Chemically modified radar absorbing materials and an associated fabrication method

A coated particle capable of withstanding corrosive environments comprising:

• a core comprising one or more layers, said core comprised of a ferromagnetic material selected from the group consisting of iron, carbonyl iron, cobalt, nickel, and alloys thereof, said core further defining an outer surface area, and
• a protective shell comprising one or more layers of at least one non-conducting material coated onto said outer surface area of said core, said protective shell shielding said core from oxidation and forming a substantially continuous layer;
• wherein said core is substantially free of said non-conducting material, such that the ferromagnetic properties of said coated particle are comparable to an uncoated particle formed from the same ferromagnetic material,
• wherein the Curie point of said coated particle is approximately equal to the Curie point of said core,
• and further wherein said coated particle exhibits a weight gain of no greater than about 3 % as determined using thermogravimetric analysis with a temperature ramp of 20° C./min and a maximum temperature of 700° C.

A coated particle capable of withstanding corrosive environments comprising:

• a core comprising one or more layers, said core comprised of a ferromagnetic material selected from the group consisting of iron, carbonyl iron, cobalt, nickel, and alloys thereof, said core further defining an outer surface area, and
• a protective shell comprising one or more layers of at least one non-conducting material coated onto said outer surface area of said core, said protective shell shielding said core from oxidation and forming a substantially continuous layer, wherein said substantially continuous layer has a thickness of up to about 0.5 microns;
• wherein said core is substantially free of said non-conducting material, such that the ferromagnetic properties of said coated particle are comparable to an uncoated particle formed from the same ferromagnetic material,
• and further wherein said coated particle exhibits a weight gain of no greater than about 3% as determined using thermogravimetric analysis with a temperature ramp of 20° C./min and a maximum temperature of 700° C.

A coated particle capable of withstanding corrosive environments comprising:

• a core comprising one or more layers, wherein said core is carbonyl iron, and wherein said core further defining an outer surface area, and
• a protective shell comprising one or more layers of silicon dioxide coated onto said outer surface area of said core, said protective shell shielding said core from oxidation and forming a substantially continuous layer;
• wherein said core is substantially free of said non-conducting material, such that ferromagnetic properties of said coated particle are comparable to an uncoated particle formed from the same ferromagnetic material,
• and further wherein said coated particle exhibits a weight gain of no greater than about 3% as determined using thermogravimetric analysis with a temperature ramp of 20° C./min and a maximum temperature of 700° C.

A coating composition comprising:

• (a) a polymeric binder, and
• (b) coated particles comprising
• (i) a core comprising comprised of a ferromagnetic material selected from the group consisting of iron, carbonyl iron, cobalt, nickel, and alloys thereof, said core further defining an outer surface area, and
• (ii) a protective shell comprising at least one layer of non-conducting material having a resistivity greater than 2500 ohm-cm, said non-conducting material coated onto said outer surface area of said core, said protective shell shielding said core from oxidation and forming a substantially continuous layer;
• wherein said core is substantially free of said non-conducting material, such that the ferromagnetic properties of said coated particle are comparable to an uncoated particle formed from the same ferromagnetic material and said coated particle exhibits a weight gain of no greater than about 3% as determined using thermogravimetric analysis with a temperature ramp of 20° C./min and a maximum temperature of 700° C. and
• wherein said polymeric is binder present in an amount sufficient to bind said coating composition together while maintaining said coated particles substantially separate from each other.

A method of producing coated particles, said method comprising:

• providing a rotatable retort mounted about a generally horizontal axis of rotation and having an outer wall;
• partially filling said retort by placing a sufficient quantity of ferromagnetic particles into said retort;
• evacuating said partially filled retort;
• supplying a gaseous composition comprising one or more active elements selected from the group consisting of silicon, chromium, aluminum and oxygen at a selected controlled pressure within said evacuated retort;
• rotating said retort during supply of said gaseous composition containing said one or more active elements at a speed sufficient to fluidize said ferromagnetic particles;
• and
• heating the exterior of said retort while said retort is rotating to transfer energy through said outer wall of said retort and to said ferromagnetic particles to effect the coating of said ferromagnetic particles with said one or more active elements within said gaseous composition.

A method of producing coated particles, said method comprising:

• providing a rotatable retort mounted about a generally horizontal axis of rotation and having an outer wall;
• partially filling said retort by placing a sufficient quantity of ferromagnetic particles into said retort, said ferromagnetic particles defining an outer surface area;
• evacuating said partially filled retort;
• supplying a gaseous composition comprising one or more active elements selected from the group consisting of silicon, chromium, aluminum and oxygen at a selected controlled pressure within said evacuated retort in a quantity sufficient to form a coating having a thickness of at least about 0.05 microns on said outer surface area of said ferromagnetic particle;
• rotating said retort during supply of said gaseous composition containing said one or more active elements at a speed sufficient to fluidize said ferromagnetic particles;
• and
• heating the exterior of said retort while said retort is rotating to transfer energy through said outer wall of said retort and to said ferromagnetic particles to effect the coating of said ferromagnetic particles with said one or more active elements within said gaseous composition.

A method of producing coated particles, said method comprising:

• providing a rotatable retort mounted about a generally horizontal axis of rotation and having an outer wall;
• partially filling said retort by placing a sufficient quantity of ferromagnetic particles into said retort;
• evacuating said partially filled retort;
• supplying a gaseous composition comprising one or more active elements selected from the group consisting of silicon, chromium, aluminum and oxygen at a selected controlled pressure within said evacuated retort, said gaseous composition further comprising an active gas selected from the group consisting of silanes, SiH4, SiF4, and SiCl4;
• rotating said retort during supply of said gaseous composition containing said one or more active elements at a speed sufficient to fluidize said ferromagnetic particles;
• and
• heating the exterior of said retort while said retort is rotating to transfer energy through said outer wall of said retort and to said ferromagnetic particles to effect the coating of said ferromagnetic particles with said one or more active elements within said gaseous composition.

A method of producing coated particles, said method comprising:

• providing a rotatable retort mounted about a generally horizontal axis of rotation and having an outer wall;
• partially filling said retort by placing a sufficient quantity of ferromagnetic particles into said retort;
• evacuating said partially filled retort;
• supplying a gaseous composition comprising one or more active elements selected from the group consisting of silicon, chromium, aluminum and oxygen at a selected controlled pressure within said evacuated retort;
• rotating said retort during supply of said gaseous composition containing said one or more active elements at a speed sufficient to fluidize said ferromagnetic particles;
• heating the exterior of said retort while said retort is rotating to transfer energy through said outer wall of said retort and to said ferromagnetic particles to effect the coating of said ferromagnetic particles with said one or more active elements within said gaseous composition;
• and oxidizing said coated particle.