Patent GB-454206-A (GB)
Title: A method for producing magnetic powder
Inventor: VOGT HANS
IPC: H01F1/22
Filed: 1936-01-30
Abstract: Magnetic powder is produced by mixing particles containing iron with materials containing silicon or aluminium to produce with the iron an alloy of high electric resistance and mechanical hardness, and heating in vacuo or in an inert or reducing atmosphere at a temperature sufficient to effect alloying without substantial sintering.  Pure iron, red iron oxide, or iron hydroxide particles may be employed, and the materials containing silicon or aluminium may also contain carbon, boron, titanium, zirconium, thorium, vanadium, antimony, arsenic, phosphorus, or tellurium.  Iron hydroxide mixed with 2 to 6 per cent of powdered silicon is heated in a rotary tube furnace for 30 minutes at 600 to 800 DEG  C. in a preheated hydrogen current, with 0,5 per cent of chlorine gas as catalyst.  The powder is cooled during 12 hours in a hydrogen atmosphere, and then treated in a ball mill.  Iron oxide may be heated in hydrogen at 600 to 700 DEG  C. in hydrogen for 1 hour, and cooled as above, the reduced powder is ground for 1 to 3 hours with 4 to 6 per cent by weight of silicon, and heated to 500 to 700 DEG  C. in a chamber which is preferably evacuated, and a small quantity of chlorine is added as catalyst and the temperature maintained for 30 minutes, after which the powder is cooled over 2 hours.  Iron hydroxide mixed with 2 1/2 per cent of silicon is heated in hydrogen with 1 per cent of chlorine for 30 minutes at 600 DEG  C. and is cooled over 6 hours.  In a further modified form of the process, iron hydroxide is heated to 650 DEG  C. in preheated hydrogen to which gaseous silicon tetrachloride acting as a catalyst and from which the silicon is released is added in a quantity to constitute 17 per cent by weight of the hydroxide over 30 minutes, the powder then being treated as above.  The heating chamber may be under reduced or increased pressure.  Other substances which may be employed as catalysts are silicon-hydrogen compounds, unstable metallic salts not reacting with hydrogen, or acids or their anhydrides such as acetic acid anhydride.  Hydrocarbons may be used as grinding agents in the ball mill, and a substance imparting an insulating skin to the particles may be employed.  More than 3 per cent of silicon is included in the initial mixture, and preferably 4 to 12 per cent of silicon is diffused into the iron particles.  The particles may be of a size from 1/2 to 20 microns, and may be moulded with an insulating binder into cores for wireless coils.ALSO:Magnetic powder, which may be moulded with an insulating binder, unspecified, into cores for wireless coils, is produced by mixing particles containing iron with materials containing silicon or aluminium to produce with the iron an alloy of high electric resistance and mechanical hardness, and heating in vacuo or in an inert or reducing atmosphere at a temperature sufficient to effect alloying without substantial sintering.  Pure iron, red iron oxide, or iron hydroxide particles may be employed, and the materials containing silicon or aluminium may also contain carbon, boron, titanium, zirconium, thorium, vanadium, antimony, arsenic, phosphorus, or tellurium.  Iron hydroxide mixed with 2 to 6 per cent of powdered silicon is heated in a rotary tube furnace for 30 minutes at 600 to 800 DEG  C. in a preheated hydrogen current, with 0,5 per cent of chlorine gas as catalyst.  The powder is cooled during 12 hours in a hydrogen atmosphere, and then treated in a ball mill.  Iron oxide may be heated in hydrogen at 600 to 700 DEG  C. in hydrogen for 1 hour, and cooled as above, the reduced powder is ground for 1 to 3 hours with 4 to 6 per cent by weight of silicon, and heated to 500 to 700 DEG  C. in a chamber which is preferably evacuated, and a small quantity of chlorine is added as catalyst and the temperature maintained for 30 minutes, after which the powder is cooled over 2 hours.  Iron hydroxide mixed with 2 1/2 per cent of silicon is heated in hydrogen with 1 per cent of chlorine for 30 minutes at 600 DEG  C. and is cooled over 6 hours.  In a further modified form of the process, iron hydroxide is heated to 650 DEG  C. in preheated hydrogen to which gaseous silicon tetrachloride acting as a catalyst and from which the silicon is released is added in a quantity to constitute 17 per cent by weight of the hydroxide over 30 minutes, the powder then being treated as above.  The heating chamber may be under reduced or increased pressure.  Other substances which may be employed as catalysts are siliconhydrogen compounds, unstable metallic salts not reacting with hydrogen, or acids or their anhydrides such as acetic acid anhydride.  Hydrocarbons may be used as grinding agents in the ball mill, and a substance imparting an insulating skin to the particles may be employed.  More than 3 per cent of silicon is included in the initial mixture, and preferably 4 to 12 per cent of silicon is diffused into the iron particles.  The particles may be of a size from 1/2 to 20 microns.