Method for inhibiting corrosion of metal

This invention relates to a method for inhibiting corrosion of a metal surface comprising coating same with a composition containing an inorganic pigment, more particularly a rust-inhibiting pigment, consisting substantially of a vitrified substance, containing a definite range of P.sub.2 O.sub.5 and MgO and having a definite range of a specific area thereof.

DETAILED DESCRIPTION OF THE INVENTION 
This invention relates to an inorganic pigment, more particularly an 
inorganic pigment useful as a rust-inhibiting pigment, and a process for 
the production thereof. 
As rust inhibiting pigments there are conventionally known minium, zinc 
chromate, lead chromate, lead suboxide, lead cyanamide and zinc powder. 
However, these rust inhibiting pigments contain poisonous metallic ion 
components such as lead and chrome and even in their manufacturing 
processes and their coating processes said poisonous substances are 
released in the living environments so that even if said substances are 
excellent for rust inhibiting effects they should not be used at all. 
Further, it is known to inhibit a rusting of metallic base body by 
immersing it into a solution or dispersion of phosphoric acid or 
phosphates of manganese phosphate, zinc phosphate, calcium phosphate and 
the like or by coating said body with the solution through spraying. 
However, said substances lack durability of rust-inhibiting effect, and to 
obtain a sufficient effect the metallic body must be retreated with 
diluted chromic acid after a treatment with phosphate whereby the coating 
process becomes complicated and the working environment is contaminated. 
The inventors of the present invention have made hard studies to obtain a 
pigment which does not cause environmental contamination and which is 
excellent in rust inhibiting effect, and as a result the present invention 
has been accomplished. 
The first object of the invention is to provide an inorganic pigment which 
contains 15.about.80% by weight of P.sub.2 O.sub.5 and 20.about.80% by 
weight of MgO in terms of oxides of phosphorus and magnesium respectively, 
in which the specific surface area is at least 0.1 m.sup.2 /g and which 
consists substantially of a vitrified substance. 
The second object of the invention is to provide an inorganic pigment which 
contains 10.about.70% by weight of P.sub.2 O.sub.5 and 5.about.75% by 
weight of MgO in terms of oxides of phosphorous and magnesium 
respectively, and more than one components selected from the group of 
aluminium, silica, calcium, manganese and boron in such proportion as 
5.about.30% by weight of Al.sub.2 O.sub.5, 10.about.50% by weight of 
SiO.sub.2, 15.about.40% by weight of CaO, 0.2.about.5% by weight of 
MnO.sub.2 and 0.1.about.4% by weight of B.sub.2 O.sub.3 in terms of oxides 
thereof, in which the specific surface area is in the range of 
0.1.about.40 m.sup.2 /g, and which consists substantially of a vitrified 
substance. 
The tirhd object of the invention is to provide a process for the 
production of an inorganic pigment, characterized in that a 
phosphorous-containing material is mixed with a magnesium-containing 
material, the mixture is heated to be molten, and the molten substance is 
quickly quenched thereby to obtain a fine vitrified substance. 
The fourth object of the invention is to provide a process for the 
production of an inorganic pigment, characterized in that there are mixed 
a phosphorous-containing material, a magnesium-containing material, 
aluminium-containing material, a silica-containing material, a 
calcium-containing material, and a manganese-containing material or a 
boron-containing material, the mixture is heated to be molten, and then 
the molten substance is quickly quenched thereby to obtain a fine 
vitrified substance. 
The invention employs, as said phosphorous-containing materials, 
orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, 
hexametaphosphoric acid, tripolyphosphoric acid, phosphorous acid, 
hypophosphorous acid or salts thereof, phosphorous pentaoxide, rock 
phosphate based on apatite (Ca.sub.3 (PO.sub.4).sub.2.CaS.sub.2), and the 
like. 
The use amount of the phosphorous-containing materials may vary depending 
upon their grade, but usually the optimum use amount will be such that the 
final composition of the pigment is between 15% and 80% by weight based on 
P.sub.2 O.sub.5. 
Further, as the magnesium-containing materials there are employed magnesium 
oxide, magnesium carbonate, magnesium silicate, magnesite, brucite, 
dolomite, serpentine, peridotite and the like. The use amount of these 
materials will be optimum, as in the case of the phosphorous-containing 
materials, in that the final composition of the pigment is between 20% and 
85% by weight based on MgO. 
With regard to the magnesium-containing material it is possible to use a 
slag of ferronickel or ferrochrome as a substitute therefor, because such 
slag usually consists of 1.about.5% by weight of CaO, 33.about.55% by 
weight of SiO.sub.2, 30.about.35% by weight of MgO, 1.about.25% by weight 
of Al.sub.2 O.sub.3 and the like and it contains magnesium oxide. 
It is also capable of obtaining a composition of the inorganic pigment of 
the invention by adding to the above materials, as necessary, 
aluminium-containing materials such as alumina, aluminium phosphate and 
alumina ore phosphate, or silica-containing materials such as siliceous 
sand, magnesium silicate, calcium silicate and sodium silicate, and by 
heating the mixture for melting. In said composition, the phosphorous and 
magnesium are adjusted as 10.about.70% by weight of P.sub.2 O.sub.5 and 
5.about.75% by weight of MgO in terms of their oxides while more than one 
components selected from the group consisting of aluminium, silica and 
calcium are adjusted as 5.about.30% by weight Al.sub.2 O.sub.3, 
10.about.50% by weight of SiO.sub.2, and 15.about.40% by weight of CaO 
respectively in terms of their oxides. Even this inorganic pigment thus 
obtained will never lose its performance. 
Further, preferably a slight amount of manganese or boron component may be 
added in addition to said composition, in view of improving the durability 
of the rust inhibiting effect of the inorganic pigment as obtained. These 
components can be easily contained by mixing with them, before melting the 
materials, a manganese-containing material such a rock manganese or a 
boron-containing material such as boron sand, etc. 
In said component in a slight amount it will be more effective to usually 
include into the final inorganic pigment, 0.2.about.5% by weight MnO or 
0.1.about.4% by weight of B.sub.2 O.sub.3 in terms of oxide thereof. 
The above substances as material are suitably mixed, the mixture is guided 
into a heat-melting apparatus such as electric furnace (three-phase 
resistance furnace) or open hearth furnace, and it is heated for melting, 
preferably at temperatures in the range 1250.degree..about.1450.degree. C. 
According to the invention it is preferable to quickly quench the obtained 
molten mixture, because there can be obtained a substantially vitrified 
substance. One of the preferable quick quenching methods is to either 
project or spray said molten substance into a lot of jetting water 
current. 
Simultaneously with the quick quenching there is obtained a glass-like 
substance which is very fine (the specific surface area by BET Process 
being at least 0.1 m.sup.2 /g). Further, it is possible to obtain the same 
effect as in the above quick quenching even to scatter said molten 
substance into water or a water mist atmosphere by using a rotary disc or 
cylinder and to cool it quickly at a temperature below 1000.degree. C. 
The glass-like substance thus obtained can be used as it is as a rust 
inhibiting pigment or a body, extender pigment, but if necessary it is 
divided further finely for use with mechanical percussion. Usually, by 
this division the specific surface area is adjusted to 1.about.40 m.sup.2 
/g. The dividing of the vitrified substance will improve the dispersing 
property to paint, accelerate the painting and serve for the formation of 
even painting film. The thus obtained pigment of the present invention is 
used by conventional means. 
As painting-film forming vehicle there are used dry oil, denaturated dry 
oil and water-soluble resins or emulsion resins such as alkyd resin, epoxy 
resin, phenol resin, melamine resin, acrylic resin, polyvinyl acetal, 
vinyl chloride resin, polyvinyl acetate, polyurethane resin, and polyester 
resin. And the present pigment is used in the form in which it is 
dispersed in said vehicles. When a painting film is formed by using the 
pigment obtained according to the invention, the film presents a higher 
rust inhibiting effect than in zinc chromate and minium which are 
conventionally most effective in rust resistance and used most widely. 
That is, in water resistancy the present pigment has the same effect as 
chrome type pigments while in salt water resistancy it gives an effect 
higher than the chrome type pigments. 
Furthermore, the specific surface area of the pigment obtained by dividing 
in the invention is usually in the range 1.about.40 m.sup.2 /g so as to be 
very excellent in transparency so that the present pigment possesses also 
a performance as a body, extender pigment, which is same as or higher than 
sedimentary barium sulphate, sedimentary potassium carbonate and alumina 
white which are conventionally used as body, extender pigments. 
As described above in detail, the present invention provides an inorganic 
pigment which does not polute the living environments, is rich in rust 
inhibiting effect and possesses also an essential feature as a body, 
extender pigment. Moreover, according to the manufacturing process of the 
invention, as described above, it is characterized by heating and melting 
the materials and quenching the obtained molten mixture rapidly, and 
therefore any particular measure need not be taken for the adjustment of 
the pigment composition or the heating means thereof. Accordingly, the 
inorganic pigment of the invention has a different merit in that it can be 
produced very cheap. 
The following examples illustrate the present invention but not to be 
construed as limiting the scope of the invention. 
In the Examples part and percent represent parts by weight and % by weight 
respectively.

EXAMPLE 1 
There were used orthophosphoric acid (first class grade chemical) as a 
phosphorous component and magnesium oxide (first class grade chemical) as 
a magnesium oxide component, these components were mixed according to the 
composition of Table 1, and the mixture was heated for melting at 
1400.degree. C. in an electric furnace for one hour. 
Then, the obtained molten substance was projected into a lot of water 
current, quickly quenched, filtered and dried thereby to obtain a 
glass-like magnesium polyphosphate. 
The glass-like magnesium polyphosphate was crushed and classified thereby 
obtaining a glass-like magnesium polyphosphate whose specific surface area 
is 5.4 m.sup.2 /g. In the test example referred to later, the glass-like 
magnesium polyphosphate obtained in Example 1 is shown as specimen 1. 
EXAMPLES 2.about.5 
Except that metaphosphoric acid or hexametaphosphoric acid was used as a 
phosphorous material, and magnesium oxide, magnesium or serpentine as a 
magnesium component material in the amounts shown in Table 1, the 
materials were heated, melted, quickly quenched and divided according to 
Example 1, and as a result there was obtained a pigment having a 
composition and a particle diameter shown in Table 1. 
TABLE 1 
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Composition of main 
components of product 
Spe- 
Ex- Material (%) cific 
am- MgO Others 
surface 
ple P.sub.2 O.sub.5 compo- 
component SiO.sub.2, 
area 
No. nent material 
material P.sub.2 O.sub.5 
MgO etc. (m.sup.2 /g) 
______________________________________ 
1 Orthophos- Magnesium 77.7 22.3 -- 5.4 
phoric acid 
oxide 
2 Metaphos- Magnesium 77.7 22.3 -- 6.2 
phoric acid 
carbonate 
3 Metaphos- Magnesium 41.0 59.0 -- 7.5 
phoric acid 
oxide 
4 Hexameta- Magnesium 87.4 12.6 -- 6.0 
phosphoric oxide 
acid 
5 Hexameta- Serpentine 
36.8 31.7 31.7 6.4 
phosphoric 
acid 
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The pigments obtained in Examples 2.about.5 are shown as specimens 2 to 5 
in the test example referred to later. It is added that among the 
materials the sepentine used was the one produced in Iwate Prefecture, 
Japan. 
EXAMPLE 6 
There were mixed 100 parts of rock phosphate (produced in Florida), 54 
parts of serpentine (produced in Iwate Prefecture) and 15 parts of 
peridotite (produced in Hokkaido), the mixture was roughly crushed and 
charged into an electric furnace thereby to be heated and melted, the 
molten substance was sprayed into a lot of water current whereby it was 
rapidly quenched, then it was guided into a sedimentation tank, and 
thereafter the sedimented substance was separated from water and dried, as 
the result of which there was obtained 156 parts of fine (mean particle 
surface area being about 0.1 m.sup.2 /g) vitrified substance. The 
composition of this vitrified substance was 20.2.about.20.6% of P.sub.2 
O.sub.5, 15.2.about.15.6% of MgO, 30.8.about.31.6% of CaO and 
22.6.about.23.6 of SiO.sub.2 in terms of oxides thereof. In the test 
example referred to later this vitrified substance is mentioned as 
specimen 6-A. 
Further, the obtained vitrified substance was divided and classified to 
finally become a fine powder whose specific surface area is 15.5 m.sup.2 
/g. This fine powder is mentioned as specimen 6-B. 
EXAMPLES 7.about.8 
100 parts of rock phosphate (produced in Florida), 75 parts of serpentine 
(produced in Iwate Prefecture) and siliceous sand or alumina were mixed in 
the proportion shown in Table 2, the mixture was heated, melted, quickly 
quenched and pulverized, and as the result there was obtained a pigment 
having a composition and a particle diameter shown in Table 2. The 
treatments were effected following Example 6. 
TABLE 2 
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Specific 
Ex- Material surface 
am- Sili- A- area 
ple ceous lum- Composition of product (%) 
(BET) 
No. sand ina P.sub.2 O.sub.5 
MgO SiO.sub.2 
Al.sub.2 O.sub.3 
CaO m.sup.2 /g 
______________________________________ 
7 20 39 18.9 14.0 25.4 19.5 22.2 7.3 
8 50 -- 18.0 16.1 44.8 -- 21.2 7.5 
______________________________________ 
The pigments obtained in these Examples are shown as specimens 7.about.8 in 
the test example referred to later. 
EXAMPLE 9 
The materials in Example 6 was added with 0.5 parts of manganese ore 
(produced in Gabon) and treatments were carried out following Example 6, 
as the result of which there was obtained a pigment including 1.2% 
MnO.sub.2 component. The powder before pulverizing in this Example is 
described as specimen 9-A while that after pulverizing is mentioned as 
specimen 9-B. 
EXAMPLE 10 
The materials in Example 6 were added with 0.5 parts of manganese ore 
(produced in Gabon) and 0.2 parts of boron sand (produced in Turkey) and 
treatments were effected following Example 6, as the result of which there 
was obtained a pigment including 1.1% MnO.sub.2 component and 0.6% B.sub.2 
O.sub.3 component. The powder before pulverizing in this Example is 
described as specimen 10-A while that after pulverizing is mentioned as 
specimen 10-B. 
TEST EXAMPLE 
Preparation of paint 
A paint having the following composition mixture is prepared by a paint 
shaker. 
______________________________________ 
Additive amount (%) 
of rust inhibiting 
0% 
pigment (Blanc) 5% 10% 
______________________________________ 
Alkyd resin 30 30 30 
(solid part) 
Body, extender 54 49.8 45.6 
pigment (calcium 
carbonate) 
Rust inhibiting 
0 4.2 8.4 
pigment 
Drier 0.84 0.84 0.84 
______________________________________ 
As the Alkyd resin there was used "BEKKOZOL J577" manufactured by Nippon 
Reichhold Co., Ltd. and as the drier there was employed a mixture of lead 
octylate and cobalt octylate in the weight ratio of 2.4/l. 
Preparation of a test piece for measuring the property of matter of painted 
film 
By using a No. 280 polished iron plate of JIS G-3141 (SPCC-SB) 
0.8.times.75.times.150 mm) the test piece was spray painted, and it was 
dried at room temperature for a week. 
Test method for water resistancy 
The test piece was immersed up to at least 90 cm deep into pure water under 
the condition of room temperature (20.+-.5.degree. C.), and it was taken 
out 3 weeks (21 days) later thereby to evaluate it. 
Test for salt water resistancy 
Test was carried out by using a salt water spray testing machine (gas 
testing machine), based on JIS 5400(7.8), under the conditions of 5% salt 
water and 250 hour spraying time. 
TABLE 2 
______________________________________ 
Additive Evaluation 
Name of amount of Water Salt water 
specimen specimen (g) 
resistancy resistancy 
______________________________________ 
Blank -- 1 1 
1 10 4 4 
2 10 4 4 
3 10 4 4 
4 10 4 4 
5 10 4 4 
6-A 10 4 4 
6-B 5 4 4 
" 10 4 5 
7 10 4 4 
8 10 4 4 
9-A 5 4 4 
9-B 10 4 5 
10-A 5 4 4 
" 10 4 5 
10-B 5 4 5 
" 10 4 5 
Comparative 
10 4 4 
specimen 1 
Comparative 
10 2 2 
specimen 2 
Comparative 
10 3 3 
specimen 3 
Comparative 
10 4 2 
specimen 4 
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Itemization of the comparative specimens: 
1: Zinc Chromate ZPC 
2: Iron Oxide Red 
3: Zinc Phosphate 
4: COLOGINON SP028 (manufactured by Mizusawa Kagaku Kogyo K.K.) 
Evaluation standard (comparative example 4 is set standard and evaluation 
4) 
5 Excellent because of less corrosive degree than standard 
4 Same corrosive degree as standard 
3 Slightly greater corrosive degree than standard, being inferior a littl 
2 Greater corrosive degree than standard, being considerably inferior 
1 Greater corrosive degree than standard, and rust is entirely noticed.