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Strontium Ferrite Disc Magnet, Sintered 4 Hours at 1100 °C (Went, Philips 1956, Ex. 34)
A strontium ferrite magnet made exactly like Went's barium ferrite of Example 34, with strontium carbonate in place of barium carbonate: 29.5 g of it to 191.7 g iron oxide, milled, fired, milled again, pressed and sintered for 4 hours. This iteration sinters at 1100 °C, where his rod held 1,220 gauss with a coercive force of 3,880 oersted.
Source: J. J. Went, G. W. van Oosterhout and E. W. Gorter (Philips), US 2,762,777 (1956), Example 34. They pressed rods; the disc size is ours. The patent does not say how to magnetise it; our way is stated. Picture: ferrite magnets, Omegatron, Wikimedia Commons, CC BY-SA 3.0.
Advanced
2 days
Instructions
1
1
Weigh strontium carbonate and iron oxide
Weigh strontium carbonate and iron oxide
Weigh 29.5 g of strontium carbonate and 191.7 g of ferric oxide, Fe2O3. The patent makes this second mixture "in exactly the same manner" as the barium one.
Materials for this step:
Strontium Carbonate29.5 g
Ferric Oxide191.7 gTools needed:
Balance Scale
Rubber Gloves
P100 Respirator2
2
Mill with ethanol for 4 hours
Mill with ethanol for 4 hours
Grind the mixture with ethanol in an iron ball mill for 4 hours. Let the ethanol evaporate, then dry the powder in a drying oven.
Tools needed:
Iron Ball Mill
Ethanol - Lab Grade, 95%
Drying Oven3
3
Presinter at 1000 °C for 4 hours
Presinter at 1000 °C for 4 hours
Fire the dry powder in air at 1000 °C for 4 hours (ours: in a lidded porcelain crucible in a muffle furnace). Let it cool.
Tools needed:
Muffle Furnace
Crucible with Lid (Porcelain)
Crucible Tongs
Heat-Resistant Gloves4
4
Mill again for 4 hours
Mill again for 4 hours
Grind the presintered product with ethanol in the ball mill for another 4 hours. Let the ethanol evaporate.
Tools needed:
Iron Ball MillEthanol - Lab Grade, 95%Drying OvenP100 Respirator5
5
Press discs at 1.5 tons per cm²
Press discs at 1.5 tons per cm²
Press the powder at 1.5 tons/cm². The patent pressed rods; we press discs. Ours: a die 20 mm across, so about 4.7 tonnes on the punch (our arithmetic: 1.5 × 3.14 cm²).
Tools needed:
Hydraulic Press
Disc Pressing Die6
6
Sinter 4 hours at 1100 °C
Sinter 4 hours at 1100 °C
Sinter the discs for 4 hours at 1100 °C in oxygen or in air. The patent's strontium rod at 1100 °C: 1,220 gauss and 3,880 oersted.
Tools needed:
Muffle FurnaceCrucible TongsHeat-Resistant Gloves7
7
Magnetise the discs
Magnetise the discs
The patent gives no magnetising method. Ours: lay a disc with its faces against the poles of a strong electromagnet, switch the current on, then off. Find which face is north with a compass.
Tools needed:
Electromagnet
CompassMaterials
2- 29.5 gPlaceholder
- 191.7 gPlaceholder
Tools Required
14- Placeholder
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