Functional fluid compositions containing erosion inhibitors

Abstract

A functional fluid composition containing a fluid base stock (e.g., a phosphate ester fluid base stock) as a major component, and an erosion inhibitor mixture as a minor component. The erosion inhibitor mixture contains at least a first erosion inhibitor (e.g., a perhalometallate or perhalometalloidate salt) and a second erosion inhibitor (e.g., an alkali metal salt of perfluoroalkyl sulfonic acid). Erosion inhibition of the functional fluid composition is improved as compared to erosion inhibition achieved using singly the first erosion inhibitor or the second erosion inhibitor, as measured by one or more of ASTM D2624, ASTM D974, ASTM D130 and ASTM D6304. A method for operating and lubricating a hydraulic system by utilizing as a hydraulic fluid, the functional fluid composition. A method for identifying erosion inhibition effectiveness of the functional fluid. The functional fluids are useful as aircraft hydraulic fluids.

1 . A functional fluid composition comprising:
 (a) a fluid base stock as a major component, wherein the fluid base stock comprises one or more phosphate ester fluid base stocks represented by the formula   
       
         
           
           
               
               
           
         
       
       wherein R 1 , R 2  and R 3  are independently a substituted or unsubstituted alkyl or aryl group; and
 (b) an erosion inhibitor mixture as a minor component; wherein the erosion inhibitor mixture comprises at least a first erosion inhibitor and a second erosion inhibitor; wherein the first erosion inhibitor comprises a perhalometallate or perhalometalloidate salt represented by the formula:
   M[AX y ] z    
 
 
       wherein A is a metal or metalloid; M is a solubilizing cation; X is a halogen; y is an integer from 1 to 7 and equal to the positive valence of A; and z is an integer from 1 to 3 and sufficient to maintain the salt electro-neutral; and wherein the second erosion inhibitor comprises an alkali metal salt of perfluoroalkyl sulfonic acid represented by the formula
   R 1 SO 3 M 
 
       where M is an alkali metal, and R 1  is a C n F 2n+1  or a cyclic C a F 2a−1  group where n is an integer of from 1 to 18 and a is an integer from 4 to 18; and
 wherein erosion inhibition of the functional fluid composition is improved as compared to erosion inhibition achieved using singly the first erosion inhibitor or the second erosion inhibitor, as measured by one or more of ASTM D2624, ASTM D974, ASTM D130 and ASTM D6304. 
 
     
     
         2 . The functional fluid composition of  claim 1  wherein the one or more phosphate ester fluid base stocks comprise trialkyl phosphate, dialkyl aryl phosphate, alkyl diaryl phosphate, triaryl phosphate, or mixtures thereof. 
     
     
         3 . The functional fluid composition of  claim 1  wherein the one or more phosphate ester fluid base stocks comprise tri-n-butyl phosphate, tri-isobutyl phosphate, n-butyl di-isobutyl phosphate, di-isobutyl n-butyl phosphate, n-butyl diphenyl phosphate, isobutyl diphenyl phosphate, di-n-butyl phenyl phosphate, di-isobutyl phenyl phosphate, tri-n-pentyl phosphate, tri-isopentyl phosphate, triphenyl phosphate, isopropylated triphenyl phosphates, butylated triphenyl phosphates, or mixtures thereof. 
     
     
         4 . The functional fluid composition of  claim 1  wherein, in the one or more phosphate ester fluid base stocks, R 1 , R 2  and R 3  are independently a substituted or unsubstituted alkyl group having from 4 to 9 carbon atoms, or an aryl group. 
     
     
         5 . The functional fluid composition of  claim 1  wherein the first erosion inhibitor comprises ammonium hexafluorophosphate (NH 4 PF 6 ), N-benzyl-N,N,N-trimethyl ammonium hexafluorophosphate (CH 3 ) 3 (CH 6 H 5 CH 2 )NPF 6 , potassium hexafluorophosphate, tetrabutyl ammonium hexafluorophosphate, ammonium tetrafluoroborate (NH 4 BF 4 ), sodium tetrafluoroborate, zinc tetrafluoroborate, sodium hexafluoroantimonate (NaSbF 6 ), ammonium hexafluoroantimonate, N-benzyl-N,N,N-triethyl phosphonium hexafluorophosphate, potassium hexafluoroantimonate, or mixtures thereof; and the second erosion inhibitor comprises potassium perfluoromethane sulfonate, potassium perfluoroethane sulfonate, sodium perfluorobutane sulfonate, sodium perfluorocyclohexane sulfonate, potassium perfluorooctane sulfonate, cesium perfluorooctadecane sulfonate, potassium perfluorocyclopentane sulfonate, potassium perfluoropentane sulfonate, or mixtures thereof. 
     
     
         6 . The functional fluid composition of  claim 1  wherein the first erosion inhibitor comprises ammonium hexafluorophosphate (NH 4 PF 6 ), N-benzyl-N,N,N-trimethyl ammonium hexafluorophosphate (CH 3 ) 3 (CH 6 H 5 CH 2 )NPF 6 , potassium hexafluorophosphate, tetrabutyl ammonium hexafluorophosphate, ammonium tetrafluoroborate (NH 4 BF 4 ), sodium tetrafluoroborate, zinc tetrafluoroborate, sodium hexafluoroantimonate (NaSbF 6 ), ammonium hexafluoroantimonate, N-benzyl-N,N,N-triethyl phosphonium hexafluorophosphate, potassium hexafluoroantimonate, or mixtures thereof; and the second erosion inhibitor comprises potassium trifluoromethane sulfonate or potassium triflate; lithium trifluoromethane sulfonate or lithium triflate; potassium 1,1,2,2,2-pentafluoroethane-1-sulfonate; potassium 1,1,2,2,3,3,3-heptafluoropropane-1-sulfonate; potassium 1,1,2,2,3,3,4,4,4-nonafluorobutane-1-sulfonate; potassium 1,1,2,2,3,3,4,4,5,5,5-undecafluoropentane-1-sulfonate; potassium 1,1,2,2,3,3,4,4,5,5,6,6,6-tridecafluorohexane-1-sulfonate; potassium 1,1,2,2,3,3,4,4,5,5,6,6,7,7,7-pentadecafluoroheptane-1-sulfonate; potassium 1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-heptadecafluorooctane-1-sulfonate; or mixtures thereof. 
     
     
         7 . The functional fluid composition of  claim 1  wherein the erosion inhibitor mixture comprises potassium hexafluorophosphate and potassium trifluoromethane sulfonate. 
     
     
         8 . The functional fluid composition of  claim 1  wherein the one or more phosphate ester fluid base stocks comprise tri-n-butyl phosphate, and the erosion inhibitor mixture comprises potassium hexafluorophosphate and potassium trifluoromethane sulfonate. 
     
     
         9 . The functional fluid composition of  claim 1  further comprising one or more of a viscosity index improver, antioxidant, acid scavenger, corrosion inhibitor, antifoam agent, and rust inhibitor. 
     
     
         10 . The functional fluid composition of  claim 1  wherein the one or more phosphate ester fluid base stocks are present in an amount of at least 70 weight percent, based on the total weight of the functional fluid composition. 
     
     
         11 . The functional fluid composition of  claim 1  wherein the erosion inhibitor mixture is present in an amount sufficient to control one or more of electrical conductivity, acidity, copper corrosion inhibition, and hydrolytic stability, of the functional fluid composition. 
     
     
         12 . The functional fluid composition of  claim 1  having an electrical conductivity of greater than 0.3 to less than 2.0 micromhos/cm determined in accordance with ASTM D2624, a total acid number from zero to less than 0.05 mg KOH/g determined in accordance with ASTM D974, a corrosiveness to copper of 1A, 1B and 2A determined in accordance with ASTM D130, and a water content from zero to less than 8000 ppm water determined in accordance with ASTM D6304. 
     
     
         13 . The functional fluid composition of  claim 1  wherein the erosion inhibitor mixture is present in an amount from 0.01 weight percent to 0.15 weight percent, based on the total weight of the functional fluid composition. 
     
     
         14 . The functional fluid composition of  claim 1  wherein the first erosion inhibitor is present in an amount from 25 weight percent to 75 weight percent, and the second erosion inhibitor is present in an amount from 25 weight percent to 75 weight percent, based on the total weight of the erosion inhibitor mixture. 
     
     
         15 . The functional fluid composition of  claim 1  wherein the weight ratio of the first erosion inhibitor to the second erosion inhibitor is from 25:75 to 75:25. 
     
     
         16 . The functional fluid composition of  claim 1  wherein the functional fluid comprises an aircraft hydraulic fluid. 
     
     
         17 . A method for operating and lubricating a hydraulic system by utilizing as a hydraulic fluid a functional fluid comprising:
 (a) a fluid base stock as a major component, wherein the fluid base stock comprises one or more phosphate ester fluid base stocks represented by the formula   
       
         
           
           
               
               
           
         
       
       wherein R 1 , R 2  and R 3  are independently a substituted or unsubstituted alkyl or aryl group; and
 (b) an erosion inhibitor mixture as a minor component; wherein the erosion inhibitor mixture comprises at least a first erosion inhibitor and a second erosion inhibitor; wherein the first erosion inhibitor comprises a perhalometallate or perhalometalloidate salt represented by the formula:
   M[AX y ] z    
 
 
       wherein A is a metal or metalloid; M is a solubilizing cation; X is a halogen; y is an integer from 1 to 7 and equal to the positive valence of A; and z is an integer from 1 to 3 and sufficient to maintain the salt electro-neutral; and wherein the second erosion inhibitor comprises an alkali metal salt of perfluoroalkyl sulfonic acid represented by the formula
   R 1 SO 3 M 
 
       where M is an alkali metal, and R 1  is a C n F 2n+1  or a cyclic C a F 2a−1  group where n is an integer of from 1 to 18 and a is an integer from 4 to 18; and
 wherein erosion inhibition of the functional fluid composition is improved as compared to erosion inhibition achieved using singly the first erosion inhibitor or the second erosion inhibitor, as measured by one or more of ASTM D2624, ASTM D974, ASTM D130 and ASTM D6304. 
 
     
     
         18 . The method of  claim 17  wherein the one or more phosphate ester fluid base stocks comprise trialkyl phosphate, dialkyl aryl phosphate, alkyl diaryl phosphate, triaryl phosphate, or mixtures thereof. 
     
     
         19 . The method of  claim 17  wherein the one or more phosphate ester fluid base stocks comprise tri-n-butyl phosphate, tri-isobutyl phosphate, n-butyl di-isobutyl phosphate, di-isobutyl n-butyl phosphate, n-butyl diphenyl phosphate, isobutyl diphenyl phosphate, di-n-butyl phenyl phosphate, di-isobutyl phenyl phosphate, tri-n-pentyl phosphate, tri-isopentyl phosphate, triphenyl phosphate, isopropylated triphenyl phosphates, butylated triphenyl phosphates, or mixtures thereof. 
     
     
         20 . The method of  claim 17  wherein, in the one or more phosphate ester fluid base stocks, R 1 , R 2  and R 3  are independently a substituted or unsubstituted alkyl group having from 4 to 9 carbon atoms, or an aryl group. 
     
     
         21 . The method of  claim 17  wherein the first erosion inhibitor comprises ammonium hexafluorophosphate (NH 4 PF 6 ), N-benzyl-N,N,N-trimethyl ammonium hexafluorophosphate (CH 3 ) 3 (CH 6 H 5 CH 2 )NPF 6 , potassium hexafluorophosphate, tetrabutyl ammonium hexafluorophosphate, ammonium tetrafluoroborate (NH 4 BF 4 ), sodium tetrafluoroborate, zinc tetrafluoroborate, sodium hexafluoroantimonate (NaSbF 6 ), ammonium hexafluoroantimonate, N-benzyl-N,N,N-triethyl phosphonium hexafluorophosphate, potassium hexafluoroantimonate, or mixtures thereof; and the second erosion inhibitor comprises potassium perfluoromethane sulfonate, potassium perfluoroethane sulfonate, sodium perfluorobutane sulfonate, sodium perfluorocyclohexane sulfonate, potassium perfluorooctane sulfonate, cesium perfluorooctadecane sulfonate, potassium perfluorocyclopentane sulfonate, potassium perfluoropentane sulfonate, or mixtures thereof. 
     
     
         22 . The method of  claim 17  wherein the first erosion inhibitor comprises ammonium hexafluorophosphate (NH 4 PF 6 ), N-benzyl-N,N,N-trimethyl ammonium hexafluorophosphate (CH 3 ) 3 (CH 6 H 5 CH 2 )NPF 6 , potassium hexafluorophosphate, tetrabutyl ammonium hexafluorophosphate, ammonium tetrafluoroborate (NH 4 BF 4 ), sodium tetrafluoroborate, zinc tetrafluoroborate, sodium hexafluoroantimonate (NaSbF 6 ), ammonium hexafluoroantimonate, N-benzyl-N,N,N-triethyl phosphonium hexafluorophosphate, potassium hexafluoroantimonate, or mixtures thereof; and the second erosion inhibitor comprises potassium trifluoromethane sulfonate or potassium triflate; lithium trifluoromethane sulfonate or lithium triflate; potassium 1,1,2,2,2-pentafluoroethane-1-sulfonate; potassium 1,1,2,2,3,3,3-heptafluoropropane-1-sulfonate; potassium 1,1,2,2,3,3,4,4,4-nonafluorobutane-1-sulfonate; potassium 1,1,2,2,3,3,4,4,5,5,5-undecafluoropentane-1-sulfonate; potassium 1,1,2,2,3,3,4,4,5,5,6,6,6-tridecafluorohexane-1-sulfonate; potassium 1,1,2,2,3,3,4,4,5,5,6,6,7,7,7-pentadecafluoroheptane-1-sulfonate; potassium 1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-heptadecafluorooctane-1-sulfonate; or mixtures thereof. 
     
     
         23 . The method of  claim 17  wherein the erosion inhibitor mixture comprises potassium hexafluorophosphate and potassium trifluoromethane sulfonate. 
     
     
         24 . The method of  claim 17  wherein the one or more phosphate ester fluid base stocks comprise tri-n-butyl phosphate, and the erosion inhibitor mixture comprises potassium hexafluorophosphate and potassium trifluoromethane sulfonate. 
     
     
         25 . The method of  claim 17  wherein the functional fluid further comprises one or more of a viscosity index improver, antioxidant, acid scavenger, corrosion inhibitor, antifoam agent, and rust inhibitor. 
     
     
         26 . The method of  claim 17  wherein the one or more phosphate ester fluid base stocks are present in an amount of at least 70 weight percent, based on the total weight of the functional fluid composition. 
     
     
         27 . The method of  claim 17  wherein the erosion inhibitor mixture is present in an amount sufficient to control one or more of electrical conductivity, acidity, copper corrosion inhibition, and hydrolytic stability, of the functional fluid composition. 
     
     
         28 . The method of  claim 17  wherein the functional fluid has an electrical conductivity of greater than 0.3 to less than 2.0 micromhos/cm determined in accordance with ASTM D2624, a total acid number from zero to less than 0.05 mg KOH/g determined in accordance with ASTM D974, a corrosiveness to copper of 1A, 1B and 2A determined in accordance with ASTM D130, and a water content from zero to less than 8000 ppm water determined in accordance with ASTM D6304. 
     
     
         29 . The method of  claim 17  wherein the erosion inhibitor mixture is present in an amount from 0.01 weight percent to 0.15 weight percent, based on the total weight of the functional fluid composition. 
     
     
         30 . The method of  claim 17  wherein the first erosion inhibitor is present in an amount from 25 weight percent to 75 weight percent, and the second erosion inhibitor is present in an amount from 25 weight percent to 75 weight percent, based on the total weight of the erosion inhibitor mixture. 
     
     
         31 . The method of  claim 17  wherein the weight ratio of the first erosion inhibitor to the second erosion inhibitor is from 25:75 to 75:25. 
     
     
         32 . The method of  claim 17  wherein the functional fluid comprises an aircraft hydraulic fluid. 
     
     
         33 . A method for identifying erosion inhibition effectiveness of a functional fluid, said method comprising:
 providing a functional fluid comprising:   (a) a fluid base stock as a major component, wherein the fluid base stock comprises one or more phosphate ester fluid base stocks represented by the formula   
       
         
           
           
               
               
           
         
       
       wherein R 1 , R 2  and R 3  are independently a substituted or unsubstituted alkyl or aryl group; and
 (b) an erosion inhibitor mixture as a minor component; wherein the erosion inhibitor mixture comprises at least a first erosion inhibitor and a second erosion inhibitor; wherein the first erosion inhibitor comprises a perhalometallate or perhalometalloidate salt represented by the formula:
   M[AX y ] z    
 
 
       wherein A is a metal or metalloid; M is a solubilizing cation; X is a halogen; y is an integer from 1 to 7 and equal to the positive valence of A; and z is an integer from 1 to 3 and sufficient to maintain the salt electro-neutral; and wherein the second erosion inhibitor comprises an alkali metal salt of perfluoroalkyl sulfonic acid represented by the formula
   R 1 SO 3 M 
 
       where M is an alkali metal, and R 1  is a C n F 2n+1  or a cyclic C a F 2a−1  group where n is an integer of from 1 to 18 and a is an integer from 4 to 18;
 determining electrical conductivity of the functional fluid in accordance with ASTM D2624; 
 determining corrosiveness to copper of the functional fluid in accordance with ASTM D130; 
 determining total acid number of the functional fluid in accordance with ASTM D974; 
 determining entrained water content in the functional fluid in accordance with ASTM D6304; and 
 identifying erosion inhibition effectiveness of the functional fluid based on results from one or more of ASTM D2624, ASTM D130, ASTM D974 and ASTM D6304. 
 
     
     
         34 . The method of  claim 33  wherein the functional fluid has an electrical conductivity of greater than 0.3 to less than 2.0 micromhos/cm determined in accordance with ASTM D2624, a total acid number from zero to less than 0.05 mg KOH/g determined in accordance with ASTM D974, a corrosiveness to copper of 1A, 1B and 2A determined in accordance with ASTM D130, and a water content from zero to less than 8000 ppm water determined in accordance with ASTM D6304. 
     
     
         35 . A functional fluid composition comprising:
 (a) a tri-n-butyl phosphate fluid base stock as a major component, and   (b) an erosion inhibitor mixture as a minor component; wherein the erosion inhibitor mixture comprises potassium hexafluorophosphate and potassium trifluoromethane sulfonate; and wherein erosion inhibition of the functional fluid composition is improved as compared to erosion inhibition achieved using singly the potassium hexafluorophosphate or the potassium trifluoromethane sulfonate, as measured by one or more of ASTM D2624, ASTM D974, ASTM D130 and ASTM D6304.   
     
     
         36 . The functional fluid composition of  claim 35  wherein the weight ratio of the potassium hexafluorophosphate to the potassium trifluoromethanesulfonate is 30:70 or 40:60. 
     
     
         37 . The functional fluid composition of  claim 35  wherein the erosion inhibitor mixture is present in an amount sufficient to control one or more of electrical conductivity, acidity, copper corrosion inhibition, and hydrolytic stability, of the functional fluid composition. 
     
     
         38 . The functional fluid composition of  claim 35  having an electrical conductivity of greater than 0.3 to less than 2.0 micromhos/cm determined in accordance with ASTM D2624, a total acid number from zero to less than 0.05 mg KOH/g determined in accordance with ASTM D974, a corrosiveness to copper of 1A, 1B and 2A determined in accordance with ASTM D130, and a water content from zero to less than 8000 ppm water determined in accordance with ASTM D6304.