• Korean Journal of Metals and Materials
• /
• v.49 no.1
• /
• pp.85-91
• /
• 2011

Alnico magnets can be used as magnetic bearings for the precise electric power measuring instruments such as watt-hour meters because they have high remanence ($B_r$), relatively high maximum energy product ($(BH)_{max}$), and excellent temperature stability. In this study, Alnico composite magnets were fabricated by appropriately mixing alnico alloy powders with epoxy resin and binder. The Alnico powders mixed with epoxy resin and a hardening agent with a mixing ratio of 96:4 were pressed and then cured to be a toroid-type ring magnet with an outer diameter (${\Phi}_{out}$) of 15 mm, an inner diameter (${\Phi}_{in}$) of 6.5 mm and a thickness (t) of 2.5 mm, respectively. The magnetic properties of the Alnico ring magnets were varied with the mixing ratio of Alnico powders that possess different average particle sizes. The Alnico ring magnet prepared by mixing 5 wt% of $50{\mu}m$ (small size) powder, 15~20 wt% of $150{\mu}m$ (medium size) powder, and 75~80 wt% of $300{\mu}m$ (large size) powder showed the best magnetic properties (remanent induction, coercive force, maximum energy product, and surface flux density). In addition, measurements of temperature and moisture characteristics for the Alnico ring magnets showed that the surface flux densities of the N and S poles decreased little and the repulsive distance between the magnets decreased as small as 0.05 mm after 10 days.

• Korean Journal of Materials Research
• /
• v.22 no.11
• /
• pp.569-574
• /
• 2012

Large single grain $Gd_{1.5}Ba_2Cu_3O_{7-y}$ (Gd1.5) bulk superconductors were fabricated by a top-seeded melt growth (TSMG) process using an $NdBa_2Cu_3O_{7-y}$ seed. The seeded Gd1.5 powder compacts with a diameter of 50 mm were subjected to the heating cycles of a TSMG process. After the TSMG process, the diameter of the single grain Gd1.5 compact was reduced to 43 mm owing to the volume contraction during the heat treatment. The superconducting transition temperature ($T_c$) of the top surface of the single grain Gd1.5 sample was as high as 93.5 K. The critical current densities ($J_cs$) at 77 K and 1T and 1.5 T were in ranges of 25,200-43,900 $A/cm^2$ and 10,000-23,000 $A/cm^2$, respectively. The maximum attractive force at 77 K of the sample field-cooled using an Nd-B-Fe permanent magnet (surface magnetic field of 0. 527 T) was 108.3 N; the maximum repulsive force of the zero field-cooled sample was 262 N. The magnetic flux density of the sample field-cooled at 77 K was 0.311T, which is approximately 85% of the applied magnetic field of 0.375 T. Microstructure investigation showed that many $Gd_2BaCuO_5$ (Gd211) particles of a few ${\mu}m$ in size, which are flux pinning sites of Gd123, were trapped within the $GdBa_2Cu_3O_{7-y}$ (Gd123) grain; unreacted $Ba_3Cu_5O_8$ liquid and Gd211 particles were present near the edge regions of the single grain Gd1.5 bulk compact.