Cleaning and liquid contact with solids – Processes – For metallic – siliceous – or calcareous basework – including...
Reexamination Certificate
2000-03-20
2001-01-23
Carrillo, Sharidan (Department: 1746)
Cleaning and liquid contact with solids
Processes
For metallic, siliceous, or calcareous basework, including...
C134S002000, C134S022170, C134S022190, C134S026000, C134S028000, C134S029000, C134S034000, C134S036000, C134S041000, C134S042000, C134S902000, C510S245000, C510S254000, C510S367000, C510S369000, C510S375000, C510S495000, C252S186280
Reexamination Certificate
active
06176937
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention concerns metal surface treatment and in particular a process for metal surface treatment employing hydrogen peroxide in aqueous acidic solution, a solution containing hydrogen peroxide for treating metal surfaces and a stabiliser system for stabilising hydrogen peroxide.
During metal processing, a metal oxide layer is often formed over all or part of the metal surface, impairing its appearance and/or suitability for further processing steps. Thus, for example, such a problem can arise for steel, including stainless steel, titanium and its alloys, copper and its alloys and even in some circumstances for aluminium. Accordingly, it is desirable to remove or at least reduce the size and extent of the metal oxide layer. Such processes can be described as metal surface cleansing, or in some instances more particularly as metal pickling or polishing or desmutting depending on the specific treatment being carried out. In one class of processes, a solution of hydrogen peroxide is employed, and often an aqueous acidic solution to remove the oxide layer.
During the course of the metal surface treatment, the removal of the oxide layer causes metal to pass into solution. It is uneconomic and wasteful of resources to discard metal treatment solutions frequently, so that over the course of time, the concentration of metal in solution increases. The metals which pass into solution are usually the commonly employed metals such as iron, copper and metals alloyed with them such as nickel, chromium and titanium. Also in some treatment processes such as in steel pickling, it is often the metal, ie iron, in solution which carries out much of the oxidation, and accordingly a significant concentration if the metal is deliberately maintained from the start of the process. These metals in acidic solution catalyse the decomposition of hydrogen peroxide so that it is desirable to find means of minimising the rate and/or extent to which the hydrogen peroxide decomposes.
In order to retard peroxide decomposition in acidic solution, it has been proposed hitherto to include a number of different inorganic or organic substances, which can often be alternatively described as chelating agents or free radical inhibitors. Without being limited to the particular mechanism by which stabilisation, ie peroxide decomposition retardation, is achieved, a number of the stabilisers can be described chemically as alcohols (U.S. Pat. No. 3,869,401, U.S. Pat. No. 3,556,883), carboxylic acids (U.S. Pat. No. 3,537,895), phosphonic acids (U.S. Pat. No. 3,122,417 U.S. Pat. No. 4,059,678) or sulphonic acids (U.S. Pat. No. 3,801,512). Amongst the lists of stabilisers proposed for acid solutions, p-hydroxybenzoic acid has been disclosed in WO 91/5079 (Solvay Interox Limited).
BRIEF SUMMARY OF THE INVENTION
It is a first object of certain aspects of the present invention to provide stabilisation means for aqueous acidic solutions of hydrogen peroxide, hydrogen peroxide solutions so stabilised and the use of such solutions for treating metals.
It is a second object of further or related aspects of the present invention to provide means for augmenting or improving the stabilisation of hydrogen peroxide using a hydroxybenzoic acid, hydrogen peroxide solutions so stabilised and their use for treating metals.
DETAILED DESCRIPTION OF THE INVENTION
According to the present invention, there is provided a stabiliser for aqueous acidic hydrogen peroxide including a hydroxybenzoic acid characterised in that it comprises
a) from 80 to 200 parts and preferably 100 to 150 parts by weight of a hydroxybenzoic acid
b) from 50 to 120 parts and preferably from 60 to 100 parts by weight of a hydrotropic aryl sulphonic acid
c) from 2.5 to 6 parts and preferably from 3 to 5 parts by weight of a hydrophobic alkaryl sulphonic acid.
Herein by the term hydroxybenzoic acid is meant an aryl group—substituted by at least one hydroxy group and by a carboxylic acid group in any position relative thereto. A particularly suitable compound within the term comprises p-hydroxybenzoic acid.
Herein by the term hydrotropic aryl sulphonic acid is meant an aryl group that is substituted by at least one short chain alkyl group and a sulphonic acid group in any position relative thereto and containing not more than 9 carbon atoms in total. A particularly suitable example, by virtue of its ready availablility and effectiveness is p-toluene sulphonic acid.
Herein by the term hydrophobic alkaryl sulphonic acid is meant an aryl sulphonic acid which is substituted by a hydrophobic alkyl group containing at least 8 carbons. Said alkyl group often contains from 10 to 20 linear carbons, usually unbranched, and in many instances from 10 to 14 carbons or mixtures, such as dodecyl or mixtures averaging about 12 carbons. A particularly suitable example is dodecylbenzene sulphonic acid, which often contains also a fraction of decyl, undecyl, terdecyl and tetradecyl groups.
In particularly preferred stabiliser compositions, the weight ratio of each of components a) : b) : c) is selected in the range of 30:20:1,±20%. In a number of related compositions containing preferred ratios, the weight ratio of component a) to component b) to component c) is selected in the range of 18 to 25:20:0.8 to 1.2.
By the employment of the three components together in the amounts and ratios disclosed above, and especially using preferred or especially ratios of the components, it is possible to obtain improved stabilisation of hydrogen peroxide in acidic solutions compared with the use of the hydroxybenzoic acid alone. Accordingly, the stabiliser of the present invention is particularly beneficial in those circumstances in which free hydrogen peroxide is maintained in solution.
Although the three components of the stabiliser are referred to as the respective acids, it will be recognised herein for each of components a), b) and c) this includes employing or introducing the component as the corresponding salt thereof for all or part of each component of the stabiliser. In use, the acidity of the metal treatment solution will dictate the chemical form and extent of ionisation of the respective component therein. To the extent that a salt is employed, such as an alkali metal (sodium) salt, then its weight is as calculated as the corresponding acid. If desired, the compositions can be at least partially neutralised by the introduction of a water-soluble alkali such as an alkali metal hydroxide, eg sodium hydroxide.
According to a second aspect of the present invention there are provided acidic metal treatment solutions containing or into which is introduced hydrogen peroxide, and containing or into which is introduced a stabiliser characterised in that the stabiliser comprises
a) from 80 to 200 parts and preferably 100 to 150 parts by weight of a hydroxybenzoic acid
b) from 50 to 120 parts and preferably from 60 to 100 parts by weight of a hydrotropic aryl sulphonic acid
c) from 2.5 to 6 parts and preferably from 3 to 5 parts by weight of a hydrophobic alkaryl sulphonic acid.
The acidity in the aqueous metal treatment solutions is typically provided by one or more mineral acids and particularly acids selected from sulphuric, phosphoric, hydrofluoric and hydrochloric acids, the selection being made at the discretion of the person wishing to conduct a metal treatment and taking into account which acids and mixtures thereof at what concentrations are suitable for the metal being treated. Additionally, if desired, a fraction of the acidity can be provided by nitric acid. The solutions intended for metal surface treatment are conventionally formulated to have a measured pH of 2 or lower, and in many instances the pH is chosen in the region of from below pH 0, eg pH-0.5 up to pH 1. It will be understood that the measured pH will arise from the interaction between the acids introduced and any other constituents in the solution. For example, and as is well known, HF complexes in solution with Fe cations releasing H+ ions and thereby lowering the measured pH compared
Colgan Sarah J.
McDonogh Colin F.
Sanders Neil J.
Carrillo Sharidan
Larson & Taylor PLC
Solvay Interox Limited
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