, thereby saving energy. This also increases the flexibility of the cleaning solution to be used as a spray-on formulation, or simplifies the design of a cleaning bath, depending on the mode of application of the solution.

Desirably the metal is rinsed with water after it has been contacted with the solution as this removes any particulate matter or soil that has been removed by the solution. Advantageously the metal is then air-dried.

Preferably the solution comprises not more than 30 weight percent surfactant, more preferably not more than 15 weight percent, and most preferably in the range 2 to 10 weight percent. For the greatest stability both before use and during use the solution comprises a surfactant system which is preferably a mixture of anionic and non-ionic surfactants, although entirely non-ionic or anionic surfactant systems may be used, each surfactant is preferably selected by screening it in the manner described in the "Screening Test" described below. This screening test uses a combination of pH and peroxide stability to identify those surfactants which are least likely to inter-react with the hydrogen peroxide during extended storage. A trial composition is prepared using 15-20% w/w of the surfactant to be screened. After sequestration with Dequest 2066, hydrogen peroxide sufficient to give a 5% w/w concentration of peroxide is added and the pH is adjusted to 9.5 by the addition of pre-sequestered caustic solution. Residual peroxide is determined by permanganate titration. To pass the test the surfactant must satisfy the following criteria. A surfactant should pass both the pH and the peroxide targets. It is possible to use small (<5 weight percent prefeπed) amounts of a surfactant that does not pass all the targets, but this is only practical when the majority of the surfactants exceed the targets by a good margin.

pH targets: pH²⁵^ >9.0 after 12 weeks at 25°C pH³⁷ ₁₂ >7.5 after 12 weeks at 37°C pH⁴⁵ ₄ >8.0 after 4 weeks at 45°C

Residual Peroxide targets: >85% after 12 weeks at 25°C

Per³⁷^ >50% after 12 weeks at 37°C

Per⁴⁵ ₄ >55% after 4 weeks at 45°C

Surfactants which pass the screening test include: a) Secondary alkane sulphonates, such as Hostapur SAS 93 a 93% active flake ex. Hoechst or Marlon PS65 a sodium n-alkane (C_13.17) sulphonate with low sodium sulphate content ex. Huls; b) Linear alkyl (C₁₀.₁₃) benzene sulphonic acids such as Marlon AS3 ex Huls; c) Alkyl ether sulphates such as Neopon LOS70, a 70% active sodium salt ex Witco; and d) Olefin sulphonates such as Hostapur OS supplied as 40% actives ex Hoechst. e) Primary alcohol (C_13.15) ethoxylates, ethoxylated with from 5 to 9 moles of ethylene oxide, preferably 7 moles, such as Synperonic A7 ex ICI / Cargo Fleet.

The solution may be stored and used at a pH in the range 7.5 to 10.5 and preferably it is used in the range pH 8 - 10. To assist in maintaining this pH the solution may further comprise a buffer to keep the pH high as the peroxide is consumed during the metal cleaning process.

For some applications the solution may advantageously further comprise a thickener to enable it to cling to vertical surfaces for sufficient time to act, e.g. in certain spray- on applications.

Whilst solutions according to the invention may be used to clean a wide range of metals, alloys and semiconductors it finds particular utility when used on alloys selected from the group comprising stainless steels, nickel alloys and brass. Likewise, although the type of soil or contaminant does not greatly affect the performance of the solution it is particularly effective on contaminants and soils which form relatively thin layers or coatings, in particular grease, soil, dye penetrants, and cooling and lubricant fluids including cutting oils.

The process may comprise the direct use of an alkaline peroxide cleaning solution in the same concentration as it is stored or the solution used in the process may be formed from a concentrate by diluting the concentrate with water prior to use. In the latter case the presence of the sequestrant(s) is additionally advantageous in that it allows the use of a less pure form of water for the dilution step while maintaining the stability of the peroxide.

The solution may be applied to the metal as a liquid by any of the processes known in the art, for example spraying, soaking and other immersion processes. The stability of the solution particularly lends itself to processes where a bath of cleaning solution is used and is most advantageously used in processes which involve multiple and repeated use of the bath for a succession of components over several days. The contact time is mainly dependent on the type of soil or contaminant being removed and also a function of the other elements of the process that contribute to removal, for example heat and agitation. A typical contact time for oil removal may be 10 minutes whereas a contact time for removal of some dyes may be as long as 6 hours.

The invention will now be further described with reference to the following non- limiting examples. In the examples Formulation T2 as defined above is compared with several Comparative formulations A to E, their composition is given in Table 7. Formulations A and B differ from T2 as regards the presence of peroxide and pH.

Table 7

Examples 1 - 13 were caπied out using metal test pieces with dimensions of 100 mm x 50 mm x 5 mm. In cleaning, tests pieces were used as received. In tests involving removal of dye penetrants pieces were degreased using acetone, after which the dye penetrant was applied to one side of the lower 50mm of the piece using a fine brush and allowed to dry for one day at ambient temperature.

For Examples 1 - 4 stainless steel test pieces cleaned by the formulation for 30mins at the temperature given were visually compared by sixteen panellists and rated on a scale of 1 to 10. 1 denotes no cleaning and 10 denotes complete cleaning. The average score is the "Clean Score".

Example 1 - Cleaning of Stainless Steel - Formulations T2 and A

Clean Score

Formulation T2 - 20°C 7.3

Formulation T2 - 40°C 7.7

Formulation T2 - 60°C 7.7

Comparative Formulation A - 20°C 3.9

Comparative Formulation A - 40°C 4.2

Comparative Formulation A - 60°C 3.2

The inclusion of hydrogen peroxide is seen to give much improved general metal cleaning.

To show that the Formulation T2 Solution remains stable after it has been used for metal cleaning aliquots were taken from the solution used at each temperature in this example and these were then stored in a plastic container at ambient temperature for an extended period. The peroxide and pH stability of each stored aliquot of Formulation T2 over time was determined by measuring the pH and determining the peroxide concentration. The results are given in Tables 8 and 9 below. It can be seen that even after use at elevated temperatures the solution remains relatively stable. Table 8 - pH stability on storage

Table 9 - Peroxide loss on storage

N = negligible (less than 2%)

Example 2 - Cleaning of Stainless Steel - Formulations T2 and B

Clean Score

Formulation T2 - 20°C 7.1 Formulation T2 - 40°C 7.3 Formulation T2 - 60°C 7.0

Comparative Formulation B - 20°C 2.6 Comparative Formulation B - 40°C 3.8 Comparative Formulation B - 60°C 4.7

The alkaline peroxide formulation gives much better general metal cleaning than the equivalent acid peroxide formulation. Example 3 - Cleaning of Stainless Steel - Formulations Tl and C

Clean Score Formulation T2 - 20°C 7.3

Formulation T2 - 40°C 7.7

Comparative Formulation C - 20°C 1.9 Comparative Formulation C - 40°C 2.7

At these energy efficient temperatures the alkaline peroxide is much better at general metal cleaning than the isoparaffin solvent.

Example 4 - Cleaning of Stainless Steel - Formulations Tl and D

Clean Score Formulation T2 - 20°C 6.7

Comparative Formulation D - 20°C 6.4

From this it can be concluded that Formulation T2 gives equivalent performance to Comparative formulation D under the conditions of this test. Formulation Tl has several advantages over D, it is less alkaline and therefore its handling and disposal is easier. Also it has superior performance on some types of contaminant as will be shown in the following examples.

Examples 5 - 13

Table 10 shows the performance of Formulation T2 on various metals with different soils and under different process conditions (temp/time). All pHs are in the range 8- 10 except for Comparative Formulation B. The "Result" column shows the absolute and relative cleanliness of each test piece assessed by a visual inspection and by a water break-free test to show if a smooth, unhindered flow of water was observed WBF means Water break free. Samples which are not WBF are not clean. Table 10

Example 14

Formulation T2 has an initial level of 5% hydrogen peroxide. In this example the rate at which the hydrogen peroxide decomposed when used for degreasing was assessed.

400ml of Formulation T2 solution were stiπed in a beaker. A test piece of superalloy material containing nickel, cobalt, tungsten, chromium, aluminium and other minor metals was coated in used engine oil and was suspended in the solution so that half the test piece was submerged, allowing for a comparison at the end of each run. The test piece was allowed to clean for 30 minutes after which a visual inspection and a water break free test were conducted to ensure complete cleaning. The hydrogen peroxide content of the Formulation T2 solution was determined. The peroxide content was found to decrease almost linearly after each successive test piece had been degreased until approximately 60% remained after 30 test pieces. The solution after this showing a considerable oily discoloration. The theoretical number of test pieces that could be degreased before peroxide content reaches zero can be extrapolated as about 75.

The 30 test pieces successfully degreased suggest that the Formulation T2 solution will continue to clean well even when the solution has received contamination such as the oil from previous test pieces.

Example 15

This example compares the degreasing qualities of Formulation T2 and Comparative Formulation E using different test contaminants.

Two test pieces of a superalloy material as in Example 14 were coated in a test contaminant and allowed to dry for 15 minutes. The first test piece was vapour cleaned in Comparative Formulation E for a few minutes. The second test piece was half submerged in the Formulation T2 at ambient temperature for a 30 minute period with the solution being slowly stiπed. The cleanliness of each test piece was then assessed by a visual inspection for any signs of grease and by a water break-free test a smooth, unhindered flow of water was observed. The results and contaminants are shown in Table 11.

All the contaminants were removed by Formulation T2 at ambient temperature, the results the fluorescent inspection oil showing an increased degreasing quality over Comparative Formulation E as evidenced by the water-break test.

XahleJI

Example 16

A copper phthalocyanine pigment stained stainless steel mixing tanks cleaned with Formulation T2 which was effective at ambient temperature in removing the pigment. Neither Comparative Formulation A nor B was effective. Removal of pigments is a common problem in industry

Example 17

Under alkaline conditions peroxide is inherently unstable, undergoing transition metal ion catalysed decomposition to oxygen and water. The sequestration system used in Formulation T2 is designed to inhibit the main transition metal ions involved in the decomposition of peroxide. This example examined whether there was any sequestrant effect over time on the transition metals used in the alloys of gas turbine components.

A test piece of superalloy as in Example 14 was allowed to soak in a cleaning bath of Formulation T2 for several hours. The test piece was then removed from the bath and a small section was cut off and examined by Scanning Electron Microscope analysis for any gross changes in the composition at three different points on the edge of the test piece. This was then compared to a further analysis that was conducted on the centre of the test piece and the actual composition of the alloy. The remaining test piece was then returned to the bath to soak in Formulation T2 for a further time and the procedure was then repeated. The Formulation T2 solution in the cleaning bath was changed on a daily basis to artificially worsen any effect that may occur.

No gross significant changes were seen in the composition of the outer edge of the test piece over the time it was in the bath containing Formulation T2 solution, showing that the Formulation T2 has no significant adverse effect on the surface composition of this alloy. Example 18

To verify that a Formulation T2 solution will still degrease metal components when it has been used repeatedly, a further test was conducted.

A superalloy test piece as in Example 14 was coated in used engine oil and suspended, so that half the test piece was submerged in the Formulation T2 solution. Various concentrations of Formulation T2 and water were used to see if a visually clean and water break free finish was obtained. The peroxide percentage was calculated for each concentration.

Table 12

As can be seen from Table 12, Formulation T2 solution will still give adequate degreasing to a low level of peroxide.

Claims

1. A metal cleaning process in which the metal is contacted with an alkaline cleaning solution comprising at least 0.1 weight percent surfactant, at least 0.05 weight percent hydrogen peroxide, and an effective amount of at least one sequestrant.

2. A process according to claim 1 in which the sequestrant is such that the solution conforms to at least one of tests A, B and C as hereinbefore defined.

3. A process according to claim 1 or claim 2 in which a said sequestrant is sodium diethylene triamine pentamethylene phosphonate.

4. A process according to any preceding claim in which said solution comprises 2,2' dipyridylamine and/or l,2'-diaminocyclohexyl tetrakis methylene phosphonic acid, in addition to said effective amount of at least one sequestrant.

5. A process according to any preceding claim wherein the ratio of hydrogen peroxide to sequestrant by weight is in the range 20 to 80.

6. A process according to any preceding claim wherein the total effective amount of sequestrant(s) is in the range 0.02 to 0.7 weight percent.

7. A process according to any preceding claim wherein the metal is contacted with the solution for between 1 and 120 minutes.

8. A process according to any preceding claim in which the metal is contacted with the solution at a temperature in the range 15 to 70°C.

9. A process according to any preceding claim in which the metal is rinsed with water after it has been contacted with the solution.

10. A process according to claim 9 in which the metal is air dried after it has been rinsed.

11. A process according to any preceding claim in which the metal is contacted with the solution in a cleaning bath.

12. A process according to claim 6 in which the solution in the cleaning bath is agitated or stiπed.

13. A process according to claims 11 or 12 in which the cleaning bath is made of a plastics material.

14. A process according to any one of claims 1 to 10 in which the solution is sprayed onto the metal.

15. A process according to any preceding claim in which the solution comprises between 0.5 and 15 weight percent surfactant

16. A process according to any preceding claim in which the solution comprises surfactants which satisfy the screening test described hereinbefore.

17. A process according to any preceding claim in which the solution comprises at least 0.2 weight percent hydrogen peroxide.

18. A process according to any preceding claim in which the solution comprises no more than 10 weight percent hydrogen peroxide.

19. A process according to any preceding claim in which the solution further comprises a buffer.

20. A process according to any preceding claim in which the solution is contacted with the metal at a pH in the range 7.5 to 10.5.

21. A process according to any preceding claim in which the metal comprises an alloy selected from the group comprising stainless steels, nickel alloys and brass.

22. A process according to any preceding claim wherein the metal has a coating selected from the group comprising grease, soil, dye penetrants, cutting oils and cooling and lubricant fluids.