The obje ctives of this project are: To improve the case of handling of pyrophoric RE-TM-X powders for magnet production. This will be achieved by employing Metal Organic Chemical Vapour Deposition (MOCVD) to deposit a thin passivating metal film on the powder particles. To develop an alternative route for the production of magnetics based upon the Osprey Spray Forming Technique.
The objectives of this project are to improve the ease of handling of pyrophoric rare earth transition metal metalloid (RE-TM-X) powders for magnet production. (This will be achieved by depositing a passivating metal film on the powder particle surfaces using a metal organic chemical vapour deposition (MOCVD) technique) and to develop an alternative route for the production of RE-TM-X magnetics based upon the Osprey spray forming route.
Spray forming, using the Osprey process, has been shown to be a feasible method for producing neodymium iron boron magnet. Tubes, in various sizes, have been successfully spray formed and found to have appropriate microstructures and energy products up to roughly 9E15 oersted. The magnetic properties were found to be slightly anisotropic and efforts are presently being made to improve the crystalline anistropy. The powder passivation work has succeeded in coating powders with nickel by MOCVD and in developing a thermogravimetric method of assessing the degree of passivation. Coating of the powders with cobalt from its acetyl acetonate has proved more difficult and efforts are continuing in this area.
This project considered both spray forming and powder coating as possible means of improving the processing technology for neodymium iron boride magnets.
It has been shown that the spray forming technique is a viable method for producing fully deuse magnets by a 1-step process direct from the liquid state. The material so produced exhibited 3-phase microstructures with a neodymium (2) iron (14) boron matrix phase. The values for remanence and energy product achieved from the spray formed material are comparable with isotropic material produced by other methods. The intrinsic coercivity, however, was somewhat lower than would normally be required for commercial applications. Further heat treatment for 1 hour at between 600 C and 650 C helps to improve this.
Metal organic chemical vapour deposition (MOCVD) has been used to apply a passivating surface coating to neodymium iron boride powders in order to improve their handling and to reduce oxidation losses during processing by the conventional powder method. Ultimately cobalt coating were produced by the thermal decomposition of cobalt acetylacetonate gas. Coarse particles can be coated readily but coating becomes increasingly difficult as the particle size is reduced.
THE PROGRAMME IS DIVIDED INTO THREE PARTS :
- PASSIVATION OF POWDERS FOR ANISOTROPIC MAGNETS
- DEVELOPMENT OF THE OSPREY PROCESS FOR ISOTROPIC MATERIAL
- IN-SERVICE TESTING OF MAGNETS
THE POWDERS WILL BE PASSIVATED USING THE TECHNIQUE OF METAL ORGANIC CHEMICAL VAPOUR DEPOSITION (MOCVD). COATED PARTICLES WILL BE EVALUATED AS TO THEIR PASSIVATING PROPERTIES BY SEM AND AES TECHNIQUES. SUITABLE POWDERS WILL BE PROCESSED INTO MAGNETS. SAMPLES OF OPTIMISED MAGNETS IN APPROPRIATE FORM WILL BE PROVIDED FOR IN-SERVICE ASSESSMENT IN ELECTRIC MOTORS.
A SEPARATE PART OF THE RESEARCH WILL BE THE DEVELOPMENT OF THE OSPREY PROCESS FOR THE SPRAY DEPOSITION OF ND-FE-B MATERIAL. THIS WORK WILL BE CARRIED OUT CONCURRENTLY WITH THE PASSIVATION STUDIES. IF THE SPRAY TECHNIQUE PROVES VIABLE, IT WILL BE USED TO DIRECTLY SPRAY FORM MAGNETIC ARC SEGMENTS ON SUITABLE POLEPIECES.
THE AIM OF THE FIRST TWO PARTS OF THE PROGRAMME, ON PASSIVATION AND SPRAY DEPOSITION, IS TO DEVELOP MORE ECONOMIC METHODS OF PRODUCING RE-TM-X MAGNETS IN A FORM MOST APPROPRIATE TO THE NEEDS OF THE END USERS (IN THE ELECTRIC MOTOR INDUSTRY).
BOTH PARTS OF THE ABOVE PROGRAMME REPRESENT CONSIDERABLE INNOVATION AND WILL RESULT IN IMPROVED PROCESSES AND PRODUCTS WHICH WILL, IN TURN, GIVE RISE TO SIGNIFICANT ECONOMIC ADVANTAGES TOGETHER WITH INCREASED EUROPEAN INDUSTRIAL COMPETITIVENESS IN WORLD MARKETS. IN PARTICULAR, OSPREY PROCESSING, AFTER DEVELOPMENT, WILL PROVIDE A ONE-STEP ROUTE FOR THE PRODUCTION OF ISOTROPIC MATERIAL WHICH WILL OBVIATE THE NEED FOR EXPENSIVE MELT SPINNING, CRUSHING AND CONSOLIDATION OPERATIONS. FURTHERMORE, SINCE THIS NOVEL TECHNOLOGY IS PATENTED THROUGHOUT THE WORLD, SUCCESSFUL DEVELOPMENT OF THE PROCESS FOR ND-FE-B WILL REDUCE EUROPEAN DEPENDENCE UPON AMERICAN AND JAPANESE PATENTS ON ALREADY ESTABLISHED PRODUCTION METHODS.