Functional fluid compositions containing erosion inhibitors

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 R1, R2 and R3 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[AXy]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
• R1SO3M
• where M is an alkali metal, and R1 is a CnF2n+1 or a cyclic CaF2a−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.

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 R1, R2 and R3 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[AXy]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
• R1SO3M
• where M is an alkali metal, and R1 is a CnF2n+1 or a cyclic CaF2a−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.

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.