Ferromagnetic power for low core loss, well-bonded parts, parts made therefrom and methods for producing same

Abstract

A ferromagnetic powder comprising ferromagnetic particles coated with a material that does not degrade at temperatures above 150° C. and permits adjacent particles to strongly bind together after compaction such that parts made from the ferromagnetic powder have a transverse rupture strength of about 8,000 to about 20,000 pounds/square inch before sintering. The coating includes from 2 to 4 parts of an oxide and one part of a chromate, molybdate, oxalate, phosphate, or tungstate. The coating may be substantially free of organic materials. The invention also includes a method of making the ferromagnetic powder, a method of making soft magnetic parts from the ferromagnetic powder, and soft magnetic parts made from the ferromagnetic powder.

What is claimed is:  
     
         1 . Ferromagnetic powder comprising: 
 a. a plurality of ferromagnetic particles having a diameter size of from about 40 to about 600 microns; and    b. a coating disposed on each of said particles, said coating comprising from about 40% to about 85% by weight of a member selected from the group consisting of FeO, Fe 3 O 4 , Fe 2 O 3 , (Fe 2 O 3 ·H 2 O) and combinations thereof; and from about 15% to about 60% by weight of a member selected from the group consisting of FePO 4 , Fe 3 (PO 4 ) 2 , FeHPO 4 , FePO 4 ·2H 2 O, Fe 3 (PO 4 ) 2 ·8H 2 O, FeCrO 4 , FeMoO 4 , FeC 2 O 4 , FeWO 4 , and combinations thereof, wherein said coating has an electrical insulation value, as determined between 1 milli-Ohm-cm.    
     
     
         2 . Ferromagnetic powder according to  claim 1 , wherein the coating has a thickness of from about 50 to about 5000 Å.  
     
     
         3 . Ferromagnetic powder according to  claim 1 , wherein said coating comprises from about 65% to about 80% by weight of a member selected from the group consisting of FeO, Fe 3 O 4 , Fe 2 O 3 , (Fe 2 O 3 ·H 2 O) and combinations thereof; and from about 20% to about 35% by weight of a member selected from the group consisting of FePO 4 , Fe 3 (PO 4 ) 2 , FeHPO 4 , FePO 4 ·2H 2 O, Fe 3 (PO 4 ) 2 ·8H 2 O, FeCrO 4 , FeMoO 4 , FeC 2 O 4 , FeWO 4  and combinations thereof.  
     
     
         4 . Ferromagnetic powder according to  claim 1 , wherein the powder is for use in soft magnetic material and said ferromagnetic particles are selected from the group consisting of particles of Fe, Fe—Si, Fe—Al, Fe—Si—Al, Fe—Ni, Fe—Co, Fe—Co—Ni, and combinations thereof; and said coating has a thickness of from about 50 to about 3000 Å.  
     
     
         5 . Ferromagnetic powder according to  claim 4 , wherein said coating comprises from about 65% to about 80% by weight of a member selected from the group consisting of FeO, Fe 3 O 4 , Fe 2 O 3 , (Fe 2 O 3 ·H 2 O) and combinations thereof; and from about 20% to about 35% by weight of a member selected from the group consisting of FePO 4 , Fe 3 (PO 4 ) 2 , FeHPO 4 , FePO 4 ·2H 2 O, Fe 3 (PO 4 ) 2 ·8H 2 O, and combinations thereof.  
     
     
         6 . Ferromagnetic powder according to  claim 5 , wherein said coating comprises a Vivianite-like material.  
     
     
         7 . Ferromagnetic powder according to  claim 1 , wherein said ferromagnetic particles have a diameter of from about 40 to about 600 microns.  
     
     
         8 . Ferromagnetic powder according to  claim 6 , wherein said coating is substantially free of organic materials.  
     
     
         9 . Ferromagnetic powder according to  claim 1 , wherein said electrical insulation value does not substantially degrade when said powder is subjected to temperatures of greater than about 150° C.  
     
     
         10 . Ferromagnetic powder for use in manufacturing magnetic material, said powder comprising: 
 a. a plurality of ferromagnetic particles having a diameter size of from about 40 to about 600 microns; and    b. a coating disposed on each of said particles, said coating comprising from about 40% to about 85% by weight of a member selected from the group consisting of FeO, Fe 3 O 4 , Fe 2 O 3 , (Fe 2 O 3 ·H 2 O) and combinations thereof; and from about 15% to about 60% by weight of a member selected from the group consisting of FePO 4 , Fe 3 (PO 4 ) 2 , FeHPO 4 , FePO 4 ·2H 2 O, Fe 3 (PO 4 ) 2 ·8H 2 O, FeCrO 4 , FeMoO 4 , FeC 2 O 4 , FeWO 4 , and combinations thereof, wherein said coating permits adjacent particles to engage one another with a force such that a part made by compressing said ferromagnetic particles having said coating disposed thereon has a transverse rupture strength of at least about 8 kpsi as measured in accordance with MPIF Standard 41.    
     
     
         11 . Ferromagnetic powder according to  claim 10 , wherein said part has a transverse rupture strength of at least about 15 kpsi as measured in accordance with MPIF Standard 41.  
     
     
         12 . Ferromagnetic powder according to  claim 10 , wherein said ferromagnetic particles are selected from the group consisting of shock resisting tool steel (0.5 C, 1.40 Mo, 3.25 Cr), carbon steel (0.9 C, 1 Mn), Tungsten steel (0.7 C, 0.3 Cr, 6 W), 3.5% Cr Steel (0.9 C, 0.35 Cr), 15% Co Steel (1.9 C, 7 Cr, 0.5 Mo, 15 Co), KS Steel (0.9 C, 3 Cr, 4 W, 35 Co), MT Steel (2.0 C, 8.0 Al), Vicalloy (52 Co, 14 V), MK Steel (16 Ni, 10 Al, 12 Co, 6 Cu), Pt—Fe, iron powder (100 Fe), FeCo (55 Fe, 45 Co) and combinations thereof and said coating has a thickness of from about 50 to about 1000 Å.  
     
     
         13 . Ferromagnetic powder according to  claim 10 , wherein said ferromagnetic particles are for use in soft magnetic materials and are selected from the group consisting of Fe, Fe—Si, Fe—Al, Fe—Si—Al, Fe—Ni, Fe—Co, Fe—Co—Ni, and combinations thereof.  
     
     
         14 . Ferromagnetic powder according to  claim 10 , wherein said coating comprises from about 65% to about 80% by weight of a member selected from the group consisting of FeO, Fe 3 O 4 , Fe 2 O 3 , (Fe 2 O 3 ·H 2 O) and combinations thereof; and from about 20% to about 35% by weight of a member selected from the group consisting of FePO 4 , Fe 3 (PO 4 ) 2 , FeHPO 4 , FePO 4 ·2H 2 O, Fe 3 (PO 4 )2·8H 2 O, and combinations thereof.  
     
     
         15 . Ferromagnetic powder according to  claim 14 , wherein said coating comprises a Vivianite-like material.  
     
     
         16 . Ferromagnetic powder comprising: 
 a. a plurality of ferromagnetic particles having a diameter size of from about 40 to about 600 microns; and    b. a coating disposed on each of said particles that permits adjacent particles to engage one another with a force such that a part made by compressing said ferromagnetic particles having said coating disposed thereon has a transverse rupture strength of at least about 8 kpsi as measured in accordance with MPIF Standard 41, wherein said coating has an electrical insulation value as determined between adjacent ones of said ferromagnetic particles that does not substantially degrade when subjected to temperatures of greater than about 150° C.    
     
     
         17 . Ferromagnetic powder according to  claim 16 , wherein said electrical insulation value, as determined between adjacent ones of said ferromagnetic particles, is at least about 1 milli-Ohm-cm.  
     
     
         18 . Ferromagnetic powder according to  claim 17 , wherein said electrical insulation value does not substantially degrade when subjected to temperatures of from about 200 to about 300° C.  
     
     
         19 . Ferromagnetic powder according to  claim 17 , wherein said coating comprises from about 65% to about 80% by weight of a member selected from the group consisting of FeO, Fe 3 O 4 , Fe 2 O 3 , (Fe 2 O 3 ·H 2 O) and combinations thereof; and from about 20% to about 35% by weight of a member selected from the group consisting of FePO 4 , Fe 3 (PO 4 ) 2 , FeHPO 4 , FePO 4 ·2H 2 O, Fe 3 (PO 4 ) 2 ·8H 2 O, and combinations thereof.  
     
     
         20 . Ferromagnetic powder comprising: 
 a. a plurality of ferromagnetic particles; and    b. a coating disposed on each of said particles, said coating comprising from about 50% to about 85% by weight of a member selected from the group consisting of FeO, Fe 3 O 4 , Fe 2 O 3 , (Fe 2 O 3 ·H 2 O) and combinations thereof; and from about 15% to about 50% by weight of a member selected from the group consisting of FePO 4 , Fe 3 (PO 4 ) 2 , FeHPO 4 , FePO 4 ·2H 2 O, Fe 3 (PO 4 ) 2 ·8H 2 O, FeCrO 4 , FeMoO 4 , FeC 2 O 4 , FeWO 4 , and combinations thereof, and wherein said coating is substantially free of organic materials.    
     
     
         21 . Ferromagnetic powder according to  claim 20 , wherein said coating comprises from about 65% to about 80% by weight of a member selected from the group consisting of FeO, Fe 3 O 4 , Fe 2 O 3 , (Fe 2 O 3 ·H 2 O) and combinations thereof; and from about 20% to about 35% by weight of a member selected from the group consisting of FePO 4 , Fe 3 (PO 4 ) 2 , FeHPO 4 , FePO 4 ·2H 2 O, Fe 3 (PO 4 ) 2 ·8H 2 O, FeCrO 4 , FeMoO 4 , FeC 2 O 4 , FeWO 4 , and combinations thereof.  
     
     
         22 . Ferromagnetic powder according to  claim 20 , wherein said coating has a thickness of from about 50 to about 5000 Å.  
     
     
         23 . Ferromagnetic powder according to  claim 21 , wherein said coating comprises a Vivianite-like material.  
     
     
         24 . A coating material for ferromagnetic particles, said coating material comprising: 
 a. from about 50% to about 85% by weight of a member selected from the group consisting of FeO, Fe 3 O 4 , Fe 2 O 3 , (Fe 2 O 3 ·H 2 O) and combinations thereof; and    b. from about 15% to about 50% by weight of a member selected from the group consisting of FePO 4 , Fe 3 (PO 4 ) 2 , FeHPO 4 , FePO 4 ·2H 2 O, Fe 3 (PO 4 ) 2 ·8H 2 O, and combinations thereof; and    c. wherein said coating permits adjacent particles to engage one another with a force such that a part made by compressing ferromagnetic particles having said coating disposed thereon has a transverse rupture strength of at least about 8 kpsi as measured in accordance with MPIF Standard 41.    
     
     
         25 . A coating according to  claim 24 , wherein said coating imparts to a part made by compressing ferromagnetic particles having said coating thereon an electrical insulation value of at least about 1 milli-Ohm-cm, as determined between adjacent ones of ferromagnetic particles having said coating disposed thereon.  
     
     
         26 . A coating according to  claim 25 , wherein said electrical insulation value does not substantially degrade when subjected to temperatures of greater than about 150° C.  
     
     
         27 . A coating according to  claim 24 , wherein said coating is substantially free of organic materials.  
     
     
         28 . A coating according to  claim 24 , wherein said coating comprises from about 65% to about 80% by weight of a member selected from the group consisting of FeO, Fe 3 O 4 , Fe 2 O 3 , (Fe 2 O 3 ·H 2 O) and combinations thereof.  
     
     
         29 . A coating according to  claim 24 , wherein said coating comprises from about 20% to about 35% by weight of a member selected from the group consisting of FePO 4 , Fe 3 (PO 4 ) 2 , FeHPO 4 , FePO 4 ·2H 2 O, Fe 3 (PO 4 ) 2 ·8H 2 O, and combinations thereof.  
     
     
         30 . A coating according to  claim 24 , wherein said coating comprises Vivianite-like material.  
     
     
         31 . A coating according to  claim 24 , wherein said transverse rupture strength is greater than about 15 kpsi, as measured in accordance with MPIF Standard 41.  
     
     
         32 . A method of making ferromagnetic powder comprising the steps of: 
 a. providing a plurality of ferromagnetic particles; and    b. treating said particles with an aqueous solution having a pH of about 5.5 and comprising from about 5 to about 50 grams per liter of a member selected from the group consisting of a primary alkaline phosphate, an alkaline chromate, an alkaline tungstate, an alkaline molybdate, an alkaline oxalate and combinations thereof; from about 0.1 to about 50 grams per liter of an oxidizing agent; and from about 0 to about 0.5 grams per liter of a member selected from the group consisting of a wetting agent, a surfactant and combinations thereof; said aqueous solution having a temperature of from about 15° C. to about 60° C., and said treating step being performed for a time period of from about 1 minute to about 20 minutes.    
     
     
         33 . A method according to  claim 32 , wherein said time period is long enough to allow the pH of the aqueous solution to come to equilibrium.  
     
     
         34 . A method according to  claim 33 , wherein said time period is from about 3 to about 10 minutes.  
     
     
         35 . A method according to  claim 32 , wherein said particles have a diameter of from about 40 to about 600 microns.  
     
     
         36 . A method according to  claim 32 , wherein said particles are soft magnetic particles and are selected from the group consisting of particles of Fe, Fe—Si, Fe—Al, Fe—Si—Al, Fe—Ni, Fe—Co, Fe—Co—Ni, and combinations thereof.  
     
     
         37 . A method according to  claim 32 , wherein said particles are selected from the group consisting of particles of shock resisting tool steel (0.5 C, 1.40 Mo, 3.25 Cr), carbon steel (0.9 C, 1 Mn), Tungsten steel (0.7 C, 0.3 Cr, 6 W), 3.5% Cr Steel (0.9 C, 0.35 Cr), 15% Co Steel (1.9 C, 7 Cr, 0.5 Mo, 15 Co), KS Steel (0.9 C, 3 Cr, 4 W, 35 Co), MT Steel (2.0 C, 8.0 Al), Vicalloy (52 Co, 14 V), MK Steel (16 Ni, 10 Al, 12 Co, 6 Cu), Pt—Fe, iron powder (100 Fe), FeCo (55 Fe, 45 Co) and combinations thereof.  
     
     
         38 . A method according to  claim 32 , wherein said aqueous solution comprises from about 1 to about 50 grams per liter of a primary alkaline phosphate selected from the group consisting of KH 2 PO 4 , NaH 2 PO 4 , NH 4 H 2 PO 4  and combinations thereof.  
     
     
         39 . A method according to  claim 32 , wherein said aqueous solution comprises an inorganic oxidizing agent selected from the group consisting of NaClO 3 , NaBrO 3 , KNO 3 , NaNO 3 , KNO 2 , NaNO 2 , H 2 O 2 , hydroxylamine, hydroxylamine sulfate, hydrazine and combinations thereof.  
     
     
         40 . A method according to  claim 32 , wherein said aqueous solution comprises an organic oxidizing agent selected from the group consisting of sodium m-nitrobenzene, nitrophenol, dinitrobenzene sulfonate, p-nitrobenzoic acid, nitrophenol nitroguanidine, nitrilloacetic acid and combinations thereof.  
     
     
         41 . A method according to  claim 39 , wherein said aqueous solution comprises from about 0.3 to about 50 grams per liter of KNO 3 or NaNO 3 .  
     
     
         42 . A method according to  claim 41 , wherein said aqueous solution comprises from about 0.5 to about 5 grams per liter of KNO 3  or NaNO 3 .  
     
     
         43 . A method according to  claim 39 , wherein said aqueous solution comprises from about 0.1 to about 50 grams per liter of KNO 2  or NaNO 2 .  
     
     
         44 . A method according to  claim 39 , wherein said aqueous solution comprises from about 0.1 to about 0.3 grams per liter of KNO 2  or NaNO 2 .  
     
     
         45 . A method according to  claim 39 , wherein said aqueous solution comprises from about 0.1 to about 50 grams per liter of NaClO 3  or NaBrO 3 .  
     
     
         46 . A method according to  claim 45 , wherein said aqueous solution comprises from about 5 to about 10 grams per liter of NaClO 3  or NaBrO 3 .  
     
     
         47 . A method according to  claim 39 , wherein said aqueous solution comprises from about 0.1 to about 2 grams per liter of hydroxylamine or hydroxylamine sulfate.  
     
     
         48 . A method according to  claim 39 , wherein said aqueous solution comprises from about 0.1 to about 2 grams per liter of hydrazine.  
     
     
         49 . A method according to  claim 39 , wherein said aqueous solution comprises from about 0.01 to about 0.1 grams per liter of H 2 O 2 .  
     
     
         50 . A method according to  claim 40 , wherein said aqueous solution comprises from about 0.3 to about 10 grams per liter of the organic oxidizer.  
     
     
         51 . A method according to  claim 32 , wherein said aqueous solution comprises from about 0.1 to about 1 gram per liter of a surfactant selected from the group consisting of sodium dodecyl benzyl sulfonate, lauryl sulfate, oxylated polyethers, ethoxylated polyethers and combinations thereof.  
     
     
         52 . A method according to  claim 32 , wherein said aqueous solution has a temperature of from about 20° C. to about 50° C.  
     
     
         53 . A method according to  claim 32 , wherein said treating step is performed for a time period of from about 3 to about 20 minutes.  
     
     
         60 . A method according to  claim 59 , wherein at least a portion of said annealing step is performed at temperatures in excess of about 200° C.  
     
     
         61 . A method according to  claim 58 , wherein said coating step is comprised of treating said particles with an aqueous solution comprising from about 5 to about 50 grams per liter of a member selected from the group consisting of a primary alkaline phosphate, an alkaline chromate, an alkaline tungstate, an alkaline molybdate, an alkaline oxalate and combinations thereof; from about 0.1 to about 50 grams per liter of an oxidizing agent; and from about 0 to about 0.5 grams per liter of a member of the group consisting of a wetting agent, a surfactant and combinations thereof; said aqueous solution being at a temperature of from about 30° C. to about 60° C., and said step of treating being carried out for a time period of from about 1 minute to about 20 minutes.  
     
     
         62 . A method of making soft magnetic parts comprising the steps of: 
 a. providing a plurality of ferromagnetic particles; and    b. coating said particles with a conversion coating that permits adjacent particles to engage one another with a force such said part made from said ferromagnetic particles with said coating has an as pressed transverse rupture strength of at least 8 kpsi, as measured in accordance with MPIF Standard 41 and which has an electrical insulation value that does not degrade at temperatures over 150° C.; and    c. consolidating said coated particles in the shape of said part.    
     
     
         54 . A method according to  claim 32 , wherein said treating step is achieved by immersing said particles in said solution.  
     
     
         55 . A method according to  claim 32 , wherein said treating step is achieved by spraying said particles with said solution.  
     
     
         56 . A method of making soft magnetic parts comprising the steps of: 
 a. providing a plurality of ferromagnetic particles;    b. coating each of said particles with a material comprising from about 40% to about 85% by weight of a member selected from the group consisting of FeO, Fe 3 O 4 , Fe 2 O 3 , (Fe 2 O 3 ·H 2 O) and combinations thereof; and from about 15% to about 60% by weight of a member selected from the group consisting of FePO 4 , Fe 3 (PO 4 ) 2 , FeHPO 4 , FePO 4 ·2H 2 O, Fe 3 (PO 4 ) 2 ·8H 2 O, FeCrO 4 , FeMoO 4 , FeC 2 O 4 , FeWO 4 , and combinations thereof; and    c. consolidating said coated particles in the shape of said part.    
     
     
         57 . A method according to  claim 56 , wherein said coating is a Vivianite-like material  
     
     
         58 . A method according to  claim 56 , further comprising the step of: 
 d. annealing said part.    
     
     
         59 . A method according to  claim 58 , wherein at least a portion of said annealing step is performed at temperatures in excess of about 150° C.  
     
     
         63 . A method of making soft magnetic parts comprising the steps of: 
 a. providing a plurality of ferromagnetic particles;    b. coating each of said particles with a material comprising an oxide and a phosphate conversion coating, said oxide and phosphate in a weight ratio of from about 2 parts oxide to about 4 parts oxide to about one part phosphate, wherein said coating is substantially free of organic materials; and    c. consolidating said coated particles in the shape of said part.    
     
     
         64 . A method according to  claim 63 , annealing said part at a temperature above 150° C.  
     
     
         65 . A soft magnetic part comprising a three-dimensional structure comprised of: 
 consolidated ferromagnetic particles each having a coating disposed thereon of a material having an electrical insulation value that does not degrade at temperatures above 150° C., said magnetic part having an as pressed transverse rupture strength as determined in accordance with MPIF Standard 41, of at least about 8 kpsi.    
     
     
         66 . A soft magnetic part according to  claim 65  wherein said electrical insulation value is at least about 1 milli-Ohm-cm, as determined between adjacent ones of said consolidated ferromagnetic particles having said coating disposed thereon.  
     
     
         67 . A soft magnetic part according to  claim 65 , wherein said transverse rupture strength is at least about 12 kpsi.  
     
     
         68 . A soft magnetic part according to  claim 66 , wherein said three-dimensional structure corresponds to a member selected from the group consisting of a rotor core, a stator core, an armature core, an actuator, an ignition choke core, an inductor core, and a solenoid core.  
     
     
         69 . A soft magnetic part comprising a three-dimensional structure comprised of: 
 consolidated ferromagnetic particles coated with a conversion coating material comprising from about 2 to about 4 parts by weight of an oxide to one part of a member selected from the group consisting of chromate, molybdate, oxylate, phosphate, tungstate and combinations thereof, wherein said coating is substantially free of organic materials, said part having a density greater than about 7.4 g/cc.    
     
     
         70 . A part according to  claim 69 , wherein said coating comprises from about two to about four parts of an oxide and about one part of a phosphate.  
     
     
         71 . A stator for an alternating current generator comprising a plurality of ferromagnetic particles consolidated in the shape of a stator core, said shape comprising an annular yoke and a plurality of integral inner circumferentially spaced projections radiating and extending inwardly and defining slots, each of said ferromagnetic particles having coated thereon a material that has an electrical insulation value that does not degrade at temperatures above 150° C., said core having an as pressed transverse rupture strength, as determined in accordance with MPIF Standard 41, of at least about 8 kpsi.  
     
     
         72 . A stator according to  claim 71 , wherein said electrical insulation value is at least about 1 milli-ohm-cm, as determined between adjacent ones of said consolidated ferromagnetic particles having said coating disposed thereon.  
     
     
         73 . A stator according to  claim 72 , wherein said electrical insulation value is at least about 2.5 milli-ohm-cm, as determined between adjacent ones of said consolidated ferromagnetic particles having said coating disposed thereon.  
     
     
         74 . A stator according to  claim 72 , wherein said material comprises from about 50% to about 85% by weight of a member selected from the group consisting of FeO, Fe 3 O 4 , Fe 2 O 3 , (Fe 2 O 3 ·H 2 O) and combinations thereof; and from about 15% to about 50% by weight of a member selected from the group consisting of FePO 4 , Fe 3 (PO 4 ) 2 , FeHPO 4 , FePO 4 ·2H 2 O, Fe 3 (PO 4 ) 2 ·8H 2 O, and combinations thereof.  
     
     
         75 . A stator according to  claim 74 , wherein said material comprises a Vivianite-like material.  
     
     
         76 . A rotor for an alternating current generator comprising: 
 a plurality of ferromagnetic particles consolidated in the shape of an elongated annular shaped cylinder defining a cylindrical void through which passes an elongated cylindrical shaft for rotating said rotor, each of said ferromagnetic particles having coated thereon a material that has an electrical insulation value that does not degrade at temperatures above 150° C., said rotor having an as pressed transverse rupture strength, as determined in accordance with MPIF Standard 41, of at least about 8 kpsi.    
     
     
         77 . A rotor according to  claim 76 , wherein said electrical insulation value is at least about 1 milli-ohm-cm, as determined between adjacent ones of said consolidated ferromagnetic particles having said coating disposed thereon.  
     
     
         78 . A rotor according to  claim 77 , wherein said electrical insulation value is at least about 2.5 milli-ohm-cm, as determined between adjacent ones of said consolidated ferromagnetic particles having said coating disposed thereon.  
     
     
         79 . A rotor according to  claim 76 , wherein said material comprises from about 50% to about 85% by weight of a member selected from the group consisting of FeO, Fe 3 O 4 , Fe 2 O 3 , (Fe 2 O 3 ·H 2 O) and combinations thereof; and from about 15% to about 50% by weight of a member selected from the group consisting of FePO 4 , Fe 3 (PO 4 ) 2 , FeHPO 4 , FePO 4 ·2H 2 O, Fe 3 (PO 4 ) 2 ·8H 2 O, and combinations thereof.  
     
     
         80 . A rotor according to  claim 79 , wherein said material comprises a Vivianite-like material.  
     
     
         81 . An armature assembly for an alternating current generator comprising a plurality of ferromagnetic particles consolidated in the shape of an armature core and a shaft for rotating said armature core, said shape comprising an elongated annular shaped cylinder defining an elongated cylindrical void through which the shaft passes, said annular shaped cylinder having a plurality of troughs at spaced intervals extending lengthwise along an exterior surface thereof, each of said ferromagnetic particles having coated thereon a material that has an electrical insulation value that does not degrade at temperatures above 150° C., said core having an as pressed transverse rupture strength, as determined in accordance with MPIF Standard 41, of at least about 8 kpsi.  
     
     
         82 . An armature according to claim  81 , wherein said electrical insulation value is at least about 1 milli-ohm-cm, as determined between adjacent ones of said consolidated ferromagnetic particles having said coating disposed thereon.  
     
     
         83 . An armature according to claim  82 , wherein said electrical insulation value is at least about 2.5 milli-Ohm-cm, as determined between adjacent ones of said consolidated ferromagnetic particles having said coating disposed thereon.  
     
     
         84 . An armature according to claim  81 , wherein said material comprises from about 50% to about 85% by weight of a member selected from the group consisting of FeO, Fe 3 O 4 , Fe 2 O 3 , (Fe 2 O 3 ·H 2 O) and combinations thereof; and from about 15% to about 50% by weight of a member selected from the group consisting of FePO 4 , Fe 3 (PO 4 ) 2 , FeHPO 4 , FePO 4 ·2H 2 O, Fe 3 (PO 4 ) 2 ·8H 2 O, and combinations thereof.  
     
     
         85 . An armature according to claim  84 , wherein said material comprises a Vivianite-like material.