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Description  |
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BACKGROUND OF THE INVENTION
I. Field of the Invention
This invention relates to aqueous compositions and processes for using
these in cleaning aluminum surfaces without causing significant
discoloring or tarnishing of the metal. More specifically, the invention
concerns the use of small amounts of sodium metasilicate alongside either
alkali metal carbonates or orthophosphates in cleaning formulations to
substantially reduce or altogether prevent alkali attack on aluminum.
II. The Prior Art
Highly alkaline solutions have proved very effective for the cleaning of
soft metals such as aluminum. These solutions easily remove baked-on food,
oleo resinous films, fatty soils, oxidized hydrocarbons, waxy deposits,
carbonaceous soils and similar encrustations which are difficult to remove
with less highly alkaline compositions. Unfortunately, alkalis readily
corrode and dissolve soft metals. Metal discoloration, tarnishment and
even pitting occur under highly basic conditions.
One response to the problem has been replacement of strong with neutral or
mildly alkaline solutions that depend primarily on detergent action. For
the more tenaciously held soils, the detergent action of surfactants have
proved ineffective. Only light duty cleaning operations are practical for
surfactants.
Sodium silicate has been widely used in passivating aluminium surfaces.
However, sodium silicate cleaners suffer from several limitations. The
most serious is the restriction on level of alkalinity. Therefore, the
high alkalinity necessary for the removal of many soils cannot be used.
Furthermore, long soaking periods or mechanical action is necessary to
accomplish the release of soil.
Barium and mercury salts have been reported to potentiate the corrosive
effects of the alkaline environment. In U.S. Pat. No. 2,303,398, mercuric
chloride reduced the corrosion of a soft metal (tin) over that of an
aqueous solution containing sodium metasilicate alone, trisodium
orthophosphate alone or combinations of metasilicate and orthophosphate.
Aluminum was suggested as having alkaline corrosion properties similar to
that of tin. Another patent, U.S. Pat. No. 3,655,582, discloses that
mixtures of barium salts with sodium metasilicate can control aqueous
sodium or potassium hydroxide corrosion of aluminum.
Smectite and attapulgite clays have been described in U.S. Pat. Nos.
4,116,849 and 4,116,851 as corrosion protection agents alongside sodium
silicates in aqueous alkaline hypohalite cleaners. These cleaners were
directed towards pre-treating kitchen housewares, especially pots, pans,
dishes, etc., which were coated with hard-to-remove food soils.
Those anti-corrosion additives of the prior art suffer a number of
shortcomings. Some are ecologically toxic; others expensive. Still others
are simply not effective enough under highly alkaline conditions. Thus,
there continues to be a need for an aluminum surface cleaner which
exhibits the efficiency of highly alkaline compositions without the
attendant shortcomings.
None of the foregoing art has suggested the synergistic relationship
between sodium metasilicate and either alkali metal carbonates or
orthophosphates. Neither have the criticality of concentration ratios and
pH ranges been previously disclosed.
The object of the present invention is to provide a simple but effective
means for cleaning aluminum surfaces.
SUMMARY OF THE INVENTION
An alkaline cleaning composition for aluminum surfaces has now been found
which avoids discoloring or tarnishing of the metal surface comprising a
mixture of alkali metal metasilicate and a compound chosen from the group
consisting of sodium carbonate, potassium carbonate, lithium carbonate,
potassium orthophosphate and sodium orthophosphate and mixtures thereof,
wherein the metasilicate salt is present in an effective amount up to
about 3% by weight of the composition and wherein the pH ranges above
about 12.0.
The present invention also provides a process for cleaning aluminum
surfaces without causing significant discoloring or tarnishing of the
metal surface. The process comprises:
(a) preparing an aqueous cleaning composition comprising a mixture of
alkali metal metasilicate and a compound chosen from the group consisting
of sodium carbonate, potassium carbonate, lithium carbonate, potassium
orthophosphate and sodium orthophosphate and mixtures thereof, wherein
sodium metasilicate is present in an effective amount up to about 3% by
weight of the composition and wherein the pH ranges above about 12.0;
(b) applying the cleaning composition to the aluminum surface requiring
cleaning; and
(c) rinsing the cleaning composition from the aluminum surface.
DETAILED DESCRIPTION OF THE INVENTION
Alkali metal carbonates or orthophosphates and sodium metasilicate are the
alkaline soil removing agents in the instant compositions. Applied singly,
these agents, even at relatively low concentrations, will attack aluminum
and other metals. Permanent damage will result ranging from a slight
dulling of the metal surface to severe discoloration and corrosive
pitting.
For instance, 1% or higher aqueous sodium carbonate will damage aluminum
when left in contact with the metal for a sufficient period of time. A 1%
sodium carbonate solution has a pH of about 11.3. Similarly, a 1% solution
of potassium carbonate (pH 11.1) will produce discoloration. Higher
concentrations will discolor more severaly. Sodium metasilicate
concentrations above 1.15% anhydrous or 2% pentahydrate, will also damage
the metal. In this case, damage begins to occur around pH 12.7. Aqueous
tribasic potassium or sodium orthophosphates have deleterious effects on
aluminum as well.
Unless specifically identified as anhydrous, all reference to sodium
metasilicate and the orthophosphates herein shall be understood as meaning
the fully hydrated forms.
Alkali-on-metal contact periods used herein are of 30 minutes duration,
unless otherwise stated. While this may appear to be a rather severe test,
it is not an unrealistic one. Time is needed to remove pyrolized food
soils from pots, pans and oven surfaces by soaking in or spraying/brushing
with an alkaline cleaning solution.
In view of the aluminum damage caused by the above alkaline agents
individually, it was unexpected and surprising to find that combining
carbonates or orthophosphates with relatively small concentrations of
metasilicate minimized or altogether prevented the attack of metal
surfaces.
Non-damaging ratios of sodium carbonate to sodium metasilicate extend from
about 20:1 to about 1:2 wherein sodium metasilicate is present in an
effective amount up to about 1% by weight of the composition and wherein
the pH ranges from about 12.3 to about 12.7. With sodium metasilicate
amounts greater than 1% to about 2% the preferred ratio of sodium
carbonate to sodium metasilicate is about 3.5:1 to about 1:1 with similar
pH restrictions.
The limiting pH value for sodium carbonate:metasilicate combinations
appears to be around 12.7; beyond this value metal attack becomes
noticeable. Some sodium carbonate:metasilicate combinations of pH less
than 12.7 may even damage aluminum. Combinations with pH above 12.7 will
consistently do harm.
With combinations of potassium carbonate and sodium metasilicate, higher pH
values may be attained without damage to aluminum. For instance, a 20%
aqueous potassium carbonate solution containing 2% sodium metasilicate has
a pH of 12.99. Metal remains untarnished after a 30 minute contact period.
The range of non-damaging potassium carbonate:sodium metasilicate extends
from about 10:1 to about 1:1 at a sodium metasilicate concentration up to
about 2% and pH range from about 12.0 to 13.1. At about the 2.5% sodium
metasilicate level there is practically no aluminum damage where the
potassium carbonate to sodium metasilicate ratio ranges from about 4:1 to
about 2.8:1.
Lithium carbonate, as other alkali metal carbonates, will attack aluminum
when applied alone. In combination with sodium metasilicate, however,
aluminum damage will be slight or none at all.
Non-damaging combinations of lithium carbonate with sodium metasilicate
range from about 1:2 to about 1:3 at a sodium metasilicate level up to
about 2% and a pH from about 12.0 to about 12.5. Low solubility confines
the lithium carbonate usage level to about 0.5%. Accordingly,
carbonate:metasilicate ratios are lower than in the potassium or sodium
carbonate situations.
Tribasic potassium orthophosphate attacks aluminum severely, particularly
when applied as a 10% or greater solution. When united with sodium
metasilicate, the orthophosphate loses its metal corrosion properties.
Downward adjustment of pH is unnecessary. For instance, a 10% potassium
orthophosphate solution has a pH of 12.36 and tarnishes aluminum. In
contrast, the same solution fortified with 1% sodium metasilicate is
non-corrosive yet has a pH of 12.7. The range of non-damaging potassium
orthophosphate to sodium metasilicate extends from about 30:1 to about
1:1, at a level up to about 1% sodium metasilicate and pH 12.0 to 13.0.
The ratios range from about 10:1 to about 1:2 and pH 12.7-13.1 where
sodium metasilicate is present in amounts greater than 1% to about 2%.
Aluminum is also damaged when it is contacted by tribasic sodium
orthophosphate. Addition of small amounts of sodium metasilicate
eliminates or greatly reduces the damage. Unexpectedly, alkalinity as
expressed by pH is not sacrificed. The pH of the combinations is higher
than that of the sodium orthophosphate alone. Non-damaging concentration
ratios of sodium orthophosphate to sodium metasilicate range from about
10:1 to about 2:1, up to about 1% sodium metasilicate and pH 12.4 to 12.7.
The ratios range from about 10:1 to about 1:1 and pH 12.5 to 12.8 where
sodium metasilicate is present in amounts greater than 1% to about 2%.
Practical application of the present invention may require the presence of
optional agents in addition to the aforedescribed alkaline systems.
Adjunct materials include surfactants, solvents, thickeners, abrasives,
perfumes, colorants, propellants and water. Surfactants and solvents
assist the cleaning process and control sudsing. Thickeners control
viscosity and flow properties. Abrasives mechanically aid cleaning.
Propellants are required where compositions are intended for aerosol
dispensing.
Surfactants employed in the instant composition can be chosen from
nonionic, anionic, amphoteric or zwitterionic detergents.
NONIONIC SURFACTANTS
Nonionic synthetic detergents can be broadly defined as compounds produced
by the condensation of alkylene oxide groups (hydrophilic in nature) with
an organic hydrophobic compound, which may be aliphatic or alkyl aromatic
in nature. The length of the hydrophilic or polyoxyalkylene radical which
is condensed with any particular hydrophobic group can be readily adjusted
to yield a water-soluble compound having the desired degree of balance
between hydrophilic and hydrophobic elements. Illustrative but not
limiting examples of the various chemical types of suitable nonionic
surfactants include:
(a) polyoxypropylene-polyoxyethylene block polymers having the formula
HO(CH.sub.2 CH.sub.2 O).sub.a (CH(CH.sub.3)CH.sub.2 O).sub.b (CH.sub.2
CH.sub.2 O).sub.c H
wherein a, b, and c are integers reflecting the respective polyethylene
oxide and polypropylene oxide blocks of the polymer. The polyoxyethylene
component constitutes at least about 40% of the block polymer. The polymer
preferably has a molecular weight of between about 1000 and 4000. These
materials are well known in the art and are available under the
BASF/Wyandotte "Pluronics" trademark.
(b) polyoxyethylene or polyoxypropylene condensates of alkyl phenols,
whether linear- or branched-chain and unsaturated or saturated, containing
from about 6 to about 12 carbon atoms and incorporating from about 5 to
about 25 moles of ethylene oxide or propylene oxide. Particularly
preferred are the nonyl phenoxy poly(ethyleneoxy)ethanol materials. One of
these, Igepal CO-630, a trademark of GAF Corporation, was found especially
useful in the present invention.
(c) polyoxyethylene or polyoxypropylene condensates of aliphatic carboxylic
acids, whether linear- or branched-chain and unsaturated or saturated,
containing from about 8 to about 18 carbon atoms in the aliphatic chain
and incorporating from 5 to about 50 ethylene oxide or propylene oxide
units. Suitable carboxylic acids include "coconut" fatty acids (derived
from coconut oil) which contains an average of about 12 carbon atoms,
"tallow" fatty acids (derived from tallow-class fats) which contain an
average of about 18 carbon atoms, palmitic acid, myristic acid, stearic
acid and lauric acid.
(d) polyoxyethylene or polyoxypropylene condensates of aliphatic alcohols,
whether linear- or branched-chain and unsaturated or saturated, containing
from about 8 to about 24 carbon atoms and incorporating from about 5 to
about 50 ethylene oxide or propylene oxide units. Suitable alcohols
include the "coconut" fatty alcohol, "tallow" fatty alcohol, lauryl
alcohol, myristyl alcohol and oleyl alcohol.
(e) long chain tertiary amine oxides corresponding to the general formula,
R.sub.1 R.sub.2 R.sub.3 N.fwdarw.O, wherein R.sub.1 is an alkyl radical of
from about 8 to about 18 carbon atoms and R.sub.2 and R.sub.3 are each
methyl or ethyl radicals. The arrow in the formula is a conventional
representation of a semi-polar bond. Examples of amine oxides suitable for
use in this invention include dimethyldodecylamine oxide,
dimethyloctylamine oxide, dimethyldecylamine oxide,
dimethyltetradecylamine oxide, dimethylhexadecylamine oxide.
(f) long chain tertiary phosphene oxides corresponding to the general
formula RR'R"P.fwdarw.O wherein R is an alkyl, alkenyl or monohydroxyalkyl
radical ranging from 10 to 18 carbon atoms in chain length and R' and R"
are each alkyl or monohydroxyalkyl groups containing from 1 to 3 carbon
atoms. The arrow in the formula is a conventional representation of the
semi-polar bond. Examples of suitable phosphene oxides are:
dodecyldimethylphosphene oxide, tetradecyldimethylphosphene oxide,
tetradecylmethylethylphosphene oxide, cetyldimethylphosphene oxide,
stearyldimethylphosphene oxide, cetylmethylpropylphosphene oxide,
dodecyldiethylphosphene oxide, tetradecyldiethylphosphene oxide,
dodecyldipropylphosphene oxide, dodecyldi(hydroxymethyl)phosphene oxide,
dodecyldi(2-hydroxyethyl)phosphene oxide,
tetradecylmethyl-2-hydroxypropylphosphene oxide, oleyldimethylphosphene
oxide and 2-hydroxydodecyldimethylphosphene oxide.
ANIONIC SURFACTANTS
Anionic synthetic detergents can be broadly described as the water-soluble
salts, particularly the alkali metal salts, of organic sulfur reaction
products having in their molecular structure an alkyl radical containing
from about 8 to about 22 carbon atoms and a radical selected from the
group consisting of sulfonic acid and sulfuric acid ester radicals. Such
surfactants are well known in the detergent art and are described at
length in "Surface Active Agents and Detergents", Vol. II, by Schwartz,
Perry & Berch, Interscience Publishers Inc., 1958, incorporated by
reference.
Among the useful anionic compounds are the higher alkyl sulfates, the
higher fatty acid monoglyceride sulfates, the higher alkyl sulfonates, the
sulfated phenoxy polyethoxy ethanols, the branched higher alkylbenzene
sulfonates, the higher linear olefin sulfonates (e.g. hydroxyalkane
sulfonates and alkenyl sulfonates, including mixtures), higher alkyl
ethoxamer sulfates and methoxy higher alkyl sulfates, such as those of the
formula RO(C.sub.2 H.sub.4 O).sub.n SO.sub.3 M, wherein R is a fatty alkyl
of 12 to 18 carbon atoms, n is from 2 to 6 and M is a solubilizing
salt-forming cation, such as an alkali metal and
##STR1##
wherein R.sup.1 and R.sup.2 are selected from the group consisting of
hydrogen and alkyls, with the total number of carbon atoms in R.sup.1 and
R.sup.2 being in the range of 12 to 18, and X and Y are selected from the
group consisting of hydrogen, alkyls from C.sub.1 to C.sub.20 and alkali
metals and mixtures thereof.
As examples of suitable synthetic anionic detergents there may be cited the
higher alkyl mononuclear aromatic sulfonates such as the higher alkyl
benzene sulfonates containing from 10 to 16 carbon atoms in the alkyl
group and a straight or branched chain, e.g., the sodium salts of decyl,
undecyl, dodecyl (lauryl), tridecyl, tetradecyl, pentadecyl or hexadecyl
benzene sulfonate and the higher alkyl toluene, xylene and phenol
sulfonates; alkyl naphthalene sulfonate, and sodium dinonyl naphthalene
sulfonate.
Other anionic detergents are the olefin sulfonates, including long chain
alkene sulfonates, long chain hydroxyalkane sulfonates or mixtures
thereof. These olefin sulfonate detergents may be prepared, in known
manner, by the reaction of SO.sub.3 with long chain olefins having 8-25,
preferably 12-21 carbon atoms. Suitable olefins have the formula
RCH.dbd.CHR.sub.1, where R is alkyl and R.sub.1 is alkyl or hydrogen.
Sulfonation produces mixtures of sultones and alkenesulfonic acids.
Further treatment converts the sultones to sulfonates. Examples of other
sulfate or sulfonate detergents are paraffin sulfonates, such as the
reaction products of alpha olefins and bisulfites (e.g., sodium
bisulfite). These include primary paraffin sulfonates of about 10-20,
preferably about 15-20 carbon atoms; sulfates of higher alcohols; and
salts of .alpha.-sulfofatty ester (e.g., of about 10 to 20 carbon atoms,
such as methyl .alpha.-sulfomyristate or .alpha.-sulfotallowate).
Examples of sulfates of higher alcohols are sodium lauryl sulfate, sodium
tallow alcohol sulfate, Turkey Red Oil or other sulfated oils, or sulfates
or mono- or diglycerides of fatty acids (e.g. stearic monoglyceride
monosulfate), alkyl poly(ethoxy)ether sulfates such as the sulfates of the
condensation products of ethylene oxide and lauryl alcohol (usually having
1 to 5 ethenoxy groups per molecule); lauryl or other higher alkyl
glyceryl ether sulfonates; aromatic poly(ethenoxy)ether sulfates such as
the sulfates of the condensation products of ethylene oxide and nonyl
phenol (usually having 1 to 20 oxyethylene groups per molecule preferably
2-12).
The suitable anionic detergents include also the acyl sarcosinates (e.g.
sodium lauroylsarcosinate), the acyl esters (e.g. oleic acid ester) of
isethionates, and acyl N-methyl taurides (e.g. potassium N-methyl
lauroyl-or oleyl tauride).
Of the various anionic detergents mentioned, the preferred salts are sodium
salts and the higher alkyls are of 10 to 18 carbon atoms, preferably of 12
to 18 carbon atoms. Specific exemplifications of such compounds include:
sodium linear tridecyl benzene sulfonate; sodium linear pentadecyl benzene
sulfonate; sodium p-n-dodecyl benzene sulfonate; sodium lauryl sulfate;
potassium coconut oil fatty acids monoglyceride sulfate; sodium dodecyl
sulfonate; sodium nonyl phenoxy polyethoxy ethanol (of 30 ethoxy groups
per mole); sodium propylene tetramer benzene sulfonate; sodium
hydroxy-n-pentadecyl sulfonate; sodium dodecenyl sulfonate; lauryl
polyethoxy ethanol sulfate (of 15 ethoxy groups per mole); and potassium
methoxy-n-tetradecyl sulfate.
The most highly preferred water soluble anionic detergent compounds are the
alkali metal (such as sodium and potassium) and alkaline earth metal (such
as calcium and magnesium) salts of the higher alkyl benzene sulfonates,
olefin sulfonates, the higher alkyl sulfates and the higher fatty acid
monoglyceride sulfates. The particular salt will be suitably selected
depending upon the particular formulation and the proportions therein.
Surfactants other than sulfates and sulfonates may be used. For example,
the anionic surfactant may be of the phosphate mono- or diester type.
These esters may be represented by the following formulas:
##STR2##
wherein: R is a fatty chain containing 10 to 18 atoms;
n is an integer from 0 to 5; and
M is any suitable cation such as alkali metal, ammonium and hydroxyalkyl
ammonium.
Particularly preferred phosphate esters are those sold under the Gafac
trademark of the GAF Corporation. Gafac PE-510 is an especially preferred
phosphate ester.
Another anionic surfactant useful by itself or in combination with other
surfactants for practice of this invention are the soaps. For economic
reasons, it will normally be a sodium or potassium soap, but any other
cation will be satisfactory that is non-toxic and does not cause unwanted
side effects in the composition. The fatty acid component of the soap may
be derived from mixtures of saturated and partially unsaturated fatty
acids in the C.sub.8 -C.sub.26 chain length region. Coconut oil and
tallow, which are the traditional soap-making materials are preferred
sources of the mixed fatty acids. Coconut oil contains predominantly
C.sub.12 and C.sub.14 saturated fatty acids. Tallow contains predominantly
C.sub.14 and C.sub.18 acids and mono-unsaturated C.sub.16 acids. However,
the invention is also particularly applicable to soaps formed from fatty
acid mixtures containing high proportions of unsaturated acids such as
oleic acid and linoleic acid. Sunflower seed oil is an example of an oil
which contains fatty acids of this type.
Anionic surfactants are employed in amounts of about 0.20% to about 5.0% by
weight of the total formulation. Preferably, the anionic surfactant is
present in about 0.25% to about 1.5%.
AMPHOLYTIC SURFACTANTS
Ampholytic synthetic detergents can be broadly described as derivatives of
aliphatic secondary and tertiary amines, in which the aliphatic radical
may be straight chain or branched and wherein one of the aliphatic
substituents contains from about 8 to about 18 carbons and one contains an
anionic water solubilizing group, i.e., carboxy, sulfo, sulfato, phosphato
or phosphono. Examples of compounds falling within this definition are
sodium 3-dodecylamino proprionate and sodium 2-dodecylamino propane
sulfonate. A particularly preferred ampholytic surfactant is Emulsogen
STH, a trademark of American Hoechst Corporation, chemically identified as
the sodium salt of an alkyl sulfamido carboxylic acid.
ZWITTERIONIC SURFACTANTS
Zwitterionic synthetic detergents can be broadly described as derivatives
of aliphatic quaternary ammonium, phosphonium and sulfonium compounds in
which the aliphatic radical may be straight chained or branched, and
wherein one of the aliphatic substituents contains from about 8 to 18
carbon atoms and one contains an anionic water solubilizing group, e.g.,
carboxy, sulfo, sulfato, phosphato or phosphono. These compounds are
frequently referred to as betaines. Besides alkyl betaines, alkylamino-
and alkylamide-betaines are encompassed within this invention.
Cocoamido-propyl-dimethyl betaine is a preferred surfactant for use with
this invention.
SOLVENTS
Solvents may be employed in the compositions of this invention. They
enhance cleaning by dissolving the fats and greases and aiding penetration
into the baked-on grease. Included among the solvents are a wide range of
water soluble or dispersible compounds. Suitable solvents can be chosen
from monohydric alcohols, polyhydric alcohols such as the alkylene
glycols, alkylene glycol ethers, ketones and esters.
Alkylene glycol derived ethers are especially preferred. Among the solvents
are included diethylene glycol diethyl ether (diethyl Carbitol),
diethylene glycol monoethyl ether (Carbitol), diethylene glycol monobutyl
ether (butyl Carbitol) and ethylene glycol monobutyl ether (butyl
Cellosolve).
N-Methyl-2-pyrrolidone, sold by the GAF Corporation under the trademark
M-Pyrol, is another preferred solvent.
The solvent is present in an amount from about 5% to 20% by weight.
OTHER COMPONENTS
Thickeners may be employed in the instant compositions. Cellulosic polymers
are among the preferred thickeners. Examples include alkyl cellulose
ethers, hydroxyalkyl cellulose ethers and carboxyalkyl cellulose ethers.
Specifically, methyl cellulose, hydroxypropyl cellulose and sodium
carboxymethyl cellulose are preferred. Gum based thickeners such as guar
gum and its derivatives and gum tragacanth are also suitable. Furthermore,
a variety of clays and other colloidal inorganics may be usefully employed
as thickeners.
The compositions may contain abrasives. Calcium carbonate based minerals
including calcite, dolomite or marble can be employed. Siliceous materials
such as silica flour, tripoli and kieselguhr are operative abrasives
herein. Mineral materials of volcanic origin such as pumice and perlite
may also be included. Diatomaceous earth and a variety of clays may be
advantageously employed in the instant invention. Particle sizes for the
abrasives range from approximately 10 to about 150 microns.
Other adjuvants such as colorants, perfumes, suds boosters, emollients and
the like can be added to enhance consumer appeal and effectiveness.
Having generally described the invention, a more complete understanding can
be obtained by reference to certain specific examples which are provided
herein for purposes of illustration only and are not intended to limit the
invention unless otherwise specified. All parts, percentages and
proportions referred to herein and in the appended claims are by weight
unless otherwise indicated.
EXAMPLES
EXAMPLE 1
Aqueous solutions of sodium carbonate were prepared and applied by means of
an eye dropper to aluminum sheets. After a 30 minute contact period, the
sheets were rinsed with distilled water and left to dry. The following
results were obtained:
______________________________________
% Sod. Carbonate
Solution
in Solution pH Effect on Aluminum
______________________________________
0.5 11.20 Slight dulling, faint
discoloration.
1.0 11.31 Slight dulling and
discoloration.
2.0 11.42 Slight/moderate dulling
and discoloration.
5.0 11.55 Moderate dulling and
discoloration.
7.0 11.61 Distinct dulling and
discoloration.
10.0 11.69 Distinct dulling and
discoloration.
______________________________________
The attack on aluminum was accompanied by slight frothing of the solutions
denoting gas formation.
EXAMPLE 2
Aqueous solutions of sodium metasilicate were applied to aluminum as
described in Example 1. The results were as follows:
______________________________________
Equivalent %
% Anhydrous Sodium
Sodium Meta-
Metasilicate silicate Solution Effect on
in Solution Pentahydrate
pH Aluminum
______________________________________
0.2875 0.5 12.19 Very faint
discoloration.
0.575 1.0 12.45 Very faint
discoloration.
1.150 2.0 12.68 Slight
discoloration.
1.725 3.0 12.81 Slight
discoloration.
2.875 5.0 12.98 Moderate dul-
ling and dis-
coloration.
4.025 7.0 13.12 Strong dulling
and discolor-
ation.
5.750 10.0 13.24 Severe cor-
rosion (dulling
and discolor-
ation very
heavy).
______________________________________
Aluminum attack was again accompanied by distinct gas formation.
EXAMPLE 3
Using the procedure outlined in Example 1, aqueous solutions of the
following mixtures of sodium carbonate and metasilicate were applied to
aluminum sheets:
______________________________________
% Sodium % Sodium Meta-
Solution
Carbonate
silicate pH Effect on Aluminum
______________________________________
0.5 1.0 12.44 No damage
2.0 1.0 12.40 No damage
5.0 1.0 12.46 No damage
10.0 1.0 12.44 No damage
20.0 1.0 12.49 No damage
9.0 1.5 12.54 No damage
0.5 2.0 12.67 No damage
1.0 2.0 12.67 No damage
5.0 2.0 12.65 No damage
8.0 2.0 12.63 Faint dulling
______________________________________
This example clearly illustrates that the combinations of sodium carbonate
and metasilicate do not damage aluminum while the individual components,
as shown in Examples 1 and 2, cause damage.
Three parameters are critical to avoidance of corrosion; these are the
total sodium metasilicate amount, the ratio of sodium carbonate to sodium
metasilicate and the solution pH. In regard to the pH factor, the
following formulation was prepared.
______________________________________
Component % Formula Grams
______________________________________
Sodium Carbonate 20 11.34
Sodium Metasilicate
30 17.01
Sodium Gluconate 10 5.67
Distilled Water 40 22.68
56.70
______________________________________
The entire 56.70 gram sample of the above composition was added to 3785
grams water (1 gallon) resulting in a solution having a pH of 12.21. This
solution was evaluated for aluminum compatibility by the test outlined in
Example 1. The composition tarnished aluminum.
EXAMPLE 4
Aqueous solutions of potassium carbonate were prepared and applied by a
method identical to that described in Example 1. The following results
were obtained:
______________________________________
% Potassium Carbonate
Solution
in Solution pH Effect on Aluminum
______________________________________
1.0 11.13 Slight dulling and dis-
coloration.
2.0 11.29 Slight dulling and dis
coloration.
3.0 11.35 Slight/moderate dulling
and discoloration.
5.0 11.50 Slight/moderate dulling
and discoloration.
______________________________________
The table demonstrates that potassium carbonate, when applied alone, at
levels of 1% and above will attack aluminum.
EXAMPLE 5
Using the method outlined in Example 1, mixtures of potassium carbonate and
metasilicate were applied to aluminum sheets:
______________________________________
% Potassium
% Sodium Meta-
Solution
Carbonate
silicate pH Effect on Aluminum
______________________________________
2.0 2.0 12.70 No damage
7.0 2.0 12.79 No damage
7.0 2.5 12.98 No damage
10.0 2.0 12.80 No damage
10.0 2.5 13.02 No damage
20.0 2.0 12.99 No damage
25.0 2.0 13.23 Faint dulling
______________________________________
The above examples illustrate again that the combinations do not damage
aluminum while the individual components (Examples 2 and 4) cause damage.
EXAMPLE 6
Lithium carbonate applied to an aluminum surface according to the method of
Example 1 produces the following results:
______________________________________
% Lithium
% Sodium Meta-
Solution
Carbonate
silicate pH Effect on Aluminum
______________________________________
0.5 -- 11.23 Dulling and dis-
coloration
0.5 1.0 12.35 No damage
0.5 2.0 12.52 Slight dulling
______________________________________
EXAMPLE 7
Potassium orthophosphate was applied to aluminum surfaces by the method
described in Example 1. The following results were obtained:
______________________________________
% Potassium Solution
Orthophosphate
pH Effect on Aluminum
______________________________________
1.0 11.93 Slight/moderate dulling
5.0 11.95 Moderate discoloration,
surrounded by dull halo
20.0 12.20 Strong discoloration,
surrounded by dull halo
______________________________________
Potassium orthophosphate alone attacks aluminum quite avidly.
______________________________________
% Potassium
% Sodium Meta-
Solution Effect on
Orthophosphate
silicate pH Aluminum
______________________________________
1.0 1.0 12.41 No damage
30.0 1.0 13.00 No damage
1.0 2.0 12.69 No damage
20.0 2.0 13.01 No damage
______________________________________
Combinations of potassium orthophosphate and sodium metasilicate do not
damage aluminum.
EXAMPLE 8
Aqueous solutions were prepared having various concentrations of tribasic
sodium orthophosphate. They were applied to aluminum surfaces by the
method described in Example 1. The following results were obtained:
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% Sodium Solution
Orthophosphate
pH Effect on Aluminum
______________________________________
2.18 12.11 Discoloration, slight dulling.
6.54 12.37 Slight discoloration, distinct
dulling.
10.9 12.51 Slight discoloration, severe
dulling.
______________________________________
Sodium orthophosphate alone attacks aluminum.
______________________________________
% Sodium % Sodium Meta-
Solution Effect on
Orthophosphate
silicate pH Aluminum
______________________________________
2.18 1.0 12.51 No damage
6.54 1.0 12.63 Very faint dulling
10.9 1.0 12.68 Faint dulling/
slight discolor-
ation
2.18 2.0 12.50 No damage
10.9 2.0 12.80 Slight dulling
______________________________________
Combinations of sodium orthophosphate and sodium metasilicate cause no or
at most slight aluminum damage. Even the slight damage is decidedly less
severe than the damage caused by orthophosphate alone. Amelioration of
damage occurs without reduction in pH. In fact, the pH of the combinations
are higher than that of the orthophosphate alone.
EXAMPLE 9
Sodium hydroxide was applied to aluminum surfaces by the method of Example
1. Results were as follows:
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0.125% sodium hydroxide, pH 12.30
slight dulling and dis-
coloration
0.25% sodium hydroxide, pH 12.54
moderate dulling, slight
discoloration
0.125% sodium hydroxide + 1.0%
faint discoloration
sodium metasilicate, pH 12.64
0.25% sodium hydroxide + 0.5%
slight dulling
sodium metasilicate, pH 12.68
______________________________________
This example shows that the combinations of sodium hydroxide with sodium
metasilicate are less corrosive, despite higher pH values, than sodium
hydroxide alone. However, when sodium carbonate is combined with sodium
metasilicate and hydroxide, the combination is more corrosive than in the
absence of sodium hydroxide. The following experiments illustrate this
effect.
______________________________________
Composition A
Component % Formula Grams
______________________________________
Sodium Carbonate 20 11.34
Sodium Metasilicate
30 17.01
Sodium Hydroxide 30 17.18
Sodium Gluconate 10 5.67
Distilled Water 10 6.50
56.70
______________________________________
The entire 56.7 gram sample of Composition A (equivalent to 2 ounces) was
added to 3785 grams distilled water (equivalent to one gallon) resulting
in a solution having a pH of 12.71.
______________________________________
Composition B
Component % Formula Grams
______________________________________
Sodium Carbonate 20 11.34
Sodium Metasilicate
30 17.01
Sodium Hydroxide 30 17.18
Distilled Water 20 11.17
56.70
______________________________________
The entire 56.7 gram sample of Composition B was added to 3785 grams of
water resulting in a solution having a pH of 12.70.
The above two compositions were evaluated for metal corrosion according to
the method described in Example 1. The solution of Compositions A and B
both corroded aluminum. In contrast, similar compositions without sodium
hydroxide were noncorrosive. Thus, where sodium carbonate and sodium
metasilicate are combined in accordance with this invention, it is
preferred that sodium hydroxide be absent.
The following examples will illustrate the practical application of our
invention in pot and pan cleaning compositions.
EXAMPLE 10
The following formula represents a pot and pan cleaner in aerosol form.
Ninety-three parts of the formula was blended with seven parts of
Propellant A-46 (blend of propane/isobutane in 17:83 ratio).
______________________________________
Component % by Wt.
______________________________________
Coco/tallow soap 0.25
Potassium carbonate
8.0
Sodium metasilicate
1.8
Igepal CO | | |
