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Strontium-Calcium Ferrite Disc Magnet: Equal Strontium and Calcium, 1280 °C (Went, Philips 1956, Ex. 27)
Charlie

Created by

Charlie

28. October 2026DE
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Strontium-Calcium Ferrite Disc Magnet: Equal Strontium and Calcium, 1280 °C (Went, Philips 1956, Ex. 27)

A ferrite with half the strontium replaced by calcium: 0.3 mol strontium carbonate and 0.3 mol calcium carbonate to 3.1 mol iron oxide, milled 15 hours, pressed and passed through a 1280 °C furnace in 10 minutes. Went's rod held 1,645 gauss with a coercive force of 2,460 oersted. Source: J. J. Went, G. W. van Oosterhout and E. W. Gorter (Philips), US 2,762,777 (1956), Example 27. They sintered rods; discs and the magnetising are ours. Picture: ferrite magnets, Omegatron, Wikimedia Commons, CC BY-SA 3.0.
Advanced
2 days

Instructions

1

Weigh the carbonates and iron oxide

Weigh 44.3 g strontium carbonate (0.3 mol), 30.2 g calcium carbonate (0.3 mol), 500.0 g ferric oxide (3.1 mol).

Materials for this step:

Strontium CarbonateStrontium Carbonate44.3 g
Calcium Carbonate - WhitingCalcium Carbonate - Whiting30.2 g
Ferric OxideFerric Oxide500 g

Tools needed:

Balance ScaleBalance Scale
P100 RespiratorP100 Respirator
2

Mill with alcohol 15 hours, dry

Grind the mixture with alcohol in a ball mill for 15 hours, then dry it.

Tools needed:

Iron Ball MillIron Ball Mill
Ethanol - Lab Grade, 95%Ethanol - Lab Grade, 95%
Drying OvenDrying Oven
3

Press at 1.5 t/cm²

Press the dry powder at 1.5 tonnes per cm² (ours: discs instead of a rod).

Tools needed:

Hydraulic PressHydraulic Press
Disc Pressing DieDisc Pressing Die
4

Pass through a 1280 °C zone in 10 minutes

Sinter at 1280 °C by passing the pieces through a 10 cm hot zone at 10 mm per minute: 10 minutes in the heat.

Tools needed:

Tube FurnaceTube Furnace
Heat-Resistant GlovesHeat-Resistant Gloves
5

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:

ElectromagnetElectromagnet
CompassCompass

Materials

3

Tools Required

11

This blueprint makes

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