US 2716068 A
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Patented Aug. 23, 19355 DE-ICING AND FREEZE DEPRESSANT COMPOSITION Jacob M. Fain, Brooklyn, N. Y., and Norman L. Hewitt, Red Bank, N. 1., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy No Drawing. Application October 21, 1952, Serial No. 316,096
3 Claims. (Cl. 106-13) This invention relates to combined de-icing and freezedepressant substances with special application to aircraft.
The formation of ice on aircraft parts has offered an important problem in aircraft use, and this problem has been accentuated by long range and high altitude flights,
often under conditions of excessive humidity. Heretofore, for de-icing purposes use has been made of various freeze-depressants capable of remaining in solution at lower temperatures; however, defects have been found in many of these substances when subjected to the severe requirements of extremely low temperature flight conditions.
An object of the present invention is to provide a surfacing material for aircraft surfaces which is effective as a de-icer to temperatures as low as 65 F. A further object is to provide a surface coating which can maintain itself free of ice for as long as ten hours under sub-freezing temperatures and without reapplication. An important object also is to provide an ice protective coating which is free of ingredients harmful to the coated substances. Still another object is to provide a coating all of the ingredients of which are effective to prevent or remove ice formations.
Further objects include the provision of a coating which is non-inflammable, which is not highly toxic, and which does not crystallize or separate in the range of use. Other objects will appear on consideration of the following de scription of a preferred form of the invention.
Monohydric alcohols, such as methyl alcohol, have long been in use as freeze depressants. These alcohols however are disadvantageous in their corrosive characteristics and high volatility requiring frequent replacement, and are therefore inferior to the polyhydric alcohols including the glycols which are stable at relatively higher temperatures, although possessing metal corrosive tendencies. Further, the use of certain soluble salts such as the salts of nitrous acid have been found useful as freeze depressants due to their high effectiveness in reduction of the freezing point as well as the limited quantities necessary to produce results.
Although any one of the above mentioned groups may be employed alone as a freeze depressant and de-icer, I have found that a composition including ethylene glycol (HOCH2CH2OH) from the glycol group and potassium thiocyanate (KCNS) and preferably including sodium nitrite (NaNOz) from the soluble salts gives highly superior results. All of these substances are freeze depressant in action and hence no inactive carrier substance is needed. The ethylene glycol with its low volatility serves as the basic material of the composition. Potassium thiocyanate dissolves readily in the glycol and thus augments the de-icing property of the composition; the sodium nitrite in addition to its freeze depressant characteristic and easy solubility imparts corrosion resistance to the composition.
In addition to the mentioned properties of this composition, it possesses other important virtues such as non-inflammability, lack of excessive toxicity, a marked retention of the deicing property, after application, for from one-half to ten hours depending on the precipitation and an absence of adverse effects on the base metals including aluminum, aluminum alloys, magnesium alloys, steel, aircraft enamels, lacquers and transparent plastics.- Moreover, the solution has a pour point below -65 F., does not crystallize or separate between 65 F. and 170 F. and maintains its useful action either in bulk mass or film formation. Outstandingly, however, the composition effectively removes ice and frost from exterior surfaces of aircraft wings, fuselage, control units and the like down to temperatures as low as 65 F.
While the proportions of the substances used in the composition are not critical, the ethylene glycol constituting approximately two-thirds by weight of the solution of potassium thiocyanate in ethylene glycol, these substances should be included within the following limits to avoid crystallization.
Parts by weight Ethylene glycol 60-66 Potassium thiocyanate 3034 Sodium nitrite 10-0 However, best results in full agreement with the objects of this invention are obtained using the following values.
Ethylene glycol 60 Potassium thiocyanate 30 Sodium nitrite 10 A composition as thus limited is found to have the following characteristics:
Specific gravity 1.35.
Pour point -94.0" F.
Flash point 302.0 F.
Corrosion Non-corrosive to aluminum, aluminum alloys, magnesium alloys and steel.
Where de-icing is the prime consideration, the proportions of glycol may be increased. In making the compositions as described above the ingredients are mixed together until solution has been effected.
It is pointed out that, by elimination of an inert carrier, both of the mutually soluble substances ethylene glycol and potassium thiocyanate are effective as freeze depressants, thus obtaining full advantage of the coating materials. It is further observed that the usefulness of the coating results from the combined action of the salt and glycol, neither of these substances separately producing the marked depression of freezing point and permanence of effect, combined with non-toxicity, non-inflammability and freedom from crystallization or separation inside the range of use including temperatures as low as 65 F. The addition of the sodium nitrite augments the depressant action and in addition, imparts important resistance to corrosive tendencies.
It is of course, evident that under certain conditions and to meet requirements of cost, etc., substances other than these specifically mentioned but having similar properties, may be used, although producing results possibly inferior to the preferred composition. For example, usable glycols include diethylene glycol, triethylene glycol, propylene glycol and polyethylene glycol. Other usable soluble salts include ammonium nitrate, potassium acetate, ammonium dichromate, ferric chloride, sodium nitrate, sodium thiocyanate and urea. In utilizing these varied substances the glycol and the sodium nitrite should form two of the elements and the proportionate parts should follow those of the preferred composition. Accordingly, the scope of the invention is restricted only as required by the claims as hereto appended.
, 4 V col, the glycol constituting approximately two-thirds 1: weight of thecomposition.
References Cited in the file of this patent UNITED STATES PATENTS Sperr Nov. 6, 1923 Bayes Apr. l1, 1939 FOREIGN PATENTS 7 10 119,642 Anstralia Mar. 15, 1945