GB1602604A

GB1602604A - Corrosion inhibiting paint compositions

Info

Publication number: GB1602604A
Application number: GB2343577A
Authority: GB
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1977-06-02
Filing date: 1977-06-02
Publication date: 1981-11-11
Also published as: AU3644278A; AU517214B2; JPS5433543A; FR2393038A1; FR2393038B3; JPS5717027B2

Description

(54) CORROSION INHIBITING PAINT COMPOSITIONS (71) We, STANDARD TELE PHONES AND CABLES LIMITED a British Company of 190 Strand, London W.C.2. England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to anti-corrosion paints and coatings for protecting metal surfaces.

Paint pigments are formed mainly from finely ground inorganic compounds. It is well known that some of these compounds provide corrosion protection of a metal surface on which the paint film is deposited.

For example zinc metal powder can be used in anti-corrosion paints for iron and steel surfaces as the zinc is oxidised in preference to the iron and steel. It has also been found that Zn++ ions from zinc oxide, zinc sulphide or zinc carbonate pigments inhibit corrosion probably by minimising the tendence to set up the corrosion inducing local electrochemical couples in the iron or steel surface. Phosphate and chromate ions are also known to be effective anticorrosion agents, and they are believed to operate by performing protective insoluble phosphate or chromate films on the metal surface.

There are, however many compounds capable of inhibiting metal corrosion, which e.g. either because of solubility problems or their high reactivity, are unsuitable for inclusion in a conventional paint composition.

Our published specification No. 1,511,381 describes anti-fouling paint compositions based on water soluble glasses which release biocidal materials into solution. The present application is concerned with paint compositions and water soluble glasses for inhibiting corrosion of metal surfaces.

According to one aspect of the invention there is provided a corrosion inhibiting paint composition adapted to inhibit corrosion of a metal surface to which it is applied, the composition including a water soluble glass dispersed in a resin carrier, in which said glass comprises phosphorus pentoxide (PzOs) and stannous oxide (SnO) which together provide the glass forming oxide and a glass modifying oxide respectively of the glass, together with an alkali metal oxide, an alkaline earth metal oxide, a group III B metal oxide or mixtures thereof, the composition of the glass being such that, when the glass is contacted with water, stannous ions are released into solution by dissolution of the glass.

According to another aspect of the invention there is provided a corrosion inhibiting oxide glass composition including phosphorus pentoxide and stannous oxide as the glass forming oxide and a glass modifying oxide respectively, together with an alkali metal oxide, an alkaline earth metal oxide, a group IIIB metal oxide or mixtures thereof, the composition of the glass being such that, when the glass is contacted with water, stannous ions are released into solution by dissolution of the glass.

Those skilled in the glass-making art will be aware that glasses generally comprise a glass forming oxide together with one or more glass modifying oxides. A glass forming oxide is defined as an oxide, for example phosphorus pentoxide or silica, which can of itself form a glass. Glass modifying oxides are defined as those oxides which, whilst they do not form glasses themselves, can form a glass in conjunction with one or more glass forming oxides, and in the process modify the physical and/or chemical properties of the glass.

According to the invention a paint pigment is formed from a glass containing stannous (Sn++) ions. The glass is formed by melting a mixture including stannous oxide (SnO) and phosphorus pentoxide, which act as a glass modifying oxide and the glass forming oxide respectively, in a reducing atmosphere. In this way a glass with a high Sn++ concentration is obtained. The water solubility of the glass is determined by small variations in the SnO/P2O5 ratio, and by the incorporation of one or more glass modifying oxides, e.g.

alkali metal oxides and/or alkaline earth metal oxides, and/or the oxides of the metals of group IIIB of the periodic table, e.g. Na2O, CaO and Awl203, in the glass. The addition of sodium oxide increases water solubility whilst the addition of calcium and aluminium oxides decreases solubility The glass is ground into a powder and is dispersed in a resinous material to form the paint.

When the glass is used as a paint pigment, e.g. for protecting an iron or steel surface, any oxidising agent, for example dissolved oxygen, which is able to pass through the paint layer will, in the presence of water, be reduced by the Sn++ ions and will therefore be unable to attack the metal.

It will be clear that it is also possible to use the glasses which release ions that are effective as anti-corrosion agents by introducing them at a controlled rate into an aqueous environment as additives to water systems. Thus, for example, the internal and external surfaces of steel water pipes may be protected in this way. The glass can be introduced in the form of monolithic solids, as enamel like metal coatings, as woven cloth or any other form in which a glass may be fabricated and is appropriate to the particular application.

WHAT WE CLAIM IS: 1. A paint composition adapted to inhibit corrosion of a metal surface to which it is applied, the composition including a water soluble glass dispersed in a resin carrier, in which sald glass comprises phosphorus pentoxide (P2O5) and stannous oxide (SnO) which together provide the glass forming oxide and a glass modifying oxide respectively of the glass, together with an alkali metal oxide, an alkaline earth metal oxide, a group III B metal oxide or mixtures thereof, the composition of the glass being such that, when the glass is contacted with water, stannous ions are released into solution by dissolution of the glass.

2. A corrosion inhibiting paint composition substantially as hereinbefore described.

3. A corrosion inhibiting oxide glass composition including phosphorus pentoxide and stannous oxide as the glass forming oxide and a glass modifying oxide respectively, together with an alkali metal oxide, an alkaline earth metal oxide. a group IIIB metal oxide or mixtures thereof, the composition of the glass being such that, when the glass is contacted with water, stannous ions are released into solution by dissolution of the glass.

4. A corrosion inhibiting glass composition substantially as described herein.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. pigment is formed from a glass containing stannous (Sn++) ions. The glass is formed by melting a mixture including stannous oxide (SnO) and phosphorus pentoxide, which act as a glass modifying oxide and the glass forming oxide respectively, in a reducing atmosphere. In this way a glass with a high Sn++ concentration is obtained. The water solubility of the glass is determined by small variations in the SnO/P2O5 ratio, and by the incorporation of one or more glass modifying oxides, e.g. alkali metal oxides and/or alkaline earth metal oxides, and/or the oxides of the metals of group IIIB of the periodic table, e.g. Na2O, CaO and Awl203, in the glass. The addition of sodium oxide increases water solubility whilst the addition of calcium and aluminium oxides decreases solubility The glass is ground into a powder and is dispersed in a resinous material to form the paint. When the glass is used as a paint pigment, e.g. for protecting an iron or steel surface, any oxidising agent, for example dissolved oxygen, which is able to pass through the paint layer will, in the presence of water, be reduced by the Sn++ ions and will therefore be unable to attack the metal. It will be clear that it is also possible to use the glasses which release ions that are effective as anti-corrosion agents by introducing them at a controlled rate into an aqueous environment as additives to water systems. Thus, for example, the internal and external surfaces of steel water pipes may be protected in this way. The glass can be introduced in the form of monolithic solids, as enamel like metal coatings, as woven cloth or any other form in which a glass may be fabricated and is appropriate to the particular application. WHAT WE CLAIM IS:

1. A paint composition adapted to inhibit corrosion of a metal surface to which it is applied, the composition including a water soluble glass dispersed in a resin carrier, in which sald glass comprises phosphorus pentoxide (P2O5) and stannous oxide (SnO) which together provide the glass forming oxide and a glass modifying oxide respectively of the glass, together with an alkali metal oxide, an alkaline earth metal oxide, a group III B metal oxide or mixtures thereof, the composition of the glass being such that, when the glass is contacted with water, stannous ions are released into solution by dissolution of the glass.

4. A corrosion inhibiting glass composition substantially as described herein.