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Strontium Ferrite Disc Magnet: Example 9 Without the Orienting Field (Gorter, Philips 1956, Ex. 9 Comparison)
Made as in Example 9 but without the first, orienting field. Gorter's comparison blocks held 2,075 gauss with a coercive force of 3,225 oersted and a (BH)max of 0.88 × 10⁶.
Source: E. W. Gorter, G. W. Rathenau and A. L. Stuyts (Philips), US 2,762,778 (1956), Example 9. 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 strontium carbonate and iron oxide
Weigh strontium carbonate and iron oxide
Weigh 29.5 g strontium carbonate and 163 g ferric oxide.
Materials for this step:
Strontium Carbonate29.5 g
Ferric Oxide163 gTools needed:
Balance Scale
P100 Respirator2
2
Mill 15 hours with alcohol, dry
Mill 15 hours with alcohol, dry
Grind in a ball mill with alcohol for 15 hours. Remove the alcohol and dry the powder.
Tools needed:
Iron Ball Mill
Ethanol - Lab Grade, 95%
Drying Oven3
3
Pre-fire 2 hours at 1000 °C in air
Pre-fire 2 hours at 1000 °C in air
Heat the powder for 2 hours at 1000 °C in an electric furnace in air. Let it cool.
Tools needed:
Muffle Furnace
Crucible with Lid (Porcelain)
Crucible Tongs
Heat-Resistant Gloves4
4
Grind 4 hours in an agate centrifugal mill
Grind 4 hours in an agate centrifugal mill
Grind the cooled material for 4 hours with alcohol in an agate centrifugal mill, then dry it. This is the pre-fired powder. Example 9 does not say how its powder was pre-fired; ours: as in Example 8.
Tools needed:
Agate Centrifugal MillEthanol - Lab Grade, 95%Drying Oven5
5
Stir into 8 % polyvinyl acetate in acetone
Stir into 8 % polyvinyl acetate in acetone
Dissolve polyvinyl acetate in acetone to a 8 % solution and stir the pre-fired powder into it, 1 cc of solution per gram of powder. The binder burns off later.
Tools needed:
Polyvinyl Acetate
AcetoneBalance Scale6
6
Mould without a first field
Mould without a first field
Put the suspension in a moulding die and remove the binder solution without any magnetic field. This is the patent's comparison block.
Tools needed:
Disc Pressing Die
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 Furnace
ElectromagnetHeat-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 the block
Magnetise the block
Magnetise the block in a field. Without the orienting field it has no preferred direction. Ours: an electromagnet. Find the north face with a compass.
Tools needed:
Electromagnet
CompassMaterials
2- 29.5 gPlaceholder
- 163 gPlaceholder
Tools Required
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