Thermal spray deposition of hollow microspheres

Abstract

Methods of forming an insulating coating from thermal spraying are provides. In one variation, the method includes thermally spraying a jetted stream having a maximum temperature of greater than or equal to about 900° C. towards a substrate to form the insulating coating on the substrate. The thermal spraying may be a high-velocity oxygen flame (HVOF) process. The jetted stream comprises a plurality of hollow microspheres, which may comprise a metal, such as nickel or iron. The insulating coating as formed has a thermal conductivity (K) of less than or equal to about 200 mW/m·K at standard temperature and pressure conditions and may have a thermal capacity (c v ) of greater than or equal to about 100 kJ/m 3 ·K.

1 . A method of forming an insulating coating comprising:
 thermally spraying a jetted stream having a maximum temperature of greater than or equal to about 900° C. towards a substrate to form the insulating coating on the substrate, wherein the jetted stream comprises a plurality of hollow microspheres comprising a first metal layer that comprises a first metal selected from the group consisting of: nickel, iron, combinations, and alloys thereof and a second metal layer that comprises a second metal selected from the group consisting of: copper, zinc, tin, nickel, combinations, and alloys thereof, wherein the maximum temperature of the jetted stream during the thermal spraying is at least about 50° C. below a melting point of the first metal layer, but greater than or equal to a melting point of the second metal layer, so that the second metal layer softens and partially or fully melts to enhance adhesion and bonding with the substrate and the insulating coating has a thermal conductivity (K) of less than or equal to about 200 mW/m·K at standard temperature and pressure conditions.   
     
     
         2 . The method of  claim 1 , wherein the insulating coating comprises a plurality of hollow microstructures having intact void regions after the thermal spraying. 
     
     
         3 . The method of  claim 1 , wherein the insulating coating has a net porosity of greater than or equal to about 80 volume %. 
     
     
         4 . The method of  claim 1 , wherein the insulating coating has a thickness of less than or equal to about 200 micrometers (μm). 
     
     
         5 . The method of  claim 1 , wherein the maximum temperature is less than or equal to about 1,400° C. 
     
     
         6 . (canceled) 
     
     
         7 . The method of  claim 1 , wherein the substrate comprises at least one metal selected from the group consisting of: iron, copper, zinc, tin, nickel, aluminum, combinations, and alloys thereof. 
     
     
         8 . The method of  claim 1 , wherein the thermal conductivity (K) is less than or equal to about 100 mW/m·K at standard temperature and pressure conditions. 
     
     
         9 . The method of  claim 1 , wherein the insulating coating has a thermal capacity (c v ) of less than or equal to about 100 kJ/m 3 ·K. 
     
     
         10 . A method of forming an insulating coating comprising:
 jetting a stream comprising a plurality of hollow microspheres from a high velocity oxygen fuel (HVOF) device towards an aluminum substrate having a bonding layer comprising at least one metal selected from the group consisting of: copper, zinc, combinations, and alloys thereof, wherein each of the plurality of hollow microspheres comprises a first metal layer comprising nickel and a second metal layer comprising a second metal selected from the group consisting of: copper, zinc, combinations, and alloys thereof, wherein the stream has a maximum temperature during the jetting that is at least about 50° C. below a melting point of the first metal layer, but greater than or equal to a melting point of the second metal layer, so that the second metal layer softens and partially or fully melts to enhance adhesion and bonding with the bonding layer; and   forming the insulating coating on the bonding layer disposed on the substrate, the insulating coating having a thermal conductivity (K) of less than or equal to about 200 mW/m·K at standard temperature and pressure conditions.   
     
     
         11 . The method of  claim 10 , wherein the insulating coating comprises a plurality of hollow microstructures having intact void regions after the thermal spraying. 
     
     
         12 . The method of  claim 10 , wherein the insulating coating has a net porosity of greater than or equal to about 80 volume % and the insulating coating has a thickness of less than or equal to about 200 micrometers (μm). 
     
     
         13 . The method of  claim 10 , wherein the maximum temperature is greater than or equal to about 900° C. to less than or equal to about 1,400° C. 
     
     
         14 . (canceled) 
     
     
         15 . The method of  claim 10 , wherein the first metal layer comprises nickel and the second metal layer comprises copper. 
     
     
         16 . The method of  claim 10 , wherein the thermal conductivity (K) is less than or equal to about 100 mW/m·K. 
     
     
         17 . The method of  claim 10 , wherein the insulating coating has a thermal capacity (c v ) of less than or equal to about 100 kJ/m 3 ˜K. 
     
     
         18 . The method of  claim 10 , further comprising sintering the insulating coating after the jetting. 
     
     
         19 . A method of forming an insulating coating comprising:
 jetting a stream comprising a plurality of hollow microspheres from a high velocity oxygen fuel (HVOF) device towards a substrate to form a layer of deposited hollow microstructures, wherein the stream has a maximum temperature during the jetting that is greater than or equal to about 900° C. to less than or equal to about 1400° C. and a supersonic velocity of greater than or equal to about 343 m/s and less than or equal to about 400 m/s, wherein each of the plurality of hollow microspheres comprises a first metal layer comprising a first metal selected from the group consisting of: nickel, iron, combinations, and alloys thereof and a second metal layer comprising a second metal selected from the group consisting of: copper, zinc, tin, nickel, combinations, and alloys thereof, wherein the stream has a maximum temperature during the jetting that is at least about 50° C. below a melting point of the first metal layer, but greater than or equal to a melting point of the second metal layer, so that the second metal layer softens and partially or fully melts to enhance adhesion and bonding with the substrate; and   sintering the layer of deposited hollow microstructures to form the insulating coating on the substrate having a thermal conductivity (K) of less than or equal to about 200 mW/m·K at standard temperature and pressure conditions and a thermal capacity (c v ) of less than or equal to about 100 kJ/m 3 ·K.   
     
     
         20 . The method of  claim 19 , wherein the sintering occurs by heating the deposited hollow microstructures to a temperature of greater than or equal to about 800° C. for greater than or equal to about 8 hours.