Title:
INHIBITION OF CORROSIVE ACTION OF FLUID DEICER COMPOSITION
United States Patent 3624243
Abstract:
Cadmium, aluminum and magnesium metal corrosion by an aqueous deicer solution containing urea, ammonium nitrate and ethylene glycol is inhibited by incorporating therein about 0.05 percent to 0.40 percent by weight of a water-soluble mercaptobenzothiazole salt and about 0.05 percent to 0.40 percent by weight of a water-soluble chromate salt. The deicer solution is preferably for use to deice aircraft runways. CROSS-REFERENCE TO RELATED APPLICATIONS This application is related to U.S. Pat. application No. 824,808, filed May 15, 1969, for Deicer Composition.
US Patent References:
Prevention of corrosion in aqueous systems
Jacoby - January 1952 - 2582129
Antifreeze compositions
Barker - October 1954 - 2692860
Formamide mixtures as de-icing materials
Hearst - October 1963 - 3108075
Deicer composition
Standish et al. - May 1965 - 3185648
Corrosion inhibitor compositions
Dulat et al. - March 1966 - 3240708
Prevention of corrosion in aqueous systems
Jacoby - January 1952 - 2582129
Antifreeze compositions
Barker - October 1954 - 2692860
Formamide mixtures as de-icing materials
Hearst - October 1963 - 3108075
Deicer composition
Standish et al. - May 1965 - 3185648
Corrosion inhibitor compositions
Dulat et al. - March 1966 - 3240708
Inventors:
Scott Jr., Herbert F. (Prince George, VA)
Moore, William P. (Chester, VA)
Moore, William P. (Chester, VA)
Application Number:
05/015292
Publication Date:
11/30/1971
Filing Date:
02/27/1970
View Patent Images:
Export Citation:
Assignee:
Allied Chemical Corporation (New York, NY)
Primary Class:
Other Classes:
106/13, 252/391, 252/389.500
International Classes:
C09K3/18; C23F11/08; C23F11/14; C23F11/18; C09K3/18
Field of Search:
252/70,73-76,71,389,391 106/13
US Patent References:
| 3297577 | Chemical deicer | January 1967 | Standish et al. |
Primary Examiner:
Rosdol, Leon D.
Assistant Examiner:
Pitlick, Harris A.
Claims:
We claim
1. A process for controlling corrosiveness to cadmium, aluminum, and magnesium metals of an aqueous deicer solution, said solution having a urea content of from about 22 percent to 26 by weight, an ammonium nitrate content of from about 28 percent to 34 percent by weight, and an ethylene glycol content of from about 25 percent to 30 percent by weight, which process comprises incorporating in said solution about 0.05 percent to 0.40 percent by weight of a water-soluble mercaptobenzothizaole salt and about 0.05 to 0.40 percent of a water-soluble chromate salt, based on the
1. A process for controlling corrosiveness to cadmium, aluminum, and magnesium metals of an aqueous deicer solution, said solution having a urea content of from about 22 percent to 26 by weight, an ammonium nitrate content of from about 28 percent to 34 percent by weight, and an ethylene glycol content of from about 25 percent to 30 percent by weight, which process comprises incorporating in said solution about 0.05 percent to 0.40 percent by weight of a water-soluble mercaptobenzothizaole salt and about 0.05 to 0.40 percent of a water-soluble chromate salt, based on the
Description:
BACKGROUND OF THE INVENTION
This invention relates to a chemical deicer composition containing urea, ammonium nitrate and ethylene glycol; in particular, it relates to the inhibition of the corrosive action thereof on cadmium, aluminum and magnesium metals.
A large number of the airports throughout the United States and other parts of the world experience snow and ice on the runways which must be cleared before normal operations may be resumed. The severity and frequency varies with respect to the geographical location. Although snow can be removed from the runways adequately by existing equipment, there is no satisfactory mechanical manner or removing ice or counteracting its low traction. Ice on runways is considered to be particularly troublesome when it occurs in patches. The most promising method of combating the problem is to melt the ice with chemicals. The more common ice melting chemicals are calcium chloride and sodium chloride. These have been extensively employed to melt ice on roads, but they are too corrosive to be used on aircraft runways. The use of urea has been approved on the basis of no harm to aircraft by several major airlines. Other airlines have used urea with mixed results, primarily because of its limited effectiveness due to its relatively high eutectic point.
A deicer solution containing primarily formamide with other materials such as acetamide and urea is disclosed in U.S. Pat. No. 3,108,075. This fluid is stated to have negligible corrosion to aluminum and copper; however, no reference is made to corrosion of cadmium or magnesium used in fabricating aircraft surfaces. Moreover, formamide is relatively expensive and has limited availability.
U.S. Pat. No. 3,185,648 relates to a solid deicer composition consisting of urea and ammonium nitrate and a corrosion inhibitor. Several corrosion inhibitors are suggested; however, we have found that none of the disclosed corrosion inhibitors are effective to eliminate corrosion of cadmium, which is used for plating aircraft surfaces, particularly landing gear.
While U.S. Pat. Nos. 3,185,648 and 3,108,075 have contributed to the art, research in this field has continued in an effort to find still better deicing compositions and better corrosion inhibitors.
SUMMARY OF THE INVENTION
An object of this invention is to provide an effective deicer solution containing a corrosion inhibitor for protection of cadmium, aluminum and magnesium metals with which the solution is contacted.
Another object of the present invention is to provide a liquid urea-ammonium nitrate-ethylene glycol deicer composition which is stable during storage at temperatures as low as 10° F. and which contains a novel inhibitor for controlling corrosiveness to cadmium.
It has been found that these and other objects are obtained by formulating an aqueous deicer composition containing about 22 to 26 percent by weight of urea, about 28 to 34 percent by weight of ammonium nitrate, about 25 to 30 percent by weight of ethylene glycol, about 0.05 to 0.40 percent by weight of a water-soluble mercaptobenzothiazole salt, and about 0.05 to 0.40 percent by weight of a water-soluble chromate salt. The chromate and mercaptobenzothiazole salts are effective to inhibit corrosiveness of the deicer solution toward cadmium, magnesium and aluminum.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
This invention relates to a composition having a low freezing point which is particularly applicable to the deicing of aircraft runways.
The composition of the present invention is an aqueous chloride-free fluid deicer composition which has a marked depressing action on the melting point of ice and which is essentially harmless to metal surfaces it may contact, including cadmium, aluminum, magnesium, and their alloys. Moreover, the deicer composition of our invention is more effective as an ice melter on a weight basis than urea.
The preferred deicer solution contains about 22 to 23 percent by weight urea, about 29 to 30 percent by weight ammonium nitrate, about 24 to 25 percent by weight ethylene glycol, about 0.05 to 0.20 percent by weight of a water-soluble mercaptobenzothiazole salt, and about 0.05 to 0.20 percent by weight of a water-soluble chromate salt, the balance of the solution substantially consisting of water. These low levels of inhibitor concentration have been found to inhibit corrosion of magnesium, aluminum and cadmium metals, including cadmium plated metal surfaces. Especially preferred water-soluble chromate salts and water-soluble salts of mercaptobenzothiazole include the readily available ammonium, sodium and potassium salts.
An especially preferred deicer solution is formulated as described above but about 0.05 to 0.50 percent by weight of an ammoniated superphosphoric acid is incorporated as corrosion inhibitor in addition to the chromate and mercaptobentothiazole inhibitors. An aqueous ammoniated superphosphoric acid is readily obtained by evaporating wet-process phosphoric acid to form superphosphoric acid, which is then diluted with water and ammoniated to pH 5-8.
An aqueous ammoniated superphosphoric acid derived from wet-process phosphoric acid and having the following properties which will hereinafter be referred to as "Solution A," has been found to be useful for purposes of the present invention;
Nitrogen 10 % by weight Phosphorus 1 (as P 2 O 5) 34 % by weight Trace minerals 1 to 2 % by weight iron (Fe 2 O 3) ca. 1.0 % by weight calcium (CaO) ca. 0.1% by weight magnesium (MgO) ca. 0.3 % by weight pH 6.0 Specific Gravity at 60° F. 1.4 Salting out temperature 0° F. 1 Distribution as % by weight of the ammonium phosphates present was about:
37% ammonium orthophosphate 49% ammonium pyrophosphate 8% ammonium tripolyphosphate 5% tetrapolyphosphate 1% higher ammonium phosphates
The preferred deicer composition of this invention can be stored at temperatures as low as about 10.4° F. without solidification of any of its components. Upon spraying the deicer solution on an iced runway, the eutectic temperature of the resulting mixture is about +16.6° F. As compared with solid deicers such as urea, the deicer solution of the present invention is particularly desirable due to ease in handling. By means of spray nozzles on a moving vehicle, the desired coverage of any area can be accurately controlled.
The instant invention is particularly useful in conjunction with melting ice and snow on airport runways, taxiways, bus and truck loading areas where most of the equipment is constructed of several metals, including cadmium, aluminum and magnesium. However, if desired, utility of the invention may also be with the melting of ice and snow on roadways, sidewalks and the like.
The composition embodied herein may be prepared in any convenient manner providing a solution of the essential components. For example, urea and ammonium nitrate may be dissolved in water, either separately or combined, and then mixed in the proper proportions with ethylene glycol and inhibitors. In any event, the method whereby the noninhibited deicing composition embodied herein is prepared is not critical and is outside the scope of this invention. Any method which produces an aqueous solution of urea, ammonium nitrate, and ethylene glycol may be used.
The following examples are provided to more fully illustrate the instant invention. They are provided for illustrative purposes only and are not to be construed as limiting the invention, which is defined by the appended claims. In the following examples, all parts and percentages are by weight unless otherwise indicated.
EXAMPLE I
A preferred deicer solution was prepared as follows: About 29.6 parts of ammonium nitrate and 22.8 parts of urea were added to 22.5 parts of water. The mixture was stirred and maintained at a temperature of 77° F. until all solids were dissolved. Then 24.9 parts of ethylene glycol was added to the solution, followed by 0.2 part of sodium chromate, tetrahydrate, and the mixture was stirred until the sodium chromate dissolved. Finally, 0.2 part of sodium mercaptobenzothiazole as a 50 percent aqueous solution was stirred into the mixture. The resulting solution was stored at temperatures as low as 10.4° F. without salting out. The deicer was used effectively to melt ice at temperatures of from -11° F. to 32° F. However, the eutectic point was about -16.6° F.
EXAMPLE II
Chief problem encountered in developing a suitable deicer solution was corrosion of cadmium, magnesium and aluminum metal surfaces, which are used in aircraft. The deicer solution of example I was tested for corrosion of magnesium, cadmium and aluminum as follows:
A. Corrosion of Magnesium
Magnesium panels were cleaned, rinsed with acetone, dried and weighed. The panels were then immersed in the deicer solution of example I for 7 days at room temperature. After the panels had been recleaned and reweighed, they were found to have a weight loss of about 2 milligrams per square inch. Five milligrams per square inch is the maximum allowable weight loss. A similar test with the deicer solution diluted with an equal part of water showed a weight loss of about 1 milligram per square inch.
In a comparative test, a deicer solution prepared as in example I but without corrosion inhibitors was tested in a similar manner with magnesium panels. Corrosion of the magnesium after a 7 day immersion was about 170 milligrams per square inch.
B. Corrosion of Cadmium
A cadmium plated steel sample and a bead of cadmium metal were immersed for 3 days at room temperature in deicer solution prepared as in example I. No cadmium deterioration or removal of cadmium plating was observed. Similar results were obtained with the deicer solution diluted with an equal part of water.
In a comparative test, a deicer solution prepared as in example I but without sodium mercaptobenzothiazole was tested in a similar manner with a cadmium plated steel sample and a bead of cadmium metal. Deterioration of the cadmium metal was visible in one minute and removal of the cadmium plating appeared complete in 5 minutes.
C. Corrosion of Aluminum
Thirty-six panels of six different aluminum alloys commonly used in aircraft construction were divided into three groups of six pairs of panels representing each alloy. Two groups of panels were used to test diluted and undiluted deicer composition and the third group with water was used as control. Tap water, a 20 percent deicer solution, and a 100 percent deicer solution, prepared in example I, were tested. The solution was applied to one side of each panel and two similar panels were placed together in sandwich style with the deicer solution between the two panels. The three groups of panels were exposed in a horizontal position at alternate intervals of 16 hours in a humidity chamber and 8 hours in an oven for a total of 7 days. The humidity chamber was maintained at 100° F. and 98 to 100 percent relative humidity. The oven was maintained at 100° F. After exposure, the panels were rinsed in warm tap water and scrubbed lightly with a soft brush. After drying the panels were examined under 15 X magnification and each panel was rated according to the following standard:
0 --No visible corrosion
1 --Very slight corrosion or discoloration
2 --Slight corrosion
3 --Moderate corrosion
4-- Extensive corrosion
Results of the standard corrosion test are listed below: ##SPC1##
EXAMPLE III
Protection of high-strength aircraft landing gear from corrosion, including stress corrosion cracking, in the presence of deicer solutions is difficult due to the sensitivity of commonly used alloys both to stress corrosion cracking and embrittlement by hydrogen. This situation is complicated by the propensity of metal platings such as cadmium to introduce hydrogen during service.
Aircraft landing gear components consist primarily of AISI Type 4340 steel heat treated to an ultimate strength as high as about 280,000 p.s.i. Type 4340 steel is also used in the 220,000 to 240,000 p.s.i. range.
The deicer solution of example I was tested by a standard hydrogen embrittlement procedure using the Lawrence Hydrogen Detection Gauge and was rated "Safe" in as far as hydrogen embrittlement is concerned for use on aircraft landing gear steel having a tensile strength of 200,000 p.s.i. or better. The deicer solution did not attack cadmium plate on the steel. These procedures satisfy the requirements of Douglas Bulletin 13-1.
EXAMPLE IV
Deicing Tests in Field
A solution applicator for applying the deicer solution of example I consisted of a 1000-gallon stainless steel tank mounted on a tandem trailer. The rig was equipped with a 27-foot boom containing nine flood type nozzles on 40-inch centers to give a 30-foot swath. Solution was sprayed through the nozzles by a positive displacement type pump driven by a ground wheel drive.
A taxiway covered with a sheet of ice one-sixteenth to one-eighth inch thick was treated with the deicer solution at rates of 15.5, 9.3, and 3.1 pounds per 100 square feet. An area treated at the highest rate had water standing on it 30 minutes after treatment. The air temperature during this test was 23°F. The next day all of the treated areas showed the effect of the deicer. The area treated with 15.5 pounds per 100 square feet was 100 percent bare and the other areas were 60 to 80 percent bare. It is also noteworthy that the treated areas did not ice up during the next icing condition, indicating a residual effect of the deicer.
EXAMPLE V
An especially preferred deicer solution was prepared as follows: About 29.4 parts of ammonium nitrate and 22.7 parts of urea were added to 22.5 parts of water. The mixture was stirred and maintained at about 75°F. until all solids were dissolved. Then 24.9 parts of ethylene glycol was added to the solution followed by 0.1 part of potassium mercaptobenzothiazole and 0.2 part of potassium chromate, and the mixture was stirred until the solids dissolved. Finally, 0.2 part of "Solution A" was stirred into the mixture. Solution A is an aqueous ammoniated superphosphoric acid containing polyphosphates, as described in detail hereinabove. The resulting deicer solution was similar to the solution of example I with respect to its salting out temperature and deicing properties. It passed all corrosion tests, previously described, for the product of example I including the standard hydrogen embrittlement test. Moreover, the combination of Solution A and sodium mercaptobenzothiazole was a particularly effective inhibitor against corrosion of cadmium plated steel. It appears that the polyphosphate in this solution provides a synergistic effect with respect to corrosion inhibition toward cadmium because solution A alone was found only slightly effective in mitigating cadmium deterioration.
This invention relates to a chemical deicer composition containing urea, ammonium nitrate and ethylene glycol; in particular, it relates to the inhibition of the corrosive action thereof on cadmium, aluminum and magnesium metals.
A large number of the airports throughout the United States and other parts of the world experience snow and ice on the runways which must be cleared before normal operations may be resumed. The severity and frequency varies with respect to the geographical location. Although snow can be removed from the runways adequately by existing equipment, there is no satisfactory mechanical manner or removing ice or counteracting its low traction. Ice on runways is considered to be particularly troublesome when it occurs in patches. The most promising method of combating the problem is to melt the ice with chemicals. The more common ice melting chemicals are calcium chloride and sodium chloride. These have been extensively employed to melt ice on roads, but they are too corrosive to be used on aircraft runways. The use of urea has been approved on the basis of no harm to aircraft by several major airlines. Other airlines have used urea with mixed results, primarily because of its limited effectiveness due to its relatively high eutectic point.
A deicer solution containing primarily formamide with other materials such as acetamide and urea is disclosed in U.S. Pat. No. 3,108,075. This fluid is stated to have negligible corrosion to aluminum and copper; however, no reference is made to corrosion of cadmium or magnesium used in fabricating aircraft surfaces. Moreover, formamide is relatively expensive and has limited availability.
U.S. Pat. No. 3,185,648 relates to a solid deicer composition consisting of urea and ammonium nitrate and a corrosion inhibitor. Several corrosion inhibitors are suggested; however, we have found that none of the disclosed corrosion inhibitors are effective to eliminate corrosion of cadmium, which is used for plating aircraft surfaces, particularly landing gear.
While U.S. Pat. Nos. 3,185,648 and 3,108,075 have contributed to the art, research in this field has continued in an effort to find still better deicing compositions and better corrosion inhibitors.
SUMMARY OF THE INVENTION
An object of this invention is to provide an effective deicer solution containing a corrosion inhibitor for protection of cadmium, aluminum and magnesium metals with which the solution is contacted.
Another object of the present invention is to provide a liquid urea-ammonium nitrate-ethylene glycol deicer composition which is stable during storage at temperatures as low as 10° F. and which contains a novel inhibitor for controlling corrosiveness to cadmium.
It has been found that these and other objects are obtained by formulating an aqueous deicer composition containing about 22 to 26 percent by weight of urea, about 28 to 34 percent by weight of ammonium nitrate, about 25 to 30 percent by weight of ethylene glycol, about 0.05 to 0.40 percent by weight of a water-soluble mercaptobenzothiazole salt, and about 0.05 to 0.40 percent by weight of a water-soluble chromate salt. The chromate and mercaptobenzothiazole salts are effective to inhibit corrosiveness of the deicer solution toward cadmium, magnesium and aluminum.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
This invention relates to a composition having a low freezing point which is particularly applicable to the deicing of aircraft runways.
The composition of the present invention is an aqueous chloride-free fluid deicer composition which has a marked depressing action on the melting point of ice and which is essentially harmless to metal surfaces it may contact, including cadmium, aluminum, magnesium, and their alloys. Moreover, the deicer composition of our invention is more effective as an ice melter on a weight basis than urea.
The preferred deicer solution contains about 22 to 23 percent by weight urea, about 29 to 30 percent by weight ammonium nitrate, about 24 to 25 percent by weight ethylene glycol, about 0.05 to 0.20 percent by weight of a water-soluble mercaptobenzothiazole salt, and about 0.05 to 0.20 percent by weight of a water-soluble chromate salt, the balance of the solution substantially consisting of water. These low levels of inhibitor concentration have been found to inhibit corrosion of magnesium, aluminum and cadmium metals, including cadmium plated metal surfaces. Especially preferred water-soluble chromate salts and water-soluble salts of mercaptobenzothiazole include the readily available ammonium, sodium and potassium salts.
An especially preferred deicer solution is formulated as described above but about 0.05 to 0.50 percent by weight of an ammoniated superphosphoric acid is incorporated as corrosion inhibitor in addition to the chromate and mercaptobentothiazole inhibitors. An aqueous ammoniated superphosphoric acid is readily obtained by evaporating wet-process phosphoric acid to form superphosphoric acid, which is then diluted with water and ammoniated to pH 5-8.
An aqueous ammoniated superphosphoric acid derived from wet-process phosphoric acid and having the following properties which will hereinafter be referred to as "Solution A," has been found to be useful for purposes of the present invention;
Nitrogen 10 % by weight Phosphorus 1 (as P 2 O 5) 34 % by weight Trace minerals 1 to 2 % by weight iron (Fe 2 O 3) ca. 1.0 % by weight calcium (CaO) ca. 0.1% by weight magnesium (MgO) ca. 0.3 % by weight pH 6.0 Specific Gravity at 60° F. 1.4 Salting out temperature 0° F. 1 Distribution as % by weight of the ammonium phosphates present was about:
37% ammonium orthophosphate 49% ammonium pyrophosphate 8% ammonium tripolyphosphate 5% tetrapolyphosphate 1% higher ammonium phosphates
The preferred deicer composition of this invention can be stored at temperatures as low as about 10.4° F. without solidification of any of its components. Upon spraying the deicer solution on an iced runway, the eutectic temperature of the resulting mixture is about +16.6° F. As compared with solid deicers such as urea, the deicer solution of the present invention is particularly desirable due to ease in handling. By means of spray nozzles on a moving vehicle, the desired coverage of any area can be accurately controlled.
The instant invention is particularly useful in conjunction with melting ice and snow on airport runways, taxiways, bus and truck loading areas where most of the equipment is constructed of several metals, including cadmium, aluminum and magnesium. However, if desired, utility of the invention may also be with the melting of ice and snow on roadways, sidewalks and the like.
The composition embodied herein may be prepared in any convenient manner providing a solution of the essential components. For example, urea and ammonium nitrate may be dissolved in water, either separately or combined, and then mixed in the proper proportions with ethylene glycol and inhibitors. In any event, the method whereby the noninhibited deicing composition embodied herein is prepared is not critical and is outside the scope of this invention. Any method which produces an aqueous solution of urea, ammonium nitrate, and ethylene glycol may be used.
The following examples are provided to more fully illustrate the instant invention. They are provided for illustrative purposes only and are not to be construed as limiting the invention, which is defined by the appended claims. In the following examples, all parts and percentages are by weight unless otherwise indicated.
EXAMPLE I
A preferred deicer solution was prepared as follows: About 29.6 parts of ammonium nitrate and 22.8 parts of urea were added to 22.5 parts of water. The mixture was stirred and maintained at a temperature of 77° F. until all solids were dissolved. Then 24.9 parts of ethylene glycol was added to the solution, followed by 0.2 part of sodium chromate, tetrahydrate, and the mixture was stirred until the sodium chromate dissolved. Finally, 0.2 part of sodium mercaptobenzothiazole as a 50 percent aqueous solution was stirred into the mixture. The resulting solution was stored at temperatures as low as 10.4° F. without salting out. The deicer was used effectively to melt ice at temperatures of from -11° F. to 32° F. However, the eutectic point was about -16.6° F.
EXAMPLE II
Chief problem encountered in developing a suitable deicer solution was corrosion of cadmium, magnesium and aluminum metal surfaces, which are used in aircraft. The deicer solution of example I was tested for corrosion of magnesium, cadmium and aluminum as follows:
A. Corrosion of Magnesium
Magnesium panels were cleaned, rinsed with acetone, dried and weighed. The panels were then immersed in the deicer solution of example I for 7 days at room temperature. After the panels had been recleaned and reweighed, they were found to have a weight loss of about 2 milligrams per square inch. Five milligrams per square inch is the maximum allowable weight loss. A similar test with the deicer solution diluted with an equal part of water showed a weight loss of about 1 milligram per square inch.
In a comparative test, a deicer solution prepared as in example I but without corrosion inhibitors was tested in a similar manner with magnesium panels. Corrosion of the magnesium after a 7 day immersion was about 170 milligrams per square inch.
B. Corrosion of Cadmium
A cadmium plated steel sample and a bead of cadmium metal were immersed for 3 days at room temperature in deicer solution prepared as in example I. No cadmium deterioration or removal of cadmium plating was observed. Similar results were obtained with the deicer solution diluted with an equal part of water.
In a comparative test, a deicer solution prepared as in example I but without sodium mercaptobenzothiazole was tested in a similar manner with a cadmium plated steel sample and a bead of cadmium metal. Deterioration of the cadmium metal was visible in one minute and removal of the cadmium plating appeared complete in 5 minutes.
C. Corrosion of Aluminum
Thirty-six panels of six different aluminum alloys commonly used in aircraft construction were divided into three groups of six pairs of panels representing each alloy. Two groups of panels were used to test diluted and undiluted deicer composition and the third group with water was used as control. Tap water, a 20 percent deicer solution, and a 100 percent deicer solution, prepared in example I, were tested. The solution was applied to one side of each panel and two similar panels were placed together in sandwich style with the deicer solution between the two panels. The three groups of panels were exposed in a horizontal position at alternate intervals of 16 hours in a humidity chamber and 8 hours in an oven for a total of 7 days. The humidity chamber was maintained at 100° F. and 98 to 100 percent relative humidity. The oven was maintained at 100° F. After exposure, the panels were rinsed in warm tap water and scrubbed lightly with a soft brush. After drying the panels were examined under 15 X magnification and each panel was rated according to the following standard:
0 --No visible corrosion
1 --Very slight corrosion or discoloration
2 --Slight corrosion
3 --Moderate corrosion
4-- Extensive corrosion
Results of the standard corrosion test are listed below: ##SPC1##
EXAMPLE III
Protection of high-strength aircraft landing gear from corrosion, including stress corrosion cracking, in the presence of deicer solutions is difficult due to the sensitivity of commonly used alloys both to stress corrosion cracking and embrittlement by hydrogen. This situation is complicated by the propensity of metal platings such as cadmium to introduce hydrogen during service.
Aircraft landing gear components consist primarily of AISI Type 4340 steel heat treated to an ultimate strength as high as about 280,000 p.s.i. Type 4340 steel is also used in the 220,000 to 240,000 p.s.i. range.
The deicer solution of example I was tested by a standard hydrogen embrittlement procedure using the Lawrence Hydrogen Detection Gauge and was rated "Safe" in as far as hydrogen embrittlement is concerned for use on aircraft landing gear steel having a tensile strength of 200,000 p.s.i. or better. The deicer solution did not attack cadmium plate on the steel. These procedures satisfy the requirements of Douglas Bulletin 13-1.
EXAMPLE IV
Deicing Tests in Field
A solution applicator for applying the deicer solution of example I consisted of a 1000-gallon stainless steel tank mounted on a tandem trailer. The rig was equipped with a 27-foot boom containing nine flood type nozzles on 40-inch centers to give a 30-foot swath. Solution was sprayed through the nozzles by a positive displacement type pump driven by a ground wheel drive.
A taxiway covered with a sheet of ice one-sixteenth to one-eighth inch thick was treated with the deicer solution at rates of 15.5, 9.3, and 3.1 pounds per 100 square feet. An area treated at the highest rate had water standing on it 30 minutes after treatment. The air temperature during this test was 23°F. The next day all of the treated areas showed the effect of the deicer. The area treated with 15.5 pounds per 100 square feet was 100 percent bare and the other areas were 60 to 80 percent bare. It is also noteworthy that the treated areas did not ice up during the next icing condition, indicating a residual effect of the deicer.
EXAMPLE V
An especially preferred deicer solution was prepared as follows: About 29.4 parts of ammonium nitrate and 22.7 parts of urea were added to 22.5 parts of water. The mixture was stirred and maintained at about 75°F. until all solids were dissolved. Then 24.9 parts of ethylene glycol was added to the solution followed by 0.1 part of potassium mercaptobenzothiazole and 0.2 part of potassium chromate, and the mixture was stirred until the solids dissolved. Finally, 0.2 part of "Solution A" was stirred into the mixture. Solution A is an aqueous ammoniated superphosphoric acid containing polyphosphates, as described in detail hereinabove. The resulting deicer solution was similar to the solution of example I with respect to its salting out temperature and deicing properties. It passed all corrosion tests, previously described, for the product of example I including the standard hydrogen embrittlement test. Moreover, the combination of Solution A and sodium mercaptobenzothiazole was a particularly effective inhibitor against corrosion of cadmium plated steel. It appears that the polyphosphate in this solution provides a synergistic effect with respect to corrosion inhibition toward cadmium because solution A alone was found only slightly effective in mitigating cadmium deterioration.