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The processing and characterisation of recycled NdFeB-type sintered magnets

Degri, Malik John Jamaji (2014)
Ph.D. thesis, University of Birmingham.

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Abstract

A study of the processing and characterisation of sintered NdFeB magnets made from recycled feed stock was undertaken. Initially the hydrogen decrepitated (HD) powder was investigated using two different milling techniques. The powders were analysed with optical microscopy, with the aid of a magnetic field. It was found that with light milling the HD powder breaks up to a similar particle size to that of the grain size of the starting material. A data logging system was built to investigate the desorption behaviour of green compacts during sintering. Desorption traces showed desorption from the matrix phase and the intergranular Nd-rich phase. The start of desorption was seen to shift to lower temperatures as the mean particle size of the green compact was reduced. For the processing route used in this work intergranular additions of neodymium hydride were required to increase the density and magnetic properties. To investigate the oxidation behaviour of lightly milled HD powder, powder was exposed to air for varying times. The exposed powder was aligned pressed and sintered. The Nd-rich desorption peak reduced with exposure time, the density and magnetic properties also reduced. Post exposure additions of Intergranular neodymium hydride to the powder recovered density and magnetic properties.

Type of Work:Ph.D. thesis.
Supervisor(s):Walton, Allan and Harris, Rex and Williams, Andrew
School/Faculty:Colleges (2008 onwards) > College of Engineering & Physical Sciences
Department:School of Metallurgy and Materials
Subjects:TN Mining engineering. Metallurgy
Institution:University of Birmingham
ID Code:5516
This unpublished thesis/dissertation is copyright of the author and/or third parties.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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