Note: Descriptions are shown in the official language in which they were submitted.
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Methods andl Compositions for Passivating Heat Exchanger Systems
FIELD OF THE INVENTION
[001] The invention relates generally to compositions and methods for
passivating surfaces of' components and parts in heat exchanger systems that
employ
coolants for heat transfer.
BACKGROUND
[002] Methods for producing heat exchange systems have changed over the years
with increased used foir lighter materials such as aluminium and alloys
thereof.
Construction methods have also changed with the use of brazing, e.g.,
controlled
atmosphere brazing or CAB with the brazing in a controlled N2 gas environment
using a
potassium fluoroaluminate flux. Flux is applied to the surfaces of the heat
exchange parts
to be joined, the assembled unit is heated in a N2 environment, and joining
occurs.
[003] Coolants (heat transfer fluids) are used to take away heat from heat
exchange
systems such as engines. It is known to add corrosion inhibitors to coolants
to reduce
corrosion of metallic systems. For example, US Patent No. 4664833 discloses a
coolant
system with a corrosion inhibiting amount of a nitrate salt. US Patent No
4,587,028
discloses non-silicate antifreeze formulations containing alkali metal salts
of benzoic acid,
dicarboxylic acids and nitrate. US patent No 4,647,392 discloses a corrosion
inhibitor
comprising the combination of an aliphatic monoacid or salt, a hydrocarbyl
dibasic acid or
salt and a hydrocarbonvl triazole.
[004] Brazed materials have been in use in cooling systems for decades.
Previously (see ASTM: STP 705 (1979 April)) "Corrosion Testing of Furnace and
Vacuum
Brazed - Aluminum Radiators"), it was thought that materials used to braze
aluminium
were chemically inert towards cooling system fluids. Recent investigations
show that the
presence of flux in heat exchanger systems such as radiators generally leads
to an increase
in the corrosion rate of' coolant fluids used in the systems. See
"Investigation of
Interaction Between Coolant Formulations and Flux Loading / Compositions in
Controlled
Atmosphere Brazed (CAB) Aluminium Surfaces in Heat Exchanger Applications" by
Jeffcoate et al., Journal of ASTM International, Vol. 4, No. 1, paper ID
JAI100421. Other
tests have shown a fas1: depletion of some coolant inhibitors in heat
exchangers,
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specifically nitrogen atid silicate-based inhibitors, along with an increase
in the pH of the
coolant fluids used in the systems which severely impact the performance of
the coolant.
[005] It is known in the art to treat metal surfaces by dipping in acidic
aqueous
phosphate solutions containing controlled amounts of zinc ions and phosphate
ions for a
sufficient period of time to form a uniformly dense phosphating coating with
adhesion and
anticorrosion properties, and specifically useful as an under coat for
electrodeposition
coating. However, phosphate salts although known to inhibit aluminum
corrosion, are
unacceptable to a numlber of original equipment manufactures. See for example,
Ford
Engineering Material 5pecifications "Coolant, Organic Additive Technology,
Concentrate," Specification No. WSS-M97BB44-C.
[006] There is a need to extend the life of coolant fluids in heat exchanger
systems employing aluminium and alloy parts, particularly systems having
brazed parts.
In one embodiment, the invention relates to a novel method to extend the life
of coolant
fluids in heat exchanger systems, utilizing a solution containing phosphate
ions to wash /
passivate the aluminium parts and components of the heat exchanger systems
prior to
contact with the coolant fluids.
SUMMARY OF THE INVENTION
[007] In one aspect, there is provided a method for treating parts in a heat
exchanger system, which parts have metal surfaces which chemically and
detrimentally
interact with additives in coolant fluids in the heat exchanger system, by
contacting the
metal surfaces with a phosphate-containing solution for the phosphate-
containing solution
to passivate the metal surface for subsequent contact with the coolant fluids.
[008] In anotlier aspect, the invention relates to the use of a phosphate-
containing
solution having a pH of 4.0 - 12.0 and containing 0.005 to 30 g/I of phosphate
ions to treat
parts in a heat exchanger system, which parts have metal surface that
chemically and
detrimentally interact with additives in coolant fluids in the heat exchanger
system. In the
treatment process, the phosphate ions in the phosphate-containing solution
reduce the
chemical activity of the metal surface for subsequent contact with the coolant
fluid.
DETAILED DESCRIFTION
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[009] Definitions for the following terms are provided herein to promote a
further
understanding of the invention.
[010] As useci herein, the term "heat exchange system" refers to applications
wherein cooling systerns are used, including but not limited to fuel cell
assemblies,
appliances and engine applications. Non-limiting examples include heater cores
and
radiators for engines as commonly used in automobiles, trucks, motorcycles,
aircrafts,
trains, tractors, generators, compressors, for various stationary engine and
equipment
applications, marine engine applications and the like.
[011] As useci herein, the term "heat exchange component" refers to parts,
bodies,
or components of heat exchange systems, including but not limited to
radiators, water
pump, thermostats, engine head, cylinder liners, separator plates in fuel
cells, heater cores,
and the like.
[012] As used herein, the term "treat," "treating" or "treated" may be used
interchangeably with "'passivate," "passivating," or "passivated," referring
to one
embodiment of the invention, wherein the heat exchanger part is washed
(brought into
contact) with the phosphate-containing solution to reduce the chemical
reactivity of the
washed surface, which is to be subsequently in contact with coolant fluids in
the heat
exchanger system.
[013] The term "heat transfer fluid" refers to a fluid which flows through a
heat
exchange system in order to prevent its overheating, transferring the heat
produced within
the system to other systems or devices that can utilize or dissipate the heat.
[014] As used herein, the term "antifreeze" composition (or fluid or
concentrate)
may be used interchangeably with "coolant," "heat transfer fluid" or "de-icing
fluid"
(composition or concentrate).
[015] As useci herein, "glycol-based" includes glycols, glycerins, as well as
glycol
ethers.
[016] In one embodiment of the invention, a method to treat heat exchanger
parts,
e.g., surfaces such as heater cores, radiators and brazed parts, etc., is
provided. The parts
are treated with a passivating solution to reduce the chemical reactivity of
their surfaces.
[017] Passiva.ting Solution: The composition for passivating surfaces in heat
exchange systems contains as its essential ingredient phosphate ions, in a pH
range of 4.0
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- 12Ø In a second enlbodiment, the composition is a neutral to slight
alkaline solution
containing phosphate ions having a pH of 6.5 - 11.
[018] The phosphate ions are present in the solution in a sufficient amount to
reduce the chemical activity of the surfaces in contact with the coolant
fluid. In one
embodiment, the sufficient amount of phosphate ions is from 0.005 to 30 g/1 of
solution.
In a second embodiment, the phosphate ions are present in an amount from 0.01
to 25 g/1
of solution In a third embodiment, from 1 to 15 g/l. In a fourth embodiment,
from 0.5 to
12 g/1. In a fifth embodiment, from 0.3 to 10 g/l.
[019] The phosphate ions can be introduced to the solution in the form of any
soluble phosphate compound including alkali metal phosphates, ammonium
phosphates,
polyphosphates, pyrophosphates, phosphoric acid, and the like. In one
embodiment, the
passivating solution comprises di potassium hydrogen phosphate (K2HP04) in
solution. In
a second embodiment, the solution comprises mono potassium phosphate (KH2PO4)
in
aqueous solution. In a third embodiment, the passivating solution is a
solution of
diarnmonium phosphate.
[020] In one embodiment, the passivating solution is aqueous based, with the
aqueous medium being selected from the group consisting of water, neutral
aqueous
solutions, acidic aqueaus solutions and basic aqueous solutions. In a second
embodiment,
the passivating solution comprises di potassium hydrogen phosphate in a water
base with
a sufficient amount of at least an alkali metal hydroxide, e.g., NaOH or KOH,
added for
its pH to be between 7 and 10. In a third embodiment, the passivating solution
has as its
base a glycol based or non-glycol based coolant, as the heat transfer fluid to
be used in the
system is subsequently a glycol or non-glycol based antifreeze.
[021 ] In one embodiment, the phosphate-containing passivating solution has as
its
base a glycol-based solution containing glycol or glycol ether in an amount of
2 to 97 wt.
% of total weight of a fmal passivating solution. In a second embodiment, the
amount of
glycol or glycol ether ranges from 2 to 50 wt. %. Non-limiting examples
include alkylene
glycols, such as ethylene glycol, diethylene glycol, propylene glycol,
dipropylene glycol;
triethylene glycol, tetraethylene glycol, pentaethylene glycol, hexaethylene
glycol,
dipropylene glycol, tripropylene glycol, tetrapropylene glycol, pentapropylene
glycol,
hexapropylene glycol and mixtures thereof and glycol monoethers such as the
methyl,
ethyl, propyl, and butyl ethers of ethylene glycol, and mixtures thereof.
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[022] In yet ainother embodiment, the phosphate-containing passivating
solution
has as its base a non-glycol aqueous medium containing at least an alkali
metal salt of
anions selected from acetates, formates, proprionates, adipiates, and
succinates, in an
amount of 2 to 97 wt. '% of total weight of a final passivating solution.
Suitable examples
of non-glycol based aqueous medium include but are not limited to glycerine,
ethanol,
potassium formate, polAssium propionate, potassium acetate, dipotassium
adipinate, and
mixturesthereof.
[023] In one embodiment, one or more components known in the art as
"phosphating accelerators" can be optionally added to the passivating
solution, allowing
the surfaces to be treated more uniformly with the phosphate ions. Examples
include m-
nitrobenzene sulfonate ions at 0.05 to 2 g/L, hydroxylamine in free or bound
form at 0.1 to
10 g/l, m-nitrobenzoate ions at 0.05 to 2 g/1, p-nitrophenol at 0.05 to 2 g/l,
hydrogen
peroxide in free or bouind form at I to 70 mg/l, organic N-oxides at 0.05 to
10 g/l,
nitroguanidine at0.1 to 3 g/1. nitrite ions at 1 to 500 mg/1, and chlorate
ions 0.5 to 5 g/l.
[024] In yet another embodiment, traditional corrosion inhibitors known in the
art
can be optionally added to the phosphate containing solution in an amount
ranging from
0.005 to 10 wt. %. Non-limiting examples include triazoles, nitrates,
nitrites, silicates,
borates, molybdates, organic aromatic and aliphatic acid salts and mixtures
thereof. In one
embodiment, the phosphate containing passivating solution further comprises at
least a
corrosion inhibitor selected from the group of alkali metal borates, alkali
metal silicates,
alkali metal benzoates, alkali metal nitrates, alkali metal nitrites, alkali
metal molybdates,
hydrocarbyl thiazoles, and mixturesthereof.
[025] The cornbination of soluble phosphate compounds and optional additives
can be blended into the aqueous medium matrix individually or in various sub-
combinations to formudate the passivating solution. The passivating solution
may be in the
form of a single package or in the form of two packages, with one containing
the
passivating solution (vrith the phosphate ions), and one containing a coolant
which can be
a diluted form of the coolant fluid to be subsequently used in the heat
exchanger system.
[026] Method for Treating / Passivatiniz Surfaces in Heat Exchanger stems: In
one embodiment, the treatment / passivating process is carried out at a
temperature ranging
from 10 to 140 C, with the passivating solution maintained at a temperature
ranging from
20 to 90 C. In one embodiment, the treating process is carried out at room
temperature.
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[027] The passivating solution can be applied to the surface to be treated
using
methods known in the art, including spraying, immersions, circulation of fluid
in cooling
system or by a no-rinse method such as using rollers. Whether the passivating
solution is
applied by spray, no-rinse method, or immersion, in one embodiment, the
treating time is
between 5 seconds and 12 hours. In a second embodiment, the time is from 30
seconds
and 6 hours. In a third embodiment, the treatment time is between 5 minutes
and 2 hours.
In a fourth embodiment, the treatment time ranges from 15 - 60 minutes.
[028] In one embodiment, after treatment with the passivating solution, the
heat
exchanger system may be drained and the treated parts are optionally rinsed
with a rinse
solvent, e.g. deionized water. In another embodiment, the system may be rinsed
with a
diluted concentration of the coolant fluid to be added to the heat exchanger
system, thus
minimizing the amount of and / or any residual effect of any passivating
solution that may
be retained in the system. Lastly, after the treatment (and optional rinsing
step), coolant
fluids for the normal operation of the heat exchanger system can be finally
added to the
system.
[029] In one embodiment, the treatment with the passivating solution may clean
the surfaces of the parts / components in the heat exchange systems. The
solution may
also remove oil, sludge, corrosion products and other undesirable contaminants
and / or
deposits on the surface of the parts. The composition may disperse and / or
dissolve these
species into the solution, which solution is subsequently removed / drained
away along
with the undesirable species in the optional rinsing step.
[030] ApplicaLtions: The passivating solution is useful for treating heat
exchanger systems having metal parts comprising components that chemically and
detrimentally interact with additives in coolant fluids. As used herein,
"chemically and
detrimentally interact with additives" means that at least an additive in the
coolant fluid is
reduced in efficacy anci / or useable lifetime, as measured by the amount of
active
ingredients in the addiitive, with a reduction of at least 25% reduction in at
least an additive
such as a corrosion inlvibitor after 2 weeks in use. 'I'he detrimental
chemical interaction
can also be shown in a change in the pH of the coolant over time, e.g., a
change in the pH
of at least + 1 after 2 wks.
[031] In one embodiment, the method is for treating heat exchanger parts
formed
by processes including. casting, rolling, forming, brazing, and combinations
of the above.
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In another embodiment, the method is for treating heat exchanger parts
comprising zinc,
magnesium, aluminiurn, alloys of these materials. In yet another embodiment,
the method
is for treating heat exchanger parts comprising aluminium and / or alloys
thereof.
[032] In one embodiment, the method is for treating heat exchanger parts
brazed
with flux materials that chemically and detrimentally interact with additives
in coolant
fluids. In another embodiment, the method is for treating parts brazed with a
fluorine-
containing flux. Non-:limiting examples of fluorine-containing fluxing
material include
potassium fluoroborate, potassium fluoroaluminate, cesium fluoroaluminate,
potassium
fluorozincate, cesium ifluorozincate, and mixtures thereof.
[033] In one embodiment, the treatment using the passivating solution
substantially inactivates the chemical reactivity of the metal surfaces in
heat exchanger
systems towards coolant fluids. In one embodiment of an Organic Acid
Technology
(OAT) coolant employing a traditional inhibitor such as nitrite, the treatment
stabilizes the
nitrite depletion when the coolant fluid is added to a heat exchanger system
employing
treated part, with a reduction in the nitrite level of less than 25% after 2
weeks in use. In a
second embodiment, the nitrite reduction level is less than 10%. In a third
embodiment,
the stability effect of the passivating treatment is shown in the pH level of
the coolant,
with the coolant pH remains essentially stable, i.e., showing a variation of
less than 10%
after 2 wks. in use.
[034] EXAMPLES. The following Examples are given as non-limitative
illustration of aspects of the present invention.
[035] In the examples, two different coolant formulations are employed, an OAT
coolant and a traditional mineral based coolant, both are from Chevron
Corporation. The
coolants have composiitions with components as listed in "l'able 1.
Table I
INHIBITOR OAT Coolant Traditional mineral
based coolant
Monoacid X X
Dibasic acid X -
Aromatic acid - X
S103 - X
NO3 - X
BaO, - X
POa - -
Triazole X X
M0041 X -
N02 X X
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[036] In the examples, coupons (cubes) of'/2" to 1" in size of brazed
aluminium
radiator parts were treated by immersion in washing fluids from 15 minutes to
ovemight
(10 hrs.). The parts were brazed with potassium fluoro aluminates as flux
materials -
which were previously considered an inert material under normal conditions.
After
washing, the coupons were immersed in the OAT coolant for a period of 2 weeks,
with the
coolant bath temperature being maintained at about 195 F. For all examples,
the OAT
coolant has a starting pH of 8.5 and a nitrite level of 580 ppm. pH level,
nitrite and
fluoride contents in the OAT coolant are measured after the 2 wk. test.
[037] Washir.ig fluid formula E is an aqueous solution employing 1- 2 wt. % di
potassium hydrogen phosphate (K2HP04). The corrosion inhibitor components
making
up the washing fluid formulae C - G are shown in Table 2 below, with the
phosphate ions
in washing fluid formulae E-G provided by di potassium hydrogen phosphate
(K2HPO4) in
the aqueous washing solutions:
Table 2
Washing fluid C D E F (OAT G (Traditional
inhibitors Coolant coolant)
Monoacid X X X
Dibasic acid X X X
Aromatic acid x
SIO3 X X
N O; X
BO
PO4 x x x
Triazole X X X X
MoO4 - X
NO- X
[038] In Exainple 1, the coupon was not treated / washed at all. In Example 2,
the coupon was washed with water. In Examples 3- 7, the coupons were treated
with the
washing fluids having compositions shown in Table 2, with the washing fluid
compositions E - G having 0.4-2 wt. % of K2HPO4 in water, the OAT coolant, or
a
traditional mineral coolant.
[039] It was found that the passivating treatment was as effective with a
short
treatment time (e.g., 15 minutes) as with a longer treatment period
(ovemight). The results
of the examples in Table 3 show that once the surface treated with E and F are
brought in
contact with standard coolant fluids, neither abnormal depletion nor pH shift
are observed.
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Additionally, there is no drastic release of fluoride that is indicative of
the reactivity of the
potassium fluoro aluminates with the coolant fluid typically used in the heat
exchanger
system.
Table 3
Example Washing Procedure Initial pH after Initial Nitrite after Fluoride
pH immer in nitrite immer in content (ppm
1 A" none 8.5 10.3 580 0 174
2 B* (water) 8.5 10.1 580 0 138
3 C* (OAT coolant) 8.5 9.6 580 103 80
4 D' traditiona.l coolant) 8.5 10.7 580 0 180
E hos hate: 8.5 8.0 580 535 75
6 F (phosphate with OAT 8.5 8.3 580 572 55
- - - - -
7 G (phosphate w/ traditional)
5
[040] For the purposes of this specification and appended claims, unless
otherwise indicated, all numbers expressing quantities, percentages or
proportions, and
other numerical values, are to be understood as being modified in all
instances by the term
"about." Accordingly, unless indicated to the contrary, the numerical
parameters set forth
are approximations that may vary depending upon the desired properties sought
to be
obtained by the present invention. It is noted that as used herein, the
singular forms "a,"
"an," and "the," include plural referents unless expressly and unequivocally
limited to one
referent. As used herein, the term "include" and its grammatical variants are
intended to
be non-limiting, such that recitation of items in a list is not to the
exclusion of other like
items that can be substituted or added to the listed items.
[0411 This Nvritten description uses examples to disclose the invention,
including
the best mode, and also to enable any person skilled in the art to make and
use the
invention. The patentable scope is defined by the claims, and may include
other examples
that occur to those skilled in the art. Such other examples are intended to be
within the
scope of the claims if they have structural elements that do not differ from
the literal
language of the claims, or if they include equivalent structural elements with
insubstantial
differences from the liiteral languages of the claims. All citations referred
herein are
expressly incorporated herein by reference.
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