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Development and assessment of new electrical steels for high frequency applications

Elgamli, Elmazeg 2023. Development and assessment of new electrical steels for high frequency applications. PhD Thesis, Cardiff University.
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This research work aims to decrease the power loss of electrical steel by enhancing its surface resistivity. The proposed approach involves introducing additional alloying elements through diffusion after the steel sheet reaches its final thickness. Various methods for increasing the resistivity of the strip have been proposed and tested. The technique involves creating a paste by mixing the diffusant element in powder form with specific solutions, which are then applied to the steel surface. Upon firing the sample, successful transfer of some elements to the steel is observed. The quantity and distribution of these elements can be controlled by adjusting the paste’s composition, the firing conditions, and the subsequent annealing processes. This thesis investigates the effects of adding manganese oxide (IV) and cobalt oxide (II, III) to electrical steel to reduce power loss and magnetostriction. The tested samples consist of non-oriented electrical steels with a composition of 2.4wt% Si-Fe and dimensions of 0.305 mm x 300 mm x 30 mm. Power loss and permeability are measured before and after treatment using a single strip tester in a magnetic field range of 0.5 T to 1.7 Tesla. The measurements are conducted using an AC magnetic properties measurement system under controlled sinusoidal conditions at different frequencies. The results demonstrate that the depth of manganese oxide (IV) diffusion decreases with varying temperatures. The optimal diffusion of manganese into the strips occurs at 525 °C, compared to 700 °C and 800 °C. Therefore, it was concluded that the power losses (W/kg) in the coating samples were improved by 7 % as compared with uncoated samples. For cobalt oxide (II, III), successful diffusion into steel is observed when added to sodium silicate solution to form a paste. This paste significantly reduces power loss in non-oriented material. The reduction achieved with cobalt paste (14% at 400 Hz, 23% at 1 kHz) surpasses that achieved with manganese paste (6% at 400 Hz and 3% at 1 kHz) on similar steel. This improvement is attributed to the absence of a porous layer containing a high percentage of the diffusing element, as seen in the manganese experiments. The relative amounts of manganese and cobalt entering the steel are difficult to compare due to the formation of the porous layer in the former case.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: 1). Electrical steel Si-Fe 2). Power losses 3). Permeability 4). Diffusion technique 5). Manganese oxide 6). Cobalt oxide
Date of First Compliant Deposit: 23 May 2024
Last Modified: 23 May 2024 11:05

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