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Oriented Barium Ferrite Disc Magnet: Set in a 9500 Oersted Field (Gorter, Philips 1956, Ex. 1)
A ceramic magnet that is stronger in one direction. Pre-fired barium ferrite powder is suspended in polyvinyl acetate dissolved in acetone and set in a strong magnetic field, so its crystals line up. The block is heated to 500 °C in a weaker field and sintered at 1280 °C. In the principal direction it held 2,650 gauss with a coercive force of 1,775 oersted and a (BH)max of 1.3 × 10⁶; at right angles only 1,260 gauss.
Source: E. W. Gorter, G. W. Rathenau and A. L. Stuyts (Philips), US 2,762,778 (1956), Example 1. They made blocks; disc size is ours. Picture: ferrite magnets, Omegatron, Wikimedia Commons, CC BY-SA 3.0.
Advanced
3 days
Instructions
1
1
Weigh barium carbonate and iron oxide
Weigh barium carbonate and iron oxide
Weigh 450 g barium carbonate and 2000 g ferric oxide. Barium carbonate is poisonous if swallowed: gloves and a dust respirator.
Materials for this step:
Barium Carbonate (Witherite)450 g
Ferric Oxide2000 gTools needed:
Balance Scale
Rubber Gloves
P100 Respirator2
2
Mill 20 hours under alcohol, dry
Mill 20 hours under alcohol, dry
Grind the mixture in a ball mill under alcohol for 20 hours, then dry it.
Tools needed:
Iron Ball Mill
Ethanol - Lab Grade, 95%
Drying Oven3
3
Pre-fire: through a 1100 °C zone in 10 minutes
Pre-fire: through a 1100 °C zone in 10 minutes
Pass the dry powder at 20 mm per minute through an electric furnace with a 20 cm hot zone at 1100 °C, in air: 10 minutes in the heat. Let it cool.
Tools needed:
Tube Furnace
Crucible with Lid (Porcelain)
Heat-Resistant Gloves4
4
Grind 12 hours with alcohol, dry
Grind 12 hours with alcohol, dry
Pulverise the pre-fired material in a ball mill with alcohol for 12 hours, then dry it. This is the pre-fired powder.
Tools needed:
Iron Ball MillEthanol - Lab Grade, 95%Drying Oven5
5
Stir into 16 % polyvinyl acetate in acetone
Stir into 16 % polyvinyl acetate in acetone
Dissolve polyvinyl acetate in acetone to a 16 % solution and stir the pre-fired powder into it, 2 cc of solution per gram of powder. The binder burns off later.
Tools needed:
Polyvinyl Acetate
AcetoneBalance Scale6
6
Orient in a 9500 oersted field
Orient in a 9500 oersted field
Put the suspension in a brass die between the poles of a magnet yoke and apply a first field of 9500 oersted. Let the acetone evaporate while the field is on. A small block forms.
Tools needed:
Disc Pressing Die
Electromagnet
Hydraulic Press7
7
Heat to 500 °C in a 2000 oersted field
Heat to 500 °C in a 2000 oersted field
Put the block in an electric furnace between the magnet's poles. With a second field of 2000 oersted along the first field's direction, heat to 500 °C, which burns off the rest of the binder. Then switch the field off.
Tools needed:
Tube FurnaceElectromagnetHeat-Resistant Gloves8
8
Sinter: through a 1280 °C zone in 5 minutes
Sinter: through a 1280 °C zone in 5 minutes
Pass the block at 20 mm per minute through an electric furnace in air at 1280 °C with a 10 cm hot zone: about 5 minutes in the heat.
Tools needed:
Tube FurnaceHeat-Resistant Gloves9
9
Magnetise in the principal direction
Magnetise in the principal direction
Magnetise the block along the direction of the first field, the principal direction. The patent magnetises it in a field in that direction; ours: an electromagnet. Find the north face with a compass.
Tools needed:
Electromagnet
CompassMaterials
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- 2000 gPlaceholder
Tools Required
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