Low friction coatings
A dry gas seal assembly for use with a rotating machine that includes a rotating shaft, the seal assembly comprises a seal face bears a solid coating comprising molybdenum disulfide, graphene oxide, and optionally polydopamine, preferably wherein the graphene oxide to molybdenum disulfide ratio is 8:10 to 10:8. A method for making a dry gas seal assembly comprises coating a homogeneous dispersion of graphene oxide and molybdenum disulfide on a seal face.
1 . A method of forming a low friction, wear-resistant seal assembly comprising: providing seal assembly components comprising a seal face substrate; suspending molybdenum disulfide flakes which have a dimension perpendicular to thickness in the range of about 300 to about 500 nanometers; in a carrier liquid to form a mixture; adding graphene oxide flakes to the mixture; forming a homogenous mixture of molybdenum disulfide and graphene oxide, and, a functionalizing agent to improve adhesion or the graphene oxide and molybdenum disulfide to the seal face substrate, wherein a weight ratio of the graphene oxide to the molybdenum disulfide is from 8:10 to 10:8 and depositing the homogeneous mixture on a portion or all of the seal face substrate, forming a wet film on the seal face substrate, and evaporating the carrier liquid to form a dry coating layer.
2 . The method of claim 1 wherein the functionalizing agent comprises poly-dopamine.
3 . The method of claim 1 wherein providing seal assembly components includes providing a mating ring having a mating ring seal face and a primary ring having a primary ring seal face; wherein the depositing on the seal face substrate comprising depositing on at least one of the mating ring seal face and the primary ring seal face and after forming the dry coating layer arranging the mating ring in housing.
4 . The method of claim 1 , wherein the carrier liquid comprises water, an alcohol, or both.
5 . The method of claim 1 , wherein the homogenous mixture is oil-free.
6 . The method of claim 1 , wherein depositing comprises spray coating.
7 . The method of claim 1 wherein the seal face substrate comprises silicon carbide.
8 . The method of claim 1 , wherein the disposing the homogenous mixture is on the silicon carbide substrate at between 20° C. and 100° C.
9 . The method of claim 1 wherein the suspended molybdenum disulfide are flakes that are commensurate in size or smaller than the graphene oxide flakes.
10 . The method of claim 1 , wherein the substrate, prior to disposing the homogenous mixture has a surface roughness of 0.05 to 0.4 Ra as measured by ISO 4288-1996.
11 . The method of claim 1 wherein the dry film coating has a coefficient of friction of no greater than about 0.02.
12 . The method of claim 1 wherein the dry film coating has a coefficient of friction of no greater than about 0.01.
13 . The method of claim 1 wherein in the dry film coating the molybdenum disulfide flakes are encapsulated or at least partially encapsulated by graphene oxide.
14 . The method of claim 1 wherein the suspended molybdenum disulfide are flakes that are smaller than the graphene oxide flakes.
15 . A dry gas seal assembly for use with a rotating machine that includes a rotating shaft, the seal assembly comprising: a mating ring having a mating ring seal face; a primary ring having a primary ring seal face; where the mating ring and primary ring are positioned such that the mating ring seal face and the primary ring seal face are adjacent and facing each other; a first biasing member that urges the primary ring seal face toward the mating ring seal face; wherein at least one of the mating ring seal face and the primary ring seal faces includes recesses formed thereon that cause a gas to be drawn between the mating ring and the primary ring due to relative rotation between the primary ring and the mating ring and form a gas layer between the mating ring and the primary ring that urges the primary ring away from the mating ring wherein the at least one of the mating ring seal face and the primary ring seal face bears a solid coating comprising molybdenum disulfide, graphene oxide, and optionally poly dopamine wherein the molybdenum disulfide is in the form of flakes which have a dimension perpendicular to thickness in the range of about 300 to about 500 nanometers and wherein a weight ratio of the graphene oxide to the molybdenum disulfide is from 8:10 to 10:8.
16 . The dry gas seal assembly of claim 15 , wherein the mating ring, primary ring and biasing member are arranged in a housing.
17 . The dry gas seal assembly of claim 15 wherein the recesses draw gas from an inner diameter of the primary ring toward an outer diameter of the primary ring or draw the gas from an outer diameter of the primary ring toward an inner diameter of the primary ring.
18 . The dry gas seal assembly of claim 15 wherein the seal face bearing the coating has a surface roughness of 0.05 to 0.4 Ra as measured by ISO 4288-1996.
19 . The dry gas seal assembly of claim 15 wherein the dry film coating the molybdenum disulfide flakes are encapsulated or at least partially encapsulated by graphene oxide.
20 . A method of use of the seal assembly of claim 15 at an operating condition including one or more of the following: an operating temperature in the range of −50 to 200° C., dry nitrogen having a dew point of no more than −40° C.