close

Вход

Забыли?

вход по аккаунту

?

Патент USA US2848309

код для вставки
United States Patent
"
- 2,848,299
Patented Aug. 19, 1958
2
ma
system of the once-through type ‘or of the recirculating
type. The undesirable effect of aluminum will be present
2,848,299
in either type of system but will be aggravated in a re
circulating system due to the concentration eifect of such
CORROSION INHIBITION IN WATER SYSTEMS
a system.
Harry Lewis Kahler, Feasterville, Chester A. Bishof,
Churchville, and William A. Tanzola, Havertown, Pa.,
"
Where the subsequent treatment of the cooling water
is
accomplished by the use of phosphates or phosphate
assignors, by mesne assignments, to Betz Laboratories,
chromate combinations, the presence of aluminum seri
Inc., a corporation of Pennsylvania
ously interferes with the effectiveness of the treatment.
No Drawing. Application January 11, 1956
10 For example, aluminum forms a complex ion with poly
Serial No. 558,415
phosphate. The polyphosphate combined in this com
plex ion cannot exert its normal function. Kahler U. S.
8 Claims. (Cl. 21-—2.7)
Patent No. 2,711,391, granted June 21, 1955, for Phos
phate-Chromate Corrosion Protection in Water Systems,
The present invention relates to the prevention of cor 15 describes the unusual effect of phosphate and chromate
rosion and slugging in industrial water systems. Aspects
in reducing pitting and tuberculation. This effect can
of the invention relate both to the process and to the
not be secured with the separate use of either phosphate
industrial water.
or chromate at equivalent concentrations.
‘
Aluminum
by forming a complex with the polyphosphate component
metal penetration, both in iron and steel, and also in 20 of the phosphate-chromate treatment, in effect decreases
aluminum and copper base alloys, through piping, heat
or eliminates the phosphate available to function with
A purpose of the invention is to reduce the average
exchangers, and other metal surfaces of an industrial
water system.
A further- purpose is to reduce pitting and tubercula
the chromate and thus decreases the inhibiting power
of the treatment.
_
~
Aluminum is also undesirable because of its precipita
25 tion with orthophosphates in a cooling system. A heavy
tion in such systems.
'
A further purpose is to reduce the sludging of alu¢
sludge is produced which tends to adhere to the heat
minum in an industrial water system.
_
exchange
'
A further purpose is to reduce the tendency of industrial
surfaces.
This
aluminum - orthophosphate
sludge is more undesirable than aluminum hydroxide
because of its greater tendency to adhereto metal surfaces.
waters containing sulphides as well as aluminum to cause
penetration, pitting and tuberculation on metal surfaces. 30
In studies made to overcome the undesirable effect of
A further purpose ‘is to introduce into an industrial
aluminum, it was discovered by the present inventors
water system a watersoluble ?uoride compound, prefer
that if water soluble ?uoride is used with water- soluble
ably in the concentration of 10 to 200 p. p. m. and most
chromate, in place of phosphate, an inhibitory effect is,
desirably in the concentration of from 20 to\50,p. p. m.,
secured similar to that of phosphate. vln addition, the
and a water soluble chromate compound preferably in 35 ?uoride possesses the valuable propertyof solubilizing
the concentration of 1 to 200 p. p. m. and most desirably
aluminum, thus reducing the precipitation. Since little
' the concentration from 10 to 40 p. p. m., either in
or no phosphate is used, aluminum orthophosphate de
he absence of aluminum or in the presence of aluminum
posit is kept to a minimum.
\
>
1
~
as an impurity, or with the deliberate addition of alu
CONDITIONS
.
OF
TEST
minum, and to maintain in the water a pH between 5 40
and 8 and preferably, especially where aluminum is pres
ent, a pH between 5 and 6.5.
A further purpose is to add from 1 to 10 p. p. m. of‘
aluminum ion to an industrial water which is de?cient
N in aluminum.
‘The tests, reported are based upon resultsobtained by
three different corrosion systems.
One was a recirculat
ingsystem operating at a ?ow rate of 0.5 feet per second
at 120° F. The second system was a once-through
45 system with a ?ow rate of 0.35 feet per second at a tem
perature of 120°. F. The third system was a spinner
type using a constant volume of water. The specimens
were spun at 1. foot per second. All of the systems
1 and 20 p. p. m. of water soluble phosphate compound,
used the same type of corrosion water made from Phila
in addition to the water soluble ?uoride compound and
50
delphia tap water to contain 100 pp. in. calcium, 30
the water soluble chromate compound, the concentra
A further purpose is to introduce into an industrial
water containing sulphide and aluminum ions, between
tion of trivalent chromium ions preferably being in the
range of 0.4 to 8 p. p. m.
Further purposes appear in the speci?cation and in
the claims.
Turbid waters and waters containing suspended solids '
p. p. in magnesium, 30 p. p. m. alkalinity, all as cal
cium carbonate, 24 p. p. m. S04, 5.5 p. p. m. oxygen,
500 p. p. 111. C1, 0.2vp. p. m. copper and-7 p. p. m. alu
minum. Sometimes H28 was introduced as noted.
The corrosion specimens were one-half 'inch by 3
usually must be pretreated prior to use for cooling water
purposes. The pretreatment used ordinarily consists of
inches by 3/16 inch high carbon steel of normal cor
rodibility having the surfaces ground to a ?nish of 20
coagulation with aluminum salts, settling and ?ltration,
although ?ltration is in some cases omitted. If the proper
microinches to allow evaluation of di?erent types of cor
rosion attack. The chemical composition of the steel’
pH for coagulation is not maintained constantly, there is
was 0.04 percent sulphur, 0.3 percent silicon, 0.9 per
cent carbon, 1.4 percent manganese, phosphorus absent.
a danger that some aluminum ion will be present in the
All percentages here given are by Weight.
.
e?luent of the treating plant. Where ?lters are not in
Before immersion the specimens vwere cleaned. with.
use, of course, some suspended aluminum precipitate
may be present in the treatment plant e?iuent, in addi—
Tripoli (an abrasive) and trisodium phosphate followed
tion to the soluble aluminum. The presence of aluminum 65 by a water rinse and then an alcohol rinse, and ?nally dry
in soluble or insoluble form may seriously interfere with
ing. After exposure was complete, the observations on
the eifectiveness of the subsequent treatment of the cool
the type of attack, the products, tuberculation'and pitting
ing water from the standpoints both of corrosion and
were made at a magni?cation of 20 diameters. The
formation of deposits.
70 chemicals used in these tests were sodium chromate,
Depending on the local conditions, the e?luent from
sodium dichromate, sodium ?uoride, sodium tripoly
such a pretreatment plant may be used in a cooling
phosphate to furnish the complex phosphate, disodiurnl
2,848,299
3.
4
phosphate to furnish the orthophosphate, acidi?ed chromic
.
The concentration of water soluble chromate compound
sulphate and in some cases aluminum sulphate.
will preferably be between 1 and 200 p. p. m., and most
desirably between 10 and 40 p. p. m., expressed as
FLUORIDE-CHROMATE IN THE PRESENCE OF
Na2Cr2O7’ ZHZO. The pH maintained in the Water should
be between 5 and 8, and especially when aluminum is
present it will preferably be between 5 and 6.5.
ALUMINUM
Table I shows the result of the treatment of the inven
tion compared to phosphate-chromate, ?uoride alone’ and
FLUORIDE-CHROMATE TREATMENT IN WATERS
CONTAINING ALUMINUM AND SULPHIDE
Many re?nery cooling waters are subject not only to
aluminum contamination but also to contamination with
chromate alone.
Test 31 shows that the phosphate-chromate treatment
run at a favorable pH of 6 with aluminum present gave
low steel penetration with pitting and tuberculation. If
no aluminum had been present, this same treatment would
hydrogen sulphide and/or organic sul?des.
have completely sti?ed the pitting attack. This is true
not only at pH 6 but also in the range from pH 5.2 to
7.8, as shown in the aforesaid Kahler patent. This
phosphate~chromate treatment also, more signi?cantly,
waters of this character also occur. When sulphide con
Natural
tamination is present, the chromate of the ?uoride-chro~
mate treatment is reduced to trivalent chromic ion. Under
these conditions it is very desirable to alter the treatment
of the invention slightly for two reasons. First it is desir
able to change the treatment to obtain maximum corrosion
allowed considerable sludging. In actual practice, this
sludging interferes with heat transfer, and even makes
protection. Second, it is desirable to make the change for
use of the phosphate treatment impractical when substan
20 minimum interference with heat transfer.
tial aluminum is present.
According to the altered technique, if the practice
The sodium ?uoride treatment alone at pH 5 and 6 in
were to feed 40 p. p. 111. water soluble ?uoride compound
Table I generally afforded some protection to the steel
expressed as sodium ?uoride and 20 p. p. m. sodium di
(about 75 percent). At pH 7 and 8 the protection was
chromate, without the sulphide contamination, in the
lower. At none of these pH levels was the pitting attack
sti?ed. Fluoride alone was able to suppress the formation 25 presence of the sulphide contamination the chromate
compound expressed as Na2Cr2Oq.2H2O would be re
of aluminum sludge at pH 5, 5.5, 6.0 and 6.5. But at
duced for example to 12.8 p. p. In. so that on reduction it
pH 7 and 8, ?uoride was not able to reduce the formation
would produce 4.5 p. p. m. trivalent chromic ion which
of aluminum sludge to any noticeable degree.
Table ‘I indicates that the sodium chromate treatment
alone at ‘pH 5, 6, 7 and 8 reduces the steel losses, but does
not always sti?e the pitting attack. However, the greatest
defect of this treatment lies in its inability to stop alumi
compound, preferably molecularly dehydrated phosphate
only sti?es the corrosion attack but satisfactorily controls
aluminum sludging. This treatment is therefore practical
found the chromic phosphate coating to be more bene
?cial than other chromic compounds.
gives satisfactory protection with a minimum interference
with heat transfer. To promote the best chromic coating,
an addition of say 5 p. p. m. of water soluble phosphate
such as sodium tripolyphosphate is made, so that the
num sludging which interferes with heat transfer.
chromic ion forms some chromic phosphate after some
Speaking generally, over the pH range 5 to 6.5, the
?uoride-chromate treatment of the present invention not 35 reversion to the orthophosphate takes place. We have
Under these conditions it may be desirable to increase
the quantity of water soluble ?uoride compound from say
in waters containing aluminum, particularly because it re
strains the aluminum from precipitating. When compared
with the phosphate-chromate treatment which allows pre- "
cipitation of aluminum, to the extent of plastering the
walls of the cooling water equipment, the ?uoride
40 to 60 p. p. m., although the amount of water soluble
?uoride will depend on the aluminum contamination.
Table IH reports laboratory results showing that
this type of treatment was satisfactory in reducing steel
loss, and in completely wiping out any pitting attack.
bene?cial reduction in aluminum precipitate.
This combination treatment, with water soluble ?uoride 45 Plant application of this same type of treatment has
proved very successful under quite corrosive conditions
and water soluble chromate, de?nitely bene?ts in cor
imparted from high concentrations of aluminum, hy
rosion protection as compared with the single ?uoride
drogen sulphide and organic sulphide. Equally success
treatment. As compared with the single chromate treat
ful results have been obtained from lower amounts of
ment and the phosphate-chromate treatment, the ?uoride
chromate treatment of the present invention makes a satis 50 ?uoride, water soluble phosphate and chromic ion.
chromate treatment of the present invention makes a very
In general when sulphide ion is present it is preferable
factory reduction in precipitation of aluminum.
Other metals such as copper base alloys and aluminum
to use from 10 to 200 p. p. m. of water soluble ?uoride
base alloys are also protected by the ?uoride-chromate
compound, expressed as sodium ?uoride, most desirably
from 20 to 50 p. p. m., from 1 to 20 p. p. m. of water
treatment as shown in Table II. The average penetration
for copper was very low. The average penetration for 55 soluble phosphate compound expressed as sodium tri
polyphosphate, and from 1 to 20 p. p. m. of water solu
aluminum was slightly high, which is expected in one day
testing. On prolonged testing this loss reduces to a satis
ble chromate compound expressed as Na2Cr2O7.2H20,
to furnish from 0.4 to 7p. p. m. of trivalent chromium
factory level. The treatment sti?ed pitting attack on both
metals.
10118.
The ?uoride and chromate may be fed as above de
Any suitable water soluble ?uoride may be used, such 60
scribed. The phosphate may be orthophosphate or
as sodium ?uoride, sodium bi?uoride (due allowance ‘be
molecularly dehydrated phosphate. As the orthophos
phate, monosodium phosphate, disodium phosphate, tri
ing made for acidity), potassium ?uoride, potassium bi
?uoride, lithium ?uoride, and ammonium ?uoride. The
alkali metal ?uorides are preferred but other water solu
ble ?uorides may be used.
The concentration of water soluble: ?uoride compound
will preferably be between 10 and 200 p. p. m. expressed
as sodium ?uoride, mostdesirably ‘between 20 and 50
pyrophosphate, tripolyphosphate, tetraphosphate, septa
phosphate, decaphosphate, hexametaphosphate, metaphos
p. p. m.
phoric acid or pyrophosphoric acid or any other water
sodium phosphate, the corresponding potassium or lithium
compounds or phosphoric acid may be used.
As a
molecularly dehydrated phosphate, sodium or potassium
Any suitable water soluble chromate or dichromate 70 soluble polyphosphate may be used.
may be used, suitable examples being sodium dichromate
dihydrate, sodium chromate anhydrous, sodium chromate
tetrahydrate, sodium chromate hexahydrate, sodium
EFFECTIVENESS OF FLUORINE-CHROMATE v.
PHOSPHATE-CHROMATE IN WATERS
CONTAMINATED WITH ALUMINUM
chromate decahydrate, potassium dichromate, potassium
chromate, ammonium dichromate and chromic acid.
75
NOT
Although the ?uoride-chromate treatment of the in
2,848,299
5
6
vention along with its various modi?cations is outstand
ingly successful in waters contaminated with aluminum,
it functions satisfactorily in waters where aluminum is
absent or is present only in insigni?cant quantities.
increased rather than decreased the average penetration
rate. On the other hand, in Table I, tests 1 and 2 show
that in the presence of aluminum, ?uoride decreased the
average penetration rate.
,
' .
-
Table IV shows results of tests made at pH 6 with 5
Comparison of Table I, test 11 with Table IV, test 4;
the same water used in the test of Table 1, except that
Table I, test 12, with Table IV, test 5; and Table I, test
aluminum was absent. The table shows that with no
13 with Table IV, test 6, indicate that in each case the
?uoride-chromate combination gives lower penetration
treatment the absence of aluminum decreased the cor
and better protection against pitting when aluminum is I
rosivity of the water. Test 1 which applies no treatment
.
indicates an average penetration of only 0.063 inch per 10 present.
year, compared with a corresponding value of 0.193 inch
It is therefore evident that not only does ?uoride over
come the detrimental effects of aluminum but the pres~
per year in Table I. Test 2_ for the phosphate chromate
ence of aluminum assists the ?uoride-chromate combina
combination, as described in the Kahler patent afore
tion _to produce excellent results in preventing corrosion.
said, produced excellent results as would be expected
There is an advantage, therefore, in adding aluminum to
when aluminum is absent. The average penetration was
the ?uoride-chromate treatment. to obtain best results
reduced to 0.003 inch per year, and pitting was com
pletely sti?ed.
with a fairly corrosive water which has no aluminum
present. The concentration of aluminum required to
Fluoride alone at 60 p. p. m. did not reduce the
give satisfactory corrosion control will vary with the
average penetration, nor did it sti?e pitting.
Table IV, tests 4 to 7 inclusive‘ with the ?uoride 20 conditions. Table V shows that for a given set of con
ditions the concentration of aluminum is a factor and
chromate combination show steadyreduction in average
must be considered. It is evident from Table V that
penetration values with increase in the ‘proportion, ‘of
in the pH range from 5 to 16, the preferable concen
chromate. Tests 4 and __5 did not completely sti?e pitting
but it was brought under control in tests'6 and 7.- In - tration of aluminum ion is 2 to 5 p. p. m. to sti?e pit
ting. At pH 7 and above a concentration of aluminum
waters without aluminum it is best to use a ratioof water”
soluble ?uoride to water soluble chromate in the region ._,ion of l to 2 p. p. m. is preferable. Generally speaking,
the average penetration of steel was satisfactory for all
between 1/3 ?uoride to 2/a, chromate and 1/6 ?uoride to
‘levels of aluminum. It is evident that aluminum addi
% chromate by weight. _
.,
,3
tions of'l to 10 p. p. m. of aluminum ion are bene?cial
The, desirable eifects obtained are a function of the
conjoint use of these two materials since tests’ 3 ‘andh‘8'h30 ‘from the standpoint of corrosion, the upper concentration
limited by the desire to maintain cleanliness of
show that neither water soluble ?uoride alone n'orl'water‘__ 1-_being
' equipment.
soluble chromate alone produced the result.
For systems which are not contaminated with alumi
It should be noted that not only does water soluble
num, it is therefore advantageous to feed aluminum with
?uoride produce a bene?t in waters containing aluminum, 35 the ?uoride-chromate treatment to obtain an optimum
but aluminum is bene?cial inorder to‘ obtain best'results
concentration of soluble aluminum depending on the pH.
in waters containing ?uoride or ?uoride-chromate com- ' '
The aluminum may be fed in any suitable water soluble
binations.
For example, in Table IV where the waters A ‘
are free of aluminum, tests‘l and 3 show that ‘?uoride
liqbl
aluminum compound, examples being aluminum sulphate,
aluminum chloride, and the like.
—*W_ater contaminated with aluminum (7 p. p. m.)
STEEL
.
l
.
.
Test
.
'
.
"
”
'
Treatment, p.“ p. in.
..
‘*
'
'
' A
‘t
‘
Corrosion Observation
pH
Aluminum
Sludge,
'
cc./l.
‘
Type Attack
'
Ave. Pene
on,
Inches/Year
Tubercles
general ........ -.
none ________ __
pitting ________ ._
present _____ __
15
03
‘shallow pitting. _____ o__
none .......... _.
none _ . _ .
00
_ _ _-
00
_._..do _____________ __do__
l
_.
0
shallow pitting.
present _ _
. .-
none __________ .-
none . . _ _
_ _ -_
pitting and gen-
some . _ _ _
_ . __
eral.
_.-__do _____________ __do-___
-
almost none..." almost none..
none-
none
_._..do__
0..
almost none___-- almost none.many ?ne pits- pitting
I
pitting ________ __
90.53;?HOQ
present _____ .
.-___do ...... _.
"
severe edge
attack.
__-__do__
‘
scattered small
.
3i ___________ __ {tg?aft’e‘
''''''
a;
4___...
>
.
20 NazCr2O1§2H2O_....
6
do _
<OQKI¢°
0
...-__do ______ _.
pits.
‘
,
pittin ____-___.______do__-__-__
g
14
0.
4
00
2,848,299
8
7
Table II.-—Water contaminated with aluminum
(5. p. p. m.)
COMPLEX FLUORIDES
The complex ?uorides such as the ?uoroborates and the
?uorosilicates were tested in the absence of phosphate
COPPER AND ALUMINUM
along with chromate and alone, and are not recom- 5
.'
'
mended. _When reference is made herein to water sol
_
'
uble ?uoride, therefore, it IS intended to designate the
material which forms the ?'uoride 1011 in water solution,
Ave.Penetrati0n
Treatment,
Test
p_p_m_
pH
Corrosion Observation Inches/Year .
Tubemles
Fitting
Cu
A]
rather than a compound which normally forms a complex
‘on’
.
.
.
.
.
.
10
1___._
40NaF—20C1__-
5
none_.____
none____ ______ __
0.010
In view of our invention and disclosure, variations
and modi?cations to meet individual whlm or_particular
40 gap-208""
4m“ 40 NaF_2uC____
5 _____go_____ mgomn (1002 ______ __
6 _____do_____ "join" (L002 ______ 0
need will doubtless become ev1dent to others skllled 1n the
1s_____ 40 NaF-200____
6_____ 40 NQF_2OC____
-
'
-
-
-‘
-
-
'
-
-
40
aF—20
e
_____
o ___________ __
0.013
7
few sgat- slight.._ ______ __
0.010
7
none ____ __ lumen"
-
o__.__ _-_
tere
art, to obtain all or part of the bene?ts of our invention
.
M02 ______ __
without copying the method and composition shown, and 15
we, therefore, claim all such insofar as they fall within
1 C=Na20n0m 21120‘
the reasonable spirit and scope of our claims.
Table 111
Treatment, p. p. m.
p. p. m.
No.
Ave.
Steel
pH
NaF
NaaPsOm
1 ____ _.
2____ _-
NazHPOr
0154*"
A1
No t'eatment
60
2.5
2.5
3.6
Has!
Penetration,
InJYr.
Pitting
7
2
6
0.236
present.
7
1 1.8
6
0.008
absent.
1 Superimposed on corrosion water described in speci?cation.
2 From 10 p. p. m. NSgOHOLZHQO'
‘ EH18 fed. 1.8 residual.
Table I V.—Water free of Al
Corrosion Observation
Test
Type Attack
1
Ave. Steel
Penetration,
Treatment, p. p. m.
Norm
Tubereles
Inches/Year
generalwithsomepitting. some ........ _-
0.063
general
none ........ _.
0. 003
pitting
do
some
do
0,059
0.014
an
do
0.009
20 NBBPIOIQ ........... -.
20 NaHzPOt..-
20 NazCt:O7.2H:O-..---_
3"-.- 60 NeF
slight pitting changing
510 N F
to general attack.
3
7""'
-
Few""""" "
0' 007
none
none """" "
0'005
pit?mr
large and ag-
0.006
50 N82CTQOL2H2O
8---" 60Na:0r=O1.2H=O
‘
gressive.
Conditions of test: Same as previous tests with Al+++
omitted, and carried out at pH 6.0.
Table V.—E?ect of aluminum concentration
Steel Ave.
Test
Treatment,
p. p. m.
Corrosive Observation
Penetration, p. p.m
Inches/Yr.
40 Nell-200 1-_
A].
pH
Tubercles
Fitting
0.003
3
- QDNaF-ZUC 1--
0.002
5 ......rl0
40 NaF-ZOO 1.-
0. 006
1
few ________ ._ few pin point _____ -_
40 NaF--20G 1--
0.005
3
few
few
40 NaF-20O 1-_
0.004
5
none.
none
6
40 NaF-2OO 1.-
0. 004
1
many small. many small ...... -_
7
40 NaF-200 1--
0.004
3
manysmall,
many small, some
largeatedge.
large .............. -.
0.006
5
l 0 indicates NmOnOzQHaO.
5
5
6
on edge.
.
40 N aF-200 1__
do
many small. small on surf., large
.
'\
~
none
many large.. large deep pits"..-
6
7
7
‘
~
2,848,299
10
Having thus described our invention, what we claim as
new and desire to secure by Letters Patent is:
5. The process of claim 4, in which the concentration
of water soluble ?uoride compound is between 20 and 50
l. The process of reducing the corrosion and sludging
p. p. m. expressed as sodium ?uoride, the concentration
of water soluble chromate compound is between 10 and
40 p. p. m. expressed as Na2Cr2O7-2H2O, and the pH is
between 5 and 6.5.
in a cooling water system, which system contains metal
parts of the class consisting of iron, steel, copper base
alloy and aluminum base alloy, and which system contains
in the water at least 1 p. p. m. of aluminum ion, which
6. The process of reducing the corrosion and sludge
in a cooling water system, which water system has metal
parts in contact with the water of the class consisting of
comprises adding to the water containing such aluminum
ion and in contact with such metal parts, water soluble
?uoride compound in concentration between 10 and 200 10 iron, steel, copper base alloy and aluminum base alloy,
p. p. m. expressed as sodium ?uoride and water soluble
chromate compound in concentration between 1 and 200
the water in the system containing at least 1 p. p. m. of
aluminum ion and also containing a sulphide, which com
p. p. m. expressed as NaZCrQOq-ZHQO, and maintaining '
prises adding to the water containing such aluminum ion
in the water a pH between 5 and 8.
and sulphide in the water system in which the water is in
2. The process of claim 1, in which the concentration 15 contact with such metal parts, water soluble ?uoride com
of water soluble ?uoride compound is between 20 and 50
pound in concentration between 10 and 200 p. p. m. ex
p. p. m. expressed as sodium ?uoride, the concentration
pressed as sodium ?uoride, water soluble chromate com
of water soluble chromate compound is between 10 and
pound in concentration between 1 and 200 p. p. in. ex
40 p. p. m. expressed as Na2Cr2Oq-2H2O, and pH is be
pressed as Na-2Cr2O1-2H2O and between 1 and 20 p. p. m.
20 of water soluble phosphate compound expressed as sodi
tween 5 and 6.5.
3. The process of claim 1, in which the relative concen
um tripolyphosphate.
tration of ?uoride compound and chromate compound is
7. The process of claim 6, in which the water soluble
between 1A ?uoride to % chromate and % ?uoride to -%
phosphate compound is a mixture of orthophosphate and
chromate by weight.
polyphosphate.
4. The process of reducing the corrosion in a cooling 25
8. The process of claim 6, in which the concentration
water system, which water system includes metal parts of
of the trivalent chromium is between 0.4 and 7 p. p. m.
the class consisting of iron, steel, copper base alloy and
aluminum base alloy, which comprises adding to the water
in the water.
and in contact with such metal parts, between 1 and 10
References Cited in the ?le of this patent
p. p. m. of aluminum ion, water soluble ?uoride com
pound in concentration betwen l0 and 200 p. p. m. ex
UNITED STATES PATENTS
pressed as sodium ?uoride, and water soluble chromate
2,203,670
compound in a concentration between 1 and 200 p. p. m.
expressed as Na2Cr2O7-2H2O, and maintaining ‘in the
water a pH between 5 and 8.
35
2,332,209
2,675,351
Buzzard ____________ __ June 11, 1940
Enquist ______________ .._ Oct. 9, 1943
Ulmer et a1 ___________ _.. Apr. 13, 1954
2,711,391
Kahler -_-.... _________ _._ June 21, 1955
Документ
Категория
Без категории
Просмотров
0
Размер файла
687 Кб
Теги
1/--страниц
Пожаловаться на содержимое документа