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The processing and characterisation of recycled NdFeB based magnets

Adrwish, Salahadin Muhammed Ali (2013)
Ph.D. thesis, University of Birmingham.

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Abstract

The scrap magnets were turned into a powder using the HD process. The powder was milled for specific times and sintered for 1-3hrs at 1090 °C. The magnet samples were measured using a permeameter to determine their magnetic properties. Cross sections of these samples were then mounted in bakelite and subject to metallographic studies using SEM analysis by means of Joel6060 and 7000.

Some of the recycled magnets did achieve magnetic properties close to the starting magnets. It was shown that the nature of the starting magnets determines the appropriate sintering conditions during recycling. Sintering for 3hrs was good for magnets with high oxygen content but too long for fresh material and magnets with lower oxygen content, as indicated by the dilatometer measurements.

Some magnets were studied further due to a lean rare content. These were treated with various heat treatments and other techniques (e.g. grain boundary diffusion) and the addition of various additives such as Dy, Co, Nd, Nband Tb.

A study of how reactive recycled magnets in 3% salt-bath (Sodium Chloride NaCI) compared with starting magnets. The corrosion study was conducted over 30 weeks where results had indicated that recycled magnets have better corrosion resistance than the original material. This was due mainly to the shape of the magnets and the magnets being anisotropic, where there is a concentration of corrosion sites on the poles. The corrosion initiated at the Nd rich phase where it propagates further as time goes on. Furthermore, the magnetic properties decrease over the period, as expected. An investigation was made into the use of scrap magnetic powder in bonded magnets using tin as binder was also undertaken.

Type of Work:Ph.D. thesis.
Supervisor(s):Harris, I .R. and Williams, A.J
School/Faculty:Colleges (2008 onwards) > College of Engineering & Physical Sciences
Department:School of Metallurgy and materials
Subjects:Q Science (General)
T Technology (General)
TA Engineering (General). Civil engineering (General)
Institution:University of Birmingham
ID Code:4122
This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder.
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