GB2070069A

GB2070069A - Thixotropic Pickling Composition

Info

Publication number: GB2070069A
Application number: GB8006087A
Authority: GB
Original assignee: ASHDOWN IND SERVICES Ltd
Current assignee: ASHDOWN IND SERVICES Ltd
Priority date: 1980-02-22
Filing date: 1980-02-22
Publication date: 1981-09-03
Also published as: GB2070069B

Abstract

The thixotropic pickling corrosion remover and/or descaling composition disclosed has an alkali metal silicate calculated as NaSiO3:5H2O in the range of from 1.5 to 6 parts, a weak non-oxidising acid in the range of from 2 to 8 parts per 1 part of sodium hexametaphosphate and Stannine LTP or the like inhibitor in the range of from 80-500 thousand p.p.m.

Description

SPECIFICATION Case I Improvements In and Relating to Industrial Ferrous Cleaning Compositions This invention relates to thixotropic pickling for corrosion removal and descaling of metals and more especially a composition in gel form for removing corrosive oxides rust from steel and other ferrous metals.

Gels have the advantage that they can be applied to surfaces which cannot be immersed for example in a bath or cleaned by circulation, for example the hulls of ships, and bulky machinery. Known gels are based on the use of finely divided silica, available under the Trade Mark "Aerosil", we have investigated such gels and find that when based on this material they are not easy to make, and are expensive to manufacture.

An object of this invention is provide a corrosion removal and descaling composition suitable for brush application to a structure, which will stay in place on a vertical surface for sufficient time for efficaceous action, and readily to provide a gel economical in manufacture.

According to this invention a corrosion removal and descaling composition comprises for one part of sodium-hexameta-phosphate; an alkali metal silicate in the range of from 1.5 to 6 parts; a weak non oxidising acid in the range of from 2 to 8 parts and Stannine L.T.P. in the range of from 1/2 to 2/25 part.

An inhibitor may be incorporated alternatively or additionally to Stannine L.T.R. in aggregate range of from 65. to 560. thousand parts per million-t.p.p.m.-for example a substituted urea compound inhibitor, preferably in the range of from 75. to 540. t.p.p.m.

Unexpectedly it is found that inorganic contamination is virtually nil and this is attributed to absence of electrolytic action. The acid may be hydrochloric or phosphoric; organic acids such as formica or acetic would in all probability be too weak, while the oxidising acids (fuming or H2SO4, HNO3) tend to attack the metal substrate. The latter cannot also formulate a satisfactory gel.

Preferably, hydrochloric acid is used for treatment of low chrome steels, and for chrome nickel steels.

Compositions according to the invention have thixotropic properties, so that they become liquid when agitated and reform a gel on cessation of shaking whereby the material may be stirred, painted onto a surface, and form a gel on the surface.

A first group of compositions according to the invention is made up of ingredients set out in Table 1, intended for low chrome steels, and inducing HCL as the acid component.

Table 1 Gel No. 1 2 3 4 5 6 7 8 9 10 Sodium Hex-Metaphosphate (parts) 1 1 1 1 1 1 1 1 1 1 Sodium Silicate (parts) 2 2 4 4 3 3 2 2 4 4 HCE (parts) 2 3 4 6 4 6 4 6 8 2 Stannine LTF (parts) 1/25 1/25 2/25 2/5 2/25 2/25 2/25 2/25 2/25 2/25 Consistency spreading ability lumpy lumpy smooth Gel. Gel. Gel. Gel. Gel. Smooth Smooth It will be seen that Gels Nos. 5 to 8 gave the best results as to consistency and spreading ability, while Nos. 3 to 10 gave some improvement on the average.

A second group of compositions intended for treatment of high chrome steels according to the invention as set out by way of example in table 2, the acid component being H3PO4.

Table 2 Gel No. 1 2 3 4 5 6 7 8 9 10 11 Sodium Hexa metal Phosphate (parts) 1 1 1 1 1 1 1 1 1 1 1 Na 5iO3 (parts) 2 2 2 3 3 3 2 2 2 2 2 H3PO4 (parts) 2 3 4 4 6 8 4 6 8 2 1 Stannine LTP (parts) 1/25 1/25 1/25 1/25 2/25 2/25 2/25 2/25 2/25 2/25 1/25 Consistency lumpy lumpy lumpy smooth sm. sm. sm. sm. sm. sm. smooth Spreading ability average av. av. good good good excellent exc. exc. exel. average In a typical batch, 1 part comprises 100 to 200 ml. so that the composition batch aggregates from 300 to 600 ml. The batch is then diluted with water to make up a quantity of 1000 ml. For larger batches, all the amounts are increased proportionately. Stannine LTF is present as an inhibitor in both groups of compositions.

The compositions are made up by disolving the phosphate in water to give a 25% weight volume solution, grade 75 sodium silicate is diluted 50/50 calculated as NaSiO3: SH2O with water and dilute inorganic acid e.g. HCL commercial grade 360 Tw. is used. The sodium hexa-metaphosphate solution is stirred whilst the sodium silicate is added, following by the acid HCL 360 Tw.-previously inhibitor and water mixed--1.17 litre H2O per 1 litre HCL with continued stirring for a further period of 5 minutes. The solution is then left to gel and that takes about 10 minutes. The gel is applied to rusted steel to an approximate 2 mm. thickness and left upwards from 8--1 0 minutes. The gel is then washed off, the metal surface rinsed, neutralised and phosphate stabilised and warehouse cleared for use.A lightly rusted steel surface can be brought back to clean metal in this time, and the surface rendered acceptable for paint priming.

For more heavily pitted surfaces susceptible to attack, a more concentrated gel is used for longer periods, e.g. 40 minutes.

When standing for a period of weeks, it is found that liquid tends to separate from the thixotropic gel. This can be rectified before use by stirring the gel and leaving it to re-set, so that there is no liability in use to electrolytic action that otherwise attracts deposits from one form of steel to another, higher on the electromotive scale, with consequent inorganic contamination and/or embrittlement.

Phosphoric acid gels are prepared by a similar procedure. An apparatus stereotyped for preparations of the compositions according to the invention is shown diagramatically in the drawing herewith .

As shown three stock tanks, 12, 3 are each connected via a perspective valve 4, 5, 6 and pump 7, 8, 9 to a blending tank, 10, which has an agitator 11 driven by a motor 12. The phosphate is admitted first to tank 10, followed in order by silicate, then acid, the agitator 11 being driven all the time, and for some minutes after addition of the acid component has ceased.

In addition supply (not shown) of water may also be provided for adjustment of the concentration of the ingredients in the tank.

Claims

1. A corrosion removal and descaling composition comprising for each one part of an alkaline metal hexa-meta-phosphate; an alkaline metal silicate in the range of from 1.5 to 6 parts, a weak nonoxidising acid in the range of from 2 to 8 parts and stannine L.T.F. in the range of from > to 2/25 of a part.

2. A composition according to claim 1 wherein the alkali metal hexa-meta-phosphate is sodium hexa-meta-phosphate.

3. A composition according to claim 1 or 2 wherein the alkali metal silicate is sodium silicate.

4. A composition according to claim 1, 2, or 3 wherein the weak and is a weak non-oxidising mineral acid;

5. A composition according to claim 4 wherein the acid is hydrochloric acid.

6. A composition according to claim 4 wherein the acid is phosphoric acid.

7. A composition according to claim 1 and comprising per part of sodium hexa-meta-phosphate, 2 to 4 parts of sodium silicate, 4 to 8 parts of hydro chloric acid, and 2/25 part of stannine L.T.F.

8. A composition according to claim 1, comprising per part of sodium hexa-meta-phosphate, 2 to 3 parts of sodium silicate, 2 to 8 parts of phosphoric acid, and 1/25-2/25 part of stannine LT.F.

9. A composition according to claim 1 substantially as set out in any column of table 2 hereinbefore.

10. A composition according to claim 1 substantially as set out in any column of table 1 hereinbefore.