being to proceed from the original diphenyl naphthyl phosphates and to vary the polynuclear group to U.S . RESEARCH determine the effect on the characteristics of the structure. The phenyl group is quite thermally stable INTO LUBRICANTS FOR so that any instability of the third group could be easily observed. HIGH TEMPERATURES Class I I was also derived directly from the original diphenyl naphthyl phosphates and in this class all were symmetrical compounds possessing a single naphthyl group. Class III was composed of com OLLOWING A GOOD DEAL OF RECENT pounds having two naphthyl groups and a varying RESEARCH AT THE SOUTHWEST RE third group. SEARCH INSTITUTE, SAN ANTONIO, TEXAS, The compounds in Class IV were prepared in an under a United States Air Force contract, a new lubric attempt to reduce the average number of naphthyl ant has been developed for use at very high temper groups per phosphate group and comprised bis- atures and a detailed report on this work has been phosphates of naphthalenediol. drawn up by the Institute for the Wright Air Develop ment Center, Wright-Patterson Air Force Base, Ohio, Class V consisted of phenylene derivatives, that is, entitled "Polynuclear Aromatic Compounds for High derivatives of dihydroxy benzene, while Class VI was Temperature Lubricants". represented by only a single compound 4,4'-biphen- ylene bis (diphenyl phosphate). The need for such research arose from the increased severity of the conditions, in particular the higher A rather large one, Class VII consisted of tris- phosphates ; that is, compounds having three identical speeds, under which aircraft and related equipment groups joined to the phosphate radical. These are now being operated. These have resulted in higher working temperatures under which the lubric compounds were prepared in order to stud y the thermal ants and hydraulic fluids currently used are becoming stability of the groups themselves, disregarding the inadequate with respect to thermal and oxidative suitability of the material as a lubricant. In this stability. While striving for increased temperature case, the performance of the group were unobscured stability it has also been necessary to avoid excessive by outside influences, except when the physical properties of the compound were such as to make man sacrifice of low-temperature fluidity. ipulation unduly difficult. Many of these were high In investigating the possibilities of developing such melting solids. high-temperature lubricants the Southwest Research Institute have approached the problem from the angle Class VI I was composed of phosphorates, compounds of aromatic phosphate esters. Begun in 1952, the having one direct carbon-phosphorus bond, instead programme covered investigations into the suitability of the usual carbon-oxygen-phosphorus linkage. The of bi- and tri-cyclic liquid polynuclear aromatic compounds in Class I X were alike in that they con compounds as high temperature lubricants and tained the 4-biphenylyl group, while Class X consisted related materials. A literature search was carried of unsymmetrical phosphates, that is phosphates out, and, from the 2,400 compounds thus obtained, having different groups attached to the phosphate 14 were selected which seemed to be of the most radical. In Class XI were placed miscellaneous promising type. These compounds were represent compounds which did not fit into any of the other ative of ethers, esters, ketones, alkylated aromatics, classes. etc. Subsequently, three other compounds were In general, it was found that naphthyl derivatives added to the list. did not have sufficient thermal stability to compensate After screening these compounds for desirable for the unwanted increase in viscosity and melting properties, in particular for thermal stability, the point. The 4-biphenylyl group possessed all the conclusion was reached that by far the most promise advantages of the naphthyl group with much better lay in the class of aryl phosphate esters. Since then thermal stability. One particular compound prepares the work has been devoted to this type of compound. bis ( -chlorophenyl) 4-biphenylyl phosphate had a Possessing remarkable stability of over 400°C. the thermal stability of over 510°C. (950°F.) and this original phosphates, diphenyl naphthyl phosphates, was by far the highest stability of any compound prepared under the contract. It was found that the were, however, low-melting solids. An attempt was chlorophenyl phosphates possessed out-standing made to achieve a liquid state at room temperature, thermal stability and seemed to be the most promising or below, yet to retain the good thermal stability of the parent compounds. This search led through the type of compound for further development. tolyl and quinolyl analogs and tris ( -chlorophenyl) During the investigations it was found possible to phosphate, and the work demonstrated that liquid vary considerably the physical properties of a com compounds of high thermal stability could bo prepared pound by incorporating three different groups and the and pointed the way to further improvement in pronounced volatilizing and viscosity-reducing effect physical properties. of the tri-fluoromethylphenyl group was observed in For the sake of convenience, the compounds several compounds which contained one or more of synthesised up to 31st July, 1954, have been grouped these groups. into arbitrary classes, each class having some feature The report of the Southwest Research Institute has in common. Class 1 consisted of diphenyl phosphates been made available by courtesy of the U.S. Depart in which the third group was varied, the intention ment of the Air Force. 32 Scientific LUBRICATION September, 1955
Industrial Lubrication and Tribology – Emerald Publishing
Published: Sep 1, 1955
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